heat flow along the nantroseize transect results from iodp expeditions 315 and 316 offshore the kii peninsula japan mal conductivity varies between about 1 0 w m 1 k 1 near the seafloor to 1 6 w m 1 k 1 at a depth of 1 km thermal conductivity generally increases with depth and correlates with variations in porosity and lithology thermal gradients along the transect are characterized by 48 sediment temperature measurements from 6 sites thermal corrections for the effects of bathymetric relief and sedimentation improve the confidence with which the heat flow values can be interpreted heat flow generally decreases with landward distance from the deformation front and varies from 70 mw m 2 just landward of the deformation front to 54 mw m 2 at sites characterizing the outer fore arc high and to 57 mw m 2 at the kumano basin site iodp heat flow measurements are significantly lower than nearby seafloor heat flow measurements this difference is most likely due to variations in bottom water temperature that have a large effect on values of seafloor heat flow thus the heat flow of the nankai accretionary prism is lower than previously thought we present thermal models of subduction along this transect and explore the impact of the initial geotherm conductive plate cooling based on the age of subducting seafloor 20 myr under predicts the observed heat flow we find a good fit to the data using a geotherm appropriate for 10 myr seafloor the extra heat is interpreted in terms of back arc thermal environments

enhanced turbulence and energy dissipation at ocean fronts the ocean surface boundary layer mediates air sea exchange in the classical paradigm and in current climate models its turbulence is driven by atmospheric forcing observations at a 1 kilometer wide front within the kuroshio current indicate that the rate of energy dissipation within the boundary layer is enhanced by one to two orders of magnitude suggesting that the front rather than the atmospheric forcing supplied the energy for the turbulence the data quantitatively support the hypothesis that winds aligned with the frontal velocity catalyzed a release of energy from the front to the turbulence the resulting boundary layer is stratified in contrast to the classically well mixed layer these effects will be strongest at the intense fronts found in the kuroshio current the gulf stream and the antarctic circumpolar current all of which are key players in the climate system

heat flow and age of the gulf of oman we present the results of twenty heat flow stations in the gulf of oman which are used to infer the first reliable age estimates for the basin a mean surface heat flux of 42 6 3 6 mw m 2 exhibits no significant regional variation after correction for thick and rapidly deposited sediments this yields an age of 70 to 100 ma according to oceanic thermal models this age is also consistent with the sediment corrected basement depths of 5 5 6 0 km and with formation during the cretaceous quiet zone the latter can explain the absence of magnetic sea floor spreading lineations heat flow measurements are also used to confirm the presence of gas hyrdate layers the measured thermal gradient yields a depth for the solid to free gas phase transition which is the same as that deduced from bright spots seen on seismic reflection profiles

the vertical chloride ion profile at the iodp site c0002 kumano basin off coast of japan abstract the vertical profiles of chloride ion cl concentration and oxygen and hydrogen isotopic ratios in pore fluids of basin fill sediments in the southern kumano basin were examined a model has been proposed to explain those profiles in conjunction with published data by invoking diffusion and advection of freshwater from methane hydrate dissolution the model requires a low initial cl concentration in the old accretionary prism below the basin before the basin began to fill with sediments it also requires little or no methane hydrate formation in the old accretionary prism given these requirements an upward fluid advection rate of 1 10 12 m s has been estimated which is very low compared to other accretionary prisms our data suggests that the tectonic compaction of the basin filling sediments and fault activity under the basin sediments have not been that active recently in the kumano basin

generalization of gas hydrate distribution and saturation in marine sediments by scaling of thermodynamic and transport processes gas hydrates dominated by methane naturally occur in deep marine sediment along continental margins these compounds form in pore space between the seafloor and a sub bottom depth where appropriate stability conditions prevail however the amount and distribution of gas hydrate within this zone and free gas below can vary significantly at different locations to understand this variability we develop a one dimensional numerical model that simulates the accumulation of gas hydrates in marine sediments due to upward and downward fluxes of methane over time the model contains rigorous thermodynamic and component mass balance equations that are solved using expressions for fluid flow in compacting sediments the effect of salinity on gas hydrate distribution is also included the simulations delineate basic modes of gas hydrate distribution in marine sediment including systems with no gas hydrate gas hydrate without underlying free gas and gas hydrate with underlying free gas below the gas hydrate stability zone for various methane sources the results are scaled using combinations of dimensionless variables particularly the peclet number and damkohler number such that the dependence of average hydrate saturation on numerous parameters can be summa rized using two contour maps one for a biogenic source and one for upward flux from a deeper source simulations also predict that for systems at steady state large differences in parameters like seafloor depth seafloor temperature and geothermal gradient cause only small differences in average hydrate saturation when examined with scaled variables although important caveats exist our model presents a unified picture of hydrate accumulations that can be used to understand well characterized gas hydrate systems or to predict steady state average hydrate saturation and distribution at locations for which seismic or core data are not available

anomalous temperatures in central scotia sea sediments bottom water variation or pore water circulation in old ocean crust we report low temperature gradients from 60 to 12 of geothermal and extrapolated temperatures offset from modern bottom water temperatures in sediments from the central scotia sea we examine possible causes bearing in mind similar anomalous measurements 18 years previously attributed at the time to instrumental error small temperature offsets 0 1 c may reflect short term bottom temperature variation within eddies of the antarctic circumpolar current low sediment temperature gradients may be caused by horizontal advection of cold water within the upper oceanic basaltic layer documented in younger ocean floor elsewhere or by northward encroachment of colder bottom waters from the antarctic peninsula shelf or weddell sea for several years prior to measurement

heat flow of the eastern canadian rifted continental margin revisited continental shelves are regions where heat flow is not measured directly by conventional marine techniques but estimated from oil exploration data with possible bias in order to overcome this problem we recently proposed a method based on neural networks geophys j int 2006 166 115 that provides better constraints on thermal conductivity it allowed us to derive 161 heat flow estimates on the eastern margin of canada where previous studies had concluded to the existence of heat flow higher than that in the adjacent continent and ocean we conversely found rather homogeneous values 45 55 mw m 2 all along and across the margins from labrador to nova scotia the difference seems essentially related to the porosity of sediments that was not taken into account in previous studies our results support a high asymmetry for the conjugate iberian canadian margins and could indicate that mantle heat flow increases abruptly from the canadian shield to the margins

upper ocean thermal structure and the western north pacific category 5 typhoons part i ocean features and the category 5 typhoons intensification abstract category 5 cyclones are the most intense and devastating cyclones on earth with increasing observations of category 5 cyclones such as hurricane katrina 2005 rita 2005 mitch 1998 and supertyphoon maemi 2003 found to intensify on warm ocean features i e regions of positive sea surface height anomalies detected by satellite altimeters there is great interest in investigating the role ocean features play in the intensification of category 5 cyclones based on 13 yr of satellite altimetry data in situ and climatological upper ocean thermal structure data best track typhoon data of the u s joint typhoon warning center together with an ocean mixed layer model 30 western north pacific category 5 typhoons that occurred during the typhoon season from 1993 to 2005 are systematically examined in this study two different types of situations are found the first type is the situation found in the western north pacific south eddy zone sez 21 26 n 127 170 e and the kuroshio 21 30

heat flow in the balearic and tyrrhenian basins western mediterranean we present the results of three detailed heat flow surveys which are used to investigate the variations of heat flow and age of the balearic and tyrrhenian basins in the western mediterranean analysis of 12 measurements within a 10 km radius from 40 01 4 55 e in the balearic abyssal plain shows a mean heat flow of 92 10 mw m 2 after correction for the effects of sedimentation this value agrees well with the predictions of plate cooling and high extension stretching models for crust of the late oligocene age proposed for the basin a similar survey with 18 measurements around 40 16 n 11 19 e in the western tyrrhenian gives a flux of 134 8 mw m 2 while the third survey of 26 measurements in the southern tyrrhenian abyssal plain at 37 17 n 12 58 e yields a slightly higher heat flow of 151 10 mw m 2 these values are within the range predicted by simple plate cooling models for the late miocene ages of the deep tyrrhenian basin thus our observations suggest that although the mode of crustal formation of these deep marginal basins is less well defined than that of the major ocean basins the thermal signature is similar also the trend of increasing heat flow from west to east through the balearic and tyrrhenian basins is in agreement with models of the formation of the western mediterranean behind an eastwardly migrating trench system in all three areas the measured flux shows significant local variability in the two westernmost surveys this can be attributed to the presence of buried high conductivity salt structures but in the third area se tyrrhenian the magnitude of the variations is several times greater than can be attributed to steady state thermal refraction alone instead evidence exists for localized hydrothermal activity linked to the small topographical relief within the survey area

thermal and compaction processes in a young rifted basin containing evaporites gulf of lions france the gulf of lions northwestern mediterranean is a young oligocene miocene rifted basin characterized by the presence of a thick evaporitic sequence observed data surface heat flow well temperatures geopressures below the evaporites crustal thinning are used to model 1 the basin forming mechanisms and 2 the intrasedimentary processes that influence the temperature history and thus the maturation of source rocks a two dimensional finite difference basin model temispack simulates the sedimentation compaction and overpressures related to the low permeability of the post rift sequence the heat transfer from the rifted lithosphere into the sediments and the level of maturation by using a kinetic approach the classic passive margin model which relates the history of heat flow and the rate of subsidence to a uniform thinning factor yields subsidence and heat flow predictions that agree with observations the recently accelerated subsidence observed in the deep margin is probably an effect of recent regional compression rather than the consequence of alternative rifting mechanisms the history of maturation of organic matter was influenced by the variation of the regional heat flow due to the rifting the effect of sedimentation or blanketing and the variability of the lithologies and porosities the undercompaction of sediments underlying the evaporites is accounted for by the model which suggests that hydraulic fracturing is taking place at present in the overpressured sediments fluid flow associated with the compaction disequilibrium has negligible thermal effect undercompacted shales below the evaporites have lower thermal diffusivity and thus higher temperatures which has a significant effect on maturation

evolution of heat flow hydrothermal circulation and permeability on the young southern flank of the costa rica rift we analyze 67 new conductive heat flow measurements on the southern flank of the costa rica rift crr heat flow measurements cover five sites ranging in oceanic crustal age between approximately 1 6 and 5 7 ma and are co located with a high resolution multi channel seismic line that extends from slightly north of the first heat flow site 1 6 ma to beyond odp hole 504b in 6 9 ma crust for the five heat flow sites the mean observed conductive heat flow is 85 mwm 2 this value is approximately 30 per cent of the mean lithospheric heat flux expected from a half space conductive cooling model indicating that hydrothermal processes account for about 70 per cent of the heat loss the advective heat loss fraction varies from site to site and is explained by a combination of outcrop to outcrop circulation through exposed basement outcrops and discharge through faults super critical convection in layer 2a extrusives occurs between 1 6 and 3 5 ma and flow through a thinly sedimented basement high occurs at 4 6 ma advective heat loss diminishes rapidly between 4 5 and 5 7 ma which contrasts with plate cooling reference models that predict a significant deficit in conductive heat flow up to ages 65 10 ma at 5 7 ma the crr topography is buried under sediment with an average thickness 150 m and hydrothermal circulation in the basement becomes sub critical or perhaps marginally critical the absence of significant advective heat loss at 5 7 ma at the crr is thus a function of both burial of basement exposure under the sediment load and a reduction in basement permeability that possibly occurs as result of mineral precipitation and original permeability at the time of formation permeability is a non monotonic function of age along the southern flank of the crr in general agreement with seismic velocity tomography interpretations that reflect variations in the degree of ridge axis magma supply and tectonic extension hydrothermal circulation in the young oceanic crust at southern flank of crr is affected by the interplay and complex interconnectedness of variations in permeability sediment thickness topographical structure and tectonic and magmatic activities with age

interrelation between surface and basement heat flow in sedimentary basins petroleum system models psm result critically depend on the computed evolution of the temperature field as psm typically only resolve the sedimentary basin and not the entire lithosphere it is necessary to apply a basement heat flow boundary condition inferred from well data surface heat flow measurements and an assumed tectonic scenario the purpose of this paper is to assess the use of surface heat flow measurements to calibrate basin models we show that a simple relationship between surface and basement heat flow only exists in thermal steady state and that transient processes such as rifting and sediment deposition will lead to a decoupling we study this relationship in extensional sedimentary basins with a 1d lithosphere scale finite element model the numerical model was built to capture the large scale dynamic evolution of the lithosphere and simultaneously solve for transient thermal processes in basin evolution such as sedimentation compaction driven fluid flow and seafloor temperature variations our analysis shows that several corrections need to be applied when using surface heat flow information for the calibration of basement heat flow in psm not doing so can lead to significant errors of up to 30 50 c at typical petroleum reservoir and source rock depths we further show that resolving sediment blanketing effects in basin modeling is crucial with the thermal impact of sediment deposition being at least as important as rifting induced basement heat flow variations

sea surface salinity variability during the indian ocean dipole and enso events in the tropical indian ocean an ocean reanalysis that covers the period from 1871 2008 is used to analyze interannual variability of sea surface salinity sss in the tropical indian ocean the reanalysis sss and the sss anomaly patterns during indian ocean dipole iod and el nino southern oscillation enso events are compared with patterns from argo sss data the mean seasonal sss variation is large in the northern bay of bengal compared to variations in the arabian sea and equatorial indian ocean during a positive iod event positive sss anomalies are found along the sumatra coast due to the combination of wind driven upwelling of subsurface high salinity waters enhanced evaporation and anomalous surface circulation the opposite is true to a lesser extent during negative iod events a dipole mode index for salinity dmis based on sss data and a new index based on the average of salinity in a region off the coast of sumatra is introduced to monitor sss variability during iod and enso events the impact of concomitant el nino events on a positive iod event is large with freshening a negative sss anomaly in the equatorial indian ocean and salting positive sss anomaly off the southern sumatra coast the impact of intense freshening reaches into the southwestern tropical indian ocean the impact of concomitant la nina with negative iod is also large with an intense freshening in the southeastern arabian sea and salting off the northern sumatra coast

variations in heat flow across the ocean continent transition in the iberia abyssal plain abstract new heat flow observations have been made in the iberia abyssal plain off the galicia margin along the transect of ocean drilling program leg 149 drill sites in order to investigate the nature of this unusually wide and deep continent ocean transition region our results indicate the presence of three separate zones average values of 47 5 3 mw m 2 in the westernmost zone iii agree with predictions of standard oceanic lithospheric models for its estimated age of 126 ma in contrast the heat flow within zone ii is 5 15 mw m 2 higher than predicted assuming that the mantle heat flow remains constant across the basin this region of high values is coincident with the location of a major intra crustal s type reflector east of odp site 900 and the anomaly is consistent with the presence of 2 3 km of primarily upper continental crust above the reflector with concentrations of radiogenic components similar to those from granodiorite samples dredged off galicia bank it is not however consistent with the low values of heat production measured on gabbroic samples from its western end at odp site 900 in zone i detailed measurements across the tilted fault block south of odp site 901 show consistent variations which closely match predictions due to the effects of basement structure and sediment deposition there is no evidence for variations due to vertical convective transport along the dipping basement fault block once corrected for these variations measurements in zone 1 yield average values that agree quite well with previous measurements across galicia bank indicating no systematic landward increase in heat flow with decreasing amounts of continental extension

upper ocean thermal structure and the western north pacific category 5 typhoons part ii dependence on translation speed abstract using new in situ ocean subsurface observations from the argo floats best track typhoon data from the u s joint typhoon warning center an ocean mixed layer model and other supporting datasets this work systematically explores the interrelationships between translation speed the ocean s subsurface condition characterized by the depth of the 26 c isotherm d26 and upper ocean heat content uohc a cyclone s self induced ocean cooling negative feedback and air sea enthalpy fluxes for the intensification of the western north pacific category 5 typhoons based on a 10 yr analysis it is found that for intensification to category 5 in addition to the warm sea surface temperature generally around 29 c the required subsurface d26 and uohc depend greatly on a cyclone s translation speed it is observed that even over a relatively shallow subsurface warm layer of d26 60 70 m and uohc 65 70 kj cm 2 it is still possible to have a sufficient enthalpy flux to intensify the storm to category 5

heat flow and depth versus age for the mesozoic northwest atlantic ocean results from the sohm abyssal plain and implications for the bermuda rise abstract heat flow in the sohm abyssal plain is measured to be 53 mw m 2 at an age of 163 ma this is 25 higher than predicted by conductive cooling models even though the sediment corrected basement depth of 6 5 km at this location is normal for its age an analysis of existing heat flow depth and geoid anomalies in the northwest atlantic shows that there is little correlation between heat flow and depth throughout the entire region depth and geoid are clearly related to the bermuda swell while the associated heat flow anomaly once adjusted for variations with age is limited to 5 mw m 2 and only decays to the south this means that the bermuda swell is probably not caused by extensive thermal reheating within the lithosphere but instead by dynamic uplift at its lower boundary due to the convective upwelling of a mantle plume the regionally high heat flow in the northwest atlantic may be a thermal remanent of previous plumes which passed beneath this region early in its history therefore depth and heat flow anomalies from this region cannot be used to provide constraints on steady state parameters of the lithosphere such as the presence or absence of a long term boundary layer at its base

numerical simulation of tropical cyclone mora using a regional coupled ocean atmospheric model tropical storms ts are highly sensitive to the behavior of nearby oceans and the only way to improve their predictability is to include all the possible factors contributing to their genesis and motion the present study evaluates the response of air sea coupling on ts mora which occurred during the pre monsoon season of 2017 mora is simulated using a non hydrostatic regional atmospheric modeling system coupled to a regional ocean modeling system model the observations show a low level rossby wave in the atmosphere during the storm genesis there was also evidence of increased sea surface height simultaneously in the form of a downwelling kelvin wave at the west coast of the bay of bengal the present study emphasizes the relationship between near surface oceanic and atmospheric circulation patterns we have tried to elucidate the process with the help of dynamical equations and model solutions we also analyze the pivotal role of the atmospheric rossby wave in the formation of the coastal kelvin wave the kelvin wave seems to produce a warm pool required to form a low pressure system which further gave rise to the tropical storm mora the changes in the temperature and salinity profile within the ocean subsurface layers during storm passage are further used for inferences regarding the vertical structure of the upper ocean due to wind generated mixing the model analysis reveals that the ocean and atmospheric counterparts responsible for storm genesis are well recorded in the coupled model when compared to the observations it was found that air sea coupling in the model made it possible to realistically capture ocean and atmospheric responses

regional overview of deep sedimentary thermal gradients of the geopressured zone of the texas louisiana continental shelf nearly 600 bottom hole temperature data from the northern continental shelf of the gulf of mexico each corrected for drilling disturbance yielded a regional map of geothermal gradient down to approximately 6 km 3 7 mi sub sea floor two geographic trends can be seen on the map first from east to west the geothermal gradient changes from values between 0 025 and 0 03 k m 0 014 and 0 016 f ft off the alabama mississippi shore to lower values of 0 015 0 025 k m 0 008 0 014 f ft off eastern louisiana and to higher values of 0 03 0 06 k m 0 016 0 033 f ft off western louisiana through texas second thermal gradients tend to be lower toward the outer continental shelf less than 0 02 k m 0 0112 f ft we believe that the observed variations are primarily attributable to the thermal effect of rapid and regionally variable sediment accumulation during the cenozoic era which resulted in the occurrence of the geopressured zone in the texas louisiana shelf in the eastern louisiana shelf where accumulation was fastest sediments down to about 6 km 3 7 mi are relatively young about

on the evolution of rifted continental margins comparison of models and observations for the nova scotian margin summary a model for the formation and evolution of rifted continental margins based on lithospheric extension during rifting and its thermal and mechanical consequences is proposed model predictions are then compared with geological and geophysical observations from a transect of the 185 ma old rifted margin off nova scotia through the scotian basin three kinematic models of the rifting process are discussed these are 1 the uniform extension model in which the amount of extension is uniform with depth but varies with position across the margin 2 the uniform extension and melt segregation model which has similar properties but also provides an explanation for the properties of the extended continental crust and its transition to oceanic crust by postulating that basaltic melt segregates from the asthenosphere and migrates to the crust and 3 the depth dependent extension model in which the first order consequences of rapidly changing rheological properties with depth in the lithosphere are included by decoupling the lithosphere into two zones with depth each of which undergoes differing amounts of extension these rift models predict the form of crustal and lithospheric thinning subsidence and temperature change once the amount of extension has been determined this is estimated from seismic measurements of present crustal thickness on the assumption that the crust had a uniform thickness equal to that currently measured in the adjacent continental region before rifting occurred rifting is also considered to occur instantaneously a time stepping thermo mechanical model is used to predict the cooling of rifted margin additional thermal contraction subsidence and its amplification by water and sediment loading thermal aspects are calculated using a finite difference model of time dependent conductive heat transport whereas regional isostatic response to loading is calculated by a finite element model the models are coupled because the temperature distribution is used to define a rheological lithosphere an elastic region with thickness that varies in time and space as the model evolves for flexural calculations in the mechanical model secondary coupling occurs through perturbations to the temperature field by sedimentary thermal blanketing and advection of heat during isostatic adjustment the model predictions of 1 sedimentary basin stratigraphy 2 moho position 3 free air gravity anomaly 4 age depth relations for deep exploratory wells and 5 subsidence and temperature histories agree well with observations from the scotian basin additional effects due to sedimentary and crustal radiogenic heat production lateral heat transport and the possible existence of a near surface brittle listric faulted region created during rifting are also considered it is concluded that a model in which rifting occurred by depth dependent extension and which includes a finite thickness for the rheological lithosphere radiogenic heat production in the sediments and crust and a brittle listric faulted crustal layer affords an accurate description of the first order processes that occur during rifting and evolution of this margin

subtropical sst dipole events in the southern indian ocean sea surface temperature sst anomalies in the subtropical southern indian ocean show interannual dipole events that are seasonally phase locked to the austral summer a positive phase of the event is characterized by cold sst anomalies in the eastern part i e off australia and warm sst anomalies in the southwestern part south of madagascar such an event is found to produce above normal rainfall over many regions in south central africa the cooling of sst in the eastern part is mainly caused by the enhanced evaporation this is associated with stronger winds along the eastern edge of the subtropical high which is strengthened and shifted slightly to the south during the event on the other hand relative decrease in the seasonal latent heat loss due to reduced evaporation dominates the warming in the southwestern part evolution of such subtropical dipole events shows quite a contrast to that of the tropical dipole events discovered recently in the indian ocean

interactions between mesoscale eddies and synoptic oscillations in the bay of bengal during the strong monsoon of 2019

characteristics of the upper tropospheric environmental flow around hurricanes abstract the upper tropospheric flow out to a radius of 2000 km around atlantic hurricanes is described using rotated coordinate composite analysis of the noaa national hurricane center operational wind set the rotated coordinate methodology designed to preserve some of the asymmetry of hurricane outflow during compositing is described in detail a rotated coordinate composite of all hurricanes from a five year period is used to study the general properties of the hurricane outflow layer coordinate rotation improves the representation of the outflow jet and the associated extrema of radial and tangential wind but tends to obscure the geographically persistent features of the upper tropospheric environment such as the midlatitude westerlies the amplitude of the asymmetric radial wind is twice that of the symmetric while the amplitudes of tangential winds are equivalent a comparison of geographic and rotated coordinate composites indicates that both the outflow jet and the midlatitude westerlies are

case for very low coupling stress on the cascadia ssubduction fault a fundamental problem in plate tectonics is the shear strength of major plate boundary faults this translates to the question whether the generally observed small earthquake stress drops of 3 10 mpa on major faults release most of the accumulated stress or only a small fraction of it there is strong evidence that the san andreas fault a major transform plate boundary is weak 20 mpa shear resistance it is not yet clear whether subduction thrust faults are also weak we present two types of evidence from the northern cascadia subduction zone that indicate very low coupling shear stress on that plate interface and hence very low strength of the subduction thrust fault comparable to that estimated for the san andreas fault first the well defined surface heat flow and heat generation allow negligible frictional heating on the plate interface the average shear stress on the fault must thus be very low over a time scale of a few million years second focal mechanism solutions for small crustal earthquakes in the southern vancouver island area indicate that the horizontal stress in the direction of plate convergence has a similar magnitude to the vertical stress this inferred stress state requires the present tectonic stress coupled across the subduction thrust fault to be very low one explanation for the weakness of the fault is the presence of near lithostatic pore fluid pressure in the region of the fault zone for which there is independent evidence the conclusion of a weak subduction thrust fault does not conflict with geodetic observations of contemporary surface deformation which indicate that the fault is currently locked accumulating strain energy toward a future great earthquake the surface deformation responds to the small 20 mpa temporal changes of the stress field associated with the subduction earthquake cycle this transient stress is superimposed on the larger background regional stress field in which the maximum compression is parallel to the margin the weakness of the cascadia subduction thrust fault and the unusual stress state of the forearc region have important implications for earthquake hazards for example a subduction earthquake may induce large strike slip earthquakes in the forearc that affect a large area

rifting in the northern norwegian greenland sea thermal tests of asymmetric spreading the analysis of heat flow seismic and topographic data collected in the northern norwegian greenland sea reveals an asymmetric evolution of the eurasian and north american plates these data are compared to predictions from three kinematic models of extension which produce asymmetry about the knipovich ridge 1 uniform asymmetric pure shear 2 lithospheric simple shear and 3 rift ridge jumping the data are consistent with a range of deformation scenarios from one ridge jump occurring at about 25 m y after the initiation of spreading to continuous asymmetric extension the simple shear model can match the data only when a detachment fault dips more steeply than 45 under svalbard tectonic and heat flow evidence suggests that asymmetry may have evolved from a combination of all three models when the mohns ridge propagating to the east encountered the preexisting northward trending spitsbergen shear zone the direction of ridge propagation shifted to the north being influenced by the abrupt change in the regional stress field at the shear zone ridge axis intersection as a result the nascent knipovich ridge entered into and propagated along the shear zone consequently formerly active shear faults became the new detachment surfaces along which new crust is minted and asymmetrically extended the high level of deviatoric stress about the mohns and knipovich ridge intersection may cause a gradual eastward migration of the knipovich ridge resulting in multiple zones of magma intrusion off axial bands of high heat flow and volcanism located along the barents sea and svalbard margin along the yermak plateau and on continental svalbard just southeast of the yermak plateau may be evidence for this migration propagation from the nansen ridge may have entered the same shear zone from the north explaining the creation of the small molloy ridge and off axis volcanism on the yermak plateau

estimation of the global amount of submarine gas hydrates formed via microbial methane formation based on numerical reaction transport modeling and a novel parameterization of holocene sedimentation this study provides new estimates for the global offshore methane hydrate inventory formed due to microbial ch4 production under quaternary and holocene boundary conditions a multi 1d model for particular organic carbon poc degradation gas hydrate formation and dissolution is presented the novel reaction transport model contains an open three phase system of two solid compounds organic carbon gas hydrates three dissolved species methane sulfates inorganic carbon and one gaseous phase free methane the model computes time resolved concentration profiles for all compounds by accounting for chemical reactions as well as diffusive and advective transport processes the reaction module builds upon a new kinetic model of poc degradation which considers a down core decrease in reactivity of organic matter various chemical reactions such as organic carbon decay anaerobic oxidation of methane methanogenesis and sulfate reduction are resolved using appropriate kinetic rate laws and constants gas hydrates and free gas form if the concentration of dissolved methane exceeds the pressure temperature and salinity dependent solubility limits of hydrates and or free gas with a rate given by kinetic parameters global input grids have been compiled from a variety of oceanographic geological and geophysical data sets including a new parameterization of sedimentation rates in terms of water depth we find prominent gas hydrate provinces offshore central america where sediments are rich in organic carbon and in the arctic ocean where low bottom water temperatures stabilize methane hydrates the world s total gas hydrate inventory is estimated at 0 82 x 10sup13 m3 2 10 x 10sup15 m3 ch4 at stp conditions or equivalently 4 18 995 gt of methane carbon the first value refers to present day conditions estimated using the relatively low holocene sedimentation rates the second value corresponds to a scenario of higher quaternary sedimentation rates along continental margins our results clearly show that in situ poc degradation is at present not an efficient hydrate forming process significant hydrate deposits in marine settings are more likely to have formed at times of higher sedimentation during the quaternary or as a consequence of upward fluid transport at continental margins

heat flow in jane basin northwest weddell sea the jane basin is a marginal basin situated immediately to the east of the south orkney microcontinent in the northwest section of the weddell sea thirty five heat flow measurements made in the jane basin ranged in value from 67 5 4 3 to 92 1 3 0 mw m2 excluding values that were corrected for tilting or were on the very edge of the basin the remaining 28 values range between 75 0 8 0 and 84 6 9 1 mw m2 magnetostratigraphy on the recovered core from ocean drilling program hole 697 which was drilled in jane basin to a depth of 322 m allowed sedimentation rates to be calculated back to 4 5 ma single channel seismic reflection data from rss shackleton allowed estimations of total sediment thickness for the jane basin to be made we calculate that the measured heat flow is only 86 89 of the actual heat flow as a result of sedimentation heat generation in the sediments contributes 1 5 1 9 mw m2to the total heat flow the corrected heat flow gives an age for the jane basin of between 25 and 32 ma from age versus heat flow comparisons similar to the age determined from basement depth the scotia sea located to the north of jane basin and the south orkney microcontinent has been dated as anomaly 10 30 ma and younger our calculated age for the jane basin would indicate that it may have been created prior to the initiation of seafloor spreading in the scotia sea evidence from major plate motions indicate that antarctica began to rotate clockwise away from south america at about 65 ma such motion may have triggered subduction along the southeast side of jane bank and the opening of jane basin as a back arc basin subduction at jane bank ended at anomaly 6a time 22 ma as evidenced by the age of the identified magnetic anomalies on the antarctic plate found immediately to the east of jane bank we conclude that jane basin opened prior to the opening of the scotia sea and that the spreading center that opened jane basin may have jumped to the scotia sea and produced the seafloor spreading there

use of cosmogenic 129i to constrain numerical models of fluid flow in marine sediments application to the blake ridge hydrate province 1 concentrations of cosmogenic iodine 129i in the pore fluid of marine sediments often indicate that the pore fluid is much older than the host sediment even when vertical flow due to sediment compaction is taken into account old pore fluid has been used in previous studies to argue for pervasive upward fluid flow and a deep methane source for hydrate deposits alternatively old pore fluid age may reflect more complex flow patterns we use a two dimensional numerical transport model to account for the effects of topography and fractures on pore fluid pathlines when sediment permeability is anisotropic we find that fluid focusing can cause significant lateral migration as well as regions where downward flow reverses direction and returns toward the seafloor longer pathlines can produce pore fluid ages much older than that expected with a one dimensional compaction model for steady state models with geometry representative of blake ridge usa a well studied hydrate province we find pore fluid ages beneath regions of topography and within fractured zones that are up to 70 ma old our results suggest that the measurements of 129i 127i reflect a mixture of new and old pore fluid however old pore fluid need not originate at great depths methane within pore fluids can travel laterally several kilometers implying an extensive source region around the deposit this type of focusing should aid hydrate formation beneath topographic highs

variability of upper ocean characteristics and tropical cyclones in the south west indian ocean track and intensity are key aspects of tropical cyclone behavior intensity may be impacted by the upper ocean heat content relevant for tc intensification known as tdy and barrier layer thickness blt here the variability of tdy and blt in the south west indian ocean and their relationships with tropical cyclones are investigated it is shown that rapid cyclone intensification is influenced by large tdy values thick barrier layers and the presence of anticyclonic eddies for tc generation in the south west indian ocean the parameter tdy was found to be important large blt values overlay with large tdy values during summer both fields are modulated by the westward propagation of rossby waves which are often associated with enso for example the 1997 1998 el nino shows a strong signal in tdy sst and blt over the south west indian ocean after this event an increasing trend in tdy occurred over most of the basin which may be associated with changes in atmospheric circulation increasing sst power dissipation index and frequency of category 5 tropical cyclones also occurred from 1980 to 2010 to further examine the links between tropical cyclones tdy and blt the ocean response to category 5 tropical cyclone bansi that developed near madagascar during january 2015 was analyzed its unusual track was found to be linked with the strengthening of the monsoonal north westerlies while its rapid intensification from category 2 to category 4 was linked to a high tdy region associated with a warm core eddy and large blt

regional heat flow variations across the sedimented juan de fuca ridge eastern flank constraints on lithospheric cooling and lateral hydrothermal heat transport seafloor heat flow has been estimated continuously along a transect on the sedimented eastern flank of the juan de fuca ridge to provide constraints on the scale and rate of lateral heat and fluid transport in the upper igneous crust and on the total flux from the young lithosphere beneath the profile extends from 20 km east of the ridge axis where turbidite sediments lap onto the oceanic crust at an age of less than 1 ma and ends 110 km east of the axis over 3 6 ma crust estimated heat flow is derived from the combination of the depth to igneous basement determined from seismic reflection profiles and basement temperatures measured in nine ocean drilling program boreholes along the transect the strategy is based on the knowledge that in this young area upper basement temperatures are locally homogenized by vigorous hydrothermal circulation and hence vary smoothly between drilling sites at the young end of the transect near the region of extensive outcrop heat flow is only 15 of that predicted for lithosphere of this age heat flow increases systematically to the east reaching the full predicted level about 20 km from the point of sediment basement onlap the anomaly can be accounted for by mixing and or eastward flow of cool water in the upper igneous crust beneath the sediment at a darcian rate of the order of 1 m yr a geochemical signature of fresh seawater in basement is observed many tens of kilometers farther to the east although the thermal signature is no longer present along the remainder of the transect the heat flow conforms very well to that predicted by simple boundary layer cooling theory once the thermal effects of rapid sedimentation on this ridge flank are accounted for

age thermal evolution and history of the black sea basin based on heat flow and multichannel reflection data abstract multichannel reflection data tugolessov et al 1985 have revealed two deeps in the basement topography of the black sea which are filled with sediments from 12 to 15 km thick the deeps lack the granitic layer and are underlain by oceanic type crust which we assume to be generated by seafloor spreading processes the age of the deeps was interpreted previously in a highly controversial manner as being from the paleozoic early mesozoic to the recent in the paper age estimations were undertaken using surficial heat flow data assuming that they are related to deep seated age dependent heat flow generated by the cooling oceanic lithosphere but that they are strongly distorted by the heating of continuously accumulating sediments as well as by additional heat input from radiogenic production within sediments using reliable thermophysical parameters of compacting sediments the distorted heat flow in the sediments was evaluated numerically this allowed us to estimate the age of the black sea deeps floor the results show that the west black sea deep is 130 to 95 m y old and the east black sea deep is nearly 110 m y old these figures support an interpretation of the black sea deeps as remnants of a late mesozoic back arc basin that evolved behind the lesser caucasian pontide island arc the inferred middle cretaceous age of the deeps is the first estimate obtained quantitatively and corresponds well with available heat flow and multichannel reflection data

thermal origin of the hawaiian swell heat flow evidence and thermal models the lithospheric reheating hypothesis for the origin of the hawaiian swell has been tested by heat flow measurements along the swell between hawaii and midway ninety five measurements at eight carefully selected sites show that the heat flux on the swell increases systematically from near normal values 52 2 mw m 2 near hawaii to values near midway 59 2 mw m 2 about 20 25 higher than normal for lithosphere of that age 110 m y this heat flow pattern is qualitatively consistent with a deep seated thermal anomaly created in a lithospheric plate moving across a fixed heat source modeling of the heat flow and bathymetry data on the hawaiian swell strongly suggest that the swell is caused by a rapid heating within 40 to 50 km depth of normal 90 m y old lithosphere over a relatively broad 500 1000 km region near hawaii this model is also consistent with gravity and geoid anomalies associated with the swell which require a low density region in the lower lithosphere and with flexure studies of seamounts in the hawaiian chain which indicate that the rigidity of the lithosphere is not significantly reduced by the reheating appendices a c are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j82 005 1 00 payment must accompany order

the interaction of supertyphoon maemi 2003 with a warm ocean eddy understanding the interaction of ocean eddies with tropical cyclones is critical for improving the understanding and prediction of the tropical cyclone intensity change here an investigation is presented of the interaction between supertyphoon maemi the most intense tropical cyclone in 2003 and a warm ocean eddy in the western north pacific in september 2003 maemi passed directly over a prominent 700 km 500 km warm ocean eddy when passing over the 22 n eddy rich zone in the northwest pacific ocean analyses of satellite altimetry and the best track data from the joint typhoon warning center show that during the 36 h of the maemi eddy encounter maemi s intensity in 1 min sustained wind shot up from 41 ms 1 to its peak of 77 m s 1 maemi subsequently devastated the southern korean peninsula based on results from the coupled hurricane intensity prediction system and satellite microwave sea surface temperature observations it is suggested that the warm eddies act as an effective insulator between typhoons and the deeper ocean cold water the typhoon s self induced sea surface temperature cooling is suppressed owing to the presence of the thicker upper ocean mixed layer in the warm eddy which prevents the deeper cold water from being entrained into the upper ocean mixed layer as simulated using the coupled hurricane intensity prediction system the incorporation of the eddy information yields an evident improvement on maemi s intensity evolution with its peak intensity increased by one category and maintained at category 5 strength for a longer period 36 h of time without the presence of the warm ocean eddy the intensification is less rapid this study can serve as a starting point in the largely speculative and unexplored field of typhoon warm ocean eddy interaction in the western north pacific given the abundance of ocean eddies and intense typhoons in the western north pacific these results highlight the importance of a systematic and in depth investigation of the interaction between typhoons and western north pacific eddies

analysis of regional slope characteristics on venus and earth regional slope values for earth and venus are calculated for each 3 o x 3 o region of topography and the global characteristics of these magnitudes are examined and compared the effects on terrestrial regional slope due to ocean loading are treated by approximating the component of seafloor depth due to the weight of the overlying water column and removing this component from the ocean topography although regional slopes on venus and earth span the same range 0 00 2 4 o 0 07o the slope frequency distributions for the two planets differ significantly the most abundant regional slope values for the terrestrial cases earth and unloaded earth are 0 0 o and reflect the presence of vast plains associated with the continental interiors and ocean abyssal plain in contrast venus exhibits a peak in slope frequency at approximately 0 09 o perhaps indicating less effective planation processes in the absence of a hydrosphere surfaces with regional slope values of 0 07o 0 24 o are substantially more common on venus than on earth slopes in this range are associated with discrete features in the lowland and upland rolling plains provinces of venus and may be indicative of a geologic process that is not commonly observed on earth only 14 1 of all venus surfaces have regional slopes above 0 24 o compared to 26 1 for earth when mean regional slope is calculated as a function of elevation a distinctive positive correlation is expressed on venus in contrast the terrestrial cases exhibit a complex relationship marked by four modes related to the presence on earth of an active hydrosphere driven weathering regime a distinctive crustal dichotomy and plate tectonics the distinctions in the regional slope characteristics between venus and earth point to a simpler less diversified geology on venus

a synthesis of heat flow determinations and thermal modeling along the nankai trough japan 1 we review marine heat flow data along the nankai trough and show that observations 30 km seaward of the deformation front are 20 below conductive predictions 129 94 mw m 2 but consistent with the global heat flow average for oceanic crust of the same age 16 28 ma heat flow values 30 km seaward of the deformation front are generally 20 higher than conductive predictions this heat flow pattern is consistent with the advection of heat by fluid flow in the subducting oceanic crust and explains both the high heat flux in the vicinity of the trench 200 and 140 mw m 2 and steep landward declines to values of approximately 60 mw m 2 over distances of 65 and 50 km along the muroto and kumano transects respectively along the ashizuri transect the lack of heat flow data precludes a definitive interpretation we conclude that fluid flow in the subducting oceanic crust leads to temperatures that are generally 25 c higher near the toe of the margin wedge and 50 100 c lower near the downdip limit of the seismogenic zone than estimated by purely conductive models

an ocean coupling potential intensity index for tropical cyclones american geophysical union 2013 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in geophysical research letters 40 2013 1878 1882 doi 10 1002 grl 50091

interannual warm and cool events in the subtropical mid latitude south indian ocean region interannual warm and cool events in the subtropical mid latitude south indian ocean region that are not associated with extreme phases of the el nino southern oscillation are examined during these events there tend to be periods of significantly anomalous rainfall in large parts of southern africa typically the sea surface temperature sst anomalies become significant during the austral autumn of the first calendar year of the event and dissipate during the spring of the following year examination of cloud cover and near surface winds suggests that atmospheric forcing may contribute towards the sst anomalies via changes in insolation and wind driven upper ocean mixing and surface fluxes

heat flow through the sea bottom around the yucatan peninsula heat flow studies were conducted in january february 1987 off the atlantic coast of mexico on board the r v akademik nikolai strakhov two areas were surveyed one transecting the salt dome province and the campeche canyon in the gulf of mexico and the other on the eastern flank of the yucatan peninsula conductive heat flow through the bottom sediments was determined as the product of vertical temperature gradient and in situ thermal conductivity measured with a thermal probe using a multithermistor array and real time processing capabilities forward two dimensional modeling allows us to estimate heat flow variations at both sites from local disturbances and to obtain average heat flow values of 51 mw m2 for the transect within the gulf of mexico and 38 and 69 mw m2 for two basins within the yucatan area sea bottom relief has a predominant effect over other environmental factors in the scatter of heat flow determination in the gulf of mexico

the effects of sedimentation and compaction on oceanic heat flow summary the estimation of environmental effects forms an important part of the interpretation of oceanic heat flow measurements in particular the perturbations associated with sedimentation and surface temperature changes must be taken into account analytical solutions can be obtained only for individual simplified versions of these problems whereas any real example is complicated by the process of sediment compaction which changes the bulk thermal properties with depth a physical model is developed which uses sediment porosity trends to predict the thermal parameters and material advection rates for an evolving sediment basement system these values are then used in a numerical solution to the heat flow equation to give estimates of the perturbed surface heat flux through time in addition to variations in sedimentation rate sediment type radioactive heat production and surface temperature changes are considered heat flow corrections may vary by up to a factor of 2 according to sediment type while radioactive heat production can offset the effects of sedimentation by as much as 40 per cent the results also indicate that alterations determined from simple analytical models tend to over estimate the true perturbation to the flux

subtropical indian ocean sst dipole events and southern african rainfall an atmospheric general circulation model agcm is used to examine how the regional atmospheric circulation and rainfall over southern africa respond to a recently observed dipole in subtropical sea surface temperature sst over the south indian ocean observations suggest that when sst is warm to the south of madagascar and cool off western australia increased summer rains occur over large areas of southeastern africa the model results suggest that this sst pattern leads to increased rainfall via enhanced convergence of moister than average air over the region increased evaporation occurs over the warm pole in the south west indian ocean and this moist air is advected towards mozambique and eastern south africa as a result of the low pressure anomaly generated over this pole which strengthens the onshore flow

a mechanism for the formation of methane hydrate and seafloor bottom simulating reflectors by vertical fluid expulsion bottom simulating reflectors bsr are observed commonly at a depth of several hundred meters below the seafloor in continental margin sedimentary sections that have undergone recent tectonic consolidation or rapid accumulation they are believed to correspond to the deepest level at which methane hydrate clathrate is stable we present a model in which bsr hydrate layers are formed through the removal of methane from upward moving pore fluids as they pass into the hydrate stability field in this model most of the methane is generated below the level of hydrate stability but not at depths sufficient for significant thermogenic production the methane is primarily biogenic in origin the model requires either a mechanism to remove dissolved methane from the pore fluids or disseminated free gas carried upward with the pore fluid the model accounts for the evidence that the hydrate is concentrated in a layer at the base of the stability field for the source of the large amount of methane contained in the hydrate and for bsrs being common only in special environments strong upward fluid expulsion into the hydrate stability field does not occur in normal sediment depositional regimes so bsrs are uncommon upward fluid expulsion does occur as a result of tectonic thickening and loading in subduction zone accretionary wedges and in areas where rapid deposition results in initial undercconsolidation in these areas hydrate bsrs are common the most poorly quantified aspect of the model is the efficiency with which methane is removed and hydrate is formed as pore fluids pass into the hydrate stability field the critical boundary in the phase diagram between the fluid plus hydrate and fluid only fields is not well constrained however the amount of methane required to form the hydrate and limited data on methane concentrations in pore fluids from deep sea boreholes suggest very efficient removal of methane from rising fluid that may contain less than the amount required for free gas production in most fluid expulsion regimes the quantity of fluid moved upward to the seafloor is great enough to continually remove the excess chloride and the residue of isotope fractionation resulting from hydrate formation thus as observed in borehole data there are no large chloride or isotope anomalies remaining in the local pore fluids the differences in the concentration of methane and probably of co2 in the pore fluid above and below the base of the stability field may have a significant influence on early sediment diagenetic reactions

in a changing climate weakening tropical easterly jet induces more violent tropical storms over the north indian ocean 1 tropical easterly jet tej of summer monsoon over the north indian ocean is weakening in recent years the absolute easterly shear shows a strong negative correlation significant at 99 9 level by students two sided t test with the number of severe storms suggesting that a decrease in easterly shear is favorable for the formation of more severe tropical storms for the first time in recorded history a category 5 hurricane formed in june 2007 together with two more severe tropical storms over the north indian ocean thus if the present decreasing trend of tej intensity continues there is a strong likelihood of the formation of tropical cyclones of hurricane intensity even during the summer monsoon presently these intense systems are known to form only in the pre and post monsoon seasons when the vertical wind shear is small

evidence for excess pore pressures in southwest indian ocean sediments brown clay cores from the madagascar and crozet basins show the following evidence of excess pore pressures large amounts of flow in increasing average sedimentation rate with age and nonlinear temperature gradients additionally many hilltops in these basins have no visible sediment cover the bare hilltops may result from periodic slumping caused by excess pore pressures calculated excess pore pressures which equal or exceed the overburden pressure were inferred from water fluxes predicted by nonlinear temperature gradients and laboratory permeability measurements by using darcy s law since pore pressures which exceed the overburden pressure are unreasonable we attribute this discrepancy to laboratory measures which underestimate the in situ permeability the widespread presence of overpressured sediments in areas of irregular topography provides a process for resuspension of clay sized particles this mechanism does not require high current velocities for the erosion of clay and therefore can be applied to many areas where no strong currents are evident carbonate rich sediments from the madagascar ridge the mozambique ridge and the agulhas plateau had almost no flow in and occurred in areas where all topography was thickly draped with sediment since the age and tectonic location of the ridges and plateaus preclude water circulation in the basement wemore attribute these differences between the brown clay and the carbonate rich material to an absence of significant excess pore pressures in the plateau and ridge sediments less

characterization of the sedimentary thermal regime along the corsair growth fault zone texas continental shelf using corrected bottomhole temperatures temperatures of deep 3 km 1 8 mi sediments along the corsair growth fault zone in the texas continental shelf are elevated relative to those off the fault zone this observation is based on a compilation of nearly 400 bottomhole temperatures bhts obtained from about 230 wells widely distributed across the continental shelf the bhts have been individually corrected for the thermal disturbance associated with drill fluid circulation the isotherm of 140 c 284 f derived from the corrected bhts shows more or less continuous peaks along the fault zone thermal gradients in the depth range of 3 to 5 km 1 8 to 3 1 mi shows higher values along the fault zone than off the fault zone these trends are similar to the previous observations made along the wilcox growth fault zone in the texas coastal plain previous studies suggest that the faults of the wilcox system serve as the conduits for hot fluids expelled from deep overpressured sediments a similar mechanism may explain the elevated temperatures along the corsair fault zone

heat flow and the thermal origin of hot spot swells the hawaiian swell revisited we present 150 new heat flow measurements obtained at eight sites along a 1230 km long profile across the hawaiian swell about 700 km ese of midway island most of the measurements include in situ thermal conductivity determinations which helped to reduce the statistical uncertainties 95 confidence at all sites to 59 mw m 2 about 20 higher than the predicted heat flow for 100 ma seafloor based on simple lithospheric cooling models thus even though there is a small increase in heat flow with age along the swell when compared with the off swell heat flux the anomalous heat flow associated with the hawaiian swell is probably of the order of 5 10 mw m 2 and arguably may not exist at all a previous investigation von herzen et al 1982 may have overestimated the magnitude of the heat flow anomaly associated with the hawaiian swell by comparing heat flux measurements on the swell with values expected for simple lithospheric cooling models the heat flow anomalies associated with the bermuda rise and the cape verde rise may also be smaller than previously estimated given the uncertainties in the heat flux on the normal seafloor surrounding these swells the lack of a significant heat flow anomaly associated with the bathymetric expression of the hawaiian swell is inconsistent with simple models of lithospheric reheating dynamic support accompanied by modest temperature increases 80 ma oceanic lithosphere

strong impact of ion filtration on the isotopic composition of chlorine in young clay rich oceanic sediment pore fluids abstract a collection of 34 pore fluids from young clay rich sedimentary piles of the shikoku basin on the philippine oceanic plate at the front of the nankai subduction zone southeast of japan were analyzed for their chloride content and chlorine stable isotope composition 35cl and 37cl reported as 37cl these pore fluids are samples from iodp sites c0011 and c0012 which penetrate deeper than 500 meters below the seafloor at both sites the 37cl values display a regular decrease with depth from about 0 seawater value at the seafloor to 8 5 and 6 5 respectively in hydrogeologically isolated low permeability sediment levels at some depths local deviations of up to 6 in 37cl interrupt the overall decreasing trends they may be interpreted as the injection of external fluids into the sedimentary piles as a result of sedimentary levels with higher permeability at the bottom of the sedimentary piles the injected fluids probably originating from the altered oceanic crust systematically have 37cl values closer to seawater literature data indicate the display of downward trends of decreasing 37cl values of the pore fluids in many other young clay rich sedimentary piles nankai trough and the japan trench accretionary prisms black ridge and juan de fuca ridge flank here we use conservation equations to demonstrate that these 37cl depth profiles can be modeled using the effect of the compaction of growing clay rich sedimentary piles on the water and chlorides including 35cl and 37cl isotopes this modeling shows that a small isotope fractionation of chlorine isotopes 37cl 35clexpulsed fluid residual fluid in the range of 1 006 to 1 001 may explain the observed negative 37cl chlorides at the bottom of the sedimentary piles the complementary positive 37cl chlorides must accumulate at the top but are very likely erased by dilution with seawater chlorides across the seafloor interface this range of chlorine isotope fractionation values is in agreement with the theory of ion filtration of phillips and bentley 1987 in which the mobility of chlorides through semi permeable clay membrane is determined by ion repulsion based on this study we show that young pore fluids in clay rich sediments of the oceanic crust are 37cl depleted chloride reservoirs they might be the source of 37cl depleted chloride fluids advected at mud volcanoes on the seafloor but do not seem to contribute largely to subduction zone magmatic tectonic metamorphic products where no such 37cl depleted chlorine is documented this in turn is a strong argument to propose that most of the clay rich sediment s pore waters are released back into the ocean rather than subducted

thermal history of deep sea sediments as a record of recent changes in the deep circulation of the eastern mediterranean 1 during three cruises of the medriff project in 1993 and 1994 154 geothermal heat flow measurements and seven ctd profiles in the water column have been collected along a 300 km sw ne oriented transect traversing the mediterranean ridge accretionary complex the original goal of the measurements was to identify areas of anomalous heat flow that could be interpreted as possible sites for fluid outflow contrary to expectations the upper few meters of the temperature profiles in the sediments showed decreasing temperature from the seafloor down to 3 to 6 m depth indicating consistently transient temperature regimes the only exception positive heat flow was found in the sirte abyssal plain measurements collected in the same area at different times indicated that the thermal structure in the bottom water and sediments had changed significantly at weekly monthly and interannual timescales one dimensional forward modeling of the conductive heat propagation into the sediment explains the observed thermal anomalies assuming up to 0 5 k warming of the bottom waters that propagated south westward from the matapan trench to the crestal area of the mediterranean ridge analysis of nonsteady state thermal profiles in the upper sediment provided time information on the onset of bottom water warming by what is now called the eastern mediterranean transient emt the sediment warming started in the matapan trench between spring 1992 and spring 1993 and reached the mediterranean ridge crest in spring summer 1993 the average propagation velocity of the thermal perturbation along the profile is about 0 5 1 6 km d 1 0 6 1 8 cm s 1

heat flow and thermal models of the barbados ridge accretionary complex the pattern of heat flow from the barbados ridge accretionary complex has been derived from marine surveys with heat flow probes from measurements in drill holes and from the depths of bottom simulating seismic reflectors caused by gas hydrate the heat flow from the accretionary complex has been simulated using a finite difference model to investigate how heat flow responds to changes in the cross sectional shape of the complex and the rate of convergence and to variations in pore fluid pressure within the complex and along the decollement at its base in the south of the complex heat flow decreases westward from the toe of the wedge towards the island arc because the downward movement of subducting lithosphere beneath the wedge and the active thickening of the accreted sedimentary sequence reduce the geothermal gradient more rapidly than thermal diffusion can maintain it localised high anomalies attributed to the flow of warm fluids along fault zones are superimposed on the conductive heat flow pattern farther west heat flow increases arcward produced partly by thermal diffusion re establishing a steeper thermal gradient where the rate of thickening is decreased but mainly by the arcward increase of frictional heating along the base of the wedge caused by the increase of slip rate and increased normal stress arising from thickening of the wedge in the north of the complex around the odp leg 110 drill sites the conductive model cannot reproduce the anomalously high heat flow measurements which can only be explained by the advection of warm pore fluids

a constraint on the shear stress at the pacific australian plate boundary from heat flow and seismicity at the kermadec forearc new heat flow measurements and relocated hypocenters that constrain the subduction geometry of the pacific plate at the kermadec trench yield an estimate of shear stress on the thrust fault with the exception of a few relatively high values 60 mw m 2 on the upper forearc region near the active volcanic ridge most of the 64 heat flow values along two profiles across the forearc range from 20 to 40 mw m 2 corrections for bottom water temperature variations that caused nonuniform temperature gradients were required for most measurements the means of the most reliable values for the northern and southern profiles are 28 9 5 8 mw m 2 n 33 and 28 9 7 2 mw m 2 n 19 respectively and the measurements show no apparent systematic variation along the profiles over the range 50 to 150 km distance from the trench the means of the 10 values at each of two sites on the pacific plate seaward of the profiles are 57 2 6 3 and 60 2 6 6 mw m 2 redeterminations of focal depths and fault plane solutions of earthquakes in the vicinity of the heat flow profiles indicate thrust faulting on a plane dipping 17 2 calculated values of heat flow for a two dimensional analytical approximation to conduction through the upper plate diffusion into the downgoing slab and advection by that slab are consistent with either a uniform stress of 40 17 mpa along the thrust fault or stress increasing linearly at 0 5 0 2 mpa km 1 with distance from the trench axis the comparable scatter in the heat flow measurements about those calculated from these simple stress distributions does not show one to be a better approximation than the other