along strike variations of earthquake apparent stress at the nicoya peninsula costa rica subduction zone oceanic plates vary in temperature topography and sediment load as they enter subduction zones these variations persist along the subduction interface causing perturbations in coupling and earthquake rupture processes we explore the effects of variable subducting plate structure on microseismicity rupture characteristics along the nicoya peninsula costa rica the subducting cocos plate has low relief along the northern and central portion of the peninsula with seamounts present at the southern tip of the peninsula we compute apparent stresses for 94 ml 2 5 4 2 earthquakes along the plate interface using waveform coda and find along strike variations that mimic bathymetric variability median stress values are higher 3 2 mpa in the smooth northern region with lower values in the central 2 1 mpa and southern 0 7 mpa segments higher apparent stresses along a zone of little suspected subduction topography imply increased coupling or higher friction along the interface these results agree with geodetic and other seismic studies that suggest variable plate coupling along the nicoya peninsula

a new estimate for present day cocos caribbean plate motion implications for slip along the central american volcanic arc velocities from 153 continuously operatinggps sites on the caribbean north american and pacic plates arecombinedwith61newlyestimatedpacic cocosseafloor spreading rates and additional marine geophysical data to deriveanewestimate of present daycocos caribbean plate motion acomparisonofthepredictedcocos caribbean di rectiontoslipdirectionsofnumerousshallow thrustsubduc tion earthquakes from the middle america trench between costa rica and guatemala shows the slip directions to be deflected 10 clockwise from the plate convergence direc tion supporting thehypothesisthatfrequentdextralstrike slip earthquakes along the central american volcanic arc result from partitioning of oblique cocos caribbean plate convergence linear velocity analysis for forearc locations in nicaragua and guatemala predicts 14 2m m yr 1 of northwestward trench parallel slip of the forearc relative to thecaribbean plate possibly decreasing inmagnitude inel salvador and guatemala where extension east of the vol canic arc complicates the tectonic setting

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

estimates of heat flow derived from gas hydrates a gas hydrate phase boundary in marine sediments is often observed as an anomalous reflector in seismic profiling data from the depth of the reflectors heat flow values can be estimated using the phase relation of the gas hydrate system and inferred density and thermal conductivity of sediments this method is applied to the data in the nankai trough around central america and along the blake outer ridge the estimated values consistent with those measured by conventional means suggest that derivation of heat flow by this method is feasible on the landward slope of the nankai trough we find that heat flow increases downslope toward the floor of the trough

magma transport of heat on io a mechanism allowing a thick lithosphere models indicate that the high heat flow from io would result in a very thin approximately 5 km silicate lithosphere overlying a molten interior if all heat was transported through the lithosphere via conduction however the presence of mountains with relief in excess of 10 km would seem to demand a thick lithosphere at least locally a significant fraction of io s heat flow may be transported via advection through volcanoes advective heat transfer permits a thicker lithosphere than does pure conduction possibly reconciling io s high heat flow with the rugged topography

large heat and fluid fluxes driven through mid plate outcrops on ocean crust geophysical data for the cocos plate sea floor suggest that basement outcrops along mid ocean ridge flanks can discharge very large quantities of heat and fluid this is indicative of high crustal permeability at the regional scale

barotropic rossby waves radiating from tropical instability waves in the pacific ocean abstracttropical instability waves are triggered by instabilities of the equatorial current systems and their sea level signal with peak amplitude near 5 n is one of the most prominent features of the dynamic topography of the tropics cross spectral analysis of satellite altimetry observations shows that there is sea level variability in the pacific ocean as far north as hawaii i e 20 n that is coherent with the sea level variability near 5 n associated with tropical instability waves within the uncertainty of the analysis this off equatorial variability obeys the dispersion relation for nondivergent barotropic rossby waves over a fairly broad range of periods 26 38 days and zonal wavelengths 9 23 of longitude that are associated with tropical instability waves the dispersion relation and observed wave properties further suggest that the waves are carrying energy away from the instabilities toward the north pacific subtropical gyre which together with the observed coherence of the sea

thermal regime of the costa rican convergent margin 2 thermal models of the shallow middle america subduction zone offshore costa rica at the costa rica margin along the middle america trench along strike variations in heat flow are well mapped these variations can be understood in terms of either ventilated fluid flow where exposed basement allows fluids to freely advect heat between the crustal aquifer and ocean or insulated fluid flow where continuous sediment cover restricts heat advection to within the crustal aquifer we model fluid flow within the subducting aquifer using nusselt number approximations coupled with finite element models of subduction and explore its effect on temperatures along the subduction thrust the sensitivity of these models to the initial thermal state of the plate and styles of fluid flow either ventilated or insulated is explored heat flow measurements on cool crust accreted at the east pacific rise are consistent with ventilated hydrothermal cooling that continues with subduction these models yield much cooler temperatures than predicted from simulations initialized with conductive predictions and without hydrothermal circulation heat flow transects on warm crust accreted at the cocos nazca spreading center are consistent with models of insulated hydrothermal circulation that advects heat updip within the subducting crustal aquifer near the trench these models are warmer than conductive predictions and cooler than conductive predictions downdip of the trench comparisons between microseismicity and modeled isotherms suggest that the updip limit of microseismicity occurs at temperatures warmer than 100 c and that the downdip extent of microseismicity is bounded by the intersection of the subduction thrust with the base of the overriding crust

thermal properties and thermal structure in the deep water coalbed basin off the shimokita peninsula japan abstract heat transport properties are significant parameters that affect geothermal processes in deep sedimentary basins we measured the thermal properties of deep sediment core samples to a depth of approximately 2500 m below sea floor mbsf whereas most previous studies have only presented data 1 k 1 and calcite cemented sandstone siltstone exhibits the highest conductivity of approximately 3 wm 1 k 1 the other thermal properties are also influenced by the porosity and lithological contrast the correlation between thermal conductivity and porosity is explained by the mixed law model of the geometric mean the one dimensional temperature depth profile at site c0020 estimated from measured thermal conductivity reveals a regression of the thermal gradient with depth and the surface heat flow of 30 mwm 2 which is consistent with the heat flow data near this site was evaluated the obtained results suggest that the linear geothermal gradient estimated from the average thermal conductivity value at shallow sediment materials could overestimate the temperature at greater depths and underestimate the heat flow

mesoscale spectral analysis of in situ horizontal and vertical wind measurements at 6 km as part of the aloha anlc 93 campaign to investigate atmospheric dynamics in situ wind measurements collected at 6 km with the gust probe sensor attached to the national center for atmospheric research electra aircraft were analyzed for 16 flight segments between 61 n and 14 s and between 92 w and 170 w over land and water horizontal wavenumber spectra for the vertical wind and both zonal and meridional horizontal wind components were calculated the zonal and meridional wavenumber spectra exhibited a decrease in the spectral slope from 1 98 0 02 for wavelengths between 2 km and 100 km to 3 18 0 06 for the longer wavelengths between 100 km and 330 km the wavenumber spectrum for the vertical wind component showed a 2 power law dependence for wavelengths in excess of 5 km and a generally flat shape at shorter wavelengths an increase in power at the wavelength of 10 km was detected for the meridional wavenumber spectrum these results were compared with predictions from two spectral models and with spectral results from other observations

non adiabaticity in mantle convection seismic observations indicate that earth s lower mantle is homogeneous as revealed by smooth depth variations of the bulk sound velocity and bullen s inhomogeneity parameter being close to one here we show with 3d spherical convection simulations that it should also be non adiabatic because a significant proportion of mantle heat sources is internal the computer simulations predict non adiabaticity of 100 300 degrees for the lower mantle geotherm with 1 01 implying that the temperature drop across the core mantle boundary exceeds 1000 degrees

fluid flow through active mud dome mound culebra offshore nicoya peninsula costa rica evidence from heat flow surveying mud extrusion is frequently observed as a dewatering phenomenon in compressional tectonic settings such as subduction zones along the middle american trench several of these features have been recently discovered this paper presents a heat flow study of actively venting mound culebra offshore nicoya peninsula and is complemented by data from geophysical surveys and coring the mud diapir is characterised by methane emission and authigenic carbonate formation at its crest and is composed of overconsolidated scaly clays and clast bearing muds compared with the conductive background heat flow the flux through the mud dome is elevated by 10 20 mw m2 possibly related to advection of heat by fluids rising from greater depth decreased chlorinity in the pore waters from gravity cores may support a deep seated fluid origin geothermal measurements across the mound and temperature measurements made with outriggers on gravity corers were corrected for the effects of thermal refraction forced by the topography of the mound corrected values roughly correlate with the topography suggesting advection of heat by fluids rising through the mound thereby generating the prominent methane anomaly over the dome and nurturing vent biota however elevated values occur also to the southeast of the mound we believe that the overconsolidated clays and carbonates on the crest form an almost impermeable lid fluids rising from depth underneath the dome are therefore partially channelled towards the flanks of the mound

fluid methane and energy flux in an active margin gas hydrate province offshore costa rica joint analysis of seafloor temperature data borehole temperature measurements and observations that constrain the position of the top and base of the gas hydrate zone ghz at sites on the non accretionary costa rican margin provide quantitative constraints on the flux of energy fluid and methane through the sediments on the overriding plate a comparison of borehole temperature data obtained in the trench at the toe of the deformed sedimentary wedge and at a midslope location indicates that the thermal regimes are perturbed by appreciable advective flux at 1 km oceanward 19 mm yr 1 and 1 4 km landward 5 7 mm yr 1 of the deformation front this observation is loosely consistent with models that predict the most rapid dewatering and highest rates of fluid expulsion within a few kilometers of the deformation front using data that constrain the thickness of the ghz at three sites on the forearc we estimate methane and fluid flux rates through application of a one dimensional analytical model that constrains the nature of the plumbing system for the gas hydrate reservoir our results indicate a two fold decrease in methane flux between a site located 400 m from the toe of the wedge and a site 12 km from the toe an intermediate site located 1 4 km from the toe of the wedge has a thick ghz extends to at least 340 365 m below seafloor that requires a very high methane supply rate 345 mol m 2 kyr 1 for a mass flux of 5 mm yr 1 we conclude that this site has the most two dimensional fluid flux regime with fluids being fed into the zone laterally by conduits and fractures and vertically by expulsion during compaction of underthrusting sediments

effect of hydrothermal circulation on slab dehydration for the subduction zone of costa rica and nicaragua abstract dehydration of subducting oceanic plates is associated with mantle wedge melting arc volcanism intraslab earthquakes through dehydration embrittlement and the flux of water into the mantle in this study we present two dimensional thermal models of the costa rica nicaragua subduction zone to investigate dehydration reactions within the subducting cocos plate seismic and geochemical observations indicate that the mantle wedge below nicaragua is more hydrated than that below costa rica these trends have been hypothesized to be due to a variation in either the thermal state or the hydration state of the subducting slab despite only small variations in plate age along strike heat flow measurements near the deformation front reveal significantly lower heat flow offshore nicaragua than offshore costa rica these measurements are interpreted to reflect an along strike change in the efficiency of hydrothermal circulation in the oceanic crust we parameterize thermal models in terms of efficient and inefficient hydrothermal circulation and explore their impact on slab temperature in the context of dehydration models relative to models without fluid flow efficient hydrothermal circulation reduces slab temperature by as much at 60 c to depths of 75 km and increases the predicted depth of eclogitization by 15 km inefficient hydrothermal circulation has a commensurately smaller influence on slab temperatures and the depth of eclogitization for both regions the change in eclogitization depth better fits the observed intraslab crustal seismicity but there is not a strong contrast in the slab thermal structure or location of the main dehydration reactions consistent with other studies these results suggest that observed along strike differences in mantle wedge hydration may be better explained by a northwestward increase in the hydration state of the cocos plate before it is subducted

the influence of sea surface temperature on surface wind in the eastern equatorial pacific weekly to monthly variability abstract temporal correlations between near equatorial surface wind and sea surface temperatures sst at 11 w in the eastern pacific ocean are investigated using data from an array of moored sensors between 5 n and 5 s the signature of tropical instability waves with periods of 20 30 days is apparent in time series of sst and both the meridional and zonal wind components results indicate the existence of a band of pronounced horizontal divergence in the surface wind field associated with the large meridional sst gradient equatorial front normally located just north of the equator perturbations of the equatorial front by the instability waves induce fluctuations in the overlying winds evidence of the air sea coupling is stronger in time series of the meridional gradients of wind and sst than between time series of the variables themselves the meridional differencing serves as a high pass filter in the space domain which removes planetary scale wind fluctuations that are unrelated to the local sst

spectral analysis of quikscat surface winds and two dimensional turbulence a spectral decomposition of quikscat surface wind vectors reveals different levels of variance and different values of the spectral slope in various regions of the world ocean for the 12 months investigated the traditional considerations on the factors affecting the shape of the spectra are reviewed and compared to the results in particular the influence of large scale synoptic systems is shown by comparing the steeper and more energetic spectra of the midlatitudes to the shallower spectra of the tropics similarly the signature of convection is investigated by comparing spectra in the tropical convectively active and dry zones of the pacific ocean spectra of vorticity and divergence are calculated along with spectral vorticity to divergence ratios their spatial and temporal variations are discussed it is hypothesized that when convection is enhanced in the tropics the spectral analysis captures the mesoscale synoptic structures in which convection is embedded and that the spectra exhibit some of the characteristics of their midlatitude counterparts i e steeper and more energetic

the nicoya convergent margin a region of exceptionally low heat flow over 100 measurements of seafloor heat flow reveal that the accretionary complex adjacent to the nicoya peninsula is characterized by remarkably low heat flow values over the accretionary prism average 28 mw m and values in the trench and the ocean crust seaward of the trench average 14 mw m we attribute the low heat flow to effective hydrothermal cooling of the upper crust on the subducting plate and suggest that extensional faults created by flexure of the lithosphere enhance hydrothermal circulation thermal models show that subduction of low temperature crust combined with significant frictional heating at the decollement can explain the low and uniform heat flow disparity between heat flow values observed on the lower trench slope with model results suggests upward advection of heat by porewater flux through broadly distributed conduits

the signature of mesoscale eddies on the air sea turbulent heat fluxes in the south atlantic ocean abstract by collocating 10 years 1999 2009 of remotely sensed surface turbulent heat uxes withsatellite altimetry data we investigate the impact of oceanic mesoscale eddies on the latent and sensibleheat uxesinthesouthatlanticocean instronglyenergeticregions suchasthebrazil malvinascon uenceand the agulhas current retro ection eddies explain up to 20 of the total variance in the surfaceturbulent heat uxes with averaged anomalies of 10 20 w m 2 cyclonic anticyclonic respectively eddies are associated with negative positive heat ux anomalies that tend to cool warm the marineatmospheric boundary layer a composite analysis of the turbulent heat ux anomalies inside the eddiesrevealsadirectrelationshipbetweeneddyamplitudeandtheintensityofsuchanomalies inaddition theseanomaliesarestrongerneartheeddycenter decayingradiallytoreachminimumvaluesoutsidetheeddies 1 introduction the ocean atmosphere system is primarily turbulent in the mesoscale band oceanic eddies play a crucialrole in transporting heat salt momentum and biogeochemical tr acersalongtheirtrajectories signi cantlyimpactingtheoceandynamicsand uxes olson 1991 wunsch 1999 morrowetal 2003 mesoscaleeddiesare coherent rotating features with typical horizontal scales of 50 300 km and time scales ranging fromweeks to months cheltonetal 2011a theyalsoexhibitparticularthermohalineverticalstructuresassoci ated with strong dynamical perturbations of the density and pressure elds olson 1991 chaigneau et al 2011 kurian et al 2011 zhang et al 2013 roullet et al 2014 these perturbations extend up to the seasurface leadingtoanomaliesonseasurfaceheight seasurfacetemperature sst andwindstress amongothers frengeretal 2013 souzaetal 2014 asaresult itisexpectedthateddiesimpacttheair sea uxesandtheoverlayingatmosphericcirculation frengeretal 2013 the turbulent latent lhf and sensible shf heat uxes are the primary processes by which the oceanreleases heat to the atmosphere cayan 1992 both the lhf and shf can be derived from bulk formulaelinking oceanic and atmospheric parameters such as air speci c humidity sst and wind speed to theheat exchanged at the air sea interface liu et al 1979 fairall et al 2003 large and yeager 2009 theanomalies caused by mesoscale eddies in some of these parameters have been recently investigated e g white and annis 2003 hausmann and czaja 2012 frenger et al 2013 souza et al 2014 chelton and xie 2010 although there is ample evidence that oceanic mesoscale features have a signi cant impact onair seaproperties thereisstillalackofknowledgeabouttheirsignatureonthesurfaceturbulentheat uxesandtheirpotentialcontributionstothenetsurfaceheatbudget the recent release of daily satellite based data from the french research institute for exploitation of thesea ifremer bentamy et al 2013 has su cient resolution to estimate the lhf and shf associatedwith mesoscale processes the present work merges satellite altimetry sea level anomaly sla data withremotely sensed surface heat uxes to investigate the impact of mesoscale ocean eddies on the lhf andshfinthesouthatlanticocean sa the sa encompasses both quiescent areas and two regions of intense energetic variability associated withthe presence of large mesoscale eddies figure 1a namely the agulhas current retro ection agr olsonand evans 1986 goni et al 1997 andthebrazil malvinascon uence bmc garzoli and garra o 1989 olson et al 1988 more speci cally we aim i to assess the mean lhf and shf anomalies induced bycyclonicandanticycloniceddiesinthesa ii todescribethespatialvariationsoftheheat uxanomaliesinvillasboasetal

gas hydrate stability and the assessment of heat flow through continental margins summary a prominent feature across some continental margins is a bottom simulating reflector bsr this seismic reflection generally coincides with the depth predicted for the base of the gas hydrate stability field because the occurrence of gas hydrates is controlled by temperature and pressure conditions it has been suggested that bsrs mark an isotherm and they have therefore been used to estimate the heat flow through continental margins crucial parameters are the temperature at bsr depth and at the seafloor and the thermal conductivity structure between the bsr and the seabed however very often the required parameters are not available and therefore they have been derived from models for gas hydrate stability and empirical relationships to obtain thermal conductivities from seismic velocities here we use downhole temperature thermal conductivity porosity and logging data from 10 ocean drilling program odp sites drilled into and through the gas hydrate field to investigate the quality of estimates our analyses and application of constraints to the makran margin off pakistan indicate the following i the temperature at bsr depth could be approximated by a seawater methane system although capillary forces chemical impurities or non equilibrium conditions can lower or increase the temperature if calibration by heat probe measurements is possible errors of geothermal gradients are less than 10 per cent otherwise uncertainties of 20 per cent or even higher may arise in addition seasonal variations of bottom water temperature have to be considered because they may affect thermal gradients by up to y10 per cent ii the impact of typical quantities of low thermal conductivity gas hydrate on the bulk thermal conductivity is insignificant iii the thermal conductivity profile between the bsr and the seabed can generally be approximated by a mean value thus iv seabed measurements should be used instead of empirical relationships which may produce errors of 5 30 per cent consequently in addition to high quality seismic data a prerequisite should be a large data set of thermal conductivities and oceanographic data heat probe measurements are recommended to constrain geothermal gradients in this case the uncertainty of heat flow is 5 10 per cent of the estimated heat flow if these data are not available errors uncertainties can reach 50 60 per cent of the calculated value

a kinematic thermal history of the earth s mantle kinematic convection models of the earth s thermal history are computed assuming that subducted slabs along with some entrained material sink all the way to the core mantle boundary the temperatures within the lithosphere and within the mantle away from sinking slabs are computed assuming that the return flow from the core mantle boundary to the surface can be considered as slow vertical advection in the models a drop in asthenospheric temperature occurs near the end of the archean when subducted material first returns to the surface this drop is about 200 c if the subducted material does not mix thermally with the mantle on its way down and if only a thin thermal layer exists at the core mantle boundary we consider the possibility that this temperature drop is an explanation for the transition between archean and proterozoic tectonic styles an implication of the kinematic scheme is that the asthenospheric temperature increases gradually during the archean until the cooler material reaches the surface after the archean the thermal evolution is similar to a well mixed model a difficulty with the convection scheme as well as with any temperature profile in the mantle which is basically adiabatic is that excessively low temperatures in the core are implied if a 100 km thick thermal boundary layer at the core mantle boundary is included then higher core temperatures occur but there is a smaller drop in asthenospheric temperature at the end of the archean

coupled ocean atmospheric waves on the equatorial front striking 20 30 day sea surface temperature waves observed along the equatorial front in the later half of the year are generally believed to be of an oceanic origin here we report the detection of atmospheric waves that are unambiguously tied to these oceanic waves using new satellite measurements of surface winds a general circulation model simulation reveals that these atmospheric waves have a shallow vertical structure trapped in the planetary boundary layer pbl unlike el nino southern oscillation where changes in deep convection are the cause of anomalous winds vertical wave motion penetrates well above the pbl and is likely to impact the distribution and transport of climatically important gas species such as ozone and dimethyl sulfide

local and remote atmospheric response to tropical instability waves a global view from space a la nina took place in the equatorial pacific in 1999 and strong tropical instability waves tiws developed causing large meanders of a sea surface temperature sst front between the equator and 3 n high resolution satellite measurements are used to describe the variability of sst surface wind velocity column integrated water vapor cloud liquid water and precipitation associated with these strong tiws in 1999 coherent ocean atmosphere patterns emerge in both the pacific and atlantic revealing rich regional characteristics in the far eastern pacific southeasterly trades strengthen weaken over positive negative sst anomalies apparently due to enhanced reduced mixing with high speed winds aloft in the central pacific we find evidence that sst induced sea level pressure changes also contribute substantially to wind fluctuations similar sst wind covariability also exists in the southern hemisphere along 2 s but the wind variability induced by unit sst anomaly is much larger than that north of the equator in the central pacific where the equatorial front is broad the northern sst pattern has a large meridional scale and reaches as far north as 6 n further to the north in the intertropical convergence zone itcz where local sst anomalies are small significant variability is found in clouds and precipitation which is further correlated with surface wind convergence in the atlantic tiw signals in sst are strongly trapped near the equator but they induce significant remote response in the itcz which takes a more southern position than its pacific counterpart and thus more susceptible to tiw influence

the effects of mesoscale ocean atmosphere coupling on the large scale ocean circulation abstract small scale variation in wind stress due to ocean atmosphere interaction within the atmospheric boundary layer alters the temporal and spatial scale of ekman pumping driving the double gyre circulation of the ocean a high resolution quasigeostrophic qg ocean model coupled to a dynamic atmospheric mixed layer is used to demonstrate that despite the small spatial scale of the ekman pumping anomalies this phenomenon significantly modifies the large scale ocean circulation the primary effect is to decrease the strength of the nonlinear component of the gyre circulation by approximately 30 40 this result is due to the highest transient ekman pumping anomalies destabilizing the flow in a dynamically sensitive region close to the western boundary current separation the instability of the jet produces a flux of potential vorticity between the two gyres that acts to weaken both gyres

hysteresis in mantle convection plate tectonics systems 1 we use simulations of mantle convection with surface yielding to show that multiple tectonic regimes are possible for equivalent system parameter values models with the same lithospheric strength parameters and the same vigor of convection can display different modes of tectonics within the region of multiple solutions the evolutionary pathway of the system is the dominant factor that determines the tectonic mode e g whether mantle convection operates in a plate tectonic like mode the extent of the multiple regimes window is found to increase with the temperature dependent viscosity contrast across the system the implication for models that seek to predict the tectonic regimes of planets is that the temporal evolution of the planet needs to be taken into account a further implication is that modeling studies can lead to different conclusions regarding the tectonic state of a planet extra solar planets in particular despite the final model parameter values remaining equivalent

methane formation at costa rica continental margin constraints for gas hydrate inventories and cross decollement fluid flow we present a numerical model study in order to quantify the effects of organic carbon poc degradation and fluid migration on methane and gas hydrate formation at odp site 1040 costa rica convergent margin various model runs show that poc degradation in upper plate sediments yields a potential for methane hydrate formation between 0 8 and 2 5 vol of pore space however observed chlorinity anomalies cannot be explained by the amount and the distribution pattern of gas hydrates moreover pore water profiles of ammonia do not match the observations setting up a moderate upward flow 0 03 cm yr 1 of methane enriched low chlorinity fluids induced by dewatering of oceanic plate sediments leads to a good approximation to measured pore water profiles thus enabling a precise estimate of poc degradation kinetics fluid flow has a strong impact on the location of the upper limit of the modeled gas hydrate occurrence zone ghoz and may increase the total amount of gas hydrate by more than 50 our best estimate of the amount of gas hydrate within the ghoz is on average 1 65 vol of pore space which corresponds to about 2 5 tg of methane per km trench within the frontal prism of slope sediments to comply with the fact that subducted pore waters are rich in sulfate and that there is striking evidence for fluid conduits at various depths we performed additional model runs where we simulated fluid flow by using a gauss type rate law allowing us to define distinct fluid sources we can demonstrate that combined methane production in the upper plate sediments and sulfate reduction at the top of the down going slab is sufficient to prevent the upward movement of the zone of anaerobic oxidation of methane aom to above the decollement at given upward advection rates steep pore water gradients along the plate boundary can be explained by lateral backflow within oceanic plate sediments on a long term in the order of at least some 100 000 years fluid flow along conduits is likely to occur at low rates with temporarily increased pulses all modeled runs are constrained by their compatibility to observed pore water profiles

natural gas hydrates on the continental slope off pakistan constraints from seismic techniques summary in october 1997 new vertical incidence wide angle reflection and refraction data were obtained on the convergent continental margin ov pakistan the most prominent feature across the entire margin into the gulf of oman is a bottom simulating reflector bsr this reflection generally coincides with the depth predicted for the base of the gas hydrate stability field on the accretionary prism the bsr is a clear reflection with inverse polarity and strata beneath the bsr show enhanced reflectivities suggesting that gas is trapped between stratigraphic layers joint inversion of wide angle and refraction data yielded a 200 m thick low velocitiy zone at bsr depth using the born expansion band limited impedance logs were calculated from deconvolved and scaled single channel data suggesting that velocity at the bsr drops by 200 m s 1 some 40 km towards the coast cdp4400 of minshull white 1989 yielded a velocity inversion of about 600 m s 1 indicating that bsr characteristics vary significantly across the continental margin ov pakistan beneath the gulf the bsr was sampled at a similar subbottom depth where seismic bright spots occur however its reflection amplitude is unusually low and seismic stratigraphy beneath the bsr did not show enhanced reflectivities joint traveltime inversion of wide angle and refraction data revealed continuously increasing velocities suggesting that an adequate supply of methane for forming free gas and gas hydrate is mainly confined to sediments incorporated into the accretionary prism we believe that these variations are related to an evolutionary process due to tectonic uplift and ongoing sedimentation as sediments are incorporated into the accretionary prism sedimentation and uplift produce an upward migration of isotherms and therefore lead to a dissociation of gas hydrates which releases methane gas and thus causes an enhancement of the bsr our survey imaged bsr properties of the abyssal plain and within the first slope basin at water depths of 3300 m and 2490 m respectively cdp4400 was located farther landwards at a depth of 1730 m within a buried and uplifted and hence more evolved slope basin we therefore suggest that in the accretionary wedge tectonic uplift and ongoing sedimentation cause hydrate recycling by upward migration of the stability field in addition tectonic dewatering may accumulate hydrate at the base of the stability field by advection of methane from depth

comparison of measured and bsr derived heat flow values makran accretionary prism pakistan abstract during the german research cruise so 124 on rv sonne fall 1997 on the makran accretionary wedge off pakistan geophysical investigations were carried out to study the thermal regime at a gas hydrate bearing sediment in a tectonically deformed accretionary wedge on a transect perpendicular to the strike of the deformation front 42 heat flow measurements were carried out accompanied by seismic reflection experiments the investigations start in the south in the abyssal plain and cover the continental slope up to 2300 m water depth the aim of this study is to compare the bsr derived heat flow denoted as estimated heat flow with the values from measurements at the seafloor this requires the calculation of sediment physical properties at depth using empirical relationships between velocity and porosity the value measured and corrected for sedimentation of 47 mw m 2 south of the deformation front is slightly higher than values reported by hutchison et al earth planetary sci lett 56 1981 252 262 in all basins the estimated heatflow is significantly higher than the measured values as a result temperatures at the bsr extrapolated from seafloor measurements are 5 6 k lower than those taken from gas hydrate stability considerations as an overall trend the estimated as well as the measured heat flow show a small decrease from the deformation front to the northward thickening prism a similar observation was made at other accretionary wedges and described by wang et al j geophys res 98 b3 1993 4121 4142 and ferguson et al j geophys res 98 b6 1993 9975 9984 within the slope basins heat flow values show little variation indicating predominantly conductive heat transport fluid flow might occur at the bounding faults where we have little control the effect of rapid sedimentation on the dynamic behavior of the bsr might also have a significant influence on the estimated heat flow values our data set shows clearly that detailed seismic surveys and good control of the subsurface velocity are absolute necessities for the comparison of measured and bsr derived heat flow values however the uncertainty of the velocity porosity relationship together with a high and only approximately established sedimentation rate represent crucial but missing constraints which can be gained only by drilling

satellite scatterometer studies of ocean surface stress and drag coefficients using a direct model this study evaluates the accuracy of estimates of sea surface friction velocity derived using a new model function that operates directly on the nasa scatterometer normalized radar cross section nrcs measurements these nrcs data are first collocated with numerous national data busy center buoys within 0 5 latitude and longitude and are then processed using the new weissman et al 1994 frontal air sea interaction experiment model to produce 25 km by 25 km spatial averages of the friction velocity for several contiguous areas within this region one method of validation of these estimates involves comparisons with friction velocity estimates derived from data collected by the buoys using bulk methods this was conducted at numerous locations the atlantic and pacific coastlines and within the gulf of mexico it is found that there is excellent agreement between these two different measurements in addition this approach enabled the derivation of estimates of the surface drag coefficient with the use of the buoy winds neutral stability winds at 10 m elevation u10n and the scatterometer surface friction velocity u this permitted the study of the dependence of this drag coefficient cd on wind speed in these different regions on spatial scales which had not previously been possible comparisons are made to previously published models of cd that only depend on wind speed with generally good agreement at winds over 6 m 1 s but with significant regional differences at winds less than 6 m 1 s

thermal regime of the costa rican convergent margin 1 along strike variations in heat flow from probe measurements and estimated from bottom simulating reflectors the thermal structure of convergent margins provides information related to the tectonics geodynamics metamorphism and fluid flow of active plate boundaries we report 176 heat flow measurements made with a violin bow style probe across the costa rican margin at the middle america trench the probe measurements are collocated with seismic reflection lines these seismic reflection lines show widespread distribution of bottom simulating reflectors bsrs to extend the spatial coverage of heat flow measurements we estimate heat flow from the depth of bsrs comparisons between probe measurements and bsr derived estimates of heat flow are generally within 10 and improve with distance landward of the deformation front together these determinations provide new information on the thermal regime of this margin consistent with previous studies the margin associated with the northern nicoya peninsula is remarkably cool we define better the southern boundary of the cool region the northern extent of the cool region remains poorly determined a regional trend of decreasing heat flow landward of the deformation front is apparent consistent with the downward advection of heat by the subducting cocos plate high wave number variability at a scale of 5 10 km is significantly greater than the measurement uncertainty and is greater south of the northern nicoya peninsula these heat flow anomalies vary between approximately 20 and 60 mw m 2 and are most likely due to localized fluid flow through mounds and faults on the margin simple one dimensional models show that these anomalies are consistent with flow rates of 7 15 mm yr 1 across the margin toe variability is significant and likely due to fluid flow through deformation structures associated with the frontal sedimentary prism

tectonic plates d thermal structure and the nature of mantle plumes it is proposed that subducting tectonic plates can affect the nature of thermal mantle plumes by determining the temperature drop across a plume source layer the temperature drop affects source layer stability and the morphology of plumes emitted from it numerical models are presented to demonstrate how introduction of platelike behavior in a convecting temperature dependent medium driven by a combination of internal and basal heating can increase the temperature drop across the lower boundary layer the temperature drop increases dramatically following introduction of platelike behavior due to formation of a cold temperature inversion above the lower boundary layer this thermal inversion induced by deposition of upper boundary layer material to the system base decays in time but the temperature drop across the lower boundary layer always remains considerably higher than in models lacking platelike behavior on the basis of model inferred boundary layer temperature drops and previous studies of plume dynamics we argue that generally accepted notions as to the nature of mantle plumes on earth may hinge on the presence of plates the implication for mars and venus planets apparently lacking plate tectonics is that mantle plumes of these planets may differ morphologically from those of earth a corollary model based argument is that as a result of slab induced thermal inversions above the core mantle boundary the lower most mantle may be subadiabatic on average in space and time if major plate reorganization timescales are less than those required to diffuse newly deposited slab material

fluid inclusion petrology and microthermometry of the cocos ridge hydrothermal system iodp expedition 344 crisp 2 site u1414 in this study we present new data from microthermometry of fluid inclusions entrapped in hydrothermal veins along the cocos ridge from the iodp expedition 344 site u1414 the results of our study concern a primary task of iodp expedition 344 to evaluate fluid rock interaction linked with the tectonic evolution of the incoming cocos plate from the early miocene up to recent times aqueous low saline fluids are concentrated within veins from both the cocos ridge basalt and the overlying lithified sediments of unit iii mineralization and crosscutting relationships give constraints for different vein generations isochores from primary reequilibrated and secondary fluid inclusions crossed with litho hydrostatic pressures indicate an anticlockwise pt evolution during vein precipitation and modification by isobaric heating and subsequent cooling at pressures between 210 and 350 bar internal over and underpressures in the inclusions enabled decrepitation and reequilibration of early inclusions but also modification of vein generations in the cocos ridge basalt and in the lithified sediments we propose that lithification of the sediments was accompanied with a first stage of vein development vu1 and vc1 that resulted from galapagos hotspot activity in the middle miocene heat advection either related to the cocos nazca spreading center or to hotspot activity closer to the middle america trench led to subsequent vein modification vc2 vu2 3 related to isobaric heating the latest mineralization vc3 vu3 within aragonite and calcite veins and some vesicles of the cocos ridge basalt occurred during crustal cooling up to recent times fluid inclusion analyses and published isotope data show evidence for communication with deeper sourced high temperature hydrothermal fluids within the cocos plate the fluid source of the hydrothermal veins reflects aqueous low saline pore water mixed with invaded seawater

a window for plate tectonics in terrestrial planet evolution abstract the tectonic regime of a planet depends critically on the contributions of basal and internal heating to the planetary mantle and how these evolve through time we use viscoplastic mantle convection simulations with evolving core mantle boundary temperatures and radiogenic heat decay to explore how these factors affect tectonic regime over the lifetime of a planet the simulations demonstrate i hot mantle conditions coming out of a magma ocean phase of evolution can produce a hot stagnant lid regime whilst a cooler post magma ocean mantle may begin in a plate tectonic regime ii planets may evolve from an initial hot stagnant lid condition through an episodic regime lasting 1 3 gyr into a plate tectonic regime and finally into a cold senescent stagnant lid regime after 10 gyr of evolution as heat production and basal temperatures wane and iii the thermal state of the post magma ocean mantle which effectively sets the initial conditions for the sub solidus mantle convection phase of planetary evolution is one of the most sensitive parameters affecting planetary evolution systems with exactly the same physical parameters may exhibit completely different tectonics depending on the initial state employed estimates of the early earth s temperatures suggest earth may have begun in a hot stagnant lid mode evolving into an episodic regime throughout most of the archaean before finally passing into a plate tectonic regime the implication of these results is that for many cases plate tectonics may be a phase in planetary evolution between hot and cold stagnant states rather than an end member

experimental evidence linking slip instability with seafloor lithology and topography at the costa rica convergent margin seismicity patterns offshore costa rica central america at the middle america trench have led to speculation that large moment magnitude m w 7 0 earthquakes are associated with subducting topographic highs in areas of high basement topography a regionally extensive nannofossil chalk unit is exposed at the seafloor on the incoming plate whereas in regions of low basement topography hemipelagic clay rich sediment is exposed because the entire sediment section is subducted at this margin lithologic variation in the uppermost subducting sediments may control plate boundary fault behavior our laboratory experiments reveal that the chalk is frictionally strong 0 71 0 88 and characterized by velocity weakening and stick slip behavior notably at elevated temperature in contrast the hemipelagic sediment is weak 0 22 0 35 and in many cases velocity strengthening we suggest that the presence of frictionally unstable carbonates at bathymetric highs may play a key previously unrecognized role in governing earthquake nucleation

heat transport efficiency for stagnant lid convection with dislocation viscosity application to mars and venus mantle convection on mars and venus is likely to occur in the regime known as stagnant lid convection we perform thermal boundary layer analyses as well as finite element simulations of stagnant lid convection with non newtonian viscosity which is believed to be more appropriate for the lithosphere and upper mantle and discuss one particular application of the results the efficiency of heat transport on the terrestrial planets as in the case of newtonian viscosity the efficiency of heat transfer in the stagnant lid regime is extremely low compared to plate tectonics for example in the absence of plate tectonics the mantle temperature on earth which is already close to the solidus would be about 700 1500 k higher for the present day value of the surface heat flux for venus the critical heat flux which can be removed without widespread melting is only 10 20 m w m2 for mars it is 15 30 m w m2 therefore there are no doubts that in the absence of mobile plates the mantle temperature would significantly exceed solidus during planetary evolution it is hypothesized that this could cause one or a combination of two possible processes 1 differentiation of radiogenic isotopes into the crust during early planetary magmatism and 2 initiation of some kind of plate tectonics as a result of plate weakening due to melting

hydrologic control of forearc strength and seismicity in the costa rican subduction zone the subduction zone beneath costa rica experiences infrequent large earthquakes in its northwestern part whereas slow slip dominates in the southeast seismic data reveal a disparity in fluid accumulation in the overriding continental crust that correlates with this change in seismic behaviour implying that spatial gradients in fluid content may control subduction zone seismicity

warm core ring velocities inferred from nscat the nasa scatterometer nscat was designed to estimate from space the wind velocity relative to the ocean surface velocity assuming that the spatial scale of the meteorological forcing giving rise to the wind is large compared with the diameter of a warm core ring it should be possible to obtain information about the currents in the ring from the demeaned scatterometer winds to test this hypothesis 14 nscat passes obtained within three days of clear avhrr derived sea surface temperature images showing a warm core ring were analyzed for evidence of circulation in the rings the residual wind vectors for the 14 scatterometer passes were binned and averaged by radial distance from ring center the mean azimuthal component of the speed compares well with adcp data collected in one of the rings a maximum of 0 89 m s 50 km from ring center compared with 0 88 m s and 1 0 m s for the two adcp transects both also at 50 km from ring center

three dimensional seismic imaging of the costa rica accretionary prism structural diversity in a small volume of the lower slope conventional two dimensional seismic reflection investigations have been generally relied upon to provide images of large to medium scale structural features in accretionary prisms we undertook a three dimensional seismic reflection survey of a small part of a prism arcward of the middle america trench off costa rica to more correctly image structure and to use the improved structural information to examine the processes of accretion this survey reveals small features with dimensions of hundreds of meters while also defining features thousands of meters in lateral extent both of which were underappreciated in conventional two dimensional data from the same area we have imaged active off scraping at the trench and both duplexing and out of sequence faulting a few kilometers arcward of the trench fault spacing and reflector geometry vary dramatically over a space of several hundred meters some of these variations are related to visible changes in morphology of the underlying oceanic basement but others are not so easily documented fault surface reflections define an architecture which may control gross fluid motion through the prism this architecture is apparently formed by duplexing and out of sequence faulting and has been maintained by periodic motion on some of the out of sequence faults the slope sediment apron records multiple phases of deformation abundant small offset reverse faults break the seafloor and indicate recent shortening of a broad region of the underlying prism a primary result of this survey is appreciation of the structural diversity across a small width of an accretionary prism

manifestation of oceanic rossby waves in long term multiparametric satellite datasets the characteristics of westward copropagating features in satellite altimetry sea surface temperature and ocean colour data are investigated throughout the global oceans between 50 north and 50 south for the period 1998 2008 a new hybrid filtering approach allowing features with periods between 37 and 410 days to pass polewards of 20 north and south and features with periods between 37 and 205 days to pass within 20 of the equator is found to isolate features whose speed is consistent with predictions of long planetary wave theory throughout much of the oceans features with wavelengths between 300 and 800 km and periods between 205 and 410 days are shown to be a significant source of temperature and chlorophyll variability between 20 and 50 north and south whilst within 20 of the equator signals in the 800 1500 km and 37 205 days range are predominant between 15 and 50 north and south observed propagation speeds are found to closely match those predicted for first mode baroclinic rossby waves by theory in the equatorial pacific and atlantic oceans features with wavelengths 800 2000 km periods 15 40 days and phase speeds 20 50 cm s 1 characteristic of tropical instability waves are preferentially observed the amplitude and phase relationship between copropagating signals in ocean colour and altimetry and sea surface temperature and altimetry is interpreted in terms of the horizontal meridional advection of mean temperature and chlorophyll gradients by rossby waves similar to what has recently been observed for non linear eddies at shorter length scales the observed phase relationships are in good agreement with the range of phases expected for horizontal advection throughout much of the oceans and consistent with the sign of the mean meridional gradients of temperature and chlorophyll these results support the view that horizontal advection be it from waves and or eddies is the dominant mode of covariation of temperature and chlorophyll with sea surface height throughout most of the oceans although the agreement between predicted and observed amplitude and phase relationships is insufficient to completely rule out vertical mechanisms in a few regions we believe that a one size fits all approach for global rossby wave studies can no longer be considered valid and although we have modified our technique to take this into account we advocate future work to develop a fully latitudinally dependent filtering methodology

tectonic structure of the convergent pacific margin offshore costa rica from multichannel seismic reflection data the middle america trench between the cocos ridge and a well studied corridor off the nicoya peninsula has a more varied morphology and structure than previously reported the morphological positive features on the lower plate significantly affect the upper plate structure the cocos ridge has uplifted the margin opposite the osa peninsula northwest of cocos ridge numerous seamounts on the oceanic crust sculptured the margin as they subducted a seamount and a huge slump in the trench axis that currently block lateral sediment transport affect the sediment currently accreted and subducted the greater portion of the trench sediment is subducted beneath a lower slope accretionary mass beneath the middle and upper slope is a margin wedge consisting of a high velocity rock with few internal reflections its upper surface has a nondirectional random relief commonly 500 m high in the middle slope area overlying this surface is a low velocity cover of slope sediment which shows little transgressive stratigraphy and can be traced landward into an inferred eocene section beneath the shelf the shelf basement is composed of nicoya complex ophiolite with the same acoustic velocity similar structure and no apparent dividing geologic boundary with the margin wedge we favor a seaward continuation of the nicoya complex to the middle slope and emphasize the evidence for a non steady state tertiary tectonic history

self consistent generation of tectonic plates in time dependent three dimensional mantle convection simulations 2 strain weakening and asthenosphere 1 in a previous paper tackley 2000b it was shown that a combination of temperature dependent viscosity and viscoplastic yielding is sufficient to give rudimentary plate tectonic like behavior in three dimensional models of mantle convection here the calculations are extended to include two complexities that have been suggested as being important in localizing deformation at plate boundaries strain weakening and the presence of a low viscosity asthenosphere introducing an asthenosphere by reducing the viscosity by a factor of 10 where material reaches a solidus 1 dramatically improves plate quality even if the asthenosphere is restricted to regions around spreading centers 2 gives good smoothly evolving platelike behavior over a wide range of yield stress values spanning an order of magnitude and 3 gives bimodal stable solutions over a range of yield stresses either immobile lid or plate behavior may be obtained depending on initial condition by contrast introducing an asthenosphere by using depth dependent viscosity has a much smaller effect on system behavior increasing strain weakening 1 improves localization at spreading centers but leads to an increasingly complex network of spreading centers fragmenting the plates 2 weakens convergent zones and can make downwellings highly episodic and 3 does not lead to pure transform boundaries in these calculations time dependent damage evolution and instantaneous strain rate weakening give very similar results all cases that display platelike behavior have very long wavelength mantle heterogeneity consistent with earth s

global ocean surface velocities from drifters mean variance el nino southern oscillation response and seasonal cycle 1 global near surface currents are calculated from satellite tracked drogued drifter velocities on a 0 5 0 5 latitude longitude grid using a new methodology data used at each grid point lie within a centered bin of set area with a shape defined by the variance ellipse of current fluctuations within that bin the time mean current its annual harmonic semiannual harmonic correlation with the southern oscillation index soi spatial gradients and residuals are estimated along with formal error bars for each component the time mean field resolves the major surface current systems of the world the magnitude of the variance reveals enhanced eddy kinetic energy in the western boundary current systems in equatorial regions and along the antarctic circumpolar current as well as three large eddy deserts two in the pacific and one in the atlantic the soi component is largest in the western and central tropical pacific but can also be seen in the indian ocean seasonal variations reveal details such as the gyre scale shifts in the convergence centers of the subtropical gyres and the seasonal evolution of tropical currents and eddies in the western tropical pacific ocean the results of this study are available as a monthly climatology

miniaturized data loggers for deep sea sediment temperature gradient measurements abstract a new probe for autonomous high precision temperature measurements in deep sea sediments has been developed by fa antares and the university of bremen and extensively tested during several expeditions the miniaturized temperature data loggers mtls were constructed to be extremely robust small 16 cm long and easy to operate in waterdepths up to 6000 m the temperature range extends from 5 to 60 c with an absolute accuracy of 0 1 k higher absolute accuracy requires calibration with a high precision thermometer the resolution of the a d converter is 16 bit which leads to a temperature resolution of 0 001 k the logging duration and sampling rate can be chosen independently up to 18 h of measurement are possible with the highest sample rate of 1 s data are stored in the non volatile memory which holds up to 64 800 measurements the probe is configured and data downloaded without opening the pressure case by using specialized software and interface hardware the mtls offer a wide variety of marine science applications wherever a high precision temperature measurement is of interest our main application is the investigation of temperature gradients in deep sea sediments where measurements of gradients over a large depth interval are required by fixing loggers on either different kinds of core barrels or on long lances during four expeditions we used the loggers to measure sediment temperature gradients in several geological settings the design of the attachments to the different carriers was varied to optimize the results for different needs these tests were highly successful and the data of high quality therefore the loggers can be recommended for regular use in marine applications

cross spectral analysis of the sst 10 m wind speed coupling resolved by satellite products and climate model simulations this study aims to determine the spatial temporal scales where the sst forcing of the near surface winds takes places and its relationship with the action of coherent ocean eddies here cross spectral statistics are used to examine the relationship between satellite based sst and 10 m wind speed w fields at scales between 10 2 10 4 km and 10 1 10 3 days it is shown that the transition from negative sst w correlations at large scales to positive at oceanic mesoscales occurs at wavelengths coinciding with the atmospheric first baroclinic rossby radius of deformation and that the dispersion of positively correlated signals resembles tropical instability waves near the equator and rossby waves in the extratropics transfer functions are used to estimate the sst driven w response in physical space w c a signal that explains 5 40 of the mesoscale w variance in the equatorial cold tongues and 2 15 at extratropical sst fronts the signature of ocean eddies is clearly visible in w c accounting for 20 60 of its variability in eddy rich regions to provide further insight on the role of ocean eddies in the sst driven coupling the analysis is repeated for two climate model ccsm simulations using ocean grid resolutions of 1 circ eddy parameterized lr and 0 1 circ eddy resolving hr the lack of resolved eddies in lr leads to a significantly underestimated mesoscale w variance relative to hr conversely the w c variability in hr can exceed the satellite estimates by a factor of two at extratropical sst fronts and underestimate it by a factor of almost six near the equator reflecting shortcomings of the ccsm to be addressed in its future developments

abrupt thermal transition reveals hydrothermal boundary and role of seamounts within the cocos plate 1 new thermal data from 18 24 ma lithosphere on the cocos plate delineate contrasting subsurface thermal conditions in adjacent sections of crust heat flow through seafloor created at the east pacific rise is generally suppressed by 70 relative to conductive lithospheric cooling models whereas heat flow through adjacent similarly aged lithosphere generated at the cocos nazca spreading center is consistent with these models the transition between thermal regimes is remarkably abrupt only 2 5 km wide indicating a shallow hydrothermal origin the transition is more closely associated with differences in the distribution of basement outcrops than with tectonic boundaries demonstrating the importance of the former in extracting heat from the lithosphere on a regional basis

fluid flow paths in the middle america trench and costa rica margin the hydrology of the subducting plate and its dewatering behavior through the shallow subduction zone is linked to the structure and deformation of the forearc prism the nature of the seismogenic zone the composition of seawater for selected elements and the composition of the residual slab subducted to depths of magma generation at the volcanic arc two locally independent systems of fluid flow govern the transport of heat and chemistry through the costa rica subduction complex a dominantly nonaccretionary subduction zone one fluid system is the margin wedge decollement and underthrust sediment section fluid sources include local sediment compaction and mineral dehydration at depth a second flow system occurs in basement beneath the sedimentary sequence on the incoming plate this region is characterized by extremely low conductive heat flow and the sediment overlying basement has pore water geochemistry similar to that of seawater flow nearly parallel to the trench could be directed by permeability associated with faults and driven by a combination of differential heating and earthquake strain cycling

structure of the costa rica convergent margin offshore nicoya peninsula we present the results of a seismic refraction survey conducted offshore costa rica near the nicoya peninsula a dip profile and three strike profiles were carried out over 22 ocean bottom hydrophones and seismographs and were also recorded by land receivers these data are used to construct a crustal structure model of the convergent margin from 20 km seaward of the middle america trench onto the nicoya peninsula the best constrained portion of our model is the velocity at the top of the margin wedge immediately below the slope apron velocities increase from 3 5 to 4 2 to 4 6 km s at distances of 10 20 and 30 50 km landward of the trench these velocities are higher than observed within margin wedges at other well studied convergent margins but lower than the velocities within the adjacent nicoya complex which are 5 5 km s at similar depths below the surface we interpret the margin wedge velocities as indicating that material similar to the nicoya complex extends seaward to near the lower slope but that fracturing alteration or accretion processes have lowered the velocity of the margin wedge with respect to the nicoya complex the seismic refraction data cannot constrain the exact thickness or velocity of a possible low velocity zone lvz overlying the subducting plate however geologically reasonable structures are only produced with a lvz 400 m thick velocities in the upper part of oceanic layer 2 are 3 5 4 0 km s within the subducting slab these velocities are unusually low for oceanic crust of this age and may correlate with a proposed highly permeable zone at the top of the subducting crust the top of the subducted slab is well resolved and deepens from 5 km depth at the trench to 15 16 km depth at the nicoya peninsula coastline the dip angle of the subducting plate increases from 6 to 13 at a distance of 30 km from the trench interplate seismicity appears to become common 55 km from the trench where the plate boundary is at 14 km depth

low heat flow from young oceanic lithosphere at the middle america trench off mexico seismic reflection profiles across the middle america trench at 20 n show a high amplitude bottom simulating reflector interpreted as marking a phase transition between methane hydrate and free gas in the pore space of both accreted and trench sediments we determine the depth of the hydrate gas phase boundary in order to estimate the geothermal gradient and hence the heat flow beneath the trench and the frontal part of the accretionary wedge which overlies the downgoing plate after correction for sedimentation heat flow values in the trench and through the accretionary wedge are only about half of the values predicted by plate cooling models for the 10 ma subducting lithosphere there is no systematic correlation between heat flow in the accretionary wedge and distance from the trench a comparison with heat flow predicted by a simple analytical model suggests that there is little shear heating from within or beneath the wedge despite the high basal friction suggested by the large taper angle of the wedge the geothermal gradient varies systematically along the margin and is negatively correlated with the frontal slope of the wedge some local peaks may be attributed to channelised fluid expulsion

heat flow variations from bottom simulating reflectors on the cascadia margin abstract a bottom simulating reflector bsr representing the base of the gas hydrate stability field was observed over a closely spaced grid of seismic lines on the continental slope of the northern cascadia margin a simple conductive model was used to calculate heat flow from the depth of the bsr a regional trend was observed in which heat flow decreased landward across the margin from an average of 80 mw m2 at a distance of 15 km from the deformation front to 65 mw m2 at a distance of 40 km this trend reflects the processes of tectonic thickening of accretionary wedge sediments and subduction of the juan de fuca plate and contrasts with the near constant heat flow across the oregon margin where the dip of the subducting plate and thus the rate of sediment thickening are slightly smaller consistent local variations were also observed notably low heat flow values over prominent topographic highs and high heat flow values over the flanks of the topographic highs at some localities over a horizontal distance of 1 2 km heat flow increased by as much as 50 from typical values of 65 to 100 mw m2 much of this variation may be due to focusing and defocusing effects of the topography alone and indicates the importance of carrying out topographic corrections to heat flow in regions of significant relief such as the continental slope however a component of the local heat flow patterns may be due to dynamic effects including the displacement of isotherms by thrust faulting and the upward migration of warm fluids along permeability channels such as faults

the influence of sea surface temperature on surface wind in the eastern equatorial pacific seasonal and interannual variability abstract the climate of the eastern pacific exhibits a pronounced equatorial asymmetry boundary layer air originating in the southern hemisphere trades crosses the equator and flows into the intertropical convergence zone itcz whose southern limit is nearly always located at least 4 to the north of the equator the sea surface temperature sst distribution is characterized by a prominent cold tongue centered 1 s a strong frontal zone centered 2 n and a warm eastward current centered near 5 n the surface wind field exhibits a pronounced horizontal divergence as the air flows northward across the oceanic frontal zone these features vary in strength in response to the annual cycle and the el nino southern oscillation phenomenon the northward cross equatorial surface winds the cold tongue and the frontal zone all tend to be strongest during the cold season july through november during the cold season of the coldest years when the cold tongue is most prominent the cross equatorial flow t

the effects of sst induced surface wind speed and direction gradients on midlatitude surface vorticity and divergence abstract the effects of surface wind speed and direction gradients on midlatitude surface vorticity and divergence fields associated with mesoscale sea surface temperature sst variability having spatial scales of 100 1000 km are investigated using vector wind observations from the seawinds scatterometer on the quick scatterometer quikscat satellite and sst from the advanced microwave scanning radiometer for earth observing system amsr e aqua satellite the wind sst coupling is analyzed over the period june 2002 august 2008 corresponding to the first 6 years of the amsr e mission previous studies have shown that strong wind speed gradients develop in response to persistent mesoscale sst features associated with the kuroshio extension gulf stream south atlantic and agulhas return current regions midlatitude sst fronts also significantly modify surface wind direction the surface wind speed and direction responses to typical sst differences of about 2 4 c are on average about 1 2 m s 1 and 4

the efficiency of plate tectonics and nonequilibrium dynamical evolution of planetary mantles consideration of the structure of dynamical equilibria in terrestrial planets using simplified descriptions of the relevant heat transport processes rigid lid convection plate tectonics and heat pipe volcanism reveals that if the efficiency of plate tectonic heat transport decreases at higher mantle temperature then it cannot govern quasi equilibrium dynamical evolution and the system is always evolving away from the plate tectonic regime a planet on which plate tectonics is less efficient at higher temperature stays in heat pipe mode longer spends less time undergoing plate tectonics and has a low and ever decreasing urey number during this phase these conclusions are based solely on the structure of the equilibria in a system with less efficient plate tectonics in the past and are independent of the mechanisms leading to this behavior commonly used quasi equilibrium approaches to planetary thermal evolution are likely not valid for planets in which heat transport becomes less efficient at higher temperature

avo study of a gas hydrate deposit offshore costa rica amplitude variation with offset avo analysis and waveform inversion are techniques used to determine qualitative or quantitative information on gas hydrates and free gas in sediments however the quantitative contribution of gas hydrates to the acoustic impedance contrast observed at the bottom simulating reflector and the reliability of quantitative avo analyses are still topics of discussion in this study common midpoint gathers from multichannel wide angle reflection seismic data acquired offshore costa rica have been processed to preserve true amplitude information at the bottom simulating reflector for a quantitative avo analysis incorporating angles of incidence of up to 60 corrections were applied for effects that significantly alter the observed amplitudes such as the source directivity avo and rock physics modelling indicate that free gas immediately beneath the gas hydrate stability zone can be detected and low concentrations can be quantified from avo analysis whereas the offset dependent reflectivity is not sensitive to gas hydrate concentrations of less than about 10 at the base of the gas hydrate stability zone bulk free gas saturations up to 5 have been determined from the reflection seismic data assuming a homogeneous distribution of free gas in the sediment assuming a patchy distribution of free gas increases the estimated concentrations up to 14 there is a patchy occurrence of bottom simulating reflectors south east of the nicoya peninsula on the continental margin offshore costa rica avo analysis indicates that this phenomenon is related to the local presence of free gas beneath the gas hydrate stability zone probably related to a focused vertical fluid flow in areas without bottom simulating reflectors the results indicate that no free gas is present

three dimensional thermal model of the costa rica nicaragua subduction zone the thermal structure of a subduction zone controls many key processes including subducting plate metamorphism and dehydration the megathrust earthquake seismogenic zone and volcanic arc magmatism here we present the first three dimensional 3d steady state kinematic dynamic thermal model for the costa rica nicaragua subduction zone the model consists of the subducting cocos plate the overriding caribbean plate and a viscous mantle wedge in which flow is driven by interactions with the downgoing slab the cocos plate geometry includes along strike variations in slab dip which induce along strike flow in the mantle wedge along strike flow occurs primarily below costa rica with a maximum magnitude of 4 cm year 40 of the convergence rate for a mantle with a dislocation creep rheology an isoviscous mantle has lower velocities along margin flow causes temperatures variations of up to 80 c in the subducting slab and mantle wedge at the volcanic arc and backarc the 3d effects do not strongly alter the shallow 35 km thermal structure of the subduction zone the models predict that the megathrust seismogenic zone width decreases from 100 km below costa rica to just a few kilometers below nicaragua the narrow width in the north is due to hydrothermal cooling of the oceanic plate these results are in good agreement with previous 2d models and with the rupture area of recent earthquakes in the models along strike mantle flow is induced only by variations in slab dip with flow directed toward the south where the dip angle is smallest in contrast geochemical and seismic observations suggest a northward flow of 6 19 cm year we do not observe this in our models suggesting that northward flow may be driven by additional factors such as slab rollback or proximity to a slab edge slab window such high velocities may significantly affect the thermal structure especially at the southern end of the subduction zone in this area 3d models that include slab rollback and a slab edge are needed to investigate the mantle structure and dynamics

revised tectonic boundaries in the cocos plate off costa rica implications for the segmentation of the convergent margin and for plate tectonic models the oceanic cocos plate subducting beneath costa rica has a complex plate tectonic history resulting in segmentation new lines of magnetic data clearly define tectonic boundaries which separate lithosphere formed at the east pacific rise from lithosphere formed at the cocos nazca spreading center they also define two early phase cocos nazca spreading regimes and a major propagator in addition to these sharply defined tectonic boundaries are overprinted boundaries from volcanism during passage of cocos plate over the galapagos hot spot the subducted segment boundaries correspond with distinct changes in upper plate tectonic structure and features of the subducted slab newly identified seafloor spreading anomalies show oceanic lithosphere formed during initial breakup of the farallon plate at 22 7 ma and opening of the cocos nazca spreading center a revised regional compilation of magnetic anomalies allows refinement of plate tectonic models for the early history of the cocos nazca spreading center at 19 5 ma a major ridge jump reshaped its geometry and after 14 5 ma multiple southward ridge jumps led to a highly asymmetric accretion of lithosphere a suspected cause of ridge jumps is an interaction of the cocos nazca spreading center with the galapagos hot spot

seafloor structural observations costa rica accretionary prism by studying seafloor morphology we can make associations between near surface deformation fluid flow and the overall structural framework of accretionary prisms in february 1994 a ds rv alvin program to the costa rica accretionary prism investigated the relationship of fluid seepage and sediment deformation by using the distribution of chemosynthetic communities and heat flow anomalies as indicators of fluid flow the active normal faults that cut the hemipelagic section on the cocos plate may provide conduits for fluids that cause the regional heat flow to be extremely low these normal faults intersect the toe of the prism at an oblique angle creating localized regions of increased deformation positive heat flow anomalies observed at the deformation front indicate diffuse fluid flow however we discovered no seep communities indicative of focused flow the seaward most seep communities discovered are in a region of active out of sequence thrusts that cut a sediment apron which covers the complex to within 3 km of the prism toe vents occur consistently at the base of the fault scarps dives on a mud diapir show extensive seep communities pock marks and authigenic carbonates evidence of fluid release is on the crest which implies a low viscosity fluid migrating upward in the center of the structure normal faults on the upper slope can be seen in cross section in the walls of a submarine canyon the faults cut the slope apron and displace the seafloor actively maintaining the critical taper of the prism

an analytic model of convection in a system with layered viscosity and plates summary we present an analytic boundary layer model for thermal convection with a finite strength plate and depth dependent viscosity the model permits solutions in which convective flow rates in the mantle exceed the plate velocity the energy balance equations for the lithosphere and convective cell are distinct and the model yields the plate velocity plate thickness and heat flow as well as the laterally averaged horizontal flow profile for a convective cell we demonstrate by inspection of the lithospheric energy balance that the dominant plate driving force depends not only on the material properties of the mantle and lithosphere but also on the velocity of the plate multiple solutions are possible with three solution branches for the plate velocity representing three distinct modes of thermal convection the branch of solutions with the largest plate velocity corresponds to the classic boundary layer solution with a plate velocity approximately equal to the maximum mantle velocity this branch reproduces the classic convective scaling laws for an isoviscous fluid and its dynamics are controlled by the mantle material properties the branch of solutions with intermediate plate velocity represents a convective cell with a sluggish lid and a plate velocity that is less than the underlying mantle velocity the dynamics for this solution branch depend on the material properties of both the mantle and the lithosphere finally the lower branch of solutions for the plate velocity yields a convective solution in which the plate velocity is determined entirely by the local dynamics of a thick and strong relative to the mantle lithosphere the dynamics of this solution branch are independent of the material properties of the mantle and depend entirely on the properties of the lithosphere the introduction of an asthenosphere or low viscosity layer lvl beneath the plate can significantly alter the dynamics of the system by affecting plate mantle coupling lowering the lvl viscosity relative to the lower mantle can promote plate motion by providing a lubricating layer however a very low viscosity lvl beneath a strong plate can decouple plate and mantle and inhibit plate motion producing a solution with a slow moving plate and a channelized flow in the lvl thus a lvl can sometimes inhibit rather than promote plate tectonics

the evolution and propagation of quasigeostrophic ocean eddies abstractthe long term evolution of initially gaussian eddies is studied in a reduced gravity shallow water model using both linear and nonlinear quasigeostrophic theory in an attempt to understand westward propagating mesoscale eddies observed and tracked by satellite altimetry by examining both isolated eddies and a large basin seeded with eddies with statistical characteristics consistent with those of observed eddies it is shown that long term eddy coherence and the zonal wavenumber frequency power spectral density are best matched by the nonlinear model individual characteristics of the eddies including amplitude decay horizontal length scale decay and zonal and meridional propagation speed of a previously unrecognized quasi stable state are examined the results show that the meridional deflections from purely westward flow poleward for cyclones and equatorward for anticyclones are consistent with satellite observations examination of the fluid transport properties of the eddies shows that an

tropical instability wave kinematics observations from the tropical instability wave experiment the kinematics of planetary waves originating from instability of the nearsurface equatorial currents are reported on using velocity measurements from an array of acoustic doppler current profilers deployed in the equatorial pacific during the tropical instability wave experiment a distinctive wave season was observed from august to december 1990 with wave energy confined primarily above the core of the equatorial undercurrent particle motions in the horizontal plane are described by eccentric ellipses oriented toward the north but tilting into the cyclonic shear of the south equatorial current the tilt is maximum near the surface just north of the equator and decreases to the south and with depth the distribution of wave variance is narrowband in both frequency and zonal wavenumber with central period zonal wavelength and westward directed phase propagation estimated to be 500 hours 1060 km and 59 cm s 1 respectively neither the meridional nor the vertical wavenumber component is statistically different from zero these results generally agree with previous findings on tropical instability waves from the atlantic and pacific oceans and in the undersampled arena of geophysical measurements they provide an example where statistical inference is supported by an ensemble of independent measurements

deep sea bottom simulating reflectors calibration of the base of the hydrate stability field as used for heat flow estimates ocean drilling program and deep sea drilling project downhole data from three areas the southwestern japan nankai margin the continental slope off peru and the blake bahama outer ridge provide temperature calibrations for bottom simulating reflectors bsr that mark the base of a clathrate hydrate stability field the inferred temperatures at bsrs provide an important reference for the mapping of geothermal gradient and heat flow from subduction zone accretionary sedimentary wedges the borehole results provide information on which stability field is applicable for the bsrs and thus calibrate the heat flow estimates while an ideal calibration has not been possible the bsr temperatures at the three sites in the temperature range 25 27 c have been estimated with uncertainties of 0 7 to 2 0 c the temperatures correspond closely to the laboratory dissociation temperatures for pure water pure methane hydrate at equivalent pressures no laboratory data are available for seawater salinity and methane at equivalent pressures but extrapolation from lower pressures gives temperatures 1 2 c lower which is just significantly different the data also could be explained by the stability curve for seawater salinity and methane with about 7 co2 or with a small amount of higher hydrocarbons but most hydrate samples that have been recovered by deep sea drilling have contained almost pure methane the uncertainties in the temperature at the bsr should contribute no more than 5 error in heat flow estimates from bsr depths if the pure water methane stability field is used

atmospheric response to mesoscale sea surface temperature anomalies assessment of mechanisms and coupling strength in a high resolution coupled model over the south atlantic many aspects of the coupling between the ocean and atmosphere at the mesoscale on the order of 20 100 km remain unknown while recent observations from the southern ocean revealed that circular fronts associated with oceanic mesoscale eddies leave a distinct imprint on the overlying wind cloud coverage and rain the mechanisms responsible for explaining these atmospheric changes are not well established here the atmospheric response above mesoscale ocean eddies is investigated utilizing a newly developed coupled atmosphere ocean regional model consortium for small scale modeling regional ocean modelling system cosmo roms configured at a horizontal resolution of 10 km for the south atlantic and run for a 3 month period during austral winter of 2004 the model simulated changes in surface wind cloud fraction and rain above the oceanic eddies are very consistent with the relationships inferred from satellite observations for the same region and time from diagnosing the model s momentum balance it is shown that the atmospheric imprint of the oceanic eddies are driven by the modification of vertical mixing in the atmospheric boundary layer rather than secondary flows driven by horizontal pressure gradients this is largely due to the very limited ability of the atmosphere to adjust its temperature over the time scale it takes for an air parcel to pass over these mesoscale oceanic features this results in locally enhanced vertical gradients between the ocean surface and the overlying air and thus a rapid change in turbulent mixing in the atmospheric boundary layer and an associated change in the vertical momentum flux

anomalously cold temperatures observed at the base of the gas hydrate stability zone on the u s atlantic passive margin in situ measurements to depths of 415 m below sea floor in methane hydrate bearing sediments on the u s atlantic passive margin indicate that temperatures at the bottom simulating reflector bsr are anomalously low by 0 5 2 9 c if the bsr marks the base of gas hydrate stability bghs several hypotheses may explain the occurrence of the bsr at inappropriate pressure temperature p t conditions 1 if the bsr does not mark the bghs then p t conditions need not be sufficient to dissociate gas hydrate at this depth 2 the bsr may lie at nonequilibrium p t conditions due to incomplete readjustment in response to upper pleistocene holocene climate change however the occurrence of the blake ridge bsr at an overly shallow depth cannot be easily explained by realistic combinations of pressure driven deepening sea level rise and temperature driven shoaling bottom water temperature changes 3 the properties of sediments or pore fluids may inhibit the stability of gas hydrate in particular capillary forces arising in the fine grained montmorillonite rich sediments of the blake ridge may lead to shoaling of the bsr in this setting

holocene forearc block rotation in response to seamount subduction southeastern peninsula de nicoya costa rica the southeastern tip of the peninsula de nicoya costa rica on the caribbean plate margin lies inboard of the rough bathy metric terrain on the subducting cocos plate and along the land ward projection of the convergence vector for the fisher seamount group the southern tip of the peninsula has nearly orthogonal coastlines and extensive well preserved holocene marine terraces

the crustal structure of the cocos ridge off costa rica 1 the submarine cocos ridge in the northwestern panama basin a bathymetric feature more than 1000 km long and 250 500 km broad is about 2 km shallower than the adjacent basin it is generally interpreted as the trace of the galapagos hot spot two 127 and 260 km long seismic wide angle sections were recorded along and across this ridge offshore the osa peninsula costa rica crustal thickening is seen everywhere along the sections on the northwestern outer ridge flank increased thickness is exclusively attributed to the upper crust and expressed by 2 km thick flow basalts the quepos plateau caps the upper crust in this area toward the center of the cocos ridge the moho deepens from 11 12 to 21 km depth and crustal thickening is almost entirely attributed to the lower crust which makes up 80 of the crust and is three times the thickness of normal oceanic lower crust it is homogeneously structured and the velocities which range from 6 5 km s at the top to 7 35 km s at the base are comparable to normal lower crust under these depth conditions and suggest no differences to a gabbroic rock composition similarities to the crustal velocity structure of iceland central kerguelen plateau and broken ridge are consistent with a formation of this 13 15 ma old cocos ridge segment by excessive magmatism in a near plate boundary setting

the nature and distribution of bottom simulating reflectors at the costa rican convergent margin summary bottom simulating reflectors bsrs at the base of the hydrate stability zone are often observed in marine seismic reflection data the compressional p wave velocity structure of a bsr offshore costa rica was analysed by applying a full waveform inversion technique the resulting velocity profile indicates that the bsr is caused by a thin low velocity layer suggesting the presence of at least a small amount of free gas in the sediment pore space in undisturbed sediment sections bsrs offshore costa rica are observed over much of the continental margin they frequently occur at shallow depths beneath the seafloor usually 100 400 m at some locations bsrs appear to intersect the seafloor this was interpreted as an indication that hydrates in the study area form partly from methane which was produced beneath the hydrate stability zone and migrated upwards in the study area the vertical movement of the hydrate stability zone relative to a given point in the sediment column one of the potential factors leading to bsr formation or suppression is controlled by both sedimentation and vertical tectonism both processes may hence play a role in controlling bsr distribution bsrs are absent in areas which have been affected by slumping except where the sedimentary section above the bsr remained intact during slumping this indicates that slope failure can cause the destruction of bsrs

crustal structure of the middle american trench off costa rica from wide angle seismic data off costa rica seismic wide angle experiments were made using marine seismic sources of high shot density and ocean bottom hydrophones obh and land stations for recording three profiles perpendicular to the middle american trench mat and one parallel to it are presented here the coverage from closely spaced obh and structural constraints from the coincident near vertical reflection seismic survey provided detailed velocity depth distributions over 4 0 km s velocities were found directly underlying the thick continental margin sediment in a margin wedge that extends from below the coastal area seaward within 10 km from the mat axis the interpretation of the wide angle data required a low velocity zone lvz between the upper and lower plate indicating its nature as subducted and underplated sediment the velocity depth distributions support the hypothesis that the continental margin wedge off costa rica is most likely an offshore extension of the nicoya complex ophiolitic rocks which are exposed along the coast the subduction of the sediments seems very efficient and the accretionary prism appears to be confined to the lower slope

low stress drop earthquakes in the rupture zone of the 1992 nicaragua tsunami earthquake tsunami earthquakes events that generate larger than expected tsunami and are deficient in high frequency seismic radiation are rare but hazardous to coastal populations one model for these events is shallow rupture through low strength materials we calculate seismic moment corner frequency and stress drop for 216 earthquakes 2 1 mw 4 7 november 2005 june 2006 within and external to the 1992 nicaragua tsunami earthquake rupture zone to test the hypothesis that differences in fault zone properties defined the limits of the 1992 tsunami rupture zone and continue to produce spatial variations in earthquake source properties mean stress drop of events within the rupture area is 1 2 mpa and 5 5 mpa for events just outside of the rupture zone with similar magnitude earthquakes in each group our results demonstrate different source parameter characteristics for microseismicity in the region of a past tsunami earthquake

variations in temperature gradients identify active faults in the oregon accretionary prism abstract a multi channel seismic survey mcs yields high resolution images of geologic structures within the oregon accretionary prism in addition to revealing the internal geometry of the prism a prominent bottom simulating reflector bsr provides indirect estimates of temperature gradients the bsr marks the phase transition within the pore space of the sediments of small amounts of solid gas hydrate above the reflector to free gas below although the absolute value of temperature gradients depends on assumptions of gas hydrate stability conditions velocity functions and seafloor temperature relative differences reflecting regional trends and local anomalies are unaffected by the assumptions involved in calculation of temperature gradient from the position of the bsr broad scale landward decreases in temperature gradient reflect the increasing depth to the oceanic crust across the accretionary prism correlation of anomalously high temperature gradients with two out of sequence thrusts indicates that these structures are currently acting as conduits for warm fluids

global analysis of the effect of fluid flow on subduction zone temperatures 1 knowledge of the controls on temperature distributions at subduction zones is critical for understanding a wide range of seismic metamorphic and magmatic processes here we present the results of 220 thermal model simulations covering the majority of known subduction zone convergence rates incoming plate ages and slab dips we quantify the thermal effects of fluid circulation in the subducting crust by comparing results with and without advective heat transfer in the oceanic crustal aquifer we find that hydrothermal cooling of a subduction zone is maximized when the subducting slab is young slowly converging steeply dipping and the crustal aquifer is ventilated near the trench incoming plate age is one of the primary controls on the effectiveness of advective heat transfer in the aquifer and the greatest temperature effects occur with an incoming plate 50 ma the thermal effects of fluid circulation decrease dramatically with increasing age of the incoming plate temperatures in the cascadia nankai southern chile colombia ecuador mexico and solomon islands subduction zones are likely strongly affected by fluid circulation for these systems only thermal models of cascadia and nankai have included fluid flow in subducting crust

eddy effects on sea surface temperature and sea surface wind in the continental slope region of the northern south china sea 1 warm and cold sea surface temperature sst tongues on weather timescales are detected in the continental slope region of the northern south china sea nscs and their effects on sea surface wind are studied using satellite observations crossing the basin scale sst front geostrophic currents between cyclonic and anticyclonic eddies induce the warm and cold sst tongues during the northeast monsoon corresponding to the warm and cold sst tongues the sea surface wind is highly uneven in spatial distribution its speed is faster slower over the warm cold sst tongues than the surrounding areas the sst and sea surface wind non uniformity in space shifts southwestward with eddy motion along the continental slope these new findings from satellite observations give us an opportunity to study oceanic eddy s roles in ocean atmosphere interaction on weather timescales

oceanic and atmospheric anomalies of tropical instability waves tropical instability waves tiws are detected in remotely sensed sea surface height ssh temperature sst and wind records of the eastern equatorial pacific analyses of tiw anomaly relationships reveal strong dynamical influence of tiws within approximately 5 of the equator the first influence is advective heat flux the primary forcing of tiw sst anomalies is advection of the meridional temperature gradient by tiw currents the second influence is modification of the wind stress and ekman pumping fields by tiw surface ocean currents by affecting surface stress and hence roughness tiw currents in this low wind region introduce a significant bias in scatterometer vector wind measurement this bias is evident in both nscat and quikscat winds the difference between wind measurements from tao moorings and scatterometers is phase locked with tiw sst oscillations these results have important implications for scatterometry and for understanding tropical dynamics thermodynamics and biogeochemistry

thermal effects of marine sedimentation in hydrothermally active areas summary a hydrothermally active ocean basin vigorous hydrothermal circulation in highly permeable basement rocks maintains a nearly constant temperature at the base of the overlying accumulating sediment section to investigate the thermal effects of sedimentation in such geological settings we have developed a simple onedimensional finite element model and applied it to cases in the northeast pacific the model accounts for differential motion of fluids and sediment grains during compaction and can be used with any porosity depth function results demonstrate clearly that the constant basal temperature of an accumulating sediment section maintained by convective heat transfer in the basement causes the section to remain thermally near steady state for even very high rates of accumulation particularly when compared to conditions estimated for a section where heat is transported in the basement by conduction a 10 kyr period of thermal recovery due to the highly diminished sediment supply during the post pleistocene further reduces the thermal effects of sedimentation by a significant amount only in rare cases where rates of accumulation exceed 10 mm yr l and sediment thicknesses exceed 1 km are the sea floor heat flow and temperatures at depth diminished significantly an example is found in middle valley of the juan de fuca ridge in a part of which over 2 km of sediment has accumulated in the past 200 kyr even in this extreme case the heat flow is estimated to be lower than that of the steady state by about only 15 per cent while rates of accumulation are also high in other parts of middle valley and in many other hydrothermally active areas such as guayamas basin escanaba trough and the eastern flank of the juan de fuca ridge these rates and the accumulated sediment thicknesses are found to be insufficient to cause appreciable thermal anomalies