frictional discharge at fault asperities origin of fractal seismo electromagnetic radiation abstract to investigate the relation between the rock friction and the fractal electromagnetic radiation before the main shock of earthquakes we conducted a friction experiment simulating the motion of an asperity on a fault plane and observed photon emissions due to electric discharge by dielectric breakdown of ambient gases from friction contacts between rock minerals this indicates that frictional discharges plasma generations could occur locally at microscopic asperities on fault surfaces from concepts on the fractal size distribution and temporal evolution of fault asperities the frictional discharge occurring at asperities on the fault plane can be one of origins of the fractal electromagnetic radiation benioff electromagnetic radiation prior to earthquakes

electric and magnetic field changes observed during a seismic swarm in pollino area southern italy abstract over the last few years seismic activity in the pollino area a sector of the calabro lucanian apennines in southern italy known as a seismic gap has been very weak however in 2011 the seismicity gradually intensified culminating in an earthquake of m w 5 0 occurred on 25 october 2012 the depth of the 2011 2012 earthquake hypocenters ranges between 2 and 10 km the seismicity results in two separate clusters and traces a north northwest south southeast fracture more evident in the western sector in this area an mt station was installed on 26 september 2012 by the institute of methodologies for environmental analysis national research council of italy imaa cnr italy at about 50 km from another mt station operating since 2003 in the agri valley tramutola southern italy such a seismic swarm occurred in the pollino area more than 3600 events in last two years with local magnitude m l 0 1 it has provided a rare opportunity to study the earthquake related temporal patterns of electromagnetic em signals and is potentially informative about ongoing seismogenic processes in this study we present several cases of em field variations associated with the passage of seismic waves the maximum amplitude of the electrical signals registered at the two mt sites and the earthquake magnitude are related by an attenuation factor that depends on the distance between the hypocenter and the mt station furthermore at the two mt sites the maximum electrical anomalies seem to be more appreciable predominantly in different directions indicating a certain directivity in the propagation of the electric field a deep analysis of em time series recorded during the mainshock m w 5 0 was performed in particular by applying time frequency misfit criteria based on the continuous wavelet transform we compared the electric field with seismic recordings and we found a good waveform similarity between signals moreover we also found an em signal that significantly anticipates the theoretical first p wave arrival at the tramutola mt station

dissolved and particulate fe in a hydrothermal plume at 9 45 n east pacific rise slow fe ii oxidation kinetics in pacific plumes production of fe iii particles in hydrothermal plumes is of fundamental importance to the long term effect of hydrothermal circulation on seawater composition to elucidate the fundamental controls on fe redox kinetics and solution particle partitioning in neutrally buoyant plumes we sampled near field 3 km plume particles at 9 45 n on the east pacific rise in 1996 returning in 1997 to sample both particulate and dissolved phases 0 40 m filter concentrations of dissolved fe varied from 320 to 20 nm in proximal 0 3 km from vent site to distal samples 1 3 km downfield constituting 85 50 of total fe respectively based on vent fluid dilution factors calculated from dissolved mn a mass balance for vent fluid fe at this site indicates that 65 of fe is lost to particulate sulfide settling in the buoyant plume and that particulate fe in distal 1 3 km samples is twice as concentrated as predicted from dilution of particles in proximal plume water these observations are consistent with a calculated fe ii oxidation half time of 3 3 h long enough that fe iii colloid production and aggregation occurs primarily in the neutrally buoyant plume at relatively high dilutions preventing generation of high particulate fe concentrations 11 56 nm observed a general investigation of fe ii oxidation rates in plumes worldwide gives fe ii oxidation half lives as short as 17 min at some atlantic sites and as long as 6 h at some pacific sites the calculations indicate that the distribution of fe particles in plumes depends chiefly on inter basin differences in ambient deep water chemistry primarily ph and dissolved o2 and on local currents driving plume dilution and to a much lesser extent on variations in primary vent fluid composition long term changes in thermohaline circulation or ocean biogeochemistry may therefore alter fe dynamics and minor element fluxes associated with global hydrothermal activity independent of variations in crustal production rates

chemical processes in buoyant hydrothermal plumes on the east pacific rise near 21 n hydrothermal plume water containing suspended particles of precipitated black smoke has been sampled from three hydrothermal vent fields on the east pacific rise near 21 n the samples were taken within the lower 22 m of the buoyant plumes directly above 273 350 c black smoker vents using go flo bottles mounted on the submersible alvin based on li as a conservative tracer of the high temperature endmember solution mixing ratios of 102 to 104 g seawater g vent water are achieved within the lower 22 m of the plumes the particle concentrations sampled in the lower 13 m of the plumes are much larger than predicted for these mixing ratios suggesting that the particles are settling within the lower part of the plume the major minerals in the smoke are pyrrhotite fe rich sphalerite pyrite unidentified fe s si and fe si s phases chalcopyrite amorphous silica sulfur fe oxyhydroxides including goethite and anhydrite present in trace quantities are barite isocubanite wurtzite covellite marcasite and unidentified silicates and alsilicates organic matter is common the composition of the plume solutions indicates that 35 25 of the hydrothermally injected fe remains in dissolved form i e 0 45 m within the lower 22 m of the plume in spite of a 3 to 9 fold excess of h2s in the vent solutions nearly all of the mn and si and most of the ba also remain in solution h2s by contrast has been largely 70 100 removed by precipitation as sulfides and sulfur but mainly by oxidation to dissolved species with intermediate oxidation states its early removal implies that 50 30 of the injected fe will eventually precipitate as primary oxides rather than as sulfides and that fe can be fractionated from the other chalcophile metals during sulfide precipitation compared with the vent water the particles are enriched in cu co ag cd al zn pb and ni by factors of 4 to 20 relative to fe and depleted in ba s si and mn scavenging from seawater may play a role in co and cu enrichment at the ngs field and for ag cd and ni at all three fields but is negligible for pb and zn these results indicate that two distinct metalliferous components are delivered to the distal regions of a plume as a result of reactions in the lower part of the buoyant plume 1 1 a dissolved component that includes about half the fe and all of the mn and will eventually precipitate as oxides and 2 2 a particulate component consisting of fine grained sulfide minerals that are enriched in ore metals by factors of 4 to 20

near vent chemical processes in a hydrothermal plume insights from an integrated study of the endeavour segment support from onc for sample collection is gratefully acknowledge as is the analytical expertise of jody spence bruno keiffer and maureen soon who helped generate the data set reported here funding for sample analysis came from an nserc discovery grant to l a c ocean networks canada is supported through the canadian foundation for innovation all data are provided in the supporting information or through onc at http dmas uvic ca datasearch

manganese and iron in hydrothermal plumes resulting from the 1996 gorda ridge event abstract we sampled hydrothermal plumes over the n gorda ridge four times between march and august 1996 to document mn and fe discharge resulting from a magmatic intrusion seafloor eruption two separate event plumes ep96a and b and chronic hydrothermal emissions lasting 6 months were characterized shipboard time series measurements of an event plume sample were used to calibrate an fe phase clock useful for estimating sample age up to 6 days after fluid discharge samples collected from ep96a and b had mn heat 2 mol mol 1 ratios similar to historical event plume observations we suggest these signature ratio values are generally characteristic of event plumes and hypothesize that mn and fe may be supplied to event plumes by different processes mn by entrainment of fluids from an extant shallow subseafloor reservoir and fe by short lived high temperature water rock reaction coincident with dike emplacement calculations based on the fe phase clock indicate that the two event plumes were released more than a month apart the largest event plume ep96a 2 3 106 m mn and 13 106 m fe formed 7 march soon after seismic activity began the smaller ep96b 0 49 106 m mn and 3 5 106 m fe was not discharged until 11 april 3 weeks after the cessation of seismic activity detectable by sosus t phase monitoring we hypothesize that the subseafloor disturbance that triggered ep96b also resulted in the episodic flushing of a reservoir of chronic plume like fluids total event plume inventories of mn and fe at n gorda ridge are much smaller than those associated with the 1986 event at n cleft segment of the juan de fuca ridge but comparable to event plume inventories at n cleft segment in 1987 and coaxial segment in 1993 mn heat values for chronic plumes over the eruption site underlying ep96a evolved from moderate 0 25 oonmol j 1 reflecting probable admixture with event plume formation fluids to high 0 7 nmol j 1 typical of chronic plumes to low 0 1 nmol j 1 similar to diffuse vent fluid values marking a complete episode of intrusion eruption induced hydrothermal discharge

magnetic and electric fields associated with changes in high pore pressure in fault zones application to the loma prieta ulf emissions we determined the electric and magnetic fields generated during failure of faults containing sealed compartments with pore pressures ranging from hydrostatic to lithostatic levels exhumed fault studies and strain measurement data limit the possible size of these compartments to less than 1 km in extent rupture of seals between compartments produces rapid pore pressure changes and fluid flow and may create fractures that propagate away from the high pressure compartment along the fault face nonuniform fluid flow results from pressure decrease in the fracture from crack generated dilatancy partial blockage by silica deposition and clearing as pressure increases a direct consequence of this unsteady fluid flow may be associated transient magnetic signals caused by electrokinetic piezomagnetic and magnetohydrodynamic effects models of these processes for fault geometries with 1 km high pressure compartments show that electrokinetic effects are several orders of magnitude larger than the other mechanisms the electrokinetic signals produced by this unsteady flow are comparable in magnitude and frequency to the magnetic signals observed prior to the ml 7 1 loma prieta earthquake of october 18 1989 provided fracture lengths are less than 200 m

temporal and spatial variability of hydrothermal manganese and iron at cleft segment juan de fuca ridge a unique data set for hydrothermal mn and fe was collected at cleft segment on the juan de fuca ridge between 1983 and 1991 the data set includes observations of focused and diffuse venting fluids and neutrally buoyant plumes formed by chronic and episodic venting manganese heat and iron heat ratios for plumes from the north end of the cleft segment were combined with independently determined estimates of plume heat flux to yield annually averaged chronic venting fluxes for mn of 0 36 0 17 mol s 1 and for fe of 0 61 0 34 mol s 1 over 6 years of plume measurements at north cleft segment observed episodic hydrothermal discharge accounted for 15 of the total vented mn and 35 of vented fe the chronic fluxes for mn and fe at a second venting center located at the south end of the cleft segment were estimated to be approximately equal to the fluxes at north cleft segment chronic plumes at north cleft segment are mixtures of focused and diffuse discharge that contribute heat mn and fe in variable proportions similar examination of south cleft segment data strongly suggests the presence of an as yet unobserved venting source relatively depleted in mn and fe but contributing substantially to the overall heat temporal and spatial variations in the concentrations of mn and fe and in mn heat and fe heat ratios for focused seafloor vents were difficult to resolve within complex chronic plumes manganese heat and iron heat ratios of megaplumes suggest they may have derived from reservoirs of diffuse fluids while smaller event plumes may have formed by different processes and have properties similar to chronic plumes the accurate assessment of segment scale hydrothermal fluxes of mn and fe requires coordinated measurements of representative seafloor sources and the neutrally buoyant plume that integrates all seafloor discharge

opposing authigenic controls on the isotopic signature of dissolved iron in hydrothermal plumes iron is a scarce but essential micronutrient in the oceans that limits primary productivity in many regions of the surface ocean the mechanisms and rates of fe supply to the ocean interior are still poorly understood and quantified iron isotope ratios of different fe pools can potentially be used to trace sources and sinks of the global fe biogeochemical cycle if these boundary fluxes have distinct signatures seafloor hydrothermal vents emit metal rich fluids from mid ocean ridges into the deep ocean iron isotope ratios have the potential to be used to trace the input of hydrothermal dissolved iron to the oceans if the local controls on the fractionation of fe isotopes during plume dispersal in the deep ocean are understood in this study we assess the behaviour of fe isotopes in a southern ocean hydrothermal plume using a sampling program of total dissolvable fe tdfe and dissolved fe dfe we demonstrate that 56fe values of dfe 56dfe within the hydrothermal plume change dramatically during early plume dispersal ranging from 2 39 0 05 to 0 13 0 06 2 sd the isotopic composition of tdfe 56tdfe was consistently heavier than dfe values ranging from 0 31 0 03 to 0 78 0 05 consistent with fe oxyhydroxide precipitation as the plume samples age the dfe present in the hydrothermal plume includes stabilised dfe species with potential to be transported to the deep ocean we estimate that stable dfe exported from the plume will have a 56fe of 0 28 0 17 further we show that the proportion of authigenic iron sulfide and iron oxyhydroxide minerals precipitating in the buoyant plume exert opposing controls on the resultant isotope composition of dissolved fe passed into the neutrally buoyant plume we show that such controls yield variable dissolved fe isotope signatures under the authigenic conditions reported from modern vent sites elsewhere and so ought to be considered during iron isotope reconstructions of past hydrothermalism from ocean sediment records

multiple hydrothermal sources along the south tonga arc and valu fa ridge 1 quantifying hydrothermal venting at the boundaries of tectonic plates is an outstanding geoscience problem considerable progress has been made by detailed surveys along mid ocean ridges mors but until recently little was known about fluid venting along volcanic arcs we present the first systematic survey for hydrothermal venting along the 425 km long south tonga arc and new chemistry data for particle and thermal plumes previously reported along an adjacent 88 km long section of the back arc valu fa ridge vfr eleven hydrothermal plumes recognized by their anomalous light backscattering eh temperature ph dissolved he 3 ch4 and total dissolvable fe and mn were identified arising from seven volcanic centers along the arc five plumes on the vfr were characterized chemically vent field density for the south tonga arc was 2 6 sites 100 km of arc front comparable to that found by surveys of the kermadec arc 1 9 to 3 8 sites 100 km and to mors in the eastern pacific average value for 2280 km of surveyed ridgecrest 3 2 sites 100 km a vent gap occurs along a 190 km section of the arc closest to the vfr and a site density twice the average for mors on the eastern edge of the pacific plate was found on this part of the vfr 6 6 sites 100 km we suggest magmas ascending under the adjacent south tonga arc have been captured by the vfr while chemical enrichments of plumes on the south tonga arc were in general slightly less than those on the kermadec arc several instances of excessive anomalies in ph suggest a similar presence of fluids enriched in magmatic volatiles co2 so2 h2s locally venting on the vfr has contributed to accumulations of 3 he fe and mn within the southern lau basin on a broader scale our results provide considerable support for the notion that venting from intraoceanic arcs on the convergent margin of the pacific plate adds significantly to the total hydrothermal input into the pacific ocean

influence of the barotropic mean flow on the width and the structure of the atlantic equatorial deep jets a representation of an equatorial basin mode excited in a shallow water model for a single high order baroclinic vertical normal mode is used as a simple model for the equatorial deep jets the model is linearized about both a state of rest and a barotropic mean flow corresponding to the observed atlantic equatorial intermediate current system we found that the eastward mean flow associated with the north and south intermediate counter currents nicc and sicc respectively effectively shields the equator from off equatorial rossby waves the westward propagation of these waves is blocked and focusing on the equator due to beta dispersion is prevented this leads to less energetic jets along the equator on the other hand the westward barotropic mean flow along the equator reduces the gradient of absolute vorticity and hence widens the cross equatorial structure of the basin mode increasing lateral viscosity predominantly affects the width of the basin modes kelvin wave component in the presence of the mean flow while the rossby wave is confined by the flanking nicc and sicc independent of the presence of the mean flow the application of sufficient lateral mixing also hinders the focusing of off equatorial rossby waves which is hence an unlikely feature of a low frequency basin mode in the real ocean

chemical and physical diversity of hydrothermal plumes along the east pacific rise 8 45 n to 11 50 n we conducted a survey of water column hydrothermal plumes along a 350 km long section of the east pacific rise epr axis stretching from 8 45 n to 11 50 n including the region at 9 45 54 n where 1991 alvin dives found evidence for recent seafloor volcanic eruptions our survey included measurements of temperature anomaly light attenuation suspended particles methane hydrogen iron manganese helium and aluminum we detected strong light attenuation plumes in two main regions south of the clipperton transform fault ctf from 9 27 n to 9 57 n and north of the ctf from 11 05 n to 11 35 n however the plumes at these two regions had very different physical and chemical characteristics south of the ctf where the ridge is thought to be magmatically robust the plumes had very high ratios of he heat methane mn and s fe plumes north of the ctf had much lower ratios of he heat methane mn and s fe these striking differences in volatile heat and volatile metal ratios suggest that the plumes in the vicinity of 9 50 n were derived from a young evolving hydrothermal system while the activity at 11 10 n is from an older stable system this survey demonstrated that water column plume measurements can be used not only to accurately locate regions of hydrothermal activity but also to determine the first order chemical and physical characteristics of the hydrothermal fluids exiting from the seafloor

anomalous phase association of ree in ferromanganese crusts from indian mid oceanic ridges evidence for large scale dispersion of hydrothermal iron abstract ferromanganese crusts collected at selected locations along the 7000 km long stretch of carlsberg central indian and southwest indian ridges are studied for bulk geochemical composition and distribution of rare earths and yttrium in major geochemical phases exchangeable carbonate mn oxide fe oxyhydroxide and residual silicate the crusts are dominated by vernadite with traces of quartz and calcite a high concentrations of major fe mn trace co ni cu zn and rare earth elements indicates that these crusts are hydrogenous in nature however the negative or no cerium anomalies in the shale normalized ree pattern indicates that some of these crusts are of mixed type hydrogenous and hydrothermal irrespective of their nature mixed or hydrogenous the phase distribution of ree y shows 70 83 of total ree y are associated with fe oxyhydroxide phase whereas only about 17 30 are associated with mn oxide phase such phase distribution is expected in mixed type crusts because it is a combination of hydrothermal where 90 of the total ree y is associated with only fe oxyhydroxide phase and hydrogenous processes where 50 of the total ree y is associated with only fe oxyhydroxide phase conversely the hydrogenous crusts also shows similar phase distributions 70 83 association with fe oxyhydroxide phase which is certainly different from typical hydrogenous crusts where both fe oxyhydroxide and mn oxide phases host equal amounts 50 each the large scale dispersion of hydrothermal particulate iron along the indian ocean ridges is likely to contribute an additional fe bound ree y pool to these crusts the positive yttrium anomaly in mn oxide phase of all these crusts substantiates the hydrothermal contribution

hydrothermal plumes along the east pacific rise 8 40 to 11 50 n plume distribution and relationship to the apparent magmatic budget abstract the interactions between hydrothermal circulation and large scale geological and geophysical characteristics of the mid ocean ridge cannot be ascertained without large scale views of the pattern of hydrothermal venting such multi ridge segment surveys of venting are accomplished most efficiently by mapping the distribution and intensity of hydrothermal plumes in november 1991 we mapped hydrothermal temperature and light attenuation c anomalies above the east pacific rise epr continuously from 8 40 to 11 50 n a fast spreading ridge crest portion bisected by the clipperton transform fault plume distributions show a precise correlation with the distribution of active vents where video coverage of the axial caldera is exhaustive 9 09 54 n elsewhere in the study area the sketchy knowledge of vent locations gleaned from scattered camera tows predicts only poorly the large scale hydrothermal pattern revealed by our plume studies plumes were most intense between 9 42 and 9 54 n directly over a march april 1991 seafloor eruption these plumes had exceptionally high c ratios compared to the rest of the study area we suggest that the phase separated gas rich vent fluids discharging here fertilize an abundant population of bacteria hydrothermal plume distributions define three categories intense and continuous 8 48 8 58 n 9 29 10 01 n and 11 05 11 27 n weak and discontinuous 8 58 9 29 n and negligible the location of each category is virtually congruent with areas that are respectively magmatically robust magmatically weak and magmatically starved as inferred from previous measurements of axial bathymetric undulations cross axis inflation and magma chamber depth and continuity this congruency implies a fine scale spatial and temporal connection between magmatic fluctuations and hydrothermal venting we thus speculate that at least along this fast spreading section of the epr cyclic replenishment eruption and freezing of the thin axial melt lens exerts greater control over hydrothermal venting than the more enduring zones of crystal mush and hot rock we found intense and continuous plumes along 33 of the surveyed ridge crest an observation implying that any point on the ridge is on average hydrothermally active one third of the time combining this result with the 20 plume coverage found along the medium rate juan de fuca ridge suggests that superfast 150 mm yr spreading ridges should support vigorous venting along 50 of their length if spreading rate and along axis plume coverage are linearly related

dissolved and particulate trace metals in hydrothermal plumes at the mid atlantic ridge seawater samples from the non buoyant plume have been collected at the tag 26 n and snakepit 23 n hydrothermal sites on the mid atlantic ridge mar and analysed for dissolved 0 4 m trace metals up to 50 of vent fluid fe is present in the 0 4 m fraction in the non buoyant plume increases in particulate concentrations of cd are accompanied by a reduction in dissolved cd to levels below ambient seawater we show that dissolved cd is scavenged from seawater in the buoyant section of the plume while cd re dissolves from the particles in the non buoyant plume up to 43 of hydrothermally injected cu is found in the 0 4 m fraction in the non buoyant plume

a model of an atlantic and pacific hydrothermal plume a turbulent entrainment model of a hydrothermal plume was modified to include the effects of vertical structure in the background temperature and salinity fields owing to the stably stratified salinity field in the pacific relatively warm salty water spreads at an equilibrium level where the plume density equals the ambient density in contrast the unstable salinity profile in the atlantic gives the plume added buoyancy and it continues to rise to an equilibrium level where it is relatively cool and fresh these attributes result from the mixing between the plume and the surrounding seawater at each level below the spreading layer the equilibrium temperature anomaly is not directly proportional to the source strength but depends on the mixing and background salinity gradient the net entrainment of surrounding seawater is greater in the atlantic plume model than in the pacific plume model for the same buoyancy flux recent data from the tag hydrothermal field at 26 n on the mid atlantic ridge and data from a vent field on the endeavor segment of the juan de fuca ridge are compared to model results the model predicts the penetration height and s characteristics of the atlantic plume and it explains some of the differences between the observed atlantic and pacific hydrothermal plumes

high resolution hydrothermal mapping of brothers caldera kermadec arc submarine edifices with caldera summits are common along volcanic arcs and much more likely than simple cones to host hydrothermal venting compared with cones however locating all vent field locations on a caldera s complex bathymetry is a daunting logistical challenge here we describe the first use of an autonomous underwater vehicle abe to fully map the distribution of near bottom hydrothermal tracers over the caldera walls and cone complex of brothers volcano the most active hydrothermal source on the southern kermadec arc sensors on abe simultaneously measured hydrothermal plume anomalies in temperature light backscattering particle concentration and oxidation reduction potential dissolved reduced species every 2 to 3 m along track local maxima in these tracers confirmed known sites on the northwestern wall and the cone summits and more precisely mapped their extents we discovered evidence for new sites throughout the entire northwestern half of the caldera wall at the base of the southeastern wall and on the flanks of both cones systematic variations in the backscattering temperature ratio identified different types of fluid discharge plumes from high temperature metal rich sources dominated the caldera wall while on top of the caldera wall and on the cones we found only plumes from low temperature diffuse flow including occasional s rich plumes source distribution on the walls appears fault controlled but we detected no sources along the deepest fault defining the rim of the downdropped caldera floor advanced deep sea survey techniques using autonomous vehicles is an indispensible and cost effective tool for acquiring a comprehensive understanding of the relationship between hydrothermal discharge and geology on individual volcanoes

the trace metal composition of suspended particles in the oceanic water column near bermuda trace metal partitioning between seawater and particles both suspended and sinking must be determined to understand and model oceanic trace metal scavenging processes in order to improve the oceanic particulate trace metal data base a newin situ pump was developed and deployed to collect suspended particles from 0 4000 m in the sargasso sea near bermuda these particles were analyzed for al fe mn co zn cu ni cd and pb major particulate carrier phases were estimated from ca opaline si and p cd is the only trace element of this group with a particulate maximum in near surface waters the other metals have low particulate concentrations mol l in near surface waters and increase with depth into the upper thermocline particulate al and fe are then uniform with depth below about 1000 m until increasing in the bottom nepheloid layer the remaining elements mn co zn cu ni and pb decrease from the mid thermocline values to lower and relatively uniform concentrations in deep waters the similarities among the vertical profiles for these metals suggest that authigenic mn oxides influence their uptake from the dissolved pool although an important or dominant role for other host phases specifically particulate organic matter is not ruled out by the data mean intermediate and deep water concentrations are al 3600 fe 1200 mn 146 co 1 5 zn 7 4 cu 15 ni 6 0 cd 0 06 and pb 2 1 pmol l these particulate al and mn values agree with previous measurements in this region but the other elements are lower by a factor of 3 fe co to 30 zn suggesting that earlier data were compromised by contamination the suspended metal data are used in a simple steady state two flux model to evaluate the role of suspended particles in determining the vertical flux of metals in the sargasso sea the model calculations indicate that removal of suspended particles in the deep 500 m water column contributes less than half of the total deep flux for all of the elements investigated except for cd this result implies that uptake of these metals onto particles in the deep central ocean is a minor factor in their oceanic mass balance if this finding is generally true for oligotrophic ocean environments whole ocean residence times for these elements must be governed largely by processes occurring either in near surface waters or at ocean margins

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

upper and intermediate circulation in the western equatorial pacific ocean in october 1999 and april 2000 1 the upper and intermediate circulation 0 1200 m in the western equatorial pacific ocean is examined thanks to lowered acoustic doppler current profiler ladcp measurements carried out during two cruises in october 1999 and april 2000 several new features of the equatorial circulation are discussed it is shown that the secondary south subsurface countercurrent ssscc laying at 6 s 400 m depth had a deep extension at 165 e with a maximum core velocity around 5 s 1000 m furthermore the equatorial intermediate current eic and the lower eic leic displayed a strong temporal variability between 165 e and 180 as these two westward currents were replaced by eastward flow along the equator on the second cruise finally during the april 2000 cruise the zonal velocity profile carried out at the equator east of the gilbert island around 175 e broke into small vertical scales possibly reflecting topographic effect and or destabilization mechanism that leads to the formation of long zonal jet like structures

basin wavelength equatorial deep jet signals across three oceans equatorial deep jets edjs are equatorially trapped stacked zonal currents that reverse direction every few hundred meters in depth throughout much of the water column this study evaluates their structure observationally in all three oceans using new high vertical resolution argo float conductivity temperature depth ctd instrument profiles from 2010 to 2014 augmented with historical shipboard ctd data from 1972 to 2014 and lower vertical resolution argo float profiles from 2007 to 2014 the vertical strain of density is calculated from the profiles and analyzed in a stretched vertical coordinate system determined from the mean vertical density structure the power spectra of vertical strain in each basin are analyzed using wavelet decomposition in the indian and pacific oceans there are two distinct peaks in the power spectra one kelvin wave like and the other entirely consistent with the dispersion relation of a linear first meridional mode equatorial rossby wave in the atlantic ocean the first meridional mode rossby wave signature is very strong and dominates in all three ocean basins rossby wave like signatures are coherent across the basin width and appear to have wavelengths the scale of the basin width with periods of about 5 yr in the indian and atlantic oceans and about 12 yr in the pacific ocean their observed meridional scales are about 1 5 times the linear theoretical values their phase propagation is downward with time implying upward energy propagation if linear wave dynamics hold

the effect of hydrothermal processes on midwater phosphorus distributions in the northeast pacific abstract the distributions of dissolved particulate and sedimentary phosphorus were measured in the region of the juan de fuca ridge to determine the impacts of hydrothermal processes on the phosphorus cycle in the oceans significant negative dissolved phosphate anomalies ranging from 0 to 60 nmol l were observed in the water column at depths between 1900 and 2300 db the largest anomalies

hydrothermal plumes along the east pacific rise 8 40 to 11 50 n particle distribution and composition the discovery of a volcanic eruption at the 9 45 52 n site on the east pacific rise epr led us to investigate how the composition of suspended matter in hydrothermal plumes may be used to provide a better understanding of the relative age and vent fluid characteristics of a ridge crest system during surface ship surveys during the troughs tropical ridge observations of underwater geochemical hydrothermal signals expedition we collected hydrothermal plume particles along a 350 km section extending from approximately 8 40 n to 11 50 n of the epr north and south of the clipperton transform fault over the segment south of the clipperton transform fault the sfe ratio in the particles ranged from about 0 9 to 10 with the highest values immediately over the new vent field at the 9 45 52 n site these enrichments exactly coincide with the elevated 3he heat and ch4mn ratios in the plumes over the same vent field the s rich particles are primarily organic and may be related to the bacteria blizzard associated with the eruption in addition very high cufe and znfe ratios were observed in the hydrothermal plumes south of the clipperton transform fault these high ratios are indicative of the predominance of high temperature h2s rich vents between 9 35 n and 9 50 n in contrast the samples from the segment north of clipperton transform fault had sfe ratios which ranged from 0 04 to 0 82 typical of mature fe rich hydrothermal plumes these results suggest that the gas rich vent fluids at the 9 45 52 n site produced the sulfur enriched particles in the water column gas rich plumes and sulfur enriched plume particles were also observed underneath the 1986 megaplume on the juan de fuca ridge jdfr suggesting a similar mode of formation north of the clipperton transform fault the hydrothermal particles are dominated by fe rich oxyhydroxide particles characteristic of mature high temperature vent fields the plume maximum is centered at 11 08 n the fe oxyhydroxide particles scavenge ca si p v cr and as from seawater for p and v the mean element fe ratios in the epr hydrothermal particles are intermediate between jdfr and tag hydrothermal systems for as the mean element fe ratios of all three systems are about the same new evidence for si scavenging by hydrothermal fe oxyhydroxide particles indicates that this sink for dissolved si in the oceans is small

the vertical structure of the zonal pressure gradient in the eastern equatorial pacific ctd data from the epocs and norpax experiments were used to construct a mean zonal pressure gradient profile between 110 w and 150 w for the 1979 to 1981 pre el nino time period the mean zonal pressure gradient referenced to 100 dbar had a value of 4 5 10 7 m s 2 at the surface and decreased to within two standard errors of zero at 200 dbar below this depth the mean was not significantly different from zero deviations from this mean were not related to fluctuations of the zonally averaged zonal wind stress between 150 w and 110 w rather the largest deviations in the boreal springs of 1979 and 1980 appeared to be associated first with vertical mode kelvin wave pulses propagating eastward along the equator the 1979 81 mean profile was also used as a reference to examine variations in zonal pressure gradient during the 1982 83 enso event the sea surface was more sharply sloped upward from the east to west in april and september 1982 before arid near the beginning of the event the surface slope was below normal in april and october 1983 vertical profiles of the zonal pressure gradient deviations showed large high vertical mode contributions during the vent than in the prevent samples

hydrothermal scavenging at the mid atlantic ridge modification of trace element dissolved fluxes abstract we have carried out an icp ms study of the distributions of trace elements fe ca mg al mn cu zn v as cr co pb y mo ag sn cd and be in particulate material collected from the tag hydrothermal plume 26 n mid atlantic ridge to examine the extent to which fluxes of dissolved trace elements emitted from hydrothermal vent fluids are balanced by the precipitation of associated particulate phases comparison of particulate trace element distributions with particulate fe concentrations within the neutrally buoyant plume reveals that the distribution of trace elements within the plume is controlled by the following processes i co precipitation from vent fluids ii scavenging from seawater and iii preferential settling from the plume and oxidative dissolution within the water column for y and be continuous scavenging from seawater appears to be important whereas for v as and cr it appears that conditions suitable for uptake into particles may be restricted to the buoyant portion of the hydrothermal plume from a comparison of trace element fe ratios in the particles and associated mid atlantic ridge vent fluids it appears that for many elements e g cu co ag pb al cd be and zn the flux of dissolved material from vent fluids is matched closely by the precipitation of hydrothermal particulate phases of the various elements studied here hydrothermal activity only appears to act as a significant source for dissolved ca and dissolved mn

environmental controls on mid ocean ridge hydrothermal fluxes abstract high temperature hydrothermal fluxes at mid ocean ridges are thought to be an important component of oceanic biogeochemical cycles however little consideration has been given to how these fluxes vary as a consequence of changing environmental conditions over earth history here we consider how changes in sea level and ocean chemistry are likely to have impacted on axis high temperature hydrothermal fluxes focusing on phanerozoic conditions changes in sea level lead to changes in hydrostatic pressure near the base of hydrothermal systems where both peak fluid rock reaction temperatures and phase separation occur in general higher global sea level will lead to higher peak temperatures of fluid rock reaction additionally phase separation at higher pressure tends to lead to formation of a more cl rich vapor that constitutes a larger mass fraction of the system these combined factors may serve to significantly modify hydrothermal fluxes even for sea level changes on the scale of 100 m changes in ocean chemistry can also affect axial hydrothermal fluxes in several ways seawater sulfate contents control the amount of anhydrite that forms which has both physical porosity filling and chemical effects the most important aspect of ocean chemistry in controlling the composition of high temperature vent fluids may be ocean salinity if evaporite formation and dissolution has changed ocean salinity substantially over the phanerozoic hydrothermal fluxes could have been greatly modified ocean chemistry also plays a large role in controlling processes operating in hydrothermal plumes and hence the net flux of elements into and out of the ocean associated with hydrothermal systems we conclude that there is a need for substantial further work to quantify the effects of sea level and ocean chemistry on high temperature hydrothermal fluxes including the development of more robust models that integrate field laboratory and theoretical observations

co seismic geoelectric potential changes observed in japan co seismic signals of geoelectric potential have been observed for several earthquakes eqs in japan it has been argued that if there are precursory changes stronger signals should be at the time of eq our results prove that co seismic signals do exist but they start with the arrival of seismic waves and not at the origin time of eqs their amplitude does not scale with the dipole length both facts indicate that the changes are local effects of passing seismic waves and not due to electric signals emitted from the seismic source observed changes contain two components oscillatory and offset decay ones the former is synchronized with seismic waves whereas the latter with a rise time of a few seconds and a decay time of 0 1 1 hour is suspected to be related to eq induced subsurface hydrological change in both cases the origin of electric potential variations may be electrokinetic

self potential modeling from primary flows this paper discusses a new method for the investigation of self potentials sp based on induced current sources the induced current sources are due to divergences of the convection current which is driven in turn by a primary flow either heat or fluid as a result of using this approach there is a shift in emphasis toward the vector flow field and its interaction with current cross coupling structure when compared with the total potential approach of nourbehecht 1963 which emphasized the primary flow potential and the voltage cross coupling this shift in emphasis is advantageous because it is analogous to the actual physical processes for example fluid flow in the ground gives rise to drag convection currents and the interaction of the convection currents with the electrical structure gives rise to the electrical potentials sp this simple physical picture should aid in developing a better intuitive understanding of the generation of sp effects the convective current approach is easily ada

atlantic equatorial deep jets space time structure and cross equatorial fluxes the so called equatorial stacked jets are analyzed with ship board observations and moored time series from the atlantic ocean the features are identified and isolated by comparing vertical wavenumber spectra at the equator with those a few degrees from the equator mode filtering gives clear views of the jets in meridional sections the typical extent being 618 in latitude the vertical structure can be well described explaining 82 of the variance by n21 stretched cosines with a gaussian amplitude tapering in the vertical the stretched wavelengths are somewhat variable fitting jets of a fixed stretched wavelength to four moored sensors in the depth range 1300 1900 m allows one to track the vertical phase of the jets with an rms error of 308 458 the resulting fit from a 20 month moored time series shows long periods of unchanging jet conditions and intermittent times of high variability there is no significant vertical propagation on these timescales nor a seasonal reversal using a composite from many different experiments interannual variability is visible however a possible mechanism for the stacked jets is inertial instability resulting from background meridional shears at the equator a condition is that the ertel potential vorticity becomes zero somewhere due to meridional asymmetries in the zonal flows the ship board observations show that this may be approximately fulfilled by the instantaneous zonal low mode flows at various depths resulting from an excess of zonal momentum south of the equator most of the time inertial instability should act to redistribute this zonal momentum and our mooring data show indeed persistent northward momentum flux but not at the depth levels expected the momentum transport might suggest that the jets can also flux or mix other properties across the equator

temporal and spatial structure of the equatorial deep jets in the pacific ocean abstract the spatial and temporal structure of the equatorial deep jets edjs in the pacific ocean is investigated using ctd station data taken on the equator from 1979 through 2001 the edjs are revealed in profiles of vertical strain z estimated from the ctd data in a stretched vertical coordinate system the majority of synoptic meridional sections were occupied over an 8 yr span west of the date line two decade equatorial time series are available at both 110 w and 140 w analysis shows the expected equatorial trapping of z but yields little new detailed information about the edj meridional structure analysis of the equatorial data yields novel results the edjs are most easily seen in the eastern pacific at and east of 140 w there they may be isolated from the influence of higher frequency rossby waves generated by surface forcing spectral analysis of equatorial z profiles shows a significant and coherent peak at 400 sdbar vertical wavelength with no 1 56 10 3 s 1 from 95 w to 142

results from a velocity transect along the equator from 125 to 159 w abstract during march april 1980 a velocity and ctd transect was made in the pacific along the equator from 110 to 180 w the horizontal baroclinic pressure gradient was observed to be primary confined between 160 and 130 w direct velocity profiles between 125 and 159 w showed the equatorial undercurrent to be a continuous feature maximum eastward transport per unit width in the undercurrent was 2 5 108 cm2 s 1 at 150 w and decreased both westward and eastward to about 1 5 108 cm2 s 1 at 159 w and at 125 w despite these variations the maximum speeds along the transect remained 150 cm s 1 beneath the undercurrent the velocities decreased and were of the order of 25 cm s 1 they exhibited small scale variation in the vertical as has recently been observed at other equatorial locations above 1600 m the vertical wavelength of these variations in the zonal component was 300 m small scale features in these zonal velocities were identifiable over 10 of longitude 1000 km the small vertical an

numerical simulation of coseismic electromagnetic fields associated with seismic waves due to finite faulting in porous media summary the electrokinetic effect is one mechanism that causes the coupling between seismic and electromagnetic energies this study deals with the numerical simulation of the electrokinetically induced coseismic electromagnetic fields associated with seismic waves created by a finite faulting in porous media the key point of our numerical technique is to combine the point source stacking method with the luco apsel chen generalized reflection and transmission method after some validation test of our simulation method we show several numerical simulation examples through a near field model we show that the point source approximation is not accurate in this configuration as well as that the position of the rupture starting point and rupture speed obviously affect the coseismic em fields then we numerically investigate the influence of different media properties on seismic waves and coseismic em fields we also carry out simulations of multilayer half space models and show the characteristics of the coseismic em fields the preliminary results indicate that our numerical technique provides an effective approach of studying coseismic electromagnetic fields associated with seismic waves due to a finite faulting in porous media

the deep currents in the eastern equatorial atlantic ocean 1 in the atlantic ocean equatorial deep jets have been observed in the central and western equatorial basin here we present three meridional velocity sections carried out in boreal summer 2000 in the eastern equatorial atlantic at that time the deep equatorial jets were observed to weaken or to vanish in the gulf of guinea toward the african coast at 10 w the comparison with currents measured one year before in boreal summer 1999 along with tracer distributions confirm the existence of an eastward route along the equator of part of the north atlantic deep water

uptake and fractionation of rare earth elements on hydrothermal plume particles at 9 45 n east pacific rise abstract particulate samples 0 45 m from a neutrally buoyant hydrothermal plume at 9 45 n on the northern east pacific rise were collected using large volume in situ filtration and analyzed for fe al mn ni and fourteen rare earth elements ree the sm fe ratio a proxy for overall ree fe and nd er light heavy ree fractionation increased moderately with decreasing particulate fe chemically the sense of these relationships matched that documented previously in the tag plume on the mid atlantic ridge german et al 1990 although particulate fe was about 10 fold lower at 9 45 n spatial trends relative to the vent source however were opposite of expectation because slow fe ii oxidation and fe iii colloid aggregation over this interval led to increased particulate fe 10 26 nm with distance from source field and sherrell submitted after subtraction of non plume background particle composition plume particles at 9 45 n and tag had indistinguishable ranges of light ree enriched fractionation relative to ambient seawater and had very similar sm fe therefore kd for fe oxyhydroxides demonstrating that plume particles in both oceans reflect to a first degree the local seawater ree composition within plume ree variations at 9 45 n were investigated using a simple mixing model which accounts for the bulk fe al mn variations in the plume using two endmembers fresh hydrothermal oxyhydroxide precipitates and ridge crest background particles composed largely of locally resuspended sediment sm fe and nd er plot linearly with mixing ratio r 0 96 implying that the observed ree trends result from mixing of these two endmembers extrapolation to the composition of pure hydrothermal precipitates suggests that nd er is fractionated relative to seawater by a factor of 1 8 during adsorption onto fresh fe oxyhydroxide particles the ridge crest background particles are 5 fold higher in sm fe and nd er is 2 49 relative to seawater partly a result of enriched terrigenous component in the resuspended matter a reinterpretation of ree at tag reveals that positive curvature in ree vs fe plots argued previously to reflect continuous ree uptake i e increasing kd german et al 1990 may result from local depletion of the dissolved ree pool by partitioning onto fe particles at fe 100 nm similar drawdown effects could contribute to the variable degrees of curvature observed for all seawater source particle reactive species in plumes that are sampled at high particulate fe concentration in sum ree behavior in hydrothermal plumes is more consistent with equilibrium adsorption and mixing of distinct particle types than with kinetic uptake control precise measurements of rees in modern ridge crest metalliferous sediments could be compared to the endmember composition calculated from the plume data to evaluate long term changes in ree of the hydrothermal component

composition and sedimentation of hydrothermal plume particles from north cleft segment juan de fuca ridge in 1990 and 1991 particles from buoyant and neutrally buoyant hydrothermal plumes above hydrothermal vents at the north cleft segment of the juan de fuca ridge were sampled to study their changing composition and fluxes away from the vent field in the rising buoyant plume 75 of the p v cr and as scavenging from seawater by hydrothermal precipitates occurs in the first 50 m above the vent cu and zn are most enriched in buoyant plume particles collected from the first few meters above the vent however the degree of enrichment decreases very rapidly with increased height above the vents due to sedimentation of the more dense cu and zn rich sulfide phases using the plume data coupled with the results of our analysis of sediment trap samples we estimated that more than 99 and 99 9 respectively of the total hydrothermal fe and mn produced at the vent field are transported beyond the vent field and dispersed in the open ocean

processes affecting the isotopic composition of dissolved iron in hydrothermal plumes a case study from the vanuatu back arc abstract hydrothermal discharge is one of multiple fe sources contributing to the marine dissolved fe budget but its relative importance remains controversial and largely unconstrained isotopic characterization of fe sources and mass balance calculations are considered as a potential tool to unravel the complex interplay of various fe fluxes but require a more profound knowledge of the processes that fractionate fe isotopes in hydrothermal plumes we present dissolved fe isotope data from two buoyant plumes and profiles traversing the non buoyant plume above the nifonea vent field in the vanuatu back arc our findings support opposing controls from precipitation of fe sulfides and fe oxyhydroxides that either enrich the heavy or the light isotopes within the residual dissolved fe fraction but also suggest significant influence from size partitioning of oxidized fe following precipitation as well as potential effects from organic complexation at low aggregation of precipitated fe oxyhydroxides or stabilization of significant fe iii aq dissolved 56 fe is only marginally affected by fe ii oxidation which strengthens the role of fe sulfide precipitation during early plume rise in determining the isotope signature of hydrothermal fe exported to the open ocean dissolved 56 fe range from 0 73 0 05 to 0 16 0 05 and suggest that sulfide rich basalt hosted hydrothermal systems and slow oxidation kinetics in the pacific favor export of stabilized dissolved fe with heavier 56 fe values than the true vent fluids 56 fe of 0 5

trace element behaviour at cold seeps and the potential export of dissolved iron to the ocean seawater samples were collected by submersible above methane seeps in the gulf of guinea regab and baboon pockmarks in order to investigate the behaviour of iron fe manganese mn and rare earth elements ree during fluid seepage our aim was to determine whether cold seeps may represent potential sources of dissolved chemical species to the ocean dissolved 0 45 m filtered samples and total dissolvable unfiltered samples concentrations were determined over 50 m long vertical transects above the seafloor and at various discrete locations within the pockmarks we show that substantial amounts of fe and mn are released into seawater during seepage of methane rich fluids mn is exported almost quantitatively in the dissolved form more than 90 of total mn mean mndiss 12 11 nmol kg 12 11 nmol kg although a significant fraction of fe is bound to particulate phases the dissolved iron pool still accounts on average for approximately 20 percent of total iron flux at vent sites mean fediss 22 11 nmol kg 22 11 nmol kg this dissolved fe fraction also appears to remain stable in the water column in contrast there was no evidence for any significant benthic fluxes of pore water ree associated with fluid seepage at the studied sites overall our results point towards distinct trace element behaviour during fluid seepage with potential implications for the marine geochemical budget the absence of any dissolved ree enrichments in bottom waters clearly indicates effective removal in sub surface sediments most likely precipitation of authigenic mineral phases at cold seeps i e carbonates represents a net sink for these elements while mn appears to behave near conservatively during fluid seepage the observed relative stability of dissolved fe in the water column above seepage sites could be explained by complexation with strong organic ligands and or the presence of fe bearing sulfide nanoparticles as reported previously for submarine hydrothermal systems considering the ubiquitous occurrence of methane vents at ocean margins cold seeps could represent a previously unsuspected source of dissolved fe to the deep ocean

vailulu u undersea volcano the new samoa 1 vailulu u seamount is identified as an active volcano marking the current location of the samoan hotspot this seamount is located 45 km east of ta u island samoa at 169 03 5 w 14 12 9 s vailulu u defines the easternmost edge of the samoan swell rising from the 5000 m ocean floor to a summit depth of 590 m and marked by a 400 m deep and 2 km wide summit crater its broad western rift and stellate morphology brand it as a juvenile progeny of ta u seven dredges ranging from the summit to the se rift zone at 4200 m recovered only alkali basalts and picrites isotopically the volcano is strongly em2 in character and clearly of samoan pedigree 87sr 86sr 0 7052 0 7067 143nd 144nd 0 51267 0 51277 206pb 204pb 19 19 19 40 the 210po 210pb data on two summit basalts indicate ages younger than 50 years all of the recovered rocks are extremely fresh and veneered with glass an earthquake swarm in early 1995 may attest to a recent eruption cycle a detailed nephelometry survey of the water column shows clear evidence for hydrothermal plume activity in the summit crater the water inside the crater is very turbid nephelometric turbidity unit ntu values up to 1 4 and a halo of smog several hundred meters thick encircles and extends away from the summit for at least 7 km the turbid waters are highly enriched in manganese up to 7 3 nmol kg providing further evidence of hydrothermal activity vailulu u is similar to loihi hawaii in being an active volcanic construct at the eastern end of a hotspot chain it differs importantly from the hawaiian model in its total lack of tholeiitic basalt compositions

deep jets in the equatorial atlantic ocean deep velocity profiles taken in the equatorial atlantic ocean show equatorially trapped deep jets with similar features to those of the indian and pacific oceans a zonal velocity of the order of 10 to 20 cm s 1 and a meridional scale of 1 in the pacific and indian oceans the zonal extent of the jets is at least 15 of longitude owing to the lack of synoptic measurements we have no information on the zonal scale in the atlantic ocean but we present here zonal velocity profiles made at a 16 month interval that have identical baroclinic structure in the western 35 w and central basin 13 w the atlantic jets have a vertical scale larger 400 600 m than those observed in the pacific ocean 250 400 m our measurements confirm the opposite directions of the jets for different seasons in the atlantic ocean furthermore for a given season the vertical profiles of zonal velocity at 35 w 0 are astonishingly similar at a 5 year interval as in the pacific and indian oceans the jets are embedded in a large vertical scale current that changes direction with time the few profiles available in the equatorial atlantic ocean suggest a seasonal reversal of the jets but neither this nor the temporal variability of the large scale current has been adequately resolved

hydromechanical coupling in response to earthquakes on the possible consequences for aftershocks numerous observations indicate that fluids circulate in the crust after an earthquake with time constants comparable to those of the aftershocks this paper provides new viewpoints concerning the relationship between the fluid flow and aftershocks the fault on which the main quake occurs is modelled using a rectangular dislocation surface that is embedded in a 3 d poroelastic half space the main event is modelled by prescribing a given amount of displacement over the dislocation surface which results in deformation throughout the surrounding crust the fluid redistribution that then ensues is modelled using the equations of poroelasticity we show that this process can lead to time dependent weakening effects the results are analysed in terms of how changes in a coulomb failure function cff evolve through time the spatial and temporal distributions of aftershocks triggered by cff are modelled on a statistical basis we test our model in various situations the spatial distribution of aftershocks is depicted in various tectonic environments and we show that the fluid flow seemingly provides a convincing mechanism for the triggering of aftershocks both off fault aftershocks and aftershocks close to the surface rupture have been modelled we have also investigated the condition under which the omori decay law and its associated time exponent p is expected and we show that the permeability should vary within a window of less than two orders of magnitude in order to match the observed value of p 1 with seismic data from the northridge event 1994 we show that a crustal permeability of 7 5 10 15 m2 allows us to describe quite well the time dependence of the aftershock however the permeability should vary proportionally to l2 where l is the scale length over which the fluid pressure equilibration occurs that is dependent on the size of the main event in order to obtain a similar decay law p 1 at every scale main event magnitude finally the link with the post seismic hydrological observations is established and we show that the fluid flow predicted in the model of the northridge event is consistent within an order of magnitude with field observations reported by muir wood king

forcing of the atlantic equatorial deep jets derived from observations the equatorial deep jets edjs are an ubiquitous feature of the equatorial oceans in the atlantic ocean they are the dominant mode of interannual variability of the zonal flow at intermediate depth on the basis of more than 10 years of moored observations of zonal velocity at 23 w the vertically propagating edjs are best described as superimposed oscillations of the 13th to the 23th baroclinic modes with a dominant oscillation period for all modes of 1650 days this period is close to the resonance period of the respective gravest equatorial basin mode for the dominant vertical modes 16 and 17 it is argued that since the equatorial basin mode is composed of linear equatorial waves a linear reduced gravity model can be employed for each baroclinic mode driven by spatially homogeneous zonal forcing oscillating with the edj period the fit of the model solutions to observations at 23 w yields a basin wide reconstruction of the edjs and the associated vertical structure of their forcing from the resulting vertical profile of mean power input and vertical energy flux on the equator it follows that the edjs are locally maintained over a considerable depth range from 500 2500 m with the maximum power input and vertical energy flux at 1300 m the strong dissipation closely ties the apparent vertical propagation of energy to the vertical distribution of power input and together with the edjs prevailing downward phase propagation require the phase of the forcing of the edjs to propagate downward

annual reversal of the equatorial intermediate current in the pacific observations and model diagnostics abstract a large reversal of zonal transport below the thermocline was observed over a period of 6 months in the western pacific ocean between 2 s and the equator from 26 2 sv 1 sv 106 m3 s 1 eastward in october 1999 to 28 6 sv westward in april 2000 to document this reversal and assess its origin an unprecedented collection of adcp observations of zonal currents 2004 06 together with a realistic ogcm simulation of the tropical pacific was analyzed the results of this study indicate that this reversal is the signature of intense annual variability in the subsurface zonal circulation at the equator at the level of the equatorial intermediate current eic and the lower equatorial intermediate current l eic in this study the eic and the l eic are both shown to reverse seasonally to eastward currents in boreal spring and winter for the l eic over a large depth range extending from 300 m to at least 1200 m the peak to peak amplitude of the annual cycle of subthermocline zonal currents at

linear pressurization method for determining hydraulic permeability and specific storage of a rock sample summary we studied the methodology and applicability of linear pressurization for determining simultaneously hydraulic permeability and specific storage of a rock sample we analytically solved the governing equation for 1 d pressure diffusion through a homogenous isotropic cylindrical rock specimen located between a downstream and an upstream reservoir considering linear pressurization of the upstream fluid as the boundary condition the solution consists of a transient and a steady state for which both differential pressure between the two reservoirs and injection rate at the upstream reservoir assume constant values since the steady state differential pressure is linearly proportional to the compressive storage of the downstream reservoir tests conducted with a systematic variation of the size of the downstream reservoir permit determining permeability and specific storage from the intercept and slope of the linear relationship alternatively simultaneous measurement of differential pressure and fluid injection rate at steady state conditions provides a basis for calculation of the hydraulic properties as previously presented for linear injection experiments were performed on fontainebleau sandstone samples to document the feasibility of the method the determined storage capacity value is used to calculate various poroelastic parameters such as bulk and pore space compressibility skempton and the effective pressure coefficient

chemical reaction rates and entrainment within the endeavour ridge hydrothermal plume the aging of the hydrothermal plume over the endeavour segment of the juan de fuca ridge was estimated by measuring the222rn3he ratio in the plume as it dispersed despite uncertainties in the source function of hydrothermal input it wa determined that the relative sequence of removal from the plume ish2 c 222rn ch4 mn where c is a measure of particle concentration and the mean life of222rn is 5 5 days h2 is removed from the plume within hours of input while mn is not removed within the two week timescale of the radon helium clock entrainment of bottom water within the buoyant plume may introduce additional chemical signatures into the spreading effluent layer over that which would be introduced by hydrothermal discharge alone this is particularly significant for those chemical species which are not greatly enriched in the vent fluids relative to bottom water concentration and which display a nutrient like profile in the deep ocean thus we found that significant fractions of the si and226ra anomalies in the plume were not of hydrothermal origin but were derived from entrained bottom water which has a higher concentration of these elements than ambient water at plume height

in situ observations of dissolved iron and manganese in hydrothermal vent plumes juan de fuca ridge in situ measurements of dissolved manganese and total dissolved iron were conducted in hydrothermal plumes over the juan de fuca ridge using a submersible chemical analyzer scanner the scanner was deployed as part of a ctd transmissometer rosette instrument package on both tow yos and vertical casts during the vents leg i cruise in 1989 dissolved manganese and total dissolved iron concentrations along with temperature and light attenuation anomalies were determined over the ridge crest every 5 s discrete samples for laboratory analyses of dissolved iron ii total dissolved iron ii iii and manganese were also collected metal to heat ratios me q measured in situ were extremely variable in one steady state plume while an event plume had constant me q uniform values of mn q in the event plume demonstrate that mn behaves conservatively in the near field plume variability in the mn q ratios in a steady state plume indicated the presence of at least two hydrothermal sources with distinct me q values a simple mixing model shows that the contribution of mn from high me q sources with a composition characteristic of black smoker vents varies between 1 and 99 within the core of the steady state plume with an average value of 55 on average over 50 of the excess heat within the plume originates from low me q ratio sources with a composition characteristic of low temperature diffuse flow vent fluids less than 4 of the volume of hydrothermal fluids in the plume originates from black smokers the fe ii concentrations were used to provide an estimate of plume age on a transect across the ridge axis plume ages were about 2 5 days on axis and 12 days off axis these plume ages were modeled to provide estimates of plume transport and horizontal diffusion and show excellent agreement with ages determined using 222rn

volcanic eruption of the mid ocean ridge along the east pacific rise crest at 9 45 52 n direct submersible observations of seafloor phenomena associated with an eruption event in april 1991 in april 1991 we witnessed from the submersible alvin a suite of previously undocumented seafloor phenomena accompanying an in progress eruption of the mid ocean ridge on the east pacific rise crest at 9 45 n 52 n the volume of the eruption could not be precisely determined although comparison of pre and post eruption seabeam bathymetry indicate that any changes in ridge crest morphology resulting from the eruption were 10 m high effects of the eruption included 1 increased abundance and redistribution of hydrothermal vents disappearance of numerous vent communities and changes in characteristics of vent fauna and mineral deposits within the eruption area since december 1989 2 murkiness of bottom waters up to tens of meters above the seafloor due to high densities of suspended mineral and biogenic particulates 3 destruction of a vent community by lava flows mass wasting and possible hydrovolcanic explosion at a site known as tubeworm barbecue in the axial summit caldera asc at 9 50 6 n 4 near critical temperatures of hydrothermal vent fluids ranging up to 403 c 5 temporal variations over a 2 week interval in both temperatures and chemical isotopic compositions of hydrothermal fluids 6 unusual compositions of end member vent fluids with ph values ranging to a record low of 2 5 salinities ranging as low as 0 3 wt nacl one twelfth that of seawater and dissolved gases reaching high concentrations 65 mmol l for both co2 and h2s 7 venting at temperatures above 380 c of visually detectable white vapor that transformed to plumes of gray smoke a few centimeters above vent orifices 8 disorganized venting of both high temperature fluids black and gray smoke and large volumes of cooler diffuse hydrothermal fluids directly from the basaltic seafloor rather than from hydrothermal mineral constructions 9 rapid and extensive growth of flocculent white bacterial mats species unknown on and under the seafloor in areas experiencing widespread venting of diffuse hydrothermal fluid and 10 subseafloor downslope migration of magma normal to the ridge axis in a network of small scale 1 5 m diameter lava tubes and channels to distances at least 100 200 m outside the asc we suggest that in april 1991 intrusion of dikes in the eruption area to 200 m beneath the asc floor resulted in phase separation of fluids near the tops of the dikes and a large flux of vapor rich hydrothermal fluids through the overlying rubbly cavernous lavas low salinities and gas rich compositions of hydrothermal fluids sampled in the eruption area are appropriate for a vapor phase in a seawater system undergoing subcritical liquid vapor phase separation boiling and phase segregation hydrothermal fluids streamed directly from fissures and pits that may have been loci of lava drainback and or hydrovolcanic explosions these fissures and pits were lined with white mats of a unique fast growing bacteria that was the only life associated with the brand new vents the prolific bacteria which covered thousands of square meters on the ridge crest and were also abundant in subseafloor voids may thrive on high levels of gases in the vapor rich hydrothermal fluids initially escaping the hydrothermal system white bacterial particulates swept from the seafloor by hydrothermal vents swirled in an unprecedented biogenic blizzard up to 50 m above the bottom the bacterial proliferation of april 1991 is likely to be a transient bloom that will be checked quickly either by decline of dissolved gas concentrations in the fluids as rapid heat loss brings about cessation of boiling and or by grazing as other organisms are re established in the biologically devastated area

nanoparticulate pyrite and other nanoparticles are a widespread component of hydrothermal vent black smoker emissions abstract the presence of nanoparticulate pyrite is reported in hydrothermal emissions from rainbow tag and snakepit on the mid atlantic ridge mar when coupled with previously collected data from east pacific rise 9 n epr and lau basin these data demonstrate that pyrite nanoparticles are a widespread component of black smoker emissions from hydrothermal vents and are found in significant concentrations at a fast spreading mid ocean ridge epr a back arc basin lau basin and a slow spreading mid ocean ridge mar the maximum percentage of filtered iron emitted as nanoparticulate pyrite was found to be as high as 25 10 and 5 respectively as a widespread component of hydrothermal vent emissions these nanoparticles may be an important source of iron to the world s oceans metals such as cu and zn are detected in pyrite containing aggregates at all sites and chalcopyrite was a component of nanoparticle aggregates at mar iron containing silicate nanoparticles are also identified and indicate that nanoparticles other than sulfides should also be considered when determining transport implications of hydrothermal vent emissions the varied morphologies and the presence of different minerals within these nanoparticles provide insight into their formation and stability

stacked jets in the deep equatorial atlantic ocean 1 middepth current measurements in the equatorial atlantic are characterized by elevated levels of energy contained in zonal flows of high baroclinic mode number these alternating zonal flows often called equatorial stacked jets have amplitudes up to 20 cm s 1 and vertical wavelengths of 600 m the jets are most pronounced in the depth range between 500 and 2500 m repeated direct velocity observations at 35 w indicate that the jets are coherent within 1 of the equator individual jets can persist for 1 2 years but they appear and decay rather irregularly the equatorial stacked jets are also found in realistic general circulation model simulations the features grow in amplitude with increasing horizontal and vertical model resolution however even at very high model resolutions their amplitudes are still underestimated in all model simulations high levels of energy related to the stacked jets are found in the vicinity of the western boundary currents wbcs depth range and strength of the wbcs in different experiments are related to depth range and strength of the jets in the interior stacked jets are characterized by eastward wave propagation suggesting that high baroclinic mode kelvin waves radiate energy generated in the wbc into the interior and form the stacked jets

hydrothermal plume particles and dissolved phosphate over the superfast spreading southern east pacific rise abstract the distribution and elemental composition of hydrothermal plume particles were mapped along the superfast spreading southern east pacific rise from the garret transform fault to 19 s hydrographic and optical data were obtained using a series of seven tow yos and thirty vertical casts employing a rosette sampler with 19 l pvc bottles for collecting discrete samples of various dissolved and particulate hydrothermal species the extent of hydrothermal plume coverage over the southern east pacific rise between 13 33 and 18 40 s is significantly greater than in other ridgecrest systems the region south of 17 20 s is characterized by significant enrichments of volatile gases resulting from magmatic input of fresh lava at the seafloor between 17 20 and 18 40 s the ratio of s fe in the plume particles is highly correlated with the dissolved gases in the neutrally buoyant hydrothermal plumes plume inventories of fe and s over this portion of the southern east pacific rise are 6 150 times higher than what has been observed over other vent fields because the total abundance of plumes is much greater in addition significant depletions 100 nmol l of dissolved phosphate over the ridge axis were observed at the depth of the hydrothermal plumes these results provide clear evidence that this section of the southern east pacific rise maintains the most extensive complex of hydrothermal plumes observed thus far on the global ridgecrest system

the rainbow hydrothermal plume 36 15 n mar the rainbow hydrothermal plume was discovered during a recent geophysical survey along 200 km of the mid atlantic ridge mar sw of the azores triple junction in which at least seven new sites of hydrothermal activity were identified here we present the first hydrographic study of the rainbow plume 36 15 n the strongest of the features located during that survey the plume is detectable from real time in situ nephelometer anomalies and extends 10 15km w e in a non transform discontinuity ntd between two adjacent ridge segments maximum anomalies in the rainbow plume indicate particle enrichments at least as large as those seen directly above the trans atlantic geotraverse tag vent field 26 n mar analysis of hydrographic data indicates a vent source at rainbow with a thermal output of up to 98 mw representing 140 of the thermal output previously attributed to tag both lines of evidence indicate the rainbow plume to be the strongest such feature yet found on the mar

iron ii distribution and oxidation kinetics in hydrothermal plumes at the kairei and edmond vent sites indian ocean deep sea hydrothermal activity cycles the entire volume of the global ocean through deep sea hydrothermal plumes at least every 4 8 103 a a rapid timescale that is comparable to global deep ocean mixing an important process within hydrothermal plumes is the oxidation of dissolved iron discharged with vent fluids leading to the co precipitation of many other vent sourced metals thus modifying gross hydrothermal fluxes to the deep ocean and acting as a net sink in the ocean chemical budgets of certain key tracers here we report direct measurements of dissolved fe ii oxidation rates from two recently discovered indian ocean vent sites that are intermediate between pacific and atlantic values thus demonstrating that the rate of iron oxidation and formation of scavenging fe iii solid phases in hydrothermal plumes varies systematically along the global deep ocean conveyor the average pseudo first order rate constant for the oxidation reaction is 0 303 h 1 and the corresponding half life 2 31 h the rate plots show some curvature however indicating additional processes possibly interactions with organic matter may also influence the net oxidation removal rate different rates of oxidation of iron in hydrothermal plumes in different ocean basins have important implications for the dispersion of produced oxide phases which in turn may impact on uptake of other metals from seawater and deposition into underlying ridge crest and ridge flank sediments

topographic control of a dispersing hydrothermal plume deep sea hydrothermal vents represent a major source of heat and chemicals to the oceans and support endemic chemosynthetic biological communities to fully understand the impact of hydrothermal activity upon the oceans however requires investigation of both the physical and the biogeochemical processes which are active in hydrothermal plumes and which serve to determine the net hydrothermal flux to the oceans we have recently conducted a detailed multidisciplinary study of the lateral dispersion of the hydrothermal plume emitted from the rainbow vent site near 36 15 n mid atlantic ridge combining velocity measurements from a lowered adcp optical back scatter measurements from a deep tow ctd and methane measurements from bottle samples we are able for the first time in the atlantic to trace a neutrally buoyant plume for a distance of over 50 km the path of the plume is seen to be heavily controlled by the local topography with a general northeast movement of water both particle and methane concentrations decrease downstream over the length of the observed plume the dataset provides an excellent opportunity to study the mixing and biogeochemical processes active in a hydrothermal plume and estimate fluxes of biogeochemical constituents

observed tracer fields structuration by middepth zonal jets in the tropical pacific abstractthe middepth ocean circulation in the tropical pacific is dominated by sets of alternating eastward and westward jets the origin and transport properties of these flow features remain in m

enhanced hydrothermal activity on an ultraslow spreading supersegment with a seismically detected melting anomaly abstract seafloor hydrothermal venting fields occur on all ocean spreading ridges osrs regardless of spreading rates however the distribution of seafloor hydrothermal activity such as frequency and spacing on ultraslow spreading osrs are poorly known chinese dayang cruises from 2015 to 2016 conducted detailed water column surveys for seafloor hydrothermal activity using a towed system with an array of turbidity sensors and a near bottom camera along the ultraslow spreading southwest indian ridge here we report the discovery of multiple hydrothermal plumes overlying segments 28 29 and 30 between the indomed and gallieni fracture zones from these data and earlier explorations in segments 25 27 we identify nine active venting sites the spatial density fs sites 100 km of active sites along the 394 km of ridge axis in our study area is thus 2 8 nearly 3 higher than predicted by the global trend of fs for ultraslow osrs in the interridge database previous studies concluded that an enhanced magma supply to the central indomed gallieni supersegment 11 8 ma is now limited to segment 27 our results indicate that although hydrothermal activity may be most concentrated in segment 27 the discoveries of active venting in segments 25 30 implies the presence of additional magma bodies across a broad extent of the indomed gallieni supersegment

real time observation of dispersed hydrothermal plumes using nephelometry examples from the mid atlantic ridge abstract as part of the 1984 1985 noaa vents program on the mid atlantic ridge nephelometry was used to provide real time detection and tracking of dispersed hydrothermal plumes at all nine 1984 study sites hydrothermal activity was detected by in situ real time nephelometer measurements and later confirmed by dissolved mn and particulate fe measurements these same techniques were employed in a site specific survey of the trans atlantic geotraverse tag area in 1985 where large water column anomalies in turbidity and in dissolved mn helped lead to the discovery of high temperature black smokers the optical response of the nephelometer was to hydrothermally derived particulate matter thus strong correlations existed between the nephelometer readings and total suspended matter r 0 98 n 34 and particulate fe r 0 88 n 32 in addition digital nephelometer data correlated well with dissolved mn r 0 88 n 78 throughout a large concentration range 0 2 31 0 nmol kg these data provide good evidence for the utility of in situ nephelometer measurements for locating and surveying plumes from hydrothermal vents it also appears possible within limits to predict concentrations of in situ total suspended matter of particulate fe and of dissolved mn

mineral microbe interactions in deep sea hydrothermal systems a challenge for raman spectroscopy in deep sea hydrothermal environments steep chemical and thermal gradients rapid and turbulent mixing and biologic processes produce a multitude of diverse mineral phases and foster the growth of a variety of chemosynthetic micro organisms many of these microbial species are associated with specific mineral phases and the interaction of mineral and microbial processes are of only recently recognized importance in several areas of hydrothermal research many submarine hydrothermal mineral phases form during kinetically limited reactions and are either metastable or are only thermodynamically stable under in situ conditions laser raman spectroscopy is well suited to mineral speciation measurements in the deep sea in many ways and sea going raman systems have been built and used to make a variety of in situ measurements however the full potential of this technique for hydrothermal science has yet to be realized in this focused review we summarize both the need for in situ mineral speciation measurements in hydrothermal research and the development of sea going raman systems to date we describe the rationale for further development of a small low cost sea going raman system optimized for mineral identification that incorporates a fluorescence minimizing design and we present three experimental applications that such a tool would enable

mechanical and electrical response due to fluid pressure equilibration following an earthquake 1 the mechanical and electrical response in a uniform porous crust are determined following a shear dislocation earthquake on an internal slip surface a uniform crust is studied because many exact analytical relations hold between the various response fields in this case the initial stress field that is created immediately following the earthquake subsequently relaxes through time as the fluid pressure equilibrates by fluid flow maps of the electric field generated due to the fluid flow electrokinetic coupling are presented using conservative estimates of the various parameters involved electric fields significantly larger than the diurnal magnetotelluric fields are generated quantitative results for how various components of the stress tensor change due to the fluid equilibration are also presented the coulomb stress can easily change by 100 and more in the months following an earthquake due to the fluid pressure equilibration