tilt of mean sea level along the pacific coasts of north america and japan the tilt of coastal mean sea level with respect to an equipotential surface is estimated using two fundamentally different approaches the geodetic approach is based on tide gauge and gps observations and a model of the geoid the ocean approach uses a high resolution dynamically based ocean model to estimate mean dynamic topography along the pacific coast of north america the two approaches give similar large scale profiles with a minimum at about 40 n and a maximum in the northern part of the gulf of alaska along the pacific coast of japan the geodetically determined coastal sea levels indicate an eastward drop of about 20 cm along the south coast and a further northward drop across tsugaru strait both of these features are reproduced by the ocean models an analysis of the alongshore momentum balance suggests that alongshore wind stress acting over the inner shelf is the primary driver of the mean sea level profile along the coast of north america several large scale features are explained using arrested topographic wave theory a similar momentum analysis and an additional study of time variability of sea level and circulation suggests that the kuroshio is the main driver of the mean sea level tilt along the south coast of japan discrepancies in the alongshore tilt of sea level estimated by the geodetic and ocean approaches along both coasts are discussed in terms of errors in the ocean and geoid models

detection of changes in ridge crest morphology using repeated multibeam sonar surveys a quantitative analysis method is developed to objectively identify significant bathymetric changes between multibeam sonar surveys of the same seafloor area the technique involves mathematical gridding of bathymetric surveys from different years co registration of grids based on prominent features covered in both surveys calculation of slope weighted depth difference grids and determination of the boundaries of statistically significant differences the resulting difference grids are used in interpreting geological processes and calculating the volume of new material added to the seafloor the method is applied to data from the southern juan de fuca ridge where a seafloor volcanic eruption of 0 05 km3 is inferred to have occurred between 1983 and 1987 camera tow data and submersible observations provide ground truth which confirms the validity of the quantitative analysis method and indicates empirically that the detection limit of the method allows new seafloor landforms measuring 1 105 m2 in area or about 200 300 m in diameter and 5 15 m in thickness to be detected through repeated sea beam bathymetric surveys

seasonal cross shelf flow structure upwelling relaxation and the alongshelf pressure gradient in the northern california current system abstractmoored observations are used to investigate the seasonal change in vertical structure of the cross shelf circulation at a midshelf location in the northern california current system a streamwise normal coordinate system is employed to eliminate meander and eddy induced biases in the cross shelf flow that are unaccounted for with an alternative commonly applied approach the resulting flow structure develops an organized pattern midway through the upwelling season in particular under upwelling favorable conditions an onshore return layer occurs just beneath the offshore surface flow and a third offshore directed layer exists at depth that does not appear to satisfy ekman dynamics to within 9 m of the bottom both subsurface layers strengthen in time over the upwelling season mechanisms to explain the mean structure are evaluated and it is suggested that the timing of the development and strengthening of both the interior onshore return flow and the offshore near bottom layer are consisten

quartz cemented breccias from the mid atlantic ridge samples of a high salinity hydrothermal upflow zone textural mineralogical chemical and fluid inclusion studies on a suite of quartz rich sulfide bearing greenstone breccias indicate that high salinity high fluid flow systems were recently active on the mid atlantic ridge south of the kane fracture zone these systems involved fluids with temperatures close to 300 c and salinities almost 3 times that of seawater rounded pebblelike fragments enclosed within a matrix of euhedral quartz crystals appear to have been cemented by quartz deposition from a moving fluid which attained velocities in excess of 1 m s homogenization temperatures and freezing point depression effects in fluid inclusions from texturally early and late quartz crystals indicate temporal evolution of fluid temperatures and nacl equivalent salinities from 290 c and 10 wt to 200 c and 4 7 wt during alteration and cementation of the breccias highly variable cobalt concentrations in the evolving hydrothermal solutions are indicated by fine scale oscillatory zoning in euhedral pyrite within the breccias a continuous supply of the high salinity fluids may be generated either by supercritical two phase separation at depths well below the level of inclusion entrapment or by retrograde dissolution of hydroxy chloride phases in the deeper portions of the hydrothermal system either model requires the initial temperature of the deeply circulating fluids to have been distinctly higher than 415 c and the fluid to have been cooled by conduction or by mixing with lower temperature seawater prior to entrapment within the inclusions

a dynamical description of fall and winter mean current profiles over the northern california shelf abstract fall and winter mean current profiles from a midshelf water depth 90 m northern california site exhibit a similar vertical structure for several different years the alongshelf flow is poleward with a maximum velocity of 5 10 cm s 1 in the middle or upper water column there is an offshore flow of about 2 cm s 1 in the upper 20 30 m an onshore flow of about 2 cm s 1 in the interior depths 35 65 m and an offshore flow of about 1 cm s 1 within 20 m of the bottom profiles are similar for averages over timescales from weeks to months mean current profiles at other midshelf sites along northern california and two sites off peru also have a similar vertical structure the vertical shear in the mean alongshelf flow is geostrophic throughout the water column that is in thermal wind balance with the cross shelf density gradient for timescales of a week or longer the thermal wind balance extends to within 1 m of the bottom and reduces the mean near bottom alongshelf flow to 1 cm s 1 or less th

microearthquakes at intermediate spreading rate ridges the cleft segment megaplume site on the juan de fuca ridge we discuss models for earthquake generation at intermediate spreading rate ridges and present results from an ocean bottom seismograph obs deployment on the cleft segment of the juan de fuca ridge jdfr although the cleft segment is spreading at approximately 6 cm yr an intermediate spreading rate it has no seismic activity detectable by land networks which provide a detection threshold of ml 4 or by northeast pacific underwater hydrophone arrays with a detection threshold of ml 2 to monitor seismicity four obss were deployed at the cleft segment for 11 days during august 1990 these obss detected 34 regional earthquakes associated with adjacent transform faults in addition 10 local microearthquakes ml 0 to 1 were observed over a 10 km segment of the ridge crest four local events were detected sufficiently well by multiple instruments to allow their hypocenters to be determined all these events occurred within the rift valley of the cleft segment spreading axis three events lie directly beneath a linear surface zone of hydrothermal venting this zone has been identified as the site of a seafloor volcanic eruption dike injection and large scale hydrothermal venting or megaplume event that occurred during 1986 and 1987 these earthquakes were located at depths coincident with the dike injection zone a possible mechanism for earthquake production might be tectonic release of stress acquired during the dike injection either along the dike zone or along the bounding faults of the rift valley an alternative mechanism may be stress release associated with hydrothermal activity and cooling of the dike a fourth event was located southeast of the linear hydrothermal venting and dike injection zone at a depth coincident with the spreading center crustal melt zone these observations suggest that the cleft segment may primarily experience seismic events correlated with periods of volcanic intrusion

the california current system in the southern california bight and the santa barbara channel recent observations in the santa barbara channel and over the california cooperative oceanic fisheries investigations calcofi southern california grid are used to examine seasonal circulation patterns in and near the southern california bight defined as the region east of the santa rosa ridge and including the santa barbara channel poleward flow relative to 500 m is found throughout the bight in all seasons except for spring and all subregions except the western part of the santa barbara channel in spring there is equatorward flow throughout the bight at all depths to 500 m though it tends to be surface or midcolumn intensified equatorward flow offshore of the bight present in all seasons narrows and accelerates into a jet like feature and simultaneously moves close to the santa rosa ridge in summer current meter data from the eastern entrance to the santa barbara channel are consistent with the seasonal results from the calcofi data and further show an upward propagation of phase at annual period with a phase speed of 1 to 2 m d 1 comparison with the calcofi ship winds suggests that poleward flow in the bight may be the result of positive wind stress curl through a sverdrup balance though the observed transport is only about 75 of that expected from the curl amplitude equatorward flow in the bight may be the result of coastal upwelling though the transport is larger than expected from the relatively weak winds in the bight and the offshore extent of the equatorward flow is about 10 rossby radii farther than might be expected for linearized coastal upwelling equatorward flow outside the bight cannot be explained as a sverdrup flow because the wind stress curl is positive throughout most of the region upward propagation of phase and downward propagation of energy may be indicative of forcing by remote wind equatorward of the bight given the complexity of possible forcing mechanisms for circulation in and near the bight a model that includes effects of remote wind forcing ekman pumping and topography is needed to explain the observations in a satisfactory way

a description of subtidal pressure field observations on the northern california continental shelf during the coastal ocean dynamics experiment during the coastal ocean dynamics experiment code along the northern california continental shelf in the spring and summer of 1981 and 1982 the first comprehensive effort to obtain all of the observations necessary to infer pressure fluctuations throughout the water column was made this is a description of the subtidal fluctuations in measured bottom pressure internal pressures inferred from moored conductivity and temperature observations and the water column total pressure anomalies computed from a combination of the two components the pressure field during code 2 april july 1982 is found to be more energetic than that in code 1 april july 1981 with more than 70 total pressure variance concentrated at frequencies of less than 15 days 1 the spatial structure of the pressure fluctuation field is characterized by coastal intensification and a tendency for poleward phase propagation like the pressures most of the code across shelf pressure difference variance is found at the lower frequencies with more than 60 of the total across shelf pressure difference variance at frequencies of less than 15 days 1 the code across shelf pressure differences are found to be in geostrophic balance with both alongshelf currents and the total alongshelf transport the alongshelf pressure difference variance is generally found to be concentrated at the lower frequencies much like that of the across shelf pressure differences most of the pressure and pressure difference variance is found to be highly coherent with wind stress the 20 day band pressure variability is apparently related to the response of the pressure field during so called relaxation events the barotropic component of the alongshelf geostrophic transport i e across shelf pressure difference has been found to be almost perfectly coherent with regional wind stress y and to propagate poleward within the code region at the same rate as y and the alongshelf pressure gradient is very important in accelerating the alongshelf flow the 5 day band pressure variability in the code region appears to result from local wind stress fluctuations the alongshelf pressure gradient was found to be of secondary importance relative to the wind in accelerating the alongshelf flow

development of a brine dominated hydrothermal system at temperatures of 400 500 c in the upper level plutonic sequence troodos ophiolite cyprus abstract microthermometric analyses of quartz hosted fluid inclusions in fresh and epidotized plagiogranites from the troodos ophiolite cyprus indicate that brine rich fluids 46 56 wt nacl equivalent at temperatures 400 500 c were pervasive throughout many of the plagiogranite bodies high salinity fe bearing inclusions along healed microfractures homogenize by halite dissolution at temperatures of 400 500 c liquid dominated low salinity 2 7 wt nacl secondary fluid inclusions are ubiquitous in all plagiogranite and gabbro samples studied homogenization of the low salinity inclusions occurs at uncorrected temperatures of 200 400 c the quartz hosted high salinity fluids represent either phase separation of hydrothermal seawater or an exsolved magmatic aqueous phase at uncorrected temperatures of 400 500 c migration and segregation of brine and vapor phases into fractures near the margins of the crystallizing plagiogranite bodies resulted in preferential entrapment of the fe rich brines in the deep seated high temperature portions of the hydrothermal system subsequent fracturing of the upper plutonic rocks at temperatures of 200 400 c allowed penetration by seawater which pervasively altered the plagiogranites hydration reactions involving formation of secondary minerals and or mixing with phase separated fluids resulted in fluid salinities two times that of seawater

a simple treatment of very low frequency wind driven sea level variations it is shown that very low frequency sea level variations can be calculated from the sum of the steric or density effect and the wind driven setup derived from barotropic dynamics provided that a weak slope criterion is met this result is shown to be consistent with a recent two layer formulation for wind driven shelf motions

the circulation and water masses in the gulf of the farallones abstract six adcp and ctd ship surveys of the continental shelf and slope in the vicinity of the gulf of the farallones ca were conducted in 1990 1992 adcp data provide much more detail on the structure of the currents over the slope and shelf in the gulf and reveal a persistent largely barotropic poleward flow with a complex mesoscale flow field superimposed the directly measured currents are not well represented by the geostrophic velocity fields derived from hydrographic casts important upper ocean circulation features include a slope countercurrent scc variable shelf circulation and submesoscale eddy like features the scc was present in all seasons and is believed due to a strong year round positive wind stress curl enhanced by point reyes its flow was poleward throughout the upper 300 m and often surface intensified poleward transport in the upper 400 m was 1 3 sv much greater than previous geostrophic estimates for the california current system constrained to a 500 dbar reference level the shelf circulation was much more variable than the scc and generally exhibited a pattern consistent with classic ekman dynamics responding to synoptic wind forcing submesoscale vortices or eddies often dominated the general flow field these eddies are thought to be generated by the frictional torque associated with current topography interactions their centers typically have a distinct water type associated with either the scc or the southward flowing california current higher spiciness anomalies representing a higher percentage of pacific equatorial water pew were typically found in the core of the scc or within anticyclonic eddies lower bland spiciness anomalies characteristic of a higher percentage of pacific subarctic water psaw were associated with cyclonic eddies while these circulation features were largely barotropic the flow also adjusted baroclinically to changes in the density field as different water types were advected by the general flow field or by mesoscale instabilities in the large scale boundary currents as they interacted with topography despite a seasonal cycle in regional wind and ocean temperature time series there is no obvious seasonal pattern in the circulation most of the temporal variability in the current appears to be due to synoptic and interannual variations in atmospheric forcing because of the very dynamic three dimensional nature of the regional circulation the gulf of the farallones is likely to be a center for active mixing and exchange between the coastal and california current waters relative to most us west coast locales

changing brine inputs into hydrothermal fluids southern cleft segment juan de fuca ridge author s wheat cg zierenberg ra paduan jb caress dw clague da chadwick ww abstract 2020 the authors in 2016 temperature recorders were recovered temperatures were measured and fluid samples were collected from vent 1 a high temperature 338 c hydrothermal discharge site on the southern cleft segment of the juan de fuca ridge coupled with previous sampling efforts this collection represents a 32 year record of discharge from a single chimney structure the longest record to date remarkably the fluid has remained brine dominated for more than three decades this brine formed during phase separation and segregation prior to initial observations in 1984 although the chloride concentration of the discharging fluid has decreased with time the fluid temperature has remained nearly constant for at least 3 3 years and probably for 15 or even 22 years compositions of the discharging fluids are consistent with inputs from a deep sourced brine which was last equilibrated at g400 c at a depth consistent with the base of the sheeted dikes and the brittle ductile transition this brine mixed diffusion or dispersion with a likely non phase separated hydrothermal fluid prior to discharge a survey of hydrothermal endmember fluids with chlorinities in excess of 700 mmol kg shows with the exception of fe a single trend between major ion concentrations and chlorinity even though data are from a range of crustal compositions spreading rates and water and magma depths calculated deep sourced brines from hydrothermal fluid data are similar to data based on fluid inclusions and estimates of brine assimilation in magmas a better understanding of brines is required given their potential duration of discharge and capacity for mobilizing metals

eastern boundary currents and coastal upwelling abstract the adjustment of the eastern coastal zone of an inviscid ocean with vertical walls to a change in wind conditions occurs in two stages after the propagation of a kelvin wave across the forced region in a time tk which is of the order of a day or two the coastal upwelling zone is temporarily in equilibrium with the wind further adjustment occurs after a time tr which is of the order of a few mouths when westward rossby dispersion of the coastal jet becomes important these time scales define three frequency ranges that characterize the response to fluctuating winds with period p 1 at high frequencies p tk short kelvin waves can destroy coherence between the forcing and response alonshore coherence of oceanic variables is small and the spectrum of the response is red even if that of the forcing is white the offshore wale of the response is the radius of deformation poleward phase propagation at kelvin wave speed c in unforced regions and at speed 2c in the forced region is prominent

chlorine stable isotope composition of the oceanic crust implications for earth s distribution of chlorine abstract this first investigation of the cl stable isotope composition of seafloor rocks reveals systematic variations in 37 cl 35 cl of the oceanic crust and its mantle source s relative to seawater chlorine isotopic measurements expressed as 37 cl relative to the seawater 37 cl 35 cl ratio of fresh morb glass hydrothermally produced amphibole containing whole rocks and smectite veins are presented all the samples analyzed are isotopically enriched 0 2 7 5 relative to seawater 0 uptake of cl into amphibole during axial hydrothermal alteration fractionates cl relative to seawater the isotopic compositions of morb glasses are between 0 2 and 7 2 this range appears to be partially due to the assimilation of cl from hydrothermally altered wallrock into morb magmas samples which are unaffected by assimilation have 37 cl between 3 and 7 2 overall the data imply that cl is isotopically fractionated between the surface and mantle reservoirs of earth calculations based on the degree of fractionation suggest that approximately 40 of the cl originally in the degassed mantle now resides on earth s surface

seasonal differences in the current and temperature variability over the northern california shelf during the coastal ocean dynamics experiment a long term moored array was maintained over the northern california continental shelf from april 1981 to april 1983 as part of the coastal ocean dynamics experiment to determine the seasonal differences in the current and water temperature characteristics the array consisted of two midshelf moorings and one upper slope mooring from april 1981 through july 1982 and one midshelf mooring from august 1982 to april 1983 the two summers were characterized by southeastward mean wind stresses upwelling favorable cold water isotherms sloping upward toward the coast and a sheared equatorward mean shelf current the intervening fall and winter were characterized by a weak mean wind stress relatively warm shelf water level isotherms and a more barotropic poleward mean shelf current in contrast to the differences in the characteristics of the means many of the characteristics of the current and temperature variability are the same for the summer and winter the vertical structure of the largest current empirical orthogonal functions eofs for each of the shelf moorings which account for more than 75 of the subtidal variance do not vary with season the current is vertically sheared oriented 15 20 clockwise relative to local isobaths near the surface and along isobaths near the bottom currents at the two shelf moorings alongshore separation 29 37 km are correlated with each other and with the local wind stress and these relationships do not exhibit a seasonal variation denser arrays of wind and current sensors during the two summers indicated that there were strong persistent variations in the wind field over relatively small scales tens of kilometers with corresponding variations in the shelf current field during the summer of 1981 but not during the summer of 1982 over the slope the largest eofs account for 56 72 of the current variance and have a vertical structure which is relatively uniform with depth during the summer fall and winter of 1981 but is strongly sheared in the upper 100 m during the summer of 1982 current observations over the slope are not correlated with either the shelf currents or the local wind stress during any season in contrast the temperature variability as described by eofs does exhibit a seasonal variation in vertical structure with the variability concentrated in the upper 20 30 m in summer and more uniform with depth in winter the near surface temperature variability over the slope is correlated with the shelf temperature variability estimates of the cross shelf heat flux due to the wind driven ekman transport accounts for a large part of the shelf temperature variability observations from the midshelf mooring maintained through the fall and winter of 1982 1983 showed evidence of the 1982 1983 el nino with persistent onshore and poleward currents and water temperatures typically above 12 c

depletion of a brine layer at the base of ridge crest hydrothermal systems the variable salinity of fluid venting from mid ocean ridges is indicative of mixing between hydrothermal seawater and fluids that have undergone supercritical phase separation in order to study the stability of a brine saturated layer that may form in the lowermost part of the hydrothermal system we have performed numerical simulations of a system that has returned into the subcritical regime for typical geological parameters it is shown that the interface between the brine layer and the overlying fluids is not very stable but vanishes by one of two dynamical mechanisms convective breakdown or vertical migration this contradicts the conventional picture of a steady layered convective system in which the brine is depleted only by dispersion and diffusion across the interface the depletion mechanism depends on the fluid dynamical stability of the brine layer convection within the brine layer results either in the convective breakdown for low excess salinity of the brine as compared to seawater or the upward migration of the interface for higher excess salinities consequently the depletion times are much shorter than for models with pure dispersion diffusion across the interface if the brine layer is static high chlorinity liquid is entrained slowly by the convecting overlying fluids leading to downward migration of the interface this gradual depletion of the brine layer results in almost constant vent salinities in agreement with measured salinities of chronic high chlorinity vents fl 2000 elsevier science b v all rights reserved

supercritical two phase separation of hydrothermal fluids in the troodos ophiolite the hot 350 c black smoker springs of the ocean floor are the vents of hydrothermal systems in which cold seawater descends below the ocean floor is heated reacts with the host rock and is transformed into metal bearing brine the salinity of these brines varies between vents from 0 7 to 2 0 times seawater salinity1 4 this variation has been ascribed to crustal hydration5 crystallization of chloride bearing minerals6 or two phase separation of seawater into components of differing salinity4 7 12 here we present fluid inclusion evidence for two phase separation in the ancient troodos sulphide forming systems of cyprus and discuss with the nacl h2o system as a model how this process could explain observed salinity variations in hydrothermal fluids

magmatic eruptions and iron volatility in deep sea hydrothermal fluids author s pester nj ding k seyfried we abstract during periods of volcanic activity hydrothermal fluid chemistry changes drastically becoming unusually dilute due to enhanced degrees of phase separation despite decreases in nearly all other metals these dilute fluids maintain surprisingly high dissolved fe concentrations this is demonstrated by a 17 yr time series from 9 50 n on the east pacific rise where two eruption cycles are separated by a decade of steady state chemical and physical conditions we report experimental data confi rming a sharp increase in fe solubility in low salinity and low density vapors that constitutes a reversal in behavior exhibited in near critical vapors characteristic of the steady state condition in accordance with field observations during the eruptions a fundamental divergence between the otherwise similar behaviors of fe and mn also results this helps explain how fe fluxes are maintained during magmatic events which may have important implications for the succession and temporal evolution of vent related fauna calibrated geochemical proxies for subseafl oor reaction conditions pressure temperature now allow us to elucidate hydrothermal processes from steady state through eruptive and recovery stages at the 9 50 n system 2014 geological society of america

coastal water circulation patterns around the northern channel islands and point conception california abstract the northern channel islands in california host multiple marine protected areas containing kelp forest ecosystems little is known about the water circulation onshore of the 20 m isobath we use water velocity recorded at 21 sites near the 15 m isobath at the islands and mainland during 1999 2012 to describe the water circulation on time scales of days to months the mean circulation is eastward or weak at the islands but poleward along the mainland speeds 0 10 cm s 1 the subinertial frequency along shelf flow is surface intensified and reverses direction on time scales of days in summer the flow becomes more poleward throughout the region the mean cross shelf flow profiles are strikingly similar at most sites with flow speeds 1 2 cm s 1 the mean flow near bottom in the vicinity of the kelp forests is offshore the time varying two layered response to wind is stronger up to 6 cm s 1 the flushing time of the shelf onshore of the 15 m isobath is short at most 2 dy at a few sites exposed to the prevailing wind up to 60 of the velocity variance is predictable from wind measured in the santa barbara channel in the lee of point conception or at the islands however regional wind explains little of the velocity variance during weak winds the velocity at some mainland but not island sites responds to pressure gradients measured along the mainland coast these pressure gradients are associated with local wind relaxations at pt conception not with remotely generated coastal trapped waves

poleward propagating subinertial alongshore surface currents off the u s west coast 1 the network comprising 61 high frequency radar systems along the u s west coast uswc provides a unique high resolution and broad scale view of ocean surface circulation subinertial alongshore surface currents show poleward propagating signals with phase speeds of o 10 and o 100 300 km d 1 that are consistent with historical in situ observations off the uswc and that can be possibly interpreted as coastally trapped waves ctws the propagating signals in the slow mode are partly observed in southern california which may result from scattering and reflection of higher mode ctws due to curvature of shoreline and bathymetry near point conception california on the other hand considering the order of the phase speed in the slow mode the poleward propagating signals may be attributed to alongshore advection or pressure driven flows a statistical regression of coastal winds at national data buoy center buoys on the observed surface currents partitions locally and remotely wind forced components isolates footprints of the equatorward propagating storm events in winter off the uswc and shows the poleward propagating signals year round

salinity variations in submarine hydrothermal systems by layered double diffusive convection various mechanisms have been proposed to explain the salinity variations in vent fluids of seafloor geothermal systems new experiments reacting diabase and evolved seawater were carried out to reproduce earlier published observations of cl depletions attributed to formation of an ephemeral cl bearing mineral the absence of any cl depletions in the present study suggests that the formation of cl bearing minerals is not sufficiently widespread to account for the observed salinity variations in the vent fluids a re evaluation of both field and laboratory evidence has led to a new model for subseafloor circulation that accounts for salinity variations as well as other chemical and mineralogic observations in place of a simple single pass convection system we propose that the seafloor systems consist of two vertically nested convection cells in which a brine layer at depth heats and drives an overlying seawater cell such layering of salinities a process known in fluid mechanics as double diffusive conve

gradients in the composition of hydrothermal fluids from the endeavour segment vent field phase separation and brine loss hydrothermal fluid samples collected in 1984 1987 and 1988 from a large vent field near 47 57 n on the endeavour segment of the juan de fuca ridge jfr have been analyzed for major and minor elements and gases there are of the order of 100 individual smoker vents on 10 large sulfide structures which are localized along faults and fault intersections across the vent field each sulfide structure has a characteristic fluid composition which varies very little from one vent orifice to the next or from year to year on a given structure however there are large gradients in fluid composition across the vent field with endmember chlorinity increasing from 255 mmol kg in the sw to 505 mmol kg in the ne end member concentrations of major elements are well correlated with chlorinity and endmember volatile concentrations in the lowest chlorinity fluids are approximately twice as high as in the highest chlorinity fluids the gradients in composition across the vent field and measured vent fluid temperatures 400 c are consistent with supercritical phase separation and loss of brine phase below the seafloor the factor of 2 variation in co2 and h2s is larger than expected for loss of a very high chlorinity brine concentrations of iron and manganese are not positively correlated with chlorinity suggesting that temperature and ph are more important in controlling metal solubility elevated ammonia and bromide chloride ratios indicate that there has been subseafloor interaction between the hydrothermal fluids and organic matter and high boron concentrations point to a sedimentary source

geochemistry of north cleft segment vent fluids temporal changes in chlorinity and their possible relation to recent volcanism hydrothermal vent fluids from the north cleft segment of the juan de fuca ridge between 44 54 and 45 00 n were sampled in 1988 1990 1991 and 1992 in 1988 chloride depleted relative to seawater diffuse fluids with low dissolved metal concentrations relative to other mid ocean ridge mor fluids were sampled over a distance of 10 km along axis in 1990 and 1991 both high temperature 200 c and diffuse vents were consistently metal and chloride enriched the end member compositions of high temperature vents and nearby diffuse vents were very similar there were small but significant correlated changes in diffuse and high temperature composition from 1990 to 1991 the large scale but temporary venting of low chlorinity fluids over the entire north cleft segment provides a resolution to the apparent mass imbalance implied by observations of continuous venting of chloride enriched fluids it is possible that a volcanic event along the north cleft segment prior to 1987 for which there is firm geologic evidence initially caused a boiling event which resulted in the preferential venting of vapor enriched fluids through 1988 followed by a transition to brine enriched fluids by 1990 high iron low sodium and low sr ca ratios in the high chlorinity fluids suggest that the brine phase has continued to react and approach reequilibration with an alteration mineral assemblage after the phase separation event the absence of chloride depleted fluids from 1990 onward and the systematics of lithium boron and manganese with chloride in the high temperature fluids from north cleft suggest that the evolution toward lower chlorinity at monolith vent from 1990 to 1992 is caused by progressive dilution of a brine with hydrothermal seawater

the role of a longshore pressure gradient in pacific northwest coastal dynamics abstract in this paper we demonstrate the importance of the seasonal barotropic longshore pressure gradient force to pacific northwest coastal dynamics values of the seasonal longshore pressure gradient corrected for gauge height relative to a level surface hickey and pola 1982 and for year to year variations enfield and alien 1980 were included in the two dimensional time dependent baroclinic finite difference model of hamilton and rattray 1978 as an external force observed wind stress stratification and bottom topography were included in the model and comparisons were made with current meter data in each of the three seasonal situations observed in the northwest pressure gradient force southward opposing local wind stress winter pressure gradient force northward opposing local wind stress summer and pressure gradient force and local wind stress both southward spring three important features of the seasonal circulation are shown to depend on the existence of the pressure gradient

quartz solubility in the two phase and critical region of the nacl kcl h2o system implications for submarine hydrothermal vent systems at 9 50 n east pacific rise abstract experiments were performed to investigate quartz solubility in cl bearing aqueous solutions at temperature 365 430 c and pressure conditions 219 381 bars near and within the two phase region of the nacl kcl h2o system dissolved sio2 concentrations increased with pressure along a given isotherm although the magnitude of this decreased with increasing proximity to the two phase boundary upon intersection of the two phase boundary however significant concentrations of dissolved sio2 characterized vapor rich fluids at both subcritical and supercritical conditions for these fluids dissolved silica concentrations ranged from 2 81 to 14 6 mmolal increasing with dissolved chloride concentration the experimental data permit regression of a density based relationship taking account of non ideal activity concentration effects which can be used to better constrain temperatures and pressures from dissolved sio2 and chloride in high temperature vent fluids at mid ocean ridges accordingly pressure and temperature conditions in subseafloor hydrothermal reaction zones at 9 50 n east pacific rise epr were estimated applying data from this experimental study to interval 1991 2002 and new field data 2004 results indicate reaction zone at conditions ranging from 420 to 430 c at 600 to 1500 m below seafloor thus conditions predicted for 9 50 n east pacific rise epr vent fluids suggest that supercritical phase separation might be more common than previously thought

wind relaxations and poleward flow events in a coastal upwelling system on the central california coast 1 when upwelling favorable winds weaken or relax in coastal upwelling systems prevailing equatorward currents often weaken and then reverse to form propagating poleward currents here the statistics of wind relaxations and poleward flow events along the south central california coast are derived using meteorological and oceanographic times series during 2000 2006 over the 7 year record 169 wind relaxations were observed about 1 every 2 weeks and 127 of these were followed by poleward flow events thermistor moorings and current profilers along the 15 m isobath at alegria point arguello point purisima and point sal recorded the poleward flows the poleward flows propagate northward at 10 30 km d 1 and appear as sequential temperature increases at the moorings wind relaxations occur throughout the year but are most frequent in september and least frequent in april when upwelling winds are strong and persistent poleward flows follow wind relaxations frequently during may through november and rarely in december and january sea level differences between santa monica and port san luis california decreased as winds relaxed consistent with forcing by alongshore pressure gradients temperature distributions at point arguello point purisima and point sal were skewed toward higher values because of the poleward flows the alongshore distance traveled by the poleward flows increased with duration of the wind relaxations and magnitudes of alongshore temperature and sea level differences prior to the relaxations

aqueous volatiles in hydrothermal fluids from the main endeavour field northern juan de fuca ridge temporal variability following earthquake activity the main endeavour field northern juan de fuca ridge experienced intense seismic activity in june 1999 hydrothermal vent fluids were collected from sulfide structures in september 1999 and july 2000 and analyzed for the abundance of h2 h2s ch4 co2 nh3 mg and cl to document temporal and spatial changes following the earthquakes dissolved concentrations of co2 h2 and h2s increased dramatically in the september 1999 samples relative to pre earthquake abundances and subsequently decreased during the following year in contrast dissolved nh3 and ch4 concentrations in 1999 and 2000 were similar to or less than pre earthquake values aqueous cl abundances showed large decreases immediately following the earthquakes followed by increases to near pre earthquake values the abundances of volatile species at the main endeavour field were characterized by strong inverse correlations with chlorinity phase separation can account for 20 50 enrichments of co2 ch4 and nh3 in low chlorinity fluids while temperature and pressure dependent fluid mineral equilibria at near critical conditions are responsible for order of magnitude greater enrichments in dissolved h2s and h2 the systematic variation of dissolved gas concentrations with chlorinity likely reflects mixing of a low chlorinity volatile enriched vapor generated by supercritical phase separation with a cooler gas poor hydrothermal fluid of seawater chlorinity decreased abundances of sediment derived nh3 and ch4 in 1999 indicate an earthquake induced change in subsurface hydrology elevated co2 abundances in vent fluids collected in september 1999 provide evidence that supports a magmatic origin for the earthquakes temperature salinity relationships are consistent with intrusion of a shallow dike and suggest that the earthquakes were associated with movement of magma beneath the ridge crest these data demonstrate the large and rapid response of chemical fluxes at mid ocean ridges to magmatic activity and associated changes in subsurface temperature and pressure

submersible observations along the southern juan de fuca ridge 1984 alvin program in september 1984 the research submersible alvin provided direct observations of three major hydrothermal vent areas along the southernmost segment of the juan de fuca ridge jfr the submersible operations focused on specific volcanologie structural and hydrothermal problems that had been identified during the preceding 4 years of photographic dredging acoustic imaging and geophysical studies along a 12 km long section of the ridge a continuously maintained from 1981 to the present net of seafloor anchored acoustic transponders allowed the observations from alvin to be directly tied to all previous u s geological survey data sets and national oceanic and atmospheric administration water column surveys from 1984 to the present the three vent areas studied are the largest of at least six areas identified by previous deep towed camera surveys that lie within a deep cleft which marks the axis of symmetry of the jfr in this region the cleft appears to be the locus of eruption for this segment of the jfr the vent areas at least in part are localized near what appear to be previous volcanic eruptive centers marked by extensive lava lake collapse features adjacent to the cleft at these sites each hydrothermal area has several active discharge sites and sulfide deposits occur as clusters 15 100 m2 of small chimneys individual large chimneys or clusters of large branched chimneys we review the dive program and present a brief synthesis of the geology of the vent sites together with sample and track line compilations

a new fe mn geothermometer for hydrothermal systems implications for high salinity fluids at 13 n on the east pacific rise abstract field and experimental investigations demonstrate the chemistry of mid ocean ridge hydrothermal vent fluids reflects fluid mineral reaction at higher temperatures than those typically measured at the seafloor to account for this and in turn be able to better constrain sub seafloor hydrothermal processes we have developed an empirical geothermometer based on the dissolved fe mn ratio in high temperature fluids using data from basalt alteration experiments the relationship t c 331 24 112 41 log fe mn has been calibrated between 350 and 450 c the apparent fe mn equilibrium demonstrated by the experimental data is in good agreement with natural vent fluids suggesting broad applicability when used in conjunction with constraints imposed by quartz solubility associated sub seafloor pressures can be estimated for basalt hosted systems as an example this methodology is used to interpret new data from 13 n on the east pacific rise where high temperature fluids both enriched and depleted in chloride 339 646 mmol kg relative to seawater are actively venting within a close proximity accounting for these variable salinities active phase separation is clearly taking place at 13 n yet the fluid fe mn ratios and the silica concentrations suggest equilibration at temperatures less than those coinciding with the two phase region these data show the chloride enriched fluid reflects the highest temperature and pressure 432 c 400 bars of equilibration consistent with circulation near the top of the inferred magma chamber this is in agreement with the elevated co 2 concentration relative to the chloride depleted fluids the noted temperature derived from the fe mn geothermometer is higher than the critical temperature for a fluid of equivalent salinity this carries the important implication that despite being chloride enriched relative to seawater these fluids evolved as the vapor component of even higher salinity brine

modern sediment dispersal and accumulation in quinault submarine canyon a summary abstract quinault canyon off the coast of washington intersects the dispersal path of modern columbia river sediments on the continental shelf study of the dynamics dispersal and accumulation of these deposits in the canyon indicates that no systematic down canyon transport occurs rather sediment dispersal is controlled primarily by the regional flow pattern suspended particulate matter is resuspended on the shelf primarily during winter storm events and advected northward as a bottom nepheloid layer bnl over the shelf cross canyon advection produces an intermediate nepheloid layer inl over the upper slope and canyon from which the suspended particulate matter settles rapidly probably in amorphous aggregates rapid short term deposition 10 1 g cm 2 yr 1 and enhanced modern accumulation generally 10 10 2 g cm 2 yr 1 are confined to the upper canyon 1600 m where fluctuations in deposition rates and grain size are related to specific shelf sediment resuspension events in the lower canyon 1600 m accumulation is slow and temporally uniform

atmospheric conditions during the spring and fall transitions in the coastal ocean off western united states we examine large scale atmospheric behavior around the time of the spring and fall transitions in the coastal ocean off the west coast of north america records of adjusted sea level asl coastal wind stress sea level atmospheric pressure slp and 500 mbar heights for the years 1971 1975 and 1980 1983 are analyzed the records cover periods of 91 days centered on the dates of the spring and fall transitions as determined from coastal adjusted sea level data empirical orthogonal functions are obtained from the asl coastal wind stress and slp records the two dominant modes of the asl and coastal wind stress are similar around the times of both the spring and fall transitions and the time series for these modes are highly correlated with one another transitionlike behavior is evident in the time series of the first modes in both spring and fall but the spring transition is more pronounced principal estimator patterns formed from the dominant empirical orthogonal functions show the spatial patterns of slp which force the asl and coastal wind stress during the transitions the slp pattern which coincides with the spring transition is the formation of a high pressure system centered at 45 n and 140 w along with the development of a low pressure cell over the southwest continental united states inspection of the 500 mbar height composites for 91 days surrounding the spring transition for the 9 years reveals the formation of a ridging pattern and diffluent flow over the western united states at the time of the transition following the transition the ridging relaxes but the diffluent flow over the continent remains for the duration of the 45 days examined here the fall transition is characterized by a rise in asl particularly north of 40 n and a change from southward to northward wind stress the slp pattern which coincides with the fall transition involves the appearance of a low pressure system off western north america centered at 50 n and 140 w representing the passage of synoptic storms through the region prior to the fall transition the 500 mbar heights are somewhat diffluent and show a trough over the southwestern united states after the transition the 500 mbar flow over the northeast pacific and north america is nearly zonal

the effect of temperature on metal mobility in subseafloor hydrothermal systems constraints from basalt alteration experiments abstract crystalline basalt was reacted with a na ca k cl fluid of seawater chlorinity at 400 350 and 300 c 400 bar and a fluid rock mass ratio of 1 to assess the effect of temperature on metal mobility in ridge crest hydrothermal systems basalt alteration at 400 c yielded a fluid chemistry characterized by high zn cu fe mn sio 2 h 2 s and h 2 concentrations lowering temperature to 350 and then to 300 c caused dissolved metal concentrations to decrease drastically black smoker vent fluids generally have measured temperatures 355 c the dissolved concentrations of zn cu fe and mn observed in these fluids however could only be achieved or exceeded during the 400 c phase of the experiment indicating that hot spring fluids have lost heat and possibly dissolved fe and base metals on ascent to the seafloor from a high temperature reaction zone the relative rates at which zn cu fe and mn achieve new steady state concentrations in response to temperature reduction during basalt alteration are cu fe zn mn thus dissolved zn and especially mn concentrations are more likely to record accurately temperatures characterizing subseafloor reaction zones while fe and cu which respond rapidly to changes in temperature are likely to precipitate along fluid flow paths especially in near seafloor locations this trend is confirmed by the relative abundance of dissolved metals in hot spring fluids variably influenced by heat loss processes calculations suggest that hot spring fluids may lose heat by conduction through sulfide mounds and chimney walls at flow rates observed for many vent systems since heat loss processes influence the chemistry especially dissolved metals as well as measured temperatures of axial hot springs fluids these effects must be taken into account to model accurately phase relations and fluid mineral equilibria in deeply seated subseafloor reaction zones

evidence for volcanic eruption on the southern juan de fuca ridge between 1981 and 1987 the formation of new ocean crust at mid ocean ridges is known to be a discontinuous process in both space and time but little is known about the frequency and duration of eruptions along an active ridge segment here we present evidence from sea beam surveys and underwater photography for the eruption of lavas along a segment of the juan de fuca ridge between 1981 and 1987 although previous studies have inferred volcanic activity on ridges in areas where recent seismicity or young lava flows have been observed1 4 none has yet had direct evidence to date such a recent submarine eruption the temporal coincidence between this eruptive episode and the megaplumes huge sudden emissions of hot mineral laden water observed over this part of the ridge5 6 in 1986 and 1987 supports previous suggestions5 10 that megaplumes are caused by sea floor spreading events

structure of two hydrothermal megaplumes the dynamic signatures of two megaplumes above the juan de fuca ridge are analyzed the chemical properties of these two lenslike masses of water were described by baker et al 1989 and clearly indicate that they were generated by massive and rapid ventings of hot hydrothermal fluid from the ridge both are nearly circular with radii of about 6 5 km the isopycnals bow upward around these cores of anomalous water leading to an anticyclonic circulation a cyclogeostrophic balance gives maximum currents at the edge of the core of 0 11 m s 1 for the first megaplume mp1 and 0 07 m s 1 for the second megaphone mp2 currents extend beyond the core to a radius of 12 15 km the centers of the cores are in nearly solid body rotation with relative voracities of 0 5 mp1 and 0 3 mp2 and potential vorticity anomalies expressed in units of equivalent relative vorticity of 0 8 mp1 and 0 6 mp2 where is the coriolis frequency the aspect ratio of each megaplume gives a burger number of 0 22 in terms of these nondimensional numbers the megaplumes are very similar to eddies of mediterranean water found in the eastern atlantic meddies despite their very different origin

submarine venting of phase separated hydrothermal fluids at axial volcano juan de fuca ridge since the discovery of high temperature venting on the east pacific rise in 19791 it has been expected2 3 because of the physical properties of sea water at pressures and temperatures encountered during submarine hydrothermal circulation4 5 that phase separated fluids would discharge from ridgecrest vents although this notion is supported by the reported large deviations in vent fluid chlorinity relative to that of sea water 40 200 6 7 by observations of venting at p t conditions clearly within the two phase region 220 bar and 420 c 8 and by fluid inclusion data9 10 unequivocal identification11 of phase separated venting fluids has remained elusive here we report observations of chloride and metal depleted gas enriched fluids from a shallow vent field on the juan de fuca ridge which confirm the expectation that phase separated effluents are delivered to the deep ocean from some sea floor venting systems

chemistry of hydrothermal solutions from the southern juan de fuca ridge fluids from three vent fields on the southern juan de fuca ridge were sampled in september 1984 using the dsrv alvin the fluids are uniquely high in both chloride which ranges up to twice the seawater value and in metal content simple vapor liquid phase separation could not have produced both the high chlorinity and gas concentrations observed in these fluids the cause of the elevated chlorinity can not be uniquely identified but may be the result of either or a combination of two processes 1 subsurface formation of a degassed brine and subsequent mixing of a small amount of this brine with a hydrothermal seawater which has not undergone a phase separation and 2 dissolution of a chloride rich phase combined with a possible small loss of gas during sampling procedures although measured temperatures were all less than 300 sup 0 c quartz geothermometry suggests that the fluids have equilibrated at greater than 340 sup 0 c quartz geobarometry is also in agreement with geophysical estimates of depth to the local magma chamber copyright american geophysical union 1987

alongshore coherence on the pacific northwest continental shelf january april 1975 abstract during the winter and spring of 1975 current observations were made simultaneously at five locations between tofino british columbia and newport oregon a distance of 480 km sea level and atmospheric pressure observations were available at three locations alongshore and wind observations at four locations computed bakun winds were available at 3 intervals low frequency 0 6 cpd fluctuations in alongshore current alongshere wind and subsurface pressure were significantly coherent over this distance forcing by the local wind dominated the response at each location alongshore current and sea level fluctuations were significantly coherent with the local alongshore wind and local phase relationships were consistent with phases predicted by the local model of hickey and hamilton 1980 the high alongshore coherence observed in the current and subsurface pressure fluctuations is shown to be a result of alongshore coherence in the forcing i e in the wind field rather than due to t

structure of the southern juan de fuca ridge from seismic reflection records twenty four channel seismic reflection records were obtained from the axial region of the southern juan de fuca ridge two profiles are normal to the strike of the spreading center and intersect the ridge at latitude 44 40 n and 45 05 n a third profile extends south along the ridge axis from latitude 45 20 n and crosses the blanco fracture zone processing of the axial portions of the cross strike lines resolved a weak reflection centered beneath the axis the reflector is at a depth similar to seismically detected magma chambers on the east pacific rise and a lau basin spreading center we suggest that the reflector represents the top of an axial magma chamber in the migrated sections the top of the probable magma chamber is relatively flat and 1 2 km wide and the subbottom depth of the chamber is greater where the depth to the ridge axis is greater

high resolution bathymetric surveys using scanning sonars lava flow morphology hydrothermal vents and geologic structure at recent eruption sites on the juan de fuca ridge the coaxial and cleft segments of the juan de fuca ridge have isolated chronic high temperature and focused hydrothermal vent sites both segments also have experienced recent volcanic eruptions which produced extensive ephemeral low temperature and diffuse hydrothermal venting to study the geologic setting of these sites high resolution bathymetric surveys at eight locations on the coaxial and cleft segments were collected between 1993 and 1999 two 675 khz scanning sonar systems were used mesotech on the submersible alvin and imagenex on the remotely operated vehicle jason the bathymetry from these surveys can be gridded at a scale of 2 4 m and contoured at 1 m and thus can resolve many fine scale features on the seafloor that are indistinguishable in multibeam bathymetry collected at the sea surface bathymetric data at this resolution are particularly useful for identifying geologic features related to diking faulting and lava flow emplacement for example the high resolution bathymetric maps show that submarine fissure eruptions that form pillow lavas last long enough to become localized and to produce point source constructs along their length and their extrusion rate is low enough that no significant drainback occurs in contrast lobate sheet flows are formed by short lived high effusion rate eruptions in which no localization of output occurs along the eruptive fissure and inflation is quickly followed by drainback resulting in extensive collapse features however if the process of submarine lava flow inflation occurs at a slower rate and over a longer period of time it can create lava rises up to 25 m high with distinctive structure and morphology the scanning sonar data also show that fissures and grabens have formed or reactivated where dikes approach the surface adjacent to recent eruptive sites the fine scale bathymetry establishes that all the hydrothermal vent sites studied at the coaxial and cleft segments are located along prominent volcanic or tectonic extensional structures which provide the physical pathway for fluids from the subsurface to the seafloor furthermore the fine scale morphology of recent lava flows can be used as a qualitative indication of eruption duration

circulation and multiple scale variability in the southern california bight abstract the oceanic circulation in the southern california bight scb is influenced by the large scale california current offshore tropical remote forcing through the coastal wave guide alongshore and local atmospheric forcing the region is characterized by local complexity in the topography and coastline all these factors engender variability in the circulation on interannual seasonal and intraseasonal time scales this study applies the regional oceanic modeling system roms to the scb circulation and its multiple scale variability the model is configured in three levels of nested grids with the parent grid covering the whole us west coast the first child grid covers a large southern domain and the third grid zooms in on the scb region the three horizontal grid resolutions are 20 km 6 7 km and 1 km respectively the external forcings are momentum heat and freshwater flux at the surface and adaptive nudging to gyre scale soda reanalysis fields at the boundaries the momentum flux is from a three hourly reanalysis mesoscale mm5 wind with a 6 km resolution for the finest grid in the scb the oceanic model starts in an equilibrium state from a multiple year cyclical climatology run and then it is integrated from years 1996 through 2003 in this paper the 8 year simulation at the 1 km resolution is analyzed and assessed against extensive observational data high frequency hf radar data current meters acoustic doppler current profilers adcp data hydrographic measurements tide gauges drifters altimeters and radiometers the simulation shows that the domain scale surface circulation in the scb is characterized by the southern california cyclonic gyre comprised of the offshore equatorward california current system and the onshore poleward southern california countercurrent the simulation also exhibits three subdomain scale persistent i e standing cyclonic eddies related to the local topography and wind forcing the santa barbara channel eddy the central scb eddy and the catalina clemente eddy comparisons with observational data reveal that roms reproduces a realistic mean state of the scb oceanic circulation as well as its interannual mainly as a local manifestation of an enso event seasonal and intraseasonal eddy scale variations we find high correlations of the wind curl with both the alongshore pressure gradient apg and the eddy kinetic energy level in their variations on time scales of seasons and longer the geostrophic currents are much stronger than the wind driven ekman flows at the surface the model exhibits intrinsic eddy variability with strong topographically related heterogeneity westward propagating rossby waves and poleward propagating coastally trapped waves albeit with smaller amplitude than observed due to missing high frequency variations in the southern boundary conditions

dynamics of wind driven upwelling and relaxation between monterey bay and point arena local regional and gyre scale controls 1 in north and central california equatorward winds drive equatorward flows and the upwelling of cold dense water over the shelf during the midspring and summer upwelling season when the winds temporarily weaken the upwelling flows between point reyes and point arena relax becoming strongly poleward over the shelf analytical and numerical models are used to describe the effect of alongshore variability of winds bathymetry and basin scale pressure gradients on the strength of upwelling and its relaxation alongshore winds weaken to the south of point reyes and the shelf becomes narrower from point reyes to monterey bay both of these lead to reduced upwelling at and to the north of point reyes causing an alongshore gradient of temperature and density on the shelf these alongshore gradients lead to an along isobath pressure gradient over the shelf that drive the relaxation flows a simple analytical model is used to explain the dynamics magnitude and structure of the relaxation flows the modeling also suggests that the depth of origin of the upwelled waters and thus their temperature is controlled by the along isobath pressure gradient that exists over the continental slope this along slope pressure gradient is also responsible for the california undercurrent in this region this pressure gradient is not generated in a model of the californian coast extending from 32 n to 42 n and integrated for several months suggesting it is caused by dynamics whose spatial or temporal scales are larger than the californian coast and or longer than several months

fluid evolution in an oceanic core complex a fluid inclusion study from iodp hole u1309 d atlantis massif 30 n mid atlantic ridge in the detachment mode of slow seafloor spreading convex upward detachment faults take up a high proportion of the plate separation velocity exposing gabbro and serpentinized peridotite on the seafloor large long lived hydrothermal systems such as tag are situated off axis and may be controlled by fluid flow up a detachment fault with the source of magmatic heat being as deep as 7 kmbsf the consequences of such deep circulation for the evolution of fluid temperature and salinity have not previously been investigated microthermometry on fluid inclusions trapped in diabase gabbro and trondjhemite recovered at the atlantis massif oceanic core complex 30 n mid atlantic ridge reveals evidence for magmatic exsolution phase separation and mixing between hydrothermal fluids and previously phase separated fluids four types of fluid inclusions were identified ranging in salinity from 1 4 to 35 wt nacl although the most common inclusions have salinities close to seawater 3 4 wt nacl homogenization temperatures range from 160 to 400 c with the highest temperatures in hypersaline inclusions trapped in trondjhemite and the lowest temperatures in low salinity inclusions trapped in quartz veins the fluid history of the atlantis massif is interpreted in the context of published thermochronometric data from the massif and a comparison with the inferred circulation pattern beneath the tag hydrothermal field to better constrain the pressure temperature conditions of trapping and when in the history of exhumation of the rocks sampled by iodp hole u1309d fluids have been trapped

active hydrothermal vents and sulfide deposits on the southern juan de fuca ridge massive sulfide deposits rich in zinc and silver were recovered from the juan de fuca ridge 500 km west of oregon in september 1981 the samples recovered are composed largely of zinc sulfide with lesser amounts of iron lead and copper sulfide most of the deposits occur at a series of hydrothermal vents within a relatively continuous depression in the center of a smooth 1 km wide valley along the ridge axis the depression appears to be formed by collapse of a lava lake possibly modified by extensional faulting the axial valley floor outside the depression is underlain by fresh glassy ferrobasalt sheet and lobate flows two types of sulfide mineral deposits were dredged from one of the hydrothermal vents 1 angular slabs of dark gray zinc sulfide and 2 subrounded fragments of porous light gray zinc sulfide the samples contain fresh sphalerite zoned wurtzite pyrite and minor amounts of marcasite galena and chalcopyrite cubanite the spreading rate of the juan de fuca ridge and the composition of the sulfide samples are generally similar to the east pacific rise lat 21 n site however the texture and geologic setting of the sulfide deposits are significantly different

the seasonal alongshore pressure gradient on the west coast of the united states the long term mean steric height 0 500 dbar data of reid and mantyla 1976 are added to relative monthly mean adjusted sea level data to obtain a seasonal time series of quasi absolute large scale 300 km sea surface elevation along the west coast of the united states from 48 n to 33 n north of 38 n the elevation slope reverses sign seasonally so that the resulting pressure gradient force is southward from october to june and northward from july to september south of 38 n the pressure gradient force is northward except during january at all latitudes and during february in the interval from 38 n to 35 n maximum northward force occurs during august and september at all latitudes the relative contributions to sea level elevation slope by seasonal heating and cooling freshwater effluent effects the alongshore component of coastal wind stress and deep ocean currents are investigated both seasonal heating and cooling and freshwater contributions to large scale elevation slope are relatively insignificant 10 in every month at all latitudes wind stress forcing determined with the barotropic steady frictional model of csanady 1978 is significant north of point conception 35 n for both the long term mean slope and its seasonal oscillation remote contributions are particularly important in the pacific northwest south of san francisco 38 n empirical evidence suggests that deep ocean currents contribute significantly to coastal elevation slope in summer and fall and in the mean deep ocean currents may also affect elevation slope along the whole coast during spring causing elevated sea level toward the north

seasonal variability of alongshore geostrophic velocity off central california seasonal variability of alongshore geostrophic velocity relative to 500 dbar is examined from 23 years of hydrographic data along two sections off central california one off point sur and the other off point conception the seasonal cycles are determined by least square fits of the gappy data records to harmonics with annual and semiannual periods attention is focused on variability over the outer continental slope geostrophic flow in the upper 100 m along both sections is coherent and predominantly annual with equatorward flow from february to september and poleward flow from october to january the flow deeper than 100 m is distinctly different along the two sections the nearshore deep flow is predominantly semiannual off point conception notably different from surface flow and poleward all year with maxima in december and june this semiannual variability at depth is a prevalent feature of the california current system the nearshore deep flow off point sur is unusual in that it is predominantly annual with maximum poleward flow in december and weak equatorward flow from march to may the seasonal variations over the continental slope compare favorably with existing models of eastern boundary current systems in two respects 1 the surface flow leads the predominantly annual wind forcing in this region by about one month and 2 the deep poleward counterflow is coherent with the local poleward barotropic pressure gradient at both locations with a phase lag of approximately 2 months however contrary to the results of existing dynamical models the semiannual poleward pressure gradient and undercurrent off point conception appear to be unrelated to the wind forcing which is predominantly annual in this region these semiannual variations are highly coupled to the semiannual flow throughout the water column inside the southern california bight suggesting that they may be topographically generated

the haida current we present evidence for a narrow poleward flowing surface current over the continental slope of northwestern british columbia and southwestern alaska named for a prominent native indian tribe of the region the haida current occurs predominantly between october and april maximal flow takes place in midwinter from november through february characteristic features of the current include a minimal extent of 200 300 km a width of 20 30 km a depth scale of 500 m and near surface temperature signatures of up to 1 c within the core of the current as well as large amplitude o 10 km mesoscale waves and eddies along its flank the wind stress and alongshore sea surface slope are shown to be the primary driving mechanisms for the current

geologic history of the summit of axial seamount juan de fuca ridge 1 multibeam 1 m resolution and side scan data collected from an autonomous underwater vehicle and lava samples radiocarbon dated sediment cores and observations of flow contacts collected by remotely operated vehicle were combined to reconstruct the geologic history and flow emplacement processes on axial seamount s summit and upper rift zones the maps show 52 post 410 ce lava flows and 20 precaldera lava flows as old as 31 2 kyr the inferred age of the caldera clastic deposits 1 2 m thick accumulated on the rims postcaldera between 31 ka and 410 ce there are no known lava flows near the summit the oldest postcaldera lava 410 ce is a pillow cone se of the caldera two flows erupted on the w rim between 800 and 1000 ce from 1220 to 1300 ce generally small eruptions of plagioclase phyric depleted mafic lava occurred in the central caldera and on the east rim larger post 1400 ce eruptions produced inflated lobate flows of aphyric less depleted and less mafic lava on the upper rift zones and in the n and s caldera all caldera floor lava flows and most uppermost rift zone flows postdate 1220 ce activity shifted from the central caldera to the upper s rift outside the caldera to the n rift and caldera floor and then to the s caldera and uppermost s rift where two historical eruptions occurred in 1998 and 2011 the average recurrence interval deduced from the flows erupted over the last 800 years is statistically identical to the 13 year interval between historical eruptions

ultra high chlorine in submarine kilauea glasses evidence for direct assimilation of brine by magma basaltic glass grains from the submarine south flank of kilauea hawai i have cl concentrations of 0 01 1 68 wt the latter being the highest cl content yet recorded for a hawaiian glass the high cl glass grains are products of brine assimilation by tholeiite magma the glasses are grains in a sandstone clast from bedded breccias draping the southwestern margin of kilauea s submarine midslope bench the clast contains two distinct suites of glass grains abundant degassed tholeiites perhaps derived from subaerial lavas of mauna loa that shattered upon ocean entry and a smaller population of kea type tholeiite n 17 analyzed that erupted subaqueously based on elevated s 780 1050 ppm h2o 0 42 1 27 wt and co2 1000 ppm six 5000 ppm and two grains have 10 000 ppm dissolved cl abundances of h2o na2o k2o and several trace elements increase regularly with cl concentration and we estimate that cl enrichment was due to up to 13 wt addition of a brine consisting of 78 h2o wt 13 cl 4 4 na 2 6 k 2 6 ca 620 ppm ba 360 ppm sr 65 ppm rb and 7 ppm pb the large amounts of brine addition argue against bulk assimilation of low porosity brine bearing rock the brine s composition is appropriate for a seawater derived hydrothermal fluid that reacted with basaltic wall rocks at t 100 c losing mg and s and gaining k ca rb ba sr and pb followed by phase separation near 500 c and 50 mpa 5 km below sea level at hydrostatic pressure brine was assimilated at or near the depth it formed as estimated on petrologic grounds but under lithostatic conditions the highest extents of assimilation either forced volatile saturation of the magma or enriched already coexisting magmatic vapor in h2o possible mechanisms for assimilation are 1 forcible injection of brine into magma during bursting of overpressured pockets heated by new dikes or 2 intrusion of magma into lenses or sills occupied by trapped brine

sst wind interaction in coastal upwelling oceanic simulation with empirical coupling observations primarilyfromsatellites haveshownastatisticalrelationshipbetweenthesurfacewindstress and underlying sea surface temperature sst on intermediate space and time scales in many regions inclusive of eastern boundary upwelling current systems in this paper this empirical sst wind stress relationship is utilized to provide a simple representation of mesoscale air sea coupling for an oceanic model forced by surface winds namely the regional oceanic modeling system roms this model formulation is applied to an idealized upwelling problem with prevailing equatorward winds to determine the coupling consequencesonflow sst stratification andwindevolutions theinitiallyuniformwindfieldadjuststhrough coupling to a cross shore profile with weaker nearshore winds similar to realistic ones the modified wind stress weakens the nearshore upwelling circulation and increases sst in the coastal zone the sst induced wind stress curl strengthens offshore upwelling through ekman suction the total curl driven upwelling exceeds the coastal upwelling the sst induced changes in the nearshore wind stress field also strengthen and broaden the poleward undercurrent the coupling also shows significant impact on the developing mesoscale eddies by damaging cyclonic eddies more than anticyclonic eddies which leads to dominance by the latter dynamically this is a consequence of cyclones with stronger sst gradients that induce stronger wind perturbations inthis particularupwellingproblemandthatarethereforegenerally moresusceptibletodisruption than anticyclones at finite rossby number the net effect is a weakening of eddy kinetic energy

hydrothermal alteration of basalt by seawater under seawater dominated conditions fresh mid ocean ridge basalt glass and diabase have been reacted with seawater at 150 300 c 500 bar and water rock mass ratios of 50 62 and 125 using experimental apparatus which allowed on line sampling of solution to monitor reaction progress these experiments characterize reaction under what we have called seawater dominated conditions of hydrothermal alteration in an experiment at 300 c basalt glass undergoing alteration removed nearly all mg2 from an amount of seawater 50 times its own mass in the process the glass was converted entirely to mixed layer smectite chlorite anhydrite and minor hematite removal of mg from seawater occurred as a mg oh 2 component incorporated into the secondary clay this produced a precipitous drop in solution ph early in the experiment accompanied by a dramatic increase in the concentrations of fe mn and zn in solution as mg removal neared completion and the glass was hydrolyzed ph rose again and heavy metal concentrations dropped at water rock ratios of 62 and 125 and 150 300 c the mineral assemblage produced was similar to that at a water rock ratio of 50 solution chemistry however contrasted with the earlier experiment in that mg concentrations in solution were greater and ph lower this caused significant leaching of heavy metals at 300 c nearly all of the na ca cu zn and co2 and most of the k ba sr and mn were leached from the silicates h2s al si and possibly co were also significantly mobilized whereas v cr and ni were not little or no seawater sulfate was reduced although submarine hot spring solutions sampled to date along mid ocean ridges clearly come from rock dominated hydrothermal systems evidence from ocean floor metabasalts and from heat flow studies indicates that seawater dominated conditions of alteration prevail at least locally both in axial hightemperature systems and in ridge flank systems at lower temperatures

chemical and mineralogical influences on concentrations of trace metals in hydrothermal fluids abstract concentrations of trace metals in hydrothermal solutions from the southern juan de fuca ridge sjfr and the tag hydrothermal field on the mid atlantic ridge are influenced by the combined effects of source rock composition brine seawater mixing and complex interplay among various metals and minerals deposited and remineralized in vent mounds and chimneys copper mo and co show predicted sharp decreases in concentration for vent fluids as temperatures decrease below 350 c however concentrations of cu in 363 c fluids at the tag site are well above values determined from seawater basalt interactions due to subseafloor refining processes and remineralization of chalcopyrite concentrations of zn cd pb as and ga do not show any temperature dependence between 214 to 363 c however zn values do correlate well with cl on an area by area basis due to subseafloor mixing of brine with altered seawater zinc levels also correlate well with concentrations of cd pb and as for all vent fluid samples as well as with basalt and zn rich sulfides implying some continuity in behavior from source rock to vent fluid to sulfide minerals gallium values correlate with zn and cl levels for the sjfr but are high relative to zn at the tag site due to subseafloor refining processes concentrations of tl follow cl k and rb consistent with the behavior predicted for tl overall the cl and zn rich fluids from the sjfr are characteristic of a brine dominated system formed during recent volcanism in contrast high temperature fluids from the tag area are representative of a system that has evolved over the past 100 000 yr with high concentrations of cu co and ga that result from higher temperatures and complex refining processes within a large vent mound

a current velocity index of ocean variability we use daily time series of the longshore component of residual detided current velocity z t measured at several depths at a single location on the continental slope to construct a current velocity index i s z z of coastal ocean variability here z is depth t is time and sgn f f2 2 1 is a normalization factor constructed from the local coriolis parameter f a friction parameter and the standard deviation of the near surface current velocity where s is the fluctuation about the time series mean sgn f 1 for the northern hemisphere and 1 for the southern hemisphere the time series of vertical shear z z is derived from the velocity difference between simultaneous current meter records separated by a vertical distance z within the upper half of the water column the index characterizes low frequency baroclinic variability over the continental margin and is linked through use of the thermal wind relation to instability processes that effect the transfer of potential energy stored in the mean cross slope density field to the kinetic energy of mesoscale meanders and eddies for eastern boundary regions the index ranges from large positive values during summer upwelling conditions to large negative values during winter downwelling conditions the transition seasons spring and fall are characterized by i 0 we demonstrate use of the index by applying it to the continental margin of southwest vancouver island using current velocity data collected from october 1989 to march 1995 at depths of 35 100 175 and 400 m at a long term mooring site results enable us to specify the start and end times of the oceanic seasons and to quantify the summer upwelling and winter downwelling intensities for the region gaps in the current meter time series prompted us to examine records of coastal sea level sea surface temperature sea surface salinity and bakun upwelling index the wind driven cross shore component of surface ekman transport as possible surrogates for the velocity index none of these time series were acceptable although the bakun index is a logical substitute for the velocity index differences between the two indices are significant and suggest that current velocity data are needed for accurate delineation of seasonal oceanic variability along continental margins

coastal trapped waves alongshore pressure gradients and the california undercurrent abstractthe california undercurrent cuc a poleward flowing feature over the continental slope is a key transport pathway along the west coast of north america and an important component of regional upwelling dynamics this study examines the poleward undercurrent and alongshore pressure gradients in the northern california current system ccs where local wind stress forcing is relatively weak the dynamics of the undercurrent are compared in the primitive equation navy coastal ocean model and a linear coastal trapped wave model both models are validated using hydrographic data and current meter observations in the core of the undercurrent in the northern ccs in the linear model variability in the predominantly equatorward wind stress along the u s west coast produces episodic reversals to poleward flow over the northern ccs slope during summer however reproducing the persistence of the undercurrent during late summer requires additional incoming energy from sea level variability applied south

local and remote forcing of currents and temperature in the central southern california bight 1 a comprehensive study of the central southern california bight shows that subtidal currents are dominated by relatively long time scales 10 25 days large alongshore scales and significant offshore and upward phase propagation a one dimensional model shows that observed fluctuating poleward propagating speeds 140 260 cm s 1 alongshore pressure gradient disturbances account for a much larger fraction of the alongshore velocity variance than local wind stress at least 40 in both seasons and have the longer periods of the dominant currents with the addition of local wind stress about half the velocity variance can be accounted for and overall about 5 more variance in spring than in summer results are consistent with generation of disturbances by remote wind stress several hundred kilometers equatorward of the bight and alongcoast propagation as low mode coastally trapped waves the large scale remote forcing is also responsible for much of the velocity variance on the adjacent shelf the semienclosed santa monica bay a nonlinear three dimensional model shows that water is pushed into the bay initially as part of a throughflow later becoming an eddy that gradually fills the bay producing counterflow on its shoreward side on the shelf local alongshore wind stress accounts for only 25 of the velocity variance in spring and none in summer the large scale disturbances also produce significant temperature fluctuations throughout the region via lateral advection of the mean alongshore temperature gradient local wind driven coastal upwelling is responsible for temperature fluctuations on the inner shelf during several 2 4 day events in spring but only very near the coastal wall

salinity of oceanic hydrothermal fluids a fluid inclusion study abstract an extensive microthermometric study of quartz epidote plagioclase anhydrite and sphalerite hosted fluid inclusions from ophiolitic semail oman and trinity california ophiolites and oceanic east pacific rise hydrothermal vents gorringe bank odp leg 111 hole 504b crust has been carried out in order to constrain a model accounting for wide salinity variations measured in the oceanic hydrothermal fluids recorded salinities in fluid inclusions vary between 0 3 and 52 wt nacl eq however more than 60 of the mean standard deviation salinities of the samples are within the range 3 2 0 3wt nacl eq microthermometric error and the mean salinity of all fluid inclusions without the brines is 4 0 wt nacl eq with a standard deviation of 1 6 wt nacl eq whereas most samples display slightly higher salinities than seawater several samples exhibit very high salinities more than two times that of seawater these high salinities are restricted to the plagiogranites semail and trinity ophiolites which mark the top of the fossil magma chamber in the transition zone between the plutonic sequence and the sheeted dyke complex the fluid inclusion population studied in the plagiogranites is characterized by the occurrence of four major fluid inclusion families 1 low to medium salinity liquid vapor fluid inclusions which homogenize into the liquid phase 2 low salinity liquid vapor fluid inclusions with pseudocritical homogenization 3 low to medium salinity liquid vapor fluid inclusions which homogenize into the vapor phase and 4 high salinity liquid vapor halite fluid inclusions which homogenize into the liquid phase by halite dissolution and exhibit salinities as high as 52 wt nacl eq these fluid inclusion families are interpreted as resulting from phase separation occurring in hydrothermal or magmatic fluids within the transition zone between the hydrothermal system and the magma chamber at temperatures higher than 500 c very low salinities less than half that of seawater have been found only in one dioritic sample from the gorringe bank mineralogical and petrological data from the semail ophiolite shows the absence of cl rich minerals furthermore hydration of the crust although very important cannot account for the large salinity variations thus the large salinity variations measured are interpreted as resulting from phase separation and generation of brine rich fluids at the top of the magma chamber this phase separation and subsequent phase segregation and brine accumulation may result in a double diffusive convection of the fluids in the hydrothermal system

trace metals in hydrothermal solutions from cleft segment on the southern juan de fuca ridge concentrations of trace metals in fe and cl rich hydrothermal solutions from the southern juan de fuca ridge sjfr have been determined and corrected for residual precipitates formed in the sampler precipitate corrections for ag cd cu mo pb sb and zn were variable contributing an average of 20 to total solution concentrations whereas corrections for co averaged less than 5 and essentially no corrections were required for fe and mn values for cu co and mo in these solutions showed a strong dependence on temperature with sharp decreases in concentrations as temperatures decreased to less than 320 c in addition and unlike most other metals studied all vent fluids from the sjfr were almost completely depleted in mo relative to seawater values of about 110 nmol kg 1 in contrast to the cu co mo group concentrations of ag cd sb and pb correlated well with those for zn and are presumed to follow a distribution that is influenced less by temperature over the 246 to 332 c range encountered in this study and more by the combined chemical processes that control zn levels along the transport pathway from the deep reaction zone to the vent orifice

an analysis of hf radar measured surface currents to determine tidal wind forced and seasonal circulation in the gulf of the farallones california united states 1 a complete year of hourly 3 km resolution high frequency radar measured surface currents covering the gulf of the farallones were analyzed with the following three primary objectives 1 describe the seasonal surface circulation 2 identify tidal currents and 3 determine the influence of wind forcing three predominant seasonal circulation regimes were identified relaxation storm and upwelling the relaxation period exhibited mean poleward flow over the slope variable equatorward flow over the shelf and cyclonic and anticyclonic eddies south of pt reyes the storm period mean flow was variable and exhibited evidence of coastally trapped buoyancy flow from the mouth of the san francisco bay the upwelling period exhibited equatorward flow throughout the gulf with regions of intensified flow at the northern and southern regions over the slope the tidal variance ranged from 4 to 60 was highest around the mouth of the bay decreased past the shelf and its spatial pattern reflected the combined influence of the k1 and m2 tidal current amplitudes k1 ellipses typically rotated clockwise throughout the gulf and decreased in amplitude past the shelf m2 ellipses were comparably more variable in orientation and magnitude harmonic tidal analyses of buoy wind data over 4 month time periods showed significant k1 amplitudes which did not appear when the analysis was done for the entire year this indicates that harmonic tidal analyses on surface currents are probably more effective at disassociating diurnal sea breeze driven currents when performed over long periods of time such as a year

mesoscale patterns in the cape sao vicente iberian peninsula upwelling region 1 the coastal upwelling region near cape sao vicente the southwestern tip of the iberian peninsula where the southern zonal coast meets the meridional western coast was studied using over 1200 advanced very high resolution radiometer avhrr satellite images of sea surface temperature and time series of sea level height wind velocities and nearshore sea surface temperature recorded at coastal sites within 200 km of the cape summer upwelling is more intense and persistent off the western coast than off the southern coast where a recurrent warm coastal countercurrent flows westward and at times turns northward along the western coast after reaching the cape in this region the equatorward current jet of cold water upwelled off the western coast is no longer bounded by a coast three preferred directions for the spreading of this water are identified the most persistent is eastward along the southern shelf break and slope possibly merging with waters previously upwelled locally which becomes separated from shore by the coastal progression of the warmer counterflow the second preferred direction results in the southward development of a cold filament feature fed by cold waters upwelled farther north and represents the southernmost extent of the intense coastal upwelling jet which overshoots the cape the least frequent feature to develop is a cold filament that grows westward at the latitude of the cape appearing to result from the meandering of the equatorward jet the coastal countercurrent is seen to interact with the equatorward jet at times of relaxation not only by separating the cold upwelled water from the coast but when it is energetic enough breaking westward offshore through the equatorward cold flow and separating the eastward and southward cold features from the upcoast cold waters empirical evidence shows the presence of an alongshore pressure gradient stronger in summer driving the coastal progression of the warm counterflow wind forcing plays an important role in the circulation by augmenting or diminishing the effect of the preexisting alongshore pressure gradients the extent of the progression of the warm coastal countercurrent along the southern and western coast is dictated by the the strength of the upwelling favorable wind stress which is able to balance and reverse the alongshore flow at least in the upper layers

widespread assimilation of a seawater derived component at loihi seamount hawaii many tholeiitic and transitional pillow rim and fragmental glasses from loihi seamount hawaii have high cl contents and cl k 2o ratios and ratios of cl to other incompatible components such as p 2o 5 h 2o etc relative to other hawaiian subaerial volcanoes e g mauna loa mauna kea and kilauea we suggest that this results from widespread contamination of loihi magmas by a cl rich seawater derived component assimilation of high cl phases such as saline brine or cl rich minerals halite or iron hydroxychlorides with high cl h 2o ratios can explain the range and magnitude of cl contents in loihi glasses as well as the variations in the ratios of cl to other incompatible elements brines and cl rich minerals are thought to form from seawater within the hydrothermal systems associated with submarine volcanoes and loihi magmas could plausibly have assimilated such materials from the hydrothermal envelope adjacent to the magma chamber our model can also explain semiquantitatively the observed contamination of loihi glasses with atmospheric derived noble gases provided the assimilant has concentrations of ne and ar comparable to or slightly less than seawater this is more likely for brines than for cl rich minerals leading us to favor brines as the major assimilant cl br ratios for a limited number of loihi samples are also seawater like and show no indication of the higher values expected to be associated with the assimilation of cl rich hydrothermal minerals although cl enrichment is a common feature of lavas from loihi submarine glasses from other hawaiian volcanoes show little kilauea or no mauna loa mauna kea evidence of this process suggesting that assimilation of seawater derived components is more likely to occur in the early stages of growth of oceanic volcanoes summit collapse events such as the one observed at loihi in october 1996 provide a ready mechanism for depositing brine bearing rocks from the volcanic edifice into the top of a submarine summit magma chamber

geology of the northern cleft segment juan de fuca ridge recent lava flows sea floor spreading and the formation of megaplumes geologic mapping and lava sampling were carried out after the discovery of large bursts of hydrothermal fluids megaplumes over the southern juan de fuca ridge in 1986 and 1987 our investigations of the northernmost section of the cleft segment have discovered 1 semicontinuous low temperature venting and one major high temperature vent site along 17 km of the neovolcanic zone and 2 very glassy lightly sedimented sheet flows and pillow mounds superimposed on older terrain over about 24 km along the northern most part the pillow mounds are documented to have erupted between 1981 and 1987 the occurrence of the megaplumes during this same time period strengthens the hypothesis that megaplumes are caused by sea floor extension events although the basalts from the entire length of the neovolcanic zone of the cleft segment appear to have been derived from the same mantle source a systematic northward increase in mg number along the segment within the neovolcanic zone indicates less shallow level differentiation to the north possibly related to the development of new magma chambers during the recent phase of sea floor spreading that has occurred there

modeling the generation of the juan de fuca eddy 1 numerical simulations with the regional ocean modeling system are used to study the generation of the cyclonic juan de fuca eddy located off the entrance of juan de fuca strait in summer an initial simulation forced with average summer upwelling favorable winds tides and buoyancy boundary conditions that maintain an estuarine flow in juan de fuca strait produces an eddy and currents that are in reasonable agreement with observations sensitivity studies are then carried out to explore the importance of these three forcing mechanisms the relative proximity of dense water in the bottom estuarine flow entering the strait is shown to lead to enhanced upwelling off cape flattery when either wind or tidal forcing is applied this upwelled water then mixes with the estuarine outflow and is advected offshore the tidal upwelling arises through three mechanisms m2 vertical excursions of nearly 20 m at 50 m depth west of the cape on the flood tide strong tidally rectified vertical velocities west of the cape and the spilling of denser bottom water over the western wall of juan de fuca canyon on the ebb tide the cyclonic eddy is a consequence of geostrophic adjustment to the doming isopycnals that arise from the upwelling these model simulations refute an earlier hypothesis that the eddy is generated when california undercurrent water is drawn up tully canyon and onto the vancouver island shelf suggesting instead that these canyon dynamics play only a secondary role in maintaining the eddy once it is formed