petrologic determination of ascent rates for the 1995 1997 soufriere hills volcano andesitic magma the recent eruption of the soufriere hills volcano in montserrat july 1995 to present october 1997 has produced a hornblende bearing andesitic lava dome it is possible to petrologically estimate changes in ascent rates of amphibole bearing magmas for certain rates of decompression a breakdown rim of fine grained anhydrous reaction products forms where amphibole is in contact with melt the thickness of the rim varies with ascent rate most of the amphibole phenocrysts in the magma storage region lack breakdown rims about 10 have 200 400 m thick coarse grained breakdown rims that are interpreted to be relicts of a past heating event study of a time series of new dome andesites showed that ascent rate increased from december 1995 0 001 m s to july 1996 0 008 m s while eruptive style remained extrusive ascent rate increased to 0 012 m s in august 1996 and the first major explosive eruption occurred on 17 18 september 1996

experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

iron and manganese diagenesis in deep sea volcanogenic sediments and the origins of pore water colloids abstract volcanogenic sediments are typically rich in fe and mn bearing minerals that undergo substantial alteration during early marine diagenesis however their impact on the global biogeochemical cycling of fe and mn has not been widely addressed this study compares the near surface 0 20 cm below sea floor cmbsf aqueous no 3 and solid phase reactive fe distributions between two volcanogenic sediment settings 1 a deep sea tephra rich deposit neighbouring the volcanically active island of montserrat and 2 mixed biosiliceous volcanogenic sediments from abyssal depths near the volcanically inactive crozet islands archipelago shallow penetration of o2 aq into montserrat sediments was observed 5 cmbsf and largely controlled by the oxidation of organic matter dissolved fe and mn distributions in montserrat pore waters were lowest in the surface oxic layer 0 3 m fe 32 m mn with maxima 20 m fe 200 m mn in the upper 1 15 cmbsf unlike montserrat fe and mn in crozet pore waters were ubiquitously partitioned between 0 2 m and 0 02 m filtrations indicating that the pore water distributions of fe and mn in the traditionally termed dissolved size fraction are dominated by colloids with respective mean abundances of 80 and 61 plausible mechanisms for the origin and composition of pore water colloids are discussed and include prolonged exposure of crozet surface sediments to early diagenesis compared to montserrat favouring nano particulate goethite formation and the elevated dissolved si concentrations which are shown to encourage fine grained smectite formation in addition organic matter may stabilise authigenic fe and mn in the crozet pore waters we conclude that volcanogenic sediment diagenesis leads to a flux of colloidal material to the overlying bottom water which may impact significantly on deep ocean biogeochemistry diffusive flux estimates from montserrat suggest that diagenesis within tephra deposits of active island volcanism may also be an important source of dissolved mn to the bottom waters and therefore a source for the widespread hydrogenous mnox deposits found in the caribbean region

an ion microprobe study on trace element composition of clinopyroxenes from blueschist and eclogitized feti gabbros ligurian alps northwestern italy some petrologic considerations abstract detailed microtextural investigations coupled with ion microprobe trace element determinations have been performed on clinopyroxenes from blueschist and eclogitized fe ti gabbros from ligurian alps northwestern italy ion microprobe analyses have also been carried out on garnets from eclogitized fe ti gabbros the aim is to understand the relations between metamorphic reactions and trace element compositions of clinopyroxenes in high pressure low temperature terranes trace and major element analyses on relicts of igneous diopsides indicate similar protoliths for both eclogites and blueschists metamorphic clinopyroxenes have variable trace element compositions which reflect the compositions of original mineral phases in particular the clinopyroxenes replacing the igneous diopside commonly retain geochemical signatures of the precursor mineral such as relatively high sc y and hree contents the trace element variations among high pressure clinopyroxenes in different textural domains are greater for blueschists than for eclogites this reflects the more limited major element equilibration of blueschists relative to eclogites in deformed eclogites the clinopyroxenes lack the geochemical signatures of the original igneous minerals most probably due to the enlargement of reaction domains caused by synmetamorphic deformation trace element partitioning between omphacite and garnet suggests that in both undeformed and deformed eclogites chemical equilibrium is locally approached and therefore the trace element composition of clinopyroxenes is controlled by the coexisting minerals for instance clinopyroxenes in eclogites are strongly hree and lree depleted i e with bell shaped pattern due to the equilibration with garnet and allanite respectively the partition coefficients for rees between omphacite and garnet are markedly lower than those reported in the literature on the basis of crystal chemical considerations we suggest that this is probably due to lower temperature conditions during formation

retrograde p t t path for the voltri massif eclogites ligurian alps italy some tectonic implications the retrograde p t trajectory of the eclogitic fe ti gabbros from the ligurian alps is constrained by the appearance of mineral parageneses post dating the na clinopyroxene garnet eclogitic assemblage and indicating the following sequence of metamorphic events 1 amphibolitic stage edenite katophorite plagioclase an33 43 oxides in symplectitic aggregates 2 glaucophanic stage a porphyroblastic glaucophanic amphibole has overgrown the symplectite winchite also occurs as thin rims around glaucophane and both amphiboles are sometimes armoured by atoll garnets 3 albite amphibolite stage barroisite katophorite albite epidote oxides chlorite overprint the glaucophanic stage minerals 4 greenschist stage represented by actinolite albite epidote oxide paragenesis the metamorphic evolution is complex and the decompression path on a p t diagram is significantly different from those defined in the literature for the voltri eclogites the main features inferred from the p t path are the following 1 the pressure climax does not match the thermal climax the maximum temperature conditions are in fact achieved during the early stage of uplift 2 a decrease in temperature suggested by the appearance of glaucophane after the amphibolitic symplectite 3 successive uplift probably accompanied by an increase in temperature the complexity of the p t path drawn for the voltri eclogites can be explained with a mechanism of successive underthrusts propagating from the innermost to the outermost sector of the ligurian alps

geochemistry of the 1989 1990 eruption of redoubt volcano part ii evidence from mineral and glass chemistry abstract early stages december 1989 of the 1989 1990 eruption of redoubt volcano produced two distinct lavas both lavas are high silica andesites with a narrow range of bulk composition 58 64 wt and similar mineralogies phenocrysts of plagioclase hornblende augite hypersthene and fe ti oxides in a groundmass of the same phases plus glass the two lavas are distinguished by groundmass glass compositions one is dacitic and the other rhyolitic sharp boundaries between the two glasses in compositionally banded pumices lack of extensive coronas on hornblende phenocrysts and seismic data suggest that a magma mixing event immediately preceeded the eruption in december 1989 textural disequilibrium in the phenocrysts suggests both magmas dacitic and rhyolitic glasses had a mixing history prior to their interaction and eruption in 1989 sievey plagioclase and overgrowths of magnetite on ilmenite are textures that are at least consistent with magma mixing the presence of two hornblende compositions one a high al pargasitic hornblende and one a low al magnesiohornblende in both the dacitic and rhyolitic groundmasses indicates a mixing event to yield these two amphibole populations prior to the magma mixing in december 1989 the pargasitic hornblende and the presence of ca rich overgrowths in the sievey zones of the plagioclase together indicate at least one component of this earlier mixing event was a mafic magma either a basalt or a basaltic andesite eruptions in 1990 produced only andesite with a rhyolitic groundmass glass glass compositions in the 1990 andesite are identical to the rhyolitic glass in the 1989 andesite cognate xenoliths from the magma chamber or conduit are also found in the 1990 lavas magma mixing probably triggered the eruption in 1989 the eruption ended when this rather viscous rhyolitic groundmass glass magma capable of entraining sidewall xenoliths magma stabalized within the conduit

failure to bloom intense upwelling results in negligible phytoplankton response and prolonged co2 outgassing over the oregon shelf during summer upwelled water with elevated co2 partial pressure pco2 and nutrients outcrops over the oregon or inner shelf as this water transits across the shelf high rates of primary production fueled by the upwelled nutrients results in net atmospheric co2 drawdown upwelled source waters typically have pco2 approaching 1000 atm that is then reduced to 200 atm for almost the entire month of july 2008 strong and persistent upwelling brought cold 8 c saline 33 5 high pco2 600 atm water to our midshelf buoy site and high pco2 water was broadly distributed over the shelf chlorophyll levels as a proxy for phytoplankton biomass were low 2 mg m 3 on the shelf during the period of most intense upwelling and satellite data showed no evidence of a downstream phytoplankton bloom a small chlorophyll increase to 4 mg m 3 was observed at our buoy site following a decrease in the strength of southward wind stress 10 days after upwelling initiated chlorophyll levels further increased to 10 mg m 3 only after a cease in upwelling these higher levels were coincident with the appearance of water masses having temperature and salinity properties distinct from recently upwelled water we suggest that rapid offshore transport and subsequent subduction before phytoplankton populations could respond is the most likely explanation for the persistent low chlorophyll and elevated surface water pco2 throughout the july upwelling event this mechanism likely dominates under conditions of strong and persistent upwelling favorable winds that coincide with close proximity of low density offshore waters which may have implications for the biogeochemical functioning of this system under future climate scenarios

time dependent wind driven flow over a shallow midshelf submarine bank 1 during summer 2001 high resolution hydrographic velocity and bio optical surveys were conducted over heceta bank off central oregon north of the bank upwelling over simple bottom topography exhibited a classic response with a midshelf baroclinic coastal jet and upwelled isopycnals the coastal upwelling jet follows the bank topography as it widens offshore before reaching the southern end of the bank where the shelf break turns almost 90 back toward the coast the ensuing adjustment involves the offshelf transport of coastal water and the material it contains the jet meanders anticyclonically in the lee of the bank before resuming its equatorward path seaward of the shelf break a pool of high chlorophyll 15 mg m 3 near surface water is found in the low velocity lee region created by the bank a low temperature high salinity bottom water pool supplied primarily from the south lies over the inshore region of the bank this bottom pool is up to 40 m thick and contains elevated levels of suspended material by creating an east west perturbation in the coastal upwelling front the flow topography interaction introduces an alongshore pressure gradient when southward upwelling favorable winds relax this alongshore pressure gradient can drive flow back to the north this leads to northward flow on the inshore side of the bank ultimately setting up the potential for recirculation around the entire bank complex on a timescale of about 10 days strong northward winds during summer lead to downwelling within 15 km of the coast accompanied by significant 0 2 m s 1 wind driven northward currents

garnet geochemistry of tungsten mineralized xihuashan granites in south china abstract the xihuashan complex intrusion in south china which is emplaced at ca 154 ma mainly comprises medium grained porphyritic biotite granite medium grained biotite granite and fine grained two mica granite medium grained biotite and fine grained two mica granites are important tungsten bearing granites and contain an unusual amount of garnet garnets from this intrusion are dominated by almandine and spessartine which constitute 94 to 99 of the total molecular composition of the garnet these garnets display unusual compositional zoning the cores of these garnets are rich in heavy rare earth element hree y ca and contain abundant hree and y rich mineral inclusions their rims are free of mineral inclusions and have low of these elements two types of fluorite inclusions exist in garnet y fluorite and y poor fluorite garnet exhibits specific mn zoning with a relatively mn poor core but a relatively mn rich rim thus constituting a specific spessartine inverse bell shaped profile that belongs to typical magmatic garnets all analyzed garnets have high ree content and exhibit hree enriched and lree depleted patterns with strong negative eu anomalies the incorporation of ree into garnet is in part controlled by its crystal chemistry with ree3 following a coupled substitution of the type fe2 mn2 1viii ree3 1viii si4 1iv z3 1iv the texture and compositional zoning of garnet suggest that garnet growth is largely controlled by the pressure temperature composition condition of magmatic evolution internal crystal chemical parameters and kinetics during mineral growth the garnet core grows in near equilibrium with magmatic melt under a relatively high pressure temperature p t condition by contrast the garnet rim grows rapidly by the coexisting melt fluid phase and co2 rich volatile environment under a relatively low p t condition which is virtually unfavorable for the incorporation of ree into the magmatic garnet structure garnet fingerprints the magmatic hydrothermal transition during crystallization of these granites

growth of the lava dome and extrusion rates at soufriere hills volcano montserrat west indies 2005 2008 the third episode of lava dome growth at soufriere hills volcano began 1 august 2005 and ended 20 april 2007 volumes of the dome and talus produced were measured using a photo based method with a calibrated camera for increased accuracy the total dense rock equivalent dre volume of extruded andesite magma 306 51 mm3 was similar within error to that produced in the earlier episodes but the average extrusion rate was 5 6 0 9 m3s 1 dre higher than the previous episodes extrusion rates varied in a pulsatory manner from 0 5 m3s 1 to 20 m3s 1 on 18 may 2006 the lava dome had reached a volume of 85 mm3 dre and it was removed in its entirety during a massive dome collapse on 20 may 2006 extrusion began again almost immediately and built a dome of 170 mm3 dre with a summit height 1047 m above sea level by 4 april 2007 there were few moderate sized dome collapses 1 10 mm3 during this extrusive episode in contrast to the first episode of dome growth in 1995 8 when they were numerous the first and third episodes of dome growth showed a similar pattern of low 0 5 m3s 1 but increasing magma flux during the early stages with steady high flux after extrusion of 25 mm3

application of a chemical leach technique for estimating labile particulate aluminum iron and manganese in the columbia river plume and coastal waters off oregon and washington in order to determine the total concentration of bioavailable trace metals in seawater measurement of both the dissolved and labile particulate fractions is necessary comparison of labile particulate metal concentrations from various researchers is limited because of differing definitions of the fraction that is potentially available to phytoplankton on a time frame of generations a comparison experiment was conducted on coastal and riverine suspended particulate matter to determine the difference between several commonly used techniques that operationally define the labile particulate trace metal fraction furthermore we compared two leach techniques for surface transect samples from within the columbia river plume and water offshore of oregon and washington united states the particulate trace metal concentration in the leachate was determined by high resolution inductively coupled plasma mass spectrometry from this comparison one chemical leach was chosen to best define the labile particulate fraction of al fe and mn a weak acid leach 25 acetic acid at ph 2 with a mild reducing agent 0 02 m hydroxylamine hydrochloride and a short heating step 10 min 90 95 c this leach was applied to three surface transects within the columbia river plume these coastal waters were found to be rich in labile particulate trace metals that are directly delivered from the columbia river and indirectly supplied via resuspension from upwelling over a broad continental shelf

groundmass crystallization of mount st helens dacite 1980 1986 a tool for interpreting shallow magmatic processes the 1980 1986 eruption of mount st helens volcano provides an unprecedented opportunity to observe the evolution of a silicic magma system over a short time scale groundmass plagioclase size measurements are coupled with measured changes in matrix glass plagioclase and fe ti oxide chemistry to document increasing groundmass crystallinity and thus to better constrain proposed physical models of the post may 18 1980 magmatic reservoir measurements of plagioclase microlite and microphenocryst sizes demonstrate that relatively rapid growth approximately 10 9 cm s of groundmass plagioclase occurred immediately subsequent to may 18 relatively rapid plagioclase growth continued through the end of 1980 at an average rate of 3x10 11 cm s plagioclase growth rates then decreased to 1x10 11 cm s through 1986 changes in groundmass crystallinity are reflected in changes in both matrix glass and plagioclase microphenocryst rim chemistry although the matrix glass composition appears to have remained approximately constant from 1981 1986 after a rapid compositional change from may 18 until the end of 1980 plagioclase microphenocrysts show increasingly more complex zoning patterns with time microphenocryst core compositions are commonly positively correlated with crystal size both of these observations indicate continuous groundmass plagioclase growth through 1986 magmatic temperatures estimated from fe ti oxide pairs are approximately constant through 1981 at eruption temperatures of 930 c and at log fo2 of 10 8 by 1985 1986 oxide temperatures decreased to 870 c chemical and textural changes can be explained by 1 rapid degassing and crystallization in response to the intrusion of magma into a shallow 4 5 km reservoir toward the end of the may 18 1980 eruption 2 continued crystallization at a much reduced rate through 1986 due to slow cooling of the shallow magma reservoir growth rates and consequent chemical changes appear to decrease at the end of 1980 this is coincident with the change in eruption style from explosive eruptions sometimes followed by dome growth to solely extrusive dome building events and can be explained by the expected viscosity increase of both degassing and increasing crystallinity the model of twostage crystallization of magma in a shallow reservoir is consistent with conclusions from gas studies casadevall et al 1983 gerlach and casadevall 1986 a b patterns of crater deformation chadwkck et al 1988 and post 1980 seismicity endo et al 1990 although it does not explain the experimental data of hill and rutherford 1989 on the growth rate of amphibole reaction rims textural measurements on mount st helens dacite can also be used to evaluate crystallization kinetics in silicic magmas systems for which experimental data is almost non existent plagioclase growth rates are 5 10 times slower than estimated plagioclase growth rates in basaltic systems a result consistent with the higher viscosity of a more silicic melt furthermore patterns of textural change both average crystal size and number density are similar to those observed during the 1984 mauna loa eruption by lipman and banks 1987 suggesting that the only modification to the crystallization behavior of plagioclase required in extrapolation from basaltic systems is a moderate decrease in rates such that the rate of crystallization scales with the melt viscosity

magma ascent rates from amphibole breakdown an experimental study applied to the 1980 1986 mount st helens eruptions recent 1980 1986 mount st helens dacites contain the phenocryst assemblage plagioclase amphibole low ca pyroxene magnetite ilmenite and rare high ca pyroxene which indicates that they all originated from an 8 km deep reservoir at 900 20 c with xh2o 0 67 in fluid according to experimental data iron titanium oxide phenocryst compositions indicate that all post may 18 dacitic magmas erupted at 900 20 c except for the final lava extrusion in october 1986 the magma reservoir may have cooled to 866 c by october 1986 amphiboles in the post may 18 1980 magma contain one or more amphibole populations characterized by reaction rims of different thicknesses the development of the amphibole reaction rims in these rocks is a response to water loss from the coexisting melt during an approximately adiabatic ascent from a deep reservoir constant p and t and isothermal decompression experiments show that during a 900 c constant rate decompression from 8 km to the surface no reaction rim develops on amphibole in 4 days a 10 m rim develops in 10 days and a 35 m rim develops in 20 days these experimental data and histograms of rim widths in 1980 1986 mount st helens dacites show that post may 18 eruptions are composed in large part of magma represented by a population of thin rimmed amphiboles magma which ascended from the deep 8 km reservoir in 6 to 10 days the remainder of each sample consists of magma containing amphiboles with reaction rims ranging from 14 to 60 m magma which apparently spent from 8 to 25 days along the conduit margins before being mixed thoroughly millimeter scale into the erupting magma the mixing in a viscous slowly ascending dacite may be enhanced by its flow through partially crystallized magma emplaced earlier and by the evolution and loss of a large vesicle population the experimental calibration of amphibole reaction rim width versus decompression time yields average ascent velocities for post may 18 dacites of about 15 30 m h for magma represented by the thick rimmed amphiboles and from 35 to 50 m hr for magma represented by the thin rimmed crystals an ascent rate of 66 m h is indicated for the may 18 1980 eruption which contains amphiboles with no reaction rims the volume of endogenous dome growth which preceded extrusion of magma newly derived from the deep source region suggests that the effective conduit volume beneath mount st helens in 1981 1982 was equivalent to a cylinder 8 km long and 8 9 m in radius

magma system recharge of mount st helens from precise relative hypocenter location of microearthquakes 1 four hundred forty seven well recorded earthquakes at mount st helens during the late 1990s are relocated with high precision using a combination of a cross correlation technique and then a procedure to obtain a one dimensional velocity structure solution together with station corrections the resulting high resolution pattern of the spatial temporal evolution of the earthquake activity along with focal mechanisms of events provide additional evidence for the presence of a magma reservoir in the depth range 5 5 10 km connected to the surface by a thin vertical conduit moreover the distribution of the events below 5 5 km yielded a much clearer view of the structures that generate the seismicity at that depth some of the deeper events occur along a sequence of faults under the influence of a radial stress field however a large number of the events occur on a nne ssw striking steeply dipping fault with slip consistent with magma being periodically injected into a truncated dike on the northwest side of this fault

in situ major and trace elements of garnet and scheelite in the nuri cu w mo deposit south gangdese tibet implications for mineral genesis and ore forming fluid records abstract garnet and scheelite are common hydrothermal silicate mineral and metal mineral in skarn or porphyry skarn deposits and can aid in constraining the composition of ore forming fluid based on in situ major and trace element analyses of garnet and scheelite from the nuri cu w mo deposit we discuss the factors and mechanisms controlling the incorporation of rare earth elements rees into the garnet and scheelite and investigate the associated hydrothermal fluid characteristics the garnets from the nuri deposit belong to the grossular andradite grandite solid solution series and range in composition from adr64grs34 to adr91grs8 the ree patterns of garnet are enriched in light rare earth elements lrees and depleted in heavy rare earth elements hrees the rees characteristics indicates that the incorporation of rees into the nuri garnet was controlled by the surface adsorption and element substitution in the mineral structure based on the cathodoluminescence cl images of scheelite two growth stages early and late stages are identified these two stages of scheelite belong to the scheelite powellite series and are enriched in lrees and depleted in hrees however the early scheelite exhibits negative or no eu anomalies 0 34 0 95 whereas the late scheelite presents positive eu anomalies 1 25 2 89 the mo content in the early scheelite is positively correlated with the eu value while the mo content in the late scheelite is negatively correlated with eu these characteristics indicate that the redox state of the ore forming fluid gradually changed from the oxidized state to the reduced state the preferred ree3 substitution for ca2 in the nuri scheelite is 3ca2 2ree3 ca where ca is a ca site vacancy the ree features of the scheelite are mainly controlled by the ree nature of the ore forming fluid according to the characteristics of trace elements in garnet and scheelite we suggest that the ore forming fluid of the nuri deposit is a magmatic fluid mixed with a slightly acidic external fluid chloride complexes may be the main transport ligand of the rees and the oxygen fugacity of the ore forming fluid gradually decreased

geochemical implications of rare earth element patterns in hydrothermal fluids from mid ocean ridges abstract rare earth element data are reported for vent fluids collected from eight deep sea hydrothermal areas including samples from sediment hosted and bare rock hydrothermal systems the morb normalized ree patterns from these diverse settings are remarkably similar to each other but distinctly different than seawater or basalt being lree enriched and possessing a strikingly positive eu anomaly the ree concentrations making up these patterns vary widely however both on a spatial and temporal basis when plotted against ionic radii these fluid trends are remarkably linear and show the same fractionation patterns exhibited by plagioclase during magma segregation this analysis suggests that the partitioning of the ree between fluid and rock during high temperature hydrothermal alteration of morb is dominated by crystochemical exchange during dissolution and recrystallization reactions at the exposed surfaces of plagioclase phenocrysts a comparison of ree ionic radii in eight coordination indicate that the partitioning of 3ree and 2eu are dominated by chemical substitution for ca 2 and sr 2 respectively these considerations predict that the total 3ree content of vent fluid varies in a systematic way during the transition from an rich morb plagioclase to ab rich hydrothermal plagioclase and that these parameters can be used as indicators of the average extent of alteration inside active hydrothermal systems

syneruptive mixing degassing and crystallization at redoubt volcano eruption of december 1989 to may 1990 abstract the 1989 1990 eruption of redoubt volcano included initial energetic vertical venting of pumiceous tephra followed by shedding of dense pyroclastic flows from successive unstable domes the suite of quenched magmatic materials thus produced coupled with detailed seismic observations provides a record of establishment and subsequent evolution of an active magma column in the upper crust the initial eruptive event involved a dacite magma with rhyolite melt and an andesite magma with dacite melt the dacite magma contains reaction rim free hornblende high cl concentrations 0 12 0 02 wt of melt and is microlite free all evidence for rapid ascent from depth in contrast the andesite component is microlite rich though this characteristic may have arisen by mixing between the two magmas rather than by slow ascent abundant dense juvenile lava like clasts with low h2o 0 1 0 3 wt were ejected in the initial eruption event implying that the magma column had reached the near surface and its upper portion had undergone degassing and bubble collapse prior to explosive disruption later eruptive events contain evidence of progressive blending of the two magmatic components as well as mixing between fresh reservoir derived and old conduit resident magma magma apparently ascended to the surface from the 6 10 km deep source chamber in a series of pulses rather than by steady flow or gradual emptying of a shallowly intruded body increased shallow long period seismicity which may indicate subsurface degassing from the flowing magma column occurred 5 days before each major eruptive event petrologic evidence indicates that each eruption contained some magma that ascended quickly from the chamber with time the proportion of new magma in eruptive batches may have decreased however even the final dome contains magma that left the chamber no more than a few days before extrusion together the pulses apparently record passage of an andesite plume through redoubt s dacite magma reservoir

interactive aggregation and sedimentation of diatoms and clay sized lithogenic material monospecific diatom cultures thalassiosira punctigera and skeletonema costatum were incubated in rotating cylinders together with clay suspensions present in a range of concentrations 5 100 mg kaolinite l 21 and as different minerals 50 mg l 21 kaolinite smectite illite and clay sized quartz powder the addition of lithogenic suspensions to diatom cultures accelerated the formation of visible aggregates in the roller tanks by a factor of 3 aggregate size decreased and density increased proportionally to the amount of kaolinite added to the diatom cultures in the presence of kaolinite and illite aggregate sizes were smaller and sinking rates lower than in the presence of smectite and quartz the influence of lithogenic matter on the sinking velocities of aggregates was ambiguous compound aggregates sank faster with increasing amounts of lithogenic matter present in cultures of t punctigera until a certain ratio between lithogenic and biogenic material was reached further increasing the amount of lithogenic matter did not increase sinking rates significantly in contrast increasing the concentration of kaolinite added to cultures of s costatum could decrease sinking velocities of the evolving compound aggregates this nonlinear behavior is argued to be primarily a function of aggregate composition on aggregate sizes and excess densities although the possibility of a mutual acceleration of vertical flux of algae and clay is confirmed the results show that the presence of lithogenic material could also decrease the downward flux of phytoplankton biomass rapid sinking of phytoplankton derived organic carbon via sedimentation of aggregates contributes significantly to the vertical transport of marine particulate organic carbon poc a process known as the biological pump volk and hoffert 1985 rapid sinking of clay sized lithogenic material can be inferred from sediment trap data wefer 1989 laboratory studies on marine aggregate formation and properties have focused on pure phytoplankton aggregates kiorboe et al 1990 riebesell et al 1991 kiorboe and hansen 1993 or on monomineralic clay aggregates kranck 1973 however coaggregation of phytoplankton and clay is a familiar phenomenon in aquatic environments first drawings of marine snow show sundry marine organisms and mineral grains embedded in a mucous matrix which dominates the aggregates by volume and appears to hold the solid compounds together tsujita 1953 avnimelech et al 1982 described enhanced floc formation and sedimentation of freshwater algae in the presence of clay and vice versa the fact that lithogenic and biogenic particles are often found in deep sediment traps during the same time interval in spite of independent occurrence in the surface water also suggests coaggregation and cosedimentation of these particles deuser et al 1983 wefer 1989 ittekkot 1993 while small amounts of both biogenic and lithogenic particles are present in all marine environments areas with elevated concentrations of lithogenic particles often show a high phytoplankton abundance at the same time and are thus particularly interesting in terms of interaction between phytoplankton and lithogenic material examples for marine en

cadmium in the waters off south morocco nature of particles hosting cd and insights into the mechanisms fractionating cd from phosphate in this study we report the distributions of total dissolvable cadmium and particulate cadmium from 27 stations in southern moroccan coastal waters 22 30 n which is part of the north west african upwelling system these distributions were predominantly controlled by upwelling of the north atlantic central waters nacw and uptake by primary production atmospheric inputs and phosphogypsum slurry inputs from the phosphate industry at jorf lasfar 33 n recently estimated as an important source of dissolved cadmium 240 tcd year 1 are at best of minor importance for the studied waters our study provides new insights into the mechanisms fractionating cadmium from phosphate in the upper 30 m the anomalies observed in terms of cd p ratios in both the particulate and total dissolvable fractions were related to an overall preferential uptake of phosphate we show that the type of phytoplanktonic assemblage diatoms vs dinoflagellates is also a determinant of the fractionation intensity in sub surface waters 30 60 m a clear preferential release of p vs cd was observed indicating that remineralization in oxygen minimum zones is a key process in sequestering cd this article is protected by copyright all rights reserved

an appraisal of endmember energy and mixing properties of rare earth garnets abstract the thermodynamic properties of rare earth aluminum ree 3 al 5 o 12 iron ree 3 fe 5 o 12 and gallium ree 3 ga 5 o 12 garnets are assessed by means of critical evaluation of the existing experimental data and thermodynamic treatment of their vibrational static and volumetric properties the mixing properties of the various ree garnet components are calculated from these endmember thermodynamic data and the interionic static potential model developed earlier for major silicate garnet components these results permit evaluation of the solubility behavior for ree in natural phases the results suggest that the mixing of ree garnet components at trace level i e below about 10 2 ppm with major silicate garnet components is virtually ideal but strong positive deviations associated with generalized polyhedral distortion of the host phase at higher concentration level of the solute prevent bulk ree solubility from exceeding a few hundreds ppm the computed rare earth element fractionations between garnet and supercritical fluid at various p t conditions put in evidence the main control operated by the intrinsic energy properties of ree garnet end members in determining the light ree heavy ree lree hree fractionation observed in natural garnet specimens

advective transport affecting metal and nutrient distributions and interfacial fluxes in permeable sediments abstract our laboratory flume experiments demonstrate that advective porewater flows produce biogeochemical reaction zones in permeable sediments leading to specific and reproducible complex patterns of fe mn and nutrients oxygenated water forced into the sediment when boundary flows were deflected by protruding sediment structures generated distinct zones of nitrification and ferric iron precipitation this inflow was balanced by ammonium rich porewater ascending from deeper sediment layers thereby creating an anoxic channel where dissolved fe2 and mn2 could reach the surface between the zones of ferric iron precipitation and fe2 upwelling a layer with increased manganese oxide and solid phase fe ii concentrations formed indicating redox reaction between these components the establishment of topography on the previously smooth sediment surface reversed the net interfacial flux of solutes while the smooth control core was found to be a sink for metals and nutrients the sediment with mounds acted as a source for these substances our experiments show that in sandy sediment with an oxidised surface layer reduced metal species can be released to the water column by flow topography interactions we conclude that advective transport processes constitute an important process controlling biogeochemical zonations and fluxes in permeable sea beds

iron and macronutrients in california coastal upwelling regimes implications for diatom blooms the supply of iron relative to that of the macronutrients nitrate phosphate and silicic acid plays a critical role in allowing extensive diatom blooms to develop in coastal upwelling regimes the presence or absence of a broad continental shelf influences the supply of iron the iron input to central california upwelling waters varies spatially and can be characterized by two end member regimes one end member which includes monterey bay and extending north to pt reyes is an iron replete regime where upwelling occurs over a relatively broad continental shelf that results in waters with high concentrations of dissolved and particulate iron 10 nm entrained together with high concentrations of nitrate and silicic acid in these iron replete regions extensive blooms of large diatoms deplete macronutrient concentrations which results in correspondingly high chlorophyll a concentrations the other end member located to the south of monterey bay off the big sur coast is an iron deplete regime where upwelling is focused offshore of a narrow continental shelf upwelled waters in the big sur region are characterized by low dissolved and particulate iron concentrations 1 nm together with high concentrations of nitrate and silicic acid extremely low iron concentrations unused nitrate and silicic acid and a low abundance of large diatoms characterize surface waters in these iron deplete regions and thus represent coastal upwelling high nutrient low chlorophyll systems limited by the micronutrient iron

temporal trends in lava dome extrusion at santiaguito 1922 2000 we present a means of extracting lava dome extrusion rates from data provided by the thematic mapper and enhanced thematic mapper plus instruments flown on the landsat satellites extrusion rates derived from the landsat data for santiaguito dome complex guatemala during november 1987 and january 2000 of 0 72 0 08 and 0 48 0 09 m3 s 1 compare favorably with ground based estimates of 0 63 0 28 and 0 48 0 17 m3 s 1 a satellite data derived set of 18 extrusion rate estimates between 1987 and 2000 along with ground based volume estimates prior to 1987 allow us to infer volumes of magma erupted since 1922 these data reveal cyclic extrusion at santiaguito each cycle begins with a 3 6 year long phase of high extrusion rate 0 5 2 1 m3 s 1 followed by a longer 3 11 years phase of low extrusion rate 0 2 m3 s 1 the 8th cycle began in 1996 and was still in its high extrusion rate phase during january 2000 with time however the durations of the low extrusion rate phases have increased peak extrusion and time averaged extrusion rates for each cycle have decreased and the difference between extrusion rates during the high and low extrusion rate phases of each cycle has decreased these trends may be the result of depressurization and exhaustion of the source in this case the current eruption may be expected to end around 2020 alternatively santiaguito may be entering a period of persistent activity maintained by a stable magma supply in this case we may expect extrusion to become less cyclic and to stabilize at 0 2 0 4 m3 s 1 however a 2 wt decrease in sio2 content of erupted products since 1970 appears to be consistent with chamber exhaustion as well as an increase in block lava flow lengths during 1970 2000

distribution and variability of iron input to oregon coastal waters during the upwelling season generally higher in spring mean of 2 1 and 33 9 nmol l 1 respectively than in summer means of 1 4 and 15 4 nmol l 1 in spring and summer high iron concentrations in surface waters were associated with both cold and saline recently upwelled waters and with fresh relatively warm water influenced by the columbia river comparison of total dissolvable iron in 0 45 mm filtered and in unfiltered samples indicated a substantial contribution from particulate iron iron concentrations in summer were generally lower than in spring throughout the water column with the exception of the near bottom where concentrations were generally higher in summer than spring optical backscatter data from moored sensors were used to infer the vertical and cross shelf transport of iron bearing particles during the upwelling season over a steep shelf cross correlation analysis showed downslope movement of particles from the deep inner shelf to the deep midshelf there was also evidence for sinking of biogenic particles at the midshelf and inner shelf but we found no evidence of upslope transport of benthic particles sufficient iron is available in this system to meet the demands of the phytoplankton which are able to make full use of available nitrate citation chase z b hales t j cowles r schwartz and a van green 2005 distribution and variability of iron input to oregon coastal waters during the upwelling season j geophys res 110 c10s12 doi 10 1029 2004jc002590

coastal upwelling in the california current system abstract coastal upwelling in the california current system has been the subject of large scale studies off california and baja california and of small scale studies off oregon recent studies of the winds along the entire coast from 25 n to 50 n indicate that there are significant along shore variations in the strength of coastal upwelling which are reflected in the observed temperature distribution active upwelling appears to be restricted to a narrow coastal band about 10 25 km wide along the entire coast but the region influenced by coastal upwelling may be much wider intensive observations of the upwelling zone during summer off oregon show the presence of a southward coastal jet at the surface a mean vertical shear a poleward undercurrent along the bottom and persistently sloping isopycnals over the continental shelf most of the upwelling there occurs during relatively short periods several days long of upwelling favorable winds during the upwelling season off oregon the offshore ekman transport is carried by the surface ekman layer and the onshore return flow occurs through a quasi geostrophic interior it is not known whether the structure and dynamics observed off oregon are typical of the upwelling zone along the entire coast though some of the same features have been observed off baja california current and future research will eventually show whether the oregon results are also applicable in the region of persistently strong upwelling favorable winds off northern california and in the region of complex bathymetry off central and southern california

the influence of magma ascent path on the texture mineralogy and formation of hornblende reaction rims abstract although hornblende reaction rims are widely used as a tool for evaluating magma ascent during volcanic eruptions very few studies constrain the manner in which they form this study investigates the influence of magma ascent path on the formation of hornblende reaction rims to do this we conducted isothermal 840 c decompression experiments using dacite pumice samples erupted in december 1989 from redoubt volcano alaska experiments were first held within the hornblende stability field determined through phase equilibria experiments for 3 to 5 days before being decompressed to different pressures ranging from 100 to 2 mpa for 1 to 30 days before being quenched decompression was performed in either multiple equal steps constant rate or in one single step results from multi step experiments show that reaction rims form preferentially at pressures from 10 to 40 mpa and that this favorable pressure range narrows and decreases with increased decompression duration hornblendes in multi step experiments are tightly enclosed by fine grained reaction rims composed of plagioclase and orthopyroxene crystals with high aspect ratios ranging from 1 to 12 for single step experiments reaction rims also form preferentially within a narrow pressure range 60 70 mpa where they consist of medium grained plagioclase titanomagnetite and orthopyroxene crystals with aspect ratios ranging from 1 to 6 that broadly surround subrounded hornblendes hornblendes from single step experiments dropped to lower pressures

garnet and scheelite as indicators of multi stage tungsten mineralization in the huangshaping deposit southern hunan province china abstract the huangshaping w mo pb zn deposit in southern hunan province south china contains multiple generations of garnet and scheelite in skarn and sulfide carbonate altered rocks optical characteristics and chondrite normalized rare earth element reen patterns obtained by in situ laser ablation inductively coupled plasma mass spectrometry analysis were used to distinguish different generations of garnet and scheelite these data show a clear correspondence of garnet reen patterns to major element zonation with hrees e g gd lu being depleted overall coarse grained garnets in the huangshaping deposit have extreme hree depletions and significant lree e g la eu enrichment particularly for ce pr and nd this indicates that rees in these garnets are the result of coupled substitutions ca2 viii 1 ree3 viii 1 and fe2 iv 1 al3 iv 1 medium grained garnets have reen patterns showing significant lree enrichment and depleted hrees with high sn contents this suggests that substitution of rees in these garnets occurs as ca2 viii 1 ree3 viii 1 sn4 iv 1 al3 iv 1 the fact that medium grained garnets have high sn contents indicates mineralizing fluids were oxidizing which is consistent with significant positive eu anomalies however hump shaped reen patterns for garnet rims suggest substitution by ca2 viii 2 na viii 1 ree3 viii 1 where nd tb are preferentially incorporated into the garnet lattice over other rees group 1a scheelite has black cores in cathodoluminescence images and reen patterns showing extreme lree enrichment and hree depletion group 1b scheelite has cores with fine oscillatory zoning and enriched lrees with depleted hrees similar to the reen patterns of group 2a scheelite that occur as rims with bright cl surrounding both group 1a and 1b scheelite the substitution mechanism for rees in these three types of scheelite is ca2 viii 3 viii 1 ree3 viii 2 with being a ca site vacancy the influence of ree speciation in the hydrothermal fluid dominates the reen patterns of these types of scheelite however for group 2b bright rims of scheelite rees are incorporated as ca2 viii 2 na viii 1 ree3 viii 1 similar to the garnet rims finally scheelite mo contents and eu values that decrease from group 1a to 2b support a temporal decrease in oxygen fugacity of the mineralizing fluids ratios of y ho and mo contents that decrease from group 1a and 1b to group 2a and 2b scheelites are similar to those in porphyry related skarn w mo and quartz vein au w deposits respectively our studies also suggest that all these scheelites in this deposit formed from magmatic fluids at the huangshaping deposit medium grained garnets associated with group 1a scheelite precipitated from evolved magmatic fluids during prograde metamorphism as indicated by their complementary y ho ratios paragentically younger scheelite particularly group 2b may have formed from dilute magmatic fluids that underwent large scale hydrothermal circulation the characteristics of group 1b and 2a scheelite likely reflect a transitional environment and fluid mixing during tungsten mineralization in the polymetallic huangshaping deposit

the magmatic feeding system of el reventador volcano sub andean zone ecuador constrained by texture mineralogy and thermobarometry of the 2002 erupted products abstract after a 26 years long quiescence el reventador an active volcano of the rear arc zone of ecuador entered a new eruptive cycle which lasted from 3 november to mid december 2002 the initial sub plinian activity vei 4 with andesite pyroclastic falls and flows shifted on 6 and 21 november to an effusive stage characterized by the emission of two lava flows andesite to low silica andesite lava 1 and basaltic andesite lava 2 containing abundant gabbro cumulates the erupted products are medium to high k calc alkaline and were investigated with respect to major element oxides mineral chemistry texture and thermobarometry inferred pre eruptive magmatic processes are dominated by the intrusion of a high t mafic magma possibly up to 1165 15 c into an andesite reservoir acting as magma mixing and trigger for the eruption before this refilling the andesite magma chamber was characterized by water content of 5 3 1 0 high oxygen fugacity nno 2 and temperatures in the upper and lower part of the reservoir of 850 and 952 65 c respectively accurate amphibole based barometry constrains the magma chamber depth between 8 2 and 11 3 km 2 2 km the 6 october 2002 seismic swarm hypocenters from 10 to 11 km preceding el reventador eruption supports the intrusion of magmas at these depths the widespread occurrence of disequilibrium features in most of the andesites e g complex mineral zoning and phase overgrowths indicates that convective self mixing have been operating together with fractional crystallization inferred from the cognate gabbro cumulates before the injection of the basic magma which then gave rise to basaltic andesite and low silica andesite hybrid layers magma mixing in the shallow chamber is inferred from the anomalous sio 2 al 2 o 3 whole rock pattern and strong olivine disequilibria both lavas show three types of amphibole breakdown rims mainly due to heating mixing processes and or relatively slow syn eruptive ascent rate decompression of the magmas the lack of any disequilibrium textures in the pumices of the 3 november fall deposit suggest that pre eruptive mixing did not occur in the roof zone of the chamber a model of the subvolcanic feeding system of el reventador consistent with the intrusion of a low al 2 o 3 crystal rich basic magma into an already self mixed andesite shallow reservoir is here proposed it is also inferred that before entering the shallow chamber the basaltic magma underwent a polybaric crystallization at deeper crustal levels

textural studies of vesicles in volcanic rocks an integrated methodology abstract vesicles in volcanic rocks are frozen records of degassing processes in magmas for this reason their sizes spatial arrangements numbers and shapes can be linked to physical processes that drive magma ascent and eruption although numerous techniques have been derived to describe vesicle textures there is no standard approach for collecting analyzing and interpreting vesicular samples here we describe a methodology for techniques that encompass the entire data acquisition process from sample collection to quantitative analysis of vesicle size and number carefully chosen samples from the lower mean and higher density vesicularity endmembers are characterized using image nesting strategies we show that the texture of even microvesicular samples can be fully described using less than 20 images acquired at several magnifications to cover efficiently the range of existing vesicle sizes a new program foams was designed to perform the quantification stage from vesicle measurement to distribution plots altogether this approach allows substantial reduction of image acquisition and processing time while preserving enough user control to ensure the validity of obtained results we present three cameo investigations on basaltic lava flows scoria deposits and pumice layers to show that this methodology can be used to quantify a wide range of vesicle textures which preserve information on a wide range of eruptive conditions

petrology and fe ti oxide reequilibration of the 1991 mount unzen mixed magma a dacitic magma 64 5 wt sio2 a mixture of phenocryst rich rhyodacite and an aphyric mafic magma was erupted during the recent 1991 1995 mount unzen eruptive cycle the experimental and analytical results of this study reveal additional details about conditions in the premixing and postmixing magmas and the nature of the mixing process the preeruption rhyodacitic magma was at a temperature of 790 20 c according to fe ti oxide phenocryst cores and at a depth of 6 to 7 km 160 mpa according to al in hornblende geobarometry the mafic magma that mixed with the rhyodacite is found as andesitic 54 to 62 wt sio2 enclaves in the erupted magma and was essentially aphyric when intruded phase equilibria indicate that an aphyric andesite at 160 mpa is 1030 c h2o saturated and possibly as high as 1130 c 2 wt h2o the composition of the rhyodacite which was mixed with the andesite is estimated to lie between 67 and 69 wt sio2 using these compositions and temperatures the temperature of the unzen magma after mixing is estimated to be at least 850 to 870 c the groundmass fe ti oxide microphenocrysts and those in pargasite bearing reaction zones around biotite phenocrysts both give 890 20 c temperatures the oxide oxide contacts give temperatures of 910 20 c the 900 30 c postmixing temperatures are consistent with phase equilibria experiments which show that the magma was not above 930 c at 160 mpa our fe ti oxide reequilibration experiments suggest that the mixing of the two magmas began within a few weeks of the eruption which is a shorter time than is calculated using available diffusion data there is also evidence that some mixing took place much closer to the time of extrusion based on the presence of unrimmed biotite phenocrysts in the magma

the magmatic plumbing system beneath santiaguito volcano guatemala abstract the silicic dome complex of santiaguito guatemala has exhibited continuous extrusive activity for 90 years despite its longevity remarkably little is known about the magmatic plumbing system beneath santiaguito here we use petrological analyses of lava samples to define this plumbing system from storage in the lower to mid crust through to extrusion onto the surface magmatic storage conditions are constrained using amphibole and plagioclase phenocrysts ascent processes are examined using the breakdown rims of amphibole phenocrysts and the texture and composition of groundmass while shallow processes are revealed by the alteration of titanomagnetites and matrix glass santiaguito magmas contain amphiboles that formed from 24 km to 12 km beneath the surface with temperatures of 940 to 980 c and f o2 of nno 0 4 to nno 1 2 amphibole breakdown rims suggest that during the final phases of ascent magma may rise from 12 km the limit of amphibole stability relatively rapidly 27 to 84 m h 1 we infer from the texture of the groundmass that melt rigidifies prior to extrusion a finding that may have important consequences for conduit dynamics

irreversible nitrate fluxes due to turbulent mixing in a coastal upwelling system 1 detailed and repeated measurements of nitrate across the oregon shelf made coincident with turbulence measurements reveal the importance of cross isopycnal mixing via turbulence in providing nitrate to the upper water column spatial distributions of vertical gradients and turbulent fluxes in the oregon coastal ocean reveal variability that could not have been resolved with traditional sampling approaches nitrate rich near bottom waters are drawn up the shelf during upwelling and back down the shelf during downwelling continuous turbulent mixing in the bottom boundary layer increases nitrate on intermediate isopycnals by several m toward the shelf this increased nitrate is consistent with measured turbulent flux of nitrate of o 0 1 mol m 2 s 1 for a period of 3 days roughly the timescale for changes in the wind and hence to the upwelling circulation our flux estimates are consistent with high biomass nutrient replete incubation based primary productivity estimates in this area and suggest that turbulent vertical nitrate transport plays a significant role in supporting the high productivity seen here offshore of 30 m depth we estimate the irreversible transport of nitrate from nitrate rich near bottom waters to be about 25 of the rate at which it is provided by upwelling the total irreversible transport is greater by some unknown amount when we consider the transport inshore of 30 m depth we suggest that the onshore transport of offshore water whether deep water during upwelling or surface water during relaxation forces the juxtaposition of strong gradients and mixing regimes such that turbulent vertical fluxes are consistently elevated in the shoreward reaches of the coastal ocean

oceanic iron supply mechanisms which support the spring diatom bloom in the oyashio region western subarctic pacific 1 multiyear 2003 2008 time series observations along the a line provided information on the temporal variability of the dissolved iron diss fe concentration in the oyashio region of the western subarctic pacific and the data indicated that there was an annual cycle in the concentration of surface diss fe occurring every year diss fe was supplied into the surface water in this region every winter and supports the spring phytoplankton bloom after development of the thermocline the diss fe concentration was drawn down during the phytoplankton bloom period and was depleted in summer in some water masses then diss fe increased from autumn to winter with the increasing depth of the surface mixed layer the high diss fe concentrations in the surface layer in winter were controlled by mesoscale oceanic intrinsic processes such as vertical winter mixing and horizontal fe rich intermediate water transport difference in magnitude of the winter mixing processes among different water masses caused the heterogeneous distribution of diss fe concentration in the surface layer moreover the vertical section profiles along a cross oyashio transect showed the occurrence of fe rich intermediate water and upward transport of materials from the intermediate water to the surface layer via tidal and winter mixing processes are important mechanisms to explain the high winter surface diss fe concentrations additionally the substantially higher diss fe no3 ratio in the winter surface layer in this studied area other than the high nutrient low chlorophyll region indicates that the winter surface water in the oyashio and the oyashio kuroshio transition zone has a high potential to stimulate phytoplankton growth

the coastal ocean off oregon and northern california during the 1997 8 el nino abstract the evolution and decay of el nino 1997 8 was observed in coastal waters off oregon in a sequence of cruises along 44 6 n from the coast to more than 150 km offshore hydrographic observations were made during eleven cruises between july 1997 and april 1999 at stations on the newport hydrographic line which had been occupied regularly from 1961 to 1971 the data from the earlier decade provide a basis for defining normal conditions and allow comparisons with the recent el nino in terms of t s spiciness and geostrophic velocity independent of el nino the ocean in july 1997 was already anomalously warm offshore of 50 km and above 100 m by september 1997 there were unambiguous indications of el nino isotherms and isohalines sloped down toward the coast indicating poleward flow over shelf and slope and anomalously spicy water was present at the shelf break in november 1997 and february 1998 shelf break waters were even warmer and there was strong poleward flow inshore of 100 km extending to depths greater than 200 m the april 1998 section closely resembled that of april 1983 another el nino year but by june 1998 the anomalies were mostly gone november 1998 was near normal and the sections from subsequent cruises resemble the mean sections from 1961 1971 four cruises between november 1997 and november 1998 included sampling at several latitudes between 38 and 45 n as expected these sections show significant alongshore gradients but also a surprising degree of homogeneity in the anomalous features associated with el nino in the temperature salinity spiciness and geostrophic velocity fields the anomalous signature of el nino was stronger at its winter peak in 1998 than in 1983 but the signature in the temperature and spiciness fields and in coastal sea level did not persist as long as in 1983 by april 1999 the coastal ocean from 38 n to 45 n was significantly colder than it had been in april 1984

the central california current transition zone a broad region exhibiting evidence for iron limitation abstract the transition zone tz of the central california current upwelling system cccs is the boundary between the cold saline coastally upwelled water and the warm less saline oligotrophic waters of the offshore california current cc the tz is a broad region that regularly exhibits chlorophyll concentrations of 1 2 g l 1 throughout the spring summer and fall seasons surface transect and vertical profile data from three cruises may 2010 june 1999 and august 2011 between 34 and 42 n show residual nitrate concentrations 5 15 m and low fe concentrations most no 3 in coastally upwelled water are transported via offshore moving filaments into the tz however since some coastal upwelling regions with narrow continental shelves do not have much fe to begin with and since fe is drawn down more rapidly relative to no 3 due to biological assimilation and scavenging these filaments transport low concentrations of fe relative to no 3 into the tz weak wind curl induced upwelling and vertical mixing in the tz also deliver fe and no 3 to the surface but at lower concentrations and lower fe no 3 than from strong coastal upwelling mesoscale cyclonic eddies in the tz are important to consider with respect to offshore surface nutrient delivery because there is a marked shoaling of isopycnals and the nutricline within these eddies allowing higher nutrient concentrations to be closer to the surface since wind curl induced upwelling and or vertical mixing occurs seaward of the continental shelf there is not enough fe delivered to the surface to accompany the no 3 by using fe no 3 ratios and calculated specific growth rates for diatoms we demonstrate that the tz of the cccs shows evidence for fe limitation of diatom blooms the tz also appears to progress further into fe limitation as the upwelling season progresses from spring into late summer this study provides some of the first field data to suggest that fe is a critical bottom up control on the ecosystem in the tz of the cccs

magma chamber properties from integrated seismic tomography and thermal modeling at montserrat it is widely believed that andesitic magmas erupted at arc volcanoes are stored in shallow reservoirs prior to eruption but high resolution images of focused regions of magma in the shallow crust are rare we integrate seismic tomography with numerical models of magma chamber growth to constrain the magma chamber beneath soufriere hills volcano montserrat our approach reveals the characteristics and dynamics of the magmatic system with a level of detail that no single method has yet achieved the integrated analysis suggests that a magma chamber of 13 km3 with over 30 melt fraction formed between 5 5 and at least 7 5 km depth a significantly higher melt fraction than inferred from the seismic data alone the magma chamber may have formed by incremental sill intrusion over a few thousand years and is likely to be a transient geologically short lived feature these volume and geometry estimates are critical parameters to model eruption dynamics which in turn are key to hazard assessment and eruption forecasting

coastal ocean response to summer upwelling favorable winds in a region of alongshore bottom topography variations off oregon 1 repeated mesoscale surveys of waters over the shelf and slope off oregon were conducted during spring and summer of 2001 to study the spatial structure of the velocity and hydrographic fields the ocean response to wind forcing is compared between a region of relatively simple topography with alongshore uniformity and a region of complex topography including a shallow submarine bank heceta bank in the simple topography region the upper water column is influenced by upwelling and fresh water from the columbia river during spring with the low salinity water located farther offshore during summer variability in the fields is mostly confined within 30 km from the coast over heceta bank the region of higher variability is broader spanning most of the shelf the coastal upwelling jet is located inshore of the pinnacle of the bank during spring moving offshore during summer the region inshore of the bank is characterized by low velocities and flow recirculation near surface fields show that the circulation evolves considerably between seasons in both regions the area influenced by upwelled water is much broader during summer dense waters found over midshelf off newport are upwelled to the north and advected south dense waters inshore of heceta bank are substantially influenced by water from the north during spring but their source is mostly from the south during summer south of the bank the separation of the jet significantly increases the cross isobath transport constituting an efficient mechanism for transport of material from the shelf into deeper waters

british columbian continental shelf as a source of dissolved iron to the subarctic northeast pacific ocean 1 the distribution of dissolved 0 4 m iron fe across the continental shelf and slope of queen charlotte sound on the west coast of canada was examined to estimate the potential of these waters as a source of fe to the fe limited waters of the subarctic northeast pacific iron profiles obtained in shelf slope and offshore waters demonstrate decreasing concentrations of fe with distance from the continent within 50 m of the shelf sediments dissolved fe concentrations were 5 3 0 3 nm this signal was detected although attenuated by 80 along the isopycnal surface at offshore stations 40 50 km seaward of the shelf break strongly suggesting cross shelf transport of an fe rich plume originating in low dissolved oxygen 3 ml l 1 130 mol kg 1 waters in subsurface water over the continental shelf several physical mechanisms that may cause these fe enriched waters to advect offshore in this region i e tidal currents and ekman transport in the bottom boundary layer coastal downwelling relaxation from upwelling and the formation of anticyclonic westward propagating coastal eddies are discussed we suggest that strong tidal currents over broad continental shelves may play a key role in fe supply to ocean basins

magma mixing in a main stage of formation of montagne pelee the saint vincent type scoria flow sequence martinique f w i contrasting with the first stage of activity at montagne pelee which built an andesitic volcano chiefly formed of brecciated lava flows and pyroclastic breccias the second main stage 40 000 to 20 000 years b p is characterized by the prevalence of scoria flows of more mafic composition many cross sections of the deposits of stage 2 show an upward magmatic evolution from early acid andesites plinian air fall and pumice flow deposits to late basaltic andesites scoria flow deposits heterogeneous banded rocks complex mineralogical associations and mineralogical disequilibrium features in the whole series are explained by mechanical mixing of contrasting magmas reversed zoning characterized plagioclase phenocrysts of both the acid and basic terms and also pyroxene phenocrysts of the mafic terms grossly uniform composition of residual glass in most macroscopically homogeneous rocks implies that chemical exchanges between liquids and local hybridization occurred plutonic rocks with cumulate textures are found in upper units of the sequence their phenocrysts anorthite salitic clinopyroxene pargasitic hornblende and ti magnetite are in equilibrium with a subalkaline basaltic interstitial liquid the same phases are commonly present as xenocrysts in the basaltic andesites it is inferred that basaltic andesites of stage 2 were firstly derived from a subalkaline basalt by crystal fractionation mixing of the basaltic andesites 52 sio2 with acid andesites 62 sio2 occurred in late stage of evolution of the series producing heterogeneous rocks of intermediate composition successive eruption of acid up to mafic magmas dominant amount of mafic rocks in the sequence and short duration of the magma mixing event shown by narrow rims of the reversely zoned phenocrysts suggest that mixing was produced by intrusion of mafic magma into a differentiated magma body we propose that hydrostatic overpressure induced by a high rate of intrusion triggered the eruption thus magma mixing would be due to a large volume of mafic magma passing through the resident magma rapid admixture of the two batches increased gas exsolution resulting in a highly explosive eruption magma mixing can thus explain the explosive dynamics of the basaltic andesites eruptions which surprisingly contrast with the relatively effusive style of the preceding andesitic stage