gas evolution in eruptive conduits combining insights from high temperature and pressure decompression experiments with steady state flow modeling abstract in this paper we examine the consequences of bubble nucleation mechanism on eruptive degassing of rhyolite magma we use the results of published high temperature and pressure decompression experiments as input to a modified version of conflow the numerical model of mastin and ghiorso 2000 u s g s open file rep 00 209 53 pp and mastin 2002 geochem geophys geosyst 3 10 1029 2001gc000192 for steady two phase flow in vertical conduits synthesis of the available experimental data shows that heterogeneous nucleation is triggered at p 120 150 mpa and leads to disequilibrium degassing at extreme h2o supersaturation in this latter case nucleation is an ongoing process controlled by changing supersaturation conditions exponential bubble size distributions are often produced with number densities of 106 109 bubbles cm3 our numerical analysis adopts an end member approach that specifically compares equilibrium degassing with delayed disequilibrium degassing characteristic of homogeneously nucleating systems the disequilibrium simulations show that delaying nucleation until p 150 mpa restricts degassing to within 1500 m of the surface fragmentation occurs at similar porosity in both the disequilibrium and equilibrium modes 80 vol but at the distinct depths of 500 m and 2300 m respectively the vesiculation delay leads to higher pressures at equivalent depths in the conduit and the mass flux and exit pressure are each higher by a factor of 2 0 residual water contents in the melt reaching the vent are between 0 5 and 1 0 wt roughly twice that of the equilibrium model

shallow conduit processes during the ad 1158 explosive eruption of hekla volcano iceland hekla is one of the most frequently active felsic volcanic systems in the world with several known pre historic large plinian eruptions and 18 historical subplinian to small plinian eruptions a common view is that plinian eruptions of hekla are relatively short lived and purely explosive events in detail these events exhibit subtle differences in terms of deposit characteristics reflecting significant differences in eruption behaviour of the 18 historical eruptions two had bulk magma compositions with 66 wt sio2 a plinian eruption in ad 1104 and a smaller less well characterised but atypical subplinian eruption in ad 1158 the ad 1158 eruption was a relatively sustained dry magmatic eruption with a more powerful opening phase followed by a lower intensity waning phase accompanied by minor destabilisation and collapse of the conduit walls we examine here the dynamics of the ad 1158 eruption focussing on the role of shallow conduit processes in modulating eruption dynamics vesicularity data constrain the relative influence of bubble nucleation growth and coalescence the juvenile pyroclasts are composed of two types of microvesicular pumice white and grey with contrasting vesicle number density vesicle size distribution and phenocryst and microlite contents textural analysis shows that these pumices reflect heterogeneity developed pre to syn eruptively in the conduit and that entrainment of longer resident magma by faster ascending magma permitted magma of contrasting maturity to be fragmented simultaneously in this regard the mixed melt of the ad 1158 eruption contrasts with the compositionally homogeneous melt phase of the more powerful ad 1104 plinian event which was typified by more uniform conduit and eruption dynamics accompanying higher average ascent rates

surface tension and bubble nucleation in phonolite magmas abstract explosive plinian eruptions tap a wide range of magma compositions including highly alkaline phonolite magma such eruptions are driven by volatiles exsolving from those magmas and so determining how gas bubbles form is important to understanding those eruptions nucleation of bubbles in silicate melts is dictated strongly by the surface tension of the melt and so this study focuses on determining for phonolite melts cylinders cored from a sodium rich phonolite were hydrated with 5 37 0 09 wt dissolved water at 150 mpa and 1150 c and then decompressed at either 1150 c or 875 c bubbles nucleated at 1150 c only when pressure dropped below 95 mpa in number densities of 10 4 5 cm 3 at 875 c bubbles nucleated only when pressure dropped below 53 mpa in number densities of 10 4 7 cm 3 depending on whether the pressure within critical bubble nuclei equals the saturation pressure or a variable lower pressure the observed number densities and nucleation rates imply that surface tension for na rich phonolite is 0 061 or 0 068 n m 1 at 875 c and 0 052 or 0 066 n m 1 at 1150 c importantly temperature has little or slightly negative impact on in contrast to the thermal impact on of rhyolite melts regardless of pressure assumption the inferred surface tensions indicate that na rich phonolite can become highly super saturated with water before bubbles nucleate which could cause them to explosively degas and erupt similar to highly viscous rhyolites

sedimentological and palaeoecological integrated analysis of a miocene channelized carbonate margin matese mountains southern apennines italy abstract lower middle miocene temperate marine carbonates occur in the matese mountains southern apennines italy these carbonates formed in an open shelf depositional system with an uneven margin 10 km long and up to 6 km wide shelf margin morphology shows multiple submarine channelized carbonate deposits which are dominated by coralline red algae and subordinate bryozoans two main channel networks pietraroia and regia piana channels with their sedimentary bodies were analysed the studied submarine channels grew by sediment accumulation as prograding bodies on a tectonic modelled substrate shallow water rhodalgal skeletal debris from moderately re mobilized up to significantly re worked built up the complex channel system fills in which sedimentary lenses overlapped and partially amalgamated one another when they were still unlithified the early channelized succession is characterized by parautochthonous bryozoan floatstone and rhodolith bryozoan floatstone representing soft muddy substrates in a low water turbulence and high turbidity setting the rhodoliths dominated by melobesioid coralline algae are sub discoidal and sub spheroidal in shape with a characteristic loosely packed inner arrangement these sediments whose latter portion underwent submarine diagenetic processes incipient to evoluted hard grounds were eroded and successively covered by shallower water gravitative deposits constituted by rhodolith floatstone rudstone their rhodoliths constituted by melobesioids mastophoroids and subordinate lithophylloids and sporolithaceans are mainly spheroidal sub spheroidal in shape with subordinate sub discoidal specimens with massive and laminar inner arrangements the lack in early lithification can be drawn back to the physiography of the channelized shelf margin to the active tectonic as well as to the temperate type carbonate dominant biogenic components the depositional surface profile and local hydrodynamic conditions were the major factors controlling sedimentary facies which differ in their relative proportions of dominant components their internal structures and sedimentary body geometries

the origin of hematite in high grade iron ores based on infrared microscopy and fluid inclusion studies the example of the conceicao mine quadrilatero ferrifero brazil petrographic and textural analysis combined with fluid inclusion studies by infrared microscopy of high grade 65 fe hematite ore samples from the conceicao deposit in the northeastern part of the quadrilatero ferrifero brazil indicate a complex process of oxidation and mineralization during two orogenic events each developed under different conditions and involving distinct fluids the earliest mineralization formed massive magnetite rich orebodies under relatively reducing conditions in the early stages of the transamazonian orogeny magnetite was oxidized martitized with the development of porous hematite crystals hematite i possibly during this stage new hematite crystals were also formed from low temperature low to medium salinity fluids as indicated by two phase fluid inclusions the origin of these fluids is still uncertain but tentatively interpreted as being modified surface water the fluids were transported along normal faults and fractures during post tectonic collapse following the transamazonian orogeny 2 1 2 0 ga and creation of the dome and keel structural pattern of the quadrilatero ferrifero these solutions were also likely responsible for the initial oxidation of the iron formations and the development of hematite i subsequent uplifted hot basement rocks or post tectonic plutons were probable heat sources for the regional metamorphism and development of a granoblastic fabric of hematite ii grains in the iron formations and high grade orebodies however the ore was only partially recrystallized as several relics of the early magnetite martite and hematite are still preserved in the granular hematite ii crystals during the brasiliano pan african orogeny 0 8 0 6 ga high salinity fluids with temperatures varying from 120 to a maximum of approximately 350 c penetrated the iron formations along shear zones crystallizing initially tabular and thereafter platy hematite crystals hematite iii and specularite forming schistose orebodies quartz veins that cut across the ore and envelop specularite plates and ore fragments formed from late stage high temperature and low salinity fluids containing co2 these later fluids did not alter the ore each of these stages of mineralization produced orebodies with distinct features recurrent hydrothermal mineralization is thought to have been responsible for the development of giant high grade iron ore deposits in structurally favorable sites fold hinges with enhanced permeability and deep faults able to conduct the fluids to the surface repeatedly over time should be important targets for exploration of new resources

an experimental study of the kinetics of decompression induced crystallization in silicic melt 1 experiments were conducted to study the temporal evolution of feldspar crystallization kinetics during isothermal decompression pinatubo dacite was held at 780 c 220 mpa fo2 nno 2 h2o saturated conditions for an equilibration period decompressed to final pressures pf ranging from 175 to 5 mpa and then held for 0 3 931 hours according to the plagioclase liquidus curve in ph2o t space for the relevant melt composition these decompressions impose effective undercoolings teff of 34 266 c growth of preexisting phenocrysts and newly formed sparse microlites dominate crystallization at 75 pf 150 mpa teff 34 93 c and equilibrium crystal modes are achieved in 168 hours microlite nucleation is the dominant transformation process for 10 pf 50 mpa teff 125 241 c and chemical equilibrium is not attained by 168 hours under these conditions slow steady decompressions typically produced normally zoned euhedral and planar faceted feldspar crystals although anhedral morphologies were produced at very low pf contrary to expectation slowly decompressed samples were usually further from chemical equilibrium than rapidly decompressed samples after similar durations below the initial pressure although counterintuitive these trends are consistent with new constraints on the relative rates of feldspar nucleation and growth controlled by teff and melt viscosity experienced during each decompression path analysis of liquid to solid transformation kinetics using ttt style diagrams shows that crystallization occurs most rapidly at 100 mpa by a crystal growth mechanism the next most efficient crystallization conditions are at 25 mpa in a crystal nucleation dominated regime

growth and high resolution paleoenvironmental signals of rhodoliths coralline red algae a new biogenic archive we investigated rhodoliths coralline red algae from a subtropical locality in the gulf of california lithothamnium crassiusculum and a subarctic locality in newfoundland lithothamnium glaciale for their potential as paleoenvironmental archives using microanalytical geochemical techniques to measure variations in 18o mg and ca rhodoliths are potentially well suited as recorders of shallow water paleoenvironmental signals because they 1 have worldwide distribution from the tropics to polar regions 2 are long lived from decades to centuries and 3 display well developed growth bands our results indicate that rhodolith growth bands preserve ultrahigh resolution records of paleoceanographic paleoclimatic change and likely constitute an important new archive for reconstructing the paleoenvironmental history of littoral neritic areas in which these algae are found the 18o content of individually sampled rhodolith growth bands ranges from 2 4 to 4 6 in l crassiusculum and from 3 2 to 0 3 in l glaciale in both cases the range of 18o values suggests a slightly lower amplitude of variation in sea surface temperature than that actually measured in the ocean at the two study sites both l crassiusculum and l glaciale show a negative offset from isotopic equilibrium electron microprobe analysis of magnesium and calcium in growth bands reveals cyclic variations with values ranging between 7 7 18 5 mol mgco3 in l glaciale and 13 2 22 5 mol mgco3 in l crassiusculum in addition electron microprobe element maps highlight individual growth bands provide a powerful approach to study rhodolith formation and indicate that the specimens we analyzed have vertical growth rates of 250 450 m yr

reprint of comparison of climate signals obtained from encrusting and free living rhodolith coralline algae abstract coralline algae have been used for sclerochronological studies throughout the last decade these studies have focused on two different growth morphologies of the photosynthetic coralline algae massive crusts forming small buildups on hard substrate and free living branching algal nodules known as rhodoliths the latter are generally found on soft substrate where they are frequently overturned by water movement and bottom feeding organisms leaving one side of the rhodolith partially buried in the sediment at any given time here we test whether either of these growth morphologies is more suitable for proxy reconstructions by comparing mg ca ratios a temperature proxy in multiple replicates of rhodoliths of lithothamnion glaciale and in rhodoliths as well as encrusting specimens of clathromorphum compactum with both species being widespread throughout the temperate and arctic regions we have chosen two north atlantic localities at nuuk fjord greenland subarctic and off the southeastern coast of newfoundland canada temperate for this study two to three mg ca ratio transects spanning 18 years of growth were analysed on multiple specimens with encrusting morphologies and along different sides of rhodoliths using laser ablation inductively coupled mass spectrometry and compared to remotely sensed sea surface temperature sst data the length of the common time span used for comparison was limited by growth interruptions in rhodoliths furthermore our comparison is based on the assumption that rhodolith growth increments are annual an assumption that has recently been challenged by mesocosm studies monthly mg ca values from multiple transects within each individual were compared and in samples from nuuk fjord significant correlations were found in 4 of 4 encrusting c compactum 4 of 4 c compactum rhodoliths and 2 of 3 l glaciale rhodoliths in newfoundland significant correlations were found in 6 of 6 encrusting c compactum comparisons average r 0 61 p

effects of tidal stresses on volcanic activity at mount etna italy 1 here we model quantitatively the stress and strain induced by tidal forces as possible triggers of mount etna eruptions during 1989 2000 and 2001 by means of 2d numerical analysis by finite difference method applied to the volcano edifice spectral and vectorial analysis of tidal acceleration indicates that the quasi diurnal semi diurnal and ter diurnal constituents may have induced decompressions up to some kpa in the shallow i e 1 500 m gas saturated magma reservoir which controlled magma vesiculation and the timing of lava fountain activity from the south east crater sec we consider the geological heterogeneities in the volcanic edifice i e rock geometries and properties feeder conduit and vent systems volcanic landforms the magma properties i e bulk modulus volatile content and the ongoing volcano tectonic stresses i e volcano flank deformations which strongly influence the response of eruptive activity to tidal forces indeed the tidal factor may act on flank deformation concomitant to shallow magma inflation the implications of our model may help understand the eruptive behaviour and the disequilibrium state of the volcano and may be useful for hazard assessment at mount etna

explosive expansion of a slowly decompressed magma analogue evidence for delayed bubble nucleation 1 while ascending in the plumbing system of volcanoes magma undergoes decompression at rates spanning several orders of magnitude and set by a number of factors internal and external to the volcano slow decompression generally results in an effusive or mildly explosive expansion of the magma but counterexamples of sudden switches from effusive to explosive eruptive behavior have been documented at various volcanoes worldwide the mechanisms involved in this behavior are currently debated in particular for basaltic magmas here we explore the interplay between decompression rate and vesiculation vigor by decompressing a magma analogue obtained by dissolving pine resin into acetone in varying proportions analogue experiments allow direct observations of the processes of bubble nucleation and growth flow dynamics and fragmentation that is not currently possible with magmatic systems our mixtures contain solid particles and upon decompression nucleation of acetone bubbles is observed we find that mixtures with a high acetone content containing smaller and fewer solid particles experience strong supersaturation and fragment under very slow decompressions despite having low viscosity while mixtures with lower acetone content with more and larger solid particles degas efficiently without fragmentation we interpret our results in terms of delayed bubble nucleation due to a lack of efficient nucleation sites we discuss how a similar mechanism might induce violent explosive expansion in volatile rich and poorly crystalline low silica magmas by analogy with the behavior of rhyolitic magmas

the role of h 2 o in rapid emplacement and crystallization of granite pegmatites resolving the paradox of large crystals in highly undercooled melts granite pegmatite sheets in the continental crust are characterized by very large crystals there has been a shift in viewing pegmatites as products of very slow cooling of granite melts to viewing them as products of crystal growth in undercooled liquids with this shift there has been a renewed debate about the role of h2o in the petrogenesis of pegmatites based on data on nucleation of minerals and new viscosity models for hydrous granite melts it is argued that h2o is the essential component in the petrogenesis of granite pegmatites h2o is key to reducing the viscosity of granite melts which enhances their transport within the crust it also dramatically reduces the glass transition temperature which permits crystallization of melts at hundreds of degrees below the thermodynamic solidus which has been demonstrated by fluid inclusion studies and other geothermometers published experimental data show that because h2o drastically reduces the nucleation rates of silicate minerals the minerals may not be able to nucleate until melt is substantially undercooled in a rapidly cooling intrusion nucleation starts at its highly undercooled margins followed by inward crystal growth towards its slower cooling hotter core delay in nucleation may be caused by competition for crystallization by several minerals in the near eutectic melts and by the very different structures of minerals and the highly hydrated melts once a mineral nucleates however it may grow rapidly to a size that is determined by the distance between the site of nucleation and the point in the magma at which the temperature is approximately that of the mineral s liquidus assuming components necessary for mineral growth are available along the growth path granite pegmatites are apparently able to retain h2o during most of their crystallization histories within the confinement of their wall rocks pegmatitic texture is a consequence of delayed nucleation and rapid growth at large undercooling both of which are facilitated by high h2o li b f and p contents in granite pegmatite melts without retention of h2o the conditions for pegmatitic textural growth may be difficult to achieve loss of h2o due to decompression and venting leads to microcrystalline texture and potentially glass during rapid cooling as seen in rhyolites in contrast slow cooling within a large magma chamber promotes continuous exsolution of h2o from crystallizing magma growth of equant crystals and final solidification at the thermodynamic solidus these are the characteristics of normal granites that distinguish them from pegmatites

rheology of bubble bearing magmas the rheology of bubble bearing suspensions is investigated through a series of three dimensional boundary integral calculations in which the effects of bubble deformation volume fraction and shear rate are considered the behaviour of bubbles in viscous flows is characterized by the capillary number ca the ratio of viscous shear stresses that promote deformation to surface tension stresses that resist bubble deformation estimates of ca in natural lava flows are highly variable reflecting variations in shear rate and melt viscosity in the low capillary number limit e g in carbonatite flows bubbles remain spherical and may contribute greater shear stress to the suspension than in high capillary number flows in which bubble deformation is significant at higher ca deformed bubbles become aligned in the direction of flow and as a result contribute less shear stress to the suspension calculations indicate that the effective shear viscosity of bubbly suspensions at least for ca 0 5 is a weakly increasing function of volume fraction and that suspensions of bubbles are shear thinning field observations and qualitative arguments however suggest that for sufficiently large ca ca greater than about 1 the effective shear viscosity may be less than that of the suspending liquid bubbles reach their quasi steady deformed shapes after strains of order one for shorter times the continuous deformation of the bubbles results in continual changes of rheological properties in particular for small strains the effective shear viscosity of the suspension may be less than that of the liquid phase even for small ca results of this study may help explain previous experimental theoretical and field based observations regarding the effects of bubbles on flow rheology

coralline red algae as high resolution climate recorders most high resolution proxy based paleoclimate research has concentrated on tropical oceans while mid and high latitude marine regions have received less attention despite their importance in the global climate system at present sclerochronological analyses of bivalve mollusks supply the bulk of annual to subannual resolution extratropical marine climate data even though interpretation is complicated by a slowdown of growth with increasing shell age hence in order to address the need for additional high resolution proxy climate data from extratropical regions we conducted the first year long in situ field calibration of the coralline red alga clathromorphum compactum in the gulf of maine united states coralline red algae are widely distributed in coastal regions worldwide and individual calcified plants can live continuously for several centuries in temperate and subarctic oceans stable oxygen isotopes extracted at subannual resolution from growth increments of monitored specimens of c compactum relate well to in situ measured sea surface temperatures during the may to december calcification period highlighting the suitability of coralline red algae as an extratropical climate archive furthermore there is a strong correlation between a 30 yr 18 o record of c compactum and an instrumental sea surface temperature record r 0 58 p 0 0008 and a proxy reconstruction derived from the bivalve arctica islandica collected in the central gulf of maine r 0 54 p 0 002

evolution of melt vapor surface tension in silicic volcanic systems experiments with hydrous melts 1 we evaluate the melt vapor surface tension of natural water saturated dacite melt at 200 mpa 950 1055 c and 4 8 5 7 wt h2o we experimentally determine the critical supersaturation pressure for bubble nucleation as a function of dissolved water and then solve for at those conditions using classical nucleation theory the solutions obtained give dacite melt vapor surface tensions that vary inversely with dissolved water from 0 042 0 003 j m 2 at 5 7 wt h2o to 0 060 0 007 j m 2 at 5 2 wt h2o to 0 073 0 003 j m 2 at 4 8 wt h2o combining our dacite results with data from published hydrous haplogranite and high silica rhyolite experiments reveals that melt vapor surface tension also varies inversely with the concentration of mafic melt components e g cao feototal mgo we develop a thermodynamic context for these observations in which melt vapor surface tension is represented by a balance of work terms controlled by melt structure overall our results suggest that cooling crystallization and vapor exsolution cause systematic changes in that should be considered in dynamic modeling of magmatic processes

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

new evidence for degassing processes during explosive eruptions measurements of pore size distribution in five samples of pumice formed during explosive eruptions of plinian type show three distinct sizes of vesicle the characteristics of the three pore size populations are similar in the samples although they were collected from plinian deposits of five different volcanoes we interpret the pore size populations as representing the degassing of silicic magma on three very different time scales the coarse population 60 m represents slow vesiculation within the magma chamber over periods of weeks months or years at small levels of gas supersaturation the medium sized population 50 5 m represents rapid vesiculation of magma on ascent to the surface during the plinian eruption over periods of minutes to hours the fine population 5 0 5 m represents bubbles formed during explosive disruption of magma and rapid ejection into the atmosphere involving short time scales a few seconds but large decompression rates

reconstructing mid to high latitude marine climate and ocean variability using bivalves coralline algae and marine sediment cores from the northern hemisphere quantifying the role and contribution of the world s oceans in past present and future global change is an essential goal in climate paleoclimate and environmental studies although the global oceans interact and influence climate greatly the marine environment is substantially under represented in key climate assessment reports especially during the last millennium ipcc 2007 see palaeoclimate chapter 6 6 the last 2000 years the under representation of marine records in key climate documents likely results from the often imprecise chronologies associated with many marine based archives which greatly hinders singular climate comparisons lag lead phasing relationships with well dated and or annually resolved archives however several marine archive records have excellent chronological constraint in particular many marine bivalve taxa and coralline algae have annual increments that form within their carbonate framework that can be used to establish an absolutely dated chronology via cross dating techniques from the marine environment additionally in some cases where sedimentation rates are high and alternative chronological dating methods exist e g tephrochronology other than radiocarbon measurements often greater than 40 years uncertainty sediment archives can provide continuous sub decadal records of environmental change for centuries to millennia this brief introductory article and accompanying special issue will focus on the utilization of bivalves coralline algae and high resolution marine sediment cores in paleoclimate and environmental studies within the most recent millennium with a focus on the northern hemisphere

the evolution of bubble size distributions in volcanic eruptions we review observations of bubble size distributions bsds generated during explosive volcanic eruptions and laboratory explosions as inferred from vesicle size distributions found in the end products unimodal polymodal exponential and power law bsds are common even in the absence of coalescence and both power law and exponential distributions have been generated in the same eruption to date theoretical models have proposed incompatible mechanisms for producing the various distributions we here present a unifying mechanism data from our laboratory analogue experiments suggest that power law distributions are associated with highly non equilibrium degassing a numerical model is developed in which bubbles nucleate repeatedly and grow in the spaces between those of previous generations where in a non equilibrium degassing scenario the volatile concentration remains high this process causes the bsd to evolve from unimodal through exponential into a power law the exponent of the power law is a measure of the number of nucleation events or the duration of the nucleation period compared with the timescale of bubble growth the mathematical inevitability of the evolution from unimodal poissonian to power law is discussed the findings may resolve the apparent contradiction between the equilibrium degassing conduit flow models and the non equilibrium degassing conditions derived from bubble growth models of explosive volcanic eruptions the process of ongoing nucleation is the mechanism whereby the volcanic system maintains near equilibrium in the case of rapid depressurisation and slow volatile diffusion

dynamic observations of vesiculation reveal the role of silicate crystals in bubble nucleation and growth in andesitic magmas abstract bubble nucleation and growth control the explosivity of volcanic eruptions and the kinetics of these processes are generally determined from examinations of natural samples and quenched experimental run products these samples however only provide a view of the final state from which the initial conditions of a time evolving magmatic system are then inferred the interpretations that follow are inexact due to the inability of determining the exact conditions of nucleation and the potential detachment of bubbles from their nucleation sites an uncertainty that can obscure their nucleation location either homogeneously within the melt or heterogeneously at the interface between crystals and melts we present results of a series of dynamic real time 4d x ray tomographic microscopy experiments where we observed the development of bubbles in crystal bearing silicate magmas experimentally synthesized andesitic glasses with 0 25 0 5 wt h 2 o and seed silicate crystals were heated at 1 atm to induce bubble nucleation and track bubble growth and movement in contrast to previous studies on natural and experimentally produced samples we found that bubbles readily nucleated on plagioclase and clinopyroxene crystals that their contact angle changes during growth and that they can grow to sizes many times that of the silicate on whose surface they originated the rapid heterogeneous nucleation of bubbles at low degrees of supersaturation in the presence of silicate crystals demonstrates that silicates can affect when vesiculation ensues influencing subsequent permeability development and effusive vs explosive transition in volcanic eruptions

3d inversion of airborne gravity gradiometry data in mineral exploration a case study in the quadrilatero ferrifero brazil abstractwe present a case study of applying 3d inversion of gravity gradiometry data to iron ore exploration in minas gerais brazil the ore bodies have a distinctly high density contrast and produce well defined anomalies in airborne gravity gradiometry data we have carried out a study to apply 3d inversion to a 20 km2 subarea of data from a larger survey to demonstrate the utility of such data and associated inversion algorithm in characterizing the deposit we examine multiple density contrast models obtained by first inverting tzz then txz tyz and tzz jointly and finally all five independent components to understand the information content in different data components the commonly discussed tzz component is sufficient to produce geologically reasonable and interpretable results while including additional components involving horizontal derivatives increases the resolution of the recovered density model and improves the ore delineation we show that gravity gradiometry data can be used to deli

reconstructing greenland ice sheet runoff using coralline algae the greenland ice sheet gris contains the largest store of fresh water in the northern hemisphere equivalent to 7 4 m of eustatic sea level rise but its impacts on current past and future sea level ocean circulation and european climate are poorly understood previous estimates of gris melt from 26 yr of satellite observations and temperature driven melt models over 48 yr show increasing melt trends there are however no runoff data of comparable duration with which to validate the relationship between the spatial extent of melting and runoff or temperature based runoff models further longer runoff records are needed to extend the melt pattern of greenland to centennial timescales enabling recent observations and trends to be put into a better historical context we have developed a new gris runoff proxy by extracting information on relative salinity changes from annual growth bands of red coralline algae we observed significant negative relationships between historic runoff relative salinity and marine summer temperature in sondre stromfjord greenland we produce the first reconstruction of runoff from a section of the gris that discharges into sondre stromfjord over several decades 1939 2002 and record a trend of increasing reconstructed runoff since the mid 1980s in situ summer marine temperatures followed an equivalent trend we suggest that since a d 1939 atmospheric temperatures have been important in forcing runoff these results show that our technique has significant potential to enhance understanding of runoff from large ice sheets as it will enable melt reconstruction over centennial to millennial timescales

vesiculation and crystallization under instantaneous decompression numerical study and comparison with laboratory experiments abstract vesiculation and crystallization in ascending magmas are key processes that control the eruption behavior and they interplay each other through the water exsolution process we conducted a numerical study in order to quantitatively understand the water exsolution and crystallization processes in natural eruptions decompression history is unknown and in laboratory experiments the amount of decompression is constant with time the numerical results which take into account homogeneous or heterogeneous nucleation and growth of bubbles with varying diffusivity of water viscosity and the amount of decompression provide a quantitative understanding of their control on bubble formation and water exsolution in the constant amount of decompression the bubble nucleation in the homogeneous nucleation can be divided into two regimes the diffusion control regime and viscosity control regime depending on the modified peclet number and the effective supersaturation in the cases of both homogeneous and heterogeneous nucleations the bubble growth is controlled by diffusion or viscosity depending on the modified peclet number and bubble number density the water exsolution rate which is controlled by the modified peclet number in the viscosity control regime and by the bubble number density and diffusive driving force in the diffusion control regime acts as an effective cooling rate in a decompression induced crystallization process a comparison of the numerical results with the results of laboratory experiments suggests that water exsolution proceeds by the diffusion limited growth of bubbles under disequilibrium vesiculation through the heterogeneous nucleation of bubbles and this in turn controls the crystallization kinetics of microlite with the homogeneous nucleation of microlite and the diffusion limited growth of crystal the several orders of variation of microlite number density with the amount of decompression in laboratory experiments can be interpreted as the effect of the amount of decompression on the driving force for the diffusive bubble growth that controls the water exsolution rate

a record of mining and industrial activities in new caledonia based on trace elements in rhodolith forming coralline red algae abstract we investigate the ability of coralline red algae to record historical nickel mining activity that occurred between the early 1960s and 1981 in the coulee river watershed southwest new caledonia laser ablation inductively coupled plasma mass spectrometry la icpms was used to determine high resolution sub annual variations of trace metal ratios mn ca fe ca ni ca and co ca in three 45 years old free living forms of the rhodolith coralline red alga sporolithon durum from ricaudy reef in the inner lagoon of new caledonia 15 km from the coulee river mouth we find increased mn ca and fe ca ratio values track the intensity of mining in the coulee river catchment whereas ni ca ratio values appear more sensitive to the ore type saprolite versus laterite that were targeted during two separate stages of mining activity mn ca fe ca and ni ca decrease following the cessation of mining in 1981 but did not reach current values until 10 years after that date surprisingly co ca variations do not correlate with mining activity but rather increase steadily through the record period we argue this relates to nickel refining and smelting activity over the past half century our results further suggest that the local inter annual rainfall variability may influence the metal concentrations recorded in the rhodoliths during the period of intense mining activity but the link between metal uptake and rainfall is not entirely clear for the entire growth period of the rhodoliths

delayed disequilibrium degassing in rhyolite magma decompression experiments and implications for explosive volcanism recent numerical models and analog shock tube experiments show that disequilibrium degassing during magma ascent may lead to violent vesiculation very near the surface in this study a series of decompression experiments using crystal free rhyolite melt were conducted to examine the development of large supersaturations due to delayed homogenous spontaneous bubble nucleation melts were saturated at 900 c and 200 mpa with either 5 2 wt dissolved h2o or with 4 2 wt h2o and 640 ppm co2 and isothermally decompressed at linear rates of either 0 003 0 025 or 8 5 mpa s to final pressures between 25 and 175 mpa additional isobaric saturation experiments 900 c 200 25 mpa using pure h2o or mixed h2o co2 fluids establish reference equilibrium solubility curves values homogenous nucleation is triggered in both h2o only and h2o co2 experiments once the supersaturation pressure pss reaches 120 150 mpa and the melt contains two times its equilibrium water contents bubble number density and nucleation rate depend on the supersaturation pressure with values on the order of 102 cm3 and 1 cm3 s for pss 120 mpa 106 cm3 and 103 105 cm3 s for pss 130 150 mpa and 107 cm3 and 106 cm3 s for pss 160 175 mpa nucleation rates are consistent with classical nucleation theory and infer an activation energy for nucleation of 1 5 10 18 j nucleus a critical bubble radius of 2 10 9 m and an effective surface tension for rhyolite at 5 2 wt h2o and 900 c of 0 10 0 11 n m the long nucleation delay limits the time available for subsequent diffusion such that disequilibrium dissolved h2o and co2 contents persist to the end of our runs the disequilibrium degassing paths inferred from our experiments contrast markedly with the equilibrium or quasi equilibrium paths found in other studies where bubble nucleation occurs heterogenously on crystals or other discontinuities in the melt at low pss homogenous and heterogenous nucleation rates are comparable however as are bubble number densities so that at a given decompression rate it appears that nucleation mechanism rather than nucleation rate determines degassing efficiency by fixing the pressure depth at which vesiculation commences and hence the time available for equilibration prior to eruption although real systems are probably never truly crystal free our results show that rhyolitic magmas containing up to 104 crystals cm3 and perhaps as high as 106 crystals cm3 are controlled by homogenous rather than heterogenous nucleation during ascent

coralline algae are global palaeothermometers with bi weekly resolution abstract high resolution palaeoclimate data are required for the holocene to resolve differences recorded by current proxies the pole to pole distribution of rhodoliths coralline algae with their annual and sub annual calcite bands make these attractive candidates for such a role these bands contain climate information in the form of elemental traces in situ temperature ist was recorded at two rhodolith beds for 1 5 years the concentrations of mgco 3 and srco 3 mol deposited in lithothamion glaciale and phymatolithon calcareum over this 18 month period were determined using electron and ion microprobes highly significant linear relationships exist between mg sr and ist as well as sea surface temperature calibration between mg concentration and ist was used to obtain a 2 year temperature profile from a subfossil rhodolith thallus indicating half the seasonal peak to peak temperature amplitude earlier during the holocene than the present day both slow growing species 1 allowed sampling resolutions of 23 year 1 which is equivalent to 1 reading every 2 weeks sub monthly mg and sr records in rhodoliths make them unique globally distributed palaeothermometers which may help refine regional climate histories during the holocene

bnd bubble number density decompression rate meter for explosive volcanic eruptions abstract this decade has been witness to substantial progress in the understanding of bubble dynamics and its role in volcanic eruptions a comparison between the results of experiments and a model for bubble nucleation shows that bubble number density bnd can be calculated as a function of decompression rate for given physical properties such as the diffusivity of water in a silicate melt and interfacial tension within an acceptable margin of error conversely in this paper we propose a method hereafter referred to as bnd decompression rate meter to estimate the decompression rate by using bnd data of natural pumice samples from volcanic eruptions as a result of the application of the bnd decompression rate meter to pumice and scoria from explosive eruptions it is found that the decompression rates increase in the range from 10 6 to 10 8 pa s with the eruption column heights these rates are proportional to the 4th power of the eruption column heights and are linear to the discharge rates the absolute values of the estimated decompression rates are very high and cannot be explained by the existing models of conduit flows in order to explain such high rates of decompression and the correlation with discharge rate we propose a possible model according to which the bubble nucleation propagates downward as a rarefaction shock wave in the conduit

homogeneous bubble nucleation in rhyolitic magmas an experimental study of the effect of h2o and co2 1 rapid decompression experiments were performed to study homogeneous bubble nucleation in a crystal free rhyolitic liquid at 800 c bubble nucleation was produced by lowering the pressure at 1 10 mpa s 1 from an initial value between 200 and 295 mpa to a final value below the volatile saturation pressure psat six volatile compositions with 4 1 7 7 wt h2o and 10 1200 ppm co2 were investigated for each composition we determined the critical pressure phon below which homogeneous nucleation can proceed the samples quenched below phon showed a nucleated core with a large number of uniformly spaced bubbles with decreasing pressure bubble number densities increased from 1015 m 3 the degree of supersaturation required for homogeneous nucleation phon psat phon increased with decreasing h2o content or increasing co2 content huge values of phon 135 to 310 mpa were measured in the h2o poor compositions 4 1 4 6 wt h2o 50 1100 ppm co2 much lower values from 60 to 160 mpa were obtained in the h2o rich compositions 7 0 7 7 wt h2o 10 630 ppm co2 the high phon in liquids with 4 5 wt h2o should result in the buildup of large degrees of supersaturation during magma ascent a very late nucleation event and a rapid explosive vesiculation by contrast rhyolitic liquids with much larger water contents have higher saturation pressures and much lower phon bubble nucleation may therefore occur at depth in the volcanic conduit favoring a subsequent near equilibrium degassing

reefal coralline algal build ups within the arctic circle morphology and sedimentary dynamics under extreme environmental seasonality abstract carbonate frameworks secreted by phototrophic organisms within the arctic circle are not well documented underwater surveys of the inner shelf off troms northern norway 70 n reveal extended fixed algal build ups which are fringed by rhodolith belts affected by storms reefd growth by coralline algae under temperature and light regimes of extreme seasonality is made possible because of a decoupling of carbon fixation during summer and utilization of stored carbon during the period of winter darkness although the annual growth of the framework constructing algae is comparatively low the annual carbonate production rate is similar to subtropical tropical counterparts because of a remarkably high standing stock early diagenetic alteration is restricted to intraparticle cementation processes which start in vivo bioerosional destruction is the dominant control on the preservation of high latitude build ups preservation of holocene autochthonous coralline algal biostromes is enhanced by rapid burial during storm events redeposition during storms is the most important process in forming a distinct sedimentary facies zonation

imaging iron ore from the quadrilatero ferrifero brazil using geophysical inversion and drill hole data abstract the quadrilatero ferrifero in southeastern brazil hosts one of the largest concentrations of lateritic iron ore deposits in the world our study area is over the southern flank of the gandarela syncline which is one of the regional synclines of the quadrilatero ferrifero the gandarela syncline is considered the brazilian megastructure with the highest perspectives for iron ore exploration most of the iron ore deposits from the quadrilatero ferrifero are non outcropping bodies hosted in the oxidized metamorphosed and heterogeneously deformed banded iron formations therefore the assessment of the 3d geometry of the iron ore body is of the utmost importance for estimating reserves and production development planning we carried out a quantitative interpretation of the iron ore deposit of the southern flank of the gandarela syncline using a 3d inversion of airborne gravity gradient data to estimate the shape of the iron ore mineralization the retrieved body is characterized by a high density zone associated with the northeast elongated iron formation the thickness and the width of the retrieved iron ore body vary along its strike increasing southwestward the presence of a large volume of iron ore in the southwest portion of the study area may be due to the hinge zone of the gandarela syncline which is the zone of maximum compression our estimated iron ore mass reveals variable dip directions in the southernmost central and northernmost portions of the study area the estimated iron body dips respectively inwards vertically and outwards with respect to the syncline axis previous geological mapping indicated continuous mineralization however our result suggests a quasi continuous iron ore body in the central part of the study area the estimated iron ore body is segmented into two parts this breakup may be related to the northwest trending faults which are perpendicular to the northeast trending axis of the gandarela syncline our estimated iron ore mass agrees reasonably well with the information provided from the lithologic logging data of drill holes in this geophysical study the estimated iron ore reserves are approximately 3 billion tons

coralline algal growth increment widths archive north atlantic climate variability over the past decade coralline algae have increasingly been used as archives of paleoclimate information encrusting coralline algae which deposit annual growth increments in a high mg calcite skeleton are amongst the longest lived shallow marine organisms in fact a live collected plant has recently been shown to have lived for at least 850 years based on radiometric dating while a number of investigations have successfully used geochemical information of coralline algal skeletons to reconstruct sea surface temperatures less attention has been paid to employ growth increment widths as a temperature proxy here we explore the relationship between growth and environmental parameters in clathromorphum compactum collected in the subarctic northwestern atlantic results indicate that growth increment widths of individual plants are poorly correlated with instrumental sea surface temperatures sst however an averaged record of multiple growth increment width time series from a regional network of c compactum specimens up to 800 km apart reveals strong correlations with annual instrumental sst since 1950 hence similar to methods applied in dendrochronology averaging of multiple sclerochronological records of coralline algae provides accurate climate information a 115 year growth increment width master chronology created from modern collected and museum specimens is highly correlated to multidecadal variability seen in north atlantic sea surface temperatures positive changes in algal growth anomalies record the well documented regime shift and warming in the northwestern atlantic during the 1990s large positive changes in algal growth anomalies were also present in the 1920s and 1930s indicating that the impact of a concurrent large scale regime shift throughout the north atlantic was more strongly felt in the subarctic northwestern atlantic than previously thought and may have even exceeded the 1990s event with respect to the magnitude of the warming

transamazonian orogeny in the southern sao francisco craton region minas gerais brazil evidence for paleoproterozoic collision and collapse in the quadrilatero ferrifero abstract the paleoproterozoic transamazonian orogeny yielded a series of discrete orogens in brazil the present field study in the quadrilatero ferrifero qf indicates that the southern sao francisco craton region of the brazilian highlands preserves a portion of one of these orogens two sets of transamazonian structures occur in this region the first consists of northwest verging folds and thrusts affecting supracrustal sequences it is suggested that this set formed in a fold thrust belt setting shortly after 2 125 ga during the closure of a passive margin basin that had initiated along the margins of a preexisting continental mass at ca 2 5 ga the second set consists of structures defining the prominent dome and keel architecture of the qf this set a consequence of the emplacement of basement domes against supracrustal rocks at 2 095 ga may reflect the consequences of orogenic collapse narrow conglomerate filled intermontane basins may have formed coevally with dome emplacement formation of an ocean basin east of the present day sao francisco craton eventually occurred in late mesoproterozoic in effect the transamazonian orogen of the qf represents the collision and collapse stages of a paleoproterozoic wilson cycle the contractional phase of the transamazonian orogeny probably represents accretion of an offshore arc to the eastern and southeastern margin of the present day sao francisco craton region the arc and an associated suture may be traced in the brasiliano pan african orogen east of the sao francisco craton northwards into the northeastern lobe of the sao francisco craton clearly initial assembly of crustal blocks to form a larger continent involving south america occurred during the paleoproterozoic 2 1 ga post transamazonian rifting of this continent created the basins which were later inverted during the brasiliano assembly of gondwana

magma degassing during the plinian eruption of novarupta alaska 1912 1 we have modeled the nucleation and isothermal growth of bubbles in dacite from the 1912 plinian eruption of novarupta alaska bubble growth calculations account for the exsolution of h2o and co2 beginning with bubble nucleation and ending when bubble sizes reproduced the observed size distribution of vesicles in novarupta pumice clasts assuming classical nucleation theory bubbles nucleated with a diameter of the order of 10 8 m and grew to sizes ranging from 10 6 m to greater than 10 3 m the typical range of vesicle sizes found in novarupta pumice the smallest vesicles in novarupta pumices are also the most abundant and bubbles with radii of 10 6 m to 10 5 m comprise almost 90 of the entire bubble population we find that these bubbles must have nucleated and grown to their final size within a few 100 milliseconds despite these extremely fast growth rates the pressures of exsolved volatiles contained within the bubbles remained high up to about 107pa in excess of ambient pressure assuming a closed system the potential energy of these compressed volatiles was sufficient to cause magma fragmentation even though only a fraction of the pre eruptive volatiles had exsolved unless the matrix glasses of novarupta pyroclasts retains a large fraction of pre eruptive volatiles the majority of magmatic volatiles 80 90 was likely lost by open system degassing between magma fragmentation and quenching

variations of upwelling intensity recorded in varved sediment from the gulf of california during the past 3 000 years circulation in the pacific ocean is periodically affected by el nino events which are a direct response to intensity changes in trade winds1 2 the appearance of anomalously warm surface water in the eastern equatorial pacific ocean is one of the most spectacular manifestations of this event warm surface water anomalies are also observed in the northern hemisphere along the californian coast and in the gulf of california in the gulf strengthened trade winds induce upwelling during the winter whereas in the summer prevailing southerly winds provoke an input of warm water from the south3 we have sampled laminated sediments from the slopes of guaymas basin to reconstruct with high resolution variations of the hydrology of surface waters in the central part of the gulf of california sedimentation rate is of the order of 4 mm yr 1 at the top and 1 2 mm yr 1 down core by analysing the oxygen isotope ratio of biogenic silica of diatoms4 we have recorded the surface water temperature variations in the guaymas basin the comparison of these fluctuations and variations of silicoflagellate abundance has allowed us to reconstruct changes in upwelling intensity during the past three thousand years the present conditions of low upwelling activity are seen to be abnormal in comparison with those prevailing in the past

nucleation and growth of bubbles on plagioclase crystals during experimental decompression degassing of andesitic melts abstract the nucleation growth and attachment detachment of gas bubbles on crystals in silicate melts is one of the key drivers of volcanic eruptions and can greatly influence their explosivity formerly oxides were considered the best candidates for heterogeneous bubble nucleation but recent studies showed that silicate crystals can also be bubble nucleation sites at 1 atmosphere atm this study examines whether bubbles can nucleate on plagioclase crystal surfaces during decompression which is a more common natural situation than 1 atm degassing experimental samples were synthesised from andesitic rock powder h2o and plagioclase seed crystals and melted and decompressed in a piston cylinder apparatus the products were imaged with 3d x ray computed tomography due to partial melting the plagioclase crystals developed sieve rims and rough crystal melt interfaces all plagioclase crystals in all samples were covered with bubbles bubble size distribution comparisons between bubbles in contact with plagioclase and bubbles in the melt show that bubbles belong to two populations generated by two different events one of which is heterogeneous nucleation on plagioclase crystal surfaces and the other is homogeneous nucleation within the melt the latter potentially accompanied by heterogeneous nucleation on oxide microlite surfaces the calculated attachment force between the bubbles and the plagioclase surface is stronger than the detachment force hence such bubbles would remain attached during crystal movements in our experiments the net buoyancy of the bubble crystal aggregates indicates that they could sink in an andesitic melt our findings highlight the need to reconsider the role of plagioclase crystals in magmatic degassing and shows interesting possibilities for magma mixing triggered degassing

re deposited rhodoliths in the middle miocene hemipelagic deposits of vitulano southern apennines italy coralline assemblage characterization and related trace fossils article i nfo an integrated analysis of rhodolith assemblages and associated trace fossils borings found in hemipelagic middle miocene orbulina marls vitulano area taburno camposauro area southern apennines italy has revealed that both the biodiversity of the constituent components and taphonomic signatures represent important aspects which allow a detailed palaeoecological and palaeoenvironmental interpretation on the basis of shape inner arrangement growth forms and taxonomic coralline algal composition two rhodolith growth stages were distinguished 1 nucleation and growth of the rhodoliths and 2 a final growth stage before burial nucleation is characterized by melobesioids and subordinately mastophoroids with rare sporolithaceans and lithophylloids the rhodolith growth main increase in size is represented by abundant melobesioids and rare to common mastophoroids very rare sporolithaceans are also present the final growth stage is dominated by melobesioids with rare mastophoroids and very rare sporolithaceans each rhodolith growth stage is characterized by a distinct suite of inner arrangement and growth form successions well diversified ichnocoenoeses gastrochaenolites trypanites meandropolydora and or caulostrepsis ento bia uniglobites micro borings related to bivalves sponges polychaetes barnacles algae fungi and bacteria are distinguished in the inner intermediate rhodolith growth stage while mainly algal fungal and bacterial micro borings are present in the outer final growth stage rhodolith growth stages and associated ichnocoenoeses indicate significant change in the depositional setting during the rhodolith growth in the vitulano area the middle miocene rhodolith assemblages formed in a shallow water open shelf carbonate platform were susceptible to exportation from their production area and then to sedimentation down to deeper water hemipelagic settings where the rhodoliths shortly kept growth and were finally buried such re deposition of unlithified or only weakly lithified i e rhodoliths and intraclasts shallow water carbonates into deeper water settings was likely favoured by storm generated offshore return currents rather than sediment gravity flows

water sources for georges bank abstract the origins of georges bank source waters can be quantified by the oxygen isotope salinity tracer regionally water is tagged by freshwater of different h 2 18 o h 2 16 o ratios and these waters can subsequently be identified after mixing downstream this conservative lagrangian tracer of source waters is useful for tracking passive plankton and larvae that may be important to sustain the georges bank ecosystem the origin of georges bank freshwater sources is primarily in the gulf of st lawrence consisting of labrador shelf water which enters via the strait of belle isle and st lawrence river water these two mix with the underlying slope water in the gulf of st lawrence and along the scotian shelf at the northeast channel the input to the gulf of maine there is a single freshwater endmember consisting of 5 6 st lawrence river water and 94 6 labrador shelf water by volume these proportions remained constant for the years 1995 1997 the water on central georges bank consists of a mixture of water entering the northeast channel with gulf of maine river outflow there is considerable interannual variation in the maine river water proportion ranging from 3 3 in 1982 to 0 23 by volume in 1996 during 1995 1998 there was no correlation between georges bank salinity which decreased monotonically and the proportion of maine river water on the bank the interannual fluctuations of salinity on georges bank are driven by variations in upstream scotian shelf sources and its mixing onto the bank and not by changes in local river outflow

kinetics of crystallization of igneous rocks the geochemistry of igneous rocks is discussed with the primary objectives of bringing together the theories underlying the kinetics of crystallization of igneous rocks and illustrating the use of these theories in understanding experimental and observational data the primary purpose of the chapter is to introduce current thinking about the kinetics of igneous rocks and to provide a basis for understanding other work a basic assumption made in the discussion is that the rate of any chemical reaction including the crystallization of igneous rocks is zero at equilibrium and proceeds at a finite rate only at a finite deviation from equilibrium as such an understanding of the processes operating in igneous rocks requires an understanding of how deviation from equilibrium affects the rates and mechanisms of the processes occurring during crystallization these processes are detailed with special emphasis given to nucleation and crystal growth jmt

heterogeneous bubble nucleation in highly viscous silicate melts during instantaneous decompression from high pressure abstract the nucleation of h 2 o bubbles in magmas has been proposed as a trigger for volcanic eruptions to determine how bubbles nucleate heterogeneously in silicate melts experiments were carried out in which high silica rhyolitic melts were hydrated at 800 c and either 50 or 125 mpa and then decompressed by 20 91 mpa at temperatures that ranged between 550 and 700 c and held at the lower pressures for 10 720 s before being quenched bubbles nucleated in number densities n b that vary between 3 10 7 and 2 10 8 cm 3 blocky shaped magnetite or the ends of needle shaped hematite acted as sites for nucleation but only if a minimum super saturation was exceeded which increases with increasing melt viscosity bubbles did not nucleate along the lengths of hematite needles nor on plagioclase both the beginning and ending times of the nucleation event increases with increasing melt viscosity using nucleation theory predictions neither the slower nucleation rates nor the changing activation of nucleation sites can be adequately explained by the differences in temperature water diffusivity or viscosity instead the variations in nucleation kinetics are best explained by changes in surface tension between melt and vapor resulting from the increasing polymerization of the melt at lower temperatures and water contents because only 10 8 bubbles cm 3 nucleate on magnetite in the rhyolite melt used almost regardless of experimental conditions results from this study may not be directly comparable to vesicle numbers in volcanic pumice of different compositions

bubble nucleation growth and coalescence during the 1997 vulcanian explosions of soufriere hills volcano montserrat abstract soufriere hills volcano had two periods of repetitive vulcanian activity in 1997 each explosion discharged the contents of the upper 0 5 2 km of the conduit as pyroclastic flows and fallout frothy pumices from a deep gas rich zone lava and breadcrust bombs from a degassed lava plug and dense pumices from a transition zone vesicles constitute 1 66 vol of breadcrust bombs and 24 79 of pumices all those larger than a few tens of m being interconnected small vesicles few hundreds of m in pumices are interpreted as pre dating explosion implying pre explosive conduit porosities up to 55 about a sixth of large vesicles in pumices and all those in breadcrust bombs are angular voids formed by syn explosive fracturing of amphibole phenocrysts an intermediate sized vesicle population formed by coalescence of the small syn explosive bubbles bubble nucleation took place heterogeneously on titanomagnetite number densities of which greatly exceed those of vesicles and growth took place mainly by decompression development of pyroclast vesicle textures was controlled by the time interval between the onset of explosion decompression and surface quench in contact with air lava plug fragments entered the air quickly after fragmentation 10 s so the interiors continued to vesiculate once the rinds had quenched forming breadcrust bombs deeper gas rich magma took longer 50 s to reach the surface and vesiculation of resulting pumice clasts was essentially complete prior to surface quench this accounts for the absence of breadcrusting on pumice clasts and for the textural similarity between pyroclastic flow and fallout pumices despite different thermal histories after leaving the vent it also allowed syn explosive coalescence to proceed further in the pumices than in the breadcrust bombs uniaxial boudinage of amphibole phenocrysts in pumices implies significant syn explosive vesiculation even prior to magma fragmentation probably in a zone of steep pressure gradient beneath the descending fragmentation front syn explosive decompression rates estimated from vesicle number densities 0 3 6 5 mpa s 1 are consistent with those predicted by previously published numerical models

bubble nucleation in rhyolite and dacite melts temperature dependence of surface tension surface tension profoundly influences the ability of gas bubbles to nucleate in silicate melts to determine how temperature impacts experiments were carried out in which high silica rhyolite melts with 5 wt dissolved water were decompressed at temperatures that ranged from 775 to 1 085 c decompressions were also carried out using dacite melts with 4 3 wt dissolved water at 1 150 c water bubbles nucleated in rhyolite only when decompressions exceeded 95 mpa at all temperatures bubbles nucleated in number densities that increased as decompression increased and at hotter temperatures at a given amount of decompression after correcting decompression amounts for temperature differences values for were estimated from nucleation rates and found to vary between 0 081 and 0 093 n m 1 surface tension decreases as temperature increases from 775 to 875 c but then increases as temperature increases to 1 085 c those values overlap previous results but only when melt viscosity is less than 104 pa s for low viscosity rhyolite there is a strong correlation of with temperature in which increases by 6 9 10 5 n m 1 c 1 that variation is robust for 5 9 wt dissolved water as long as melt viscosity is 104 pa s more viscous rhyolite deviates from that correlation probably because nucleation is retarded in stiffer melts bubbles nucleated in dacite when decompressions exceeded 87 mpa and occured in one or more events as decompression increased surface tension is estimated to be 0 083 0 001 n m 1 and when adjusted for temperature agrees well with previous results for colder and wetter dacite melts at a given water content dacite melts have lower surface tensions than rhyolite melts when corrected to a fixed temperature

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

the long lived mollusc arctica islandica a new paleoceanographic tool for the reconstruction of bottom temperatures for the continental shelves of the northern north atlantic ocean the carbonate shell of the bivalve arctica islandica has been recognized for more than a decade as a potentially important marine geochemical biorecorder owing to this species great longevity 200 years and wide geographic distribution throughout the northern north atlantic ocean a region vital to global climate and ocean circulation however until now this potential has not been realized owing to the difficulty of precisely sampling the shell of this slow growing species using newly available automated microsampling techniques combined with micromass stable isotope mass spectrometry a stable oxygen isotope record 1956 1957 and 1961 1970 has been obtained from a live captured 38 year old a islandica specimen collected near the former position of the nantucket shoals lightship 41 n 69 w the shell s 18o signal is compared with an expected signal derived from ambient bottom temperature and salinity data recorded at the lightship for the same period the results show that a islandica s 18o record 1 is in phase with its growth banding confirming the annual periodicity of this species growth bands 2 is in oxygen isotopic equilibrium with the ambient seawater 3 shows a consistent shell growth shutdown temperature of 6 c which translates into an 8 month may december shell growth period at this location and 4 records the ambient bottom temperature with a precision of 1 2 c these results add important information on the life history of this commercially important shellfish species and demonstrate that a islandica shells can be used to reconstruct inter and intra annual records of the continental shelf bottom temperature

vesiculation of may 18 1980 mount st helens magma the may 18 1980 eruption of mount st helens washington produced both white and gray pumice similar in composition but varying in phenocryst microlite and vesicle content the white pumice has fewer phenocrysts no microlites and higher vesicularity and is thus less dense than the gray in addition vesicles in the white pumice are larger and more interconnected than those in the gray both white and gray have effective crystal free vesicularities 85 7 and 72 2 respectively close to the traditionally accepted fragmentation vesicularity of 75 77 given that the two pumice types were erupted concurrently for several phases of the eruption and therefore probably had similar eruption paths we suggest that differences in vesicularity and vesicle size distributions result from the presence or absence of microlites the presence of microlites in the gray pumice not only increased the magma viscosity and effective vesicularity but appears to have aided bubble nucleation and hindered bubble expansion and coalescence thus magmas with microlites may fragment at a lower bulk vesicularity than those without microlites fragmented microlite bearing clasts are also likely to expand less after fragmentation and therefore more closely preserve the bubble distribution and structure at the time of magma fragmentation

robust 3d gravity gradient inversion by planting anomalous densities we have developed a new gravity gradient inversion method for estimating a 3d density contrast distribution defined on a grid of rectangular prisms our method consists of an iterative algorithm that does not require the solution of an equation system instead the solution grows systematically around userspecified prismatic elements called seeds with given density contrasts each seed can be assigned a different density contrast value allowing the interpretation of multiple sources with different density contrasts and that produce interfering signals in real world scenarios some sources might not be targeted for the interpretation thus we developed a robust procedure that neither requires the isolation of the signal of the targeted sources prior to the inversion nor requires substantial prior information about the nontargeted sources in our iterative algorithm the estimated sources grow by the accretion of prisms in the periphery of the current estimate in addition only the columns of the sensitivity matrix corresponding to the prisms in the periphery of the current estimate are needed for the computations therefore the individual columns of the sensitivity matrix can be calculated on demand and deleted after an accretion takes place greatly reducing the demand for computer memory and processing time tests on synthetic data show the ability of our method to correctly recover the geometry of the targeted sources even when interfering signals produced by nontargeted sources are present inverting the data from an airborne gravity gradiometry survey flown over the iron ore province of quadrilatero ferrifero southeastern brazil we estimated a compact iron ore body that is in agreement with geologic information and previous interpretations

clustered streamlined forms in athabasca valles mars evidence for sediment deposition during floodwater ponding a unique clustering of layered streamlined forms in athabasca valles is hypothesized to reflect a significant hydraulic event the forms interpreted as sedimentary are attributed to extensive sediment deposition during ponding and then streamlining of this sediment behind flow obstacles during ponded water outflow these streamlined forms are analogous to those found in depositional basins and other loci of ponding in terrestrial catastrophic flood landscapes these terrestrial streamlined forms can provide the best opportunity for reconstructing the history of the terrestrial flooding likewise the streamlined forms in athabasca valles may provide the best opportunity to reconstruct the recent geologic history of this young martian outflow channel

mg ca ratios in coralline algae record northwest atlantic temperature variations and north atlantic oscillation relationships climate variability in the north atlantic has been linked in part to the north atlantic oscillation nao the nao influences marine ecosystems in the northwestern atlantic and transport variability of the cold labrador current understanding historic patterns of nao variability requires long term and high resolution climate records that are not available from instrumental data here we present the first century scale proxy record of sea surface temperature sst variability from the newfoundland shelf a region from which other annual resolution shallow marine proxies are unavailable the 116 year record was obtained from three sites along the eastern newfoundland shelf using laser ablation inductively coupled mass spectrometry determined mg ca ratios in the crustose coralline alga clathromorphum compactum the alga is characterized by a high mg calcite skeleton exhibiting annual growth increments and a century scale lifespan results indicate positive correlations between interannual variations in mg ca ratios and both station based and gridded instrumental sst in addition the record shows high spatial correlations to sst across the newfoundland shelf and the gulf of st lawrence before 1950 the mg ca proxy record reveals significant departures from gridded temperature records while the newfoundland shelf is generally considered a region of negative correlations to the nao the algal time series as well as a recent modeling study suggest a variable negative relationship with the nao which is strongest after 1960 and before the mid 1930s

proterozoic first order sedimentary sequences of the sao francisco craton eastern brazil abstract the sao francisco craton in eastern brazil hosts sedimentary sequences deposited between the paleoarchean 3300 ma and late neoproterozoic 580 ma proterozoic successions occurring in this region comprise five 1st order sedimentary sequences which besides episodes of global significance record major basin forming events the ca 8000 m thick minas itacolomi 1st order sequence exposed in the brazilian mining district of the quadrilatero ferrifero and containing as marker bed the lake superior type caue banded iron formation tracks the operation of a wilson cycle in the paleoproterozoic era the quartz arenite dominated espinhaco i and ii sequences record at least two major rift sag basin forming events which affected the host continent of the sao francisco craton at around 1 75 ga and 1 57 ga the macaubas sequence and its correlatives in the extracratonic domains witness the individualization of a sao francisco congo plate in synchronicity with the break up of rodinia in the cryogenian period the sao francisco congo plate together with various fragments derived from rodinia reassembled to form gondwana in the ediacaran period in the course of the gondwana amalgamation orogenic belts developed along the margins of the craton its interior converted into foreland basins received the shallow water carbonates and pelites of the bambui 1st order sequence and its correlatives

tropical seasonality in the late campanian late cretaceous comparison between multiproxy records from three bivalve taxa from oman abstract geochemical proxy records from calcite shells of bivalves constitute an important archive for the reconstruction of palaeoenvironmental conditions on sub annual timescales however the incorporation of these trace element and stable isotope proxies into the shell is influenced by a multitude of physiological and environmental factors that need to be disentangled to enable reliable reconstruction of palaeoclimate and palaeoenvironment in this study records of multiple proxies in three bivalve taxa from the same late campanian locality in oman are used to study the expression of various geochemical proxies in relation to each other and to the palaeoenvironment micro x ray fluorescence mapping allows the localization discussion and evasion of diagenetically altered parts of the fossil shells x ray fluorescence line scanning calibrated with laser ablation inductively coupled plasma mass spectrometry is used to measure trace element profiles through well preserved calcitic parts of the shells records of stable carbon and oxygen isotope ratios of shell calcite are combined with these high resolution trace element concentration profiles to study sub annual variations in shell chemistry and reconstruct changes in the palaeoenvironment of the bivalves on a seasonal scale spectral analysis routines are used to detect cyclicity in stable isotope 18o and 13c and trace element mg ca sr ca s ca and zn ca records differences in seasonal expression between these chemical proxies and between individual shells are discussed in terms of the relative influence of palaeoenvironment and potential species specific physiological effects stable oxygen isotope ratios between shells suggest a local palaeotemperature seasonality of 8 c around an annual mean of 28 c with the shell of the rudistid torreites sanchezi milovanovici yielding slightly higher average temperatures the discussion of the application of various mg ca palaeotemperature calibrations on mg ca records in these bivalve species emphasizes the complexity of using trace element proxies in extinct bivalve species it shows that long term changes in mg ca ratios in ocean water need to be taken into account and that mg ca ratios in bivalves might be influenced by vital effects sr ca and s ca ratios in these fossil taxa are likely controlled by growth and metabolic rates of the shell although an influence of local salinity on strontium to calcium ratios cannot be excluded sub annual variations in zinc concentrations in shell calcite may reflect seasonal variations in palaeoproductivity and redox conditions in the water column

alpine proglacial suspended sediment dynamics in warm and cool ablation seasons implications for global warming summary data on suspended sediment dynamics and loads obtained from the torrent du glacier noir ecrins massif se france during the unusually warm 2003 and cooler 2004 ablation seasons are used to indicate the likely future impacts of climate warming on suspended sediment transport processes in temperate alpine proglacial zones suspended sediment concentration ssc and discharge q were continuously monitored for 16 day periods during july 2003 and july 2004 ssc was monitored by automated pump sampling during diurnal events in each season and supplemented by a 10 min turbidity record q was monitored at a range of flows and a rating curve used to convert a 10 min water level record into q air temperature at was also logged at 10 min intervals throughout the study comparison of the 2003 and 2004 monitoring periods showed that daily mean at measured at the site was 1 2 c higher in 2003 mean q was 2 3 times higher and the suspended sediment load ssl was between 3 1 and 4 1 times greater in july 2003 than for the same period in the 2004 ablation season there is an increase in ssc during the 2004 observation period which is less apparent in 2003 most likely because higher ats and consequently higher q earlier in the 2003 melt season had removed available sediment before the study took place in july the rating curve method for estimating ssl produced a total load for the 16 day study period in 2003 which when corrected upwards to account for statistical bias was 10 314 743 t or 95 of the load estimated from the turbidity record for the same period in 2004 the corrected ssc q rating curve estimate was 2504 126 t while the estimate from the turbidity record was 743 112 t though a more sensitive turbidity sensor produced a higher estimate of 3474 302 t while the different ssl estimation methods in 2004 are not in perfect agreement the contrast between the two seasons is nevertheless very clear and is largely attributed to a mean monthly regional air temperature increase of 2 0 c over most of the 2003 ablation season the 2003 ssl record compared with 2004 can be used to gain an insight into the impact of higher air temperatures resulting from global warming on ssl such changes in ssls have important implications for sediment transfer from mountain to piedmont zones for stream ecology for downstream channel stability and flood risk and for the hydro electric industry

the tectonic evolution of the quadrilatero ferrifero minas gerais brazil abstract the structural framework of the quadrilatero ferrifero is the result of two main deformational events the first is an extensional event of palaeoproterozoic age between 2 100 and 1700 ma the transamazonian event which resulted in the formation of archaean granite gneiss domes and the nucleation of regional synclines in the overlying rio das velhas and minas supergroups strata such regional synclines are continuous with each other and are bordered by structural granite gneiss highs at the contact between these units ductile brittle to ductile extensional shear zones are developed representing the dislocation surfaces of archaean blocks this tectonism is probably related to the evolution of a metamorphic core complex formed in the hinterland to the west of a transamazonian collision zone which structured the paramirim craton the second event is compressive and associated with the closure of the pan african brasiliano proto ocean 650 500 ma situated to the east of quadrilatero ferrffero qf during this event a west verging fold and thrust belt ftb developed causing inversion amplification translation and rotation of the basinal synclines the ftb affected mainly the eastern portion of qf and obliterated many of the tectonic features of the extensional event

bubble nucleation in rhyolitic melts experiments at high pressure temperature and water content abstract we report the first measurement of bubble nucleation in hydrated rhyolitic melts in response to pressure release two rhyolitic obsidians one containing less than 1 of microlites of fe ti oxides and the other about 20 of various crystals were hydrated at 150 mpa and 780 850 c after saturation was reached 5 3 5 5 wt water pressure was lowered and the samples were allowed to nucleate and grow bubbles for various amounts of time before the final rapid quenching of the experiments the results demonstrate the importance of heterogeneous nucleation microlites of fe ti oxides are very efficient as sites for bubble nucleation in their presence modest nucleation was observed even after decompression by 6 10 8 bubbles cm 3 in the absence of microlites no nucleation occurred at p mpa at p 10 mpa bubbles also nucleated on crystals of biotite zircon and apatite modest nucleation 10 3 10 5 cm 3 took place even in crystal free samples but it was still heterogeneous when p exceeded 80 mpa nucleation in crystal free samples became extensive 10 5 10 7 cm 3 the lack of correlation of bubble density with either time or decompression suggests that nucleation was still heterogeneous nucleation rates were controlled mainly by the availability of sites rates were faster than 10 6 cm 3 s 1 when microlites were present and faster than 10 5 cm 3 s 1 in the absence of microlites at p 70 mpa narrow size distributions in most samples suggests that nucleation took place immediately after the pressure drop the experimental data we present here indicate that the presence or absence of efficient nucleation sites can lead to two distinct modes of bubble formation when a large number of efficient sites e g fe ti oxide are present bubble nucleation requires very little supersaturation and to a good approximation gas and magma are in equilibrium in magmas that are crystal free or contain crystals that are inefficient at nucleating bubbles very high degrees of supersaturation are required in order to initiate nucleation these two modes of exsolution may lead to contrasting styles of convection pressure build up and eruption

dynamics of deep submarine silicic explosive eruptions in the kermadec arc as reflected in pumice vesicularity textures abstract despite increasing recognition of silicic pumice bearing deposits in the deep marine environment the processes involved in explosive silicic submarine eruptions remain in question here we present data on bubble sizes and number densities number of bubbles per unit of melt matrix for deep submarine erupted pumices from three volcanoes healy raoul sw and havre along the kermadec arc sw pacific to investigate the effects of a significant 1 km overlying water column and the associated increased hydrostatic pressure on magma vesiculation and fragmentation we compare these textural data with those from chemically similar subaerially erupted pyroclasts from nearby raoul volcano as well as submarine erupted tangaroan fragments derived by non explosive buoyant detachment of foaming magma from macauley volcano also along the kermadec arc deep submarine erupted pumices are macroscopically similar colour density texture to subaerial or shallow submarine erupted pumices but show contrasting microscopic bubble textures deep submarine erupted pyroclasts have fewer small

bubble nucleation in magmas a dominantly heterogeneous process abstract bubble nucleation is at the heart of magma ascent and degassing nucleation kinetics control how easily a magma exsolves its volatiles and thereby its explosivity close to the surface homogeneous nucleation i e without assistance from crystal substrates or other phases often requires attainment of large supersaturation pressures p n 100 mpa the change in pressure required for onset of nucleation while heterogeneous nucleation on pre existing crystals can occur at significantly lower values p n p n given experimental constraints on pressure conditions at the onset of nucleation decompression rate meters e g toramaru 2006 also relate the number density of bubbles in pyroclasts a readily obtained textural characteristic to rates of pressure change dp dt during ascent all these treatments require an explicit or implicit decision as to whether magma degassing was dominated by homogeneous or heterogeneous nucleation which is guided by the choice of surface tension values this contribution exploits the current textural datasets available for eruptions involving a variety of magma compositions to test the assumptions that homogeneous and or heterogeneous nucleation dominate bubble vesiculation in natural melts the comparison between pyroclast textures and those obtained via decompression experiments in the laboratory indicates that supersaturation pressures and decompression rates required for homogeneous nucleation are unrealistically high for natural magmas i review the arguments for and against homogenous nucleation and defend the alternate view that heterogeneous nucleation may dominate in all magma types including rhyolites in order to solve this central debate our focus needs to be shifted towards understanding the pre decompression phase equilibria and textural characteristics of magnetite in addition to the state of the melt structure

magma dynamics at mid ocean ridges by noble gas kinetic fractionation assessment of magmatic ascent rates abstract despite its impact in understanding oceanic crust formation and eruptive styles of related volcanism magma dynamics at mid ocean ridges are poorly known here we propose a new method to assess ascent rates of mid ocean ridge basalt morb magmas as well as their pre and sin eruptive dynamics it is based on the idea that a rising magma can reach a variable degree of both co2 supersaturation in melt and kinetic fractionation among noble gases in vesicles in relation to its ascent rate through the crust to quantify the relationship we have used a model of multicomponent bubble growth in morb melts developed by extending the single component model of proussevitch and sahagian a a proussevitch d l sahagian dynamics and energetics of bubble growth in magmas analytical formulation and numerical modeling j geophys res 103 1998 18223 18251 to co2 he ar gas mixtures after proper parameterization we have applied it to published suites of data having the required features glasses from pito seamount and mid atlantic ridges our results highlight that the investigated morb magmas display very different ranges of ascent rates slow rises of popping rock forming magmas that cross the crust 0 01 0 5 m s slightly faster rates of energetic effusions 0 1 1 m s up to rates of 1 10 m s which fall on the edge between lava effusion and hawaiian activity inside a single plumbing system very dissimilar magma dynamics highlight the large differences in compressive stress of the oceanic crust on a small scale constraints on how the systems of ridges work as well as the characteristics of the magmatic source can also be obtained our model shows how measurements of both the dissolved gas concentration in melt and the volatile composition of vesicles in the same sample are crucial in recognizing the kinetic effects and definitively assessing magma dynamics an effort should be made to correctly set the studied samples in the sequence of volcanic submarine deposits where they are collected enhanced knowledge of a number of physical properties of gas bearing mor magmas is also required mainly noble gas diffusivities to describe multicomponent bubble growth at a higher confidence level

a combined u th he and cosmogenic 3he record of landscape armoring by biogeochemical iron cycling u th he geochronology and cosmogenic 3he in iron oxides reveal mineral precipitation ages as old as 55 ma and exposure ages greater than 5 ma for canga cemented plateaus in the quadrilatero ferrifero brazil showing that lateritic profiles overlying banded iron formation bif landscapes in tropical regions have a long history of surface exposure the long term erosion history obtained from cosmogenic 3he on bif plateaus confirms that relic surfaces persist in the landscape for millions of years combined 3he and u th he dating shows that cangas are preferentially goethite cemented by biogeochemical reactions in the subsurface importantly pebbles of hematite magnetite in colluvia or shallow creeks draining the canga cemented plateaus record a much longer exposure history than in situ canga blocks showing that even older duricrusts now eroded once blanketed these plateaus physically stable but biogeochemically dynamic cangas armor the landscape by pervasive and recurrent iron cycling and cementation slowing down the delivery of weathered bif or friable hematite magnetite ore to erosion

decompression experiments identify kinetic controls on explosive silicic eruptions 1 eruption intensity is largely controlled by decompression induced release of water rich gas dissolved in magma it is not simply the amount of gas that dictates how forcefully magma is propelled upwards during an eruption but also the rate of degassing which is partly a function of the supersaturation pressure pcritical triggering gas bubble nucleation high temperature and pressure decompression experiments using rhyolite and dacite melt reveal compositionally dependent differences in the pcritical of degassing that may explain why rhyolites have fueled some of the most explosive eruptions on record

the impact of dissolved co2 on bubble nucleation in water poor rhyolite melts abstract volcanic eruptions of h 2 o poor rhyolite are enigmas because gas bubbles are needed to drive eruptions but experimental evidence suggests that bubbles cannot nucleate because there is insufficient h 2 o to overcome the free energy associated with the formation of the bubble melt interface in this study we examine whether co 2 in the melt can solve that enigma possibly by nucleating co 2 enriched bubbles that are then used by h 2 o or lowering the surficial free energy we use experimental decompressions to examine the affect of dissolved co 2 at conditions both where h 2 o alone can nucleate bubbles and where h 2 o activity is too poor to nucleate bubbles experiments using co 2 free hydrated rhyolite melt at 875 900 c conditions find that bubbles nucleate when h 2 o 4 34 4 74 wt once h 2 o supersaturates c the ratio of the initial h 2 o content to the expected amount at equilibrium at low pressure by 2 3 rhyolite melts with less h 2 o do not nucleate bubbles even when c 3 equally hydrated rhyolite melt that also contains 500 1000 ppm co 2 nucleates bubbles similarly in terms of the critical c except that co 2 bearing rhyolite must decompress more to reach a given c that difference is just a result of the change in h 2 o solubility in the presence co 2 it thus appears that bubble nucleation in rhyolite melt is dictated by c and does not change in the presence of co 2 importantly molten rhyolite that is too h 2 o poor to nucleate bubbles will not nucleate them if they are co 2 rich the vesiculation of such melts requires that bubbles nucleate heterogeneously

high resolution analysis of trace elements in crustose coralline algae from the north atlantic and north pacific by laser ablation icp ms we have investigated the trace elemental composition in the skeleta of two specimens of attached living coralline algae of the species clathromorphum compactum from the north atlantic newfoundland and clathromorphum nereostratum from the north pacific bering sea region amchitka island aleutians samples were analyzed using laser ablation inductively coupled plasma mass spectrometry la icp ms yielding for the first time continuous individual trace elemental records of up to 69 years in length the resulting algal mg ca sr ca u ca and ba ca ratios are reproducible within individual sample specimens algal mg ca ratios were additionally validated by electron microprobe analyses amchitka sample algal sr ca u ca and ba ca ratios were compared to algal mg ca ratios which previously have been shown to reliably record sea surface temperature sst ratios of sr ca from both clathromorphum species show a strong positive correlation to temperature dependent mg ca ratios implying that seawater temperature plays an important role in the incorporation of sr into algal calcite linear sr ca sst regressions have provided positive but weaker relationships as compared to mg ca sst relationships both algal mg ca and sr ca display clear seasonal cycles inverse correlations were found between algal mg ca and u ca ba ca and correlations to sst are weaker than between mg ca sr ca and sst this suggests that the incorporation of u and ba is influenced by other factors aside from temperature

wetting behavior of partial melts during crustal anatexis the distribution of hydrous silicic melts in polycrystalline aggregates of quartz the equilibrium distribution of hydrous silicic melts in polycrystalline aggregates of quartz was characterized in a series of partial melting and melt distribution experiments in the systems quartz albite orthoclase h2o and quartz anorthite h2o at 650 to 1000 mpa and 800 to 900 c near equilibrium textures in these experiments are characterized by very low quartz quartz melt wetting angles and by a substantial number of thin melt films along grain boundaries wetting angles in the h2o saturated experiments are as follows 18 at 800 c 1000 mpa and 12 at 900 c 1000 mpa in the granitic system 18 at 850 c 650 mpa 15 at 900 c 650 mpa and 15 at 900 c 1000 mpa in the quartzanorthite system in the granitic system at 900 c 1000 mpa a decrease of h2o content in melt from 17 wt at saturation to 6 wt results in a slight increase of wetting angle from 12 to 16 these low wetting angles and the observation that many grain boundaries are wetted by melt films indicate that the ratio of quartz quartz to quartz melt interfacial energies ss s1 is high 2 secondary electron imaging of fracture surfaces of melt poor samples provided a three dimensional insight into the geometry of melt at low melt fraction melt forms an interconnected network of channels along grain edges as predicted for isotropic systems with wetting angles below 60 this high permeability geometry suggests that the segregation of granitic melts is not as sluggish as previously anticipated simple compaction calculations for a permeability range of 10 12 to 10 9 m2 indicate that segregation may operate at low to moderate melt fractions below 30 vol within relatively short time scales i e 105 to 106 years quartzmelt textures show significant deviations from the equilibrium geometries predicted for isotropic partially molten systems the most consistent deviation is the pervasive development of crystallographically controlled planar faces of quartz these faces provide definitive evidence for non isotropic quartz melt surface energy for most silicates other than quartz the grain scale distribution of partial melts deviates even more significantly from equilibrium distributions in isotropic systems accordingly in order to describe adequately melt distributions in most natural source regions the equilibrium model should be modified to account for anisotropy of solid liquid interfacial energy

experimental constraints on degassing of magma isothermal bubble growth during continuous decompression from high pressure numerical models predict that rapid ascent of hydrous magma can lead to supersaturation of dissolved volatile constituents possibly leading to explosive eruption we have performed controlled decompression experiments to investigate the ascent rates required to maintain bubble melt equilibrium high silica rhyolitic melts were saturated with water at 200 mpa and 825 c decompressed to lower pressures at constant rates of 0 025 0 25 0 5 and 1 0 mpa s 1 and then rapidly quenched isobarically other samples were saturated with water over the pressure range investigated to determine equilibrium water solubility in order to quantify degassing efficiency during decompression at a decompression rate of 0 025 mpa s 1 melt vapor equilibrium was maintained over the entire pressure range examined 200 to 17 5 mpa a single bubble nucleation event occurred in response to decompression and quenched bubble sizes can be modeled by a equilibrium bubble growth model that takes into account the number density of bubbles at decompression rates of 0 25 0 5 and 1 0 mpa s 1 rhyolitic melts could not degas in equilibrium when pressure decreased from 200 mpa to 140 mpa and water supersaturation p in the melt reached up to 60 mpa with higher values at faster decompression rates further pressure release resulted in near equilibrium degassing and p dropped significantly in each case p decreased when bubbles exceeded 10 vol a single heterogeneous bubble nucleation event occurred in each experiment when p 20 mpa no other bubbles nucleated despite p reaching 60 mpa which is probably too low to trigger homogeneous nucleation compared to estimates for magma decompression rates during lava dome eruptions our results indicate that magmas can degas efficiently throughout their ascent to the surface in explosive eruptions decompression rates may exceed those of this study and hence melts may become supersaturated with water such fast decompressions are expected however only when magma is highly vesicular which would aid approach to equilibrium degassing

poisson magnetization to density ratio and magnetization inclination properties of banded iron formations of the carajas mineral province from processing airborne gravity and magnetic data

diverse patterns of ascent degassing and eruption of rhyolite magma during the 1 8 ka taupo eruption new zealand evidence from clast vesicularity k lauea hawaii like vesuvius and etna is a frequently active volcano associated with a national park which is a focus for volcano tourism two contrasting summit eruptions at k lauea in 2008 2009 and 1959 emphasize how even small eruptions on populous volcanoes have significant impact on both hawaii volcanoes national park hvnp and the surrounding communities the effects are typically more indirect and social than direct physical but have significant fiscal repercussions the former include both positive benefits and negative impacts as an illustration direct consequences of the 1959 eruption were the rerouting of the major park access road and destruction of a summer camp but benefits included an unprecedented surge in visitor numbers and construction of nature trails that are now the most visited asset in the park both positive and negative impacts have increased in intensity with time due to growth in the resident population and visitor numbers for example the entire park has been evacuated twice during the ongoing 2008 2009 eruption

insights into volcanic conduit flow from an open source numerical model 1 numerical models that calculate the fluid dynamics of explosive volcanic eruptions have been used with increasing frequency to understand volcanic processes and evaluate volcanic hazards yet those who develop such models rarely make them publicly available so that they can be verified used and possibly improved by other scientists in this paper i present a visual interactive open source numerical model that calculates steady state flow of magma and gas in vertical eruptive conduits and contains user friendly utilities for quickly determining physical thermodynamic and transport properties of silicate melts h2o gases and melt gas crystal mixtures the model represents an advance over previously published conduit models by incorporating a non arrhenian viscosity relation for hydrous silicate melts a relation between viscosity and volume fraction of gas that depends on capillary number and adiabatic temperature changes in the mixture using established thermodynamic relations for melts and h2o gas respectively volcanologists who have not had access to conduit models have frequently approximated conduit flow using an analytical equation for incompressible laminar newtonian pipe flow which predicts that the mass flux is proportional to the fourth power of conduit radius and inversely proportional to mixture viscosity the model presented here which is not much more difficult to use than a back of the envelope calculation shows that the pipe flow approximation significantly overestimates the sensitivity of mass flux to both conduit radius and mixture viscosity results from the model also show that viscous heating in the lower conduit which is not considered in most other models may increase the mass flux of large silicic eruptions by several percent and decrease the viscosity of the mixture at the fragmentation depth by a few tens of percent

comparison of climate signals obtained from encrusting and free living rhodolith coralline algae abstract coralline algae have been used for sclerochronological studies throughout the last decade these studies have focused on two different growth morphologies of the photosynthetic coralline algae massive crusts forming small buildups on hard substrate and free living branching algal nodules known as rhodoliths the latter are generally found on soft substrate where they are frequently overturned by water movement and bottom feeding organisms leaving one side of the rhodolith partially buried in the sediment at any given time here we test whether either of these growth morphologies is more suitable for proxy reconstructions by comparing mg ca ratios a temperature proxy in multiple replicates of rhodoliths of lithothamnion glaciale and in rhodoliths as well as encrusting specimens of clathromorphum compactum with both species being widespread throughout the temperate and arctic regions we have chosen two north atlantic localities at nuuk fjord greenland subarctic and off the southeastern coast of newfoundland canada temperate for this study two to three mg ca ratio transects spanning 18 years of growth were analysed on multiple specimens with encrusting morphologies and along different sides of rhodoliths using laser ablation inductively coupled mass spectrometry and compared to remotely sensed sea surface temperature sst data the length of the common time span used for comparison was limited by growth interruptions in rhodoliths furthermore our comparison is based on the assumption that rhodolith growth increments are annual an assumption that has recently been challenged by mesocosm studies monthly mg ca values from multiple transects within each individual were compared and in samples from nuuk fjord significant correlations were found in 4 of 4 encrusting c compactum 4 of 4 c compactum rhodoliths and 2 of 3 l glaciale rhodoliths in newfoundland significant correlations were found in 6 of 6 encrusting c compactum comparisons average r 0 61 p

bubble development in explosive silicic eruptions insights from pyroclast vesicularity textures from raoul volcano kermadec arc critical to understanding explosive eruptions is establishing how accurately representative pyroclasts are of processes during magma vesiculation and fragmentation here we present data on densities and vesicle size and number characteristics for representative pyroclasts from six silicic eruptions of contrasting size and style from raoul volcano kermadec arc we use these data to evaluate histories of bubble nucleation coalescence and growth in explosive eruptions and to provide comparisons with pumiceous dome carapace material density vesicularity distributions show a scarcity of pyroclasts with 65 75 vesicularity however pyroclasts closest to this vesicularity range have the highest bubble number density bnd values regardless of eruptive intensity or style clasts with vesicularities greater than this 65 75 pivotal vesicularity range have decreasing bnds with increasing vesicularities interpreted to reflect continuing bubble growth and coalescence clasts with vesicularities less than the pivotal range have bnds that decrease with decreasing vesicularity and preserve textures indicative of processes such as stalling and open system degassing prior to vesiculation in a microlite rich magma or vesiculation during slow ascent of degassing magma bubble size distributions bsds and bnds show variations consistent with 65 75 representing the vesicularity at which vesiculating magma is most likely to undergo fragmentation consistent with the closest packing of spheres we consider that the observed vesicularity range may reflect the development of permeability in the magma through shearing as it flows through the conduit these processes can act in concert with multiple nucleation events generating a situation of heterogeneous bubble populations that permit some regions of the magma to expand and bubbles to coalesce with other regions in which permeable networks are formed fragmentation preserves the range in vesicularity seen as well as any post fragmentation pre quenching expansion which may have occurred we demonstrate that differing density pyroclasts from a single eruption interval can have widely varying bnd values corresponding to the degree of bubble maturation that has occurred the modal density clasts the usual targets for vesicularity studies have likely undergone some degree of bubble maturation and are therefore may not be representative of the magma at the onset of fragmentation

airborne geophysical data leveling based on line to line correlations a new technique removes the leveling errors in airborne geophysical data based on an assumption that the data are continuous i e not renulled or recalibrated from line to line a single flight line is selected as a reference to level and tie all survey lines to this continuously varying datum the leveling errors are determined in a least squares sense from the reference line and the adjacent line to be leveled the technique markedly improves the quality of the unleveled raw data and works best if the reference line overlaps most of the line being leveled this method cannot distinguish a linear geologic feature in the direction of flight lines from a leveling error the technique initially was developed for airborne electromagnetic em data in cases where tie line leveling works poorly however it may also be used for airborne magnetic and other data in which case tie lines used in conventional leveling techniques are not needed

experimental constraints on permeable gas transport in crystalline silicic magmas the gas and fluid transport in magmas via permeable flow through interconnected bubble networks controls the rate of outgassing from magmas ascending in volcanic conduits and the fluid transport in the mushy boundary layer of magma reservoirs hence clarifying its mechanism and rate is crucial to understanding the explosivity of volcanic eruptions and the evolution and dynamics of a magma reservoir recent experimental studies have determined the gas permeabilities in crystal free rhyolite and basalt however no experimental study has investigated the effect of the crystal contents on the permeable gas transport in magmas in this study we performed decompression experiments for hydrous rhyolitic melts having crystallinities of 30 and 50 vol to examine the effect of crystals on the bubble microstructure and gas permeability during magma vesiculation size controlled 100 meshed corundum crystals were used as an analog of the phenocrysts in silicic magmas microstructural analyses using x ray ct showed that bubbles coalesce and their connectivity increases with a decrease in the final pressure after the decompression that is an increase in the vesicularity as long as the vesicularities of melt part in the crystal free basis melt vesicularity were similar no clear effect of the crystallinity on the degree of bubble coalescence and connectivity was observed at melt vesicularities 68 vol this result indicates that the permeable fluid transport through a deep volcanic conduit which has been proposed on the basis of the observations of volcanic gases and natural products is so slow that other processes like shear deformation or magma convection may be needed to explain the observations

improving the detection of shell alteration implications for sclerochronology abstract sclerochronology makes use of fossil shell archives to establish records allowing for investigation of high resolution environmental dynamics nevertheless this potential can often not be fully exploited due to the interplay between paleoenvironmental variability vital effects and the potential diagenetic modification of skeletal materials which often results in highly complex records a novel dynamic approach aiming to separate pristine from altered shell material for paleoclimate and paleoenvironmental reconstructions is proposed seventeen fossil bivalve shells requieniid rudists pectinids and chondrodonts from two neighbouring lower cretaceous albian shallow water sections lusitanian basin western portugal were analysed for their major and trace elemental compositions using high resolution quantitative xrf line scans their complex records were subject to a novel statistical analysis protocol which tested mono and multi species datasets as well as comparing shells from both locations characteristic elemental associations reveal the differential impact of early and late diagenetic alteration processes the incorporation of elements associated with detrital contribution fe si al is attributed to syn depositional bioerosion shell boring in clear contrast shell portions showing a strong correlation between fe and mn are indicative of later diagenetic alteration the influence of each process is different at each site revealing local differential alteration pathways mono specific comparisons provides identical geochemical responses suggesting that intra specific differences do not control the observed elemental patterns in contrast inter species tests rendered a clear separation in the way elements are incorporated in the shells of pectinids and requieniids e g as evidenced by differences in mg or sr content such differences can be linked to differential biomineralization pathways easily detected by the applied method we present a new dynamic method for distinguishing pristine from altered shell material not relying on arbitrary diagenetic thresholds for trace element content by clearly identifying shell alteration pathways syn to post depositional processes are recognized a progressive cleaning of the elemental dataset allows paleoenvironmental studies to be based on the most pristine data contributing to unravelling the complex interplay between climate environmental dynamics and their impact on biomineralization processes and sclerochronological archives

coralline algal mg o bond strength as a marine pco2 proxy past ocean acidification recorded in the geological record facilitates the understanding of rates and influences of contemporary pco 2 enrichment most ph reconstructions are made using boron however there is some uncertainty associated with vital effects and isotopic fractionation here we present a new structural proxy for carbonate chemistry mg o bond strength in coralline algae coralline algae were incubated in control 380 matm pco 2 moderate 750 matm pco 2 and high 1000 matm pco 2 acidification conditions for 24 months raman spectroscopy was used to determine skeletal mg o bond strength there was a positive linear relationship between pco 2 concentration and bond strength mediated by positional disorder in the calcite lattice when accounting for seasonal temperature the structural preservation of the carbonate chemistry system in coralline algal high mg calcite represents an alternative approach to reconstructing marine carbonate chemistry significantly it also provides an important mechanism for reconstructing historic atmospheric co 2 concentrations