the uwekahuna ash member of the puna basalt product of violent phreatomagmatic eruptions at kilauea volcano hawaii between 2800 and 210014c years ago abstract kilauea volcano s reputation for relatively gentle effusive eruptions belies a violent geologic past including several large phreatic and phreatomagmatic eruptions that are recorded by holocene pyroclastic deposits which mantle kilauea s summit area and the southeast flank of adjacent mauna loa volcano the most widespread of these deposits whose original distribution can be reconstructed is the uwekahuna ash member of the puna basalt a basaltic surge and fall deposit emplaced during two or more eruptive episodes separated by a few decades to several centuries the first episode occurred between 2770 70 and 2265 50 14 c yr ago it included two major pyroclastic surges each preceded by unusually vigorous lava fountaining from a vent near the volcano s summit before the second eruptive episode 2110 120 14 c yr ago plants had re colonized the rainforest environment northeast of the summit and at least two lava flows from mauna loa had buried parts of the first episode deposits the second episode also began with vigorous lava fountaining followed by widespread lithic ashfall a third major surge and finally a fourth fountaining event before the final pumice deposit could be significantly reworked it was partly buried by picritic basalt flows that are unusual in kilauea s summit area in proximal areas the uwekahuna ash member is more than 1 m thick locally 5 m and includes lithic blocks up to 0 8 m in diameter coarse primarily lithic debris was deposited around the vent by laterally expanding surges fallout deposits accumulated preferentially to the northeast under the influence of high altitude counter tradewinds the area devastated by surges and originally buried by at least 15 cm of the uwekahuna was about 420 km 2 the bulk volume of the deposits was approximately 0 3 km 3 including less than 0 1 km 3 of juvenile material juvenile constituents are olivine tholeiitic basalts similar in major element composition to typical kilauea summit lava flows but variations in both major elements and trace elements suggest that the eruptions tapped more than a single uniform source region we infer that the eruptions which produced the uwekahuna were driven by water interacting with a fluctuating magma column magma withdrawal episodes may have been accompanied by large volume submarine effusive eruptions and by summit collapse the volume extent and character of the uwekahuna deposits underscore the hazards posed by relatively infrequent but potentially devastating explosive eruptions at kilauea as well as at other basaltic volcanoes

stratigraphy of the pleistocene phonolitic cao grande formation on santo antao cape verde highlights two new phonolitic tephra units complementing the two previously known first radiometric ages of the cgf contemporaneously evolution of the cgf and the tope de coroa marine correlations improve tephra volume estimations for cg i and ii abstract the cao grande formation cgf on the western plateau of santo antao island is part of the younger volcanic sequence that originated from both basanitic and nephelinitic magmatic suites respectively called cova and coroa suites based on our detailed revised stratigraphy of the cgf including two yet unknown tephra units we can show that both suites produced multiple highly differentiated eruptions over a contemporaneous period correlations of cgf tephras with marine ash layers provide distal dispersal data for cao grande i cg i and also identify two highly explosive phonolitic eruptions that pre date the cgf tephra deposits known on land within the cgf the lowermost 220 7 ka old unit canudo tephra ct cova suite comprises phonolitic fall deposits and ignimbrites it is partly eroded and overlain by debris flow deposits marking a hiatus in highly differentiated eruptions the phonolitic cg i tephra coroa suite consists of an initial major plinian fall deposit and associated ignimbrite and terminal surge deposits this is immediately overlain by the phonolitic to phono tephritic cao grande ii cg ii cova suite a complex succession of numerous fallout layers and density current deposits cg i and cg ii have radiometric ages of 106 3 ka and 107 15 ka respectively that are identical within their error limits the youngest cgf unit the furninha tephra ft coroa suite consists of three foidic phonolitic fall deposits interbedded with proximal scoria deposits from a different vent the phonolitic eruptions switched to and fro between both magmatic suites in each case with a stronger first followed by a weaker second eruption each eruption evolved from stable to unstable eruption columns during their terminal phases both magma systems also leaked evolved dome forming lavas next to the tephras distal ashes increase the cg i tephra volume to 10 km3 about twice the previously published estimate the tephra volume of cg ii is 3 km3 ct and ft are too poorly exposed for volume estimation the characteristics of the cgf tephra units outline hazard conditions that may be expected from future evolved explosive eruptions on the western plateau of santo antao

ice record of a large eruption of deception island volcano antarctica in the xviith century a well marked volcanic ash layer was found at 145 9 m depth in a 154 3 m ice core recovered in 1981 on james ross island antarctic peninsula ash composition analysis indicates that we are dealing with an eruption of the deception island volcano located some 200 km northwestward from james ross island regional lake sediments seem also to have recorded the eruption its date some 350 years ago has been determined precisely by comparison with a well dated south pole station ice core the strength and regional to global impact of the event are discussed it is concluded it was most probably the largest eruption of this volcano over the studied time period this exceptional layer was used to adjust the dating of the core

ignimbrites of the roque nublo group gran canaria canary islands non welded lithic rich ignimbrites hereintermed the roque nublo ignimbrites are the most distinctive deposits of the pliocene roque nublo group which forms the products of second magmatic cycle on gran canaria they are very heterogeneous with 35 55 volume lithic fragments 15 30 mildly vesiculated pumice 5 7 crystals and 20 30 ash matrix the vitric components pumice fragments and ash matrix are largely altered and transformed into zeolites and subordinate smectites the roque nublo ignimbrites originated from hydrovolcanic eruptions that caused rapid and significant erosion of vents thus incorporating a high proportion of lithic clasts into the eruption columns these columns rapidly became too dense to be sustained as vertical eruption columns and were transformed into tephra fountains which fed high density pyroclastic flows the deposits from these flows were mainly confined to palaeovalleys and topographic depressions in distal areas close to the coast line where these palaeovalleys widened most of the pyroclastic flows expanded laterally and formed numerous thin flow units the combined effect of the magma water interaction and the high content of lithic fragments is sufficient to explain the characteristic low emplacement temperature of the roque nublo ignimbrites this fact also explains the transition from pyroclastic flows into lahar deposits observed in distal facies of the roque nublo ignimbrites the existence of hydrovolcanic eruptions generating high density pyroclastic flows unable to efficiently separate the water vapour from the vitric components during transport also accounts for the intense zeolitic alteration in these deposits

fogo volcano cape verde islands seismicity derived constraints on the mechanism of the 1995 eruption seismic data recorded in the vicinity of the active vent of the 1995 fogo eruption global volcanism network bulletin 1995 20 3 2 4 is used to constrain the associated stress field and deformation using the frequency content of the seismograms to distinguish between brittle fracture of cold host rock and deformation in the vicinity of the intruding magma a sub vertical dyke with 060 strike is identified as the feeder of the eruption and delineated down to a depth of about 4 km the local stress field during the eruption is estimated from composite focal mechanisms besides the expected 3 direction normal to the dyke a group of focal solutions point to a stress field with nearly dyke parallel 3 which is interpreted as a re adjustment of the edifice following the eruption maybe partially controlled by gravity this effect may have increased the instability of the steep eastern flank of the island since the deformation detected during the magma drainback is compatible with predominantly dip slip motion on east dipping surfaces

a multi isotope b sr o h and c and age dating 3h 3he and 14c study of groundwater from salinas valley california hydrochemistry dynamics and contamination processes 1 the chemical and isotope 11b 10b 87sr 86sr 18o 16o 2h h 13c 12c 14c and 3he 3h compositions of groundwater from the upper aquifer system of the salinas valley in coastal central california were investigated in order to delineate the origin and processes of groundwater contamination in this complex system the salinas valley has a relatively deep confined 400 foot aquifer overlain by a 180 foot aquifer and a shallower perched aquifer all made up of alluvial sand gravel and clay deposits groundwater from the aquifers have different 14c ages fossil 14c 21 3 percent modern carbon pmc for the 400 foot aquifer and modern 14c 72 2 98 2 pmc for the 180 foot aquifer fresh groundwater in all aquifers is recharged naturally and artificially through the salinas river the two modes of recharge can be distinguished chemically we identified several different saline components with distinguishable chemical and isotopic fingerprints 1 saltwater intrusion in the northern basin has c1 concentrations up to 1700 mg l a na cl ratio less than seawater a marine br cl ratio a ca cl ratio greater than seawater 11b between 17 and 38 and 87sr 86sr between 0 7088 and 0 7096 excess dissolved ca relative to the expected concentration for simple dilution of seawater correlates with 87sr 86sr ratios suggesting base exchange reaction with clay materials 2 agriculture return flow is high in no3 and so4 with a 87sr 86sr 0 7082 11b 19 and 13c between 23 and 17 the 3h 3he ages 5 17 years and 14c data suggest vertical infiltration rates of irrigation water of 3 10 m yr 3 nonmarine saline water in the southern part of the valley has high total dissolved solids up to 3800 mg l high so4 na cl ratio 1 11b between 24 and 30 and 87sr 86sr 0 70852 this groundwater may have acquired its geochemical signature from leaching of sedimentary rocks associated with the coast range marine deposits of mesozoic to early cenozoic age the combination of different geochemical and isotopic fingerprints enables us to delineate the impact of salt sources in different areas of the valley and to reconstruct the origin of the so4 enriched no3 depleted saline plume that is located west of the city of salinas we suggest that the latter is derived from a mixture of different natural saline waters rather than from anthropogenic contamination

evidence for winter spring denitrification of the stratosphere in the nitrate record of antarctic firn cores a firn core from within the polar vortex in the weddell sea sector of antarctica shows nitrate peaks that occur in the spring or early summer they are far less prominent in two other cores from sites that are further north although other data are needed circumstantial evidence suggests that the peak may be due to sedimentation of polar stratospheric clouds from the stratosphere during winter and spring no change in the form of the peak is seen over the last three decades it may be possible to observe past stratospheric conditions over longer time scales from ice cores but other sources may obliterate the signal in ice from the glacial periods 34 refs 5 figs

glaciochemistry of polar ice cores a review human activities have already modified the chemical composition of the natural atmosphere even in very remote regions of the world the study of chemical parameters stored in solid precipitation and accumulated on polar ice sheets over the last several hundred thousand years provides a unique tool for obtaining information on the composition of the preindustrial atmosphere and its natural variability over the past this paper deals with the chemistry of polar ice focused on the soluble mineral na nh4 k ca mg h f cl no3 so4 and h2o2 and organic methanesulfonate ch3so3 formate hcoo acetate ch3coo and formaldehyde hcho species and their interpretation in terms of past atmospheric composition aerosols and water soluble gaseous species we discuss ice core dating the difficulties connected with trace measurements and the significance of the ionic composition of snow we examine temporal from the last decades back to the last climatic cycle and spatial including examples from coastal as well as central areas of greenland and antarctica variations in the ionic budget of the precipitation and evaluate ice core studies in terms of the chemical composition of our past atmosphere we review 1 how greenland and antarctic ice cores that span the last few centuries have provided information on the impact of human activities and 2 how the chemistry of deep ice cores provides information on various past natural phenomena such as climatic variations glacial interglacial changes el nino volcanic eruptions and large boreal forest fires

hydrothermal alteration of hemi pelagic sediments experimental evaluation of geochemical processes in shallow subduction zones abstract laboratory hydrothermal experiments provide unique information regarding the fate of volatile and or incompatibles e g b li and as during oceanic crust subduction examination of chemical redistribution between the subducted slab mantle wedge arc volcanics and overlying ocean water during subduction is critical to gain further insight into arc volcanism and chemical oceanic budgets for instance efficient mobilization of b at shallow depths may be a key aspect of its oceanic budget and can help to explain the systematics of b 11b and b 10be in arc lavas fluid rock interactions at elevated temperatures and pressures in accretionary prisms were studied using a rocking autoclave hydrothermal apparatus to monitor sediment porewater interaction over the range of 25 to 350 c at 800 bars clay rich hemi pelagic sediments from the decollement zone of ocean drilling program site 808 nankai trough were reacted with nacl cacl2 solutions at water rock ratios of 3 5 to 1 5 w w to mimic alteration processes in the shallow subduction zone fluids were extracted at 25 50 c intervals and were analyzed for major and trace chemical constituents the fluid chemistry changed significantly during the course of these experiments but there was generally only minor modification of the solid phase only b li as br and pb are significantly depleted during the heating cycle dissolved na mg and so4 decreased sharply and nh4 sio2 k b and li increased at t 300 c calcium drops gradually at low temperatures but concentrations rise sharply at t 300 c decomposition of organic matter so42 depletion and mg fixation dominate at low temperatures however albitization of calcic plagioclase leads to marked na depletions and ca enrichments at t 300 c dissolved sio2 remained below saturation with respect to quartz and amorphous silica throughout the entire experiment b and li mobilization with large isotopic fractionations occurred at low temperature exchangeable b 11b 15 is completely leached before reaching 150 c substantial o2 exchange between fluids and the solid phase occurred at t 200 c in the spiked experiment where 18o varies more than 100 in the fluids during retrograde cooling dissolved mg so4 ca si k and sr are released as a result of carbonate or anhydrite dissolution and marked b re adsorption occurred at temperatures below 60 c

stable isotope air temperature relationships in ice cores from dolleman island and the palmer land plateau antarctic peninsula whilst stable isotope analysis of ice cores yields the best quantitative evidence for past climate there remains considerable uncertainty about the detailed relationship between the isotopic composition and air temperature analysis of two ice cores from the antarctic peninsula a 47 2 m core from the palmer land plateau 74 oi s 70 38 w and a 32 m core from dolleman island 70035 2 s 60055 5 w has shown that an oxygen isotope temperature relationship exists at a resolution of inter annual variations during the period 1938 86 all the major regional temperature anomalies known from climatic records at several stations are visible in the isotope profiles including the overall temperature increase between 1960 and 1980 an isotope temperature gradient of 0 5 o 6 c is indicated for the climatic interpretation of isotopic fluctu

temporal variations in marine chemical concentrations in coastal areas of eastern antarctica and associated climatic causes abstract snow pit and a firn core samples obtained from coastal areas in the eastern lambert basin of eastern antarctica enabled us to investigate the temporal variations in soluble marine ion concentrations and the possible mechanisms influencing their variations the concentrations of seasonal sea salt ions na cl and mg2 at the coastal site lh406 were maximal in the spring and minimal in the summer broad maximal values also occurred in the winter and minimal values occurred in the summer in the interior site zg050 the sea ice extent sie in the indian ocean sector of eastern antarctica followed similar temporal distribution patterns two sulfur compounds so42 and msa experienced seasonal variations similar to those observed for sea salt ions at the lh406 site however distinct variations were reported at the zg050 site the variations in nssso42 levels in the zg050 snow pit that occurred over a 14 year period were positively correlated with variations in sie however this relationship was different from that at the western lambert basin the change in direction of the supplementary prevailing wind during 1994 1995 produced a significant change in the concentrations of marine ions a change in the source region may be the primary cause of this difference

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

glaciological studies at siple station antarctica potential ice core paleoclimatic record the quality and utility of the records of oxygen isotopic abundances dust concentrations and anionic concentrations preserved in the ice at siple station 75 55 s 84 15 w are assessed from four shallow 20 m cores the combination of high accumulation 0 56 m a 1 w e and low mean annual temperature 24 c preserves the prominent seasonal variations in 18 which are very spatially coherent sulfate concentrations vary seasonally and in conjunction with 18 will allow accurate dating of deeper cores from siple station the concentrations of insoluble dust are the lowest measured in antarctica making siple station an excellent location to examine large increases in atmospheric tubidity the seasonal variations and annual fluxes of the anions are examined for the last two decades ad 1966 85 with regard to probable sources an unusually high sulfate flux in 1976 may reflect the february 1975 eruption of mount ngauruhoe new zealand no annual signal in nitrate concentration is confirmed and no unusually high nitrate fluxes support the suggestion of nitrate production by large solar flares however nitrate flux is higher for the latter half of the 1970s and early 1980s possibly reflecting the recent loss of stratospheric ozone finally comparison of the 18 o record with available surface temperature data ad 1957 85 reveals that multi year trends along the western coast of the antarctic peninsula are recorded at siple more importantly comparison with areally weighted temperature reconstructions suggests that the 18 record may reflect larger scale persistent trends in the high southern latitudes the strong spatial coherence of the preserved records the potential for accurate dating and possible relevance to larger scale processes make siple station an excellent site for paleoenvironmental reconstruction from ice cores

the boron isotope systematics of the yellowstone national park wyoming hydrothermal system a reconnaissance abstract boron concentrations and isotope compositions have been measured in fourteen hot spring waters two drill hole waters an unaltered rhyolite flow and hydrothermally altered rhyolite from the geothermal system in yellowstone national park wyoming the samples are representative of the major thermal areas within the park and span the range of fluid types for the fluids the b concentrations range from 0 043 2 69 mm kg and the 11 b values range from 9 3 to 4 4 there is no relationship between the dissolved b concentrations or isotope compositions with the concentration of any major element other than cl or physical property each basin is characterized by a restricted range in b cl ratios and 11 b values hot spring waters from the morris basin upper geyser basin calcite springs and clearwater have 11 b values close to that of unaltered rhyolite 5 2 and are interpreted to have derived their b from this source waters from mammoth hot springs sheepeater and rainbow springs have lower 11 b values close to 8 these lower values may reflect leaching of b from sedimentary rocks outside the yellowstone caldera but they are similar to the 11 b value of hydrothermally altered rhyolite 9 7 hence the light boron isotope compositions recorded in these hot spring waters may reflect leaching of previously deposited hydrothermal minerals cooler springs along the yellowstone river just outside the park boundary have lower b concentrations and higher 11 b values that may reflect mixing with shallow meteoric water

boron isotopic compositions of brine sediments and source water in da qaidam lake qinghai china abstract the isotopic compositions of boron in da qaidam lake quinghai have been determined by using the technique of thermal ionization mass spectrometry of cesium tetraborate the brines are enriched in 11b with an average 11b of 5 49 2 34 compared with those of lake sediments and boron minerals produced by the lake the apparent isotopic fractionation factors between brine and lake sediments as well as boron minerals are 0 988 0 001 and 0 986 0 001 respectively source water 11b values range from 11 72 to 16 69 depending on their origin

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

eruptive mechanisms of the puig de la garrinada volcano olot garrotxa volcanic field northeastern spain a methodological study based on proximal pyroclastic deposits abstract an ephemeral and proximal outcrop at the quaternary basaltic puig de la garrinada cinder volcano was studied in order to decipher eruptive mechanism variations in the course of a single eruption once the volcanostratigraphy was established and recorded by photographs a very detailed sampling of underlying lava flows bombs and a large number of fine sized lapilli and ash beds was carried out an ad hoc description card was elaborated for study under stereo microscope in order to identify the different types of materials that form the volcanic cone ten material types were recognised sedimentary accidental clasts massive lava accidental clasts bombs xenoliths xenocrysts and phenocrysts oxidised scoria scoria with oxidised film fluidal pyroclasts non fluidal pyroclasts and coatings subsequent studies under sem eds and basic chemical characterization of the samples whole rock xrf for major and trace elements and empa were conducted all these studies make possible the reconstruction of the eruptive history of the la garrinada volcano which shows a transition from initial strombolian activity to gradually incorporated phreatomagmatic activity this permits the calculation of magma eruption rates magma column oscillations and aquifer interactions with magma column since our general conclusions agree well with the discrimination of eruptive episodes obtained from the stereo microscope description card macroscopic volcanostratigraphy and chemical results it is proposed that a similar study protocol quick volcanostratigraphy logging photographic record detailed sampling description following this card might be useful in the reconstruction of eruptive activity of other cinder cones in the garrotxa region and elsewhere and therefore can provide a good and quick methodological tool especially when rapid field description and sampling is required ephemeral outcrops risky sampling during active eruptive episodes etc moreover the conducted sampling allows for subsequent studies on the same set of pyroclasts

boron and oxygen isotope systematics for a complete section of oceanic crustal rocks in the oman ophiolite abstract boron content and the isotopic composition of boron and oxygen were determined for a complete 5 3 km thick oceanic crust in the wadi fizh area of the oman ophiolite a fragment of cretaceous oceanic lithosphere obducted onto the arabian shield the depth profiles of the 18 o values and the secondary mineral assemblages are consistent with successively higher temperature hydrothermal alterations occurring with increasing depth the upper pillow basalts underwent low temperature alteration 18 o 10 the lower pillow basalts and upper sheeted dikes 18 o 6 to 10 the lowermost sheeted dike complex and upper gabbros underwent high temperature alteration at 300 450 c 18 o 450 c 18 o 18 o values compared with the adjacent rocks suggesting the production of 18 o enriched melt the boron content of the rocks in the oceanic crust decreases in both abundance and range with increasing stratigraphic depth 1 4 29 1 g g in pillow lava 7 9 g g on average 1 5 11 6 g g in sheeted dike complex 5 3 g g on average 1 6 5 0 g g in dolerite dike in gabbro 2 9 g g on average 0 25 3 8 g g in gabbro 1 3 g g on average considering an original boron content of 0 72 0 47 g g for basalt and 0 06 0 09 g g for gabbro boron from seawater was incorporated into the rocks through hydrothermal alteration even at temperatures higher than 300 c the 11 b values systematically increase with stratigraphic depth 1 1 to 11 9 in pillow lava 5 5 on average 1 1 to 17 5 in sheeted dike complex 6 3 on average 8 3 to 18 6 in dolerite dike in gabbro 13 9 on average 7 3 to 17 7 in gabbro 12 0 on average the whole rock 11 b values negatively correlate with the 18 o values suggesting that the 11 b values of altered rocks are essentially controlled by isotopic equilibrium with hydrothermal fluids and the increase in the 11 b values is caused by a decrease in the rock fluid boron isotopic fractionation factor with increasing alteration temperatures the 11 b values estimated for hydrothermal fluids from rocks completely altered at 300 450 c range from 28 to 33 values indistinguishable from those of vent fluids observed at modern mid ocean ridges the boron content of the bulk oceanic crust of the oman ophiolite is estimated to be 3 6 g g and the 11 b value is estimated at 7 9 in contrast to previous views the hydrothermally altered gabbro section is a large boron sink accounting for 30 of the total boron in the oceanic crust with a high 11 b value of 13 this boron enriched high 11 b lower oceanic crust may impact estimates of the 11 b value of fluid liberated from the subducted oceanic slab which is believed to largely control the 11 b value of arc magma generated in the mantle wedge

a reinterpretation of sea salt records in greenland and antarctic ice cores it has recently been shown that much sea salt aerosol around the coast of antarctica is generated not from open water but from the surface of newly formed sea ice previous interpretations of ice core records have disregarded the sea ice surface as a source of sea salt the majority of sea salt aerosol at halley research station originates from frost flowers rather than open water and the seasonal cycle of sea salt in aerosol at halley appears to be controlled by ice production in the weddell sea as well as variations in wind speed frost flowers are also an important source of aerosol at siple dome suggesting that variations in sea salt concentrations in the core and other cores drilled in similar locations may be reflecting changes in sea ice production rather than changes in transportation patterns for greenland cores and those from low accumulation inland sites in antarctica it is not simple to calculate the proportion of sea salt originating from frost flowers rather than open water however modelling studies suggest that a sea ice surface source contributed much of the flux of sea salt to these sites in glacial periods suggesting that interpretations of ice core records from these locations should also be revisited

transport and release of transition elements during early diagenesis sequential leaching of sediments from manop sites m and h part i ph 5 acetic acid leach sediments from manop sites m and h in the eastern tropical pacific ocean can be partitioned into operationally defined phases by means of a sequential leach procedure this paper reports the results of the first leach in the sequence an acetic acid solution buffered as p h 5 with sodium acetate this leach is designed to remove carbonate bound and sorbed cations the only cation bound in a consistent ratio to calcium in the carbonate is strontium the molar ratio is 2 10 3 in contrast transition metals are sorbed onto the surfaces of other sedimentary particles the proportions sorbed range from 2 to 10 of the total manganese about 10 of the total nickel and copper and less than 1 of the total iron the pool of sorbed metals in surface sediments is sufficiently large and the rate of biological stirring is sufficiently rapid for this metal reservoir potentially to dominate the porewater reservoir in supplying metals to ferromanganese nodules a simple model for nodule growth based upon transfer of metals through this reservoir suggests that only 1 of the sedimentary sorbed metals within a radius of 2 to 9 cm is required to support typical nodule growth rates

phreatomagmatic explosions of rhyolitic magma experimental and field evidence 1 experimental studies on explosive molten fuel coolant interaction mfci using basaltic melt compositions and water as the coolant have provided insight into the physical processes of basaltic and andesitic phreatomagmatic volcanism abundant field evidence indicates that rhyolitic and dacitic phreatomagmatism occurs in nature but it has not been possible until now to generate laboratory mfci explosions from the interaction between high silica melts and water under laboratory conditions the high viscosity of these melts apparently prevents formation of an effective hydrodynamic premix of melt and water the documented precursor of experimental explosive mfci caused by mafic melts our new experiments utilized samples from a rhyolitic tuff ring volcano in mexico tepexitl an experimental approach was developed in which premixing conditions were generated by mechanical deformation of the melt leading to brittle type fragmentation at the melt water interface physical measurements recorded during laboratory explosion provide quantitative evidence for rhyolitic explosive mfci additionally a comparison of experimentally produced particles with natural ones from tepexitl deposits show nearly identical chemical mineralogical composition grain size and grain morphology detailed textural analysis confirmed the presence of phreatomagmatically produced particles in both experimental and natural analog particles the results from this series of experiments indicate that under natural conditions stress induced magma fracturing can lead to a critical magma water interface growths and trigger phreatomagmatic explosions of high silica magma the water source for these eruptions may include shallow aquifers surface water bodies strong precipitation and intrusion into ice or wet unconsolidated sediments

snow chemistry across antarctica un updated compilation of published and new data of major ion ca cl k mg na no3 so4 and methylsulfonate ms concentrations in snow from 520 antarctic sites is provided by the national itase international trans antarctic scientific expedition programmes of australia brazil china germany italy japan korea new zealand norway united kingdom the united states and the national antarctic programme of finland the comparison shows that snow chemistry concentrations vary by up to four orders of magnitude across antarctica and exhibit distinct geographical patterns the antarctic wide comparison of glaciochemical records provides a unique opportunity to improve our understanding of the fundamental factors that ultimately control the chemistry of snow or ice samples this paper aims to initiate data compilation and administration in order to provide a framework for facilitation of antarctic wide snow chemistry discussions across all itase nations and other contributing groups the data are made available through the itase web page http www2 umaine edu itase content syngroups snowchem html and will be updated with new data as they are provided in addition recommendations for future research efforts are summarized

decadal timescale links between antarctic peninsula ice core oxygen 18 deuterium and temperature the antarctic peninsula region has exprienced a long term warming trend over the twentieth century with the 1971 90 mean at faraday being 1 9 c warmer than the mean over 1903 41 based on expedition reports for the period prior to 1900 there is conflicting evidence from different data sources an initial interpretation of isotopic data from ice cores suggests that the nineteenth century was warmer than the twentieth century in contrast snow accumulation rate data for the nineteenth century from the same ice cores suggest lower temperatures here we investigate these facts by studying the links between atmospheric temperature over the antarctic peninsula circulation parameters and isotopic data over the period of instrumental records we show that the relationships between these variables are complex and highly spatially variable in particular the correlations between temperature and 18o and d are generally of the order r 0 5 or less on timescales of one to five years conflicts between evidenc

elemental dispersion and stable isotope fractionation during reactive fluid flow and fluid immiscibility in the bufa del diente aureole ne mexico evidence from radiographies and li b sr nd and pb isotope systematics the 31 6 0 3 ma old bufa del diente alkali syenite ne mexico intruded a sequence of cretaceous limestones with intercalated sub horizontal chert layers the cherts acted as aquifers that facilitated transport of brines and pegmatitic melts within the shallow level 1 kbar contact metamorphic aureole fluid driven reactions between chert and marble wallrock and the influx of late melts and various fluids gave rise to distinct chemical and isotopic signatures within the aquifer and across the zones of infiltration and fluid driven reaction aqueous brines of magmatic origin produced thick wollastonite mantles around the chert layers wollastonite formation occurred at the expense of limestone and chert and generated co2 this co2 induced fluid unmixing into an aqueous brine and a low density co2 rich fluid which was lost to the overlying marble where it oxidized organic matter and caused 13c and 18o shifts in a zone some 5 10 cm wide after wollastonite formation the chert aquifers were locally intruded by pegmatite veins carrying alkali feldspar quartz aegirine augite eudialyte zircon and apatite aqueous fluids that exsolved during crystallization of the pegmatite veins escaped along late cross fractures and migrated along the inner and outer borders of the wollastonite margins chemical dispersion patterns of u al na k p s fe and ree across the chert to marble boundary and its metasomatic rims are shown by autoradiography and neutron induced radiography scavenging of cations at mineralogical contacts and cation transport into the marbles occurred only on the mm to cm scale isotopic data for pb and sr across a simple metachert marble boundary and for pb sr nd b and li across a metachert pegmatite marble sequence demonstrate the following 1 the pb and sr isotopic signature of early fluids was buffered by the carbonate wallrock only late fluids shielded from wallrock interaction by a wollastonite mantle variably preserved a memory of their initial magmatic signature 2 since the nd isotope signature of marble and chert is bound to calcite and clay minerals systematic shifts to unradiogenic nd in marble reflect loss of carbonate bound nd as the wollastonite margin is approached nd in the wollastonite margin is dominated by nd originally bound to clay minerals the later emplacement of the pegmatite which carried the nd isotope signature of its alkali syenite source had little effect on the nd isotopic composition of the wollastonite rim 3 although the li and b isotopic compositions reflect the alkali syenite source they are also affected by isotopic fractionation and partitioning between melt fluid and solids

premixing of magma and water in mfci experiments experimental studies have been performed to evaluate pre explosive water melt mixes with respect to explosive volcanic molten fuel coolant interaction mfci i e phreatomagmatic explosion remolten ultrabasic volcanic rock was used as a magma simulant measurement of the explosion intensity was used to determine optimal premixing conditions a well defined optimal range was found for the hydrodynamic mixing energy differential flow speed of 4 2 m s as well as for the water melt mass ratio 0 03 to 0 04 under experimental conditions the mass flux of water had a minor influence on the explosion intensity additionally transparent mixing experiments with silicon oil and inked water were carried out they indicate a direct dependence of the pre explosive water melt interface area on the explosion intensity the experimental results show that the contact conditions of water and melt required for explosive mfci may easily be established in natural volcanic systems thus explosive mfci is a probable mechanism of explosive volcanism

chemical evolution of mid ocean ridge hot springs abstract chemical analyses yielding elemental concentrations of major and minor elements of four hot springs on the east pacific rise at 21 n and 10 hot springs from the southern trough of the guaymas basin gulf of california provide a basis for thermodynamic modeling of conductive cooling of the hydrothermal endmembers mixing of the hydrothermal endmember with seawater and reaction of an epr type fluid with sediment of bulk chemical composition corresponding to unaltered sediment from dsdp hole 477 in the guaymas basin results of the calculations indicate that conductive cooling of endmember fluids within closed chimneys and conduits accounts for the solution composition of one vent on the east pacific rise and several vents in guaymas basin mixing of the hydrothermal fluids with seawater yields a prediction of mineral assemblages closely approximating those observed in samples of chimneys from the east pacific rise and drill cores in guaymas basin the hypothesis that guaymas basin hydrothermal fluids result from interaction of an epr type fluid with sediment cover in guaymas basin is supported by calculations which predict an increase in ph to a value similar to guaymas basin fluids an order of magnitude decrease in metal concentrations and an excellent agreement between predicted mineral assemblages as a function of extent of interaction with sediment and observed mineral assemblage distribution with depth

sources and transport pathways of marine aerosol species into west antarctica sixteen high resolution marine aerosol na so4 records from spatially distributed international trans antarctic scientific expedition itase ice cores spanning the last 200 years from the pine island thwaites and ross drainage systems and the south pole are used to examine sources sea spray and frost flowers and transport pathways of marine aerosols into west antarctica factors contributing to the amount of marine aerosols transported inland include sea ice extent the presence of open water features polynyas leads wind strength and direction and the strength and positioning of low pressure systems analysis of so4 na ratios indicates that frost flowers can contribute significantly 40 to the na budget of antarctic ice cores higher na concentrations in the ross drainage system may result from greater production of marine aerosols related to frost flowers in the ross sea region in association with greater sea ice extent and larger open water areas significant positive correlations of sea ice extent and the na time series exist in some regions of west antarctica higher wind speeds in winter and higher na concentrations when slp is

rb sr evidence for punctuated illite smectite diagenesis in the oligocene frio formation texas gulf coast the size fractions of a suite of upper oligocene frio formation shale samples taken from below 10 500 ft in a well on the texas gulf coast fall on a rb sr isochron corresponding to an age of 23 6 0 8 m y the isochron shows an initial 87 sr 86 sr ratio of 0 7088 0 0004 this suggests that regularly interstratified illite smectite simultaneously equilibrated soon after burial over a range of burial depths at 7 000 8 000 ft shallower than at present oxygen isotope values for these clays are also consistent with equilibration under shallower burial conditions such a pattern conflicts with the prevailing idea of a gradual illitization of smectite with progressive burial a new model of episodic or punctuated diagenesis is proposed whereby sudden diagenesis is initiated by a change in pore water chemistry clay reaction occurs over a range of temperature at this time such that the deeper clays are transformed completely to 80 illite and the shallow clays are transformed less completely subsequent pore water chemical changes inhibit further clay reaction and the mineralogic gradient and the isotopic signature formed at 23 6 m y b p are frozen in seven to eight thousand feet of additional post oligocene burial has not resulted in the creation of younger illite smectite consequently there is no evidence that illite smectite diagenesis is currently taking place in the frio formation

coastal antarctic aerosol and snowfall chemistry aerosol samples have been collected at three stations on the coast of antarctica at dumont d urville station samples have been collected for 4 years at halley station for 2 years and at neumayer station for 12 years fresh snow samples have also been collected at the three sites at halley daily surface snow samples were taken as well as firn cores covering the sampling period meteorological including upper air data are available at the three sites in the subsequent papers of this special section the data from the three stations have been combined in order to make general statements about the chemistry of aerosol in coastal antarctica about the differences between sectors of antarctica and about the relationship between air concentrations and the chemistry that is eventually seen in ice cores this paper summarizes the samples collected and the sampling methods used at the three sites it also highlights the main role of each paper in this special section

the boron isotopic composition of altered oceanic crust samples of drilled oceanic crust from dsdp holes 417a 417d and 418a and odp hole 735b and oceanic crust from the oman and cyprus ophiolites were analyzed for b contents and 11b composite samples from dsdp holes 417a 417d and 418a were used to represent the upper 550 m of altered oceanic crustal layer 2a whole rock samples from the troodos ophiolite cyprus and the oman ophiolite wer selected to represent crustal layer 2b dikes composite samples from odp hole 735b were used to represent crustal layer 3 the b content of the dsdp composites ranges from 7 2 ppm to 104 ppm and correlates with both 18o and k showing that it is a good indicator of the extent of low temperature alteration the 11b of the dsdp composites varies between 2 5 and 5 4 the b content of the samples from the troodos ophiolite ranges from 2 4 ppm to 8 1 ppm 11b varies from 0 9 to 7 8 the b content of the oman ophiolite samples ranges from 5 0 ppm to 11 1 ppm 11b varies from 1 6 to 16 9 the b content of the samples from odp hole 735b ranges from 1 1 ppm to 7 1 ppm 11b varies from 4 3 to 24 9 the general pattern displayed by these samples is one of greatest and most variable b enrichment at the top of the crust and least enrichment at the bottom of the section all of these samples are enriched compared to unaltered morb which is believed to have a b content of approximately 0 5 ppm the 11b values of deeper samples from layers 2b and 3 are more variable and generally higher than those from layer 2a boron contents and 11b are not correlated the data from the dsdp site 417418 composites indicate that the 11b of fluid circulating in the upper crust changes only slightly during alteration increasing by an average of 5 1 with an accompanying decrease in b concentration of 7 low temperature alteration appears to be a water dominated process resulting in minor modification of circulating seawater a minimum water rock ratio of 400 is calculated for these samples implying a minimum low temperature seawater flux through the upper oceanic crust of 3 4 1014 l y the average b content of altered oceanic crust as represented by these samples is 5 2 1 7 ppm and the average 11b is 3 4 1 1 this average isotopic composition is measurably different from the apparent average of oceanic sediments supporting the idea that 11b could be useful for identifying the source s of b in island arcs

snow chemistry on james ross island antarctic peninsula more than 400 firn samples were collected at an altitude of 1660 m on the small ice sheet covering james ross island northeastern coast of the antarctic peninsula chemical analysis of these samples provides information about the marine background aerosol composition in the area the samples cover the years 1975 1979 pit samples and the last 15 years firn core samples major impurities na k ca al h so4 and no3 were determined by using flameless atomic absorption neutron activation acid titration or ion chromatography aerosols are contributed mainly by the surrounding ocean however secondary aerosol deposition h2so4 and hno3 is also important all samples were found to be slightly acidic ph generally in the range 5 6 strong seasonal variations maximum values in summer are found in the h2so4 deposition a photochemical mechanism is proposed to explain the local production of h2so4 from gaseous marine sulfur compounds from these results a yearly deposition of 0 13 tg of h2so4 is calculated for the entire antarctic continent

boron isotopic composition of fumarolic condensates from some volcanoes in japanese island arcs boron samples from 40 fumarolic condensates from volcanoes in the ryukyu arc satsuma iwo jima and shiratori iwo yama and the north east japan arc usu shinzan showa shinzan esan and issaikyo yama all have 11b10b ratios close to 4 07 higher values from 4 09 to 4 13 were only observed in condensates from volcanoes in the southernmost end of the north east japan arc nasu dake the northern part of the izu bonin arc hakone and the north mariana arc ogasawara iwo jima these higher values suggest geological interaction of the magmas with sea water enriched in 11b

ice core records as sea ice proxies an evaluation from the weddell sea region of antarctica 1 ice core records of methanesulfonic acid msa from three sites around the weddell sea are investigated for their potential as sea ice proxies it is found that the amount of msa reaching the ice core sites decreases following years of increased winter sea ice in the weddell sea opposite to the expected relationship if msa is to be used as a sea ice proxy it is also shown that this negative msa sea ice relationship cannot be explained by the influence that the extensive summer ice pack in the weddell sea has on msa production area and transport distance a historical record of sea ice from the northern weddell sea shows that the negative relationship between msa and winter sea ice exists over interannual 7 year period and multidecadal 20 year period timescales national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data suggest that this negative relationship is most likely due to variations in the strength of cold offshore wind anomalies traveling across the weddell sea which act to synergistically increase sea ice extent sie while decreasing msa delivery to the ice core sites hence our findings show that in some locations atmospheric transport strength rather than sea ice conditions is the dominant factor that determines the msa signal preserved in near coastal ice cores a cautious approach is thus required in using ice core msa for reconstructing past sea ice conditions including the need for networks of ice core records and multiproxy studies to assess the significance of past msa changes at different locations around antarctica

accumulation variability derived from an ice core from coastal dronning maud land antarctica a 100 m long ice core was retrieved from the coastal area of dronning maud land dml antarctica in the 2000 01 austral summer the core was dated to ad 1737 by identification of volcanic horizons in dielectrical profiling and electrical conductivity measurement records in combination with seasonal layer counting from high resolution oxygen isotope d 18 o data a mean long term accumulation rate of 0 29 m a 1 w e was derived from the high resolution d 18 o record as well as accumulation rates during periods in between the identified volcanic horizons a statistically significant decrease in accumulation was found from about 1920 to the present a comparison with other coastal ice cores from dml suggests that this is a regional pattern

constraints on water transport and alteration in the oceanic crust from the isotopic composition of pore water the oxygen isotopic compositions of pore fluids from sediments of older oceanic crust commonly decrease with depth increases in calcium ion concentrations always accompany the 18o 16o decreases these changes are attributed principally to the alteration of basalts or alteration of volcanic ash in the sediments oxygen isotope material balance calculations suggest that 5 20 of the upper kilometer of basalt is altered at the time of subduction of the oceanic crust this corresponds to a flux of 18o into the oceanic crust of 2 3 1015 moles per million years evaluation of the oxygen and hydrogen isotope data from the pore fluids also suggests that the principal process of mass transfer in the sediments of older oceanic crust is diffusion convection of water in the basalts of the oceanic crust appears to continue until subduction

saline groundwater in israel its bearing on the water crisis in the country abstract one of the major causes for the deterioration of water quality bearing heavily on the water crisis in israel is the ongoing contamination of its water resources by saline water bodies the present paper reviews the geochemical processes forming saline water lists and explains certain chemical and isotopic parameters which enable understanding these processes and describes the saline groundwater bodies and various salinization phenomena occurring in the country s various aquifers deterioration of groundwater in israel is caused by numerous natural processes such as encroachment of sea water migration of connate highly pressurized brines penetrating into fresh groundwater by subsurface dissolution of soluble salts originating in surrounding country rocks and by water rock interaction in addition to sea water two saline water bodies were identified as the main factors causing salinization of fresh groundwater a ca chloride brines encountered in the jordan dead sea rift valley in various parts of the negev and of the coastal plain and b na chloride saline water identified in the subsurface of the negev and in the southern part of the coastal plain intensive exploitation of groundwater in israel has disturbed the natural equilibrium which prevailed between fresh and saline water the newly established groundwater flow regimes have facilitated the migration of saline water bodies their participation in the active hydrological cycle and the progressive contamination of fresh groundwater these processes which were not anticipated by planners and water resources managers emphasize that large scale groundwater exploitation was undertaken without giving sufficient consideration to the occurrence and subsurface migration of saline water and brines

a 340 year record of biogenic sulphur from the weddell sea area antarctica detailed records of methanesulphonic acid msa and non sea salt sulpha te nss so have been obtained from ice cores drilled on dolleman island on the east coast of the antarctic peninsula i0 35 2 s 60 55 5 w annual average concentrations of msa arc presented for the period i 652 1992 over this lime span the mean ann ual concen tration of msa is 0 69 eq 1 1 cr 0 33 n 340 the range is 0 13 2 35 eq 1 1 a nd the msa nss s04 2 ratio is 0 22 the high msa concentration reflects the proximity of the weddell sea believed to be a region of high marine phyt0plankton production t he overa ll mean nss so concentration is about 66 of the total sulphate d eposited in the snowfall low frequency variations of msa and oxygen isolope signals correla te closely indicat ing that they may be modulated by similar atmospheric processes positive correlations are observed between the oxygenisotope signature and both l 1sa r 0 4 1 and nss s04 2 r 0 50 signilicant at the 99 level a small negative correlation can be seen between both species and the annual duration or sea ice a t scoria bay laurie island in the south orkneys since 1902 msa r 0 23 and nss so r 0 29 significant at 95 confidence no significant link between high msa concentrations and el nino even ts is observed at this location

the sedimentary cycle of the boron isotopes abstract marine sediments contain two isotopically distinct components a non desorbable fraction with 11b between 4 3 and 2 8 per mil n 10 and a desorbable component with 11b between 13 9 and 15 8 per mil n 6 the adsorption coefficient k for the uptake of b from seawater by fluvial suspended material mississippi has an experimentally determined value of 1 54 0 05 the associated isotope fractionation factor is 0 974 0 003 empirical values for k determined from the analysis of marine sediments n 6 were between 3 and 4 the amount of b adsorbed onto fluvial suspended material during estuarine mixing is about 9 109 moles yr based on pore water data adsorption experiments and comparative size fraction analyses suspended sediments from the mississippi river vs bottom deposits from the delta there is no evidence for the incorporation of b into detrital sediments at low temperature however the high b content of bauer deep metalliferous sediments must be due to incorporation of seawater b during formation of authigenic silicates the 11b of these minerals is 2 3 per mil hydrothermally altered sediments from dsdp hole 477 guaymas basin gulf of california have variable b contents from 33 ppm similar to the unaltered detritus to 1 2 ppm in the recrystallized material the latter has 11b as low as 9 0 per mil substantially lower than the unaltered material hydrothermal solutions collected from vents adjacent to the hole have boron contents elevated by about a factor of 4 relative to seawater and 11b between 16 5 and 23 2 per mil the b mobilized from the sediments is isotopically fractionated with the fluids being preferentially enriched in the heavy isotope analysis of an oxisol profile developed over granite in the guyana shield showed that boron is partially mobilized during weathering with an isotopic offset of 2 5 per mil between bedrock and soil the observed enrichment of b in shales relative to igneous rocks does not occur during weathering or during exposure to seawater at low temperature incorporation occurs only during burial diagenesis at temperatures greater than about 60 c however the enrichments cannot be attained during a single cycle of primary weathering and burial but must be cumulative over many cycles

decompression rate of magma at fragmentation inference from broken crystals in pumice of vulcanian eruption abstract decompression rate of magma at fragmentation immediately before or after fragmentation was determined using broken crystals found in the pumices ejected during the vulcanian explosion of sakurajima volcano japan the combined analysis of textural data obtained from the natural pumice samples and a simple model for the crystal fracturing in vesiculating viscous magma indicated a decompression rate 7 0 10 3 7 8 10 4 pa s for the ejecta produced during the later phase of vulcanian explosion this result suggests that the short duration of the vulcanian explosion is controlled by the rapid decrease of the magma ascent rate to a vent an understanding of the control mechanism of the termination of an eruption by precise prediction of the eruption process is essential for both volcanology and hazard mitigation

frost flowers as a source of fractionated sea salt aerosol in the polar regions frost flowers collected from the surface of new sea ice near the brunt ice shelf antarctica show depletion in sulphate and sodium relative to other sea water ions this is consistent with loss of mirabilite na2so4 during formation of the brine from which the frost flowers grow aerosol generated from frost flowers would have higher sodium sulphate ratios than aerosol generated from sea water this would explain low values of non sea salt sulphate encountered in winter aerosol and winter layers in ice cores at coastal antarctic sites calculations confirm that the frost flower source should be significant compared to an open water source for coastal regions

dielectric stratigraphy of ice a new technique for determining total ionic concentrations in polar ice cores a 133 m deep antarctic ice core from dolleman island antarctic peninsula has been profiled by dielectric measurements in the af lf 20 hz 100 khz frequency range this has revealed large variations in dielectric relaxation and conductivity down the core a comparison with the chemical stratigraphy along 45 m of the core demonstrates for the first time the decisive role played by acids and salts in determining the electrical behaviour of natural ice the total ionic concentration along the ice core can be deduced from the dielectric response this technique may be applied rapidly in the field and as it requires no contact between ice core and electrodes the core is maintained in pristine condition for later chemical analysis

alteration of the oceanic crust implications for geochemical cycles of lithium and boron abstract fresh tholeiitic basalt glass has been reacted with seawater at 150 c water rock mass ratio of 10 and fresh diabase has been reacted with a na k ca cl fluid at 375 c water rock mass ratios of 1 2 and 5 to understand better the role of temperature basalt composition and water rock mass ratio on the direction and magnitude of b and li exchange during basalt alteration at 150 c slight but nevertheless significant amounts of b and li were removed from seawater and incorporated into a dominantly smectite alteration phase at 375 c however b and li were leached from basalt b behaved as a soluble element and attained concentrations in solution limited only by the b concentration in basalt and the water rock mass ratio li however was less mobile for example at water rock mass ratios of 1 2 and 5 the percent of li leached from basalt was 58 70 and 92 respectively this suggests some mineralogic control on li mobility during hydrothermal alteration of basalt especially at low water rock mass ratios in general these results as well as those for b are consistent with the temperature dependent chemistry of altered seafloor basalt and the chemistry of ridge crest hydrothermal fluids based on the distribution and chemistry of products of seafloor weathering low 150 c and high temperature hydrothermal alteration of basalt and the chemistry of ridge crest hydrothermal fluids it was estimated that alteration of the oceanic crust is a li source for seawater this is not true for b however since the hot spring flux estimated for b is balanced by low temperature basalt alteration these data coupled with b and li flux estimates for other processes e g continental weathering clay mineral adsorption authigenic silicate formation and formation of siliceous skeletal material yield new insight into the b and li geochemical cycles calculations performed here indicate relatively good agreement between the magnitude of b and li sources and sinks the geochemical cycle of b however may be affected by serpentinization of mantle derived peridotite in oceanic fracture zones serpentinites are conspicuously enriched in b and if the b source for these rocks is seawater then an additional b sink exists which must be integrated into the b geochemical cycle however until more data are available in terms of areal extent of serpentinization serpentite chemistry and isotopic composition the importance of b in these rocks with respect to the b geochemical cycle remains speculative at best

chilled margin fragmentation as a trigger for transition from strombolian to phreatomagmatic explosive activity at cova de paul crater santo antao cape verde islands sudden transitions from effusive or mildly explosive eruptions to violent phreatomagmatic explosive activity can occur at high elevation vents on oceanic island volcanoes here we describe near vent deposits around the large cova de paul crater on santo antao cape verde islands which provide insights into the transition from strombolian magmatic to violently explosive phreatomagmatic activity during one such eruption the strombolian deposits change from welded spatter to bedded clinkery scoria to angular blocky scoria and contain a distinct population of strongly banded low vesicularity angular sub glassy clasts with strongly prolate vesicles these sub glassy clasts also form a discrete layer of larger blocks at the transition to the overlying phreatomagmatic deposits they are compositionally identical to the strombolian scoria and are interpreted to be fragments of flow banded chilled margins from the walls of the eruptive conduit the layer of large sub glassy blocks records disintegration and expulsion of the chilled margins at the transition to phreatomagmatic activity we interpret the sequence from spatter through clinkery scoria to blocky scoria as recording an increase in groundwater inflow into the conduit from pressurised aquifers but at coolant input ratios below those required for explosions the shattering of the chilled margins to produce the bed of large sub glassy blocks appears to have allowed a much greater water flow into the conduit leading to the phreatomagmatic explosive phase of the eruption

a 200 year sulfate record from 16 antarctic ice cores and associations with southern ocean sea ice extent chemistry data from 16 50 115m deep sub annually dated ice cores are used to investigate spatial and temporal concentration variability of sea salt ss so4 2 and excess xs so4 2 over west antarctica and the south pole for the last 200 years low elevation ice core sites in western west antarctica contain higher concentrations of so4 2 as a result of cyclogenesis over the ross ice shelf and proximity to the ross sea polynya linear correlation analysis of 15 west antarctic ice core so4 2 time series demonstrates that at several sites concentrations of ssso4 2 are higher when sea ice extent sie is greater and the inverse for xsso4 concentrations of xsso4 2 from the south pole site east antarctica are associated with sie from the weddell region and west antarctic xsso4 2 concentrations are associated with sie from the bellingshausen amundsen ross region the only notable rise of the last 200 years in xsso4 around 1940 is not related to sie fluctuations and is most likely a result of increased xsso4 2 production in the mid low latitudes and or an increase in transport efficiency from the mid low latitudes to central west antarctica these high resolution records show that the source types and source areas of ssso4 2 and xsso4 2 delivered to eastern and western west antarctica and the south pole differ from site to site but can best be resolved using records from spatial ice core arrays such as the international trans antarctic scientific expedition itase

determining flow type shear rate and shear stress in magmas from bubble shapes and orientations we interpret the shear environments that produced bubble textures in obsidian samples using the results of theoretical numerical and experimental studies on the deformation of bubbles in shear flows in particular we use the shapes and orientations of bubbles vesicles in obsidian to estimate shear rates and shear stresses and assess flow type simple vs pure shear this technique can be used to determine shear rates in volcanic conduits the origin of pyroclastic obsidian and the emplacement history and dynamics of obsidian flows a spherical bubble in a viscous fluid subjected to a low reynolds number steady flow field deforms until it reaches a steady shape and orientation bubble deformation is governed by the competing stresses from shearing that deforms and surface tension that rerounds the ratio of these stresses is the capillary number ca because the relationships among ca bubble orientation and shape differ for pure and simple shear we can distinguish between these flow types using preserved bubble geometries furthermore because ca is a function of shear rate we can use relationships between ca and the magnitude of deformation to calculate shear rates when melt viscosity and surface tension are known to demonstrate the potential of the technique we examine three obsidian samples chosen for diversity of origin and texture two of the samples have low crystallinities and banding defined by layers of different vesicularity bubble geometries in a spatter fed obsidian flow sample record deformation by pure shear whereas a juvenile obsidian clast from a pyroclastic fall deposit records predominantly simple shear a third sample from an obsidian flow has banding marked by variable concentrations of microlites and shows bubble deformation most consistent with dominantly simple shear and some bubble relaxation the highest shear rate and shear stress are recorded by the pyroclastic obsidian shear rate 0 01 s 1 shear stress 60 kpa the spatter fed obsidian flow sample deformed by pure shear records the lowest shear stress 4 9 kpa the obsidian flow sample deformed by simple shear records the lowest shear rates 10 6 6 10 6 9 s 1 despite high shear stresses 22 36 kpa because of the high viscosity of the degassed rhyolite 0 13 wt water