vertical wind distribution in the polar thermosphere during horizontal e region experiment hex campaign 1 vertical winds in the thermosphere were measured with two fabry perot interferometers at the poker flat research range pfrr and eagle observatory alaska during the horizontal e region experiment hex campaign feburary and march 2003 since these two observatories have almost the same geomagnetic latitude we could deduce vertical wind distributions along the same auroral arc the oi557 7 nm and oi630 0 nm emissions were separated using a dichroic mirror which enabled us to estimate temporal variations in vertical winds in the e and f regions simultaneously to measure the optical auroral distribution we used all sky imagers at the pfrr we had 13 clear nights out of a total of 23 we obtained the following results from the observations 1 the temporal variations in vertical wind observed at oi557 7 nm at the two observatories had a high degree of correlation despite being 300 km apart the correlation coefficients exceeded 0 6 on six of the 13 nights the chance of exceeding a correlation coefficient of 0 6 on an individual night is about 0 1 2 the correlation was relatively low in the oi630 0 nm observation 3 some low correlation cases for both wavelengths indicated that the location of the auroral arc with respect to the observatory was different for the two sites namely whether the auroral arc was poleward or equatorward of the observational area these results suggest that the vertical wind structures along one auroral arc are uniform at least 300 km apart this wind distribution was consistent with previous works in most cases but some exceptions were also found

relative contribution of ionospheric conductivity and electric field to the auroral electrojets data from continuous scans of the chatanika radar beam along the magnetic meridian plane are used to determine the latitudinal profile of height integrated ionospheric conductivities and horizontal electric fields from which the latitudinal distribution of ionospheric currents is deduced the observations cover invariant latitudes between 62 and 68 where the ims alaska meridian chain of magnetometers was also in operation although the conductivities and the electric fields are interrelated the relative importance of the two in driving the eastward and westward auroral electrojet currents can be assessed it is found that for moderate and large current densities i e 0 2 a m the northward electric field strength increases as the magnitude of the eastward electrojet in the evening sector increases the height integrated hall conductivity stays generally at the level of 10 mhos even when the current density becomes as large as 1 a m however when the eastward electrojet is small substantial electric fields of 10 20 mv m may still exist as if the magnetosphere has a persistent voltage source there appear to be two distinct components to the westward electrojet in the midnight and early morning sestors 0300 mlt is dominated by a strong southward electric field

geochemistry of geothermal waters from the gonghe region northwestern china implications for identification of the heat source the gonghe geothermal region located in the northeastern part of qinghai tibet plateau is the most geothermally active in qinghai province the geothermal waters from three hydrothermal areas qiabuqia guide and xinghai of gonghe are characterized with different hydrochemical types nevertheless their d and 18o data suggest that they are all of meteoric origin most gonghe samples are far away from the full equilibrium line in na k mg triangular diagram implying that na k geothermometer is generally not suitable for calculating the reservoir temperatures in comparison silica geothermometers perform much better and give more accurate temperature estimations the hydrochemistry of the gonghe geothermal waters is distinctively different from that of the hot springs from rehai a well known magmatic hydrothermal area located in the tengchong volcanic region of yunnan province southwestern china indicating that the geothermal anomaly in gonghe is not related to an underlying magma chamber instead the strong hydrothermal manifestation there is more likely to be supported by the intense deep tectonic activities moreover the possible existence of radioactive heat source can not be ruled out at this stage

modeling substorm current systems using conductivity distributions inferred from de auroral images images of auroral emissions observed with dynamics explorer 1 de 1 are used to calculate ionospheric conductivities over the polar region the combination of ground based magnetometer data and the inferred conductivities enables us to estimate on a global scale the distributions of ionospheric electric fields and currents and field aligned currents as well as the joule heating production rate with a time resolution of 12 min although our inference of the conductivity distribution requires further improvements the following conclusions may be drawn from this work 1 the westward electrojet is in general collocated with the region of high auroral luminosity while the region of relatively low luminosity in the evening sector is collocated with the eastward electrojet 2 the upward field aligned currents exist in the brightest auroral region on the poleward side of the evening auroral oval and on the equatorward side of the morning oval however the magnitudes of these upward currents are not in proportion to the auroral luminosities suggesting that the characteristic energies of precipitating electrons carrying the upward currents and generating the auroral luminosities may be different 3 a significant amount of ionospheric currents can flow in regions where there are no bright auroral emissions an example of this effect is found over the poleward half of the westward electrojet in the morning sector where the electric field is the main contributor to the ionospheric currents 4 the distribution of calculated field aligned currents displays many localized structures which characterize the development of the substorm current system previous satellite observations may represent gross time averages of such complicated distributions

scientific results of the u s ims ground based program the scientific results of the u s international magnetospheric study ims ground based program available to the author up to february 1982 are summarized included are results derived from 1 magnetometers of the ims meridian chains 2 incoherent scatter radars 3 a balloon campaign and 4 optical spectroscopic observations a large body of data obtained during the ims remains to be analyzed and published

ionospheric characteristics of a detached arc in the evening sector trough simultaneous measurements by the isis 2 satellite and the chatanika incoherent scatter radar have been used to identify the ionospheric characteristics of a detached arc in the evening sector trough region on 26 february 1977 at 0737 ut the isis 2 auroral scanning photometer detected a detached arc at 65 north geomagnetic latitude that extended from approximately 1900 mlt to 2100 mlt the arc was about 2 wide in latitude and was separated by about 3 from the equatorward edge of the diffuse aurora the ratio of observed emission intensity at 557 7 nm to that at 391 4 nm was low indicating a fairly hard electron distribution the isis 2 energetic particle detector observed energetic electron precipitation e 40 kev in the detached arc the chatanika radar found that the detached arc consisted of several narrow ionization enhancements with peak e region electron densities of about 1 105 cm 3 at 95 km altitude the major enhancements were about 20 km 0 2 wide in latitude and were spaced about 50 km 0 5 apart their widths and spacings were steady for about 40 minutes this persistent spatial pattern suggests the presence of an energetic electron precipitation mechanism that is periodic in latitude and extended in longitude

biogeography of the lord howe rise region tasman sea abstract the two principal aims of this study were to synthesise physical and biological information to characterise the lord howe rise lhr region and to use recent survey collections of benthic invertebrates mostly large benthic epifauna to describe its biogeography at regional and sub regional scales the lhr region is large 1 95 million km2 spans tropical and cool temperate latitudes 18 4 to 40 3 s and is influenced by several ocean currents notably the east australian current and the tasman front our analyses revealed that biological patterns were related to two groups of geomorphic morphotypes found in this topographically complex region subdued bathymetric features expansive soft sediment basins and plateaus and raised bathymetric features scattered seamounts guyots knolls and pinnacles raised bathymetric features in the lhr region were more likely to support richer and more abundant epifaunal assemblages dominated by suspension feeding invertebrates on hard substrata compared to subdued features which were dominated by infauna and detritivores in soft sediments however this trend does not apply to all raised bathymetric features e g gifford guyot with variations in depth elevation latitude and particularly substrata affected the composition of biological assemblages in addition some demersal fishes ophiuroids and other benthic invertebrates showed distinct north south delineations that coincide with the influence of the tasman front and thermal gradients while the lack of spatially and temporally replicated data in the region limits our interpretation of survey data paleo environmental processes and examples from other regions provide some indication of how dispersal influences migration speciation and endemism in the lhr region although our current knowledge is limited it is hoped that this review will help inform future studies in the area as equitable examination of biological geological and oceanographic characteristics will facilitate future assessments of lhr biogeography and permit the inclusion of this region in biogeographic studies with a national or global context

the bimodal ph distribution of volcanic lake waters abstract volcanic lake waters have a bimodal ph distribution with an acidic mode at ph 0 5 1 5 and a near neutral mode at ph 6 6 5 with relatively few samples having ph 3 5 5 to investigate the reasons for this distribution the irreversible water rock mass exchanges during the neutralization of acid so4 cl waters with andesite under both low and high temperature conditions were simulated by means of the eq3 6 software package version 7 2 reaction path modeling under low temperature and atmospheric pco2 and fo2 suggests that several homogeneous and or heterogeneous ph buffers exist both in the acidic and neutral regions but no buffer is active in the intermediate central ph region again the same titration under high temperature hydrothermal magmatic conditions is expected to produce comparatively infrequent aqueous solutions with ph values in the 3 5 5 range upon their cooling below 100 c substantially different ph values are obtained depending on the cooling paths either through boiling or conductive heat losses these distinct ph values are governed by either hso4 and hcl aq in poorly neutralized aqueous solutions or the co2 aq hco3 couple and the pco2 value as well in neutralized aqueous solutions finally mixing of the acid lake water with the aqueous solutions produced through high temperature titration and cooled below 100 c is unlikely to generate mixtures with ph values higher than 3 unless the fraction of the acidic water originally present in the lake becomes very small which means its virtually complete substitution summing up the evidence gathered through reaction path modeling of the neutralization of acid lake waters with andesite both at low and high temperatures explains the scarcity of volcanic lake waters with measured ph values of 3 5 5

late quaternary sea level highstands in the tasman sea evidence from lord howe island abstract lord howe island situated 600 km east of australia provides a unique opportunity to evaluate late quaternary highstands of sea level in the tasman sea the mid ocean island which is the site of the southernmost coral reef is composed of basalts of late tertiary age and calcarenites derived from bioclastic reefal carbonates both erosional and depositional evidence of late quaternary highstands of sea level is preserved uranium series disequilibrium dating of coral clasts from a calcarenite beach facies at neds beach on the northeast of the island yielded a mean age of 136 000 yr b p thermoluminescence dating of the quartz sand fraction from the same deposit using fine grained and coarse grained methods yielded ages of 138 000 and 116 000 yr b p respectively these ages are interpreted to indicate that this beach unit within which fossil bones and eggs of the extinct horned turtle meiolania are found formed during the last interglacial when the sea was 2 4 m above present benches and platforms developed on tertiary basalt and on late pleistocene calcarenite on the more sheltered lagoonal shore on the west of the island indicate a sea level up to 1 5 m higher than present during the holocene cemented boulder conglomerates ca 3000 yr b p at north head and emergent mollusc rich carbonate muds ca 900 yr b p within an embayment fill at old settlement beach further support this interpretation these palaeo sea level data from the tasman sea support previous estimates of the height of the last interglacial sea surface relative to eastern australia and supplement a growing body of evidence for a higher sea level in the region during the mid to late holocene

geochemistry of hot springs in the tengchong hydrothermal areas southwestern china abstract as an important volcanic geothermal region in china tengchong belongs to the mediterranean himalayas geothermal belt and is characterized by wide distribution of volcanic rocks fifty eight hydrothermal areas have been identified in tengchong among which the rehai hydrothermal system is the most geothermally active the geothermal waters from rehai are mainly na hco 3 cl and na hco 3 types whereas those from the other hydrothermal areas are mainly na hco 3 na ca hco 3 ca hco 3 ca mg hco 3 mg na ca hco 3 and mg ca hco 3 types both quartz geothermometer and k mg geothermometer indicate that the rehai geothermal field has higher subsurface temperatures than the other hydrothermal areas except for three rehai samples most geothermal water samples collected from tengchong are far from the full equilibrium line in giggenbach s triangular diagram suggesting that the complete chemical re equilibrium has not been achieved as these geothermal waters flow upward from reservoirs towards spring vents and possibly mix with cooler waters statistical analysis shows that cl b li rb and cs are the characteristic constituents of the tengchong geothermal waters and the good linear relations among these elements in the rehai geothermal waters reflect the existence of a deep parent geothermal liquid pgl below rehai an enthalpy chloride diagram of the rehai geothermal waters suggests that the parent geothermal liquid has cl concentration of 291 mg l and enthalpy of 1495 j g the pgl ascends to the surface through different channels and may cool by conduction of heat to reservoir host rocks by boiling or by mixing with cooler shallow groundwaters

evening co rotating patches a new type of aurora observed by high sensitivity all sky cameras in alaska 1 we observed an interesting auroral event at poker flat research range pfrr mlat 65 5 using an all sky imaging system this aurora which appeared in the evening 16 19 mlt during a geomagnetically quiet period maintained its patch structure and position for more than 40 minutes these patches were distinct in oi 557 7 nm and n2 427 8 nm emissions at this time pfrr was located at a lower latitude region than the auroral oval an extended plasmasphere was observed a few hours beforehand with the akebono satellite in the afternoon sector this evidence suggests that the particles causing this aurora precipitate from the extended duskside plasmasphere we believe that the imaging observation from the ground using our technique is an effective method for investigating dynamics around the plasmapause a still partially unexplored region of space

natural pollutants of northern lake baikal hot and cold springs in the northwestern shore of lake baikal are investigated as natural pollutants of the lake which can interfere with its chemistry the study includes chemical analyses of lake water samples from different depths in the north baikal basin as well as waters of hot and cold onshore springs and baikal tributaries collected in 2007 through 2013 thermal waters in the shore of lake baikal have much higher so4 cl f na and sio2 concentrations than those in the lake water as well as ten to hundred times greater enrichments in li rb cs ga as and w mineral water in cold springs is generally similar to the baikal water with respect to total dissolved solids tds and major and trace element chemistry however the milky cold spring discovered in the lower reaches of the b cheremshan river within a few km from the lake stands out in its unusual ca mg so4 composition low ph 3 57 and high tds 535 mg l and trace element enrichments in al mn ni co zn y and ree the concentrations of these elements are still higher up to one or two orders of magnitude in suspended solids abundant in the spring water this water composition is typical rather of mine drainage in sulfide mineralization provinces and prompts the existence of a sulfide orebody in the area mn co ni zn and cd occur in the dissolved form and their concentrations in stream water near the b cheremshan inlet into baikal are only slightly lower than immediately downstream of the spring ree and y are ten times lower because of precipitation from the river water however all metals the spring water leaches from the surrounding rocks eventually end up in lake baikal although the spring has much greater enrichments relative to the baikal water in a number of elements it hardly can cause any significant change to the lake composition only local chemical anomalies of mn al co ni zn cd ree and y can be expected in the bottom sediments where the lake uptakes the b cheremshan stream

the insular shelves of the faial pico ridge azores archipelago a morphological record of its evolution shelves surrounding reefless volcanic ocean islands are formed by surf erosion of their slopes during changing sea levels posterosional lava flows if abundant can cross the coastal cliffs and fill partially or completely the accommodation space left by erosion in this study multibeam bathymetry high resolution seismic reflection profiles and sediment samples are used to characterize the morphology of the insular shelves adjacent to pico island the data show offshore fresh lava flow morphologies as well as an irregular basement beneath shelf sedimentary bodies and reduced shelf width adjacent to older volcanic edifices in pico these observations suggest that these shelves have been significantly filled by volcanic progradation and can thus be classified as rejuvenated despite the general volcanic infilling of the shelves around pico most of their edges are below the depth of the last glacial maximum revealing that at least parts of the island have subsided after the shelves formed by surf erosion prograding lava deltas reached the shelf edge in some areas triggering small slope failures locally decreasing the shelf width and depth of their edges these areas can represent a significant risk for the local population hence their identification can be useful for hazard assessment and contribute to wiser land use planning shelf and subaerial geomorphology magnetic anomalies and crustal structure data of the two islands were also interpreted to reconstruct the long term combined onshore and offshore evolution of the faial pico ridge the subaerial emergence of this ridge is apparently older than previously thought i e before 850 ka

acid hot springs discharged from the rehai hydrothermal system of the tengchong volcanic area china formed via magmatic fluid absorption or geothermal steam heating across mainland china tengchong is geothermally unique because both magmatic hydrothermal systems and late cenozoic volcanic activities have been observed there rehai located in the tengchong volcanic area is the only hydrothermal system in mainland china discharging acid springs with very low ph values two types of acid geothermal waters were identified one is sulfate waters with low chloride concentrations and ph levels as low as around 2 the other has slightly higher chloride concentrations and is marked with diversified hydrochemical types both types of acid springs at rehai are immature waters and far from being equilibrated with a thermodynamically stable mineral assemblage comprising albite k feldspar muscovite and clinochlore characteristic for felsic rock hosted reservoirs in contrast to those neutral chloride springs at rehai that are formed via boiling conductive cooling or mixing with cold groundwaters of a parent geothermal liquid pgl the sulfate rich acid waters discharged from the diretiyan area the dagunguo area and the shizitou spring of rehai are essentially locally perched groundwaters heated by h2s rich steam separated from deep geothermal fluid the acidity of these waters originates from the oxidation of h2s in near surface environment in contrast the acid waters with higher chloride concentrations are the results of mixing between steam heated waters and neutral chloride waters the geochemical geneses of the rehai geothermal springs inferred based on stable hydrogen and oxygen isotopes are generally identical unlike active volcanic areas across the world there is a lack of acid waters at rehai formed through partial neutralization of magmatic fluid possibly owing to the comparatively deep seated magma chamber there no less than 7 km deep

sediments and history of the rottnest shelf southwest australia a swell dominated non tropical carbonate margin abstract the rottnest shelf is a narrow wave dominated open shelf on the passive continental margin of southwest australia adjacent to a hinterland of low relief and sluggish drainage high physical energy low nutrients in cool subtropical waters and rapid postglacial transgression have limited carbonate productivity restricted grain types and reworked the transgressed surface to form only a thin given sufficient time the rottnest shelf could recover from drowning and form blanket like skeletal carbonates thin

response of coral reefs to climate change expansion and demise of the southernmost pacific coral reef received 21 may 2010 revised 20 june 2010 accepted 6 july 2010 published 3 august 2010 1 coral reefs track sea level and are particularly sensitive to changes in climate reefs are threatened by global warming with many experiencing increased coral bleaching warmer sea surface temperatures might enable reef expansion into mid latitudes here we report multibeam sonar and coring that reveal an extensive relict coral reef around lord howe island which is fringed by the southernmost reef in the pacific ocean the relict reef in water depths of 25 50 m flourished in early holocene and covered an area more than 20 times larger than the modern reef radiocarbon and uranium series dating indicates that corals grew between 9000 and 7000 years ago the reef was subsequently drowned and backstepped to its modern limited extent this relict reef with localised re establishment of corals in the past three millennia could become a substrate for reef expansion in response to warmer temperatures anticipated later this century and beyond if corals are able to recolonise its surface citation woodroffe c d b p brooke m linklater d m kennedy b g jones c buchanan r mleczko q hua and j zhao 2010 response of coral reefs to climate change expansion and demise of the southernmost pacific coral reef geophys res lett 37 l15602 doi 10 1029 2010gl044067

carbonate lithofacies as paleolatitude indicators problems and limitations abstract detailed study of miocene carbonates in the mediterranean region and their analogues on modern carbonate shelves in the mediterranean sea brazil and other areas reveals at least three major types of carbonate platform lithofacies in addition to the classic tropical coral reef chlorozoan lithofacies a chloralgal lithofacies similar to the chlorozoan but without hermatypic corals b rhodalgal lithofacies characterized by abundant encrusting coralline algae and c molechfor lithofacies consisting of benthic foraminifers molluscs echinoids bryozoans and barnacles these carbonate lithofacies present complex distribution patterns seemingly related primarily to latitude and depth that control water temperature although other factors e g water circulation river discharge suspended sediment controlling water salinity and temperature nutrient content light penetration etc also play important roles chloralgal and rhodalgal lithofacies can be considered two transitional terms between the two end members the chlorozoan lithofacies which characterizes shallow tropical shelves and the molechfor lithofacies which characterizes colder and or deeper areas detailed textural and sequential analysis are required for satisfactory interpretation of these lithofacies in ancient rocks

chemical characteristics of the crater lakes of popocatetetl el chichon and nevado de toluca volcanoes mexico abstract three crater lakes from mexican volcanoes were sampled and analyzed at various dates to determine their chemical characteristics strong differences were observed in the chemistry among the three lakes nevado de toluca considered as dormant el chichon at a post eruptive stage and popocatepetl at a pre eruptive stage not surprisingly no influence of volcanic activity was found at the nevado de toluca volcano while the other volcanoes showed a correlation between the changing level of activity and the evolution of chemical trends low phs so 4 2 and f decreased irregularly at el chichon from 1983 until 1997 major cations concentrations also diminished at el chichon a 100 increase in the so 4 2 content was measured at popocatepetl between 1985 and 1994 an increase in the mg cl ratio between 1992 mg cl 0 085 and 1994 mg cl 0 177 was observed at popocatepetl before the disappearance of the crater lake in 1994 it is concluded that chemical analysis of crater lakes may provide a useful additional tool for active volcano monitoring

a 20 m middle pleistocene sea level highstand bermuda and the bahamas due to partial collapse of antarctic ice marine deposits at 20 3 m on the tectonically stable coastlines of bermuda and the bahamas support the hypothesis of a partial collapse of the antarctic ice sheet during the middle pleistocene beach sediments fill a sea cave at 22 m in bermuda and horizontal fenestrae filled beds crop out on platforms at two sites as high as 21 m in eleuthera bahamas carbonate beach sands are bound by an early generation of isopachous fibrous cement that is characteristic of a phreatic marine environment amino acid racemization and tims thermal ionization mass spectrometry dates constrain the age of the deposits to between 390 and 550 ka while proxy evidence supports a correlation with oxygen isotope stage 11 this direct geologic evidence of a 20 decrease in polar ice during the middle pleistocene has important implications for the stability of ice sheets during warm interglaciations

subtropical carbonates in a temperate realm modern sediments on the southwest australian shelf the southwestern continental margin of australia 19 degrees s 22 degrees s in the western indian ocean is transitional between cool water and warm water carbonate realms it comprises the incipiently rimmed flat topped steep fronted rottnest shelf in the south the uniform subtropical starved carnarvon ramp off shark bay and the ningaloo fringing reef in the north the margin is strongly influenced by the poleward flowing warm nutrient poor leeuwin current which promotes overall downwelling and strong summer equatorward blowing winds which generate local seasonal upwelling the structurally quiescent northern part of the rottnest shelf with minimum accommodation is characterized by luxuriant stands of sea grasses and macrophytes growing on coralline encrusted hardgrounds and rooted in sediments rich in coralline algae and larger symbiont bearing foraminifers together with abundant cool water elements such as bryozoans molluscs and small foraminifers halimeda is poorly calcified and does not contribute to the sediment azooxanthellate corals although present are not common such a sediment pattern has many analogs in the geologic record especially the early cenozoic the incipient rim is a morphologically complex linear ridge system interpreted to be a buried mid pleistocene barrier reef or beach dune complex the northern part of the ridge complex is capped by the houtman abrolhos reef platforms subphotic sediments on the deep outer shelf and upper slope affected by seasonal upwelling are typical cool water poorly sorted bryozoan dominated deposits rich in small foraminifers and sponge spicules the inner part of the more structurally active carnarvon ramp ranges from steep eolianite cliffs to hypersaline environments of shark bay to the ningaloo fringing reef mid ramp sediment especially off shark bay is mostly relict or stranded and foraminifer dominated sand with abundant mg calcite cemented intraclasts these sediments accumulating on a relatively barren seafloor likely represent attenuated carbonate production brought about by downwelling and episodic incursions of saline shark bay derived waters onto the ramp the outer ramp is either planktic foraminiferal sand sorted by strong bottom currents or spiculitic mud such sedimentation patterns should typify the western margins of large ocean basins during those periods in geologic history when circumglobal equatorial circulation was active and equatorial gateways narrow in contrast to eras of supercontinents when cool water carbonate sedimentation and upwelling prevailed in similar settings furthermore because low latitude trade winds relax during glacial epochs and the cool water upwelling belt moves equatorward into otherwise tropical realms temperate and subtropical sedimentation patterns in these regions should oscillate at the 100 ky scale in the stratigraphic record

a new coral reef province in the gulf of carpentaria australia colonisation growth and submergence during the early holocene abstract multibeam sonar mapping drill cores and underwater video data have confirmed the existence of a previously unknown coral reef province in the gulf of carpentaria australia seven reefs comprised of coral limestone that support living corals have been mapped so far and as many as 50 other reefs may exist in the region u th ages show that reef growth commenced shortly after limestone pedestals were submerged by rising sea level around 10 5 kyr bp making them the oldest holocene reefs known in australia reef growth persisted for 2 0 kyr but it had ceased at most locations by 7 0 kyr bp measurements of reef growth rates 0 95 to 4 m kyr 1 indicate that the reefs were unable to keep pace with contemporaneous rapid sea level rise 10 m kyr 1 which is consistent with a give up reef growth history core samples from reef platforms demonstrate that pleistocene limestone is exposed at depths of 27 and 30 m below present mean sea level these depths represent regionally significant phases of reef growth during a prolonged sea level still stand we conclude that the reefs are therefore mostly relict features whose major phase of growth and development relates to an earlier pre holocene sea level still stand

use of reaction path modeling to identify the processes governing the generation of neutral na cl and acidic na cl so4 deep geothermal liquids at miravalles geothermal system costa rica abstract the eq3 6 software package was used to investigate the irreversible water rock mass exchanges governing the production of neutral na cl and acidic na cl so 4 geothermal liquids circulating at depth into the miravalles geothermal system first we reconstructed the in situ reservoir composition including ph we evaluated the boundary conditions p co 2 p h 2 s and or p o 2 which are necessary for the implementation of reaction path modeling we estimated the thermodynamic affinity of the reservoir liquids with respect to relevant hydrothermal solid phases and we identified possible compositions of the initially acidic meteoric magmatic liquids then we modeled both the interaction between meteoric magmatic fluids and calc alkaline volcanic rocks and the interaction between neutral na cl waters and highly altered volcanic rocks reaction path modeling was performed through a purely stoichiometric approach without considering the kinetics of irreversible mass exchanges results of reaction path modeling suggest that the neutral na cl liquids hosted in the miravalles geothermal reservoirs are produced through interaction between initially acidic magmatic meteoric aqueous solutions and volcanic rocks and represent the final product of this process however the deep acid na cl so 4 liquids of miravalles are not intermediate products in this process they are instead generated through interaction of neutral na cl waters with volcanic rocks affected by advanced argillic alteration representing old solfataras buried by later volcanics as suggested by robert o fournier about 10 years ago

the geomorphology of the flanks of the lord howe island volcano tasman sea australia abstract the flanks of mid ocean volcanoes are inherently unstable features especially in the constructional phase of development when the volcano is active lateral and vertical stresses are placed on the volcanic edifice as it builds with the flanks continuing to be unstable up to at least 1 ma after volcanism has ceased the flanks of the lord howe island volcano record this period of greatest instability and a subsequent period in which marine and subaerial erosion have dominated its geomorphic evolution lord howe island lies in the tasman sea of the southern pacific region and is the subaerial remnant of a miocene mid ocean volcano the island has only recently entered reef building seas and therefore has been subject to marine erosive processes over the past 5 6 ma the island is unique as it sits on the stable drowned continental crust of the lord howe rise rather than oceanic crust like many other mid plate basaltic islands multibeam sonar bathymetry data were collected to a depth of 3500 m where the island flanks grade into the surrounding planar sea floor several slump features are evident the largest being over 130 km2 in area these features are inferred to be old late tertiary based on an extensive cover of marine sediment as indicated by low multibeam backscatter intensity and subdued topography most likely the slumps formed during the immediate post eruptive stage of volcano evolution before the bulk of the subaerial portion of the volcano was removed by marine erosion flank processes are now dominated by the deposition of carbonate sediment composed of mollusc and foraminiferal remains based on radiocarbon and stable isotope analyses of a sediment core 760 m depth collected on a trough in the centre of the volcanic edifice quaternary sediment was likely deposited predominantly during glacial periods the erosional morphology sediment cover and tectonic stability of the region suggest that the flanks of the volcano are at present relatively stable

geomorphology of submerged reefs on the shelf edge of the great barrier reef the influence of oscillating pleistocene sea levels the submerged reefs on continental margins and surrounding oceanic islands are important archives of past climates eustatic sea level oscillations and oceanographic processes australia s north eastern submerged shelf edge reefs have previously been explored but all studies have been limited by either low resolution single beam profiles or by their limited spatial extent the aim of this study is to improve the understanding of the origin and development of submerged shelf edge reefs terraces and related features on the great barrier reef gbr and the influence of pleistocene sea level oscillations on their distribution and geomorphology we investigated the first large scale 1400 km2 3d bathymetry and acoustic backscatter dataset of four widely spaced sites located across ca 650 km along the shelf edge at ribbon reefs 1 5 noggin pass viper reef and hydrographers passage we provide a comprehensive description and systematic classification of the shelf edge features and constrain their spatial distribution and geomorphologic variability using a wide range of quantitative morphometrics fifteen features are defined four of which are the focus of this study including terraces pinnacles ridges and channels using modern reefs within the gbr for comparison we interpret these as fringing reefs patch and barrier reefs and tidal channels respectively the influence of gross shelf geomorphology and oceanographic factors driving the observed variability within and between sites is discussed in conjunction with mid late pleistocene sea level oscillations we observed two distinct types of reef growth characterised by the degree of development which we interpret as analogous to juvenile and mature modern reefs of the gbr juvenile reefs are very common and occur within each site at depths of less than 50 m to greater than 100 m they are defined as discontinuous peaked barrier reefs peaked patch reefs and fringing reefs mature reefs are less common and develop exclusively at a depth range of ca 50 70 m these reefs are defined as flat topped continuous barrier and double barrier reefs through a comparison with published mid late pleistocene sea level oscillations we note that the depth range of mature reefs is consistent with the depth of repeated low amplitude 20 m eustatic sea level oscillations and independent of the relative time spent at sea level we conclude that repeated low amplitude sea level rises provide the much needed accommodation space for vertical accretion that is not provided during stillstands without inducing reef drowning which can be caused by high amplitude sea level rise low amplitude sea level falls are also less detrimental than high amplitude falls in terms of habitat compression together the effects of enhanced reef accretion and limited habitat compression at depths of 50 70 m have lead to a concentrated net gain in vertical relief that is not observed elsewhere on the shelf edge

simultaneous chatanika radar and s3 2 satellite measurements of ionospheric electrodynamics in the diffuse aurora simultaneous chatanika radar and s3 2 satellite measurements have been used to investigate the spatial variation of the auroral zone ionosphere near the equatorward edge of the diffuse aurora during early evening satellite passes on 2 days in february 1976 the equatorward boundary of the diffuse aurora was nearly overhead at chatanika the configurations of e region ionization and conductivity were nearly identical in both passes but the latitudinal variations of f region ionization were quite dissimilar during both passes the ionospheric electric field in the diffuse aurora was directed northward as a result the closing current of the field aligned current system was primarily a pedersen current and the eastward electrojet was larger than the northward ionospheric current although the morphology of ionospheric conductivity was very similar on the 2 days different patterns were observed for the latitudinal distribution of electric field and field aligned current

coherent radar estimates of average high latitude ionospheric joule heating the scandinavian twin auroral radar experiment stare and sweden and britain radar experiment sabre bistatic coherent radar systems have been employed to estimate the spatial and temporal variation of the ionospheric joule heating in the combined geographic latitude range 63 8 72 6 corrected geomagnetic latitude 61 5 69 3 over scandinavia the 173 days of good observations with all four radars have been analyzed during the period 1982 to 1986 to estimate the average ionospheric electric field versus time and latitude the ae dependent empirical model of ionospheric pedersen conductivity by spiro et al 1982 has been used to calculate the joule heating the latitudinal and diurnal variation of joule heating as well as the estimated mean hemispherical heating of 1 7 1011 w are in good agreement with earlier results average joule heating was found to vary linearly with the ae au and al indices and as a second order power law with kp the average joule heating was also examined as a function of the direction and magnitude of the interplanetary magnetic field it has been shown for the first time that the ionospheric electric field magnitude as well as the joule heating increase with increasingly negative southward bz

the chemistry of fumarolic vapor and thermal spring discharges from the nevado del ruiz volcanic magmatic hydrothermal system colombia on the basis of three sets of gas samples taken during the three months preceding the november 13 1985 eruption of nevado del ruiz from fumaroles on the crater floor the composition of the vapors discharged following minor eruptive activity in september corresponded to that of an essentially magmatic gas during the subsequent quiet period in october the proportion of a hydrothermal component in the vapor discharge increased steadily up until the major eruption the gases were found to be exceptionally high in total sulfur and are super saturated with respect to elemental sulfur their thermodynamic equilibration temperatures range from 200 to 600 c gases and waters from fumaroles and thermal springs on the flanks of the volcano are likely to be derived from a two phase vapor brine envelope surrounding the magmatic system the chemistry of the fumarole discharges is compatible with the assumption of an eruptive mechanism involving the build up of pressure in an extensive vapor zone by gas released from an essentially stagnant already extensively degassed body of magmatic material at depth production of such a residual gas over extended periods may account for the large amount of so2 discharged from the volcano in relation to the small amount of ejected solids

late pleistocene palaeocenography of the tasman sea implications for the dynamics of the warm pool in the western pacific quantitative analyses of planktonic foraminifera from 47 core top samples spatially distributed through the tasman sea and cores rc12 113 e36 23 dsdp sites 588 592 593 and odp site 828a from a n s transect supplemented with stable isotope analyses indicate that three planktonic foraminiferal assemblages defined by factor analysis on core top material correlated with three hydrographic modes defined on the basis of sea surface temperatures temperature profiles seasonal changes in temperature and mixed layer depth similar assemblages were found in down core material along the tasman sea transect that combined with semi quantitative analyses of foraminiferal assemblages provinces and the coiling ratio of globorotalia truncatulinoides allows reconstruction of the position of the tasman front or the subtropical divergence during the late brunhes chron the results indicate that the tasman front migrated from its present position at 30 s to 26 s during the last glacial maximum the northward migration of the tasman front may indicate a reduction in volume of the equatorial warm pool and or an increase in the strength of cool subtropical water masses the late pleistocene distribution of g truncatulinoides left coiling from appears to be related to the formation of subantarctic mode water thermostads this relationship may explain the evolutionary origin of this species in the southwest pacific at 2 4 ma simultaneously with the onset of late pliocene glaciations the past position of the subtropical convergence is reconstructed by means of coilingv directions in neogloboquadrina pachyderma the convergence apparently migrated slightly north of 43 s core e36 23 during glacial stages 6 10 and 12

hydrogeochemical processes occurring in the hydrothermal systems of the gonghe guide basin northwestern china critical insights from a principal components analysis pca the gonghe guide basin is a geologically complex area located in the northeastern qinghai tibet plateau although it is far away from the himalayan geothermal belt hot springs with high contents of sio2 li b and as are widely distributed there principal components analysis pca was used to identify the geochemical genesis of the major constituents in geothermal waters and cold groundwaters from the study areas as well as the related hydrogeochemical processes the results indicate that these constituents can be represented by six factors factor 1 f li k and sio2 factor 2 ec cl and na factor 3 ph text hco 3 mg2 and ca2 factor 4 b as fe and al factor 5 text so 4 2 and sr and factor 6 text no 3 generally the dissolution of silicate and carbonate minerals is the predominant geochemical processes responsible for the occurrence of the constituents that constitute factors 1 and 3 respectively in contrast although halite is not a primary mineral in the aquifer matrix its leaching results in the enrichment of chloride and sodium in the groundwaters which make significant contributions to the high ec values of some water samples although arsenic and boron are associated with factor 4 elevated levels of these elements in groundwater may be derived from the leaching of crystalline rocks like granite and gneiss rather than the input of potential magmatic fluids moreover anthropogenic activity has an impact on the hydrochemistry of the groundwaters as well as indicated by the elevated concentrations of nitrate the sole component of factor 6 in some samples it is also worth noting that the pca results may not match well with the hydrogeochemical analyses factor 5 is composed of sulfate and strontium whereas celestite is unlikely to be the primary source of sulfate in groundwater

the application of geochemistry to bicarbonate thermal springs with high reservoir temperature a case study of the batang geothermal field western sichuan province china abstract the batang geothermal field located at the north eastern margin of the qinghai tibet plateau is a high temperature geothermal system with two main geothermal areas namely bogexi and rekeng the rehai geothermal field is also a high temperature geothermal system with a magmatic heat source which shows geothermal manifestations similar to those in batang especially in the rekeng area in this study we compared the chemical compositions of different thermal springs in the batang geothermal field with those in the rehai geothermal field to ascertain whether the thermal spring waters in batang are also influenced by magma degassing or not further we investigated the hydrogeochemical processes involved in forming the various thermal springs in the batang geothermal field we find that the thermal waters in the batang geothermal field are not influenced by magma degassing although inorganic carbon including hco3 and co32 is the dominant anion component of most of the thermal waters in the batang geothermal field so42 is present in variable amounts in this area the mixing of the thermal waters with steam containing some amount of h2s generated by metamorphism probably causes the relatively high so42 concentration in the neutral thermal springs also beneath the rekeng area there is a deep reservoir with the temperature of about 180 c a shallow reservoir of a relatively low temperature of about 75 c was also identified in the eastern part about half of the thermal spring waters in rekeng directly originate in the deep reservoir mixing with little or no snow melt water and steam conversely no steady reservoir exists beneath the bogexi area we attribute the high levels of ca2 mg2 and tic total inorganic carbon in the thermal spring waters in the bogexi area to the carbonate geologic stratum distributed at the outlets of the springs

mineralogical crystal morphological and isotopic characteristics of smooth slope travertine deposits at reshuitang tengchong china abstract reshuitang is an important active hydrothermal area in the tengchong geothermal field and is characterized by many hot springs and their associated deposits detailed mineralogical crystal morphological and stable isotopic investigations of the smooth slope fossil travertines at reshuitang and hydrochemical studies of two active springs around the fossil travertines were conducted to study their genesis the results show that 1 the modern springs discharge waters with high temperature 70 c near neutral ph 6 3 8 34 and high saturation indices of calcite and aragonite 2 the fossil travertines contain calcite and small amounts of mn fe oxides halite thenardite and non carbonate debris 3 the calcite include ray crystals dendrite crystals platy crystals and spike crystals and 4 13c and 18o of the fossil travertines at reshuitang range from 1 59 to 0 87 and 6 48 to 7 80 respectively according to comparison between the travertines at reshuitang and other travertines in tengchong all these travertines are thermogene travertines with a large contribution of mantle degassing to their parent co2 but are formed at different temperatures the fossil travertines at reshuitang similar to those at shuzhishi are formed at high temperatures near 100 c which results in weak microbial activities during the formation of the fossil travertines most of the calcite crystals at reshuitang were non equilibrium products precipitated directly from the spring waters during the deposition process while the spike crystals originated from diagenetic dissolution of large calcite crystals comparison between the fossil travertines at reshuitang and other smooth slope travertines from other areas shows these smooth slope travertines have different lithofacies and fabrics in smooth slope environments temperature may control the distribution and development of microbes and the intensity of co2 degassing and consequently cause the precipitation of contrasting fabrics and lithofacies

sand and rhodolith gravel entrainment on the mid to outer shelf under a western boundary current fraser island continental shelf eastern australia abstract carbonate sediments on the east australian continental shelf off fraser island represent a transition from the warm water tropical carbonate deposits in the north i e the great barrier reef to cool water temperate carbonate deposits in the south on the outer shelf in 40 140 m water depth these deposits are characterised by pebble to cobble sized rhodoliths current meter data obtained from this area demonstrates that near bed southward flowing currents of up to 130 cm s occur episodically to depths of over 70 m these current events may last for several days and are probably related to intrusions of the east australian current a western boundary current onto the shelf flume experiments on different size classes of rhodoliths suggests that the threshold speed referenced to 100 cm above the bed u 100 cr for 10 mm diameter rhodoliths is of the order of 45 cm s whereas u 100 cr for 50 mm diameter rhodoliths is of the order of 80 cm s therefore the shelf currents measured are competent to initiate rhodolith movement percentage exceedence of these threshold speeds ranges from 1 to 10 surface waves also generate nearbed oscillatory flows which when combined with the steady current are considered to be important in initiating movement of the rhodoliths

magmatic fluid input explaining the geochemical anomaly of very high arsenic in some southern tibetan geothermal waters abstract tibet is characterized by extremely high terrestrial heat flow and widely distributed hydrothermal systems among which many are discharging geothermal waters with extremely high arsenic concentrations from over 10 mg l to up to 126 mg l the distribution of these high arsenic waters is basically in accordance with the location of the indian continental subduction zone a detailed analysis indicates that host rock leaching alone cannot explain the observed arsenic anomaly instead substantial contribution of arsenic from the underlying magma chambers is postulated which are likely mantle derived intrusions that have been severely contaminated by the very thick crustal material below southern tibet possibly including deep seated arsenic rich sedimentary rocks alternatively the partial melts at crustal depths reflected by the detected low velocity and or high conductivity anomalies in southern tibet serving as the magmatic heat source of the high arsenic hydrothermal systems may also form indirectly under the high temperature conditions generated by mantle upwelling or due to crustal thickening low sulfide concentrations further promote high dissolved arsenic concentrations with little formation of thioarsenates and no precipitation of limiting arsenic sulfide phases in contrast mantle magmas less affected by crustal contamination serving as the heat source of many hydrothermal systems in rift zones and hot spots worldwide where the crust is thinner are releasing magmatic fluids lower in arsenic and higher in mantle sulfur species overall the existence of a magmatic heat source alone does not ensure the formation of geothermal waters with very high arsenic concentrations and geothermal waters from sedimentary rock hosted systems are neither necessarily arsenic rich the most critical factor controlling the arsenic concentration of geothermal water discharging from a magmatic hydrothermal system is the geological genesis of the magma fluid and its chemical composition

response of the dayside auroral and electrodynamic processes to variations in the interplanetary magnetic field the response of the dayside auroral and electrodynamic processes to variations in the interplanetary magnetic field imf is examined with multi instrument data from the viking and dmsp f7 satellites as well as ground magnetometer data the event selected which occurred on october 5 1986 was previously identified as a high latitude dayside form by murphree and elphinstone 1988 imf by was positive during most of the viking auroral uv observation whereas imf bz made a transient southward excursion followed by a sharp increase to 8 nt the results are summarized as follows 1 there were two auroral belts extending westward from the early afternoon sector the equatorward belt was persistent throughout the event and was embedded in the cps bps precipitation region whereas the poleward belt was in the open field line region and was associated with northward imf bz 2 a new auroral spot emerged in the afternoon sector just poleward of the previously active region delayed 10 min from the sudden increase in imf bz this time lag is ascribed to the travel time of the new imf orientation from the subsolar point to a solar wind magnetosphere interaction site tailward of the dayside cusp as well as to the response time of the dayside auroral acceleration process 3 the new auroral activity expanded both eastward and westward during the first few minutes and then expanded primarily westward across the noon meridian forming the poleward belt the speed of the westward extension in the second phase was comparable to the speed of the ionospheric convection 4 the dayside auroral process has a finite decay constant which is inferred to be at least 10 min 5 the response time of the midday ionospheric convection to imf variations is estimated to be a few to several minutes

the diurnal and latitudinal variation of auroral zone ionospheric conductivity the great spatial and temporal variability of auroral ionospheric conductivity significantly influences the ionospheric closure path for high latitude field aligned currents because these closure paths can extend to low latitudes changes in auroral zone conductivity can influence the global electric field distribution in this paper synoptic chatanika radar observations of auroral zone conductivity that cover 62 to 68 geomagnetic latitude are presented they are representative of quiet winter active winter and equinoctial conditions during the daytime the solar contribution to the height integrated conductivity is well represented by p h 5 10 cos1 2 where is the solar zenith angle the nighttime height integrated pedersen and hall conductivities p and h in the electron density trough are at times below our detection threshold of 0 5 mho following magnetic substorm onset enhanced conductivity regions move southward and intensify as the recovery phase begins the conductivity pattern recedes northward and diminishes the onset and cessation of precipitation associated with these events can be as abrupt as a few minutes in one example the behavior of p and h are examined in the vicinity of the harang discontinuity which was quite sharp 30 min in local time at the harang discontinuity on that day the ratio of h to p decreased indicating a softening of the precipitating energy distribution

orbital forcing of the marine isotope stage 9 interglacial milankovitch orbital forcing theory has been used to assign time scales to many paleoclimate records however the validity of this theory remains uncertain and independent sea level chronologies used to test its applicability have been restricted largely to the past approximately 135 000 years here we report u series ages for coral reefs formed on henderson island during sea level high stands occurring at approximately 630 000 and approximately 330 000 years ago these data are consistent with the hypothesis that interglacial climates are forced by northern hemisphere summer solar insolation centered at 65 degrees n latitude as predicted by milankovitch theory

an introductory perspective on non tropical shelf carbonates abstract this brief account introduces the topic of non tropical shelf carbonate deposits both modern and ancient specific aspects of which are described and discussed in the 22 accompanying papers in this special issue of sedimentary geology non tropical shelves are loosely defined as lying poleward of the present limit of development of hermatypic coral reefs or beyond the mean annual surface water isotherm of about 20 c typically near 30 latitude most geoscientists have traditionally regarded shallow water carbonate formation as a low latitude phenomenon however wherever the rate and extent of terrigenous sediment dilution is small the potential exists for extensive deposits of skeletal carbonate to accumulate on shelves beyond the sub tropics the facies attributes of the modern non tropical carbonates are distinctive and contrast significantly with the structural lithological faunal floral mineralogical and diagenetic character of their tropical counterparts in the rock record non tropical limestones probably occur throughout the phanerozoic but generally remain to be identified and or interpreted as such they are presently described mainly from the ordovician permian and tertiary quaternary periods of major continental glaciations and accentuated latitudinal thermal gradients a uniformitarian approach to the recognition and interpretation of ancient shallow marine limestones requires acceptance of both tropical and non tropical carbonate facies models

components facies and ramps redefining upper oligocene shallow water carbonates using coralline red algae and larger foraminifera venetian area northeast italy abstract chattian mixed carbonate siliciclastic deposits from two palaeogeographic units of southern alps the lessini shelf and venetian foreland basin of northeast italy are studied with respect to facies distributions and controlling ecological factors on dominant biogenic components these ramp depositional systems are located in the western southern alps on the lessini shelf and in the eastern southern alps in the venetian foreland basin the successions show an extensive geographic distribution of at least 150 km 40 km at the southern margin of the southern alps palaeoenvironments are inferred following microfacies characteristics and floral and faunal indicators especially those of coralline red algae and larger foraminifera an inner to middle homoclinal ramp morphology is reconstructed based on facies distributions and taxonomic and coralline algal growth form proxy data the distribution along depositional strike shows variation from thinner carbonate dominated sequence in the west monti berici and monti lessini to a more variable mixed carbonate siliciclastic dominated environment to the east vittorio veneto alpago facies character and occurrence are controlled by local hydrodynamic conditions and varying water turbidity of the studied ramp depositional system the general facies succession shows a transgressive sequence from the proximal inner to proximal middle ramp a shoal belt of trough cross bedded sandstones occurs in a proximal inner ramp position in all of the studied areas in a gentle dipping homoclinal ramp most benthic organisms inhabited the relatively quite environments off these shoals in a distal inner ramp setting basinward environments proximal middle ramp constitute areas of maximal carbonate production and consist primarily of larger foraminiferal facies and rhodolith pavements larger foraminifera represented by two larger foraminiferal assemblages are most diversified in the shallower settings near the fair weather wave base distal inner proximal middle ramp whereas coralline algae predominate in deeper areas proximal middle ramp constructing extensive rhodolith pavements rhodolith pavements are distinguished with respect to rhodolith shape size growth forms and coralline algal taxonomic composition larger foraminifera are interpreted with respect to shell structures shell architectures and comparable recent counterparts the analysed benthic communities thrived in a mesotrophic regime within trophic gradients constrained by fluvial influence coralline algal dominance and a moderately diverse larger foraminiferal assemblage suggest a tropical warm temperate transition the considerable stability imposed on sediments by the rhodolith pavement must also have significantly contributed to the maintenance of a middle ramp profile bulge this study will contribute to a better understanding of oligocene carbonates which have received less attention than their eocene or miocene counterparts

observations of structured optical emissions and particle precipitation equatorward of the traditional auroral oval 1 high sensitivity all sky images from south central alaska show the common occurrence of slow moving faint optical emissions at 557 7 and 427 8 nm well equatorward of the discrete aurora these emissions appear over a continuum of forms ranging from homogenous longitudinal bands to bands with irregular structure on their poleward edge to widely distributed arrays of vortex like curls and widely spaced spots on the order of 10 km in diameter these forms appear to correspond to various stages in the temporal evolution of nearly corotating precipitation regions populated by particles injected from more distant areas of the magnetosphere and may exhibit morphological control by an instability operating on cold plasma near the plasmapause although these phenomena are most common in the evening hours and typically persist for hours at a time one case demonstrates that the features can remain throughout the night on occasion these faint optical features appear to be colocated with regions of enhanced background counts in dmsp particle measurements and to be associated with the ring current outer radiation belt region equatorward of subauroral polarization streams saps the features can occur in conjunction with hf and mf radio frequency absorption at levels which are often too low to show up on routine absorption instruments such as the riometer this has practical implications on the operation and interpretation of ionospheric interaction experiments carried out in the subauroral region

hydrogeochemistry and environmental impact of geothermal waters from yangyi of tibet china abstract the yangyi geothermal field located 72 km northwest to lhasa city capital of tibet has a high reservoir temperature up to at least 207 2 c the geothermal waters from both geothermal wells and hot springs belong to the hco 3 co 3 na type factor analysis of all the chemical constituents shows that they can be divided into two factors f 1 factor receives the contributions of so 4 2 cl sio 2 as b na k and li whereas f 2 factor is explained by hco 3 f co 3 2 ca 2 and sr 2 the f 1 factor can be regarded as an indicator of the reservoir temperature distribution at yangyi but its variable correlation with the results of different geothermometers na k quartz and k mg does not allow one to draw further inferences different from f 1 the f 2 factor is an indicator of a group of hydrogeochemical processes resulting from the co 2 pressure decrease in geothermal water during its ascent from the deep underground including transformation of hco 3 to co 3 2 precipitation of ca 2 and sr 2 and release of f from some fluoride bearing minerals of reservoir rocks the plot of enthalpy vs chloride prepared on the basis of na k equilibrium temperatures suggests that a parent geothermal liquid pgl with cl concentration of 185 mg l that of sample yyt 8 and enthalpy of 1020 j g corresponding to a temperature of 236 237 c i e somewhat higher than that of sample yyt 6 is present in the geothermal reservoir of the yangyi area below both the qialagai valley and the bujiemu valley although the samples less affected by mixing and cooling yyt 6 and yyt 7 come from the second site the discharge of geothermal waters with high contents of toxic elements such as b as and f into the luolang river the only drinking water source for local residents has caused slight pollution of the river water great care should therefore be taken in the geothermal water resource management at yangyi

the paradox of drowned carbonate platforms and the origin of cretaceous pacific guyots geochemical stratigraphic and palaeolatitudinal data from deep boreholes drilled through pacific guyots flat topped seamounts help to explain the drowning of these cretaceous shallow water carbonate platforms that once thrived through the accumulation of biogenic and inorganic calcium carbonate sediment in mid oceanic regions the platforms drowned sequentially over a 60 million year interval while they were being transported northward by pacific plate motion through a narrow equatorial zone 0 10 s such platforms were apparently resistant to the effects of cretaceous oceanic anoxic events although the mechanism responsible for drowning remains unknown the tropics have not always been the refuge for atolls that they are today

hydrogeochemistry of high temperature geothermal systems in china a review as an important part of the mediterranean himalayas geothermal belt southern tibet and western yunnan are the regions of china where high temperature hydrothermal systems are intensively distributed of which rehai yangbajing and yangyi have been investigated systematically during the past several decades although much work has been undertaken at rehai yangbajing and yangyi to study the regional geology hydrogeology geothermal geology and geophysics the emphasis of this review is on hydrogeochemical studies carried out in these geothermal fields understanding the geochemistry of geothermal fluids and their environmental impact is critical for sustainable exploitation of high temperature hydrothermal resources in china for comparison the hydrogeochemistry of several similar high temperature hydrothermal systems in other parts of the world are also included in this review it has been confirmed by studies on cl and stable isotope geochemistry that magma degassing makes an important contribution to the geothermal fluids from rehai yangbajing and yangyi though meteoric water is still the major source of recharge for these hydrothermal systems however the mechanisms of magma heat sources appear to be quite different in the three systems as recorded by the 3he 4he ratios of escaping geothermal gases a mantle derived magma intrusion to shallow crust is present below rehai although the intruding magma has been heavily hybridized by crustal material by contrast the heat sources below yangbajing and yangyi are inferred to be remelted continental crust besides original sources the geochemistry of characteristic constituents in the geothermal fluids have also been affected by temperature dependent fluid rock interactions boiling and redox condition changes occurring in the upper part of hydrothermal systems and mixing with cold near surface waters the geothermal fluids from rehai yangbajing and yangyi contain very high concentrations of some toxic elements since local drinking water sources may be mixed with geothermal water and irrigation with water containing geothermally derived harmful elements possibly leading to accumulation in crops consumed by human beings the natural geothermal spring discharge or anthropogenic geothermal wastewater drainage of these fields poses a threat to the environment and human health future research work should focus on estimation of stable o and h isotope compositions of magmatic water related to high temperature hydrothermal systems in china which is of significance for the quantitative source study of geothermal fluid recharged by degassed magmatic waters attention should also be paid to some constituent species in geothermal fluid of strong environmental significance such as thioarsenate that is crucial for the fate of as discharged from geothermal springs especially sulfidic hot springs

fluid geochemistry and geothermometry applications of the kangding high temperature geothermal system in eastern himalayas abstract high temperature geothermal systems hold an enormous capacity for generating geothermal energy the kangding area is a typical high temperature geothermal field in the himalayan geothermal belt hydrogeochemical gas geochemical and isotopic investigations were performed to identify and qualify the main hydrogeochemical processes affecting thermal water composition including mixing and degassing and then to estimate a reliable reservoir temperature nine water samples and four geothermal gas samples were collected and analysed for chemical and isotopic components the results demonstrate the alkaline deep geothermal water is the mixtures of approximately 75 snow melt water and 25 magmatic water it is enriched in na k f li and other trace elements indicating the granite reservoir nature the shallow geothermal water is the mixtures of approximately 30 upward flow of deep geothermal water and 70 meteoric cold water high concentrations of ca mg and hco3 indicate the limestone reservoir nature there is no remarkable oxygen isotope shift in the geothermal water since the rapid circulation is difficult to trigger off strong water rock interaction co2 is the predominant geothermal gas accounting for more than 97 of total gases in volume percentage the concentration of co2 degassing ranged from 0 4 mol l 1 to 0 8 mol l 1 via geothermometrical modelling as a result the geothermal water ph increased from 6 0 to 9 0 and approximately 36 of the total sio2 re precipitate the sources of co2 are the metamorphism of limestone and magmatic degassing based on the composition of carbon isotope the appropriate geothermometers of na k and na li yield reservoir temperature of 280 c the geothermometrical modelling developed to eliminate the effects of co2 degassing yields temperature of 250 c the silica enthalpy mixing model yields temperature of 270 c with no steam separation before mixing

variability of the harang discontinuity as observed by the chatanika radar and the ims alaska magnetometer chain the relative location of ionospheric parameters and ground magnetic perturbations in the vicinity of the harang discontinuity is examined for this purpose we use combined observations of the chatanika incoherent scatter radar and of the ims alaska meridian chain of magnetometers which were continuously measuring the crucial ionospheric parameters near the harang discontinuity when a sizeable substorm took place the harang discontinuity as defined by the reversal of the north south electric field is found to be located at 1 2 poleward of the discontinuity identified by the conventional method of using ground magnetic perturbations it is also found that the relative location of auroral conductivity enhancements is quite variable depending perhaps upon substorm time during relatively quiet times and the early stage of a substorm a conductivity enhancement occurs only on the poleward side of the harang discontinuity defined by the electric field reversal whereas the enhancement surges equatorward extending beyond the discontinuity during the maximum to recovery phase of a substorm

intense growth phase events of substorms over the past few decades several events of the intense growth phase preceding the expansion onset of substorms were reported we reexamine these events using an extensive set of data including ground based magnetograms at auroral latitudes solar wind data from the wind and imp 8 satellites and auroral uv images from the polar and viking satellites magnetograms show that the intense auroral electrojet is located in the early morning sector during these events a common feature among the corresponding solar wind conditions for these events is the existence of a period of southward interplanetary magnetic field imf preceded by a prolonged northward imf this intense growth phase however seems to be independent of the imf by polarity enhanced auroras in the early morning sector appear during the growth phase these auroras are consistent with relatively large geomagnetic disturbances during these events indicating that enhanced conductances combined with enhanced electric field caused by southward imf play an important role in the auroral electrojet during these intense growth phase events

arsenic and thioarsenic species in the hot springs of the rehai magmatic geothermal system tengchong volcanic region china abstract rehai is the sole geothermal area in mainland china that discharges both acidic and alkaline hot springs with phs ranging from 1 4 to 10 0 the hot springs in rehai are also characterized by a wide range of arsenic concentrations with the highest being 1 35 mg l analysis of the arsenic geochemistry indicates that the alkaline and neutral hot springs in rehai have high arsenic concentrations the alkaline hot springs represent arsenic rich boiled reservoir fluids and the neutral hot springs represent mixtures of these reservoir fluids with non thermal waters and or condensed steam the enrichment of arsenic in the deep reservoir fluids also called primary fluids is primarily attributable to the leaching of reservoir rocks at high temperatures but a possible arsenic contribution from magmatic fluids cannot be ruled out the acidic springs in contrast have much lower arsenic concentrations because they are a mixture of non thermal oxygenated waters and condensed steam both of which are depleted in arsenic in addition to arsenite and arsenate mono di and tri thioarsenates have been detected in the rehai geothermal waters the arsenic speciation in the rehai hot springs is primarily linked to the formation processes of the various secondary fluids at the surface and their sulfide concentrations in addition the speciation is also affected by the ph values and the redox potentials of the waters compared to the springs along secondary e w trending faults the chloride rich springs along the main n s trending faults are generally much less affected by mixing with non thermal waters and or condensed steam they are also more enriched in sulfide and thioarsenates consequently represent a greater proportion of the total arsenic this is the first study to report the thioarsenic geochemistry of hot springs in china

coastal wetlands reveal a non synchronous island response to sea level change and a palaeostorm record from 5 5 kyr to present here we describe environmental change on lord howe island lhi 31 30 s 159 05 e over the last 5500 cal bp derived from the analysis of the accumulating sediments in four coastal wetlands grain size analyses loss on ignition loi and micrometre resolution x ray fluorescence xrf geochemical data were combined with 10 accelerator mass spectrometry ams 14c dates to determine a chronology of environmental change sedimentary coastal features were initiated on the drowned lhi basalt coastline after 4500 cal bp which was followed by gradual development of wetland environments from 4200 cal bp to present within this period a series of high intensity storm events are recorded perhaps related to low pressure systems including cyclones and east coast low ecl events a lack of synchronicity between the studied sites resulted from their position in the landscape relative to the coast features within the lagoon and greater sediment availability after 2800 cal bp as sediment filled sinks in the

isotopic and chemical composition of water and steam discharges from volcanic magmatic hydrothermal systems of the guanacaste geothermal province costa rica the guanacaste geothermal province encompasses three major geothermal systems each centered on its respective volcanic structure rincon de la vieja to the nw miravalles in the center and tenorioto the se each shows corresponding sets of surface manifestations vapor discharges from fumaroles and steam heated pools at altitudes 500 m lower temperature so4cl springs on the lower slopes of the respective volcano and cooler neutral cl springs to the s of the volcanic chain at altitudes 500 m the production of hco3 rich waters is limited to a narrow belt stretching to the s of miravalles volcano chemical and isotopic evidence suggests that the neutral cl waters also discharged from deep wells are derived from a more primitive clso4 water formed by transfer of readily mobilised originally magmatic constituents to deeply circulating groundwater isotopic evidence suggests that this groundwater is derived largely from areas to the north of the volcanic chain the presence of immature waters within drillable depth is indicated by the incursion of an acid so4 water into a well at miravalles after deepening to 2000 m as the cl waters rise they start to boil the separated vapors feed the fumaroles and steam heated features at the surface the residual water travels underground to be discharged some 5 25 km to the s the uniformity in chemical and isotopic compositions of the neutral cl waters is compatible with the assumption that the individual thermal systems are linked at depth to form large contiguous geothermal reservoirs beneath the guanacaste geothermal province

characteristics of nighttime medium scale traveling ionospheric disturbances observed over alaska 1 we focused on propagating wave like structures which frequently appeared in the o i 630 0 nm airglow images obtained by an all sky imager installed at poker flat research range 65 1 n 147 4 w magnetic latitude 65 6 in alaska these events are classified as medium scale traveling ionospheric disturbances mstids on the basis of the wavelength and propagating speed the unique points of our observation are 1 the two dimensional structures of mstids in the subauroral region are revealed 2 the horizontal direction of the electric field can be estimated from the motion of the evening co rotating patch ecp aurora appearing simultaneously and 3 neutral winds are simultaneously observed by a fabry perot spectrometer statistical study of these mstid events from november 2001 to april 2002 indicates the following characteristics the mstids were observed almost every evening and sometimes in the morning but were not observed at midnight typical propagating speed direction and wavelength of the wave phenomena were about 135 m s southwestward and about 250 km respectively when the mstids appeared northward neutral winds and westward plasma drifts were dominant this indicates that the perkins instability does not contribute to the development of mstids in the alaska region the vertical wavelength analysis using the dispersion relation of gravity waves with the observed wave parameters and background winds suggests that the observed mstids over alaska are the atmospheric gravity waves agws as a case study temporal variation of an mstid event on 21 december 2001 is shown results of a ray tracing analysis of this event suggest that the agws come from the equatorward edge of the auroral oval

critical depth for the survival of coral islands effects on the hawaiian archipelago coral islands drown when sea level rise exceeds the maximum potential of coral reefs to grow upward about 10 millimeters per year during the holocene transgression 18 000 years ago to present sea levels rose at rates of up to 10 to 20 millimeters per year and most coral island reefs situated deeper than a critical depth of30 to 40 meters below present day sea level drowned coral islands that did not drown during the holocene transgression apparently all developed on antecedent foundations shallower than critical depth during low stands in sea level during the pleistocene these islands were elevated and subject to subaerial erosion today in the hawaiian archipelago the depth of drowned banks is inversely related to summit area smaller banks are progressively deeper evidently because of erosional truncation during low sea level stands bank summit area may therefore be an important factor determining the failure or success of coral islands

shore platform development around lord howe island southwest pacific this paper describes the morphology of near horizontal basalt and calcarenite shore platforms around lord howe island as well as the lithological and process environment in which they occur the morphology of platforms around the island is highly varied for instance they occur at a wide range of elevations between low tide level and several metres above the highest tides and their width ranges between just a few metres to over 100 m however common to most platforms is that they have near horizontal surfaces that terminate abruptly in a steep scarp at their seaward edge correlations indicate that the variability in platform elevation and width is attributable to variability in key parameters of erosion such as rock resistance and shoreline water depth whereas wider platforms occur in rocks of lesser resistance platform elevation is shown to increase both as rock resistance and the depth of water at the shoreline increases wave exposure has a significant control on platform width in some instances but an over arching relationship was not detected most platforms around the island appear to have developed over the holocene and a conceptual model is proposed to account for the varied morphology of platforms that have developed over this period resistant plunging cliffs occur along about 18 of the rocky coastline of lord howe island and represent the starting point for the model where cliffs have yielded to wave erosion platforms have been initiated at an elevation controlled predominantly by rock resistance and shoreline water depth at lord howe island narrow platforms up to about 20 m wide in exposed locations generally occur about 4 to 6 m above high tide level and have apparently been subject to very infrequent erosion shore platforms about 20 to 40 m wide have generally formed in less resistant rocks are somewhat lower at about 2 to 3 m above high tide level and have been subject to more frequent erosion over the holocene most basalt platforms around the island fall within these first two categories but there are some instances of platforms about 50 m wide these platforms have formed in rocks of comparatively low resistance and are relatively low in elevation occurring close to the level of high tide an interesting feature of some of these wide platforms is that unlike the morphology of narrower platforms raised ramparts sometimes occur on their outer edge

environmental impacts of geothermal waters with extremely high boron concentrations insight from a case study in tibet china abstract boron is a potentially toxic element in the environment and commonly enriched in high temperature geothermal waters in this study seven typical boron rich geothermal areas in tibet china were selected as the study areas for comprehensively investigating the geochemistry of geothermal boron and its environmental impact the geothermal waters were classified into four types acid low boron waters acid high boron waters neutral alkaline low boron waters and neutral alkaline high boron waters the enrichment of boron in the neutral alkaline high boron geothermal waters is attributed to the input of magmatic fluids whereas the host rock leaching is the primary boron source for the neutral alkaline low boron geothermal waters the acid low boron waters are essentially locally perched groundwaters heated by geothermal vapors separated from flashed deep geothermal fluids and thereby their boron comes mainly from the limited leaching of the host rocks of the shallow aquifers as for the acid high boron waters they could be formed via a mixing between acid low boron waters and neutral alkaline geothermal waters with the latter as the primary boron source the boron species in these geothermal waters comprise mainly h3bo3 b oh 4 polyborate ions and fluoroborate complexes all of which are affected by the ph temperature and f and b concentrations of the waters when the geothermal waters flow out of the hot spring vents the rapid changes in unstable parameters like ph and water temperature will lead to the conversion of b oh 4 and polyborate ions to h3bo3 the discharge of the boron rich geothermal waters has contaminated the surface waters and sediments in and around the investigated geothermal areas in turn the boron sorbed onto into the hot spring sediments is liable to be released either in short term if it is originally exchangeable boron or in long term if carbonates fe mn oxides or organic matters sulfides combined boron this study enhances the understanding of geothermal boron speciation and its environmental impact and provides insights for rational exploitation of hydrothermal resource without inducing geothermal boron pollution

altitudinal comparison of dayside field aligned current signatures by viking and dmsp f7 intermediate scale field aligned current systems dayside large scale and intermediate scale field aligned current fac signatures are examined with multi instrument measurements from viking and dmsp f7 at magnetic conjunctions the present paper reports four such conjunction events with an emphasis on an event that occurred on october 13 1986 in these four events both viking and dmsp f7 crossed prenoon fac systems approximately along meridians the altitude of dmsp f7 was 835 km whereas that of viking ranged from 8500 to 12 000 km the electric to magnetic field ratio measured by viking indicates that intermediate scale fac systems as well as large scale fac systems are often quasi stationary this is also supported by the comparison between the viking and dmsp f7 magnetic measurements the only obvious exception is the equatorward part of the october 13 event in which the viking and dmsp f7 measurements are better explained in terms of alfven waves in two other events the viking signature projected to the dmsp f7 altitude is significantly more structured than the dmsp f7 signature although the electric to magnetic field ratio observed by viking suggests that the associated facs were quasistationary this apparent discrepancy is possibly ascribed to the fact that viking stays longer in fac systems and therefore has more chance to observe temporal changes in facs however such temporal effects must operate longer than the alfven transit time so that fac systems become quasi stationary although the generation mechanism s of intermediate scale fac systems remains an open question possibilities include a localized shear of plasma convection and a localized merging between the solar wind and magnetospheric field lines

submerged fossil reefs discovered beyond the limit of modern reef growth in the pacific ocean abstract balls pyramid is the southernmost island in a linear island chain in the southwest pacific ocean 24 km south of the limit of known coral reef formation at lord howe island this paper describes the geomorphometric structure of the shelf surrounding balls pyramid through the application of remote sensing data to create a high resolution digital elevation model of the shelf 5 m cell size and seafloor feature classification seafloor features were delineated using the bathymetry model together with slope backscatter and sub bottom profile data the average depth of the 260 6 km2 shelf was 55 m 21 m with the majority of shelf area 77 within 30 60 m water depth dominating the shelf is an extensive mid shelf reef at 30 50 m depth dissected by basin and channel features outer shelf reef and platform features surround the mid shelf with terrace sequences marking the seaward outer shelf rim in 65 100 m depth sub bottom profiles and backscatter data demonstrate substantial accumulation up to 16 5 m of unconsolidated sediments within basin and channel features the submerged mid shelf reefs of balls pyramid are similar to the fossil coral reef system discovered on the lord howe island shelf implying origins as a drowned coral reef system this paper reveals complex shelf topography with extensive submerged reefs on what was previously considered to be a planated volcanic shelf outside of reef forming seas

major hydrogeochemical processes in the two reservoirs of the yangbajing geothermal field tibet china abstract the yangbajing geothermal field with the highest reservoir temperature in china is located about 90 km northwest to lhasa city capital of tibet where high temperature geothermal fluids occur both in shallow and deep reservoirs the geophysical survey by the indepth international deep profiling of tibet and the himalayas project group proved the existence of magmatic heat source at yangbajing in the study area the hydrochemistry of cold surface waters and groundwaters and that of thermal groundwaters from both reservoirs are distinctively different however analysis of the relationship between enthalpy values and cl concentrations of cold groundwaters and geothermal fluids indicates that the geothermal fluids from the shallow reservoir were formed as a result of mixing of cold groundwaters with geothermal fluids from the deep reservoir in other words the geothermal fluids from the deep reservoir flowed upwards into the shallow reservoir where it was diluted by the shallow cold groundwaters to form the shallow geothermal fluids with much lower temperature a binary mixing model with two endmembers the cold groundwaters and the deep geothermal fluids was proposed and the mixing ratios for the geothermal fluid from each shallow well were estimated using the mixing ratios the concentrations of some constituents in shallow geothermal fluids such as as b sio 2 so 4 2 and f were calculated and their differences with the actual concentrations were estimated the results show that the differences between estimated and actual concentrations of as and b are small the average absolute values being only 1 9 and 7 9 respectively whereas those of sio 2 so 4 2 and f are much bigger indicating that other hydrogeochemical processes are responsible for the concentrations of these constituents it is postulated that sio 2 precipitation due to water temperature decrease h 2 s oxidation and ion exchange between oh in geothermal waters and exchangeable f in fluoride bearing silicate minerals during the geothermal fluid upflow might be the causes for the observed concentration differences

carbonates calibrated against oceanographic parameters along a latitudinal transect in the gulf of california mexico trophic resources are an important control governing carbonate production though this importance has long been recognized no calibration exists to quantitatively compare biogenic assemblages within trophic resource fields this study presents a field calibration of carbonate producers in a range of settings against high resolution in situ measurements of nutrients temperature and salinity with its latitudinal extent from 30 to 23 n the gulf of california mexico spans the warm temperate realm and encompasses nutrient regimes from oligo mesotrophic in the south to eutrophic in the north accordingly from south to north carbonates are characterized by i coral dominated shallow carbonate factories 5 20 m water depth with average sea surface temperatures of 25 c min 18 c max 31 c average salinities of 35ae06 and average chlorophyll a levels which are a proxy for nutrients of 0ae25 mg chl a m 3 max 0ae48 min 0ae1 ii red algal dominated subtidal to inner shelf carbonate formation 10 25 m in the central gulf of california exhibiting average temperatures of 23 c min 18 c max 30 c average salinities of 35ae25 and average chl a levels of 0ae71 chl a m 3 max 5ae62 min 0 iii molluskan bryozoan rich inner to outer shelf factories in the northern gulf of california 20 50 m with average sea surface temperatures of only 20 c min 13 c max 29 c average salinities of 35ae01 and average contents of 2ae2 mg chl a m 3 max 8ae38 min 0 by calibrating sedimentological data with in situ measured oceanographic information in different environments the response of carbonate producers to environmental parameters was established and extrapolated to carbonates on a global scale the results demonstrate the importance of recognizing and quantifying trophic resources as a dominant control determining the biogenic composition and facies character of both modern and fossil carbonates

holocene lagoonal sedimentation at the latitudinal limits of reef growth lord howe island tasman sea abstract the southernmost limit to coral reef growth occurs on lord howe island 33 30 s 159 05 e where a discontinuous fringing reef flanks the western side of the island coring and radiocarbon dating indicate that carbonate sediments were first deposited within the lagoon around 6500 radiocarbon years bp coincident with sea level reaching close to its modern level high energy conditions dominated the reef with robust branching corals dominating the developing reef growth of the reef crest between 6000 and 5000 yr bp is inferred to have caused a reduction in the energy conditions within the lagoon resulting in mud deposition during this period sedimentation occurred at average rates of around 5 mm yr though locally up to 10 mm yr which infilled almost all the available accommodation space in the lagoon by 4000 yr bp most of the lagoon had accreted to a level very close to the modern lagoon floor having accumulated over 11 m of sediment in the northern part of the lagoon and possibly up to 30 m in the south sediments younger than 3000 yr bp form a thin veneer over these older units with the main deposition being confined to embayments the coastal plain and the infilling of blue hole depressions the reef and lagoon fringing lord howe island appear to have developed their present form primarily during a phase of luxuriant growth in the mid holocene

thermoluminescence dating of aceolianites from lord howe island and south west western australian abstract views differ as to how the deposition of aeolianites correlate with glacial interglacial cycles this study evaluates the potential of thermoluminescence tl dating to determine the timing of aeolianite deposition at two australian sites the study areas are rottnest island and the fremantle coastline in western australia and lord howe island in the tasman sea the chronostratigraphy of aeolianite on lord howe island has been comprehensively examined by brooke 1999 whereas the depositional chronology of western australian aeolianite is known only from dating at one or two key sites tl dating provides a chronological framework for both sites and reveals that the timing of deposition of these aeolianites is probably related to sediment supply dune and minor associated marine deposits of lord howe island appear to have been emplaced mainly during sea level highstands when the shelf surrounding the island was flooded and beach sediments accumulated in contrast the aeolianites upon rottnest island and along the adjacent western australian coastline seem to have been deposited during periods of both high and low sea level indicating a more continuous supply of shallow marine sediments

fluid geochemistry of the cuopu high temperature geothermal system in the eastern himalayan syntaxis with implication on its genesis abstract high temperature geothermal fluids dissolve constituents pertinent to water rock interaction and magmatic volatile absorption resulting in high total dissolved solid tds values however this study focuses on the hydrochemical evolution of the low salinity hco3 na type high temperature geothermal fluid in cuopu eastern himalayas the geothermal water is recharged by local precipitation and glacier water from surrounding mountains the tds values are below 834 mg l and the constituents are mainly products of the water carbon dioxide rock interactions lacking magmatic volatile dissolved in the fluid the geothermal water reaches an almost complete chemical equilibrium with the feldspar or plagioclase enriched reservoir rock in a reducing condition the reservoir temperature is between 175 c 200 c while the temperature could reach up to 400 c in the deep crustas indicated by the carbon isotopic exchange equilibrium between co2 and ch4 the infiltrated glacier water was heated during its circulation within the hot thickened crust and continued dissolving the crustal metamorphic gas such as radiogenic helium and limestone metamorphic co2 until the junction of the two sets of faults provided an ascending channel for it upon rising along the conduit the geothermal water mixed with cold groundwater to different degrees approximately 0 015 mol l co2 escaped from the geothermal fluid when it scattered as bubbling hot springs on the surface of the anisotropic porous quaternary sediments such kind ofhydrochemical evolution of lowsalinity alkaline hco3 na type water represents a typical formation mechanism of the high temperature geothermal systems along the himalayas

chatanika radar and s3 2 measurements of auroral zone electrodynamics in the midnight sector measurements made by the incoherent scatter radar at chatanika alaska have been combined with s3 2 satellite data to study the relationships between conductivities electric fields and currents near the harang discontinuity three s3 2 passes were chosen for the study based on the quality of the radar and satellite data and the availability of supplementary ground and space based observations the radar measured electric fields and conductivities as a function of latitude and local time the satellite measured the latitudinal distribution of electric field and field aligned current during the three polar passes the dominant field aligned current in the midnight sector is upward equatorward of this current a downward sheet is observed which is the eastern end of the evening sector region 2 sheet poleward of the upward current are several sheets of varying directions and magnitudes these sheets are associated with active aurora during substorms the most intense electric fields were located at the poleward and equatorward boundaries of the upward current sheet a model is presented which demonstrates the self consistency of the observed relationships between conductivities electric fields and currents

sr isotopic variation in shallow water carbonate sequences stratigraphic chronostratigraphic and eustatic implications of the record at enewetak atoll sr isotope data from two boreholes within the lagoon at enewetak atoll have been used to evaluate the use of such data to correlate date and monitor sea level change in shallow water carbonate sequences correlative stratigraphic intervals of relatively invariant 87sr separated by abrupt transitions to lower 87sr with increasing depth are recognized in both boreholes conversion of 87sr values to age via calibration with the seawater 87sr trend with age indicates that correlative and synchronous deposition of atoll sediments occurred at 0 4 1 2 and 2 1 ma in contrast a 5 m y hiatus is recognized in one borehole but not the other sr isotope stratigraphy sis is a powerful stratigraphic and chronostratigraphic tool in shallow water carbonate sequences only when significant secular variation of 87sr occurs and retention of depositional 87sr values is demonstrated the latter is best demonstrated when 87sr data are integrated with 18o 13c sr content data and petrographic observations several diagenetically altered intervals have greater 87sr values low 13c values and low sr ca ratios relative to adjacent intervals a combination that is consistent with open system meteoric diagenesis calcite cements from these intervals have early pleistocene 1 2 ma 87sr values despite their occurrence well within the late pliocene 2 1 ma sequence thus local sedimentological and diagenetic processes have produced intralagoon variability in the sis of the two boreholes complicating subsurface stratigraphic correlations the occurrence of anomalously young calcite cement relative to adjacent limestone is a direct response of the interaction of sea level change and meteoric phreatic diagenesis whereby overlying metastable carbonates with greater 87sr values are dissolved during periods of atoll emergence and sea level lowstand liberating sr and soil gas co2 to the pore fluid which is then incorporated into downflow meteoric phreatic diagenetic calcite the stratigraphic relation between the sites of carbonate dissolution and diagenetic calcite precipitation suggest an early pleistocene 1 2 ma sea level fall of between 34 and 64 m moreover the stratigraphic position and inferred age of paleophreatic lens calcite when backtracked for subsidence suggest that early pleistocene 1 2 ma sea level was 72 81 m range of 60 100 m below present sea level the enewetak record of early pleistocene sea level lowstand elevation agrees reasonably well with proxy sea level records inferred from sequence stratigraphy and deep sea foraminiferal 18o data however the enewetak record of the amplitude of early pleistocene sea level change is more consistent with the deep sea foraminiferal 18o proxy than the sequence stratigraphy proxy

tide influenced high energy environments and rhodolith associated carbonate deposition on the outer shelf and slope off the miyako islands southern ryukyu island arc japan sediments distributed off the miyako islands southern ryukyus japan include rhodoliths larger foraminifera cycloclypeus and or bryozoan dominated carbonates of low mud content on the outer insular shelf and planktonic foraminiferal mud free carbonate sand on the slopes sidescan sonograms show large scale 2 d subaqueous dunes in the deeper shelf sediments which suggest a nw se flow direction sea bottom photographs of the slope sediments to depths of 1000 m show small scale 2 d or 3 d ripples those sedimentologic features suggest the existence of relatively high speed currents on both the shelf and slope in the area current direction and velocity have been directly measured to clarify the origin and character of the current governing the area where the rhodoliths large foraminifera are distributed the results of measurements carried out at 14 stations at depth ranges of 14 to 799 m show that the direction and velocity of the currents on the shelf and slope change semi diurnally at most shelf stations the currents at high tide are to the north northwest i e from the pacific ocean to the east china sea conversely the currents at low tide are to the south southeast from the east china sea to the pacific ocean on the slope current movements are to the west at high tide and to the east at low tide it is concluded therefore that the currents on the shelf and slopes are tidally related current speed is small in protected areas and is high on the open shelf and shelf slopes the ryukyu island arc interrupts the tidal northwestern and southeastern flow this interaction probably develops substantial turbulence and topography induced upwelling and therefore forms a natural site for the formation of mud free and or coarse sediments with rhodoliths and large formainifera

magnetotelluric images of deep crustal structure of the rehai geothermal field near tengchong southern china broadband 0 004 4096 s magnetotelluric mt soundings have been applied to the determination of the deep structure across the rehai geothermal field in a quaternary volcanic area near the indo eurasian collisional margin tensorial analysis of the data show evidence of weak to strong 3 d effects but for approximate 2 d imaging we obtained dual mode mt responses for an assumed strike direction coincident with the trend of the regional scale faults and with the principal impedance azimuth at long periods the data were subsequently inverted using different approaches the rapid relaxation inversion models are comparable to the sections constructed from depth converted invariant impedance phase data the results from full domain 2 d conjugate gradient inversion with different initial models are concordant and evoke a picture of a dome like structure consisting of a conductive 50 1000 m cap which is about 5 6 km thick in the central part of the known geothermal field and thickens outwards to about 15 20 km the anomalous structure rests on a mid crustal zone of 20 30 m resistivity extending down to about 25 km depth where there appears to be a moderately resistive 30 m substratum the mt images are shown to be in accord with published geological isotopic and geochemical results that suggested the presence of a magma body underneath the area of study

seasonal dependence of large scale birkeland currents the seasonal dependence of large scale birkeland currents has been determined from the analysis of vector magnetic field data acquired by the triad satellite in the northern hemisphere statistical characteristics of single sheet i e net currents and double sheet birkeland currents were determined from 555 triad passes during the summer and 408 passes during the winter more complicated multiple sheet current systems were not included in this study the average kp value for the summer events is 1 9 and for the winter events is 2 0 the principal results include the following 1 the single sheet birkeland currents are statistically observed more often than the double sheet currents in the dayside of the auroral zone during any season the single sheet currents are also observed more often in the summer than in the winter as much as 2 to 3 times as often depending upon the mlt sector 2 the intensities of the single and double sheet birkeland currents on the dayside from approximately 1000 mlt to 1800 mlt are larger during the summer in comparison to winter by a factor of about 2 3 the intensities of the double sheet birkeland currents in the nightside the dominant system in this local time do not show a significant difference from summer to winter 4 the single and double sheet currents in the dayside between 0600 and 1800 mlt appear at higher latitudes by about 1 to 3 during the summer in comparison to the winter these characteristics suggest that the birkeland current intensities are controlled by the ionospheric conductivity in the polar region the greater occurrence of single sheet birkeland currents during the summertime supports the suggestion that these currents close via the polar cap when the conductivity there is sufficiently high to permit it since the intensities of birkeland currents are larger during periods of greater ionospheric conductivity an important source but perhaps not the only source of these currents must be a voltage generator in the magnetosphere possibly related to the convective electric field

meteoric interaction with magmatic discharges in japan and the significance for mineralization the andesitic volcanoes kirishima kyushu and esan hokkaido discharge 94 to 225 c hcl bearing vapors from summit fumaroles at kirishima a geothermal system exists on the flanks of the large volcanic massif 1500 m relief and 12 km radius in contrast esan is a small dome 600 m relief and 1 km radius with ephemeral hot springs the chemical and isotopic compositions of the fumarole gases and condensates and of waters from hot springs indicate that esan discharges are dominated by magmatic water and gases whereas those at kirishima are mainly meteoric the kirishima geothermal system contains acid fluids that are neutralized by interaction with the host rock and dilution by meteoric ground water the acidity is probably of magmatic origin a large ground water carapace at kirishima condenses a majority of magmatic volatiles and metals before they can discharge to the surface in contrast to esan where the volatiles including metals degas to the atmosphere this suggests that a meteoric system may be necessary to condense metals in this high level volcanic environment to provide a situation conducive to hydrothermal mineralization at epithermal depths

carbonate sedimentation on subtropical shelves around lord howe island and balls pyramid southwest pacific abstract lord howe island and balls pyramid are mid oceanic basaltic islands 20 km apart in the tasman sea subaerial carbonates dating back at least 350 ka and a holocene fringing reef occur on lord howe island no reefs or subaerial carbonate deposits occur on balls pyramid both islands sit near the centre of wide shelves that are on average 40 50 m deep with a distinct break of slope between 70 and 100 m depth the lord howe shelf is characterised by a discontinuous drowned ridge which rises to 30 m depth and is located between the mid shelf and shelf edge it is composed of limestone and is interpreted as a fossil reef being veneered by holocene coralline algae early to middle holocene branching coral gravel is found in the lee of the fossil reef indicating limited give up reef growth during the postglacial transgression the surface sediments across the shelf are calcareous except in close proximity to the island where volcanic content is significant coralline algae represent the dominant grain type with minor amounts of coral bryozoans halimeda and foraminifera are common however they are not volumetrically important rhodoliths and molluscs occur near the shelf edge and appear to have accumulated at times of lower sea level these subtropical shelves are mid oceanic examples of the transition between tropical and temperate carbonate sedimentation they indicate the potential for carbonate production on broad planated shelves outside reef forming seas