trace element transport rates in subduction zones evidence from th sr and pb isotope data for tonga kermadec arc lavas abstract trace element and th sr and pb isotope data for young lavas from the tonga kermadec arc in the southwest pacific suggest that geochemical variations in the lavas along the arc are linked to differences in the material being subducted beneath the arc lavas from the southern kermadec segment of the arc have relatively radiogenic pb isotope compositions which reflects a contribution from subducted sediment in contrast much of the pb in tonga lavas is derived from the altered oceanic crust in the subducting pacific plate and lavas from the northernmost tonga islands of tafahi and niuatoputapu contain pb and sr derived from the subducted part of the louisville seamount chain the origin of the pb in the lavas from these two islands can thus be traced to a point on the subducting slab and this observation is used to estimate the rate at which trace elements are transported beneath the arc our calculations suggest that fluid soluble elements such as u sr and pb are transported from the subducted slab across the mantle wedge and back to the surface in lavas over a period of approximately 2 3 ma and that magmas are erupted at the surface less than 350 ka after the melts are generated in the mantle wedge

formation and palaeozoic evolution of the gorny altai altai mongolia suture zone south siberia zircon u pb constraints on the igneous record abstract the altai sayan fold belt epitomises how phanerozoic island arc continental crust contributed to the growth of the palaeo eurasian continent its formation is dominated by the closure of the palaeo asian ocean pao when island arc systems and gondwana derived terranes accreted to the siberian margin relics of the pao related tectonic units and associated granitoids occur along the ophiolitic charysh terekta ulagan sayan suture ctuss between gorny altai and altai mongolia zircon la icp ms u pb dating of this igneous record constrains the multi stage geodynamic pao evolution primitive kuznetsk altai island arc crust formed at the siberian margin during the ediacaran early cambrian 525 555 ma this island arc matured during the middle late cambrian 510 ma and was consumed by pao subduction in the late cambrian early ordovician 480 490 ma forming the siberian early caledonian accretion collision belt south of the ctuss granitic magmatism occurred within gondwana derived altai mongolia during the middle late ordovician 450 470 ma palaeo kazakhstan assembly and during a silurian early devonian 400 425 ma andean type collision middle late devonian 360 395 ma granitoids were emplaced as a result of the collision of altai mongolia with siberia during final pangaea amalgamation the suture was strike slip reactivated associated magmatism 295 ma the youngest 220 255 ma sampled granitoids originated in an intra plate setting

ice core paleovolcanic records from the st elias mountains yukon canada 1 we previously reported a record of regionally significant volcanic eruptions in the north pacific using an ice core from eclipse icefield st elias mountains yukon canada the acquisition of two new ice cores from eclipse icefield along with the previously available eclipse icefield and mount logan northwest col ice cores allows us to extend our record of north pacific volcanism to 550 years before present using a suite of four ice cores spanning an elevation range of 3 5 km comparison of volcanic sulfate flux records demonstrates that the results are highly reproducible especially for the largest eruptions such as katmai a d 1912 correlation of volcanic sulfate signals with historically documented eruptions indicates that at least one third of the eruptions recorded in st elias ice cores are from alaskan and kamchatkan volcanoes although there are several moderately large volcanic explosivity index vei 4 eruptions recorded in only one core from eclipse icefield the use of multiple cores provides signals in at least one core from all known vei 4 eruptions in alaska and kamchatka since a d 1829 tephrochronological evidence from the eclipse ice cores documents eruptions in alaska westdahl redoubt trident and katmai kamchatka avachinsky kliuchevoskoi and ksudach and iceland hekla several unidentified tephra bearing horizons with available geochemical evidence suggesting alaskan and kamchatkan sources were also found we present a reconstruction of annual volcanic sulfate loading for the north pacific troposphere based on our ice core data and we provide a detailed assessment of the atmospheric and climatic effects of the katmai eruption

frost rings in trees as records of major volcanic eruptions new data about climatically effective volcanic eruptions during the past several thousand years may be contained in frost damage zones in the annual rings of trees there is good agreement in the timing of frost events and recent eruptions and the damage can be plausibly linked to climatic effects of stratospheric aerosol veils on hemispheric and global scales the cataclysmic proto historic eruption of santorini thera in the aegean is tentatively dated to 1628 26 bc from frost ring evidence

volcanic aerosol perturbations and strong el nino events no general correlation we test the hypothesis that el nino southern oscillation enso events are caused or enhanced by volcanic aerosol perturbations using two methods 1 a case by case comparison of the 16 strongest el nino events of the last 150 years with the characteristics of the largest concurrent volcanic events and 2 comparison of the timing of strong el nino events and the independently determined record of stratospheric optical depth perturbations many eruptions that occurred near times of strong el nino years produced small amounts of stratospheric aerosols in many cases the relative timing of the two events argues against triggering the correlation of 4 of 11 peaks in global stratospheric optical depth 0 025 within 3 years of strong el nino events over the last 150 years is what would be expected by chance moreover five strong el ninos occurred between 1915 and 1960 when the stratosphere was largely free of volcanic aerosols of the three strongest tropical volcanic aerosol perturbations that coincided with or were followed by strong el ninos in the period studied krakatau in 1883 el chichon in 1982 and pinatubo in 1991 the two modern ones occurred after the earliest sst warming of the el nino events the coincidence of these two phenomena indicates no causative relationship

chronological refinement of an ice core record at upper fremont glacier in south central north america the potential to use ice cores from alpine glaciers in the midlatitudes to reconstruct paleoclimatic records has not been widely recognized although excellent paleoclimatic records exist for the polar regions paleoclimatic ice core records are not common from midlatitude locations an ice core removed from the upper fremont glacier in wyoming provides evidence for abrupt climate change during the mid 1800s volcanic events krakatau and tambora identified from electrical conductivity measurements ecm and isotopic and chemical data from the upper fremont glacier were reexamined to confirm and refine previous chronological estimates of the ice core at a depth of 152 m the refined age depth profile shows good agreement 1736 10 a d with the sup 14 c age date 1729 95 a d the delta sup 18 o profile of the upper fremont glacier ufg ice core indicates a change in climate known as the little ice age lia however the sampling interval for delta sup 18 o is sufficiently large 20 cm such that it is difficult to pinpoint the lia termination on the basis of delta sup 18 o data alone other research has shown that changes in the delta sup 18 o variance are generally coincident with changes in ecm variance the ecm data set contains over 125 000 data points atmore a resolution of 1 data point per millimeter of ice core a 999 point running average of the ecm data set and results from f tests indicates that the variance of the ecm data decreases significantly at about 108 m at this depth the age depth profile predicts an age of 1845 a d results indicate the termination of the lia was abrupt with a major climatic shift to warmer temperatures around 1845 a d and continuing to present day prediction limits error bars calculated for the profile ages are 10 years 90 confidence level thus a conservative estimate for the time taken to complete the lia climatic shift to present day climate is about 10 years suggesting the lia termination in alpine regions of central north america may have occurred on a relatively short decadal timescale c 2000 american geophysical union less

a northern hemisphere volcanic chemistry record 1869 1984 and climatic implications using a south greenland ice core the effect of volcanic emission of acidic aerosols on climate is well documented the presence of acid droplets in the stratosphere can reduce transmissivity and hence decrease surface temperatures since the amount and chemical composition of erupted material has important effects on regional climate knowledge of past volcanic events is of extreme importance detailed glaciochemical records provide the only milieu wherein the geochemistry of paleovolcanic events can be fully documented we present a detailed sulfate and chloride record from an ice core drilled at site 20 d 40 km sw of dye 3 in southern greenland the record spans the time period 1869 1984 with chemical analyses of approximately eight samples per year time series decomposition and locally weighted scatter plot smoothing techniques were used to extract long term trends from the data so that individual volcanic eruptions could be documented a number of events identified here have been unnoticed previously and a high percentage of the major chemical signatures documenting these events is associated with large decreases in temperature in the latitudinal zone 60 90 on many authors have pointed out that the amount of volcanic acids such as hci and h2s04 injected into the atmosphere has a very important influence on global climate yet this volcanic input has been difficult to quantify prior to 1960 our data help to alleviate this problem these individual events can be compared to available frost tree ring data from north america further establishing a volcanism climatic linkage

climatic signal of ice melt features in southern greenland the stratigraphie record of melt features in intermediate depth polar ice cores has provided valuable data on past summer climate1 3 the thermal drilling technique used in previous studies precluded extending this record beyond a few hundred years recently however a 901 m deep ice core was mechanically drilled in southern greenland the excellent core quality and improved techniques for measuring melt features have resulted in an 2 200 yr record with consistently high quality data we report here that the temporal variations in melt feature abundance expressed as annual melt per cent amp provide proxy data on summer climate that can complement other records extending back thousands of years the amp profile indicates that relatively warm summers prevailed from about ad 950 until ad 1500 culminating in the thirteenth and fourteenth centuries the periods from about 300 to 150 bc ad 350 to 550 and ad 1550 to 1800 had relatively little summer melting

impurity sources of f cl no3 and so4 2 in greenland and antarctic precipitation five polar impurity sources are proposed anthropogenic no3 and so42 in recent greenland but not antarctic snow marine aerosols the dominant cl source volcanic eruptions which produce detectable but variable peaks in so42 f and or cl concentrations biogenic sulfurous gases from soil and coastal waters the dominant source for so42 in nonvolcanic strata an unidentified source of background nitrate which is more active in the northern hemisphere and which displays a summer concentration maximum solar activity and supernova events do not modulate no3 concentrations in greenland snow

depletion of atmospheric nitrate and chloride as a consequence of the toba volcanic eruption continuous measurements of so42 and electrical conductivity ecm along the gisp2 ice core record the toba mega eruption at a depth 2590 95 to 2091 25 m 71 000 5000 years ago major chemical species were analyzed at a resolution of 1 cm per sample for this section an 6 year long period with extremely high volcanic so42 coincident with a 94 depletion of nitrate and 63 depletion of chloride is observed at the depth of the toba horizon such a reduction of chloride in a volcanic layer preserved in an ice core has not been observed in any previous studies the nearly complete depletion of nitrate to 5 ppb encountered at the toba level is the lowest value in the entire 250 000 years of the gisp2 ice core record we propose possible mechanisms to explain the depletion of nitrate and chloride resulting from this mega eruption

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

a 220 year continuous record of volcanic h2so4 in the antarctic ice sheet continuous h2so4 profiles observed in snow from several antarctic locations reveal four major volcanic events of the past two centuries agung krakatoa tambora and another large scale event not recorded historically acid deposition and interhemispheric distribution mechanisms are quantified and then used to obtain an order of magnitude estimate for the h2so4 emissions from these eruptions

heavy carbon travertine related to methane generation a case study of the big tarkhan cold spring kerch peninsula crimea abstract the big tarkhan cold spring is located within the bulganak zone of mud volcanism in the northern kerch peninsula crimea the spring waters mainly have cl hco 3 na ca chemistry and temperatures from 18 to 23 c active travertine deposition at the site produces abundant calcite and minor amounts of siderite halite tincalconite trona gaylussite northupite and amorphous iron hydroxides calcite contains the impurities of 0 26 2 16 wt mgo up to 0 87 wt feo 0 15 0 73 wt sro 0 28 0 98 bao up to 0 43 wt mno and 0 09 0 60 na 2 o active travertines are depleted in ree ree 2 6 4 8 ppm compared to the inactive ones the kerch travertine calcite shows unusual carbon and oxygen isotope compositions 8 1 12 5 vpdb 13 c and 10 1 12 9 vpdb 18 o their isotopic and trace element signatures including ree patterns suggest their relation to basinal waters and origin from the organic rich clayey maikop fm which is the principal source rock of the area the big tarkhan travertine deposits are associated with thermogenic methane production

impact of the cerro hudson and pinatubo volcanic eruptions on the antarctic air and snow chemistry atmospheric records of sulfate and msa in aerosols were obtained by year round samplings in the boundary layer at two coastal antarctic sites neumayer 1983 1995 and dumont d urville 1991 1997 at dumont d urville and neumayer the non sea salt sulfate nssso42 level observed from october 1991 to october 1993 exceeded by 44 and 48 ng m 3 respectively the mean level 150 ng m 3 observed during nonvolcanic years the neumayer and dumont d urville records first exhibit spring october to december 1991 nssso42 concentrations exceeding mean spring concentrations by some 100 to 150 ng m 3 caused by a significant poleward transport of the cerro hudson volcanic aerosol in the lower stratosphere beneath the polar vortex and possibly in the middle upper troposphere limited to 10 ng m 3 during winter 1992 the nssso42 perturbation reached 78 ng m 3 in fall 1993 at neumayer the latter enhancement corresponds to the input of the pinatubo volcanic aerosol advected through stratosphere troposphere air mass exchanges an enhancement of nssso42 concentrations is also recorded in snow layers deposited between 1991 and 1993 at various sites located over the high antarctic plateau on the basis of these firn data the relative impact of the three latest volcanic eruptions of global concern namely mount agung 1963 el chichon 1982 and pinatubo together with cerro hudson 1991 was evaluated in terms of sulfate input at high southern latitudes the fallout of sulfate in central antarctic snow following the cerro hudson pinatubo eruptions was slightly lower than fallout after the mount agung eruption sulfate fallout after el chichon was 2 to 3 times lower than that from either mount agung or pinatubo the enhancement of sulfate levels detected in central antarctic snow deposits during the 1991 1993 time period allows us to estimate a mean atmospheric sulfate perturbation of around 60 ng m 3 in the boundary layer of these regions i e at least 35 higher than that seen at coastal sites this observation suggests that coastal antarctic regions are less sensitive than the high plateau in detecting volcanic sulfate fallouts following eruptions of global concern atmospheric near surface year round sampling achieved at coastal antarctic sites reveals no significant enhancement of the nitrate level over 1992 and 1993 suggesting that volcanic aerosols have had a limited effect on the transfer of nitric acid from the lower antarctic stratosphere to the boundary layer in these regions

multiple sources for sea rafted loisels pumice new zealand sea rafted loisels pumice is one of the few stratigraphic markers used to correlate late holocene coastal deposits in new zealand along with underlying sea rafted products of the local taupo eruption of ca 1800 yr b p these events have been used to bracket the first arrival of humans at new zealand loisels pumice is dacitic to rhyolitic sio263 78 wt in composition but individual clasts are homogeneous sio2range 1 wt characteristics include very low k2o 0 5 1 75 wt and rb 25 ppm and a mineralogy dominated by calcic and mafic xenocrysts similar features are shared by pumices of the tonga kermadec arc suggesting a common tholeiitic oceanic source interclast diversity of loisels pumice suggests that it is the product of several eruptive events from different volcanoes the differences in glass and mineral compositions found at various sites can be explained if the deposits are from different events a multisource origin can also partially explain the discrepancy in reported14c ages ca 1500 600 yr b p from different localities therefore the value of loisels pumice as a stratigraphic marker is questionable and it does not constrain the arrival of humans the predominant westward drift of historic tonga kermadec arc pumices and prevailing ocean currents suggest a long anticlockwise semicircular transport route into the tasman sea before sea rafted pumice arrival in new zealand the diversity of the pumices indicates that silicic eruptions frequently occur from the predominantly basic oceanic volcanoes

continent derived vitric mud and mafic arc rocks in deep kermadec trench diamictons abstract bimodal volcanogenic sediments dredged from depths greater than 7 km on the kermadec trench inner slope at latitude 31 s comprise diamictons of mudstone basalt and dolerite clasts enclosed in noncalcareous mud the mud and mudstones are medium to high k rhyolitic vitric mud of continental arc derivation that has been transported 900 km from new zealand all contain minor shards of kermadec arc low k rhyolitic glass all mudstones appear to be quaternary but one basalt clast gave a latest miocene k ar age 7 84 0 64 ma there have been at least three periods of deposition of mud and two or three episodes of emplacement of diamict the present trench slope is 10 24 and diamicts are interpreted to be deposits of debris flows of varying fluidity graded mafic volcanic sand beds are interpreted to be deposits of turbidity currents or sandy debris flows the degree of consolidation of mudstone clasts along with the presence of compaction faults suggests burial followed by re exhumation implying that redeposition processes may be deep reaching shallow water fossils and calcareous mudstone clasts originating above the carbonate compensation depth c 4 5 km plus clasts of basalt and dolerite sourced locally on the crest of the kermadec arc reached the lower trench slope in gravity flows that bypassed the mid slope terrace there was extensive mixing of products from various eruptions and sources during multiple episodes of transportation and during deposition and redeposition on the lower trench slope a range of agencies and routes is available to carry new zealand taupo volcanic zone derived vitric mud to the kermadec trench both low level and high level winds plus the north flowing deep western boundary current dwbc of antarctic bottom water the latter washes the raukumara plain forearc basin and the western trench slope to depths as shallow as 2 3 km we infer that ashfall tephra carried over the raukumara plain by the prevailing low level southwesterly wind is the principal source of the muds found in the trench the relative purity of the vitric mud in the trench might be explained by the tendency of rhyolitic material to dominate sediment dispersal systems in the aftermath of very large caldera eruptions confinement of the mud to the lower trench slope is probably caused by the tendency of dwbc surges of 20 cm s to veer 10 30 clockwise of the trench axis the continent derived volcanic ash on the subducting slab may influence oceanic arc magma composition

assessment of the record of the 1982 el chichon eruption as preserved in greenland snow variability in the so42 and cl time series for the 1980s from 12 shallow snow pits across the greenland ice sheet is used to evaluate the record of the 1982 el chichon eruption and the potential for recording a moderate northern equatorial eruption in a single greenland ice core composition of volcanic glass found in spring 1983 snow in one of the pits in the summit region matches that from el chichon glass thereby verifying the deposition of material from the eruption high na and cl concentrations in this same layer probably represent deposition of the reaction products of halite and h2so4 as observed in the stratosphere following the eruption these findings and the presence of a cl signal in five of the other pits indicate that the cl aerosol component of some eruptions has the potential to remain aloft for at least 1 year after the eruption some of these aerosols may be adsorbed onto tephra particles distinct so42 peaks that can be confidently linked to el chichon were found in only 50 of the records developed through subseasonal sampling however in several other pits an elevated baseline thought to represent more lengthy periods of el chichon aerosol deposition as opposed to deposition from a single snowfall event were observed smoothing of the original data by the calculation of annual so42 flux resulted in the presence of high flux values between 1982 and 1984 years thought to be affected by el chichon aerosol deposition in 9 of the 12 pits these results suggest that a single ice core from anywhere in greenland may record a signal from a northern equatorial eruption of magnitude similar to that of el chichon about 75 of the time this is despite the overall high levels of so2 4 deposition from anthropogenic sources that now make identification and quantification of the volcanic so2 portion of the record more difficult than obtaining the same data for preindustrial volcanism nevertheless composite records from all the pits sampled yielded stratospheric loading 20 mt and optical depth 0 13 estimates similar to stratospheric and satellite based measurements following the eruption equally high so42 concentration and flux values in snow from 1980 to 1982 reflect deposition from the series of middle to high northern latitude volcanic eruptions 1979 1981

characteristics and possible source of a 1479 a d volcanic ash layer in a greenland ice core abstract a microparticle concentration peak in a gisp2 ice core contains volcanic glass shards of rhyolitic composition that correspond in age to the 1479 1480 a d mt st helens wn eruption these glass shards are compositionally similar to the wn tephra and constitute 83 of the total particle population the shards are very coarse grained up to 40 m diameter suggesting rapid transport from their source to greenland a major sulfate peak in the ice occurs approximately 4 months after deposition of the glass shards this difference in depositional timing suggests primarily tropospheric transport of the ash and stratospheric transport of the sulfate aerosol large scale climatic perturbations following this eruption were evidently negligible glaciochemical seasonal indicators suggest a late fall to early winter 1479 a d eruption

mineralogy and origin of surficial uranium deposits hosted in travertine and calcrete from central jordan abstract secondary uranium encrustations are hosted in thick travertine and calcrete deposits of pleistocene recent age in central jordan the central jordan varicolored marble and travertine are equivalent to the active metamorphic area in maqarin north jordan more than 100 samples were collected from the outcrops of the varicolored marble travertine calcrete and the yellow uranium encrustations the secondary yellow encrustations are mainly composed of uranyl vanadate complexes tyuyamunite ca uo 2 2 v 2 5 o 8 3 h 2 o strelkinite na2 uo2 2v2o8 6 h2o solid solution series are the major components and their composition reflects changes in the ca na ratio in solution potentially new vanadium free calcium uranate phases restricted to the varicolored marble were identified with cao uo3 ratios different from the known mineral vorlanite cau6 o4 carbon and oxygen isotope data from calcite in the varicolored marble are characterized by rayleigh type enrichment in light isotopes associated with release of 13c and 18o enriched co2 by high temperature decarbonation during combustion of the bituminous marl stable isotope results from uranium hosted travertine and calcrete varieties exhibit a wide range in isotopic values between decarbonated and normal sedimentary carbonate rocks the depleted 13c and 18o values in the travertine are related to the kinetic reaction of atmospheric co2 with hyperalkaline ca oh 2 water the gradual enrichment of 13c and 18o values in the calcrete towards equilibrium with the surrounding environment is related to continuous evaporation during seasonal dry periods uranium mineralization in central jordan resulted from the interplay of tectonic climatic hydrologic and depositional events the large distribution of surficial uranium occurrences hosted in travertine and calcrete deposits is related to the artesian ascending groundwater that formed extensive lakes along nnw sse trending depressions fresh groundwater moved upward through the highly fractured phosphate bituminous marl and varicolored marble to form unusual highly alkaline water hydroxide sulfate type enriched with sensitive redox elements among which were u and v

the influence of volcanic eruptions on growth of central european lowland trees in ne germany during the last millennium abstract palaeoclimate proxies have shown links between climate changes and volcanic activity however not much is known about the impact of volcanic outbursts on growth of lowland trees we investigate the effect of large volcanic eruptions on the growth rate of trees the study is based on an unexplored comprehensive database with 1128 samples of long tree ring width trw chronologies of quercus robur l and pinus sylvestris l correlating with forest net primary production npp originating from three different sites in eastern germany greifswald eberswalde and saxony this study focuses on trees in rarely examined temperate zones where tree growth is less temperature limited growth relationships were compared against 52 large volcanic eruptions known for the last 1000 years dendrochronological methods revealed a predominantly negative 60 2 effect of large volcanic eruptions on the tree ring chronologies nevertheless also positive 31 7 and neutral 8 7 tree growth reactions were detected in the tree ring width chronologies of q robur and p sylvestris we detected a negative influence on tree growth for up to four years after large eruptions the chronologies of q robur revealed a stronger negative response 68 1 than those of p sylvestris 53 however at the greifswald site both tree species 79 q robur and 73 p sylvestris show a negative response in tree growth after every volcanic eruption furthermore the results suggest that volcanic aerosols originating from the northern hemisphere cause a greater reduction in tree growth than aerosols being emitted from southern hemisphere volcanoes which might be related to the long distances between trees and volcanoes as well as the global atmospheric circulation patterns this study demonstrates that the effects of major volcanic eruptions are less clear in trees from central european lowlands than in trees growing at the altitudinal or latitudinal timberlines

tree ring and summer temperature response to volcanic aerosol forcing at the northern tree line kola peninsula russia potential linkages between volcanic activity and a 403 year record of pinus sylvestris l scots pine growth and summer temperatures estimated from tree ring widths are evaluated from an arctic tree line site on the kola peninsula northwestern russia the joint occurrence of volcanic eruptions and severe negative ring width values is more than four times that expected by chance a composite average of temperatures indicates that a 0 72 c temperature reduction is typical for the year immediately following volcanic eruptions while tree growth is reduced for up to two decades the greenland ice sheet project 2 gisp2 volcanic sulphate record shows a small but significant correlation with summer temperatures volcanic aerosols originating at low and middle latitudes appear to cause the greatest ring width reduction and cooling

post late glacial calcareous tufas from the kurai fault zone southeastern gorny altai russia abstract calcareous tufa deposits have been discovered in the chibitka river valley near lake cheybek kohl at the junction of the kurai and teletsk kurai large active faults in the southeastern gorny altai russia at an altitude of 1800 2000 m fossil tufa is composed of calcite and cements holocene grey colluvium and glacial till deposited by the late glacial chibitka glacier current tufa precipitation has been observed from a low flow spring with cold 10 c hco 3 so 4 ca mg water 6 86 the stable isotope composition of spring water is 5 8 vpdb 13 c of dissolved inorganic carbon and 14 5 vsmow 18 o modern tufa consists of thin laminated mg calcite and sr aragonite crusts with abundant algae and biofilms on their surfaces both modern and fossil tufas are depleted in ree a total of 0 40 16 4 ppm and 0 40 3 80 ppm respectively and share similar paas normalised ree y spectra with hree enrichment and slight progressive lree depletion the modern tufas show positive 13 c values of 0 1 to 0 9 vpdb while the fossil ones have an isotopically lighter composition of 13 c 4 1 to 1 9 vpdb the 18 o range is very narrow 13 0 to 13 8 vpdb both stable isotope and trace element signatures including ree patterns of the tufas indicate precipitation from cold groundwaters subjected to prolonged interaction with a carbonate aquifer the baratal group of limestone and dolostone in a cold continental climate similar to the present conditions tufa deposition in the lake cheybek kohl area began with the onset of post late glacial global warming and permafrost degradation unlike the fossil tufa formation current precipitation of freshwater carbonates has been microbially mediated the discovered tufa deposits provide new palaeoclimatic and active tectonic proxies in the southeastern gorny altai

distribution and origin of igneous rocks from the landward slopes of the mariana trench implications for its structure and evolution the landward slope of the mariana trench is composed largely of igneous rocks serpentinites and serpentinized ultramafic rocks occur at nearly all structural levels on the slope from depths of 8000 to 1200 m seamountlike features on the trench slope break are the surface expression of serpentinite diapirs cumulate and massive gabbros are found several varieties of volcanic rocks are common including boninites altered and metamorphosed basalts andesites and dacites the chemical characteristics of the volcanic rocks indicate that nearly all are products of island arc volcanism together with the gabbros these volcanic rocks represent what is probably a late eocene arc complex these rocks were probably the first volcanic products to result from the subduction of the pacific plate beneath the phillippine sea plate their exposure on the trench slope today implies a significant amount of tectonic erosion of the landward slope since eocene time most of this removal of material appears to have occurred during the early stages of subduction there are isolated occurrences on the landward slope of rock assemblages including alkalic basalts chert hyaloclastites upper cretaceous siliceous sediments and shallow water limestones these assemblages are very similar to rocks dredged from seamounts on the offshore flankmore of the trench and their presence on the landward slope suggests that since the cessation of vigorous tectonic erosion there has been episodic accretion of seamount fragments to the landward slope less

slip rate variations on faults during glacial loading and post glacial unloading implications for the viscosity structure of the lithosphere abstract many active faults in extensional and contractional tectonic settings experienced a slip rate increase after the last glacial period when the volume of nearby glaciers and lakes decreased this post glacial slip rate increase is caused by transient stresses that are generated by the unloading induced rebound and superimposed on the tectonic background stress field as the latter is different for normal and thrust faults the response to loading and unloading should depend on the fault type here we use finite element models including a fault in rheologically layered lithosphere to explore the conditions under which both normal and thrust faults experience a post glacial slip rate increase the results show that a post glacial slip rate increase occurs on normal faults if the lower crust is stronger than the lithospheric mantle whereas thrust faults accelerate if the lower crust is weaker than the lithospheric mantle these findings imply that the response of faults to mass fluctuations on the earth9s surface may provide constraints on the rheological stratification of the lithosphere we use our results to make predictions on the viscosity structure of the basin and range province and northern scandinavia where palaeoseismological data document a pronounced increase in seismicity as a result of post glacial unloading and rebound

a 100 year record of north pacific volcanism in an ice core from eclipse icefield yukon territory canada iceland and the 1989 redoubt alaska eruptions non sea salt so4 2 residuals above a robust spline and empirical orthogonal function eof analysis were used to identify volcanic so4 2 signatures volcanic sulfate values are more conservatively identified by the eof analysis as sulfate deposition from other sources is more robustly accounted for some eruptions are also recorded as peaks in non sea salt chloride the volcanic signals in the eclipse ice core are mostly attributable to alaskan aleutian or kamchatkan eruptions conversely the eclipse ice core provides a poor record of globally significant tropical eruptions these results are promising for the development of longer ice core based records of paleovolcanism in the north pacific rim index terms 0305 atmospheric composition and structure aerosols and particles 0345 4801 0370 atmospheric composition and structure volcanic effects 8409 8409 volcanology atmospheric effects 0370 keywords yukon territory ice cores volcanism atmospheric effects kamchatka alaska

the bouma sequence and the turbidite mind set abstract conventionally the bouma sequence bouma a h 1962 sedimentology of some flysch deposits a graphic approach to facies interpretation elsevier amsterdam 168 pp composed of ta tb tc td and te divisions is interpreted to be the product of a turbidity current however recent core and outcrop studies show that the complete and partial bouma sequences can also be interpreted to be deposits formed by processes other than turbidity currents such as sandy debris flows and bottom current reworking many published examples of turbidites most of them hydrocarbon bearing sands in the north sea the norwegian sea offshore nigeria offshore gabon gulf of mexico and the ouachita mountains are being reinterpreted by the present author as dominantly deposits of sandy debris flows and bottom current reworking with only a minor percentage of true turbidites i e deposits of turbidity currents with fluidal or newtonian rheology in which sediment is suspended by fluid turbulence this reinterpretation is based on detailed description of 21 000 ft 6402 m of conventional cores and 1200 ft 365 m of outcrop sections the predominance of interpreted turbidites in these areas by other workers can be attributed to the following 1 loose applications of turbidity current concepts without regard for fluid rheology flow state and sediment support mechanism that result in a category of turbidity currents that includes debris flows and bottom currents 2 field description of deep water sands using the bouma sequence an interpretive model that invariably leads to a model driven turbidite interpretation 3 the prevailing turbidite mind set that subconsciously forces one to routinely interpret most deep water sands as some kind of turbidites 4 the use of our inability to interpret transport mechanism from the depositional record as an excuse for assuming deep water sands as deposits of turbidity currents 5 the flawed concept of high density turbidity currents that allows room for interpreting debris flow deposits as turbidites 6 the flawed comparison of subaerial river currents fluid gravity flows dominated by bed load transport with subaqueous turbidity currents sediment gravity flows dominated by suspended load transport that results in misinterpreting ungraded or parallel stratified deep sea deposits as turbidites and 7 the attraction to use obsolete submarine fan models with channels and lobes that require a turbidite interpretation although the turbidite paradigm is alive and well for now the turbidites themselves are becoming an endangered facies

record of volcanism since 7000 b c from the gisp2 greenland ice core and implications for the volcano climate system sulfate concentrations from continuous biyearly sampling of the gisp2 greenland ice core provide a record of potential climate forcing volcanism since 7000 b c although 85 percent of the events recorded over the last 2000 years were matched to documented volcanic eruptions only about 30 percent of the events from 1 to 7000 b c were matched to such events several historic eruptions may have been greater sulfur producers than previously thought there are three times as many events from 5000 to 7000 b c as over the last two millennia with sulfate deposition equal to or up to five times that of the largest known historical eruptions this increased volcanism in the early holocene may have contributed to climatic cooling

new geochemical evidence for the youngest toba tuff in india abstract new geochemical data on tephra samples from a layer present at several archeological sites in india support correlation of this layer to the youngest toba tuff erupted from northern sumatra about 74 000 yr ago the data show that the indian tephra layer is not a correlative of older tephra erupted from toba as has been suggested on the basis of artifact assemblages previously published geochemical data on the indian tephra beds was based on bulk ash samples containing mineral and clay contaminants and the resulting variability in analyses did not allow identification or discrimination of individual eruptive events our new data were collected on individual glass shards and small purified glass separates which have greater resolving power in fingerprinting acheulian and paleolithic artifacts found at some of the indian tephra sites do not reflect the antiquity of the tephra bed as they occur in fluvial sediments and may be reworked

global surface temperature responses to major volcanic eruptions the impacts of pollution resulting from large explosive volcanic eruptions on the atmospheric heat budget and planetary albedo are not in doubt1 2 however the effects of volcanic aerosols on the surface climate are less clear and still controversial3 4 in a previous study5 it was shown that significant surface cooling occurs over the landmasses of the northern hemisphere in the first few months after a major eruption in that hemisphere here we extend that work using new surface air temperature compilations based on land and marine data6 for both the northern and southern hemispheres our results indicate that major northern hemisphere eruptions have an immediate effect on the northern hemisphere average surface temperature but little or no effect on the southern hemisphere average southern hemisphere eruptions affect both southern and northern hemisphere temperatures after a lag of between six months and a year

gravity flows and rock recycling on the tonga landward trench slope relation to trench slope tectonic processes dredge samples collected from the flanks of the frontal arc platform from the mid slope forearc terrace and from the lower landward slope of the tonga trench are dominated by arc derived volcaniclastic sediment and calcareous ooze much of the sediment was delivered by sediment gravity flows recycling of older fossils and rocks is very widespread with evidence for several cycles of erosion and deposition in a single sample steep slopes and outcropping rock have prevailed around the frontal arc platform throughout the late neogene probably driven by movement on bounding normal faults the upper trench slope is dominated by coarse grained turbidites and debris flows the mid slope terrace receives mainly finer grained turbidites with fewer coarse turbidites and debris flows the lower trench slope is dominated by clast rich debris flows containing a majority of clasts of volcaniclastic deposits derived from the upper trench slope and mid slope terrace mixed with arc substrate and ocean plate rocks

historic eruptions of tambora 1815 krakatau 1883 and agung 1963 their stratospheric aerosols and climatic impact abstract decreases in surface temperatures after the eruptions of tambora 1815 krakatau 1883 and agung 1963 were of similar magnitude even though the amount of material dust and volatiles injected into the stratosphere by these three events differed greatly large amounts of fine ash and volatiles were dispersed into the upper atmosphere by krakatau and tambora the agung eruption in 1963 was a much smaller vulcanian type eruption which injected dust and volatiles into the stratospheric aerosol layer more directly analyses of magmatic volatiles indicate that the agung eruption was proportionately richer in so 2 and cl than either tambora or krakatau relative amounts of fine ash produced by the tambora krakatau and agung eruptions are estimated at about 150 20 1 whereas the masses of atmospheric sulfate aerosols produced were on the order of 7 5 3 1 decreases in surface temperature of a few tenths of a degree c for several years following volcanic eruptions are primarily a result of the sulfate aerosols rather than of the silicate dust the similarity in the atmospheric response after these three eruptions supports the idea of limiting mechanisms on volcanic stratospheric aerosol loading which is suggested by microphysical processes of aerosol particles fluctuations in stratospheric aerosol optical depth seem to be controlled to a large degree by high intensity sulfur rich eruptions e g agung 1963 which may however be relatively small in total ejecta volume such eruptions leave little geologic record but appear as acidity peaks in polar ice cores

glacier dynamics palaeohydrological changes and seismicity in southeastern altai russia and their influence on human occupation during the last 3000 years abstract the 3 ka chronology of climatically driven glacier fluctuations and upper tree limit variations dates of strong prehistoric earthquakes and fluvial system transformation are established for the se altai mountains of south siberia on the basis of radiocarbon and dendrochronological dating this time period of prosperity of the altai nomadic cultures is characterized by more arid and cold climate in comparison with the first half of the holocene during the last 3 ka glacier advances occurred at 2300 1700 cal bp historical stage and 13th 19th centuries aktru stage lia the recurrence interval of strong prehistoric earthquakes is estimated as 400 years the final draining of the holocene lake in the chuya intermountain depression took place about 1500 cal bp all these natural events together with political and social factors controlled the nomadic population their habitat and the patterns of evolution and migration of nomadic cultures within the se altai aridity intensification and cooling enhanced by anthropogenic impact brought deforestation of the eastern part of the chuya depression

provenance of the detrital component of deep sea sediments from the sw pacific ocean based on mineralogy geochemistry and sr isotopic composition abstract clay mineralogy and chemical and strontium isotope compositions have been used to determine the detrital components of deep sea sediments from the sw pacific ocean continental detritus derived mainly from the new zealand landmass is characterised by high illite and chlorite contents and 87 sr 86 sr ratios close to 0 7110 this material eroded from the eastern margin of both islands is transported into deeper water by turbidity currents and hemipelagic processes and is carried northwards by the strong western boundary current as far north as the samoan basin due to the great distance from source and unfavourable prevailing winds the contribution of aeolian dust from the australian deserts to the sediment appears to be relatively small particularly in the northernmost part of the region in the vicinity of the oceanic volcanic islands of tonga samoa and the cook islands volcaniclastic material including heavy minerals pyroxene and magnetite pumice glass shards proximally and smectite clays distally is dispersed into the sediments by turbidity currents and airfall in areas of very low sedimentation distant from landmasses the sediments contain significant amounts of authigenic material rsos characterised by high concentrations of transition metals and rare earth elements strontium isotopes together with trace element compositions have proved particularly useful in determining the relative proportions of the detrital types the contrasting 87 sr 86 sr ratios and sr contents of the various source rocks permit the use of binary mixing relationships whch indicate that sediments less than 35 km from the cook islands contain 80 volcanic detritus and those more than 1200 km away contain up to 20 volcanic detritus

development of sediment drifts approaching an active plate margin under the sw pacific deep western boundary current the abyssal pacific ocean is fed by a 1000 km wide deep western boundary current dwbc that flows northward along the continental margin east of new zealand between the passive margin of chatham rise and the subduction zone of kermadec trench a distance of 1200 km the dwbc has formed a suite of sediment drifts over a depth range of 2200 5700 m airgun and 3 5 khz profiles record a variety of drift types that reflect regional variations in bathymetry sediment supply and the tectonic volcanic framework on chatham rise the dwbc has deposited a sinuous linear body along the south flank 3000 m an extensive apronlike drift on the north flank 2200 4500 m and a ridgelike drift about the rise base 4500 5200 m the flow has also deposited a body of sediment over 400 km long within a moat at the base of the nearby louisville seamount chain further downcurrent the 250 km long rekohu drift 3600 4190 m has developed northward to 39 s south of this latitude drifts comprise mainly reworked pelagic hemipelagic material and sediment transported from distant southerly sources in contrast drifts north of 39 s have received a major injection of terrigenous sediment from hikurangi channel which runs 1400 km from new zealand eastward across the hikurangi plateau to disgorge on to the abyssal floor at the plateau edge en route turbidity current overspill from the channel has moved north under the influence of the shallow dwbc to contribute to a series of small ridge and patch drifts among the numerous seamounts on the plateau at 3500 4200 m off hikurangi channel mouth a large fan has accumulated the dwbc has extended the fan into a drift running over 250 km along the base of hikurangi plateau 5150 5770 m toward kermadec trench here drift sediment becomes increasingly disrupted by mass wasting associated with the active subduction in this area the seismic stratigraphy reveals the drifts to rest mainly on a widespread erosional surface that is interpreted to mark the inception of the dwbc in the region with the late oligocene opening of the australian antarctic seaway drift construction commenced during the miocene but was punctuated in the late miocene by another period of erosion that coincided with increased bottom water production in antarctica deposition resumed in plio pleistocene times when large quantities of sediment from the rapidly rising landmass of new zealand were injected into the boundary current the modern flow continues to affect drift deposition as manifest by an active boundary channel along the foot of hikurangi plateau and widespread scour zones and sediment wave fields

a 10 century comparison of prominent bipolar volcanic events in ice cores measurements of key chemical and physical parameters made along continuous and selected long sections of polar ice cores provide reliable past snow accumulation rates and other environmental records the prime accumulation indicators include variations found in the stable isotopes ionic constituents and acidity concentration levels and physical changes in the strata and structure cross correlations of the time series curves resulting from multiparameter analyses of ice cores from antarctica nby89 sp78 bs68 and greenland cr74 d3 81 d3 18c have been made the results permit construction of a bipolar chemical stratigraphy chronology of volcanic events that is coherent with the 18 o and electrical conductivity method data sets and consistent back in time with historically recorded volcanic activity a bihemispheric comparison of high non sea salt so 4 2 peaks shows strong correlation at 1885 1836 1816 1810 1459 1346 1287 1278 1259 1228 and 1168 a d at time of snow deposit the prominent 1259 a d volcanic signal appears to be a significant bipolar ice core index horizon

volcanic deposits in antarctic snow and ice major volcanic eruptions are able to spread large amounts of sulfuric acid all over the world acid layers of volcanic origin were detected for the first time a few years ago by hammer in greenland ice the present paper deals with volcanic deposits in the antarctic the different methods that can be used to find volcanic acid deposits in snow and ice cores are compared electrical conductivity sulfate and acidity measurements numerous snow and ice samples collected at several antarctic locations were analyzed the results reveal that the two major volcanic events recorded by h2so4 fallout in antarctic ice over the last century are the eruptions of krakatoa 1883 and agung 1963 both located at equatorial latitudes in the southern hemisphere the volcanic signals are found to be particularly well defined at central antarctic locations apparently in relation to the low snow accumulation rates in these areas it is demonstrated that volcanic sulfuric acid in snow is not even partially neutralized by ammonia the possible influence of antarctic volcanic activity on snow chemistry is also discussed using the three recent eruptions of the deception island volcano as examples only one of them seems to have had a significant effect on the chemistry of snow at a location 200 km from this volcano it is concluded that antarctic volcanic ice records are less complicated than greenland records because of the limited number of volcanos in the southern hemisphere and the apparently higher signal to background ratio for acidity in antarctica than in greenland

mid bathyal current scours and sediment drifts adjacent to the hikurangi deep sea turbidite channel eastern new zealand evidence from echo character mapping abstract late quaternary sedimentary processes on the northwest chatham rise continental slope and southern hikurangi trough eastern new zealand have been examined using 3 5 khz seismic reflection profiles together with piston cores high frequency echo character mapping of the region shows that the slope has been dominated by current controlled sedimentary processes whereas turbidite processes characterise the adjacent part of the southern hikurangi trough on the slope north of mernoo saddle a 580 m deep bathymetric passage between the eastern south island continental shelf and the chatham rise a 160 km alongslope by 30 km wide region of current crosion occurs between 700 m and 2300 m depths within this region are several northeast trending channels 5 20 km wide and up to 105 km long scoured obliquely down slope these scours are inferred to have been formed mainly during glacial periods by a northward flowing current of subantarctic water passing through the mernoo saddle then braiding as it cascaded down and acoss the mid slope before merging again further east into a contour current on the unstable lower slope of the north chatham rise the lower slope in between and below the scours comprises a complex of coalescing sediment drifts the adjacent part of the southern hikurangi trough is characterised by a canyon leveed channel system receiving turbidites from the eastern south island continental margin and cook strait mapping reveals a meandering channel up to 10 km wide on the floor of the trough with a left bank dominated levee east of cook strait where the trough widens

mediterranean vegetation lake levels and palaeoclimate at the last glacial maximum the apparent conflict between pollen evidence for widespread artemisia steppe1 6 implying semi arid conditions and geomorphological evidence for high lake levels4 7 11 has produced controversy about the ice age palaeoclimate of the mediterranean region here we use a water balance model12 to predict catchment runoff and a biome model13 to predict vegetation type to reconstruct the palaeoenvironment around lake loannina a type locality for the northern mediterranean region we show that both sets of evidence are compatible with a summer dry winter wet regime with seasonal temperature anomalies similar to those predicted by atmospheric model simulations of the last glacial maximum14 18 the drying effect of the cold north atlantic ocean may have been counteracted in winter by increased storm frequency under a southward shifted jet stream as shown by several atmospheric models16 18

use of paleo records in determining variability within the volcanism climate system abstract volcanic eruptions that inject large quantities of sulfur rich gases into the stratosphere have the capability of cooling global climate by 0 2 0 3 c for several years after the eruption equatorial eruptions will impact global climate whereas mid latitude eruptions can cool climate in the hemisphere of origin magnitude of cooling varies by latitude and it is possible for warming to occur in certain regions primarily during the winter although instrumental records have been used to quantify the volcanic impact on climate they are limited in their temporal and spatial coverage and the style and magnitude of eruptions occurring over the two centuries of instrumental records is limited a thorough evaluation of the range of variability in the volcanism climate system requires a multidisciplinary approach that includes the analysis of ice core records geological data atmospheric measurements and visual phenomena tree ring records and other proxy data evaluation of these longer time series indicates that multiple volcanic eruptions have the potential to force climate over decadal to multi decadal time frames especially when these eruptions enhance or extend pre existing cool conditions on the other hand a lack of climatically significant eruptions may result in warmer average temperatures over decadal time frames because the volcanic cooling component within the climate system is absent mega eruptions like the toba eruption of 71 000 73 000 yr ago may impact climate on centennial time frames through positive feedback mechanisms evidence exists which indicates that environmental changes associated with rapid climatic fluctuations such as crustal loading unloading with glaciation deglaciation and variability in glacial meltwater loading on ocean basins may cause an increase in volcanic activity

tectonic controls on sedimentation and diagenesis in the tonga trench and forearc southwest pacific sedimentation in the tonga forearc is dominated by the redeposition of volcaniclastic sediment from the arc volcanic front by mass flows and turbidity currents onto the adjacent tonga platform the shallowest flattest part of the forearc region the greatest sediment thicknesses accumulate in debris aprons close to the volcanic front collision of seamounts notably the capricorn seamount and the louisville ridge with the forearc radically shortens and steepens the adjacent modern trench slope allowing sediment to be redeposited deep into the trench rotation usually arcward of existing basins on the midslope during collision generates angular unconformities while synchronous uplift of the outer forearc high results in canyon development and downcutting along the eastern edge of the tonga platform collision also reactivated major across strike fault zones on the forearc the zones are subsequently exploited by canyons depositing sediment into the trench collapse and renewed extension of the forearc in the wake of collision result in the development of small perched basins measuring approximately 5 km by 15 km in the midslope area this morphology is especially developed at 18 30 s to 20 s implying a 2 3 m y interval for their formation following louisville ridge collision trenchward of these depocenters sedimentation is slow resulting in manganese crust formation and localized mass wasting along fault scarps over longer periods of time 5 m y tectonic erosion reestablishes a wide gently sloping forearc into which canyons incise the shallow tonga platform by headwall erosion and collapse

travertines depositional morphology and the bacterially constructed constituents abstract investigation of travertine accumulations throughout central italy and the west central u s has shown that the carbonate is precipitated in response to both inorganic and organic processes individual deposits range up to 85 m thick and hundreds of square kilometers in areal extent all of the carbonate is low magnesian calcite water chemistry temperature and morphology of the accumulation greatly influence the constituents comprising these deposits harsh environmental situations favor inorganic deposits while increasingly more moderate conditions result in the formation of a greater abundance of organically precipitated material morphological variations of travertine deposits recognized include 1 waterfall or cascade 2 lake fill 3 sloping mound fan or cone 4 terraced ound and 5 fissure ridge gross morphology internal stratification and constituents comprising these deposits vary systematically depending upon the type of accumulation and chemistry of the waters bacterially precipitated calcite forms a large percentage of the carbonate in many travertine accumulations exceeding 90 of the framework grains comprising some of the lake fill deposits bacteria are among the first taxa to inhabit and reproduce in harsh spring environments and produce a variety of fascinating constituents the bacteria are primarily rods generally 0 2 m in diameter and less than 1 0 m in length the rods readily decay resulting in calcite crystals loaded with micropores the basic building block of bacterially constructed travertine is a clump of bacteria averaging 20 m in diameter enclosed in a single crystal of calcite aggregates of these crystals produce a variety of deposits including 1 crudely laminated carbonate mud 2 finely laminat d layers of mud 3 intraclasts 4 foam rock and 5 shrubs the shrubs are most striking commonly forming layers 1 3 cm thick but also producing bacterial pisoids at some locales bacterial stromatolites composed of layers of shrubs alternating with finely laminated layers of bacterial mud comprise essentially the entire deposit the shrub layers are the result of flourishing summer growth of bacteria and furthermore show remarkable daily laminae 0 1 0 5 mm thick the importance of bacteria in the formation of travertine and their universally recognized abundance in modern sediments provides an impetus for a reexamination of the role of bacteria in the origin of other types of ancient deposits

discriminant function analysis of glass chemistry of new zealand and north american tephra deposits major trace and rare earth element analyses of volcanic glass are used separately or in combination for correlating quaternary tephras often by graphical or simple comparative methods we have taken a statistical approach using discriminant function analysis dfa to assess the relative discriminating power of the different elements in volcanic glasses from several tectonovolcanic provinces we found that major oxides are powerful discriminating variables for widespread tephras from the taupo volcanic zone in new zealand and here they can be more discriminating than trace elements a wide selection of tephras from the western united states can also be distinguished on major oxides alone particularly those from cascade range volcanoes for tephras from large intracontinental calderas such as long valley or yellowstone ree and trace elements are more effective at discriminating than major oxides however tephras erupted from the long valley area can be distinguished on major oxide composition by dfa despite their similar chemistry the selection and relative significance of different elements for discriminating tephras depends on the total data set being compared as well as the source volcano and the individual eruptive events caution must be exercised in the nonstatistical selection of compositional data for characterizing tephras dfa is a more powerful and objective tool for the comparison of tephra chemistry

late cretaceous pelagic sediments volcanic ash and biotas from near the louisville hotspot pacific plate paleolatitude 42 s abstract dredging on the deep inner slope of the tonga trench immediately north of the intersection between the louisville ridge hotspot chain and the trench recovered some late cretaceous maestrichtian slightly tuffaceous pelagic sediments they are inferred to have been scraped off a recently subducted late cretaceous guyot of the louisville chain in the vicinity of the louisville hotspot present location 50 26 s 139 09 w late cretaceous location 42 s longitude unknown late cretaceous rich diatom radiolarian silicoflagellate foraminiferal and coccolith biotas accumulated on the flanks of the guyot and are described in this paper rich sponge faunas are not described inoceramus prisms are present volcanic ash is of within plate alkalic character isotope ratios in bulk carbonate 18o 2 63 to 0 85 13c 2 98 to 3 83 are normal for pacific maestrichtian sediments the local ccd may have been shallower than the regional ccd because of high organic productivity in some samples late cretaceous materials have been mixed with neogene materials mixing may have taken place on the flanks of the guyot during transit across the western pacific or on the trench slope during or after subduction and offscraping about 0 5 ma

regional sediment recycling in the abyssal southwest pacific ocean an active plate boundary with a high sediment output three major submarine channels and the world9s largest deep western boundary current dwbc make up an extensive recycling system along the 4500 km continental margin east of new zealand seismic reflection sedimentary and oceanographic data demonstrate that detritus from the rising mountains of the new zealand plate boundary is transferred to the southwest pacific abyssal floor by turbidity currents flowing along solander 450 km long bounty 950 km and hikurangi 1400 km channels these conduits discharge directly into the dwbc which transports material north to form a series of sediment drifts the northernmost drift containing sediment from hikurangi channel and eroded drifts to the south is now subducting into kermadec trench geochemical data suggest that sediment is recycled through the mantle to re emerge in the arc volcanic rocks thus one cycle is completed and a new one begins

c and o stable isotope variability in recent freshwater carbonates river krka croatia three types of recent carbonate precipitates from the river krka croatia were analysed 1 bulk tufa from four main cascades in a 34 km long section of the river flow through the krka national park 2 a laminar stromatolite like incrustation formed in the tunnel of a hydroelectric power plant close to the lowest cascade and 3 recent precipitates collected on artificial substrates during winter spring and summer periods stable isotope compositions of carbon d 13 c and oxygen d 18 o in the carbonate and organic carbon d 13 corg were determined and compared with d 18 o of water and d 13 c of dissolved inorganic carbon dic the source of dic which provides c for tufa precipitation was determined from the slope of the line dic dic0 1 vs d 13 c dic dic dic0 sayles curry 1988 the d 13 c value of added dic was 13ae6 corresponding to the dissolution of co2 with d 13 c between 19ae5 and 23ae0 vienna pee dee belemnite vpdb the observed difference between the measured and calculated equilibrium temperature of precipitation of bulk tufa barriers indicates that the higher the water temperature the larger the error in the estimated temperature of precipitation this implies that the climatic signals may be valid only in tufas precipitated at lower and relatively stable temperatures the laminar crust comprising a continuous record of the last 40 years of precipitation shows a consistent trend of increasing d 13 c and decreasing d 18 o the lack of covariation between d 13 c and d 18 o indicates that precipitation of calcite was not kinetically controlled for either of the elements d 13 c and d 18 o of precipitates collected on different artificial substrates show that surface characteristics both of substrates and colonizing biota play an important role in c and o isotope fractionation during carbonate precipitation

the possible effects of large 19th and 20th century volcanic eruptions on zonal and hemispheric surface temperatures abstract the contribution of volcanic material to the stratosphere from major eruptions within the last two centuries has been estimated using volcanological criteria including eruption type eruption column height volume and duration of eruption and composition and degree of fragmentation of magma the chronology of major explosive volcanic eruptions is compared with a record of mean surface temperature deviation t for the same interval constructed from all available temperature data the temperature records are divided into 6 latitudinal zones allowing analysis for individual zones where temperature changes induced by aerosol perturbation might be intensified we focus on the explosive volcanic events which by our estimates injected the most material into the stratosphere these include tambora 1815 krakatau 1883 santa maria 1902 katmai 1912 and quizapu 1932 such eruptions appear to have produced a consistent but small temperature decrease on the order of 0 2 to 0 5 c on a hemispheric scale for periods ranging from one to five years although these changes are similar to background temperature variations the maximum change in t after some of these explosions appears to lag by up to three years in going from equatorial to polar latitudes somewhat smaller eruptions e g agung 1963 and possibly cosiguina 1835 seem to have produced about the same perturbation in t as the larger eruptions this suggests either a limiting mechanism on loading of the aerosol layer after a volcanic eruption or that the composition of injected material i e the ratio of silicate dust to volatiles and composition of the volatiles may significantly effect stratospheric optical depth perturbation temperatures do not remain depressed for a longer period after a series of closely timed eruptions e g the 1881 1889 or the 1902 1903 sequences than after single events

subduction of a late cretaceous seamount of the louisville ridge at the tonga trench a model of normal and accelerated tectonic erosion the hotspot generated louisville ridge is a 4000 km chain of seamounts typically 2 2 5 km high and 10 40 km in diameter and an underlying crustal swell 1 5 km high and 100 km wide trending nnw across the southwestern pacific the northwest end of the ridge collides with the north trending tonga trench 26 s which just north of that point is exceptionally deep 10 8 km and lacks both a turbidite wedge and a bordering accretionary complex the collision zone is moving rapidly southward multichannel seismic reflection data in the collision zone show a west dipping subsurface platform 2 3 km beneath the lower western trench slope which is interpreted as the flat summit of a subducted guyot motuku of the louisville chain projected eastward the summit plain passes 1 2 km above the trench floor dredging of the nearby inner trench wall recovered uppermost cretaceous maestrichtian oceanic pelagic sediments interpreted to be fragments of the sedimentary mantle of a subducted louisville seamount the principal effects of hotspot ridge collision with a sediment starved trench are 1 the impacting seamounts are subducted rather than accreted and 2 although some seamount rocks are temporarily accreted the inner trench wall is tectonically eroded arcward at rates possibly as high as 50 km m y accelerated tectonic erosion is related to 1 fracturing shearing and general weakening of arc substrate rocks as they are lifted by the swell penetrated by impacting seamounts and left to collapse as the ridge moves away 2 a more effective removal of weakened rock in underthrusting grabens which are larger in the crustal swell 3 a possible elevation of the subduction decollement to account for the removal of as much as 30 000 km of material from a 400 km sector of the trench in 1 million years and 4 a reduction in supply of arc derived debris resulting from the gap in arc volcanism accompanying subduction of the ridge normal tectonic erosion in the tonga trench is apparently minor and we conclude that the bulk of the 37 000 km of material which fills subducting grabens each million years is arc derived volcanic and pelagic sediment

morphology and history of the kermadec trench arc backarc basin remnant arc system at 30 to 32 s geophysical profile microfossil and k ar data abstract knowledge of the time span of arc activity essential for correct tectonic reconstructions has been lacking for the kermadec arc system but is supplied in this paper through study of microfossils contained in dredge samples and k ar ages on dredged basalt clasts the kermadec system at south latitudes 30 to 32 in the southwest pacific comprises from west to east the colville ridge remnant arc havre trough backarc basin kermadec ridge active arc and kermadec trench site of west dipping subduction of pacific plate lithosphere beneath the australian plate data are presented from two traverses dredge magnetic single channel seismic across the whole system an important transverse tectonic boundary the 32 s boundary lies between the two traverse lines and separates distinct northern 32 25 s and southern 32 36 s sectors the northern sector is shallower and well sedimented with broad ridges and a diffuse backarc basin the southern sector is deeper with narrow ridges and steep escarpments facing inwards to a little sedimented rifted backarc basin the kermadec ridge slopes smoothly trenchward to a mid slope terrace forearc basin with minor sediment fill at 5 6 km water depth a steeper 10 24 and more rugged lower trench slope is mantled with new zealand sourced rhyolitic vitric mud diamictons containing locally derived mafic volcanic clasts one clast is of late miocene age k ar age 7 84 ma the arc kermadec ridge is capped by active volcanoes very young k ar ages