the role of partial melting in the 15 ma geochemical evolution of gran canaria a blob model for the canary hotspot the subaerial portion of gran canada canary islands was built by three cycles of volcanism a miocene cycle 8 5 15 ma a pliocene cycle 1 8 60 ma and a quaternary cycle 1 8 0 ma only the pliocene cycle is completely exposed on gran canaria the early stages of the miocene cycle are submarine and the quaternary cycle is still in its initial stages during the miocene sio2 saturation of the mafic volcanics decreased systematically from tholeiite to nephelinite for the pliocene cycle sio2 saturation increased and then decreased with decreasing age from nephelinite to tholeiite to nephelinite sio2 saturation increased from nephelinite to basanite and alkali basalt during the quaternary in each of these cycles increasing melt production rates sio2 saturation and concentrations of compatible elements and decreasing concentrations of some incompatible elements are consistent with increasing degrees of partial melting in the sequence melilite nephelinite to tholeiite the mafic volcanics from all three cycles were derived from co2 rich garnet lherzolite sources phlogopite ilmenite sulfide and a phase with high partition coefficients for the light rare earth elements lree u th pb nb and zr possibly zircon were residual during melting to form the miocene nephelinites through tholeiites phlogopite ilmenite and sulfide were residual in the source of the pliocene quaternary nephelinites through alkali basalts highly incompatible element ratios e g nb u pb ce k u nb pb ba rb zr hf la nb ba th rb nb k nb zr nb th nb th la and ba la exhibit extreme variations in many cases larger than those reported for all other ocean island basalts but these ratios correlate well with degree of melting survival of residual phases at higher degrees of melting during the miocene cycle and differences between major and trace element concentrations and melt production rates between the miocene and pliocene tholeiites suggest that the miocene source was more fertile than the pliocene quaternary source s we propose a blob model to explain the multi cycle evolution of canary volcanoes and the temporal variations in chemistry and melt production within cycles each cycle of volcanism represents decompression melting of a discrete blob of plume material small degree nephelinitic and basanitic melts are derived from the cooler margins of the blobs whereas the larger degree tholeiitic and alkali basaltic melts are derived from the hotter centers of the blobs the symmetrical sequence of mafic volcanism for a cycle from highly undersaturated to saturated to highly undersaturated compositions reflects melting of the blob during its ascent beneath an island in the sequence upper margin corelower margin volcanic hiatuses between cycles and within cycles represent periods when residual blob or cooler entrained shallow mantle material fill the melting zone beneath an island

bayesian analysis of radiocarbon chronologies examples from the european late glacial although there are many late glacial ca 15 000 11 000 cal yr bp proxy climate records from northwest europe some analysed at a very high temporal resolution decadal to century scale attempts to establish time stratigraphical correlations between sequences are constrained by problems of radiocarbon dating in an attempt to overcome some of these difficulties we have used a bayesian approach to the analysis of radiocarbon chronologies for two late glacial sites in the british isles and one in the adriatic sea the palaeoclimatic records from the three sites were then compared with that from the grip greenland ice core although there are some apparent differences in the timing of climatic events during the early part of the late glacial pre 14 000 cal yr bp the results suggest that regional climatic changes appear to have been broadly comparable between greenland the british isles and the adriatic during the major part of the late glacial i e between 14 000 and 11 000 cal yr bp the advantage of using the bayesian approach is that it provides a means of testing the reliability of late glacial radiocarbon chronologies that is independent of regional chronostratigraphical climatostratigraphical frameworks it also uses the full radiocarbon inventory available for each sequence and makes explicit any data selection applied potentially therefore it offers a more objective basis for comparing regional radiocarbon chronologies than the conventional approaches that have been used hitherto copyright 2004 john wiley sons ltd

devensian lateglacial environmental changes in britain a multi proxy environmental record from llanilid south wales uk abstract a multi proxy environmental record for the devensian weichselian lateglacial and early holocene periods which includes pollen plant macrofossil coleopteran geochemical and stable isotope data is described from a site at llanilid south wales uk the geochronology of the sequence is derived from two age depth models which show a broad measure of agreement over much of the profile this data set provides the basis for a detailed reconstruction of changing environmental conditions in western britain during the transition from the last cold stage to the present holocene interglacial ca 15 000 10 000 cal yr bp two marked cooling episodes are recorded during the course of the lateglacial interstadial greenland interstadial 1 with mean july temperatures falling by more than 5 c from a maximum of around 20 c during the early interstadial and by a further 4 5 c around 13 100 cal yr bp the initial drop in temperature led to a reduction in juniperus scrub while the second and more abrupt temperature decline resulted in a significant contraction in areas of betula woodland a relatively slight and short lived warming during the later interstadial enabled tree birch to expand once again mean july temperatures of 10 11 c characterised the loch lomond younger dryas stadial greenland stadial 1 between ca 12 600 and 11 400 cal yr bp during which time a scrub tundra with betula salix and a range of open habitat taxa became established locally the onset of the holocene interglacial at ca 11 400 cal yr bp is marked by an abrupt temperature rise of the order of 9 c and by the rapid expansion of betula woodland the llanilid palaeoclimate record is similar to that from the gransmoor site in northeast england and also to the climatic sequence inferred from the grip ice core particularly during the later part of the lateglacial interstadial ca 14 000 12 600 cal yr bp during the loch lomond younger dryas stadial and in the early holocene the llanilid chronology is less secure during the early part of the lateglacial interstadial pre 14 000 cal yr bp but it is possible that warming may have begun earlier in this part of western britain than in greenland

the rotokawa geothermal system new zealand an active epithermal gold depositing environment the rotokawa geothermal system is less than 20 000 yrs old and is situated in a sequence of pleistocene and recent volcanic rocks and underlying mesozoic graywacke basement in the taupo volcanic zone a region dominated by extensional tectonics at lease 12 different hydrothermal explosition breccias are preserved in surface outcrops the largest eruptive site being a crater of 1 5 km in diameter which formed about 6 060 years ago and is presently occupied by an acid lake lake rotokawa with a ph approximately 2 significant bedded sulfur deposits which formed in an earlier crater lake exist beneath the present lake the deep fluids are dilute chloride 0 022 mole kg waters having higher reduced sulfur concentrations h 2 s approximately 7x10 super 3 mole kg than any previously studied active geothermal system a maximum temperature of 320 degrees c has been measured in the system water rock interaction has given rise to a zone of propylitic alteration at depth which is overlain by a region of advanced and intermediate argillic alteration extensive boiling occurs at depth an sulfide minerals such as sphalerite galena chalcopyrite and argentite occur sporadically with ubiquitous pyrite argentiferous alunite occurs in the advanced argillic alteration zone clasts of silicified lake beds in the hydrothermal explosion breccias commonly contain pyrite and carry subeconomic gold values of up to 0 1 g metric ton thermal waters discharging on the northeast shore of the lake are depositing gold ore grade arsenic and antimony sulfide rich muds which also contain high concentrations of tungsten thallium mercury silver and gallium this surface deposit is estimated to contain about 250 kg 8 000 oz of gold and has been deposited during the past 1 800 yrs since the formation 6 060 yrs ago of the large hydrothermal explosion crater in which lake rotokawa is now situated about 12 0 million oz 370 metric tons of gold may have been transported into the environment beneath the crater it is estimated that 1 7 to 3 3 million oz of gold may have been deposited in the upper 300 to 400 m underlying lake rotokawa from hydrothermal fluids initially saturated with gold

a seismic study of lithospheric flexure in the vicinity of tenerife canary islands seismic data have been used to determine the crustal and upper mantle structure of tenerife canary islands a volcanic island of tertiary age located on 140 ma oceanic crust reflection data show that oceanic basement dips gently towards the island forming a flexural moat which is infilled by 2 3 km of well stratified material the moat is characterised by a major angular unconformity which we attribute to volcanic loading of pre existing oceanic crust and overlying sediments and the subsequent infilling of the flexure by material that was derived at least in part from the islands refraction data show that the flexed oceanic crust has a mean thickness of 6 41 0 42 km and upper and lower crustal velocities of 4 8 5 4 km s 1 and 6 7 7 3 km s 1 respectively the flexure which has been verified by gravity modelling can be explained by a model in which tenerife and adjacent islands have loaded a lithosphere with a long term 106 yr elastic thickness of approximately 20 km seismic and gravity data suggest that up to 1 5 105 km3 of magmatic material has been added to the surface of the flexed oceanic crust which assuming an age of 6 16 ma for the shield building stage on tenerife implies a magma generation rate of about 0 006 to 0 02 km3 a 1 this rate is similar to estimates from other african oceanic islands e g reunion and cape verdes but is significantly less than that which has been calculated at hawaii there is no evidence in either the seismic or gravity data that any significant amount of magmatic material has underplated the flexed oceanic crust the crustal and upper mantle structure at tenerife therefore differs from other oceanic islands such as hawaii and marquesas where 4 km of underplated material have been reported

evolution of ocean island rifts the northeast rift zone of tenerife canary islands the northeast rift zone of tenerife presents a superb opportunity to study the entire cycle of activity of an oceanic rift zone field geology isotopic dating and magnetic stratigraphy provide a reliable temporal and spatial framework for the evolution of the ne rift zone which includes a period of very fast growth toward instability between ca 1 1 and 0 83 ma followed by three successive large landslides the micheque and guimar collapses which occurred approximately contemporaneously at ca 830 ka and on either side of the rift and the la orotava landslide between 690 10 and 566 13 ka our observations suggest that canarian rift zones show similar patterns of development which often includes overgrowth instability and lateral collapses collapses of the rift flanks disrupt established fissural feeding systems favoring magma ascent and shallow emplacement which in turn leads to magma differentiation and intermediate to felsic nested eruptions rifts and their collapses may therefore act as an important factor in providing architectural and petrological variability to oceanic volcanoes conversely the presence of substantial felsic volcanism in rift settings may indicate the presence of earlier landslide scars even if concealed by postcollapse volcanism comparative analysis of the main rifts in the canary islands outlines this general evolutionary pattern 1 growth of an increasingly high and steep ridge by concentrated basaltic fissure eruptions 2 flank collapse and catastrophic disruption of the established feeder system of the rift 3 postcollapse centralized nested volcanism commonly evolving from initially ultramafic mafic to terminal felsic compositions trachytes phonolites and 4 progressive decline of nested eruptive activity

experiments on rift zone evolution in unstable volcanic edifices large ocean island volcanoes frequently develop productive rift zones located close to unstable flanks and sites of older major sector collapses flank deformation is often caused by slip along a decollement within or underneath the volcanic edifice we studied how such a stressed volcanic flank may bias the rift zone development the influence of basal lubrication and lateral flank creep on rift development and rift migration is still poorly constrained by field evidence here our analog experiments provide new insights we injected colored water into gelatin cones and found systematic orientations of hydro fractures dikes propagating through the cones at the base of the cone diverse friction conditions were simulated by variation of the basal creep conditions we modeled radial dike swarms collinear rift zones and three armed rift systems it is illustrated that a single outward creeping flank is sufficient to modify the entire rift architecture of a volcano the experiments highlight the general unsteadiness of dike swarms and that the distribution and alteration of weak substratum may become a major player in shaping a volcano s architecture

improved age modelling approaches as exemplified by the revised chronology for the central european varved lake soppensee abstract one of the key factors in understanding past climate change is the development of robust age models that have sufficient chronological precision for comparing different palaeoclimate archives while retaining accuracy recent developments in bayesian age modelling are applied here to the swiss varve lake soppensee we develop revised age models for this sequence using the available stratigraphic information to constrain the calibrated radiocarbon ages we begin by using stratigraphical order as the only constraint and then sequentially increase the information incorporated into the model using relative varve age sample depth and varying depositional models within this bayesian framework we develop internally robust models that significantly improve the dating precision and are applicable to both varved and non varved sequences we then compare the model output to wider chronological information such as the age of the laacher see tephra in order to test the model accuracy the results of this exercise suggest that these methods can be used to build very reliable improved age models in a variety of records

seismotectonics of the canary islands abstract a revision of the seismicity both historical and instrumental for the canary islands is presented the occurrence on may 9 1989 of an earthquake of magnitude 5 2 between the islands gran canaria and tenerife followed by a large number of aftershocks have been interpreted on seismotectonic grounds the main conclusion is that a horizontal compressional stress regime in nw se direction is present in the region which is compatible with the tectonics in the northwestern part of the african continent

seismostratigraphy of the western flanks of el hierro and la palma canary islands a record of canary islands volcanism abstract a cruise carried out aboard the spanish r v hesperides using a 255 inch3 airgun allowed to identify three main seismostratigraphic units in the western submarine flanks of the islands of la palma and el hierro canary islands the time structure and thickness maps of each unit together with the interpretation of the seismic facies demonstrate that the evolution of the canary islands is recorded in the marine basin the structure maps show that the older reflectors dip to the nw in contrast to the present day sea floor which dips to the wnw the thickness maps also show that the depocentre moved from a position parallel to the northwest african margin to a position now occupied by the island of la palma despite the high sedimentation rates of hemipelagic background sedimentation in the study area the three seismic units can be interpreted in terms of their relation to the canarian volcanism unit i was deposited before the initiation of volcanism and the arrival of volcaniclastic flows and is thus mainly if not entirely composed of hemipelagic sediments unit ii seems to reflect the shield phases of the easternmost edifices and as such would be constituted by the distal products of erosion and mass wasting of these islands unit iii in contrast results mainly from the shield phase of the two westernmost islands la palma and el hierro and as such reflects more proximal conditions as demonstrated by the presence of lateral collapse deposits from these islands

environmental arsenopyrite stability and dissolution theory experiment and field observations arsenopyrite has traditionally been considered to be chemically unstable in the surficial environment however field evidence demonstrates that arsenopyrite does not readily decompose under water saturated near surface conditions arsenopyrite occurs in the heavy mineral suite of a variety of thin sediments in southern new zealand with no evidence for chemical corrosion these sediments have been water saturated but within metres of the surface for 10 60 28000 and 2 million years these observations of long term arsenopyrite stability are in accord with geochemical predictions based on recent experimentally determined thermodynamic data for arsenopyrite calculations using the new thermodynamic data suggest that arsenopyrite has similar eh ph stability range to pyrite except under acid conditions ph 4 where arsenopyrite should transform to realgar or orpiment calculated as concentrations in equilibrium with the pyrite arsenopyrite assemblage in the surficial environment are 0 01 0 1 ppm similar to groundwater in arsenopyrite bearing rocks in this study 0 005 0 3 ppm and these waters may be in chemical equilibrium arsenopyrite decomposes in oxidised waters to yield up to 1100 ppm dissolved as in the laboratory and up to 400 ppm dissolved as in mine processing waters these concentrations of dissolved as are several orders of magnitude lower than equilibrium solubility of arsenopyrite because of kinetic effects and development of protective oxide coatings on arsenopyrite grains mine tailings containing arsenopyrite should be chemically stable during longterm storage provided they are kept water saturated and moderately reduced d 2003 elsevier science b v all rights reserved

ams radiocarbon dating and varve chronology of lake soppensee 6000 to 12000 14c years bp for the extension of the radiocarbon calibration curve beyond 10000 14c y bp laminated sediment from lake soppensee central switzerland was dated the radiocarbon time scale was obtained using accelerator mass spectrometry ams dating of terrestrial macrofossils selected from the soppensee sediment because of an unlaminated sediment section during the younger dryas 10000 11000 14c y bp the absolute time scale based on counting annual layers varves had to be corrected for missing varves the soppensee radiocarbon verve chronology covers the time period from 6000 to 12000 14c y bp on the radiocarbon time scale and 7000 to 13000 calendar y bp on the absolute time scale the good agreement with the tree ring curve in the interval from 7000 to 11450 cal y bp cal y indicates calendar year proves the annual character of the laminations the ash layer of the vasset killian tephra massif central france is dated at 8230 140 14c y bp and 9407 44 cal y bp the boundaries of the younger dryas biozone are placed at 10986 69 cal y bp younger dryas preboreal and 1212 86 cal y bp allerod younger dryas on the absolute time scale the absolute age of the laacher see tephra layer dated with the radiocarbon method at 10 800 to 11200 14c y bp is estimated at 12350 135 cal y bp the oldest radiocarbon age of 14190 120 14c y bp was obtained on macrofossils of pioneer vegetation which were found in the lowermost part of the sediment profile for the late glacial the offset between the radiocarbon 10000 12000 14c y bp and the absolute time scale 11400 13000 cal y bp in the soppensee chronology is not greater than 1000 years which differs from the trend of the u th radiocarbon curve derived from corals

vertical distribution of as iii and as v in a coastal sandy aquifer factors controlling the concentration and speciation of arsenic in the stuarts point groundwater system northern new south wales australia arsenic species were measured in a bundled piezometer installed in the holocene barrier of the stuarts point coastal sands aquifer northern new south wales australia vertical distribution shows two peaks of elevated as concentration at a depth of 10 11 m concentrations of as tot as v and as iii are in the range of 52 85 38 67 and 14 18 mg l respectively and the ratio of as v as iii is well above 1 at 3 7 2 7 the second peak at a depth of 25 m shows the highest concentrations of as tot as v and as iii with values reaching 337 125 and 212 mg l respectively the as v as iii ratio is below 1 at 0 6 0 7 high as tot and as v concentrations at shallower depths are associated with acidic conditions and very low concentrations of all ions desorption of as from al hydroxides and as enriched feoxyhydroxides are plausible mechanisms releasing as into the groundwater system the elevated concentration of as tot and as iii at 25 m is potentially related to the leaching of the clay surfaces elevated hco3 and alkaline ph conditions at this depth cause desorption of as which is later present as as iii species in the reducing environment the high concentrations of hco3 further reduce the possible extent of as sorption on fe and mn oxyhydroxides the identification of as in a groundwater system associated with the coastal barrier sand dune environment raises serious questions of the suitability of human consumption of untreated groundwater drawn from these aquifer types further investigation both in australia and globally are needed to classified the extent of this hydrogeochemical occurrence near coastal communities that rely on groundwater 2003 elsevier science ltd all rights reserved

eruptive and structural history of teide volcano and rift zones of tenerife canary islands the teide and pico viejo stratocones and the northwest and northeast rifts are products of the latest eruptive phase of the island of tenerife initiated with the lateral collapse of its northern flank that formed the las canadas caldera and the icod la guancha valley ca 200 ka the eruptive and structural evolution of this volcanic complex has been reconstructed after detailed geological mapping and radioisotopic dating of the significant eruptive events a set of 54 new 14 c and k ar ages provides precise age control of the recent eruptive history of tenerife particularly teide volcano the third highest volcanic feature on earth 3718 m above sea level 7 km high and unique in terms of its intraplate setting the development of the teide pico viejo volcanoes may be related to the activity of the northwest and northeast rifts volcanic and intrusive activity along both rift zones may have played an important role in activating the gravitational landslide and in the subsequent growth nested within the collapse embayment of an increasingly higher central volcano with progressively differentiated magmas the coeval growth of the central volcano with sustained activity along the rifts led to a clear bimodal distribution in composition of eruptive products with the basaltic eruptions in the distal part of the rifts and phonolitic and more explosive eruptions in the central area where the differentiated stratocones developed current volcanic hazard in tenerife is considered to be moderate because eruptive frequency is low explosivity is modest and the eruptive activity of the teide stratocone seems to have declined over the past 30 k y with only one eruption in this period 1150 yr b p

reaction path modelling in the as s system a case study for geothermal as transport abstract geochemical speciation and reaction path modelling with the geochemists workbench gwb software was used to investigate zonal as sulphide mineral precipitation and as transport in an active geothermal field the uzon caldera kamchatka a new compilation and critical review of published experimental and theoretical thermodynamic data for as phases was used to modify and update a supcrt92 database with important missing phases the equilibrium constants for these as phases were then added or modified in the current gwb database speciation calculations predict that the sampled fluids are undersaturated with respect to as phases and aqueous as is dominantly transported as the complex h3aso3 aq and to a lesser extent the as sulphide complexes as2s3 aq has2s4 and as2s42 modelling the changes in concentration of dissolved as between the samples 0 2 8 6 mg kg indicates a strong dependence on redox log o2 g from 53 to 60 and temperature 95 65 c and illustrates the importance of mixing between the hydrothermal fluid and an oxygenated fluid reaction path models that follow the cooling of a h2s aq dominated as enriched 15 mg kg fluids from 125 to 25 c with sliding redox from log o2 g 55 to 60 predict the mineral paragenesis native as pyrite realgar pyrite orpiment pyrite pyrite this mineral sequence closely resembles the natural layering observed in the uzon caldera although field measurements contain a lower reduced s concentration than the model the error margin in the measured sulphide inherent from in situ oxidation during sampling is enough to account for the discrepancy despite assumptions in fluid parameters and modelling approaches as well as deficiencies in the thermodynamic data and an equilibrium approach this study has shown that acceptable and useful analogues for natural as rich systems can be developed

lake sediments record cycles of sediment flux driven by large earthquakes on the alpine fault new zealand large earthquakes in mountain regions commonly trigger extensive landsliding and are important drivers of erosion but the contribution of this landsliding to long term erosion rates and seismic hazard remains poorly understood here we show that lake sediments record postseismic landscape response as a sequence of turbidites that can be used to quantify erosion related to large moment magnitude m w 7 6 earthquakes on the alpine fault new zealand alpine fault earthquakes caused a threefold increase in sediment flux over the 50 yr duration of each postseismic landscape response this represents considerable delayed hazard following earthquake induced strong ground motion earthquakes were responsible for 27 of the sediment flux from the lake catchment over the past 1100 yr leading us to conclude that alpine fault earthquakes are one of the most important drivers of erosion in the range front of the southern alps

proglacial lake sediment records reveal holocene climate changes in the venezuelan andes lake sediment records from the cordillera de merida in the northern venezuelan andes document the history of local glacial variability and climate changes during the holocene w12 ka to the present the valleys that contain these lakes have similar bedrock compositions and hypsometries but have different headwall elevations and aspects which makes them useful for investigating the magnitude of past glaciations there was widespread glacial retreat in the venezuelan andes during the early holocene after which most watersheds remained ice free and thus far only valleys with headwalls higher than w4400 m asl contain evidence of glaciation during the last w10 ka there was a pronounced shift in sediment composition for the montos headwall w4750 m asl and los anteojos headwall w4400 m asl records during the middle holocene from w8 0 to 7 7 ka when conditions appear to have become ice free and drier there is tentative evidence that the glacier in the mucubaji valley headwall w4609 m asl advanced from w8 1 to 6 6 ka and then retreated during the latter stages of the middle holocene clastic sediment accumulation in other nearby lake basins was either low or decreased throughout most of the middle holocene as watersheds stabilized under warmer and or drier conditions in the montos record there was another major shift in sediment composition that occurred from w6 5 to 5 7 ka similar to other regional records that suggest conditions were drier during this period overall the late holocene was a period of warmer and wetter conditions with ice extent at a minimum in the northern tropical andes there were also punctuated decadal to multi centennial periods of higher clastic sediment accumulation during the last w4 ka likely in response to periods of cooling and or local precipitation changes in watersheds with headwalls above 4600 m asl there is evidence of glacial advances during the little ice age w0 6e0 1 ka the pattern of glacial variability is generally similar in both the northern and southern tropics during the little ice age suggesting that ice margins in both regions were responding to colder and wetter conditions during the latest holocene the observed pattern of holocene climate variability in the venezuelan andes cannot be explained by insolation forcing alone and tropical ocean influences were likely associated with the observed glacial and lake level changes

hotspot volcanism close to a passive continental margin the canary islands the canarian archipelago is a group of volcanic islands on a slow moving oceanic plate close to a continental margin the origins of the archipelago are controversial a hotspot or mantle plume a zone of lithospheric deformation a region of compressional block faulting or a rupture propagating westwards from the active atlas mountains fold belt have been proposed by different authors however comparison of the canarian archipelago with the prototypical hotspot related island group the hawaiian archipelago reveals that the differences between the two are not as great as had previously been supposed on the basis of older data quaternary igneous activity in the canaries is concentrated at the western end of the archipelago close to the present day location of the inferred hotspot this is the same relationship as seen in the hawaiian and cape verde islands the latter archipelago associated with a well defined but slow moving mantle plume shows anomalies in a plot of island age against distance which are comparable to those seen in the canary islands these anomalies cannot therefore be used to argue against a hotspot origin for the canaries individual islands in both archipelagoes are characterized by initial rapid growth the shield building stages of activity followed by a period of quiescence and deep erosion erosion gap which in turn is followed by a post erosional stage of activity the absence of post shield stage subsidence in the canaries is in marked contrast with the major subsidence experienced by the hawaiian islands but is comparable with the lack of subsidence evident in other island groups at slow moving hotspots such as the cape verdes comparison of the structure and structural evolution of the canary islands with other oceanic islands such as hawaii and reunion reveals many similarities these include the development of triple mercedes star rift zones and the occurrence of giant lateral collapses on the flanks of these rift zones the apparent absence of these features in the post erosional islands may in part be a result of their greater age and deeper erosion which has removed much of the evidence for their early volcanic architecture we conclude that the many similarities between the canary islands and island groups whose hotspot origins are undisputed show that the canaries have been produced in the same way

denmark strait during the late glacial maximum and marine isotope stage 3 sediment sources and transport processes abstract the sediment records from north and south of denmark strait cores ps2644 and md99 2323 and on the kangerlussuaq trough mouth fan ktmf md99 2260 are evaluated for the period 12 to 60 cal ka bp with the goal of evaluating 1 the relative roles of the greenland and iceland ice sheets in sediment composition 2 the processes of sediment supply and 3 the relationship if any between the atmospheric derived ice core records and glacial marine sediment history these questions were addressed using counts of coarse 2 mm ice rafted debris ird magnetic susceptibility grain size spectra and sediment mineral composition a significant difference in these variables occurred between ms3 and mis2 with the latter showing small to modest abrupt changes in felsic and mafic minerals and in ird compared to larger and less variable changes during mis2 the dominant bedrock source archived in the cores is the cenozoic basaltic outcrops from east greenland and iceland 60 but there are frequent pulses of felsic rich sediments 17 36 which coincided with greenland stadials there is also a persistent detrital carbonate input the largest shift in most sediment proxies occurred 28 30 cal ka bp reflecting the sustained expansion of the ice sheets the grain size spectra on the snorri drift md99 2323 reflected complex depositional histories involving the supply of poorly sorted glacially derived sediment sand silt and clay and reworking by bottom currents

environmental mercury and arsenic sources in fossil hydrothermal systems northland new zealand northland new zealand has been affected by natural hot water spring systems depositing elevated concentrations of mercury and arsenic over the past 5 million years due to the different erosion levels of these hot water systems four principal types of mercury and arsenic occurrences are found active hot springs layered surface deposits sinters deposited by hot springs highly fractured rock zones formed immediately beneath hot springs and chemically altered and mineralized rock from the deeper roots of hot spring systems mercury occurs principally as cinnabar and as a minor impurity 1 wt in phosphate minerals and iron sulfides particularly marcasite mercury is irregularly distributed through limonitic cements formed during oxidation arsenic occurs as a minor impurity 1 wt in phosphate minerals and iron sulfides particularly marcasite arsenic is also variably dispersed through limonite but not necessarily with mercury decomposition of marcasite constitutes the most significant source of mercury and arsenic pollution from the studied sites release of mercury and arsenic into the environment from marcasite phosphates and limonite is enhanced by acidification of the sites down to ph of 2 caused by oxidation of iron sulfides mercury and arsenic concentrations of up to 100 parts per billion should be expected in waters near the deposits these concentrations are in excess of recommended drinking water levels

submarine landslides around the canary islands the morphology and structure of the submarine flanks of the canary islands were mapped using the gloria long range side scan sonar system bathymetric multibeam systems and sediment echosounders twelve young 2 ma giant landslides have been identified on the submarine flanks of the canary islands up to now older landslide events are long buried under a thick sediment cover due to high sedimentation rates around the canary islands most slides were found on the flanks of the youngest and most active islands of la palma el hierro and tenerife but young giant landslides were also identified on the flanks of the older 15 20 ma but still active eastern islands large scale mass wasting is an important process during all periods of major magmatic activity the long lived volcanic constructive history of the islands of the canary archipelago is balanced by a correspondingly long history of destruction resulting in a higher landslide frequency for the canary islands compared to the hawaiian islands where giant landslides only occur late in the period of active shield growth the lower stability of the flanks of the canaries is probably due to the much steeper slopes of the islands a result of the abundance of highly evolved intrusive and extrusive rocks another reason for the enhanced slope instability is the abundance of pyroclastic deposits on canary islands resulting from frequent explosive eruptions due to the elevated volatile contents in the highly alkalic magmas dike induced rifting is most likely the main trigger mechanism for destabilization of the flanks flank collapses are a major geological hazard for the canary islands due to the sector collapses themselves as well as triggering of tsunamis in at least one case a giant lateral blast occurred when an active magmatic or hydrothermal system became unroofed during flank collapse

slope failures on the flanks of the western canary islands abstract landslides have been a key process in the evolution of the western canary islands the younger and more volcanically active canary islands el hierro la palma and tenerife show the clearest evidence of recent landslide activity the evidence includes landslide scars on the island flanks debris deposits on the lower island slopes and volcaniclastic turbidites on the floor of the adjacent ocean basins at least 14 large landslides have occurred on the flanks of the el hierro la palma and tenerife the majority of these in the last 1 million years with the youngest on the northwest flank of el hierro as recent as 15 thousand years in age older landslides undoubtedly occurred but are difficult to quantify because the evidence is buried beneath younger volcanic rocks and sediments landslides on the canary island flanks can be categorised as debris avalanches slumps or debris flows debris avalanches are long runout catastrophic failures which typically affect only the superficial part of the island volcanic sequence up to a maximum thickness of 1 to 2 km they are the commonest type of landslide mapped in contrast slumps move short distances and are deep rooted landslides which may affect the entire thickness of the volcanic edifice debris flows are defined as landslides which primarily affect the sedimentary cover of the submarine island flanks some landslides are complex events involving more than one of the above end member processes individual debris avalanches have volumes in the range of 50 500 km3 cover several thousand km2 of seafloor and have runout distances of up to 130 km from source overall debris avalanche deposits account for about 10 of the total volcanic edifices of the small relatively young islands of el hierro and la palma some parameters such as deposit volumes and landslide ages are difficult to quantify the key characteristics of debris avalanches include a relatively narrow headwall and chute above 3000 m water depth on the island flanks broadening into a depositional lobe below 3000 m debris avalanche deposits have a typically blocky morphology with individual blocks up to a kilometre or more in diameter however considerable variation exists between different avalanche deposits at one extreme the el golfo debris avalanche on el hierro has few large blocks scattered randomly across the avalanche surface at the other icod on the north flank of tenerife has much more numerous but smaller blocks over most of its surface with a few very large blocks confined to the margins of the deposit icod also exhibits flow structures longitudinal shears and pressure ridges that are absent in el golfo the primary controls on the block structure and distribution are inferred to be related to the nature of the landslide material and to flow processes observations in experimental debris flows show that the differences between the el golfo and icod landslide deposits are probably controlled by the greater proportion of fine grained material in the icod landslide this in turn relates to the nature of the failed volcanic rocks which are almost entirely basalt on el hierro but include a much greater proportion of pyroclastic deposits on tenerife landslide occurrence appears to be primarily controlled by the locations of volcanic rift zones on the islands with landslides propagating perpendicular to the rift orientation however this does not explain the uneven distribution of landslides on some islands which seems to indicate that unstable flanks are a weakness that can be carried forward during island development this may occur because certain island flanks are steeper extend to greater water depths or are less buttressed by the surrounding topography and because volcanic production following a landslide my be concentrated in the landslide scar thus focussing subsequent landslide potential in this area landslides are primarily a result of volcanic construction to a point where the mass of volcanic products fails under its own weight although the actual triggering factors are poorly understood they may include or be influenced by dyke intrusion pore pressure changes related to intrusion seismicity or sealevel climate changes a possible relationship between caldera collapse and landsliding on tenerife is not in our interpretation supported by the available evidence

the channel between gran canaria and tenerife constructive processes and destructive events during the evolution of volcanic islands seismic sidescan sonar bathymetric multibeam and odp ocean drilling program data obtained in the submarine channel between the volcanic islands of gran canaria and tenerife allow to identify constructive features and destructive events during the evolution of both islands the most prominent constructive features are the submarine island flanks being the acoustic basement of the seismic images the build up of tenerife started following the submarine stage of gran canaria because the submarine island flank of tenerife onlaps the steeper flank of gran canaria the overlying sediments in the channel between gran canaria and tenerife are chaotic consisting of slumps debris flow deposits syn ignimbrite turbidites ash layers and other volcaniclastic rocks generated by eruptions erosion and flank collapse of the volcanoes volcanic cones on the submarine island flanks reflect ongoing submarine volcanic activity the construction of the islands is interrupted by large destructive events especially by flank collapses resulting in giant landslides several miocene flank collapses e g the formation of the horgazales basin were identified by combining seismic and drilling data whereas young giant landslides e g the guimar debris avalanche are documented by sidescan bathymetric and drilling data sediments are also transported through numerous submarine canyons from the islands into the volcaniclastic apron seismic profiles across the channel do not show a major offset of reflectors the existence of a repeatedly postulated major ne sw trending fault zone between gran canaria and tenerife is thus in doubt the sporadic earthquake activity in this area may be related to the regional stress field or the submarine volcanic activity in this area seismic reflectors cannot be correlated through the channel between the sedimentary basins north and south of gran canaria because the channel acts as sediment barrier the sedimentary basins to the north and south evolved differently following the submarine growth of gran canaria and tenerife in the miocene

the 2011 2012 submarine eruption off el hierro canary islands new lessons in oceanic island growth and volcanic crisis management forty years after the eruption of the teneguia volcano on la palma 1971 the last volcanic event in the canary islands a submarine eruption took place in 2011 off shore el hierro the smallest an

exotic pollen as an indicator of variable atmospheric circulation over the labrador sea region during the mid to late holocene variability in the abundance of exotic non native pollen in sediment cores has long been considered as a potential proxy for changing atmospheric circulation but the difficulty of gaining sufficient total exotic pollen and the incomplete under standing of atmospheric pollen transport patterns has hindered its application in light of recent advances in the study of pollen transport we present an exotic pollen record from two fjord sediment cores taken from the west placentia bay newfoundland and east narsaq sund greenland labrador sea as a basis for studying variations in regional atmospheric circulation the two cores cover the last ca 5500 years and indicate a shift in dominant spring summer air masses at ca 2000 southern greenland and 3000 cal a bp newfoundland transporting reduced concentrations of pollen from southerly and south westerly vegetation zones this may suggest a shift away from more dominantly zonal atmospheric circulation a feature of positive north atlantic oscillation years to more frequent meridional circulation these results support sea ice sea surface temperature proxy reconstructions from newfoundland investigated as part of the same project which also suggest increased winter atmospheric circulation during the early part of the time period studied in this region more positive north atlantic oscillation years and therefore more zonal atmospheric circulation are associated with increased atmospheric circulation in both the winter and the summer seasons copyright 2011 john wiley sons ltd

high resolution stratigraphy and zircon u pb geochronology of the middle triassic buchenstein formation dolomites northern italy precession forcing of hemipelagic carbonate sedimentation and calibration of the anisian ladinian boundary interval orbitally forced cyclic variations in sedimentary sequences provide evidence for short term fluctuations of earth climate and a tool for high resolution timescale calibration we here present stratigraphic and geochronological evidence for precession forcing in middle triassic hemipelagic limestones of the buchenstein formation dolomites northern italy high resolution stratigraphy of several correlative sections of the buchenstein formation documents a coherent cycle pattern isotope dilution thermal ionization mass spectrometry zircon u pb geochronology of tuffs bracketing the cyclic interval reveals an average cycle duration of 18 5 2 1 kyr consistent with a shorter climatic precession cycle in the middle triassic compared with today this suggests a predominantly precession controlled climate in this low latitude setting of the western tethys and allows high precision calibration of the anisian ladinian boundary interval from integrating cyclostratigraphic and u pb geochronological constraints our best estimate for the age of the anisian ladinian boundary is 241 464 0 064 0 097 0 28 ma we also provide precise estimates for lithostratigraphic boundaries biostratigraphic markers and magnetic reversals within the boundary interval stratigraphic intervals with elevated sedimentation rate record a sub milankovitch signal that may be equivalent to patterns in adjacent carbonate platforms such as the latemar platform the origin of this sub milankovitch signal remains unknown but highlights the potential to investigate shorter term climatic variations in mesozoic sedimentary sequences supplementary material isotope dilution thermal ionization mass spectrometry u pb and laser ablation inductively coupled plasma mass spectrometry trace element data tables as well as the results of the bayesian age modelling are available at https doi org 10 6084 m9 figshare c 3861817

the effects of flank collapses on volcano plumbing systems the growth of large volcanoes is commonly interrupted by episodes of flank collapse that may be accompanied by catastrophic debris avalanches explosive eruptions and tsunamis el hierro the youngest island of the canary archipelago has been repeatedly affected by such mass wasting events in the last 1 ma our field observations and petrological data suggest that the largest and most recent of these flank collapses the el golfo landslide likely influenced the magma plumbing system of the island leading to the eruption of higher proportions of denser and less evolved magmas the results of our numerical simulations indicate that the el golfo landslide generated pressure changes exceeding 1 mpa down to upper mantle depths with local amplification in the surroundings and within the modeled magma plumbing system stress perturbations of that order might drastically alter feeding system processes such as degassing transport differentiation and mixing of magma batches

bacterial s layer preservation and rare arsenic antimony sulphide bioimmobilization in siliceous sediments from champagne pool hot spring waiotapu new zealand siliceous sinter loose sediments and suspended flocs in champagne pool an anoxic hot 75 c spring at waiotapu new zealand are composed of opaline silica and metal rich sulphides that contain many well preserved mineralized microbes detailed analysis by transmission electron microscopy and energy dispersive spectrometry has shown that bacterial cell wall and capsular material is preserved by the immobilization of high levels of as sb and s in the organic matrix calculation of the probable metal species in the spring water suggests that arsenic and antimony are present in solution as negative and neutrally charged sulphide or hydroxide complexes such as has 2 s 4 h 3 aso 3 and hsb 2 s 4 the early adsorption of these complexes onto reactive groups on the bacterial surface may be paramount in the excellent preservation of cell morphology as biomineralization progresses biomineral composition commonly becomes dominated by the precipitation of a supersaturated al rich amorphous silica phase biomineralization commonly preserves s layers an ordered mosaic of proteins on the outer surface of the cell wall these are the finest ultrastructure details thus far found in microbes preserved by hydrothermal mineralization and can be used as an aid to identify microfossils the s layers preserved here probably belong to clostridium thermohydrosulfuricum or desulfotomaculum nigrifacans

revised ages of late holocene tephras in beppu bay central kyushu southwest japan abstract in this study we revised eruptive ages especially the aso and yufu volcanoes central kyushu by analyzing a sediment core of southwestern beppu bay southwest japan where undisturbed sediments are continuously deposited in a dysoxic basin we identified two ash fall layers in the sequence covering the last ca 3000 years by using the refractive index of volcanic glasses and other parameters these layers were likely correlated with n2 ash of the aso volcano and yufu dake 1 ash yf1 of the yufu volcano on the basis of the refractive indices of volcanic glasses heavy mineral compositions special distribution and facies according to high precision age models the eruptive ages 68 2 probability range of these tephras were 1470 1490 and 2010 2100 cal yr bp respectively and concordant with reported ages of previous research these precise ages of tephras improve linking or dating in the various environments and contribute to investigation of environmental changes or sedimentary process from source to sink

the solubility of as2s3 and speciation of as in dilute and sulphide bearing fluids at 25 and 90 c abstract the solubility of synthetic crystalline as 2 s 3 in o 2 free dilute and sulphide bearing solutions has been determined at temperatures of 25 and 90 c the predominant dissolved as species are h 3 aso 0 3 and h 2 as 3 s 6 orpiment solubility is limited by the reactions 0 5as 2 s 3 3h 2 o h 3 aso 0 3 1 5hs 1 5h pk 25 23 11 0 11 pk 90 18 83 0 05 1 5as 2 s 3 1 5hs 0 5h h 2 as3s 6 pk 25 3 61 09 pk 90 3 42 0 06 a formational free energy for orpiment has been calculated as g 0 f 96 72 kj mol measured concentrations of as in hot springs of the taupo volcanic zone new zealand are consistent with those predicted using the solubility reactions and equilibrium constants of this study in sampled springs ph 2 6 97 100 of the dissolved as is present as h 3 aso 0 3 when h 3 aso 0 3 is the dominant as species orpiment deposition is likely to occur in response to fluid cooling in the sub aerial environment

pleistocene to holocene transition in the central basin of the gulf of thailand based on geoacoustic survey and radiocarbon ages abstract record of the last glacial maximum and postglacial sea level rise in the central gulf of thailand some 140 km offshore of the malay peninsula was studied along a nw striking section water depth 55 82 m below the present msl by means of geoacoustic surveys shallow gravity coring and radiocarbon dating the record comprises evidence of valley incision followed by estuarine to marine transgression which was interrupted by deltaic progradation the valley incision and delta formation are attributed to the kelantan river draining the malay peninsula the delta growth was halted at 10 4 cal kyr bp by transgressive ravinement followed by emplacement of a thin condensed mantle of modern marine muds such age is compatible with the fast but diachronous nature of this transgressive event that according to previous estimates began in the central sunda shelf at 11 11 5 cal kyr bp and reached the head of the thailand bay at 8 7 cal kyr bp the presence of deltaic deposits within postglacial transgressive systems tract is uncommon on extremely wide and accommodation dominated shelves such as the sunda shelf and is here interpreted to reflect a combination of decelerating sea level rise 13 10 cal kyr bp with increased precipitation and sediment yield coupled with the reactive nature of the kelantan river catchment

last glacial pollen climate reconstructions from northland new zealand despite wide ranging interest in the vegetation and climate of northland new zealand during the last glacial cycle the region and timeframe lack quantitative climate reconstructions while land based pollen records have tended to be poorly dated and fragmentary the region is also important for geochronology due to the co occurrence of the rotoehu tephra a widely dispersed isochron near the current limits of radiocarbon dating and extensive subfossil wood remains of agathis australis with strong dendrochronological and dendroclimatological potential we present new pollen records and temperature reconstructions from three sites set in coastal dune belts from western mid northland 35 s all containing rotoehu tephra that collectively span the last 70 ka the phases and amplitude of temperature changes broadly align with those reported from elsewhere in new zealand and with marine isotope climate stratigraphic records including maximum temperature depression of 6 8 c during the last glacial maximum we argue that these climatic patterns are intimately linked to shifts in the southern westerly wind belt the northern margins of which extend to the region today correspondence between the northland temperature shifts and atmospheric co2 supports the model of ocean atmosphere co2 flux modulated by latitudinal migration of the southern westerlies copyright 2017 john wiley sons ltd

holocene dust deposition in the ili basin and its implications for climate variations in westerlies dominated central asia abstract understanding holocene paleoclimate in arid central asia aca is helpful for predicting future climate however holocene climate patterns and their forcing mechanisms across aca are vigorously debated in the context of global climate change here we present a holocene loess profile sgx from the ili basin in the westerlies dominated central asia based on high resolution medium grained 38 63 m quartz optically stimulated luminescence osl dating and grain size and color measurements we reconstruct the holocene paleoclimate osl geochronology indicate that this sgx loess profile covers the last 11 5 ka and grain size analyses reveal that the sediments are sandy loess and the environmentally sensitive fractions are

consolidation and incipient oxidation of alkaline arsenopyrite bearing mine tailings macraes mine new zealand abstract fine grained ca 15 m arsenopyrite bearing mine tailings have been exposed to drying and oxidation for 4 a pending relocation the tailings are still partly covered by a pond of decanted pore waters the water table in drying tailings has lowered by 1 3 m and desiccation cracks up to 2 cm wide have formed on the 1 m scale extending through the unsaturated zone tailings in the unsaturated zone have similar pore water contents to saturated tailings typically 16 32 wt water saturated tailings retain alkaline ph ca 10 from the mine cyanidation plant but ph lowers progressively towards ca 7 near the surface or near desiccation cracks in the unsaturated zone the redox state of the tailings changes in parallel with ph with an empirical relationship eh mv 55 ph 290 water in the remnant decant pond reflects this relationship also unsaturated tailings have variable but low permeabilities typically 10 3 to 10 4 m day and more permeable horizons have allowed incursion of oxygenated air and or rain water from desiccation cracks sulphide grains in all tailings examined are unaltered sulphides and solutions in the tailings are out of thermodynamic equilibrium predicted from the redox ph conditions due to kinetic constraints incursion of rain water locally facilitates deposition from pore waters of insoluble fe oxide and arsenate minerals thus fixing as in the dry unsaturated tailings

earlier history of the 70 ma old canary hotspot based on the temporal and geochemical evolution of the selvagen archipelago and neighboring seamounts in the eastern north atlantic major element trace element and sr nd pb isotope data combined with 40ar 39ar age determinations of volcanic rocks from the selvagen islands and neighboring seamounts in the eastern north atlantic reveal the earlier history of the 70 ma old canary hotspot a basanitic to phonolitic late shield stage intrusive complex 29 ma is exposed on selvagem pequena the evolution of selvagem grande can be divided into three magmatic phases a tephritic to phonolitic late shield stage intrusive complex 24 26 ma and two rejuvenated or post erosional stages 8 12 and 3 4 ma consisting of alkali basalt basanite and rare phonolite during the early to mid miocene volcanic hiatus 12 24 ma the top of the volcano was beneath sea level as evidenced by marine carbonate sediments 13 24 ma dated through correlation of 87sr 86sr with the seawater sr isotope curve the geochemistry of the shield stage lavas indicates that they derive from plume sources whereas the post erosional lavas are derived from metasomatized lithospheric sources five sampled seamounts to the east and northeast of the islands range in composition from alkali basalt and basanite to phonolite samples from dacia conception bank and lars were dated at 9 17 and 68 ma respectively geochemical data suggest that the dredged samples come from the post erosional stage of volcanism and therefore the dates represent minimum ages for the seamount volcanoes the elevation of erosional platforms formed at wave base decrease from selvagen grande 100 m above sea level to lars seamount 900 m below sea level suggesting a southwest to northwest age progression and that all of these seamounts are older than the selvagen islands trace element and sr nd pb isotopic composition of the selvagen islands and neighboring seamounts are consistent with their origin from the canary plume interaction of the weak canary mantle plume with a slow moving plate appears to be responsible for generating a 450 km wide irregular hotspot track extending 800 km from the youngest canary island of hierro in the southwest to lars seamount in the northeast

crustal structure gravity anomalies and flexure of the lithosphere in the vicinity of the canary islands summary simple elastic plate models have been used to calculate the flexure of the lithosphere caused by volcanic loading at the canary islands and sediment loading at the moroccan continental margin by comparing the calculated flexure to observations based on seismic refraction and free air gravity anomaly data constraints have been placed on the long term 106 years elastic thickness of the lithosphere te the best fit between the calculated and observed flexure in the vicinity of the canary islands is for te 20 km this value of te also explains seismic reflection data in regions that flank the island provided that the lithosphere underlying the moroccan margin is sufficiently weak te 5 km for sediment loading to contribute little to the island flexure a backstripping study in which gravity data are used to constrain the value of te supports the suggestion that the lithosphere underlying the moroccan margin like its conjugate at the baltimore canyon trough is weak although sediment loading at the moroccan margin appears therefore to have exerted little influence on the structure of the canary islands there is evidence that island flexure may have influenced the stratigraphic development of the moroccan margin especially in the region of the slope anticline a te of 20 km is about 15 km lower than would be expected on the basis of the thermal age of the oceanic lithosphere that underlies the canary islands similar low values have been reported from oceanic islands in the pacific superswell region of french polynesia where they have been attributed to re heating of the lithosphere by one or more hotspots a general e w age progression of the volcanic rocks suggests that the canary islands were also generated by a hotspot they lack however the topographic swell and gravity geoid high which usually accompanies these features one possibility is that the low te values are the result of a pre existing weakness in the oceanic crust a te of 20 km is large enough however for a significant part of the mantle to still be involved in the support of the island loads a more likely explanation is thermal weakening by a hotspot which has been localized enough to reduce te but not to produce a swell or gravity geoid high irrespective of its cause the low te suggests that oceanic lithosphere does not necessarily progressively increase its strength with age so that even 140 ma old lithosphere is vulnerable and can in some regions be significantly weakened by later thermal and mechanical processes

implications for the early shield stage evolution of tenerife from k ar ages and magnetic stratigraphy abstract the combined use of field geology radioisotopic dating and magnetic stratigraphy applied to the old shield volcanoes of tenerife provides a reliable time framework for the early shield stage evolution of the island the greater part of this new set of ages obtained from sequences of lava flows is in agreement with the astronomical polarity time scale this approach illustrates that previous k ar data collected without a comprehensive stratigraphy should be viewed with caution and in some cases discarded altogether the shield volcanoes of tenerife encompass a relatively small number of magnetozones an observation consistent with the relatively short periods of growth shown by the new ages 1 2 my the island was constructed by the aggregation of three successive shields the roque del conde central shield between about 11 9 and 8 9 ma and the teno 6 2 5 6 ma and anaga 4 9 3 9 ma volcanoes this new oldest subaerial age of tenerife fits with the others obtained in the canaries in a clear west to east monotonous age progression one of the main restrictions for hotspot related island chains

growth and persistence of hawaiian volcanic rift zones hawaiian volcanic rift zones are modeled by representing the rifts and adjacent volcano flanks as long ridges with the geometry of flattened triangular prisms the intrusion of dikes along the axis of a rift requires a mechanism to generate the appropriate dike trapping stress field within the prism possible factors that affect the state of stress in the prism include multiple dike intrusion along the ridge axis faulting and gravitational sagging of the topography in extreme models with very steep slopes and high poisson s ratio corresponding to the gelatin models of rift zones by fiske and jackson 1972 results of finite element calculations indicate that gravity induced stresses are sufficient to trap a dike into propagating within the prism and parallel to the rift zone as proposed by fiske and jackson however the mechanism does not work for gently sloping flanks or a more acceptable poisson s ratio of about 0 25 additionally trapping stresses in the gravity loading and density stratification models will not persist after a few dike injection episodes therefore in mature hawaiian rift zones with possibly thousands of dikes additional processes must act to control the stresses that permit continued dike intrusion and rift persistence it is proposed that accommodation to dike emplacement occurs by slip on deep faults possibly of the type proposed for the 1975 kalapana hawaii earthquake as suggested by others for this earthquake the faults could coincide with the contact of the volcano with the seafloor within the weak seafloor sediments such faulting not only provides a means for the flanks to adjust continuously to intrusions but also generates the stress patterns needed to constrain future dikes to propagate along the rift axis other possible faulting mechanisms such as shallow gravity slides and normal faulting of the flanks do not appear to favor rift zone persistence in this model the horizontal stress generated by a standing column of magma at the time of dike emplacement the stresses in the ridges and the fault strength are coupled this results in a feedback between the maximum height that magma can rise along the rift fault friction and fault width through this feedback the slope of the volcano flank is controlled by the fault friction when applied to kilauea volcano the model yields an estimate for the coefficient of fault friction as high as 0 39 assuming normal hydrostatic pore fluid pressure an implication of this model supported by other studies is that rift intrusion and lateral spreading could be major contributors to volcano growth

analysis of vegetation and climate change during late pleistocene from ziro valley arunachal pradesh eastern himalaya region abstract vegetation and climate during later part of late pleistocene have been reconstructed from ziro valley arunachal pradesh eastern himalaya based on pollen data along with carbon isotope and magnetic susceptibility data the study reveals that the area and the vicinity is occupied by mixed broad leaved conifer forest and pine grass savanah at variable densities at least since 66 000yr bp the phases of expansions and declines of oaks with decline and increase of pines and grasses probably occurred under increase warm moist and decrease cool dry of s w monsoon precipitation respectively the increasing trend of s w monsoon and temperature is recorded during 44 000 to 34 000 cal yr bp synchronizing with the peat development and which peaked at around 35 000 cal yr bp this may link to the interstadial phase during the last major glacial cycle in the himalayan region it is also reflected in the decline of 13c value indicating dominance of c 3 type of vegetation the increased values of fd and lower values lf magnetic susceptibility recorded during the phase of the peat deposit further advocate s higher monsoon intensity impact of expansion of glacier felt with peak lgm around 20 000 cal yr bp is perceived tree line had moved to lower altitudes due to increased aridity and low temperature during this time existence of savannah type of vegetation is also evident by the increase of c4 taxa decreased fd and increased lf susceptibility also indicate reduced s w monsoon intensity

location and orientation of eruptive fissures and feederdykes at mount etna influence of gravitational and regional tectonic stress regimes abstract lava extrusion from fissures on the flanks of the etna volcano is a common feature of recent activity as evidenced by the eruptions of 1971 1981 1983 and 1985 and was of similar importance during prehistoric times we propose here a model within which the location and orientations of the large majority of historic eruptive fissures on etna s flanks together with their feeder dykes are explained within the framework of a gravitational stress regime stress orientations within this regime are controlled largely by the gross morphology of the volcano but are significantly modified by local topographic anomalies we propose that the gravitational stress regime largely supercedes an earlier developed regional tectonic stress regime which still operates in the sub volcanic basement and may remain the dominant control of eruptive fissure and feeder dyke disposition at lower altitudes on the flanks the proposed model is supported by 1 detailed examination of fissure locations and orientations and the relationship between fissure azimuths and topography 2 precise horizontal distance measurement and vertical ground deformation studies of a recent eruption and 3 qualitative physical modelling experiments in which coloured water is injected into solidified gelatine solutions representing variously shaped volcanic constructs a cautious approach is advocated when extrapolating trends of spatially limited fissure segments for the purpose of locating potential sites of magma ascent and implications of the model for hazard analysis are outlined

building and testing age models for radiocarbon dates in lateglacial and early holocene sediments the growing importance of understanding past abrupt climate variability at a regional and global scale has led to the realisation that independent chronologies of past environmental change need to be compared between various archives this has in turn led to attempts at significant improvements in the required precision at which records can be dated radiocarbon dating is still the most prominent method for dating organic material from terrestrial and marine archives and as such many of the recent developments in improving precision have been aimed at this technique these include 1 selection of the most suitable datable fractions within a record 2 the development of better calibration curves and 3 more precise age modelling techniques while much attention has been focussed on the first two items testing the possibilities of the relatively new age modelling approaches has not received much attention here we test the potential for methods designed to significantly improve precision in radiocarbon based age models wiggle match dating and various forms of bayesian analyses we demonstrate that while all of the methods can perform very well in some scenarios caution must be taken when applying them it appears that an integrated approach is required in real life dating situations where more than one model is applied with strict error calculation and with the integration of radiocarbon data with sedimentological analyses of site formation processes

rift zone reorganization through flank instability in ocean island volcanoes an example from tenerife canary islands the relationship between rift zones and flank instability in ocean island volcanoes is often inferred but rarely documented our field data aerial image analysis and 40ar 39ar chronology from anaga basaltic shield volcano on tenerife canary islands support a rift zone flank instability relationship a single rift zone dominated the early stage of the anaga edifice 6 4 5 ma destabilization of the northern sector led to partial seaward collapse at about 4 5 ma resulting in a giant landslide the remnant highly fractured northern flank is part of the destabilized sector a curved rift zone developed within and around this unstable sector between 4 5 and 3 5 ma induced by the dilatation of the curved rift a further rift arm developed to the south generating a three armed rift system this evolutionary sequence is supported by elastic dislocation models that illustrate how a curved rift zone accelerates flank instability on one side of a rift and facilitates dike intrusions on the opposite side our study demonstrates a feedback relationship between flank instability and intrusive development a scenario probably common in ocean island volcanoes we therefore propose that ocean island rift zones represent geologically unsteady structures that migrate and reorganize in response to volcano flank instability

the distribution of basaltic volcanism on tenerife canary islands implications on the origin and dynamics of the rift systems abstract one of the most characteristic features of volcanic islands is the existence of rift zones defined commonly as orientated eruptive fissures or parallel rows of elongate cinder cones and dyke swarms occasionally these rifts can appear at the birth of the volcanic island and persist until the last episodes of its constructions controlling the form and structure of the island e g azores islands in the case of tenerife canary islands it is possible to observe two rift zones santiago del teide and dorsal rifts running nw se and ene wsw marked by parallel rows of aligned cones and eruptive fissures additionally at the southern part of the island southern volcanic zone basaltic volcanism is characterized by scattered vents and apparently non coherently orientated eruptive fissures some authors relate the existence of the latter volcanism to a n s running rift zone that defines the third branch of a three armed rift system in the island in the present paper we first investigate the tectonic controls on the distribution of basaltic volcanism at the southern volcanic zone and their relation with the nw se and ene wsw rifts the numerical results obtained suggest that basaltic volcanism of the southern part of tenerife can be easily explained as the result of a extensional stress field derived from the combined effects of the nw se and ene wsw rifts as a second objective we have also investigated the origin of the santiago del teide and dorsal rift zones and their role on the formation of the original shield volcano and the subsequent evolution of the whole island our numerical results contrast with previously published explanations on the origin of the tenerife rifts that included fracturing due to volcano spreading or to deformation of the volcano due to magma intrusion we consider that volcanic activity in tenerife began throughout fissural volcanism along these structures that were already present in the oceanic basement progressively accumulating the basaltic series that gave rise to the construction of the composite shield volcano

the adsorption behavior of thioarsenite on magnetite and ferrous sulfide abstract thioarsenite tasiii is an important arsenic as species under sulfidic environments adsorption behavior of tasiii on iron fe bearing minerals affects the transformation and the distribution of as at solid liquid interface in this study we investigated the formation of tasiii species in the mixed arsenite and sulfide asiii s ii solutions with different s as ratios and adsorption behavior of tasiii on the surface of magnetite fe3o4 and ferrous sulfide fes it was found that the extent of s substitution of tasiii was enhanced with the increasing s as molar ratio in the asiii s ii solutions the adsorption experiments showed that as in the asiii s ii solutions was adsorbed to a less extent on two fe minerals than that of asiii in circumneutral to alkaline solutions indicating that tasiii has lower affinity to fe3o4 and fes the adsorption of tasiii on the surface of fe3o4 led to hydrolyzation and asiii is the main sorbed species on the surface of fes the extent of s substitution of tasiii was promoted and as sulfide surface precipitate may form overall the formation of tasiii species is the vital factor affecting the redistribution of as between solid and aqueous phase in sulfidic environment

reflection seismic investigations in the volcaniclastic apron of gran canaria and implications for its volcanic evolution high resolution reflection seismic data obtained around gran canaria allow a detailed and consistent correlation of seismic reflectors of the northern and southern canary basins with the lithology drilled by dsdp leg 47a sse of gran canaria as well as with major phases of volcanic activity on gran canaria as mapped onshore two prominent reflectors were chosen as marker horizons and correlated with the drilled lithology the results indicate that reflector r7 above the miocene volcaniclastic debris flows v1 v3 reflects the shield building phase of gran canaria reflector r3 is interpreted as corresponding with the pliocene roque nublo formation the top of the massive island flank of gran canaria defined by seismically chaotic facies extends 44 to 72 km off the coast of gran canaria west of gran canaria the flank of tenerife onlaps the steeper and older flank of gran canaria which in turn is onlapping the older flank of fuerteventura to the east in a similar way erosional channels which can also be traced up to 50 km from the area between gran canaria and fuerteventura into the deeper northern basin have been identified in the bathymetry the data presented provide new detailed information for modelling the submarine and subaerial evolution of the central canary islands of gran canaria and tenerife i e the timing of their shield building phases and later stages of major volcanic activity as reflected by the position of prominent seismic reflectors in the seismic stratigraphy

sulfur redox chemistry governs diurnal antimony and arsenic cycles at champagne pool waiotapu new zealand abstract champagne pool a sulfidic hot spring in new zealand exhibits distinct diurnal variations in antimony sb and arsenic as concentrations with daytime high and night time low concentrations to identify the underlying mobilization mechanisms five sites along the drainage channel of champagne pool were sampled every 2 h during a 24 h period temporal variations in elemental concentrations and sb as and sulfur s speciation were monitored in the discharging fluid total trace element concentrations in filtered and unfiltered samples were analyzed using icp ms and sb as and s species were determined by ic icp ms sulfur speciation in the drainage channel was dominated by thiosulfate and sulfide at night while sulfate dominated during the day the distinct diurnal changes suggest that the transformations are caused by phototrophic sulfur oxidizing bacteria these bacteria metabolize thiosulfate and sulfide in daylight to form sulfate and as suggested by modeling with phreeqc elemental sulfur sulfide consumption during the day results in undersaturation of antimony sulfides which triggers the additional release of dissolved sb for as diurnal cycles were much more pronounced in speciation than in total concentrations with di and trithioarsenate forming at night due to excess sulfide and monothioarsenate forming from arsenite and elemental sulfur during the day sulfur speciation was thus found to control sb and as in terms of both solubility and speciation

recovery of the forest ecosystem in the tropical lowlands of northern guatemala after disintegration of classic maya polities we employed paleolimnological methods to investigate tropical forest recovery and soil stabilization that followed abandonment of agricultural systems associated with disintegration of classic maya polities ca a d 800 1000 we used lithological geochemical magnetic and palynological data from sediment cores of lake peten itza in the maya lowlands of northern guatemala sediment core chronology was developed using radiocarbon dates on terrestrial wood and charcoal fragments our results indicate that in the absence of large human populations and extensive farming activities peten forests recovered under humid climate conditions within a span of 80 260 yr soil stabilization postdates pollen evidence of forest regrowth stratigraphically and required between 120 and 280 yr we conclude that the tropical forest ecosystem in the watershed of lake peten itza had been reestablished by the early postclassic period a d 1000 1200

diachronous evolution of sea surface conditions in the labrador sea and baffin bay since the last deglaciation assessing changes in sea surface conditions due to the effects of past freshwater outflow through baffin bay and davis strait to the labrador sea hereafter referred to as the baffin bay corridor

transition from circular to stellate forms of submarine volcanoes large volcanic islands and guyots have stellate forms that reflect the relief of radiating volcanic rift zones multiple volcanic centers and embayments due to giant flank failures small mid ocean ridge volcanoes in contrast are commonly subcircular in plan view and show only embryonic rift zones in order to characterize the transition between these two end members the morphology of 141 seamounts and guyots was studied using the shape of the depth contour at half the height of each edifice irregularity was characterized by measuring perimeter distance elongation and moment of inertia of the contours assuming an ideal edifice is circular the analysis reveals a general transition over 2 4 km edifice height best transition estimate 3 km while some large edifices 4 5 km high show no major embayments or ridges suggesting considerable variation in the effectiveness of mechanisms that cause flank instability and growth of rift zones the various origins of the transition are discussed and the upper limit of magma chambers many of which lie above the basement of the larger edifices is proposed to affect the morphologic complexity via a number of mechanisms and is an important factor affecting the mode of growth the origins of the truncated cone shape of mid ocean ridge volcanoes are also discussed of the eruption mechanisms that have been proposed to explain their flat summits the most likely mechanisms involve eruption from small ephemeral magma bodies lying within the low density upper oceanic crust the discussion includes speculations on factors affecting the depths of magma chambers beneath oceanic volcanoes supporting table is available via web browser or via anonymous ftp from ftp kosmos agu org directory append username anonymous password guest subdirectories in the ftp site are arranged by paper number information on searching and submitting electronic supplements is found at http www agu org pubs csupp about html

the distribution of basaltic volcanism on tenerife canary islands implications on the origin and dynamics of the rift system reply to the comment by carracedo et al

effects of canary hotspot volcanism on structure of oceanic crust off morocco analysis of over 6400 km of multichannel seismics mcs and 50 sonobuoy reflection and refraction experiments reduced both in the domain of x t and tau p shows that a region within the jurassic quiet zone off morocco underwent dramatic changes as a result of the passage of the lithosphere over the canary hotspot commencing approximately 60 ma a seismic unit ucf interpreted as volcanic in origin is observed within the sediments in a region characterized by a broad bathymetric swell it shows diffractions from its upper surface and an internally chaotic seismic facies and pinches out between sedimentary units of continuous subparallel facies a velocity inversion is noted between the ucf 4 7km s and the underlying sediment 3 1 km s the ucf is time transgressive it lies near the cretaceous s tertiary boundary in the northern portion of the study area and is younger to the south kinematic studies of the movement of the canary hotspot relative to africa show that the hotspot first appeared off nw africa about 60 ma and was located beneath oceanic crust in the region where the ucf is observed depth to basement measurements in areas not effected by the hotspot show a consistent linear trend of increased depth with age in areas effected by the hotspot the thermal rejuvenation is evident as basement depths shoal with increased proximity to the present hotspot the reheating of the crust resets the thermal age of the lithosphere with many of the properties of crust of a younger age subsidence curves of the reheated crust off morocco show good correlation to subsidence curves of other reheated crust on a global basis a zone characterized by high crustal velocities 7 1 7 4 km s and greater crustal thicknesses by 1 2 km is observed in an area that corresponds to the bathymetric swell the region of the ucf and the reelevated basement the high velocities and increased crustal thickness are interpreted to be the result of underplating and assimilation of existing oceanic crust caused by the canary thermal anomaly the presence of high crustal velocities coupled with a thickened crustal section has been noted on various passive margins of the world they have generally been attributed to the thermal processes associated with continental rifting off morocco we believe that similar thermally induced phenomena have occurred but that here the heat anomaly was the midplate volcanism associated with the canary hotspot

climate proxies for the last 17 3 ka from lake hazar eastern anatolia extracted by independent component analysis of μ xrf data abstract the elemental composition of lake sediment cores is often the result of several independent processes in this study we attempt to extract statistically independent climate related signals from xrf multi element data of a core drilled from lake hazar in eastern anatolia using the independent component analysis ica method in addition we analysed ostracod shells for oxygen and carbon isotopes the ica method has advantages over traditional dimension reduction methods such as principal component analysis or factor analysis because it is based on maximal statistical independence rather than uncorrelatedness where independence is a stronger property the hz11 p03 core which represents the last 17 3 ka was recovered from lake hazar which at times formed the headwaters of the tigris applying the ica method we selected two out of six independent components by measuring distance correlation similarity we propose that one of the selected components can be read as a proxy for temperature and the other for precipitation in this region our results indicate that the region was relatively cold and wet during the late glacial between 17 3 and 14 8 ka bp and wet and warm during bolling allerod the lake level dropped below today s level during the younger dryas stadial 12 49 and 11 76 ka bp forming a marked hiatus in the core s stratigraphic record during the beginning of the holocene while precipitation values were high the temperature gradually increased until 8 ka bp between 8 and 5 ka bp the region was warm but extremely dry after 5 ka bp around 3 5 ka bp temperatures suddenly fell and three abrupt dry phases are observed around 3 5 ka and 2 8 ka and 1 8 ka bp

the behaviour of antimony released from surface geothermal features in new zealand abstract antimony rich geothermal features in the taupo volcanic zone tvz of new zealand s north island drain directly into surface aquatic environments the discharge from champagne pool a mixed alkali chloride sulfate hot spring at wai o tapu geothermal field contains up to 194 g l sb the discharge from frying pan lake a chloride sulfate hot spring at waimangu geothermal field contains up to 21 5 g l sb at champagne pool downstream concentrations of sb show distinct diurnal variations particularly in winter when concentrations in the early morning were less than half those measured mid afternoon changes in sulfide sulfate equilibria and direct stibnite oxidation may explain this phenomenon in the discharge from frying pan lake sb exhibits little diurnal variation most 80 of the dissolved sb released from champagne pool is removed from solution at alum lake an acid sulfate hot pool containing elevated levels of dissolved sulfide therefore relatively little sb is discharged into the freshwater drainage in the area however in the absence of a sulfide rich feature at waimangu most of the sb discharged from frying pan lake remains dissolved and is transported into the freshwater drainage system of lake rotomahana the contrast in sb behaviour between these two sites confirms the importance of dissolved sulfide and low

14c ams wiggle matching of raised bog deposits and models of peat accumulation abstract high resolution accelerator mass spectrometer ams 14 c dates of selected plant macrofossils from the raised bog engbertsdijksvenen eastern netherlands show century scale wiggles analogous to the radiocarbon calibration curve we used three relative time scales viz based on depth mass and pollen concentration respectively to match the peat ams dates to the calibration curve this procedure is repeated for one conventionally dated core for each relative time scale realistic confidence intervals are calculated depth appears to be the best time scale for certain stratigraphical units of a core this justifies using depth for wiggle matching conventionally dated mire cores published by others even when 14 c errors are larger our evidence shows four major sources of 14 c variation for mire deposits compared to treerings 1 dating error due to sample composition this includes a reservoir effect demonstrated for many bulk peat samples 2 hiatuses causing a sudden leap of peat 14 c age 3 changing accumulation rates apparent from a break in the slope of the peat 14 c ages 4 sampling error these results shed doubt on the assumed continuities in theoretical peat accumulation models both mire stratigraphy and changing accumulation rates can be explained in qualitative hydrological terms more evidence for a previously discovered reservoir effect in bog deposits is presented though the physical biological mechanisms remain uncertain

the distribution of arsenic iii and arsenic v in geothermal waters examples from the massif central of france the island of dominica in the leeward islands of the caribbean the valles caldera of new mexico u s a and southwest bulgaria abstract data for as iii as v and total as for various types of geothermal spring water are given the different species of as were separated at the time of sampling after filtration acidification and dilution where necessary using an anion exchange method total as as iii and as v were determined by flameless atomic absorption spectrometry the total as content ranges from 5 to 1800 g l 1 samples from dominica show evidence of different sulfur arsenic oxidation kinetics as iii being the major component 85 99 in fluids from deep levels of the geothermal reservoir and also 99 in oxidized waters of the acid sulfate type the bicarbonate spring water of the valles caldera new mexico contains more as iii than as v but there as v is the major component of the acid sulfate springs as iii proves to be the predominant form 60 100 in the warm alkaline waters from southwest bulgaria a selection of co 2 rich spring waters from the central massif france cezallier is analysed two groups are distinguished on the basis of major element chemistry and total as content oxidized forms are mainly encountered in the first group including a well sample containing 0 5 as iii the as iii content of the second group ranges from 10 to 70 these preliminary results indicate that the fluids directly related to hydrothermal systems contain mainly as iii whereas acid sulfate springs have a variable as iii content bicarbonate waters are generally enriched in oxidized as in the absence of springs or sinks within a geothermal region the total as concentration may display conservative properties but both as iii and as v may be reactive during mixing and cooling

k ar ages and magnetic stratigraphy of a hotspot induced fast grown oceanic island el hierro canary islands abstract the combined use of accurate radiometric dating and magnetic stratigraphy can be applied to define the main stages of the building of oceanic volcanic islands this method has been successfully applied on the island of el hierro the westernmost island of the canaries archipelago for the emerged part of this island built in the last 1 2 ma magnetic stratigraphy and mapping show the presence of four consecutive subchrons k ar dating of eighteen samples in stratigraphic sequences using an unspiked technique produced ages consistent with the general volcanic stratigraphy the ages show that the magnetic polarity zones correlate to the upper part of the matuyama and to the brunhes chrons the jaramillo normal polarity subchron of the upper part of the matuyama reverse polarity chron is recorded in one of the lava sequences the lower limit of this event is constrained by two ages of 1 04 0 02 ma and one of 1 05 0 02 ma close to the value deduced from the astronomically tuned magnetic polarity time scale apts the volcanic history can be summarised by two consecutive main basaltic volcanic edifices the el tinor active during the upper part of the matuyama chron and the el golfo edifice constructed during the brunhes chron

calibration of radiocarbon results pertaining to related archaeological events with the advent of the high precision radiocarbon calibration curve there is an increasing demand from archaeologists for results previously reported on the radiocarbon scale to be expressed on the calendar scale furthermore there is a general realization within the archaeological community that much more information can be derived from radiocarbon dating if the samples are taken from coherent well chosen contexts and if any available substantive archaeological information is included in the data analysis this paper describes how the bayesian approach to statistical data analysis can be used for the calibration of groups of radiocarbon results in situations where archaeological information is available a priori about the relationships between the contexts being dated recent innovations in the implementation of the bayesian paradigm are used and the methodology is illustrated by the analysis of data arising from two archaeological excavations

new age controls on the tephrochronology of the southernmost andean southern volcanic zone chile the chronology of over 50 tephra layers preserved in a lake sediment core from laguna la trapananda llt in the southern portion of the andean southern volcanic zone ssvz chile is constrained by new radiocarbon age determinations which span the period from late pleistocene glacial retreat to the late holocene the tephra are correlative with tephra previously described from other lake cores in the region and are attributed to explosive eruptions of the ssvz volcanoes mentolat hudson maca and potentially cay the new age determinations are used to estimate the ages of the 50 tephra in the llt core as well as those from the other previously described lake cores in the area by a bayesian statistical method the results constrain the frequency of explosive eruptions of the volcanic centers in the southernmost ssvz they indicate that there was essentially no increase in the rate of eruptions from late glacial to recent times due to deglaciation they also provide isochrones used to constrain the depositional histories of the small lacustrine systems within which they were deposited and they provide a tephrochronologic tool for other paleoclimatic paleoecologic archaeologic and tephrochronologic studies in central patagonia

regional climate change from peat stratigraphy for the mid to late holocene in central ireland at the millennial scale bog surface wetness bsw records show a clear holocene climate event stratigraphy with major phases comparable with other regional climate proxies such as chironomid inferred temperature records moving towards the centennial scale however and towards the limits of chronological certainty within the records regional differences are apparent which likely reflect the more heterogeneous precipitation patterns which occur on shorter timescales the bsw data presented in this paper are reconstructed from testate amoebae assemblages from central ireland and are compared with other regional records the results suggest that this region is in phase with the north of ireland in terms of timings and durations of climate change but the comparisons are less clear with a stacked and tuned record from northern britain that shows an apparent offset compared to the irish records this may reflect variations in past regional precipitation or be a function of the tuning and stacking process the broad phases of comparison between the irish records and the extension of the central irish record back to 6000 cal bp allow comparisons with low frequency temperature reconstructions from chironomids which also show a broad level of correlation with cooler temperatures relating to wetter bsw at centennial to millennial timescales

factors controlling peat compaction in alluvial floodplains a case study in the cold temperate cumberland marshes canada abstract subsidence due to peat compaction may have important implications in alluvial floodplains because it leads to wetland loss land inundation and damage to buildings and infrastructure furthermore it potentially influences spatial and temporal river sedimentation patterns and hence the evolution of alluvial floodplains as the vast majority of peatlands occur in cold temperate regions alluvial plains situated in such areas are most susceptible to these implications to determine which locations within alluvial floodplains are most vulnerable to high amounts of compaction induced subsidence it is necessary to quantify compaction and to identify which factors influence the amount and rate of peat compaction for this we carried out field work in the cumberland marshes east central saskatchewan canada guided by the following two questions 1 how much peat compaction has occurred over the past decades to centuries and 2 which factors control the amount and rate of peat compaction at the same timescale to address these questions we used methods involving construction of stratigraphic cross sections organic matter content and bulk density measurements and radiocarbon dating a new sampling device was devised to sample uncompacted peat in the field results show that peat layers have compacted up to 43 within a few centuries with compaction rates of up to 6 08 mm yr the dominant factors influencing peat compaction are 1 organic matter content 2 stress imposed on a peat layer and to a lesser extent 3 plant species composition in an alluvial setting crevasse splays and natural levees are sites that are most susceptible to high amounts of peat compaction at short timescales 100 102 years sheet like splay deposits initially compact underlying peat uniformly whereas differential compaction commonly occurs beneath natural levees due to lateral variations in sediment thickness subsidence due to peat compaction creates additional accommodation space and hence locally enhances floodplain sedimentation rates

growth structure instability and collapse of canarian volcanoes and comparisons with hawaiian volcanoes recent onshore and offshore investigations in the canarian archipelago especially in the western islands of la palma and el hierro have greatly improved the understanding of the genesis and evolution of these islands and allow interesting comparisons with other hotspot induced oceanic island volcanoes especially the hawaiian archipelago genesis induced by hotspot activity and consequently shield and post erosional stages of growth allow the definition of similar main stratigraphic units the canarian and hawaiian volcanoes show common constructional and structural features such as rift zones progressive volcano instability and multiple gravitational collapses however the canaries present some important geological differences from the prototypical hotspot volcanoes of the hawaiian islands particularly the absence of significant subsidence the canarian volcanoes remain emergent until completely mass wasted by gravitational collapses and erosion volcanic formations over 20 million years are observable in outcrop in the canaries including the seamount stages of growth in several of the islands

comparison of arsenic and molybdenum geochemistry in meromictic lakes of the mcmurdo dry valleys antarctica implications for oxyanion forming trace element behavior in permanently stratified lakes abstract water samples were collected for arsenic as and molybdenum mo analysis from different depths in lakes hoare and fryxell both of which are located in the taylor valley within the mcmurdo dry valleys of antarctica sampling depths within each lake were chosen to capture variations in as and mo concentrations and as speciation in the oxic mixolimnia and anoxic monimolimnia of these meromictic lakes arsenic concentrations ranged from 0 67 nmol kg 1 to 3 54 nmol kg 1 in lake hoare and from 1 69 nmol kg 1 to 17 5 nmol kg 1 in lake fryxell molybdenum concentrations varied between 5 05 nmol kg 1 and 43 nmol kg 1 in lake hoare and between 3 52 nmol kg 1 and 25 5 nmol kg 1 in lake fryxell concentrations of as and mo generally increased with depth in the mixolimnion of each lake consistent with uptake near the ice water interface by organic particles and or fe mn oxides oxyhydroxides followed by gravitational settling and regeneration remineralization at depth in the vicinity of the redoxcline arsenic concentrations either remained constant hoare or increased with depth fryxell in the anoxic monimolimnia whereas mo exhibited dramatic decreases in concentrations across the redoxcline in both lakes geochemical modeling predicts that as and mo occur as thioanions in the anoxic bottom waters of lakes hoare and fryxell and further that the contrasting behavior of both trace elements reflects the respective reactivity of their thioanions towards fe sulfide minerals such as mackinawite fes and or pyrite fes 2 more specifically the geochemical model suggests that fe sulfide mineral precipitation in the anoxic monimolimnia of both lakes regulates dissolved sulfide concentrations at levels that are too low for as sulfide minerals e g orpiment realgar to precipitate whereas mackinawite and or pyrite react s with particle reactive thiomolybdate anions possibly forming an fe mo s mineral that precipitates and hence leads to mo removal from solution

arsenic retention and remobilization in muddy sediments with high iron and sulfur contents from a heavily contaminated estuary in china the wuli estuary and its offshore area the bay of jinzhou have received large amount of wastewater and smelting slag from a non ferrous smelter for decades we collected three sediment cores from the wuli estuary the middle and the mouth of the bay of jinzhou respectively chemical sequential extraction and x ray absorption near edge structure spectrometry xanes for arsenic as accompanying with fe mn tom s and ca analyses were conducted to investigate as retention and remobilization in this estuary bay system the concentrations of as in the sediment up to 3400 g g and porewater up to 1100 g l have been significantly elevated in the wuli estuary and serious as contamination has been spreading to the bay of jinzhou sequential extraction displayed that adsorbed as was the dominant form of as in sediments from the wuli estuary but in the bay of jinzhou xanes data showed that a portion of as 10 was precipitated as as sulfides correlation analysis showed that total as ast hcl extractable as ashcl in sediment correlated well with total fe fet and hcl extractable fe fehcl in the estuary with fehcl total s st and acid volatile sulfur avs in the middle of the bay and with avs in the mouth of the bay the results indicated that as retention in the wuli estuary is very likely fe controlled region while the impact of s becomes more pronounced in the bay of jinzhou pseudo partition coefficients pseudo kd for ast the ratio of dissolved ast in porewater to ast in sediment decreased systematically from the wuli estuary to the mouth of the bay of jinzhou indicating that mobility of as decreased during the migration and digenetic processes the dominant form of dissolved as in porewater was present in the form of asiii 87 100 in the wuli estuary the reduction of arsenate asv to arsenite asiii 23 91 mediated by microbial activities was the most important cause for as release from solid to aqueous phase whereas the role of reductive dissolution of fe in remobilization of as was likely very limited

lateglacial and holocene environmental changes in the southern urals reflected in palynological geochemical and diatom records from the lake syrytkul sediments abstract a multi proxy study including lithology geochemistry diatom analysis and palynology of the lake syrytkul sediments provides continuous environmental reconstruction of the lateglacial and holocene in the southern urals and make it possible to compare the role of natural and anthropogenic factors in lake history the lake syrytkul sediment records reflect the main lateglacial and holocene paleoclimate changes the lateglacial holocene transition 11 600 11 500 cal bp expressed in all palaeorecords was followed by great limnological and vegetation changes the climatic changes of 7400 and 4300 cal bp were fixed in all lake sediment records vegetation and lake ecosystem were less affected by global climate events the preboreal oscillation 11 200 11 000 cal bp 8 2 ka event and regional climate events 10 350 cal bp 9750 cal bp 9000 cal bp and 2000 cal bp as follows from lake sediment records the environment deterioration after the holocene climatic optimum started in different time in the range of 6300 5100 cal bp due to various sensitivities of different proxies to paleoclimate parameters the climate events were the main drivers for the dynamics of the southern urals lake ecosystems during almost the entire lake history the role of the human factor in the change of the lake ecosystem was critical since the beginning of the twentieth century despite the adjacent karabash copper smelter as the source of considerable technogenic contamination it was a dam constructed 100 years ago that had the greatest impact on the lake system this event is reflected in all sediment records especially diatom and geochemical changes in the diatom species composition and sediments geochemistry of the shortest human impact period are comparable in magnitude to the response of the lake ecosystem to the lateglacial holocene transition

as sb bi au mineralization in the baogutu gold deposit xinjiang nw china here we report the occurrence of some uncommon mineral assemblages including paakonenite aurostibite native arsenic native antimony and native bismuth found in the baogutu gold deposit in the western junggar xinjiang nw china the mineralization could be generally subdivided into two types the gold bearing quartz vein type mineralization and disseminated mineralization in the wall rocks the sulfide minerals in gold lodes commonly include pyrite arsenopyrite marcasite and stibnite however the l7 lode in no 4 orebody and the l1 lode in no 11 orebody of the baogutu gold deposit are quite different in terms of their mineral assemblages the l7 lode contains native arsenic quartz veins in shallow levels and stibnite quartz veins at depth gold bearing minerals electrum native gold and rarely aurostibite mainly coexist with paakonenite stibnite native arsenic and native antimony the crystallization of as and sb bearing minerals was likely to have consumed h2s from the hydrothermal fluid which probably triggered the precipitation of native gold the l1 lode consists of several discontinuous sulfide dominated lensoid orebodies the massive sulfide ores that produced most of the gold resource are characterized by an intimate association between native bismuth and native gold mineralization

thiosulphate in surficial geothermal waters north island new zealand abstract thiosulphate is present in hot springs streams and thermal pools of the taupo volcanic zone and ngawha new zealand at concentrations of 1 2 1 3 10 5 m to 7 05 0 12 10 4m formed as a metastable product of sulphide oxidation thiosulphate is buffered in the presence of elemental s according to 0 5 s 8 3 h 2 o s 2 o 3 2 2 h 2 s a q 2 h unless all sulphide present has been bacterially oxidised to sulphate a steady state concentration of thiosulphate is maintained as a soft base thiosulphate is capable of complexing several transition metals the thermodynamically predicted speciation of ag in champagne pool for example indicates a ag s2o3 2 3 activity similar to that of agcl2 though less than that of ag hs 2

the western altmark versus flintbek palaeoecological research on two megalithic regions this investigation focuses on the human induced transformation of landscapes by comparing two small scale megalithic regions on the north german plain for this study two test areas were defined each measuring 36 km 2 archaeological information and palaeoecological proxies were implemented to investigate changes of the environment related to human activities of the neolithic funnel beaker culture fbc during the period from ca 3800 2800 cal bc the chronological framework was constructed with the help of bayesian and aoristic modelling of ams dates combining archaeological and radiometric information charcoal from the megalithic tombs provided on site data that show human impact induced by the construction and further use of the graves off site data originated from two pollen profiles of nearby bogs they supply additional information on local and regional landscape development the ratio of light demanding to shade tolerant woody species represents the degree of woodland openness it is a value which can be determined for both anthracological as well as palynological data a comparison of both proxies led to divergent results for the two chosen areas the proxies can be associated quite well for the haidberg area with regard to openness whereas missing accordance of both palaeoecological data sets in the flintbek region provides a strong argument for human impact on local levels a settlement phase indicated by various non arboreal pollen taxa was not confirmed for the altmark haidberg area before 3050 cal bc but in the nearby area of beetzendorf 7 km distance at least since ca 3200 cal bc in the flintbek region two settlement phases of the fbc are visible separated by a phase of forest regeneration which was attributed to changes of settlement behaviour within the local neolithic societies c 2013 elsevier ltd all rights reserved

comment on the distribution of basaltic volcanism on tenerife canary islands implications on the origin and dynamics of the rift systems by a geyer and j marti tectonophysics 483 2010 310 326 in their article geyer and marti 2010 propose that the evolution and origin of the volcanic islands which constitute the canarian archipelago are strongly controlled by regional tectonic atlantic and african structures in their fig 1a they sketch the geometry of the iberian and moroccan microplates and the respective boundary zones with respect to africa nubia and eurasia mantovani et al 2007 dashed lines indicating presumed plate boundaries cross the canarian archipelago which will therefore be located along a lithospheric fracture the boundary between the moroccan and african nubia microplates this regional fracture extends from the atlas to the atlantis fracture zone coinciding in parts with the propagating fracture postulated by anguita and hernan 1975 in fig 1b of geyer and marti 2010 dashed lines indicate the orientation of the most evident tectonic structures visible on the ocean floor as we show in this comment all of these mapped faults are artifacts

first discovery of holocene alaskan and icelandic tephra in polish peatlands despite the discovery of cryptotephra layers in over 100 peatlands across northern europe holocene cryptotephra layers have not previously been reported from polish peatlands here we present the first holocene tephra findings from two peatlands in northern poland at bagno kusowo peatland we identify the most easterly occurrence of the ad 860 b tephra recently correlated to the white river ash wrae derived from mount churchill alaska a shorter core from linje peatland contains tephra from the askja 1875 eruption extending the spatial distribution and regional importance of this icelandic tephra in eastern europe our research indicates the potential of cryptotephra layers to date and correlate the growing number of palaeoenvironmental studies being conducted on polish peatlands and contributes towards the development of a regional holocene tephrostratigraphy for poland

implications of s1 tephra findings in dead sea and tayma palaeolake sediments for marine reservoir age estimation and palaeoclimate synchronisation abstract here we report on the first findings of a cryptotephra in the holocene lacustrine sediment records of the dead sea and tayma palaeolake nw arabian peninsula the major element glass composition of this rhyolitic tephra is identical to the distal s1 tephra layer identified in the yammouneh palaeolake lebanon in a marine sediment record from the se levantine basin and in the sodmein cave archaeological site in egypt the s1 tephra corresponds to the early holocene dikkartin dome eruption of the erciyes dag volcano in central anatolia turkey and has been dated in the marine record at 8830 140 cal yr bp we present new age estimates of the s1 tephra based on radiocarbon dating of terrestrial plant remains and pollen concentrates revealing ages of 8939 83 cal yr bp in the dead sea sediments and 9041 254 cal yr bp in tayma the precise date from the dead sea allows refining the early holocene marine reservoir age in the se levantine sea to ca 320 50 years synchronisation of marine and terrestrial palaeoclimate records in the eastern mediterranean region using the s1 tephra further suggests a time transgressive expansion of the early holocene humid period

integrating the intimate records using tephrochronology rising to the challenge little has challenged our understanding of climate change more so than the abruptness with which large scale shifts in temperature occurred during the late quaternary the causal mechanisms driving

a numerical approach to 14c wiggle match dating of organic deposits best fits and confidence intervals c 14 wiggle match dating wmd of peat deposits uses the non linear relationship between c 14 age and calendar age to match the shape of a sequence of closely spaced peat c 14 dates with the c 14 calibration curve a numerical approach to wmd enables the quantitative assessment of various possible wiggle match solutions and of calendar year confidence intervals for sequences of c 14 dates we assess the assumptions advantages and limitations of the method several case studies show that wmd results in more precise chronologies than when individual c 14 dates are calibrated wmd is most successful during periods with major excursions in the c 14 calibration curve e g in one case wmd could narrow down confidence intervals from 230 to 36 yr c 2003 elsevier science ltd all rights reserved

a new approach to triggering mechanism of volcano landslides based on zeta potential and surface free energy balance abstract the layers of almagre iron rich deposits from tenerife island are the result of thermal metamorphism of soils in contact with lava flow 1073 1273 k these layers of small thickness relative to the basaltic wash are interesting for geotechnical study because the stability of the deposits is determined by the weakest element in this case almagre which acts as a sliding plane the flow of maritime air over the hillsides of the volcanic islands increases the content of cations in ashes deposits this modifies the superficial properties of material that composes the substratum this modification affects the retention of water and the cohesion of material making up the deposit the results show that the presence of sodium and magnesium increased the hydrophobicity of the material which had a weak water retention capacity and strong cohesion at basic ph when there is iron in solution repulsion between the particles is greater than one obtained with other studied electrolytes hence the deposit is less stable and almagre under saturated water conditions constitutes an ideal layer for landslides

mid to late holocene oceanographic variability on the southeast greenland shelf a reconstruction of oceanographic variability of the past 5800 years on the southeast greenland shelf was obtained by analysing a combined marine sediment record based on two cores from the same site cores fox04g 05r were retrieved from a side basin to a cross shelf trough connecting the 900 m deep sermilik fjord with the irminger sea in the northwestern north atlantic the record was analysed in terms of grain size distribution xrf and benthic and planktonic foraminiferal content and the chronology was obtained on the basis of 210pb and 14c dating the late holocene paleoceanographic variations in the record were characterised by a marked influence from the irminger current ic at the onset of the record at 5800 cal yr bp and the regional holocene climatic optimum between 5200 and 4200 cal yr bp after 3600 cal yr bp neoglacial cooling with increased influence of polar waters from the east greenland current egc diminished the influence from the ic between 1500 and 700 cal yr bp the environment

a multi proxy reconstruction of oceanographic conditions around the younger dryas holocene transition in placentia bay newfoundland abstract a marine sediment core from placentia bay off the south coast of newfoundland was studied to reconstruct past oceanographic conditions based on a multiproxy approach including diatoms benthic foraminifera grain size analysis ip25 x ray fluorescence calcium carbonate and total organic carbon content based on 6 radiocarbon dates the 513 5 cm long core spans the age interval from ca 13 to 10 cal kyrs bp and thus captures the transition from the younger dryas stadial into the holocene at sub decadal resolution the younger dryas was characterized by cold arctic water taxa of diatoms and benthic foraminifera and a stratified water column with high sea ice cover and low productivity due to strong influence of the labrador current during the second half of the younger dryas after ca 12 2 cal kyrs bp the influence of the labrador current gradually decreased and sea ice conditions became more variable the transition towards the holocene is characterized by a sequence of events starting with turnovers in the biogenic proxies followed by an abrupt retreat of sea ice and a rise in productivity these events are believed to be related to a northward migration of the gulf stream labrador current oceanic front the younger dryas termination is directly followed by a detrital carbonate layer associated with the final phase of the heinrich 0 event linked to laurentide ice sheet dynamics during the early holocene productivity remained high with minimal sea ice cover reduced stratification and stronger influence of warmer gulf stream derived waters

deposition models for chronological records abstract long term sedimentary sequences provide a wealth of useful information for research into the palaeo environment especially in relation to past climate change shorter records provide similar information in many archaeological contexts however if such records are to be used to provide precise timing of events and more critically the relative timing between different records methods are needed to provide accurate and precise age depth models for these sequences given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence even with layer counted chronologies the uncertainties are sometimes hard to quantify this paper outlines a range of bayesian models for deposition which have been implemented in the computer programme oxcal these models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research