rabaul caldera papua new guinea volcanic hazards surveillance and eruption contingency planning abstract planning for volcanic contingencies at the rabaul caldera complex is a difficult task requiring urgent attention in view of the results of volcano surveillance and historical eruption frequency historical eruption periodicities have ranged from about 2 to 59 years the most recent eruptions were in 1937 1943 and caused more than 500 fatalities in may 1937 surveillance since 1971 has revealed uplift of part of the caldera floor and increasing seismicity in a ring structure believed to define the caldera bounding fault or faults these phenomena are interpreted as the prelude to a possible eruption potential eruption sites are all close to rabaul town and outlying residential areas and include the volcanoes of sulphur creek last active about 1850 vulcan and tavurvur 1937 1943 and rabalanakaia but new sites should also be considered in relation to the results of volcano surveillance a wide range of volcanic hazards accompanying different scales of eruption must be considered for the rabaul area the most likely types of eruption may be similar to the relatively small events that have been witnessed over the last century whose hazards included air fall tephra pumice rafts pyroclastic flows and surges volcanic earthquakes volcanic gas discharges tsunamis lightning strikes and the fall of mud rain torrential run off and mudflows as a result of accompanying rain storms other potential eruption types of much larger scale could involve cauldron subsidence which could cause destructive tsunamis and could be accompanied by explosive activity of major proportions air fall tephra is considered to be one of the main hazards from a future eruption and its effects in and around rabaul are primary influences in the choice of evacuation routes and points of refuge hence theoretical tephra dispersal patterns have been considered in some detail air fall tephra deposition from rabaul eruption clouds at heights of less than about 4 km is determined by a biannual change in wind direction from southeast in may to october november trade winds to northwest during the monsoon from december to march april in contrast clouds that rise higher than about 4 km are blown by east winds all year round another principal hazard is pyroclastic flows and surges which took place during the 1937 vulcan eruption but have until recently been overlooked although flows or surges or both are clearly distinguishable on eruption photographs the lack of suitable evacuation routes and problems in choosing safe and reasonably accessible refuge points compound the difficulties in preparing a practicable contingency plan however in small moderate eruptions the safest areas around rabaul are considered to be at the duke york islands about 30 km to the east and at cape gazelle about 25 km to the southeast seaborne evacuation to main ports in central new britain or on the neighbouring islands of new ireland and bougainville or overland evacuation using a southwards expanded road system would be necessary in the event of forewarning of a major eruption

seismic energy releases from volcanoes seismic energy release during the precursory eruptive and declining stages of volcanic activities provides various information about the mechanisms of volcanic eruptions and the temporary developments of their activities hitherto the energy release patterns from precursory earthquake swarms were used to predict the eruption times especially of andesitic or dacitic volcanoes in this paper the discussion is expanded to quantify the total amount of seismic energy released at the threshold of volcanic eruptions with reference to the results observed at several volcanoes the results generally indicate that the cumulative seismic energy release from the precursory earthquake swarms exceed 1017 18ergs before eruptions at any andesitic or dacitic volvanoes this allows the seismic efficiency or the ratio of energy radiated seismically and the energy required for the volumetric expansion to be estimated by incorporating available deformation data with the seismic data the dependency of seismic efficiency on the type of volcanic activity i e non explosive outbreaks phreatic and magmatic eruptions dome formation etc was evaluated from observations at a few volcanoes that provided a variety of examples

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

feedbacks between climate and surface water in northern africa during the middle holocene observations indicate that the area of lakes and wetlands in northern africa was considerably greater during the middle holocene than at present simulations are designed to examine whether expanded surface waters may have had a significant impact on the strength of the summer monsoon of northern africa three experiments with the national center for atmospheric research community climate model ncar ccm3 are analyzed a modern and two middle holocene 6000 years before present simulations one with and one without prescribed expanded surface water there is a significant increase in the strength of the summer monsoon in the middle holocene simulation due to the enhanced seasonal insolation cycle the addition of surface waters result in a june july and august mean increase in the net surface radiation 5 an increase in the latent heat flux 30 a decrease in the sensible heat flux 10 and an increase in the near surface specific humidity 5 compared to the middle holocene simulation without surface water changes the changes in these simulated climate variables are comparable in scale to changes due to orbital forcing alone the expanded surface waters result in a cooling of the atmosphere and anticyclonic flow over the large water bodies in summer relative to the simulation without surface water changes the combination of increased atmospheric moisture and altered circulation results in significant changes to the precipitation distribution in northern africa including a small increase in the zonal mean july precipitation to the north of the lakes and a decrease to the south the geographic distribution of the precipitation with surface water changes is qualitatively in better agreement with observations than the distribution with orbital forcing alone but still does not fully match the expansion implied by observations nor the expansion required to produce the simulated middle holocene surface waters used in this study the results of this study suggest that surface waters were an important factor in the climate of northern africa during the middle and early holocene and that they must be included for accurate simulation of this climate

land surface feedbacks and palaeomonsoons in northern africa we ran a sequence of climate model experiments for 6000 years ago with land surface conditions based on a realistic map of palaeovegetation lakes and wetlands to quantify the effects of land surface feedbacks in the saharan region vegetation induced albedo and moisture flux changes produced year round warming forced the monsoon to 17 25 n two months earlier and shifted the precipitation belt 300 km northwards compared to the effects of orbital forcing alone the addition of lakes and wetlands produced localised changes in evaporation and precipitation but caused no further extension of the monsoon belt diagnostic analyses with biome and continental hydrology models showed that the combined land surface feedbacks although substantial could neither maintain grassland as far north as observed 26 n nor maintain lake megachad 330 000 km

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

late quaternary variations in tree cover at the northern forest tundra ecotone 1 accurate land cover reconstructions are essential to understanding the past and present biogeochemical and biogeophysical interactions between the land surface and atmosphere and the impacts of these interactions on climate here we quantitatively reconstruct late quaternary shifts in woody cover across the northern hemisphere forest tundra ecotone based on a synthesis of northern hemisphere pollen records and contemporary observations of woody cover from the advanced very high resolution radiometer sensor our reconstructions document the expansion of northern hemisphere forests following deglaciation and reveal significant hemispheric asymmetries in the holocene position steepness and history of the forest tundra ecotone in western canada for example forest expansion and infilling continued through the holocene while in much of northern asia forests reached their maximal expansion during the early holocene then retreated the woody cover reconstructions are generally consistent with macrofossil based reconstructions of northern tree line dynamics and complement them by extending study of the northern forest tundra ecotone from the tree line limit well mapped by macrofossils to the entire ecotone using the lund potsdam jena dynamic vegetation model we estimate that changes in northern forest density resulted in at least a 47 7 gt c increase in aboveground carbon sequestration between 21 and 9 ka a 13 9 gt c increase between 9 and 6 ka and a 3 5 gt c loss of aboveground carbon from northern forests after 6 ka this trajectory is consistent with atmospheric carbon isotopic measurements for the holocene which suggest carbon uptake by the terrestrial biosphere until 6 ka and small carbon releases from the terrestrial biosphere afterward

records of the nd isotope composition of seawater from the bay of bengal implications for the impact of northern hemisphere cooling on itcz movement abstract this study presents a record of planktonic foraminiferal neodymium isotopic gradients along a north south transect in the bay of bengal during time slices of late holocene and last glacial maximum lgm age together with a record of planktonic foraminiferal variation in the northern bay of bengal 15 n over the last 195 ky in late holocene core top planktonic foraminifera the north south end gradient rises from nonradiogenic values of 12 at 20 n to 10 at 5 n in parallel with the modern surface salinity gradient controlled by discharge of himalayan rivers in the northern bay during the lgm end increased throughout the bay the contrast between northernmost and southernmost sites decreased and maximum end values of 6 5 occurred between 12 and 15 n a small part of the shift to higher mean end throughout the bay during the glacial may arise from a uniform increase in deposition of far field dust from arabian and persian gulf regions however the spatial pattern of end variation between lgm and late holocene also suggests a shift from modern dominance of nonradiogenic nd sources from the ganges brahmaputra basin to lgm dominance of more radiogenic nd sources from arakan coastal rivers over the last 195 ky at 15 n the most radiogenic end values of 7 occur at glacial maxima and the most nonradiogenic values of 11 occur during interglacials end values are highly correlated with glacial interglacial variations in planktonic foraminiferal 18o in this record shifts in river sources from the more northerly ganges brahmaputra watershed to the more southerly arakan coastal river systems respond dominantly to inter tropical convergence zone itcz movement driven by northern hemisphere cooling during 100 ky glacial interglacial cycles with a small component of variation on precessional timescales the nonlinear correlation of end with ice volume suggests that itcz movement responds to aerial coverage of ice sheets and snow rather than to ice thickness and volume these data add support to recent general circulation models of itcz response to northern hemisphere ice sheets which simulate decreased glacial precipitation in the ganges brahmaputra basin and increased glacial precipitation in the southern arakan coastal basin

high resolution record of environmental changes and tephrochronological markers of the last glacial holocene transition at lake lautrey jura france this paper presents the results of a multiproxy investigation including volume magnetic susceptibility mineral and pollen analyses of late glacial sediments from lake lautrey jura france small scale lithological variations have been identified with high stratigraphic resolution in order to establish lithostratigraphic correlations between cores measurements combined with mineralogical analyses provide information on past sedimentary processes this combined approach reflects major changes in terrestrial habitats and soil processes which may relate to the climatic events characterising the late glacial climatic warming and cooling phases during warm intervals the record indicates increased lake productivity via carbonate precipitation and decreased input of detrital material in contrast cooler intervals show reduced lake productivity catchment area instability and increased detrital inputs several short interruptions in reforestation and in soil stabilisation can be identified and linked with abrupt colder events occurring through the bolling a general trend of warming is recorded from the coldest part of the younger dryas three tephra layers were also detected the mineral composition analyses show that the upper tephra layer corresponds to the laacher see eruption eifel germany while the lower ones may relate to the volcanic activity of the chaine des puys massif central france around 13 000 cal yr bp these two events recognised for the first time outside the massif central region may provide additional chronostratigraphic markers for the late glacial sedimentary records of the jura mountains and northern alps copyright 2004 john wiley sons ltd

disentangling the roles of late miocene palaeogeography and vegetation implications for climate sensitivity the impact of rising co2 on future climate remains uncertain but the evidence for high co2 in the palaeorecord suggests that past climates could provide a potentially quantifiable indication of climate in a high co2 world one such past time period is the late miocene 11 6 5 3 ma for which co2 reconstructions indicate higher levels than those of preindustrial and similar to the present atmospheric level 400 ppm the late miocene palaeorecord suggests a much warmer and wetter northern hemisphere than preindustrial however vegetation feedbacks are an important component of the climate system and vegetation distribution reconstructions from the palaeorecord have been shown to be very different to the present vegetation distribution we examine the roles that different vegetation and palaeogeography play in climate sensitivity for the late miocene and consider the implications for potential future climate change to do this we use coupled atmosphere ocean vegetation simulations of late miocene and potential modern climates forced by three different co2 concentrations with vegetation perturbation experiments and make quantitative comparisons to the palaeorecord optimal regions to target late miocene palaeodata acquisition for the purposes of informing about future climate include north america northern africa australia paraguay and southern brazil and northeastern asia these regions are those which the model results predict to be most sensitive to co2 forcing but where the local temperature response to co2 forcing is similar between the simulated potential modern and late miocene climates the model results suggest that climate sensitivity to co2 forcing is directly affected by the palaeogeographic configuration and that the inferred climate sensitivity for doubled co2 is 0 5 0 8 c higher for the late miocene than we might expect for future climate because of differences in synergy the greater land mass at high northern latitudes during the late miocene and the differences in vegetation distribution predictions that result combined with differences in ocean circulation and the effect of sea ice make the late miocene boundary conditions more sensitive to co2 forcing than the modern boundary conditions

the 1975 1977 crisis of la soufriere de guadeloupe f w i a still born magmatic eruption on july 8 1976 eruptive activity broke out at la soufriere de guadeloupe f w i after about one year of increasing seismic activity seismic activity continued to increase until august 1976 reaching more than 1500 events a 200 fold increase over the preceding quiet period of a few years and an energy output of about 1017 ergs in a day a total of 26 major phreatic eruptions similar to the july 8 outburst took place during an eight months period the steam blasts that characterized the eruptions gave rise to particle and sometimes block charged plumes that deposited an estimated 106 m3 of solids the h2o rich gases emitted during the blasts presumably contained other gases h2s so2 co2 that were partly adsorbed on solid particles all material was erupted at temperatures of the order of 100 to 200 c the observation of vertical migration of earthquake foci in less than a few hours and over about 6 km depth and of abnormal variations of the geomagnetic field indicate a deep energy source for the phreatic eruptions a small proportion of the gases adsorbed on solid particles had a magmatic origin however most of the steam and the tephra seemed to originate from superficial levels of a hydrothermal system similar phreatic eruptions have occurred several times in recorded history in the case of la soufriere the origin of the phreatic eruptions is best described by an abnormal energy input versus steady state from a crustal magma chamber the occurrence of truly magmatic eruptions is presumably inhibited by an extensive hydrothermal system the abrupt release of more power from the magma chamber could have resulted in an explosive pyroclastic eruption substantial improvement of the guadeloupe volcano observatory has followed the 1975 1977 crisis permanent telemetered geophysical networks and regular geochemical observations have provided a five year data base of the volcano behavior in its noneruptive state which can be compared to crisis situations

energy partition in the 1982 eruption of el chichon volcano chiapas mexico abstract the 1982 eruption of el chichon volcano chiapas mexico has been extensively investigated from various standpoints including seismicity tephra geology atmospheric effects and tectonic structure in this paper the six largest of a series of explosions are isolated considering various sources of information then the seismic energy released by volcanic earthquakes and tremor is estimated using seismograms of low magnification in order to avoid saturation of seismic wave amplitudes the explosion kinetic energy is evaluated by two methods one by the initial velocity of the ejecta and the other by the air wave data recorded at a distance both the results are roughly coincident the thermal energy is classified into two components that transferred by volcanic ejecta and that consumed by convective clouds the thermal energy released by the explosions is very large compared with that of mechanical energy such as the seismic energy and explosion kinetic energy after the last major explosion of april 4 a type volcanic earthquakes swarmed till the end of april their occurrence rate decreased with time in an aftershock like sequence these earthquake swarms may have been due to post eruptive readjustment of the stress field within and near the volcano such seismic activity contrasts with other examples of similar major eruptions which were followed by growth of lava domes in the new craters after the paroxysmal eruptions the 1982 eruption of el chichon volcano has not been followed by the growth of a lava dome within the newly formed crater

mid holocene land surface conditions in northern africa and the arabian peninsula a data set for the analysis of biogeophysical feedbacks in the climate system large changes in the extent of northern subtropical arid regions during the holocene are attributed to orbitally forced variations in monsoon strength and have been implicated in the regulation of atmospheric trace gas concentrations on millenial timescales models that omit biogeophysical feedback however are unable to account for the full magnitude of african monsoon amplification and extension during the early to middle holocene 9500 5000 years b p a data set describing land surface conditions 6000 years b p on a 1 1 grid across northern africa and the arabian peninsula has been prepared from published maps and other sources of palaeoenvironmental data with the primary aim of providing a realistic lower boundary condition for atmospheric general circulation model experiments similar to those performed in the palaeoclimate modelling intercomparison project the data set includes information on the percentage of each grid cell occupied by specific vegetation types steppe savanna xerophytic woods scrub tropical deciduous forest and tropical montane evergreen forest open water lakes and wetlands plus information on the flow direction of major drainage channels for use in large scale palaeohydrological modeling the data set is available in digital form by anonymous ftp

alteration of a basaltic glass in an argillaceous medium the salagou dike of the lodeve permian basin france analogy with an underground nuclear waste repository abstract volcanic basaltic glasses are commonly considered to be very suitable natural analogs of vitrified waste packages intended for geological disposal the studied basaltic glass of the salagou dike lodeve basin france intruded into a permian argillaceous formation about 1 4 ma ago provides a means of assessing the long term behavior of nuclear waste glass in an argillaceous repository concept this study is based on combining chemical mineralogical and isotopic investigations the occurrence of a palagonite film no more than 1 2 mm thick characterizes the basaltic glass alteration in contact with the argillaceous host rock the chemical and structural properties of the palagonite suggest constant volume alteration the alteration rates estimated from palagonite thickness and age of the glass are comparable to those measured on natural glasses altered in nonargillaceous media the occurrence of the studied argillaceous material in contact with the basaltic glass did not result in long term alteration kinetics significantly different from those measured in simple glass water systems mineralogical chemical and isotopic data obtained on the basaltic and argillaceous components suggest that an aqueous fluid flowed primarily at the glass argillite interface and did not propagate in the argillaceous host rock beyond 5 cm from the basaltic dike the elements released by alteration of the basaltic glass notably strontium did not diffuse into the surrounding clay this conclusion is important from the perspective of a natural analog for a deep geological repository for nuclear waste and highlights the major role of the structural properties of the clayey barrier

response of the north african summer monsoon to precession and obliquity forcings in the ec earth gcm we investigate for the first time the response of the north african summer monsoon to separate precession and obliquity forcings using a high resolution state of the art coupled general circulation model ec earth our aim is to better understand the mechanisms underlying the astronomical forcing of this low latitude climate system in detail the north african monsoon is strengthened when northern hemisphere summer insolation is higher as is the case in the minimum precession and maximum obliquity experiments in these experiments the low surface pressure areas over the sahara are intensified and located farther north and the meridional pressure gradient is further enhanced by a stronger south atlantic high pressure area as a result the southwesterly monsoon winds are stronger and bring more moisture into the monsoon region from both the northern and southern tropical atlantic the monsoon winds precipitation and convection also extend farther north into north africa the precession induced changes are much larger than those induced by obliquity but the latter are remarkable because obliquity induced changes in summer insolation over the tropics are nearly zero our results provide a different explanation than previously proposed for mechanisms underlying the precession and especially obliquity related signals in paleoclimate proxy records of the north african monsoon the ec earth experiments reveal that instead of higher latitude mechanisms increased moisture transport from both the northern and southern tropical atlantic is responsible for the precession and obliquity signals in the north african monsoon this increased moisture transport results from both increased insolation and an increased tropical insolation gradient

experimental constraints on shock induced microstructures in naturally deformed silicates abstract planar deformation features pdfs in various minerals have long been accepted as evidence of impact induced deformation the uniqueness of this association was challenged in the context of the k t boundary extinction debate after mosaicism and microstructures similar to pdfs were reported from the products of explosive volcanism as a result of this debate a significant volume of new experimental and observational data on the development of shock induced microstructures has become available over the last ten years the results reveal that factors such as pre shock temperature pulse duration and crystallographic orientation of target minerals to the shock wave have a primary influence on how these microstructures develop data from diamond anvil cell and high pressure friction experiments reveal that the same solid state amorphization process that produces shock induced pdfs at low temperatures also occurs at much lower strain rates in static experiments the experimental data indicate that the amorphization process is thermally activated and that the character of the resulting pdfs is a function of the applied strain rate shock induced amorphization occurs along those crystallographic planes that are most readily transformed to the high pressure phase during very short pulse durations and produces pdfs that are visible at the optical scale lower strain rate deformation produces tem scale amorphization with orientations that are more homogeneously distributed throughout the target mineral and produces no optically visible pdfs the data confirm the uniqueness of multiple intersecting sets of optically visible pdfs as a diagnostic indicator of hypervelocity impact the data also support the hypothesis that the amorphization process can occur at a wide range of strain rates and that the limiting pressure for the process is controlled by the phase stability of the target mineral under the applied loading conditions not by the hel the data also suggest that the onset pressure the maximum pressure and the pressure range for producing optically visible pdfs decrease with increasing temperature and decreasing strain rate as the pressure range for optically visible pdf formation decreases it is replaced by homogeneous amorphization as observed in the anvil cell experiments thus the uniqueness of multiple intersecting sets of optically visible pdfs to hypervelocity impact is not due to a unique process but rather to a specific set of loading conditions that produce an optically visible microstructure likewise single sets of microdeformations observed in volcanic rocks are produced by the same process but at different loading conditions that preclude the development of multiple intersecting sets of pdfs the data also indicate that shock mosaicism which occurs above the hel represents a plastic response of the target mineral to loading rates that are too large to be accommodated by crystal plastic mechanisms observational data for some naturally deformed samples from the k t boundary the vredefort dome and volcanic rocks along with the experimental observations are used to constrain the range of conditions under which the natural microstructures form and to understand the differences between microstructures produced by impact volcanic and other natural processes finally some possible mechanisms for producing the microstructures observed in volcanic rocks are proposed

role of the biosphere in the mid holocene climate of west africa received 26 june 2001 revised 2 december 2001 accepted 5 march 2002 published 16 january 2003 1 in previous studies a zonally symmetric synchronously coupled biosphereatmosphere model zonalbam which includes explicit representation of ecosystem dynamics has been developed and validated based on current conditions over the region of west africa here we use zonalbam to study the response of the coupled biosphereatmosphere system to changes in the earth s orbital forcing during the middle holocene 6k yrs bp and the relative contribution of vegetation feedbacks simulations in which vegetation conditions were fixed to the current distribution show that an orbitally induced increased seasonality in insolation for the middle holocene by itself results in a 1 1 northward shift in the location of the southern margin of the sahara as compared to current solar forcings when vegetation is allowed to be dynamic a 2 4 northward shift is simulated however when dynamic vegetation is initialized to palaeovegetation a 5 1 northward shift is simulated bringing results more consistent with palaeoevidence based on previous studies on the role of the gradient of moist static energy on the dynamics of large scale tropical circulations a mechanism for the enhancement of the summer monsoon circulation has been developed our results suggest that multiple equilibria could have coexisted over the region of west africa during the middle holocene furthermore based on previous studies on the current climate over the region we hypothesize that transitions between the different equilibria could have taken place during the middle holocene causing the southern desert margin to migrate between 18 1n and 21 4n and shaping climate variability index terms 0315 atmospheric composition and structure biosphere atmosphere interactions 3322 meteorology and atmospheric dynamics land atmosphere interactions 3344 meteorology and atmospheric dynamics paleoclimatology 9305 information related to geographic region africa keywords west africa holocene vegetation dynamics monsoon climate change insolation

soil feedback drives the mid holocene north african monsoon northward in fully coupled ccsm2 simulations with a dynamic vegetation model we explore climate vegetation interactions in mid holocene north africa with a suite of community climate system model ccsm2 simulations the ccsm includes synchronously coupled atmosphere ocean sea ice land and vegetation models the ccsm s present day precipitation for north africa compares well with simulations of other models and observations mid holocene data reveal a wetter and greener sahara compared to the present the ccsm exhibits a greater closer to the expected precipitation increase than other models and in response grasses advance from 18 75 to 22 5 n in much of north africa precipitation is enhanced locally by the northward advance of grasses but suppressed regionally mainly due to an insufficient albedo decrease with the expansion of vegetation prior studies have always lowered the surface albedo with the expansion of vegetation in north africa in the ccsm s mid holocene simulations the albedo decreases more because wetter soils are simulated darker than drier soils than due to expanding vegetation these results isolate albedo as the key ingredient in obtaining a positive precipitation vegetation feedback in north africa two additional simulations support this conclusion in the first simulation the desert s sandy soil textures are changed to loam to represent increased organic matter soil water retention and grass cover increase albedo decreases somewhat precipitation responds with a small yet widespread increase in the second simulation a darker soil color is prescribed for this region now the monsoon advances north about 4 these results illustrate a north african monsoon highly sensitive to changes in surface albedo and less sensitive to changes in evapotranspiration

a scenario of the 1883 krakatau tsunami abstract the 1883 krakatau tsunami provides an important clue for solving the mechanisms of the eruption of krakatau first sea waves of volcanic origin are basically classified the travel times of the crest of the largest tsunami in the 1883 krakatau eruption are recalculated taking the wave heights and the sea depths along the path into consideration as a special case of sea waves air waves coupled with those of the sea are examined and the necessary conditions of their generation are discussed the sea depths must be around 5 km the sea wave paths require long stretches of sea and the magnitudes of volcanic explosions must be large to produce the air sea waves the information collected suggests that the tsunamis registered at batavia jakarta were not air sea waves some results of the recent reflection survey of the subbottom materials and a supplemental gravity survey in the krakatau area are introduced to provide further evidence for explosive mechanisms the origin times of the onset and the crest of the tsunami and the air wave both registered at batavia are calculated from their travel times adopting these origin times the author reconstructs a scenario of the tsunami in order to generate a tsunami as long as about 60 km wave length successive developments of surges and water domes seem to be necessary

seismic precursors of the february 10 1990 eruption of kelut volcano java abstract kelut volcano eastern java indonesia erupted on february 10 12 1990 seismic activity and an increase of temperature and acoustic noise in the crater lake appeared three months before the eruption and were the main precursory signs of this eruption during the pre eruptive stage the number of events was eight per day on average and the cumulative seismic energy released was 5 6 10 15 erg these low values are uncommon for an andesitic volcano seismic activity mainly consisted of swarms of very shallow volcano tectonic earthquakes many of which were part of seismic multiplets in the last three weeks before the eruption seismic activity remained at a very low level this quiescent period was followed 24 hours prior to the eruption initiation by an intense swarm of low energy events which progressively became continuous spasmodic tremor most of the data obtained during the pre eruptive stage are consistent with a process of fracturation of a shallow and low strength plug blocking the eruptive conduit before the eruption several observations suggest that water is an important element in the preeruptive and eruptive phenomena at kelut volcano in particular the monochromatic events observed at kelut are characterized by one narrow peak in their spectra the estimations of q value and impedance contrast for these events suggest that the fluid which fills the source resonator could be water

last glacial maximum and holocene climate in ccsm3 abstract the climate sensitivity of the community climate system model version 3 ccsm3 is studied for two past climate forcings the last glacial maximum lgm and the mid holocene the lgm approximately 21 000 yr ago is a glacial period with large changes in the greenhouse gases sea level and ice sheets the mid holocene approximately 6000 yr ago occurred during the current interglacial with primary changes in the seasonal solar irradiance the lgm ccsm3 simulation has a global cooling of 4 5 c compared to preindustrial pi conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at lgm tropical sea surface temperature sst cools by 1 7 c and tropical land temperature cools by 2 6 c on average simulations with the ccsm3 slab ocean model suggest that about half of the global cooling is explained by the reduced lgm concentration of atmospheric co2 50 of present day concentrations there is an increase in the antarctic circumpolar current an

regional energy budget control of the intertropical convergence zone and application to mid holocene rainfall shifts in the latitude of the intertropical convergence zone a region of intense tropical rainfall have often been explained through changes in the atmospheric energy budget specifically through theories that tie rainfall to meridional energy fluxes these quantitative theories can explain shifts in the zonal mean but often have limited relevance for regional climate shifts such as a period of enhanced precipitation over saharan africa during the mid holocene here we present a theory for regional tropical rainfall shifts that utilizes both zonal and meridional energy fluxes we first identify a qualitative link between zonal and meridional energy fluxes and rainfall variations associated with the seasonal cycle and the el nino southern oscillation we then develop a quantitative theory based on these fluxes that relates atmospheric energy transport to tropical rainfall when applied to the orbital configuration of the mid holocene our theory predicts continental rainfall shifts over africa and southeast asia that are consistent with complex model simulations however the predicted rainfall over the sahara is not sufficient to sustain vegetation at a level seen in the palaeo record which instead requires an additional large energy source such as that due to reductions in saharan surface albedo we thus conclude that additional feedbacks such as those involving changes in vegetation or soil type are required to explain changes in rainfall over africa during the mid holocene shifts in the latitude of the tropical rainfall band are constrained by meridional energy fluxes calculations show that combining zonal and meridional energy fluxes can explain past regional rainfall variations like the african humid period

precursory seismicity of the 1994 eruption of popocatepetl volcano central mexico popocatepetl volcano is located in the central mexican volcanic belt within a densely populated region inhabited by over 20 million people the eruptive history of this volcano indicates that it is capable of producing a wide range of eruptions including plinian events after nearly 70 years of quiescence popocatepetl reawakened in december 21 1994 the eruptive activity has continued up until the date of this submission and has been characterized by a succession of lava dome growth and destruction episodes similar to events that have apparently been typical for popocatepetl since the fourteenth century in this regime the episodes of effusive and moderately explosive activity alternate with long periods of almost total quiescence in this paper we analyze five years of volcano tectonic seismicity preceding the initial eruption of the current episode the evolution of the v t seismicity shows four distinct stages which we interpret in terms of the internal processes which precede an eruption after a long period of quiescence the thermal effects of a magma intrusion at depth the fracturing related to the slow development of magma related fluid pathways the concentration of stress causing a protracted acceleration of this process and a final relaxation or redistribution of the stress shortly before the initial eruption are reflected in the rates of v t seismic energy release a hindsight analysis of this activity shows that the acceleration of the seismicity in the third stage asymptotically forecast the time of the eruption the total seismic energy release needed to produce an eruption after a long period of quiescence is related to the volume of rock that must be fractured so imposing a characteristic threshold limit for polygenetic volcanoes limit that was reached by popocatepetl before the eruption

analysis of the seismic activity associated with the 2010 eruption of merapi volcano java abstract the 2010 eruption of merapi is the first large explosive eruption of the volcano that has been instrumentally observed the main characteristics of the seismic activity during the pre eruptive period and the crisis are presented and interpreted in this paper the first seismic precursors were a series of four shallow swarms during the period between 12 and 4 months before the eruption these swarms are interpreted as the result of perturbations of the hydrothermal system by increasing heat flow shorter term and more continuous precursory seismic activity started about 6 weeks before the initial explosion on 26 october 2010 during this period the rate of seismicity increased almost constantly yielding a cumulative seismic energy release for volcano tectonic vt and multiphase events mp of 7 5 10 10 j this value is 3 times the maximum energy release preceding previous effusive eruptions of merapi the high level reached and the accelerated behavior of both the deformation of the summit and the seismic activity are distinct features of the 2010 eruption the hypocenters of vt events in 2010 occur in two clusters at of 2 5 to 5 km and less than 1 5 km depths below the summit an aseismic zone was detected at 1 5 2 5 km depth consistent with studies of previous eruptions and indicating that this is a robust feature of merapi s subsurface structure our analysis suggests that the aseismic zone is a poorly consolidated layer of altered material within the volcano deep vt events occurred mainly before 17 october 2010 subsequent to that time shallow activity strongly increased the deep seismic activity is interpreted as associated with the enlargement of a narrow conduit by an unusually large volume of rapidly ascending magma the shallow seismicity is interpreted as recording the final magma ascent and the rupture of a summit dome plug which triggered the eruption on 26 october 2010 hindsight forecasting of the occurrence time of the eruption is performed by applying the material failure forecast method ffm using cumulative real time seismic amplitude rsam calculated both from raw records and on signals classified according to their dominant frequency stable estimates of eruption time with errors as small as 4 h are obtained within a 6 day lapse time before the eruption this approach could therefore be useful to support decision making in the case of future large explosive episodes at merapi

a natural analogue of nuclear waste glass in compacted bentonite abstract a marine based argillaceous rock containing volcanic glass shards has been investigated to infer the long term durability of vitrified nuclear waste in compacted bentonite which is a candidate for buffer material constituting the engineered barrier system for nuclear waste disposal fission track ages indicate that the volcanic glass shards andesitic scoria have been buried in the argillaceous rock for about 1 ma neither glass matrix dissolution nor precipitation on the surface was seen under an optical microscope little leaching of any element has been recognized by analyses using an electron microprobe analyzer secondary ion mass spectrometry analysis however indicates significant hydration which may dominantly be a permeation of molecular water as an indicator of durability of glass against groundwater a normalized mass loss of si nl si has been evaluated for the volcanic glass based on free energy for hydration the difference between estimated nl si of the volcanic glass and that of a simulated waste glass is within one order so that the volcanic glass may be analogous to a waste glass with respect to durability to water the argillaceous rock is analogous to the compacted bentonite with respect to physical properties such as dry density unconfined compression strength porosity and hydraulic conductivity the ambient physical and chemical conditions surrounding the volcanic glass have been also investigated temperature was in the range from 4 to 30 c due to the burial history of the volcanic glass over most of the past 1 ma the volcanic glass has been in contact with groundwater originating from seawater thermodynamic calculations indicate 1 ph 7 74 7 94 of the groundwater has mainly been controlled by dissolution of carbonate minerals 2 the redox potential eh 34 73 mv of the groundwater has dominantly been controlled by decomposition of organic materials to produce ch 4 g and 3 activity of aqueous silica of the groundwater was in equilibrium with sio 2 amorphous because of the equilibrium between aqueous silica and sio 2 amorphous the volcanic glass did not dissolve during the burial vitrified nuclear waste sealed in compacted bentonite therefore will not dissolve significantly if buried in an environment as mentioned above

holocene carbon cycle dynamics based on co2 trapped in ice at taylor dome antarctica a high resolution ice core record of atmospheric co2 concentration over the holocene epoch shows that the global carbon cycle has not been in steady state during the past 11 000 years analysis of the co2 concentration and carbon stable isotope records using a one dimensional carbon cycle model uggests that changes in terrestrial biomass and sea surface temperature were largely responsible for the observed millennial scale changes of atmospheric co2 concentrations

quantifying the role of biosphere atmosphere feedbacks in climate change coupled model simulations for 6000 years bp and comparison with palaeodata for northern eurasia and northern africa the lmd agcm was iteratively coupled to the global biome1 model in order to explore the role of vegetation climate interactions in response to mid holocene 6000 y bp orbital forcing the sea surface temperature and sea ice distribution used were present day and co2 concentration was pre industrial the land surface was initially prescribed with present day vegetation initial climate anomalies differences between agcm results for 6000 y bp and control were used to drive biome1 the simulated vegetation was provided to a further agcm run and so on results after five iterations were compared to the initial results in order to identify vegetation feedbacks these were centred on regions showing strong initial responses the orbitally induced high latitude summer warming and the intensification and extension of northern hemisphere tropical monsoons were both amplified by vegetation feedbacks vegetation feedbacks were smaller than the initial orbital effects for most regions and seasons but in west africa the summer precipitation increase more than doubled in response to changes in vegetation in the last iteration global tundra area was reduced by 25 and the southern limit of the sahara desert was shifted 2 5 n north to 18 n relative to today these results were compared with 6000 y bp observational data recording forest tundra boundary changes in northern eurasia and savana desert boundary changes in northern africa although the inclusion of vegetation feedbacks improved the qualitative agreement between the model results and the data the simulated changes were still insufficient perhaps due to the lack of ocean surface feedbacks

both differential and equatorial heating contributed to african monsoon variations during the mid holocene the sahara was significantly greener 11 5 kya and during multiple earlier interglacial periods but the mechanisms related to the greening of the sahara remain uncertain as most climate models severely underestimate past wet conditions over north africa the variations in the african monsoon related to the greening of the sahara are thought to be associated with the variations in the inter hemispheric differential heating of earth caused by orbital variations however how orbital variations affect regional climate is not well understood using recent theory that relates the position of the tropical rain belt to the atmospheric energy budget we study the effect of orbital forcing during the mid holocene on the african monsoon in simulations provided by the third phase of the paleo model intercomparison project pmip3 we find that energy fluxes in the african sector are related to orbital forcing in a complex manner contrary to generally accepted theory orbital modulation of seasonal differential heating alone is shown to be a weak driver of african monsoon variations instead net atmospheric heating near the equator which modulates the intensity and extent of seasonal migrations of the tropical rain belt is an important but overlooked driver of african monsoon variations a conceptual framework that relates african monsoon variations to both equatorial and inter hemispheric differential solar heating is presented

local magnitude coda magnitude and radiated energy of volcanic tectonic earthquakes from october 2010 to december 2011 at sinabung volcano indonesia in august 2010 sinabung volcano began erupting after more than a thousand years of dormancy following several weeks of phreatic eruptions the eruptions ceased and sinabung entered what became an inter eruptive period of dominantly seismic unrest while standard equations for understanding the size of an earthquake local magnitude ml coda magnitude mc and seismic energy release er have long been developed it is best practice to fine tune these relations for a given region and period of study to more accurately describe seismicity and to directly compare it with other volcanic systems more accurate descriptions of magnitudes and energy release are vital to accurate volcanic eruption forecasting and evaluation of seismic and volcanic risk in this study we use high frequency volcano tectonic vt earthquakes recorded on a temporary three component network installed between october 2010 and december 2011 in the region around sinabung volcano to better constrain the seismic parameters of and better understand this previously unstudied volcano we determine region specific formulas for ml mc and er as follows mathrm m mathrm l log 10 a 1 1252 log 10 r 0 0280 r 2 5427 kern0 5em mathrm m mathrm c 0 7764 log 10 t coda 0 0676 r 0 7185 kern0 5em mathrm and kern0 5em log 10 left mathrm e mathrm r right 1 5720 mathrm m mathrm l 11 5258 where a r and tcoda are maximum amplitude on a wood anderson seismogram hypocentral distance km and the coda duration s respectively constants in the ml equation have physically interpretable meanings the constant for the geometrical spreading term log10r term equals one for perfect spherical spreading of the waveform our value is greater than one and thus suggests that wavefronts spread at a slightly different rate than for simple spherical spreading the constant for the attenuation term r term is consistent with locally mapped attenuative deposits limestones and tuffs and previous 3d tomographic results our mc equation differs from a previous study likely because different data in a different time period were used earthquake hypocenters are consistent with those located in previous tomographic studies and we interpret the earthquakes in this study as distal vt earthquakes induced by continued magmatic intrusion at sinabung over the period of october 2010 december 2011

geophysical characteristics of dacite volcanism the 1977 1978 eruption of usu volcano abstract the 1977 1978 eruption of usu volcano is discussed from the geophysical standpoint as a classic example of dacite volcanism the activities of dacitic volcanoes are characterized by persistent earthquake swarms and remarkable crustal deformations due to the high viscosity of the magmas the former include shocks felt near the volcanoes and the latter accompany formation of lava domes or cryptodomes the hypocenters of the earthquakes occurring beneath usu volcano have been located precisely their distribution defines an earthquake free zone which underlies the area of doming within the summit crater this zone is regarded as occupied by viscous magma the domings within the summit crater forming the cryptodomes have amounted to about 160 m in addition to uplift they showed thrusting towards the northeast as a result the northeastern foot of the volcano has contracted by about 150 m the relation between crustal deformation and earthquake occurrence is examined and it is found that the abrupt domings are accompanied by the larger earthquakes m 3 4 3 both the seismic activity and the ground deformation are shown to have a unique and common energy source the energy of activities of usu volcano consists of the explosive type the deformation type and the seismic type the second and the third are in parallel with each other in discharges and both energies are complementary to the explosive energy the explosive energy and the seismic energy have been calculated for an explosion sequence and it is concluded that the deformation energy is about 10 times greater than the seismic energy the discharge rate of the seismic energy and the upheaval rates of the cryptodomes have continued to decrease since the outburst of the eruption except for a small increase at the end of january 1978 eruptions are governed not only by the supply of the energies but also by the depth of the magma which has gradually approached the surface the last eruption occurred in october 1978 however the crustal deformations and the earthquake swarms are still proceeding as of january 1980 albeit at a lower rate of activity

vegetation and soil feedbacks at the last glacial maximum abstract vegetation feedback at the last glacial maximum lgm about 21 000 calendar years ago remains an unresolved question a global atmospheric general circulation model agcm is asynchronously coupled with an equilibrium terrestrial biosphere model in the present study the coupled model is then used to investigate the influences of vegetation and soil feedbacks on the lgm climate it is found that the simulated geographical distribution of vegetation at the lgm differs from the present pattern dramatically and glacial vegetation cover tends to be reduced on average vegetation feedback alone leads to an annual surface temperature decrease of 0 31 c over the lgm ice free continental areas additional soil feedback reinforced vegetation induced cooling over high latitude eurasia and from the eastern middle east eastward to the indian peninsula significantly in the tropics a terrestrial annual surface cooling of 0 45 c is produced by vegetation and soil feedbacks it is shown that vegetation and soil feedbacks partly reduce data model discrepancy as produced by the agcm alone in some regions such as central africa the indian peninsula south china and north australia

characteristics of micro earthquake swarms preceding eruptions at showa crater of sakurajima volcano japan abstract the showa crater of sakurajima an andesitic volcano in japan resumed eruptive activity in june 2006 for the first time in 58 years explosive eruptions at the showa crater have been active since 2009 micro earthquake swarms have sometimes been observed in the 1 or 2 h preceding these eruptions since 2012 and have frequently occurred during periods of low eruptive activity these precursory micro earthquakes are dominated by high frequency 5 6 hz components and no clear s wave and are thus classified as bh type earthquake swarms the hypocenters of the earthquakes are located in a shallow region depth of approximately 1 km near the showa crater prior to the eruptions the onset of inflation has been observed by extensometers followed by precursory earthquake swarms 30 min to 1 h later in the case of insufficient ground contraction the precursory earthquakes reoccur when the strain reaches the same level it showed just before the eruptions occurred from the occurrence period and pattern of the precursory earthquakes it appears they may be generated within a narrow conduit leading to the showa crater

paleoclimatic variations in west africa from a record of late pleistocene and holocene lake level stands of lake bosumtwi ghana abstract a detailed investigation of geomorphological evidence of paleoshorelines and exposed stratigraphic sections of lake deposits combined with a chronology based on radiocarbon dated charcoal and in situ 14c dating of wave polished bedrock provide important new constraints on lake level changes of lake bosumtwi ghana thick sequences of laminated silts alternating with transgressive sands and deltaic gravels attest to a long history of climatically controlled lake level variations the post glacial rise in lake level began sometime after 16 3 ka reached stable levels first at 14 5 0 6 ka and then rose again after ca 14 3 ka a significant lake level regression spanned the interval from 12 6 0 3 to 11 6 0 5 ka synchronous with the younger dryas deep lake conditions were reestablished after ca 11 ka at which time the lake overtopped the crater overflow continued until 8 8 0 5 ka when another significant but short lived regression occurred deep but probably not overflowing conditions were again reestablished by 7 2 0 3 ka and continued until around 3 2 0 1 ka when lake level dropped precipitously multicentury late holocene highstands occurred at 2 2 0 1 and 1 7 0 2 ka although these were significantly lower than those registered in the late glacial and early holocene the timing of late glacial events is similar to those recorded elsewhere in africa and the higher latitudes and likely reflects the dominant control of high latitude northern hemisphere conditions on the african tropics during the times of large northern hemisphere ice sheets mid to late holocene variations appear to be less coupled with changes across africa and elsewhere suggesting that regional forcing may be more important during warmer periods

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

intercomparison of simulated global vegetation distributions in response to 6 kyr bp orbital forcing abstract the response of ten atmospheric general circulation models to orbital forcing at 6 kyr bp has been investigated using the biome model which predicts equilibrium vegetation distribution as a diagnostic several common features emerge a reduced tropical rain forest as a consequence of increased aridity in the equatorial zone b expansion of moisture demanding vegetation in the old world subtropics as a consequence of the expansion of the afro asian monsoon c an increase in warm grass shrub in the northern hemisphere continental interiors in response to warming and enhanced aridity and d a northward shift in the tundra forest boundary in response to a warmer growing season at high northern latitudes these broadscale features are consistent from model to model but there are differences in their expression at a regional scale vegetation changes associated with monsoon enhancement and high latitude summer warming are consistent with palaeoenvironmental observations but the simulated sh

causes and mechanisms of the 2011 2012 el hierro canary islands submarine eruption 1 el hierro eruption started on 10 october 2011 after an unrest episode that initiated on 17 july 2011 this is the first eruption in the canary islands that has been tracked in real time although being submarine and not directly observable the data recorded allowed its reconstruction and to identify its causes and mechanisms seismicity surface deformation and petrological data indicate that a batch of basanitic magma coming from a reservoir located at a depth of about 25 km below the el hierro island was emplaced at shallower depth creating a new reservoir about 10 12 km above where magma evolved until the initiation of the eruption the characteristics of seismicity and surface deformation suggest that the necessary space to accumulate magma at this shallower position which coincides with the crust mantle boundary beneath el hierro was created in about 2 months by elastic deformation and magma driven fracturing of the crust after this first intrusion episode part of the magma started to migrate laterally toward the se for nearly 20 km always keeping the same depth and following a path apparently controlled by stress barriers created by tectonic and rheological contrasts in the upper lithosphere this lateral migration of magma ended with a submarine eruption at about 5 km offshore from the southern corner of el hierro island the total seismic energy released during the unrest episode was of 8 1 1011 j and the total uplift previous to the onset of the eruption was of 40 mm combining geological geophysical and petrological data and numerical modeling we propose a volcanological model of the causes and mechanisms of el hierro eruption that shows how the stress distribution in the crust beneath el hierro which was influenced by rheological contrasts tectonic stresses and gravitational loading controlled the movement and eruption of magma we also discuss the implications of this model in terms of eruption forecast in the canary islands

early holocene greening of the afro asian dust belt changed sources of mineral dust in west asia production transport and deposition of mineral dust have significant impacts on different components of the earth systems through time and space in modern times dust plumes are associated with their source region s using satellite and land based measurements and trajectory analysis of air masses through time reconstruction of past changes in the sources of mineral dust as related to changes in climate however must rely on the knowledge of the geochemical and mineralogical composition of modern and paleo dust and that of their potential source origins in this contribution we present a 13 000 yr record of variations in radiogenic sr nd hf isotopes and rare earth element ree anomalies as well as dust grain size from an ombrotrophic rain fed peat core in nw iran as proxies of past changes in the sources of dust over the interior of west asia our data shows that although the grain size of dust varies in a narrow range through the entire record the geochemical fingerprint of dust particles deposited during the low flux early holocene period 11 700 6 000 yr bp is distinctly different from aerosols deposited during high dust flux periods of the younger dryas and the mid late holocene 6 000 present our findings indicate that the composition of mineral dust deposited at the study site changed as a function of prevailing atmospheric circulation regimes and land exposure throughout the last deglacial period and the holocene simulations of atmospheric circulation over the region show the northern hemisphere summer westerly jet was displaced poleward across the study area during the early holocene when northern hemisphere insolation was higher due to the earth s orbital configuration this shift coupled with lower dust emissions simulated based on greening of the afro asian dust belt during the early holocene likely led to potential sources in central asia dominating dust export to west asia during this period in contrast the dominant western and southwest asian and eastern african sources have prevailed during the mid holocene to modern times

sahel megadroughts triggered by glacial slowdowns of atlantic meridional overturning 1 the influence of the large scale ocean circulation on sahel rainfall is elusive because of the shortness of the observational record we reconstructed the history of eolian and fluvial sedimentation on the continental slope off senegal during the past 57 000 years our data show that abrupt onsets of arid conditions in the west african sahel were linked to cold north atlantic sea surface temperatures during times of reduced meridional overturning circulation associated with heinrich stadials climate modeling suggests that this drying is induced by a southward shift of the west african monsoon trough in conjunction with an intensification and southward expansion of the midtropospheric african easterly jet

hydrothermal minerals and alteration rates at surtsey volcano iceland the volcanic island surtsey off the south coast of iceland was created by volcanic activity in 1963 1967 core from a 181 m deep hole extending 123 m below sea level shows the results of 12 yr of hydrothermal alteration of basaltic tephra the primary cause of heating of the tephra and of development of the hydrothermal system was the intrusion of dikes below sea level at present the hottest part of the hole at a maximum temperature of 150 c is cooling at 0 9 c per year palagonitization of sideromelane glass a dominant constituent of the tephra is an important alteration process that is strongly temperature dependent the rate doubling for every 12 c increase at 60 c 90 is palagonitized above 120 c olivine crystals are replaced on their edges by nontronite the thickness of clay doubles for each 8 c increase ten hydrothermal minerals have crystallized in the tephra at 25 to 150 c the dominant species are smectite nontronite analcite phillipsite and tobermorite the primary clay species of palagonite is probably nontronite other minerals are halite opal calcite chabazite xonotlite anhydrite and gypsum no major differences in mineral occurrence are noted above and below sea level but phillipsite and tobermorite tend to grow larger below sea level even at the same temperature analcite appears at lower temperature 55 c above sea level than below sea level 75 c anhydrite is most abundant deep in the hole where inflowing cool sea water precipitated sulfate due to reduced sulfate solubility at higher temperatures

impacts of dust reduction on the northward expansion of the african monsoon during the green sahara period the west african monsoon wam is crucial for the socio economic stability of millions of people living in the sahel severe droughts have ravaged the region in the last three decades of the 20th c

mid holocene drylands a multi model analysis using paleoclimate modelling intercomparison project phase iii pmip3 simulations this study examines changes in aridity levels during the mid holocene approximately 6000 cal yr ago using multi model simulations from the paleoclimate modelling intercomparison project phase ii

mechanisms for the onset of the african humid period and sahara greening 14 5 11 ka bp abstract the mechanisms leading to the onset of the african humid period ahp 14 500 11 000 yr ago are elucidated using two different climate vegetation models in a suite of transient glacial interglacial simulations covering the last 21 000 yr a series of sensitivity experiments investigated three key mechanisms local summer insolation and ice sheet evolution vegetation albedo precipitation feedback and co2 increase via radiative forcing and fertilization that control the climate vegetation history over north africa during the last glacial termination the simulations showed that neither orbital forcing nor the remote forcing from the retreating ice sheets alone was able to trigger the rapid formation of the ahp only both forcing factors together can effectively lead to the formation of the ahp the vegetation albedo precipitation feedback enhances the intensity of the monsoon and further accelerates the onset of the ahp the experiments indicate that orbital forcing and vegetation albedo precipit

mid holocene greening of the sahara first results of the gaim 6000 year bp experiment with two asynchronously coupled atmosphere biome models the mid holocene green sahara represents the largest anomaly of the atmosphere biosphere system during the last 12 000 years although this anomaly is attributed to precessional forcing leading to a strong enhancement of the african monsoon no climate model so far has been able to simulate the full extent of vegetation in the sahara region 6000 years ago here two atmospheric general circulation models lmd 5 3 and echam 3 are asynchronously coupled to an equilibrium biogeography model to give steady state simulations of climate and vegetation 6000 years ago including biogeophysical feedback the two model results are surprisingly different and neither is fully realistic echam shows a large northward extension of vegetation in the western part of the sahara only lmd shows a much smaller and more zonal vegetation shift these results are unaffected by the choice of green or modern initial conditions the inability of lmd to sustain a green sahara 6000 years ago is linked to the simulated strength of the tropical summer circulation during the northern summer monsoon season the meridional gradient of sea level pressure and subsidence over the western part of northern africa are both much weaker in echam than in lmd in the present as well as the mid holocene these features allow the surface moist air flux to penetrate further into northern africa in echam than in lmd this comparison illustrates the importance of correct simulation of atmospheric circulation features for the sensitivity of climate models to changes in radiative forcing particularly for regional climates where atmospheric changes are amplified by biosphere atmosphere feedbacks