eruptive history of earth s largest quaternary caldera toba indonesia clarified single grain laser fusion sup 40 ar sup 39 ar analyses of individual sanidine phenocrysts from the two youngest toba indonesia tuffs yield mean ages of 73 plus minus 4 and 501 plus minus 5 ka in addition glass shards from toba ash deposited in malaysia were dated at 68 plus minus 7 ka by the isothermal plateau fission track technique these new determinations in conjunction with previous ages for the two oldest tuffs at toba establish the chronology of four eruptive events from the toba caldera complex over the past 1 2 m y ash flow tuffs were erupted from the complex every 0 34 to 0 43 m y culminating with the enormous 2500 3000 km sup 3 youngest toba tuff eruption caldera formation and subsequent resurgence of samosir island timing of this last eruption at toba is coincident with the early wisconsin glacial advance the high precision sup 40 ar sup 39 ar age eruption of such magnitude may provide an important marker horizon useful as a baseline for research and modeling of the worldwide climatic impact of exceptionally large explosive eruptions

dissolved constituents and sr isotopes in river waters from a mountainous island the danshuei drainage system in northern taiwan abstract taiwan is a typical active orogenic belt situated at the collision boundary between the eurasian continental plate and the philippine sea plate dissolved major and trace constituents as well as sr and sr isotopes in river waters collected from the danshuei river basin in northern taiwan have been studied to evaluate chemical weathering processes the results of principal component analysis show that the ion sources in these river waters can be categorized into 3 major components chemical weathering seasalt contribution and local anthropogenic input the chemical weathering is the most dominant factor that contributes about 85 of total variances significantly increased na cl and ca cl as well 87 sr 86 sr were observed in most upper stream samples the na cl and ca cl ratios in the dahan stream however are much higher than the shindien stream even though average rainfall is stronger in the shindien drainage basin chemical evidence from river waters supports less intense weathering in the region selective dissolution of secondary calcites explains the observed high ca cl sr cl and ca na in the dahan stream these results highlight the potential importance of tectonic factors such as uplift and physical erosion in studying chemical weathering in an active orogenic belt the variations of 87 sr 86 sr in the danshuei river are quite large reflecting some strata that released sr most of the upstream waters exhibit more radiogenic 87 sr 86 sr 0 713243 0 714338 due to weathering of ambient low grade metamorphic rocks 0 71678 0 72216 the distributions of cl sr and 87 sr 86 sr in the main stream were affected by somewhat conservative mixing with sources varing between ambient rocks and seasalt in the upper dahan stream heavy 87 sr 86 sr ratios were coincident with large deviations of na cl from the average seawater value as high as 40 the degree of chemical weathering in ambient rocks plays a dominant role in affecting the distribution of sr and 87 sr 86 sr in the danshuei river this isotopic characteristic makes 87 sr 86 sr an invaluable tracer for studying source mixing migration pathways and chemical weathering in an active orogenic belt

potential atmospheric impact of the toba mega eruption 71 000 years ago an approx 6 year long period of volcanic sulfate recorded in the gisp2 ice core about 71 000 5000 years ago may provide detailed information on the atmospheric and climate impact in the toba mega eruption deposition of these aerosols occur beginning of an approx 1000 year long stadial event but not immediately before the longer glacial period beginning approx 67 500 years ago total stratospheric loading estimates over this approx 6 year period range from 2200 to 4400 mt of h sub 2 so sub 4 aerosols the range in values is given to compensate for uncertainties in aerosol transport magnitude and longevity of the atmospheric loading may have led directly to enhanced cooling during the initial two centuries of this approx 1000 year cooling event 25 refs 2 fig 1 tab

geochemical tracers of sediment sources to san francisco bay river inflow and suspended sediment flux to san francisco bay are dominated by the sacramento and san joaquin river systems suspended sediments collected from rivers within the sacramento and san joaquin drainage basinsshow distinct chemical and sr isotope signatures reflecting their distinct bedrock lithologies concentrations of sm nd k and rb and 8 7 sr 8 6 sr ratios in suspended sediments increase from north to south in sierra nevada rivers and are significantly higher in the san joaquin drainage than in the sacramento drainage we show that variations in the geochemistry of fine grained detrital sediments cored beneath the bay can be used to assess the relative contributions of suspended sediment and inflow from these two major drainages in california for the sampled intervals over the past 1850 yr the proportion of suspended sediment from the sacramento drainage relative to the san joaquin drainage ranged between 5 and 85 average value of 55 compared with a modern value of 91 the current predominance of sediment entering san francisco bay from the sacramento drainage may be the result of greater trapping of sediments by reservoirs within the san joaquin drainage basin changes in the relative proportion of sediment from the sacramento and san joaquin drainages may reflect changes in the position of the storm track over california

tsunami inundation modeling in constructed environments a physical and numerical comparison of free surface elevation velocity and momentum flux abstract a laboratory benchmark test for tsunami inundation through an urban waterfront including free surface elevation velocity and specific momentum flux is presented and compared with a numerical model coulwave the physical model was a 1 50 scale idealization of the town seaside oregon designed to observe the complex tsunami flow around the macro roughness such as buildings idealized as impermeable rectangular blocks free surface elevation and velocity time series were measured and analyzed at 31 points along 4 transects optical measurements of the leading bore front were used in conjunction with the in situ velocity and free surface measurements to estimate the time dependent specific momentum flux at each location the maximum free surface elevation and specific momentum flux sharply decreased from the shoreline to the landward measurement locations while the cross shore velocity slowly decreased linearly the experimental results show that the maximum specific momentum flux is overestimated by 60 to 260 if it is calculated using the each maximum values of the free surface elevation and cross shore velocity comparisons show that the numerical model is in good agreement with the physical model at most locations when tuned to a friction factor of 0 005 when the friction factor decreased by a factor of 10 from 0 01 to 0 001 the average maximum free surface elevation increased 15 and the average cross shore velocity and specific momentum flux increased 95 and 208 respectively this highlights the importance of comparing velocity in the validation and verification process of numerical models of tsunami inundation

sample preparation effects on illite crystallinity measurement grain size gradation and particle orientation abstract specimen thickness is the main experimental factor controlling the results of illite crystallinity ic or crystallite size measurements on sedimentation slides different values obtained from thick and thin preparations are due to grain size gradation effects which may exclude larger and higher ordered grains from contributing to the diffraction orientation effects control the measured peak intensity the change from poor particle orientation in thick slides to high orientation in very thin slides is marked by an increase in specimen density diminishing non basal reflections and by a strong increase in peak intensity a plateau with constant peak breadths is observed if thin slides of well ordered platy illites are used a similar plateau can be recognized for thick preparations of specimens from less ordered materials but not from well ordered ones therefore it is suggested that ic is determined on very thin sedimentation slides with a thickness of 0 25 mg cm2 or less ultrasonic and h2o2 treatments enhance the degree of particle orientation by destruction of grain aggregates and organic compounds leading to smaller peak breadths and higher intensities

weathering rates and 87sr 86sr ratios an isotopic approach the 87sr 86sr ratios of precipitation throughfall groundwater streamwater and mineral matter were analyzed precipitation strontium ratios are around 0 71 throughfall which is affected by strontium from the mineral soil has ratios of 0 72 0 73 and shallow groundwater in a drug well and runoff have ratios around 0 73 0 74 there is a tendency for this relationship to be reversed for discharge higher ratios are associated with lower discharges water from a fracture zone gave the highest value 0 78 approaching the value of the bedrock around 0 85 a calcium budget which reflects the mean conditions over a few years has been calculated this budget indicates that weathering should be of the order of 8 kg ca ha 1yr 1 to maintain the pool of exchangeable calcium at a constant level the major anion in the runoff is suphate which has entered the system in the form of acid rain sulphur deposition has been rather constant over the last two decades if acidification had an effect on weathering of silicates this would have shown up in a tendency of the strontium isotope ratios toward higher values in the soil pool and in runoff water thus its seems from the observed ratios that at least a major portion of the excess calcium export resulting from sulphur deposition is taken from the soil pool resulting in a gradual acidification of the soil

a northern oscillation relating northern hemispheric pressure anomalies and the indian summer monsoon analysis of the causes of the indian monsoon have concentrated on climatological phenomena in the southern hemisphere such as el nino and the southern oscillation by contrast we have examined meteorological records for the northern hemisphere 0 180 spanning much of this century we find that zonally integrated mean sea level pressure anomalies across eurasia during january to april exhibit a statistically significant negative correlation between values for higher and sub tropical latitudes we further find that there is an association between above normal activity of the indian monsoon and a steep poleward directed pressure anomaly gradient which tends to persist through the summer and may indicate a strong zonal flow in the circumpolar westerlies on the other hand when this pressure anomaly gradient reverses zonality is disturbed and the indian monsoon tends to be drier than usual under these conditions the circumpolar flow becomes persistently meridional as a result of a predisposition to blocking and splitting of the jet

short crested waves in the surf zone this study investigates short crested waves in the surf zone by using the mesh free smoothed particle hydrodynamics model gpusph the short crested waves are created by generating intersecting wave trains in a numerical wave basin with a beach we first validate the numerical model for short crested waves by comparison with large scale laboratory measurements then short crested wave breaking over a planar beach is studied comprehensively we observe rip currents as discussed in dalrymple 1975 and undertow created by synchronous intersecting waves the wave breaking of the short crested wavefield created by the nonlinear superposition of intersecting waves and wave current interaction result in the formation of isolated breakers at the ends of breaking wave crests wave amplitude diffraction at these isolated breakers gives rise to an increase in the alongshore wave number in the inner surf zone moreover 3 d vortices and multiple circulation cells with a rotation frequency much lower than the incident wave frequency are observed across the outer surf zone to the beach finally we investigate vertical vorticity generation under short crested wave breaking and find that breaking of short crested waves generates vorticity as pointed out by peregrine 1998 vorticity generation is not only observed under short crested waves with a limited number of wave components but also under directional wave spectra

strontium isotopes as indicators of mineral weathering in catchments determination of the 87sr 86sr ratio in rain water stream water soils and rocks in two scottish catchments has provided useful information on mineral weathering over a period of 26 months the 87sr 86sr ratio in rain water had mean values of 0 7095 and 0 7098 n 12 whereas stream water had mean values of 0 7080 n 16 in catchment in devonian andesites with strontium isotope ratios of 0 7117 0 7232 in the rocks and soils and 0 7184 n 16 in catchment of cambrian metamorphic rocks with strontium isotope ratios of 0 7360 0 8218 in the rocks and soils respectively the mineralogy consists predominantly of varying proportions of quartz plagioclase feldspar and k feldspar with some mica and chlorite the fact that the 87sr 86sr ratios in the stream in the andesitic catchment are lower than for the rain water probably indicates preferential weathering of plagioclase feldspar releasing 86sr rather than k feldspar and mica which contain greater amounts of 87sr the 87sr 86sr ratio acts as a tracer for the origin of the solutes in the stream water long term monitoring of the strontium isotope ratio in stream water could be a potential means of detecting relative changes in soil weathering rates due to environmental change

the origin and migration of mud volcano fluids in taiwan evidence from hydrogen oxygen and strontium isotopic compositions abstract mud volcanoes are important gateways for deep fluids to migrate upward and provide windows for studying fluid sediment interaction at depth fluids emitted from 40 terrestrial mud volcanoes were collected in southern and eastern taiwan to study their chemical compositions including h o and sr isotopes 87sr 86sr and 88 86sr relative to seawater the mud volcano fluids are depleted in cl mg so42 and d and are elevated in b ba li and 18o possibly due to water rock interaction and clay dehydration mainly smectite to illite transformation in the source region the distribution of sr in mud volcano fluids shows patterns associated with their localities and geological settings most fluids have higher 87sr 86s than seawater indicating water rock interaction at depth the low na 87sr 86s and high ca fluids emitted from eastern taiwan imply intense interaction with igneous basement most fluids have higher sr cl and lower 88sr than seawater except mud volcanoes in the northern chu kou fault which emit low sr cl and extremely high 88sr up to 0 82 fluids we performed laboratory carbonate precipitation experiments that indicate that these high sr isotope ratios are caused by co precipitation of carbonates from high alkalinity fluids mud volcano fluids in taiwan originate at depth and their chemical compositions are controlled by the host rock degrees of water rock interaction and clay dehydration but also are masked by retrograde progresses such as carbonate precipitation during migration our results show that an approach combining water isotopes d and 18o and strontium isotopes 87sr 86sr and 88 86sr provides a robust tool for tracing fluid sources and migration pathways in accretionary prisms

short wave amplification and extreme runup by the 2011 tohoku tsunami watermarks found during the post event surveys of the 2011 tohoku tsunami confirmed extreme runup heights at several locations along the central to northern part of the sanriku coast japan we measured the maximum height of nearly 40 m above mean sea level at a narrow coastal valley of the aneyoshi district wave records by offshore gps buoys suggest that the remarkably high runup was associated with a leading impulsive crest of the tsunami amplified by local bathymetry and topography in order to elucidate the underlying amplification mechanism we apply a numerical model to reproduce the measured distribution of tsunami heights along the target coastline a series of numerical tests under different boundary conditions suggests that a spectral component with a dominant period of 4 5 min in the leading wave play a key role in generating the extreme runup further analyses focusing on the aneyoshi district confirm that the short wavelength component undergoes critical amplification in a narrow inlet our findings highlight the importance of resolving offshore waveforms as well as local bathymetry and topography when simulating extreme runup events

teleconnections between the subtropical monsoons and high latitude climates during the last deglaciation the major deglacial intensification of the southwest monsoon occurred at 11 450 150 calendar years before present synchronous with a major climate transition as recorded in greenland ice an earlier event of monsoon intensification at 16 000 150 calendar years before present occurred at the end of heinrich layer 1 in the atlantic and parallels the initial rise in global atmospheric methane concentrations and the first abrupt climate changes in the antarctic thus the evolution of the monsoonal and high latitude climates show teleconnections but hemispheric asymmetries superimposed on abrupt events the monsoonal climate shows high frequency variability of 1785 1450 and 1150 year oscillations and abrupt climate change seems to occur when at least two of these oscillations are in phase

the role of the indian summer monsoon and the mid latitude westerlies in himalayan glaciation review and speculative discussion new dates for late quaternary glaciations in the himalayas show that during the last glacial cycle glaciations were not synchronous throughout the region rather in some areas glaciers reached their maxima at the global glacial maximum of c 18 20 ka bp whereas in others glaciers were most extensive at c 60 30 ka bp comparison of these data with palaeoclimatic records from adjacent regions suggest that on millennial timescales himalayan glacier fluctuations are controlled by variations in both the south asian monsoon and the mid latitude westerlies

abrupt post glacial climate events in west asia and north africa monsoon domains regions beyond the present or past penetration of the indian and african monsoons have experienced several large and abrupt climatic fluctuations over the past 13 14c kyr pollen and lake records from west asia western tibet and rajasthan east africa ethiopia and west africa western sahara sahel and subequatorial africa were selected on the basis of chronological control sensitivity of both site and environmental indicators to climate change the continuity of the record and interdisciplinary control of the palaeoclimatic interpretation conditions wetter than those of today prevailed during the early mid holocene period but major dry spells are recorded at all sites during the intervals 11 0 9 5 kyr bp 8 7 kyr bp and 3 4 kyr bp several records also suggest dry events of minor amplitude around 6 kyr bp potential boundary forcings of insolation and sea surface and tropical land surface conditions are discussed the solar radiation accounts for the general envelop of the post glacial monsoon fluctuations but explains neither the timing nor the amplitude of the short term changes in spite of apparent covariation between fluctuations in sea surface conditions in the north atlantic and the monsoon record no direct mechanism could be found relating the intensity of the oceanic thermohaline conveyor belt to the monsoon strength changes in tropical land surface conditions soil moisture negative feedback and changes in ch4 production from wetlands provide a more satisfactory hypothesis for explaining abrupt reversal events

tsunami generation above a sill the generation of surface waves by seafloor displacement is a classic problem that arises in the study of tsunamis the generation of waves in a two dimensional domain of uniform depth by uplift or subsidence of a portion of a flat bottom boundary has been elegantly studied by hammack tsunamis a model of their generation and propagation ph d thesis california institute of technology 1972 for idealized motions the physical problem of tsunami generation is more complex even when the final displacement is known from seismic analysis the deforming seafloor includes relief features such as mounts and trenches here following kajiura j oceanogr soc jpn 28 260 277 1972 we investigate analytically the effect of bathymetry on the surface wave generation by solving the forced linear shallow water equation while kajiura s geometry consisted of a step type bottom bathymetry with a rectangular uplift to understand the effect of the continental shelf on tsunami generation our model bathymetry consists of an uplifting cylindrical sill initially resting on a flat bottom a geometry which helps evaluate the effect of seamounts on tsunami generation we find that as the sill height increases partial wave trapping reduces the wave height in the far field while amplifying it above the sill

milankovitch band forcing of sub milankovitch climate variability during the pleistocene climate variability at periods from 10 kyr to 12 kyr that originates from milankovitch band forcing is quantified at three locations for the late pleistocene eastern equatorial pacific ocean drilling program site 846 eastern equatorial atlantic odp site 663 and northeastern atlantic deep sea drilling project site 609 variability at these periods is not present in the primary milankovitch forcing so no linear linkage to milankovitch band variations is possible however these periods are equal to harmonics of precession band oscillations the magnitude of interactions between processes that occur at different timescales can only be resolved in time series data through application of higher order statistics through such an application we demonstrate that up to 75 of the variance in the 10 to 12 kyr band in the sediment records is nonlinearly transferred from precession band 19 23 kyr variations within the millennial to sub milankovitch band defined as the band of variance ranging from 15 to 2 kyr approximately 1 3 of the variability in the records studied is consistent with a low frequency milankovitch band origin this variability may derive from high sensitivity of the tropics to summertime insolation in both hemispheres relative to wintertime insolation a mechanism having equatorial origin and related to low latitude precession variations appears consistent with the observations because the phase coupling between 10 to 12 kyr oscillations and precession is resolved this result has implications for development of models which seek to explain global climate variations on this timescale

boron sources and transport mechanisms in river waters collected from southwestern taiwan isotopic evidence abstract boron b isotopes are sensitive tracers for constraining water rock interactions and pollution sources in river systems in this study we analyzed 11b using multi collector inductive coupled plasma mass spectrometry in addition to major and trace elements to delineate b sources and transport mechanisms in two river catchments the largest kao ping river and the most polluted erren river in southwestern taiwan dissolved 11b values vary more than 35 in kao ping river but keep relatively constant in erren river 12 2 26 7 four major b sources identified in these river waters are cyclic seasalt water rock interaction geothermal water and anthropogenic inputs all specimens collected near the estuaries were influenced strongly by the seawater b 4 5 mg l and 11b 39 5 the erren river results provide unique information on b and 11b compositions in anthropogenic sources in particular for fertilizer and hog manure characterized with high b up to 3 43 mg l and intermediate 11b average 13 the low 11b values in 2006 kao ping river are attributed to contributions from local geothermal inputs average 2 5 ppm and 2 prior to massive landslides caused by 2009 morakot typhoon mass balance calculations suggest that major contribution of b in river waters was derived from silicate weathering characterized by low b and intermediate 11b contributed approximately 49 97 in 2010 kao ping river the detected changes of 11b w rock reaches a maximum variation of 18 during chemical weathering in catchment and highlights the importance of water rock interaction enhancement after major climatic events

seismology energy radiation from the sumatra earthquake we determined the duration of high frequency energy radiation from indonesia s great sumatra andaman earthquake 26 december 2004 to be about 500 seconds this duration can be translated into a rupture length of about 1 200 km which is more than twice as long as that inferred from body wave analyses performed soon after the event our analysis was able rapidly to define the extent of rupture thereby aiding the assessment of seismic hazard in the immediate future

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

tracing the distribution of erosion in the brahmaputra watershed from isotopic compositions of stream sediments bank sediments and suspended loads of the brahmaputra river and its important tributaries were collected from the himalayan front to bangladesh along with most of the important tributaries chemical and isotopic compositions of the sediments are used to trace sediment provenance and to understand erosion patterns in the basin overall isotopic compositions range from 0 7053 to 0 8250 for sr and nd from 20 5 to 6 9 this large range derives from the variable proportions of sediments from himalayan formations with high sr isotopic ratios and low nd and transhimalayan plutonic belt with lower sr isotopic ratios and higher nd the latter are exposed to erosion in the tsangpo and in the eastern tributary drainages overall erosion of the himalayan rocks is dominant representing ca 70 of the detrital influx compositions of the brahmaputra main channel are rather stable between 0 7177 and 0 7284 for sr and between 14 4 and 12 5 for nd throughout its course in the plain from the siang tsangpo at the foot of the himalayan range down to the delta this stability despite the input of large himalayan rivers suggests that the siang tsangpo river represents the major source of sediment to the whole brahmaputra geochemical budget implies that erosion of the namche barwa zone represents about 45 of the total flux at its outflow before confluence with the ganga from only 20 of the mountain area higher erosion rates in the eastern syntaxis compared to the other himalayan ranges is related to the rapid exhumation rates of this region possibly triggered by higher precipitation over the far eastern himalaya and the high incision potential of the tsangpo river due to its very high water discharge

temporal variability in the northern arabian sea oxygen minimum zone omz during the last 225 000 years the northern arabian sea is one of the few regions in the open ocean where thermocline water is severely depleted in oxygen the intensity of this oxygen minimum zone omz has been reconstructed over the past 225 000 years using proxies for surface water productivity water column denitrification winter mixing and the aragonite compensation depth acd changes in omz intensity occurred on orbital and suborbital timescales lowest o2 levels correlate with productivity maxima and shallow winter mixing precession related productivity maxima lag early summer insolation maxima by 6 kyr which we attribute to a prolonged summer monsoon season related to higher insolation at the end of the summer periods with a weakened or even non existent omz are characterized by low productivity conditions and deep winter mixing attributed to strong and cold winter monsoonal winds the timing of deep winter mixing events corresponds with that of periods of climatic cooling in the north atlantic region

slow earthquakes and nonvolcanic tremor nonvolcanic tremor is observed in close association with geodetically observed slow slip events in subduction zones accumulating evidence points to these events as members of a family of slow earthquakes that occur as shear slip on the downdip extensions of fault zones in a regime that is transitional between a frictionally locked region above and a freely slipping region below by virtue of their locations and their properties slow earthquakes are certain to provide new insights into the behavior of earthquakes and faulting and into the hazard they embody

dust response to seasonal atmospheric forcing proxy evaluation and calibration eolian grain size and flux were measured on samples from 11 arabian sea sediment traps deployed 200 1250 km offshore the timing of increased grain size is coincident with the onset of strong summer monsoon winds and dust storm activity over the arabian peninsula and middle east data spanning a full annual cycle show that eolian grain size is highly correlated with barometric pressure r 0 91 and wind speed r 0 84 enabling calibration of the downcore record in terms of these primary meteorological variables eolian flux is highly correlated with organic carbon flux r 0 80 both increase 6 8 weeks after the grain size increase and summer monsoon onset this lag and the low correlation between eolian grain size and eolian flux r 0 36 likely result from the differential sinking rates of large and small dust particles in the surface waters as well as biological scavenging associated with monsoon induced productivity marily to aridity and vegetation cover at the source and 3 that grain size is primarily a function of atmospheric transport capacity these findings are based on statistical relation ships linking dust flux to glacial interglacial climate change 5 o and grain size to biological indicators of wind driven upwelling such relationships are well documented and have provided a reasonably robust framework for interpreting the downcore dust record rea 1994 provides an excellent overview however direct evaluation of links between at mospheric dynamics dust aerosols and deep sea sediments in the modem environment are needed to better understand

far field tsunami hazard from mega thrust earthquakes in the indian ocean summary we evaluate far field tsunami hazard in the indian ocean basin based on hydrodynamic simulations of ten case studies of possible mega earthquakes at the major seismic zones surrounding the basin they represent worst case scenarios of seismic rupture along the full extent of seismogenic faults having supported large earthquakes in the historical record in a series of numerical experiments in which the source parameters of the 2004 sumatra tsunami are allowed to vary one by one while keeping the seismic moment and the fault orientation unchanged we document that the main patterns of far field tsunami amplitudes are remarkably robust with respect to nominal variations in such parameters as hypocentral depth exact centroid location and slip distribution on the fault plane these results validate the concept of modelling case scenarios of potential future earthquakes whose source is by definition imprecise we consider seismic sources located at the extremities of the 2004 sumatra andaman rupture namely along the southern coast of sumatra and in the andaman myanmar province along the makran coast of pakistan and iran and also along the southern coast of java where the possibility of a large interplate thrust earthquake cannot be entirely dismissed the results of our hydrodynamic simulations indicate that the distribution of maximum amplitudes in the indian ocean basin is primarily controlled by the classical effect of source directivity and additionally by refraction and focusing along bathymetric features as a result many provinces in the basin could be threatened by higher tsunami amplitudes than in 2004 this pattern is particularly important along the coast of east africa from somalia to and including south africa in madagascar and the mascarene islands especially under a south sumatra scenario involving an earthquake comparable to or even possibly larger than the 1833 event whose epicentral area is widely believed to be under enhanced seismic risk as a result of stress transfer from the 2004 and 2005 ruptures to the northwest possibly even in the wake of the 2007 bengkulu earthquakes

all toba tephra occurrences across peninsular india belong to the 75 000 yr b p eruption abstract a controversy currently exists regarding the number of toba eruptive events represented in the tephra occurrences across peninsular india some claim the presence of a single bed the 75 000 yr old toba tephra others argue that dating and archaeological evidence suggest the presence of earlier toba tephra resolution of this issue was sought through detailed geochemical analyses of a comprehensive suite of samples allowing comparison of the indian samples to those from the toba caldera in northern sumatra malaysia and importantly the sedimentary core at odp site 758 in the indian ocean a core that contains several of the earlier toba tephra beds in addition two samples of toba tephra from western india were dated by the fission track method the results unequivocally demonstrate that all the presently known toba tephra occurrences in peninsular india belong to the 75 000 yr b p toba eruption hence this tephra bed can be used as an effective tool in the correlation and dating of late quaternary sedimentary sequences across india and it can no longer be used in support of a middle pleistocene age for associated acheulian artifacts

source variability of sediments in the shihmen reservoir northern taiwan sr isotopic evidence abstract high turbidity in water reservoirs during the monsoon season has caused serious problems for drinking water quality in taiwan in this study we collected stream waters and streambed sediments including bed loads and fresh landslide deposits in the dahan stream and analyzed 101 87 sr 86 sr ratios in different grain size fractions in the streambed sediments from the upper catchment and 3 sediment cores from the shihmen reservoir as well as dissolved major and trace elements in stream waters to identify possible changes of sediment sources in the reservoir the 87 sr 86 sr ratios in stream water and streambed sediments ranged from 0 71296 0 71349 and 0 71714 0 71843 respectively the large sr isotopic difference between the paired stream water and streambed sediments are evidence for disequilibrium water rock interaction in the weathering limited regions the sr isotopic compositions in bulk sediments and various grain size fractions showed no clear spatial variability however there is an interesting relationship between grain sizes and sr isotope ratios implying effects of mineral sorting during sediment transportation the illite crystallinity and the illite chemistry index of streambed sediment suggest moderate to strong chemical weathering in this regions the dissolved constituents in the dahan stream support that silicate weathering is the predominated controlled mechanism and only minor carbonate dissolution occurred near the central mountain range the 87 sr 86 sr ratios in the sediment cores suggest that modern reservoir sediment is mainly derived from the upper watershed composed of primarily oligocene sedimentary rocks however the sediment sources have changed significantly since the reservoir built 37 years ago the 87 sr 86 sr ratios were spread widely outside the present day observations in the dahan catchment the homogeneous distribution of 87 sr 86 sr in the upper reservoir cores reflected disturbance due to recent turbidity events within the reservoir these new chemical and isotopic data provide useful spatial and temporal information of weathering sources in a high denudation sub tropical mountainous watershed

variability of east asian winter monsoon in quaternary climatic extremes in north china in order to examine high frequency variations of east asian winter monsoon in quaternary climatic extremes two typical loess paleosol sequences in the chinese loess plateau were investigated sandy layers in the loess deposits the upper sand and lower sand layers l9 and l15 respectively which represent a high resolution record of paleomonsoon changes have been sampled at intervals of 5 6 cm from sections at luochuan and xifeng the grain size and magnetic susceptibility was measured for all samples the grain size results a proxy of winter monsoon strength indicate that the winter monsoon strength fluctuated on a millennial timescale during cold climatic extremes with climatic events of a few hundred to a few thousand years however the winter monsoon was relatively stable during warm periods the magnetic susceptibility signal a proxy of summer monsoon intensity is practically constant over the same period this is tentatively explained by the assumption that the summer monsoon intensity was too low to be recorded in the magnetic susceptibility signal the intensified winter monsoon events show periodicities in a range of 1000 to 2770 yr with a dominant cycle of approximately 1450 yr the detection of this oscillation in older glacial stages strongly suggests that it may be a pervasive cycle of the cold climatic phases of the quaternary millennial scale variations of the winter monsoon may be caused by instability of the westerly jet which is determined by temperature differences between the polar and the equatorial regions

controls over the strontium isotope composition of river water abstract strontium concentrations and isotope ratios have been measured in river and ground waters from the ganges orinoco and amazon river basins when compared with major element concentrations the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments 1 1 typical drainage basins containing limestones evaporites shales and alumino silicate metamorphic and igneous rocks 2 2 shield terrains containing no chemical or biogenic sediments and 3 3 the floodplains that constitute the largest areas of many large rivers the strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks the strontium isotope composition of the limestone endmember generally lies within the phanerozoic seawater range which buffers the 87 sr 86 sr ratios of major rivers a major exception is provided by the rivers draining the himalayas where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks the strontium isotope systematics of rivers draining shield areas are controlled by the intense transportlimited nature of the weathering reactions and thereby limits variations in the strontium flux from these terrains floodplains are only a minor source of dissolved strontium to river waters and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans the most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large scale regional metamorphism of the type produced during continental collision both mechanisms provide a means for increasing the 87 sr 86 sr ratio of the global riverine flux

grain size separation and sediment mixing in arctic ocean sediments evidence from the strontium isotope systematic the 87 rb 86 sr and 87 sr 86 sr ratios of laptev sea sediments of arctic ocean sediments and of suspended particulate matter spm from siberian rivers lena and khatanga form pseudo isochrons due to grain size separation processes which are referred to as lena mixing envelope lme and as flood basalt envelope fbe at the land ocean transition the reduction of the particle velocity causes a deposition of coarser grained material and the contact with saline water enhances a precipitation of finer grained material the coarse grained material is enriched in sr showing less radiogenic 87 sr 86 sr ratios whereas fine grained material is depleted in sr relative to rb showing more radiogenic 87 sr 86 sr ratios the experimentally determined spread of the 87 rb 86 sr and 87 sr 86 sr ratios as a function of grain size in one sediment sample is on the same order as the natural spread of the 87 sr 86 sr ratios observed in all samples from the arctic ocean chemical index of alteration cia for the lena river spm tend to confirm previous observations that chemical alteration is negligible in the arctic environment thus these pseudo isochrons reflect an average age and the average isotope composition in the river drainage area calculated apparent ages from the fbe reflect the age of the siberian flood basalt of about 220 ma and the initial ratio of 0 707 1 reflects their mantle origin the age calculated from the lme of about 125 ma reflects accidentally the jurassic and cretaceous age of the sediments drained by the lena river and the initial ratio of 0 714 1 reflects the crustal origin of their source rocks comparison of geographical locations reveals that all samples from the eastern laptev sea east of 120 degrees e fall along the lme whereas all samples from the western laptev sea west of 120 degrees e fall between lme and fbe mixing calculations based on 143 nd 144 nd measurements not influenced by grain size show that about 75 of the western laptev sea sediments originate from the lena drainage area whereas about 25 of the sediments are delivered from the siberian flood basalt province sediments from the central arctic ocean are isotopically related to the lena drainage area and the siberian flood basalt province however sediments from the arctic ocean margins close to novaya semlya greenland the fram strait and svalbard originate from sources not yet identified c 1999 elsevier science b v all rights reserved

the low latitude monsoon climate during dansgaard oeschger cycles and heinrich events during the last 100 000 years dansgaard oeschger cycles d o cycles and heinrich events have been the dominant signal of past climate variability over greenland and the north atlantic the succession of stadials cold and interstadials warm associated with these cycles has been documented in records from the entire northern hemisphere south america new zealand antarctica the south atlantic and the southern ocean evidently climate forcing in the d o band affects both hemispheres the origin and cause of these teleconnected patterns is still unknown even if a large proportion of the cooling in europe and northern asia during heinrich events is a meteorological response to cold surface water in the north atlantic resulting from the surge of the laurentian and scandinavian ice sheets but this does not imply that the d o cycles are a priori caused by the collapse of these large icesheets a severe challenge to a primary origin from the northern ice sheet and north atlantic comes from the observation that warming in antarctica and the circumpolar current leads the north atlantic changes by some 1500 years charles et al 1996 blunier et al 1998 in the second part of the paper we investigate new deep sea records from the low latitude monsoon system mainly corroborating the result of schulz et al 1998 that the indian monsoon showed d o variability the abundance of eolian dust indicating continental humidity aridity in core 70kl from the arabian sea shows humid intervals which seem to correlate with temperature maxima in the antarctic vostok ice core apparently the low frequency sub milankovitch variability of the monsoon is associated with the southern hemisphere the d o scale component in the monsoonal climate on the other hand shows a succession of short humid intervals the sequence is most closely comparable to the greenland temperature record and to the stadial interstadial succession in the pacific santa barbara basin odp 893 in order to understand the global forcing of climate change in the d o band it appears necessary to quantify the phase relationships not only between d o cycles in the polar ice cores bender et al 1994 blunier et al 1998 steig et al 1998 but also between the low latitude pacific indian ocean and the high latitude records

orbital forcing of freshwater input in the zaire fan area clay mineral evidence from the last 200 kyr abstract late quaternary sediments recovered in a core from the area of the zaire fan central africa were analyzed for clay mineral composition in order to reconstruct fluctuations in the sediment input and freshwater discharge of the zaire river clay mineral assemblages are dominated by kaolinite and smectite which both originate mainly from the zaire river and contain only minor contributions of eolian dust smectite crystallinity and chemical character of illites fe mg or al rich are used to track sediment input from the zaire river and assess fluctuations in the freshwater discharge both parameters record a high latitude forcing of river runoff at 100 ka periodicities reflecting glacial aridity and increased runoff during interglacials 1 5 and 7 this signal is also observed in kaolinite smectite ratios which represent the extension and intensity of the freshwater plume of the zaire river clay mineral proxies reveal that river discharge and associated sediment input fluctuated in tune with precessional cycles of african monsoon intensity increased eolian input of kaolinite rich dust with intensified northeast trades during glacials flattens the precessional signal in kaolinite smectite ratios

radiogenic isotopes systematics and applications to earth surface processes and chemical stratigraphy radiogenic isotopes have wide application to chemical stratigraphy geochronology provenance studies and studies of temporal changes in earth surface processes this paper briefly reviews the principles of radiogenic isotope geochemistry and the distribution of a number of elements of interest in the environment and then uses this information to explore the range of applications to chemical stratigraphy and other fundamental subjects of sedimentary geology many of these applications center on the reconstruction of secular variations in paleoseawater isotope signals these seawater isotope curves can be used for stratigraphic correlation and to assess changes through earth history in processes such as tectonic uplift climate change biogeochemical cycling ocean circulation crustal growth and surface water evolution understanding the modern biogeochemical cycle of the element isotope system of interest is essential for gaining the maximum information regarding the operation of ancient cycles the main sources of uncertainty for reconstructing seawater isotope curves involve diagenetic alteration sample impurities and errors in age assignments rigorous sample selection criteria and pretreatment methods are keys to reconstructing the most accurate seawater isotope curves applications are discussed for the rb sr sm nd la ce lu hf re os u th pb k ar and cosmogenic isotope systems d 2003 elsevier b v all rights reserved

orbital insolation forcing of the indian monsoon a motor for global climate changes abstract both modern and ancient indian summer monsoons are driven by transequatorial pressure differences directly coupled with the insolation difference between the northern and southern subtropical hemispheres a high resolution record of upwelling and dust flux from the western arabian sea resembles an insolation based indian summer monsoon index this index and the observed monsoonal climate variations share major elements on the orbital obliquity and precessional band with the specmap marine oxygen isotope record representing global ice volume the long term evolution of the index mirrors almost exactly the insolation changes at 65 n showing that the forcing of low latitude climate variability has a structure similar to that of the insolation forcing in the high northern latitudes moreover insolation forcing in the low latitudes directly controls atmospheric processes in the african indian and asian monsoon being responsible for a huge amount of transequatorial water vapour and therefore latent heat transport millennial scale variability of the monsoonal climate is concentrated at periodicities near 1100 1450 1750 and 2300 years these cycles are not strictly periodic but occur in bands with specific activity phases and amplitude increases during warm stages and interstadials for the 1100 and 1750 yr cycles whereas the 1450 yr cycle dominates the cold intervals

grain size and srnd isotopes as tracer of paleo bottom current strength northeast atlantic ocean abstract a crucial question in modern paleoceanographic research is how vigourous was the bottom current in the glacial north atlantic ocean distribution of sediment grain size can provide such information if the characteristics of the source functions are known the interest of this paper is to use the sr nd isotopic composition of lithic particles as a tracer of origin in order to determine possible changes in the source function over the last 185 kyr grain size distribution data are derived from a sediment core in the icelandic basin gardar drift the distribution pattern reveals a well sorted silt size modal size 20 m in the glacial deposits sr and nd isotopic composition measured on separate size fractions indicates a more constant local origin iceland for the silt fraction than for the fine fraction these data suggest that the increase in the silt fraction during glacial periods is related primarily to an increase in the bottom current strength rather than to changes in sediment supply i e ice rafting turbidity current the increase in vigour of the bottom current recorded during the isotopic stages 6 4 and the last post glacial periods could have been initiated by a southward shift of the zone of deep water formation in the northern part of the icelandic basin

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

implications of late eocene to early miocene clay mineral assemblages in mcmurdo sound ross sea antarctica on paleoclimate and ice dynamics abstract the clay mineral assemblages of upper eocene to lower miocene sediments recovered at the ciros 1 and mssts 1 drill sites on the mcmurdo sound shelf antarctica were analyzed in order to reconstruct the cenozoic antarctic paleoclimate and ice dynamics the assemblages are dominated by smectite and illite with minor amounts of chlorite and kaolinite the highest smectite amounts and best smectite crystallinities occur in the upper eocene part of ciros 1 below 425 445 mbsf they indicate that during their deposition chemical weathering conditions prevailed on the nearby continent large parts of east antarctica were probably ice free at that time but some glaciers reached the sea and contributed to the glaciomarine sedimentation in contrast only minor total amounts of smectite are present in oligocene and younger sediments due to the shift to mainly physical weathering on an ice covered antarctic continent however relative smectite percentages rise to more than 60 during two late oligocene intervals ca 27 5 26 2 and 25 0 24 5 ma and during one early miocene interval starting at ca 23 3 ma these intervals are characterized by ice masses coming probably from the south where volcanic rocks acted as a source as also indicated by the composition of the sand and gravel fractions during the other intervals the ice came from the west where the physical erosion of basement rocks and sedimentary rocks of the beacon supergroup in the transantarctic mountains provided high illite concentrations because the two drill sites are only 4 km apart their clay mineral records can be correlated this led to a new interpretation of the oligocene paleomagnetic data of the mssts 1 site and to a more detailed lithostratigraphic correlation of the miocene parts of the cores

climatic and tectonic controls on chemical weathering in the new zealand southern alps abstract climatic and tectonic controls on the relative abundance of solutes in streams draining the new zealand southern alps were investigated by analyzing the elemental and sr isotope geochemistry of stream waters bedload sediment and hydrothermal calcite veins the average relative molar abundance of major cations and si in all stream waters follows the order ca2 50 si 22 na 17 mg2 6 k 5 for major anions the relative molar abundance is hco3 89 so42 7 cl 4 weathering reactions involving plagioclase and volumetrically small amounts of hydrothermal calcite define the ionic chemistry of stream waters but nearly all streams have a carbonate dominated ca2 and hco3 mass balance stream water ca sr and 87sr 86sr ratios vary from 0 173 to 0 439 mol nmol and from 0 7078 to 0 7114 respectively consistent with the ionic budget these ratios lie solely within the range of values measured for bedload carbonate ca sr 0 178 to 0 886 mol nmol 87sr 86sr 0 7081 to 0 7118 and hydrothermal calcite veins ca sr 0 491 to 3 33 mol nmol 87sr 86sr 0 7076 to 0 7097 streams draining regions in the southern alps with high rates of physical erosion induced by rapid tectonic uplift and an extremely wet climate contain 10 more ca2 and 30 more sr2 from carbonate weathering compared to streams draining regions in drier more stable landscapes similarly streams draining glaciated watersheds contain 25 more sr2 from carbonate weathering compared to streams draining non glaciated watersheds the highest abundance of carbonate derived solutes in the most physically active regions of the southern alps is attributed to the tectonic exhumation and mechanical denudation of metamorphic bedrock which contains trace amounts of calcite estimated to weather 350 times faster than plagioclase in this environment in contrast regions in the southern alps experiencing lower rates of uplift and erosion have a greater abundance of silicate versus carbonate derived cations these findings highlight a strong coupling between physical controls on landscape development and sources of solutes to stream waters using the southern alps as a model for assessing the role of active tectonics in geochemical cycles this study suggests that rapid mountain uplift results in an enhanced influence of carbonate weathering on the dissolved ion composition delivered to seawater

rapid climate transitions in a coupled ocean atmosphere model recent geochemical data1 2 have challenged the view that rapid climate fluctuations in the north atlantic at the end of the last glacial were caused by the thermohaline circulation of the ocean being switched on or off instead these data suggest that the circulation pattern must have switched between a warm deep mode and a cold shallow mode probably associated with different sites of deep convection3 here i present simulations with a three dimensional ocean model coupled to an idealized atmosphere which show this kind of transition the mechanism for the transition is a rearrangement of convection in the north atlantic triggered by a brief freshwater pulse this results in a drop in sea surface temperature in the north atlantic by up to 5 c within less than 10 years the rate of north atlantic deep water nadw forma tion is the same in the cold climate as in the warm climate but nadw sinks to intermediate depths only while antarctic bottom water pushes north to fill the entire abyssal atlantic

the role of disseminated calcite in the chemical weathering of granitoid rocks accessory calcite present at concentrations between 300 and 3000 mg kg 1 occurs in fresh granitoid rocks sampled from the merced watershed in yosemite national park ca usa loch vale in rocky mountain national park co usa the panola watershed ga usa and the rio icacos puerto rico calcite occurs as fillings in microfractures as disseminated grains within the silicate matrix and as replacement of calcic cores in plagioclase flow through column experiments using de ionized water saturated with 0 05 atm co2 produced effluents from the fresh granitoid rocks that were dominated by ca and bicarbonate and thermodynamically saturated with calcite during reactions up to 1 7 yr calcite dissolution progressively decreased and was superceded by steady state dissolution of silicates principally biotite mass balance calculations indicate that most calcite had been removed during this time and accounted for 57 98 of the total ca released from these rocks experimental effluents from surfically weathered granitoids from the same watersheds were consistently dominated by silicate dissolution the lack of excess ca and alkalinity indicated that calcite had been previously removed by natural weathering the extent of ca enrichment in watershed discharge fluxes corresponds to the amounts of calcite exposed in granitoid rocks high ca na ratios relative to plagioclase stoichiometries indicate excess ca in the yosemite loch vale and other alpine watersheds in the sierra nevada and rocky mountains of the western united states this ca enrichment correlates with strong preferential weathering of calcite relative to plagioclase in exfoliated granitoids in glaciated terrains in contrast ca na flux ratios are comparable to or less than the ca na ratios for plagioclase in the subtropical panola and tropical rio icacos watersheds in which deeply weathered regoliths exhibit concurrent losses of calcite and much larger masses of plagioclase during transport limited weathering these results indicate that the weathering of accessory calcite may strongly influence ca and alkalinity fluxes from silicate rocks during and following periods of glaciation and tectonism but is much less important for older stable geomorphic surfaces

nonstationary phase of the plio pleistocene asian monsoon paleoclimate records indicate that the strength of the asian summer monsoon is sensitive to orbital forcing at the obliquity and precession periods 41 000 and 23 000 years respectively and the extent of northern hemisphere glaciation over the past 2 6 million years the timing phase of strong monsoons has changed by 83 degrees in the precession and 124 degrees in the obliquity bands relative to the phase of maximum global ice volume inferred from the marine oxygen isotope record these results suggest that one or both of these systems is nonstationary relative to orbital forcing

slow slip events and seismic tremor at circum pacific subduction zones 1 it has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements however only recently has a fuller spectrum of strain release processes including normal slow and silent earthquakes or slow slip events and continuous and episodic slip been observed and generated by numerical simulations of the earthquake cycle despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive the concurrence of seismic tremor with slow slip episodes in cascadia and southwestern japan provides insight into the process of slow slip a perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface alternatively evidence is accumulating to support the notion that tremor results from shear failure during slow slip global observations of the location spatial extent magnitude duration slip rate and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation most slow slip events occur just downdip of the seismogenic zone consistent with rate and state dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation at a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault bringing it closer to or farther from earthquake failure respectively this paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide with a focus on circum pacific subduction zones trends in global observations of slow slip events suggest that 1 slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it 2 different frictional properties likely control fast versus slow slip 3 the depth range of slow slip may be related to the thermal properties of the plate interface and 4 the equivalent seismic moment of slow slip events is proportional to their duration mo different from the mo 3 scaling observed for earthquakes

the southwest indian monsoon over the last 18 000 years previously published results suggest that the strength of the sw indian monsoon can vary significantly on century to millenium time scales an observation that has important implications for assessments of future climate and hydrologic change over densely populated portions of asia we present new well dated multi proxy records of past monsoon variation from three separate arabian sea sediment cores that span the last glacial maximum to late holocene to a large extent these records confirm earlier published suggestions that the monsoon strengthened in a series of abrupt events over the last deglaciation however our data provide a somewhat refined picture of when these events took place and suggest the primacy of two abrupt increases in monsoon intensity one between 13 and 12 5 ka and the other between 10 and 9 5 ka this conclusion is supported by the comparisons between our new marine data and published paleoclimatic records throughout the african asian monsoon region the comparison of data sets further supports the assertion that maximum monsoon intensity lagged peak insolation forcing by about 3000 years and extended from about 9 5 to 5 5 ka the episodes of rapid monsoon intensification coincided with major shifts in north atlantic european surface temperatures and ice sheet extent this coincidence coupled with new climate model experiments suggests that the large land sea thermal gradient needed to drive strong monsoons developed only after glacial conditions upstream of and on the tibetan plateau receded cold north atlantic sea surface temperatures european ice sheets and extensive asian snow cover it is likely that abrupt changes in seasonal soil hydrology were as important to past monsoon forcing as were abrupt snow related changes in regional albedo our analysis suggests that the monsoon responded more linearly to insolation forcing after the disappearance of glacial boundary conditions decreasing gradually after about 6 ka our data also support the possibility that significant century scale decreases in monsoon intensity took place during the early to mid holocene period of enhanced monsoon strength further highlighting the need to understand paleomonsoon dynamics before accurate assessments of future monsoon strength can be made

three dimensional tsunami generation simulation due to sea bottom deformation and its interpretation based on the linear theory summary the present study investigates the tsunami generation process by using 3 d numerical simulations and the linear potential theory first we evaluate the relation between sea bottom elevation and sea surface elevation as function of source size l sea depth h and source duration t based on 3 d numerical simulations the surface elevation decreases with increasing sea depth and source duration the difference between the sea bottom and the sea surface elevation appears when the source size is smaller than approximately 10 times the sea depth for a short source duration the linear potential theory can precisely predict the numerical simulation results based on the theory we can consider the tsunami generation as two spatial lowpass filter processes in which the cut off wavenumbers are given by the sea depth and the source duration the criteria for small source size and short source duration are given as l 13h and t l 8c respectively where c is the phase velocity of the tsunami we then simulate the tsunami generation of the 1896 sanriku tsunami earthquake japan the simulated sea surface elevation is significantly different from the sea bottom elevation which suggests the need for correction of the sea depth and source duration for the precise evaluation of the initial water height distribution to include these effects in 2 d simulations we can use the impulse response function and add the fractional sea surface uplift within the time step to the sea surface for each time step

a 2 200 years periodicity in the asian monsoon system we have carried out a high resolution study of fluctuations in upwelling intensity along the oman margin western arabian sea through the last 19 130 years based on several marine microfossil indices of upwelling we document a periodicity of 2 200 years in the upwelling indices which would be governed by the south west sw monsoon with such a periodicity our data further demonstrate greater amplitude in the variability of the sw monsoon during the holocene than during the last glacial period our reported 2 200 years periodicity has two implications 1 oceanic circulation changes partly influence monsoon strength at sub milankovitch cycles 2 previously documented 2 300 years periodicity in atmospheric 14c might be induced by oceanic circulation changes

oxygenation changes in the deep western arabian sea during the last 190 000 years productivity versus deepwater circulation 1 fluctuations in the abundance of selected foraminiferal indicator species and diversity allowed the reconstruction of changes in deepwater oxygenation and monsoon driven organic matter fluxes in the deep western arabian sea during the last 190 kyr times of maximum surface production coincide with periods of intensified sw monsoon as shown by the abundance of globigerina bulloides and enhanced carbonate corrosion benthic ecosystem variability in the deep arabian sea is not exclusively driven by variations in monsoonal upwelling and related organic matter supply to the seafloor but also by changes in deepwater ventilation deepening of the base of the oxygen minimum zone omz below 1800 m water depth is strongly coherent on the precessional band but lags proxies of sw monsoon strength by 4 to 6 kyr the out of phase relationship between omz deepening and maximum sw monsoon strength is explained by temporal changes in the advection of oxygen rich deepwater masses of north atlantic and antarctic origin this process affected the remineralization and burial efficiency of organic matter in the deep arabian sea resulting in the observed phase lag between maximum monsoon strength and organic carbon preservation

rupture process of the 1944 tonankai earthquake ms 8 1 from the inversion of teleseismic and regional seismograms 1 we digitized teleseismic and regional records of the 1944 tonankai earthquake we used the multiple time window method to invert these records for the spatial and temporal distribution of slip and rake we assume a 220 140 km fault with a spacing of 20 20 km and a maximum rupture velocity of 2 5 km s the inversion resolved an asperity along the accretionary wedge and under the shima and atsumi peninsulas the rupture propagated from southwest to northeast and there was little slip near the hypocenter consistent with the absence of uplift in the overlying submarine forearc basin the peak slip is 2 3 m and the total seismic moment is 2 4 1028 dyn cm mw 8 2 we compared the predicted and observed vertical geodetic displacements and inferred that the limit of rupture is consistent with the change from subsidence to uplift west of the atsumi peninsula this suggested that the earthquake did not rupture the plate interface in the tokai gap we modeled the tsunami using sea bottom displacements generated from this slip model the tide gauge amplitudes and frequency content are consistent with those predicted resolution tests from inverting synthetic seismograms computed using a simplified slip model indicated that the combination of teleseismic and regional data sets best recovers the asperity locations and peak slips given similar station geometry and degrees of freedom an inversion of the synthetic regional data set indicates that slip artifacts can occur early in the rupture process due to many clipped records while the inversion of synthetic teleseismic data set had less resolution and recovered only 50 of the peak slip

10be study of rapid erosion in taiwan cosmogenic 10be was measured using accelerator mass spectrometry in soils and sediments to study the erosion of taiwan which has the highest denudation rate in the world the river sediments in taiwan have very low 10be concentrations around 5 million atoms per gram about 145 the world wide average this is the direct consequence of its high sediment yield of more than 1000 mg cm2 yr 70 times the world average combining these values we found that for taiwan as a whole the 10be output to the sea only slightly exceeds the input from the rain a situation typical of many areas around the world therefore even in this example of extremely rapid erosion 10be seems to remain a useful indicator for erosion status the total 10be inventory found in a soil profile from a geologically stable area is at least 18 of the maximum possible inventory the minimum age thus estimated for the soil is 0 11 ma in reasonable agreement with estimates from other means the maximum erosion rate for this area thus estimated is at most 0 14 mg cm2 yr four orders of magnitude slower than the average value observed for taiwan we also demonstrate that the shelf sediments around taiwan have received the admixing of a 10be rich component from the ocean and would give a poor estimate for material eroded from taiwan

global cooling forced increase in marine strontium isotopic ratios importance of mica weathering and a kinetic approach abstract the knowledge of how and why marine 87 sr 86 sr ratios changed helps understand the impacts of many processes on the global biogeochemical cycle in the geological past here we examine the possible influence of global cooling on the evolution of marine 87 sr 86 sr curve by a kinetic approach the importance of mica weathering is emphasized due to its high content of radiogenic strontium and low activation energy in weathering reaction since the activation energy determines the sensitivity of weathering rate in response to temperature changes global cooling will increase the 87 sr 86 sr ratio of continental flux by relatively preferential weathering of mica based on the average strontium contents and 87 sr 86 sr ratios of the mica minerals in the exposed upper continental crust a kinetic model is established to survey the response of riverine 87 sr 86 sr to the changes of global temperatures the model result indicates that the increase of riverine 87 sr 86 sr caused by global cooling can solely account for most of the increase in seawater 87 sr 86 sr since 3 4 myr b p this finding emphasizes that the weathering kinetics is an important mechanism relating the global climate change to marine 87 sr 86 sr curve and the marine 87 sr 86 sr curve should be used with great care in the climate weathering tectonic connections

the global reach of the 26 december 2004 sumatra tsunami numerical model simulations combined with tide gauge and satellite altimetry data reveal that wave amplitudes directionality and global propagation patterns of the 26 december 2004 sumatra tsunami were primarily determined by the orientation and intensity of the offshore seismic line source and subsequently by the trapping effect of mid ocean ridge topographic waveguides

kinetic and mineralogic controls on the evolution of groundwater chemistry and 87sr 86sr in a sandy silicate aquifer northern wisconsin usa abstract substantial flowpath related variability of 87sr 86sr is observed in groundwaters collected from the trout lake watershed of northern wisconsin in the extensive shallow aquifer composed of sandy glacial outwash groundwater is recharged either by seepage from lakes or by precipitation that infiltrates the inter lake uplands 87sr 86sr of groundwater derived mainly as seepage from a precipitation dominated lake near the head of the watershed decreases with progressive water chemical evolution along its flowpath due primarily to enhanced dissolution of relatively unradiogenic plagioclase in contrast 87sr 86sr of groundwater derived mainly from precipitation that infiltrates upland areas is substantially greater than that of precipitation collected from the watershed due to suppression of plagioclase dissolution together with preferential leaching of sr from radiogenic phases such as k feldspar and biotite the results of a column experiment that simulated the effects of changing residence time of water in the aquifer sand indicate that mobile waters obtain relatively unradiogenic sr whereas stagnant waters obtain relatively radiogenic sr nearly the entire range of strontium isotope composition observed in groundwaters from the watershed was measured in the experimental product waters the constant mobility of water along groundwater recharge flowpaths emanating from the lakes promotes the dissolution of relatively unradiogenic plagioclase perhaps due to effective dispersal of clay mineral nuclei resulting from dissolution reactions in contrast episodic stagnation in the unsaturated zone along the upland recharge flowpaths suppresses plagioclase dissolution perhaps due to accumulation of clay mineral nuclei on its reactive surfaces differences in redox conditions along these contrasting flowpaths probably enhance the observed differences in strontium isotope behavior this study demonstrates that factors other than the calculated state of mineral saturation must be considered when attempting to simulate chemical evolution along flowpaths and that reaction models must be able to incorporate changing contributions from reacting minerals in the calculations

simulation of an abrupt change in saharan vegetation in the mid holocene climate variability during the present inter glacial the holocene has been rather smooth in compar ison with the last glacial nevertheless there were some rather abrupt climate changes one of these changes the desertication of the saharan and arabian region some 4 6 thousand years ago was presumably quite important for human society it could have been the stimulus leading to the foundation of civilizations along the nile euphrat and tigris rivers here we argue that saharan and arabian de sertication was triggered by subtle variations in the earth s orbit which were strongly amplied by atmosphere vegeta tion feedbacks in the subtropics the timing of this tran sition however was mainly governed by a global interplay between atmosphere ocean sea ice and vegetation

modulation and amplification of climatic changes in the northern hemisphere by the indian summer monsoon during the past 80 k y high frequency suborbital variations dansgaard oeschger cycles characterize the climatic history of the northern hemisphere as observed in greenland ice cores deep sea sediments of the north atlantic the californian borderland the arabian sea the south china sea and the chinese loess area paleoceanographic data from core kl126 from the bay of bengal in combination with data from the other asian monsoonal areas indicate that the feedback processes involving snow and dust of the tibetan plateau vary the summer monsoon capacity to transport moisture into central south asia and into the atmosphere we postulate that the summer monsoon initiates amplifies and terminates these cycles in the northern hemisphere

size dependent geochemical signatures of holocene loess deposits from the hexi corridor china well dated holocene loess sequences from uplifted river terraces at the northern margin of the tibetan plateau are characterised by their chemical grain size sr isotope and their oxygen and carbon isotope composition of the carbonate fractions prevailing wind directions suggest the source areas of the loess to be largely restricted to dry lands in northwest china and the deserts north to the hexi corridor e g badain jaran and tengger desert which receive fluvial input by rivers draining the qilian shan the dry lands of northwest china are one of the most important dust source areas globally local and conditions make the investigated loess sequences insensitive to element leaching the loess is characterised by a relatively narrow variation of sr 87 sr 86 0 7139 0 7164 the sr 87 sr 86 ratios of surface and carbonate bound sr are similar 0 7114 and 0 7111 and lower than those of silicate bound sr 63 2 mu m fractions similar to 0 7196 2 mu m fractions similar to 0 7247 since the clay fractions have higher caco3 contents than the silt fractions the isotopic contrast between the silicate debris of clay and silt size is camouflaged in the bulk compositions of these grain size fractions oxygen isotope and chemical compositions of clay and silt sized carbonate particles differ significantly silt sized loess carbonates formed authigenically and they are largely present as coatings of silicate grains whereas clay sized carbonate particles are of remote provenance and precipitated under evaporative conditions in line with further implications from the multi proxy study upward trends in the composition of the pedogenic carbonate document climate change to drier conditions after the mid holocene c 2009 elsevier ltd all rights reserved

ba sr ca sr and 87sr 86sr ratios in soil water and groundwater implications for relative contributions to stream water discharge abstract barium sr and ca sr ratios have been used to model the relative importance of different sources of stream water major and trace element concentrations together with 87sr 86sr ratios were measured in precipitation soil water groundwater and stream water in a small 9 4 km2 catchment in northern sweden the study catchment is drained by a first order stream and mainly covered with podzolized quaternary till of granitic composition it is underlain by a 1 8 ga granite a model with mixing equations used in an iterative mode was developed in order to separate the stream water into 3 subsurface components soil water shallow groundwater and deep groundwater contributions from precipitation are thus not included in the model this source may be significant for the stream water generation but it does not interfere with the calculations of the relative contributions from the subsurface components the results show that the deep groundwater constitutes between 5 and 20 of the subsurface water discharge into the stream water the highest values of the deep groundwater fraction occur during base flow soil water dominates during snowmelt seasons whereas during base flow it is the least important fraction soil water accounts for 10 100 of the subsurface water discharge into the stream water shallow groundwater accounts for up to 80 of the subsurface water discharge with the lowest values at peak discharge during snowmelt seasons and the highest values during base flow the validity of the model was tested by comparing the measured 87sr 86sr ratios in the stream water with the 87sr 86sr ratios predicted by the model there was a systematic difference between the measured and modelled 87sr 86sr ratios which suggests that the fraction of soil water is overestimated by the model especially during spring flood as a consequence of this overestimation of soil water the amount of shallow groundwater is probably underestimated during this period however it is concluded that the differences between measured and predicted values are relatively small and that element ratios are potentially effective tracers for different subsurface water flowpaths in catchments

detrital fine grained sediment contribution from taiwan to the northern south china sea and its relation to regional ocean circulation article i nfo results of clay mineralogy in 140 samples collected in major rivers and lakes in southwestern taiwan and on the seafloor off taiwan in the northeastern south china sea scs combined with clay mineral records of the pearl river drainage basin rivers in luzon and the south china shelf and slope are used to semi quantitatively evaluate the detrital fine grained sediment contribution of taiwan to the northern scs the clay mineral assemblage of the taiwan sourced sediments consists dominantly of illite average 56 and chlorite 41 with very scarce kaolinite and smectite their respective distribution from the rivers and lakes to the seafloor off taiwan does not show obvious basin wide differences linear correlations of illite chemistry index with illite crystallinity and of illite crystallinity with kaolinite present two end members of provenances the pearl river and taiwan for the south china shelf and slope assuming that kaolinite in the northern scs is provided completely from the pearl river the contribution of taiwan in clay minerals is evaluated as 29 to the south china shelf and 23 to the south china slope respectively accordingly the contribution of the pearl river to the south china shelf and slope is 52 and 31 respectively the luzon arc accounts for the rest of clay mineral components for the northern scs mainly by providing smectite the bashi strait crossed branches of the southward deep north pacific deep water and the northward surface kuroshio current in the western pacific may transport taiwan sourced suspended sediments westwards to the northern scs

sph modeling of dynamic impact of tsunami bore on bridge piers abstract the smoothed particle hydrodynamics sph method is applied to investigate the impact of a tsunami bore on simplified bridge piers in this study this work was motivated by observations of bridge damage during several recent tsunami events and its aim is to further the understanding of the dynamic interaction between a tsunami bore and a bridge pier this study is carried out by simulating a well conducted physical experiment on a tsunami bore impingement on vertical columns with an sph model gpusph the influences of bridge pier shape and orientation on free surface evolution and hydrodynamic loading are carefully examined furthermore the unsteady flow field that is around and in the wake of the bridge pier is analyzed finally gpusph is applied to explore the hydrodynamic force caused by the bridge pier blockage the wave impact on structures and the bed shear stress around a bridge pier due to a strong tsunami bore

sm nd isotope systematics in deep sea sediments clay size versus coarser fractions sm nd studies were carried out on last glacial and holocene sediments from the labrador sea three grain size fractions were analyzed for each sediment the clay size fraction 2 m the fine cohesive silts 2 10 m and the coarse silts 10 63 m in most cases sm nd s ignatures are different from one grain size to anot her in addition different sm nd signatures are derived fr om the clay size fractions compared to the cohesive silt fraction indicating that the cohesive fraction is heterogeneous and that distinct origins in terms of source areas are implied silt fractions record the influence of supplies from the north american precambrian shield whereas clay size fractions 2 m are more sensitive to s edimentary input from the eastern basins in relati on with deep currents coupling sm nd studies on silt and c lay fractions may be a powerful tool to unravel the evolution of deep circulations versus detrital supplies

amplitude variations of 1470 year climate oscillations during the last 100 000 years linked to fluctuations of continental ice mass we describe amplitude variations of a 1470 year y signal in the oxygen isotope record from the gisp2 ice core as a function of continental ice mass as recorded in sea level variations the 1470 y signal is closely tied to dansgaard oeschger interstadial events which perturbed the climate system on a global scale large amplitude 1470 y oscillations occur only if continental ice mass exceeds a threshold level equivalent to sea level at approximately 45 m and are tied to times of change in ice mass minima of the 1470 y signal in the greenland ice are associated with short time intervals of relatively stable phases of sea level and with reduced climate variability in the entire periodicity range between approximately 550 5000 y

source discriminants for near field tsunamis summary we present numerical simulations of tsunami run up in the near field for a data set of 72 models of sources involving both seismic dislocations and landslides by varying one by one the parameters describing the source and the receiving beach we are able to separate their individual influence on the amplitude and distribution of run up which we characterize by forming several dimensionless parameters principally the ratio i 2 of its maximum amplitude to its lateral extent along the beach we find that i 2 remains less than 10 4 for seismic dislocation sources but is greater than this threshold for all physically realistic models of underwater landslides thus it can be used as a discriminant for the nature of the source of a near field tsunami for seismic dislocations we also consider the ratio i 1 of maximum run up to seismic slip on the fault plane and validate numerically the previously suggested rule of thumb that this ratio cannot be much greater than 1 in the case of underwater landslides we show that the distribution of near field run up is primarily controlled by the 2 d wall of water displaced on the ocean surface as an initial condition to the simulation and is practically independent of its extension in the third dimension perpendicular to the beach we apply this approach to nine profiles of tsunami run up obtained experimentally during recent field surveys and show that our method successfully identifies the 1998 papua new guinea tsunami as having been generated by an underwater landslide thus confirming the results of shipboard and hydroacoustic investigations it also strongly suggests a similar mechanism for the generation of the near field aleutian tsunami of 1946 april 1