diatom inferred salinity in palaeolakes an indirect tracer of climate change lakes in arid and semi arid regions respond to climatic change through shifts in lake water volume and ionic concentration because diatom distribution is highly correlated with lake hydrochemistry diatoms can be used to infer changes in salinity and brine composition and thus to infer past climates here we critically examine the use of diatom inferred salinity as a climate proxy with examples taken from both modern waterbodies and sedimentary profiles sediment records may contain assemblages mixed from periods or sites of differing hydrochemistries because of the high degree of spatial and temporal heterogeneity in saline systems dissolution and diagenesis in saline brines may further complicate interpretation of sedimentary assemblages furthermore threshold effects salinity regulation via groundwater seepage antecedent conditions and other aspects of local hydrology may modify the relationship between salinity change and climatic forcing these complexities necessitate critical examination of the ecology and taphonomy of sedimentary assemblages as well as evaluation of potential non linearities in the salinity climate relationship through comparison of diatom inferred salinity with other proxy records of hydrochemical change historical documents where they exist and with other regional lake systems

paleovegetation simulations of lowland amazonia and implications for neotropical allopatry and speciation paleovegetation modeling simulations of the lowland amazon basin were made to assess the relative importance of glacial climate and atmospheric co2 for altering vegetation type and structure as well as to explore the potential physiological mechanisms underlying these ecosystem level responses modeling results support the view that widespread invasion of grasslands into the amazon lowlands during the last glaciation was not likely glacial cooling was probably responsible for maintaining glacial forest cover via its effects in reducing photorespiration and decreasing evapotranspiration which collectively improve plant carbon and water relations modeling results confirm that leaf area index lai a common proxy for canopy density is highly sensitive to independent and interactive changes in climate and low concentration of atmospheric co2 and the results show considerable region to region variation during the last glaciation heterogeneous variations in glacial vegetation lai may have promoted allopatric speciation by geographically isolating species called vicariance in the forest sub canopy the proposed vicariance hypothesis incorporating spatial variations in canopy density conforms to many of the essential tenets addressed by previous neotropical speciation models but also helps to overcome some of their inconsistencies c 2001 university of washington

an 15 000 year record of el nino driven alluviation in southwestern ecuador debris flows have deposited inorganic laminae in an alpine lake that is 75 kilometers east of the pacific ocean in ecuador these storm induced events were dated by radiocarbon and the age of laminae that are less than 200 years old matches the historic record of el nino events from about 15 000 to about 7000 calendar years before the present the periodicity of clastic deposition is greater than or equal to 15 years thereafter there is a progressive increase in frequency to periodicities of 2 to 8 5 years this is the modern el nino periodicity which was established about 5000 calendar years before the present this may reflect the onset of a steeper zonal sea surface temperature gradient which was driven by enhanced trade winds

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

source parameters of the shallow 2012 brawley earthquake imperial valley resolving earthquake parameters especially depth is difficult for events occurring within basins because of issues involved with separating source properties from propagational path effects here we demonstrate some advantages of using a combination of teleseismic and regional waveform data to improve resolution following a bootstrapping approach local ss s differential arrivals from a foreshock are used to determine a local layered model which can then be used to model teleseismic depth phases pp sp and ss using the cut and paste cap method for which all strike dip rake and depth variations are sampled for several crustal models we find that regional data prove the most reliable at fixing the strike whereas the depth is better constrained by teleseismic data weighted solutions indicate a nearly pure strike slip mechanism 59 1 with a centroid depth of about 4 0 km and an m w of 5 4 for the mainshock of the 2012 brawley earthquake

depth determination of the 2010 el mayor cucapah earthquake sequence m 4 0 the 2010 m w 7 2 el mayor cucapah earthquake ruptured a zone of 120 km in length in northern baja california the geographic distribution of this earthquake sequence was well constrained by waveform relocation the depth distribution however was poorly determined as it is near the edge of or outside the southern california seismic network here we use two complementary methods to constrain the focal depths of moderate sized events m 4 0 in this sequence we first determine the absolute earthquake depth by modeling the regional depth phases at high frequencies 1 hz we mainly focus on pn and its depth phases ppn and spn which arrive early at regional distance and are less contaminated by crustal multiples to facilitate depth phase identification and to improve signal to noise ratio we take advantage of the dense southern california seismic network and use array analysis to align and stack pn waveforms for events without clear depth phases we further determine their relative depths with respect to those with known depths using differential travel times of the pn direct p and direct s phases recorded for event pairs focal depths of 93 out of 122 m 4 0 events are tightly constrained with absolute uncertainty of about 1 km aftershocks are clustered in the depth range of 3 10 km suggesting a relatively shallow seismogenic zone consistent with high surface heat flow in this region most aftershocks are located outside or near the lower terminus of coseismic high slip patches of the main shock which may be governed by residual strains local stress concentration or postseismic slip

a vegetation and fire history of lake titicaca since the last glacial maximum fine resolution fossil pollen and charcoal analyses reconstruct a vegetation and fire history in the area surrounding lake titicaca 3810 m peru bolivia since ca 27 500 cal yr bp hereafter bp time control was based on 26 accelerator mass spectrometer ams radiocarbon dates seventeen ams dates and 155 pollen and charcoal samples between ca 17 500 bp and ca 3100 bp allow a centennial scale reconstruction of deglacial and early to mid holocene events local and regional fire signals were based on the separation of two charcoal size fractions 180 m and 179 65 m charcoal abundance correlated closely with the proportion of woody taxa present in the pollen spectra little or no pollen was detected in the sedimentary record prior to ca 21 000 bp very cold climatic conditions prevailed with temperatures suggested to be at least 5 8 c cooler than present increases in pollen concentration suggest initial warming at ca 21 000 bp with a more significant transition toward deglaciation ca 17 700 bp between 17 700 bp and 13 700 bp puna brava is progressively replaced by puna and sub puna elements the most significant changes between the pleistocene and the holocene floras were largely complete by 13 700 bp providing an effective onset of near modern conditions markedly earlier than in other andean records fire first occurs in the catchment at ca 17 700 bp and becomes progressively more important as fuel loads increase no evidence is found of a rapid cooling and warming coincident with the younger dryas chron a dry event between ca 9000 bp and 3100 bp with a peak between 6000 and 4000 bp is inferred from changes in the composition of aquatics and the marsh community as pollen of cyperaceae is replaced by poaceae apiaceae plantago and the shrub polylepis human disturbance of the landscape is evident in the pollen spectra after ca 3100 bp with the appearance of weed species

the geochemical evolution of halite structures in hypersaline lakes the dead sea israel depressions in the floor of the southern basin of the dead sea contain dense 1 26 l 29 g cm 3 brines which formed by evaporation at the lake s surface absorbance of solar radiation heats these brines by about 2 4 c d l as long as the density gradient of the lake prevents overturn as a result bottom halite is dissolved in the warmer brines at about 0 4 g nacl liter c i continuous heating of the brine of these holes and cooling of the overlying liquids at night causes frequent overturns of the brine column followed by mixing and cooling of the nacl rich brine the extra load of halite is precipitated near the holes in the form of halite cones and mushroomlike structures whereas the initial nacl supply to the growing halite structures comes from the floor of the lake the later growth stage is supported by nacl supplied from the upper evaporating brine layer crude mass and heat balances show that the proposed model may well explain the occurrence and distribution of halite islands in the dead sea the model may be applicable to any shallow enough a few meters hypcrsaline lake that is saturated with respect to halite the dead sea is composed of a ca chloridic brine the evolution of which has been proposed by starinsky 1974 the physiography limnology and sedimentological regime of the lake have been studied and described by neev and emery 1967 among many others the dead sea is comprised of two parts a northern basin 300 m deep which forms the bulk of the lake s volume and area and a southern shallow mostly 2 4 m deep basin fig 1 dwindling precipitation since about 1930 klein 1985 and diversion of water from the dead sea drainage system for agricultural needs resulted in the continuous lowering of the lake level at a rate of 50 cm yr l finally toward the end of the 1 960s the two basins became separated since then the brine level in the southern basin is maintained artificially evaporation of the brine results in enrichment of most of its dissolved salts with respect to their concentrations in the northern basin exceptions are na and s042 which are precipitated from

boron isotope geochemistry as a tracer for the evolution of brines and associated hot springs from the dead sea israel abstract a boron isotope study combined with analyses of elemental boron lithium and chlorine is used to suggest that brines from the dead sea and on shore hypersaline thermal springs hamme yesha hamme zohar and hamme mazor are the products of interaction of evaporated seawater with detrital sediments the high 11b values of the dead sea brines 55 7 to 57 4 versus nbs 951 and the hot springs 52 2 to 55 7 and low b li ratios 2 0 to 2 3 and 2 5 to 2 7 respectively relative to seawater indicate preferential removal of 10b from the brines and hence boron adsorption onto clay minerals the brackish en feshcha springs and the freshwater en dawid and nahal arugot springs yield lower b contents and 11b values 37 7 to 40 6 and 33 8 to 36 9 respectively the 11b values and b contents of diluted dead sea brines lie on calculated mixing lines between the composition of the brackish and freshwater springs with the composition of the dead sea the 11 b values of the hot springs however given their boron content are significantly lower than those of the mixing lines thus waters from the hot springs cannot be a mixing product of the dead sea brine with freshwater instead the dead sea brine has evolved from the brines of the hot springs through further isotopic fractionation and boron adsorption onto detrital sediments

crustal and upper mantle velocity structure of the salton trough southeast california this paper presents data and modelling results from a crustal and upper mantle wide angle seismic transect across the salton trough region in southeast california the salton trough is a unique part of the basin and range province where mid ocean ridge transform spreading in the gulf of california has evolved northward into the continent in 1992 the u s geological survey usgs conducted the final leg of the pacific to arizona crustal experiment pace two perpendicular models of the crust and upper mantle were fit to wide angle reflection and refraction travel times seismic amplitudes and bouguer gravity anomalies the first profile crossed the salton trough from the southwest to the northeast and the second was a strike line that paralleled the salton sea along its western edge we found thin crust 21 22 km thick beneath the axis of the salton trough imperial valley and locally thicker crust 27 km beneath the chocolate mountains to the northeast we modelled a slight thinning of the crust further to the northeast beneath the colorado river 24 km and subsequent thickening beneath the metamorphic core complex belt northeast of the colorado river there is a deep apparently young basin 5 6 km unmetamorphosed sediments beneath the imperial valley and a shallower 2 3 km basin beneath the colorado river a regional 6 9 km s layer between 15 km depth and the moho underlies the salton trough as well as the chocolate mountains where it pinches out at the moho this lower crustal layer is spatially associated with a low velocity 7 6 7 7 km s upper mantle we found that our crustal model is locally compatible with the previously suggested notion that the crust of the salton trough has formed almost entirely from magmatism in the lower crust and sedimentation in the upper crust however we observe an apparently magmatically emplaced lower crust to the northeast outside of the salton trough and propose that this layer in part predates salton trough rifting it may also in part result from migration of magmatic spreading centers associated with the southern san andreas fault system these spreading centers may have existed east of their current loca tions in the past and may have influenced the lower crust and upper mantle to the east of the current salton trough

determining moho depth beneath sedimentary basins using regional pn multiples the study of the moho beneath thick sedimentary basins involving natural earthquakes is challenging as low velocity materials often cause strong reverberations that mask moho signals here we develop a method to determine the depth of the moho by taking advantage of the presence of the sediments the method utilizes the first pn crustal multiple from regional earthquakes pnpn and its differential travel time with respect to pn pnpn is usually weak in amplitude thus it is difficult to identify in regions without a sedimentary cover however pnpn is significantly amplified in the presence of low velocity sediments because of an increase in the near surface p to p reflection coefficient the arrival time amplitude and wave shape of pnpn if normalized by the reference pn are insensitive to earthquake source parameters such as focal mechanism and focal depth we demonstrate the potential of this method using both 1d and 2d waveform simulations synthetic waveforms suggest that pmppn and pnpmp one pn leg merges to pmp near the source or the receiver largely contribute to the pnpn amplitudes which depend on the near surface structure at their free surface p to p reflection points we further validate the method with two field examples in the imperial valley one is near the united states mexico border and the other is in oklahoma in the central united states both examples suggest that the method can be used to study the moho either near the source or the receiver

subsurface geometry of the san andreas fault in southern california results from the salton seismic imaging project ssip and strong ground motion expectations the san andreas fault saf is one of the most studied strike slip faults in the world yet its subsurface geometry is still uncertain in most locations the salton seismic imaging project ssip was undertaken to image the structure surrounding the saf and also its subsurface geometry we present ssip studies at two locations in the coachella valley of the northern salton trough on our line 4 a fault crossing profile just north of the salton sea sedimentary basin depth reaches 4 km southwest of the saf on our line 6 a fault crossing profile at the north end of the coachella valley sedimentary basin depth is 2 3 km and centered on the central most active trace of the saf subsurface geometry of the saf and nearby faults along these two lines is determined using a new method of seismic reflection imaging combined with potential field studies and earthquakes below a 6 9 km depth range the saf dips 50 60 ne and above this depth range it dips more steeply nearby faults are also imaged in the upper 10 km many of which dip steeply and project to mapped surface fault traces these secondary faults may join the saf at depths below about 10 km to form a flower like structure in appendix d we show that rupture on a northeast dipping saf using a single plane that approximates the two dips seen in our study produces shaking that differs from shaking calculated for the great california shakeout for which the southern saf was modeled as vertical in most places shorter period t 1 s shaking is increased locally by up to a factor of 2 on the hanging wall and is decreased locally by up to a factor of 2 on the footwall compared to shaking calculated for a vertical fault

moisture changes and fluctuations of the westerlies in mediterranean central chile during the last 2000 years the laguna aculeo record 33 50 s abstract the multi proxy study of lacustrine sediments from laguna aculeo 33 50 s provides detailed information about moisture changes in the lowlands of mediterranean central chile during the last 2000 years the lake lies just at the northern border of the strong westerlies influence with dry summers and humid winters geochemical sedimentological and diatom analyses provide evidence for an arid period between cal 200 bc and ad 200 and a subsequent increase in moisture after cal ad 200 abundant clastic layers in the core represent flood events periods with a higher frequency of flood events indicate an increased intensity of the westerlies more winter frontal system activity and possibly enso related variability probably comparable to modern conditions in mediterranean central chile periods of high clastic input occur around cal ad 200 400 500 700 especially around cal ad 1300 1700 and around ad 1850 1998 during the last 50 years at least eight flood events were detected correlating mainly with el nino years a very short drier period also occurred in the late 1960s in recent decades human impact has resulted in a eutrophication of the lake

a seismic refraction survey of the imperial valley region california the u s geological survey conducted an extensive seismic refraction survey in the imperial valley region of california in 1979 the imperial valley is located in the salton trough an active rift between the pacific and north american plates forty shots fired at seven shot points were recorded by 100 portable seismic instruments at typical spacing of 0 5 1 km more than 1300 recording locations were occupied and more than 3000 usable seismograms were obtained we analyzed five profiles using a standard ray tracing program constructed a contour map of reduced travel times from our most widely recorded shot point and modeled an existing gravity profile across the salton trough results are itemized 1 all models have in common a sedimentary layer vp 1 8 5 0 km s a transition zone vp 5 0 5 65 km s a basement vp 5 65 km s in the imperial valley 5 9 km s on the bordering mesas and subbasement vp 7 2 km s 2 the sedimentary layer ranges in thickness along the axis of the salton trough from 3 7 km salton sea to 4 8 km u s mexican border on the bordering mesas it is quite variable in thickness 3 the transition zone is about 1 km thick in most places in the imperial valley there are no marked velocity discontinuities in this zone between the sedimentary layer and basement on the bordering mesas however there is a discontinuity at the top of this zone 4 there are apparently two types of basement on the bordering mesas basement is crystalline igneous and metamorphic rocks in the imperial valley basement is mostly lower greenshist facies sedimentary rocks based primarily on the smooth transition in character from sediment to basement arrivals the low value of basement velocity and the fact that deep 4 km wells in the valley penetrate only the upper part of the known cenozoic stratigraphic column for the salton trough 5 the subbasement or intermediate crustal layer ranges in depth along the axis of the salton trough from 16 km salton sea to 10 km u s mexican border gravity modeling requires that this layer deepen and or pinch out beneath the bordering mesas and mountain ranges based on its high velocity and the presence of intrusive basaltic rocks in the sedimentary section in the imperial valley the subbasement is thought to be a mafic intrusive complex similar to oceanic middle crust 6 several structures are seen that affect basement transition zone and deeper parts of the sedimentary layer they include a scarp along the imperial fault as much as 1 km down to the northeast and a scarp passing roughly along the topographic boundary between the imperial valley and the bordering mesa to the west as much as 3 km down to the east we interpret the latter scarp to be the suture or rift boundary between the older crystalline basement on the mesa and the younger metasedimentary basement in the imperial valley 7 on a contour map of reduced travel time from our most widely recorded shot point subtle patches of early arrivals among otherwise late arrivals in the central imperial valley correlate well with known geothermal resource areas having reservoir temperatures of more than 150 c apparently the salton trough is a location where new crust is being generated as the rift opens mafic intrusive rocks fill it from below as sedimentary rocks fill it from above rifting and intrusion produce high heat flow that metamorphoses the sedimentary rocks to shallow depth metasedimentary basement in the imperial valley and thus consolidates the new crust

salt precipitation and dissolution in the late quaternary dead sea evidence from chemical and δ 37 cl composition of pore fluids and halites abstract the chemical composition and 37 cl of pore fluids from the icdp core drilled in the deepest floor of the terminal and hypersaline dead sea and halites from the adjacent mount sedom salt diapir are used to establish the dynamics of halite precipitation and dissolution during the last interglacial and glacial periods between 132 and 116 thousand years ago ka halites precipitated in the lake resulting in the expulsion of na and cl from the residual solution over 50 of the cl reservoir was removed resulting in a decrease in the na cl ratio from 0 57 to 0 19 this process was accompanied by a decrease in 37 cl values in the precipitating halites and the associated residual cl in the lake the observed decrease fits a rayleigh distillation curve with a fractionation factor of nacl dead sea solution 0 32 0 12 determined in the present study this behavior implies negligible contribution of external sources of cl to the lake during the main peak of the last interglacial mis5e subsequently during the last glacial ca 117 to 17 ka dissolution of halite took place the na and cl inventory were replenished accompanied by an increase in na cl from 0 21 to 0 55 and in the 37 cl values from 0 46 to 0 12 while the lake underwent significant dilution during that time the decrease in salinity was somewhat suppressed by the dissolution of the halite which was mostly derived from mount sedom salt diapir

episodic sediment accumulation on amazonian flood plains influenced by el nino southern oscillation continental scale rivers with a sandy bed sequester a significant proportion of their sediment load in flood plains the spatial extent and depths of such deposits have been described and flood plain accumulation has been determined at decadal timescales but it has not been possible to identify discrete events or to resolve deposition on near annual timescales here we analyse 210 pb activity profiles from sediment cores taken in the pristine beni and mamore river basins which together comprise 720 000 km2 of the amazon basin to investigate sediment accumulation patterns in the andean amazonian foreland we find that in most locations sediment stratigraphy is dominated by discrete packages of sediments of uniform age which are typically 20 80 cm thick with system wide recurrence intervals of about 8 yr indicating relatively rare episodic deposition events ocean temperature and stream flow records link these episodic events to rapidly rising floods associated with la nina events which debouch extraordinary volumes of sediments from the andes we conclude that transient processes driven by the el nino southern oscillation cycle control the formation of the bolivian flood plains and modulate downstream delivery of sediments as well as associated carbon nutrients and pollutants to the amazon main stem

strontium isotope evidence on the history of oilfield brines mediterranean coastal plain israel abstract the isotopic composition of sr in oil field brines from the mediterranean coastal plain was determined in 18 drillholes 13 of which are oil producing wells the brines are characterized by salinities ranging from 35 to 93 g l tds sr from 28 to 350 mg l sr ca molar ratios from 0 011 to 0 053 and 87 sr 86 sr ratios from 0 7075 to 0 7090 e a 0 7081 0 0004 2 the brines are classified into two groups 1 a mavqi im group brines with relatively high 87 sr 86 sr ratios 0 7087 and 0 7090 sampled from elastics dolomites and anhydrites of upper miocene age 2 b heletz group brines with relatively low 87 sr 86 sr ratios 0 7075 to 0 7081 sampled from sandstones and dolomites of lower cretaceous age equations were derived to show the relations between 87 sr 86 sr ratio of the brines and the processes through which they evolved dolomitization and dissolution reprecipitation it is suggested that both groups of brines originated from mediterranean evaporated seawater during the messinian desiccation the strontium isotope composition of the seawater is reflected in that of both groups of brines the mavqi im group containing the original 87 sr 86 sr ratio 0 7088 the heletz group evolved later on through exchange reactions of those primary brines with a carbonate sequence of cretaceous age and consequently new 87 sr 86 sr ratios 0 7078 could have been developed the effect of the dissolution reprecipitation reactions on the carbonate rocks is estimated to be very slight only around 1 by weight

amazonian paleoecological histories one hill three watersheds abstract data from the hill of six lakes in the northwestern brazilian amazon region provide three records of paleoclimatic and vegetation change in lowland amazonia that span the last 170 000 years three lakes verde pata and dragao which occupy separate watersheds on the hill provide the most detailed image yet obtained of ice age conditions in lowland amazonia well dated sedimentary records for fossil palynological charcoal cation and pigment data are presented the data indicate the continuous presence of mesic forest throughout the last ice age oscillations of lake level are recorded and the lowstands are attributed to reduced precipitation inputs to systems delicately balanced between water loss leakage through the floor of the basin and gain precipitation gross stratigraphy algal remains and paleochemistry suggest that the stands of high and low lake level were cyclic apparently correlating precessional orbital variation times of lake lowstand coincide with wet season december january february djf insolation minima the strongest of eight lowstand cycles occurred ca 35 000 to 27 000 cal bp even during lowstand episodes pollen is well preserved and provides a clear signal of uninterrupted forest cover the principal lowland elements are continuously present in the record suggesting the long term quaternary availability of the lowland forest biome in this region however during the late pleistocene the forest changed in composition with the expansion or invasion of montane floral elements creating communities of the mesic forest biome without modern analogs while precipitation cycles were causing lake levels to rise and fall the principal influence on vegetation appears to have been cooling in the late pleistocene the population expansion of montane elements at lower elevations is consistent with a cooling of 4 5 c

internal structure of the dead sea leaky transform rift in relation to plate kinematics abstract the structures along the dead sea transform rift are related to the motions of the sinai and arabia plates which border it and to the irregularities of their boundaries the total slip was 105 km left lateral but the present structures were formed mainly during the last 40 km of slip which probably occurred in the plio pleistocene along the southern half of the transform the strike slip motion takes place on en echelon faults this produces rhomb shaped grabens or pull aparts which are sometimes composite and in which there is local crustal separation thus much of the transform is leaky these structures occur in a morpho tectonic rift valley delimited by normal faults which express a small component of transverse extension along a few segments the shape of the transform is such that lateral motion produces local transverse compression the geometric relations of the structures along the transform define an eulerian pole of relative plate motions at 32 8 n 22 6 e 0 5 the older motion was somewhat different and is described by a pole located about 5 west of the above then the component of transverse extension and crustal separation was much smaller than now while local transverse compression was more important the northern half of the dead sea transform has an irregular shape and the bordering plates did not remain rigid as lateral motion continued here transverse compression is often important

pore fluids in dead sea sediment core reveal linear response of lake chemistry to global climate changes pore fluids extracted from a 456 m sediment core recovered within the framework of a multinational and international continental scientific drilling program icdp co sponsored effort at the bottom of the terminal dead sea recorded the chemical variations in the deep lake over the past 220 k y mg 2 and br were shown to be conservative in the pore fluids increasing in concentration during interglacial periods diluting during glacials and providing excellent proxies for deep lake net water balance changes furthermore the na cl ratio recorded the process of halite precipitation and dissolution induced by these hydrological changes mg 2 and br records follow a glacial interglacial pattern such as observed in atmospheric co 2 concentrations and global sea surface temperatures albeit with a phase offset at the end of the last interglacial ca 116 ka there is a delay in onset of dilution of the deep lake most likely due to the limnological transition from holomictic to meromictic conditions the increase in deep lake concentrations at last glacial termination i is delayed as a result of freshwater input into the deep lake during the cooler younger dryas period there is a persistent relationship between precipitation in the watershed and north atlantic sea surface temperatures similar to conditions observed over the past instrumental record deviations from the long term trends occurred during interglacial periods marine isotope stages mis 5e and mis 1 when the deep dead sea was significantly diluted and coincided with mediterranean sapropel layers s5 and s1

a reevaluation of the evidence for a younger dryas climatic reversal in the tropical andes abstract a review of the evidence for a younger dryas equivalent climatic reversal in the tropical andes shows that a number of hypotheses need to be reassessed assumptions of the el abra cold and humid phase in colombia are compromised by insufficient dating control periods of glacier advance in peru and bolivia lack sufficient dating control to be correlated with the european younger dryas only glaciers on the quelccaya ice cap in peru may have advanced shortly before the onset of the european climatic reversal but even there a correlation is questionable a late glacial advance in the chimborazo area in ecuador is considerably older than previously suggested the same glacier advance has been dated to earlier than 12 000 bp in other areas of ecuador the emerging picture suggests two phases of glacier advances in the tropical andes 13 000 12 000 bp and 9000 10 000 bp both may have been caused by increasing precipitation unequivocal evidence for a cold younger dryas event in the tropical andes has yet to emerge

ice core palaeoclimate records in tropical south america since the last glacial maximum ice core records spanning the last 25 000 yr from the tropical andes of south america are reviewed these records from quelccaya huascaran and sajama present a high temporal resolution picture of both the late glacial stage lgs and the holocene climatic and environmental conditions in the south american andes late glacial stage conditions at high elevations appear to have been cooler than today although the magnitude of the inferred cooling differs with the particular proxy used e g snowline depression pollen ice cores insoluble dust and anion concentrations in the ice cores reveal that lgs hydrological conditions in the tropics 9 s were much drier than today whereas in the subtropics 18 s lgs conditions were much wetter this probably reflects the migration of the tropical hadley cell in response to a different meridional temperature gradient low nitrate concentrations in the lgs ice from both huascaran and sajama suggest that the amazon basin forest cover may have been much less extensive discussed is the conundrum surrounding the use of d 18 o as a palaeothermometer in the tropics where temperatures exhibit little seasonal variation yet the ice core records suggest that d 18 o records temperature variations on decadal to millennial time scales finally evidence is presented for a strong twentieth century warming copyright 2000 john wiley sons ltd

sinkhole swarms along the dead sea coast reflection of disturbance of lake and adjacent groundwater systems more than a thousand sinkholes have developed along the western coast of the dead sea since the early 1980s more than 75 of them since 1997 all occurring within a narrow strip 60 km long and 1 km wide this highly dynamic sinkhole development has accelerated in recent years to a rate of 150 200 sinkholes per year the sinkholes cluster mostly over specific sites up to 1000 m long and 200 m wide which spread parallel to the general direction of the fault system associated with the dead sea transform research employing borehole and geophysical tools reveals that the sinkhole formation results from the dissolution of an 10 000 yr old salt layer buried at a depth of 20 70 m below the surface the salt dissolution by groundwater is evidenced by direct observations in test boreholes these observations include large cavities within the salt layer and groundwater within the confined subaquifer beneath the salt layer that is undersaturated with respect to halite moreover the groundwater brine within the salt layer exhibits geochemical evidence for actual salt dissolution na cl 0 5 0 6 compared to na cl 0 25 in the dead sea brine the groundwater heads below the salt layer have the potential for upward cross layer flow and the water is actually invading the salt layer apparently along cracks and active faults the abrupt appearance of the sinkholes and their accelerated expansion thereafter reflects a change in the groundwater regime around the shrinking lake and the extreme solubility of halite in water the eastward retreat of the shoreline and the declining sea level cause an eastward migration of the fresh saline water interface as a result the salt layer which originally was saturated with dead sea water over its entire spread is gradually being invaded by fresh groundwater at its western boundary which mixes and displaces the original dead sea brine accordingly the location of the western boundary of the salt layer which dates back to the shrinkage of the former lake lisan and its transition to the current dead sea constrains the sinkhole distribution to a narrow strip along the dead sea coast the entire phenomenon can be described as a hydrological chain reaction it starts by intensive extraction of fresh water upstream of the dead sea continues with the eastward retreat of the lake shoreline which in turn modifies the groundwater regime finally triggering the formation of sinkholes

changes in the thermo haline structure of the dead sea 1979 1984 abstract from 1979 to 1984 the overall water balance of the dead sea was characterized by a water deficit however an excess of freshwater inflow during the 1979 80 rainy season resulted in a 3 year long meromictic phase this was followed by three consecutive overturns of the water column in december 1982 1983 and 1984 the buildup and dissipation of the seasonal thermocline and halocline is followed throughout this period which covers a wide range of water balance situations the gravitational stabilities of the summer pycnoclines measured in terms of n 2 3 10 2 s 2 are at least one order of magnitude greater than the values reported in freshwater lakes and oceans the contributions of temperature and salinity to n 2 and to the integrated stability w are examined separately and their interdependence is pointed out two irreversible effects in the evolution of the properties of the water masses are identified 1 a monotonic increase in the density of the deep waters and 2 a monotonic shift of the nacl saturation curve towards higher salinities

the solubility of halite as a function of temperature in the highly saline dead sea brine system the dead sea brine is characterized by high ionic strength 9 10 m and a ca cl composition the lake is currently saturated with respect to aragonite gypsum and halite harned s rule is applied to calculate the saturation index of halite in the dead sea brine system this system includes brines at ionic strengths in the range of 9 l 6 1 derived from evaporating dead sea brine to facilitate the calculation we determined new interaction coefficients experimentally these were found to be a function of the ionic strength of the solution as well as of the temperature 25 c anaa mgc12 0 002611 0 00905 anac1 caci 0 001501 0 00650 3 5 c anac l m cl 0 002831 0 01972 anacl caci 0 002071 0 01851 50 c anaci m l 0 002261 0 01416 anaci cacl 0 001561 0 01315 the new parameters are used to predict the effect of temperature on halite precipitation in the lake from both the evaporating surface layer and the entire upper water body the calculated weight of halite expected to precipitate before the onset of carnallite precipitation is on the order of lo o t at the present rate of evaporation at least 120 yr will pass before that point is reached

the last glacial maximum stability and change in a western amazonian cloud forest the climatic and vegetation history of a western amazonian cloud forest is documen ted in a continuous pollen record spanning the full last glacial period between 43 5 and 22k cal yr bp the chronology for this record is based on eight radiocarbon dates yielding a low resolu tion pollen analysis for the region a bioclimatic envelope model was generated on the basis of mod ern altitudinal distributions and the pollen data which produced a glacial palaeotemperature estimate of ca 5 c relative to present palaeoecological evidence of continuous moist cloud forest cover in the basin indicates that western amazonian forests were not fragmented during the lgm this evidence supports wet conditions in western amazonia at the lgm and further refutes hypotheses of amazonian aridity during the last ca 44k cal yr bp copyright 2005 john wiley sons ltd

optical properties of the dead sea 1 the dead sea located in the rift valley between jordan and israel is a hypersaline lake resulting in unique biogeochemistry and optical properties in the spring of 2004 we conducted two days of physical and optical measurements in the lake because of the significant effect of dissolved salts on the optical properties of water our analysis required a novel processing approach to obtain dissolved and total inherent optical properties from the measurements in addition we show that the lake s salinity can be estimated from measurements of hyper spectral absorption or attenuation spectra in the red and infrared parts of the spectrum using published values of specific absorption of dissolved nacl despite the fact that the lake s salt chemistry is complex in situ observations demonstrated that the lake has a two layer structure with a warm and more turbid layer at the top 20 30 m and a clearer colder layer below both the particulate and dissolved absorption are well approximated by exponentially decreasing functions with the spectral slope of the particulate absorption about half that of the dissolved fraction and consistent with other aquatic environments both have relatively low and similar magnitudes in the blue o 0 15 m 1 mean particle size was observed to increase with depth consistent with precipitating salt crystals observed in past campaigns shown here to play a major role in the lake s optical properties

seasonal variations of halite saturation in the dead sea hypersaline lakes and seas were common in the past precipitating thick evaporitic salt deposits the only modern analogue for the paleo limnology of deep salt saturated aquatic environments exists in the dead sea in this study we present new insights from the dead sea on the role of seasonal thermohaline stratification and water balance on the seasonal and depth variations of the degree of saturation of halite salt and the rate of halite growth along the water column we developed methodologies to accurately determine the empirical degree of halite saturation of the lake based on high accuracy densitometry and to quantify halite growth rate along the water column during summer the epilimnion is undersaturated and halite is dissolved whereas during winter the entire water column is supersaturated and crystallizes halite this result is not trivial because the variations in the water balance suggest the opposite summer is associated with higher loss of water by evaporation from the lake compared to the winter hence the thermal effect overcomes the hydrological balance effect and thus governs the seasonal saturation cycle the hypolimnion is supersaturated with respect to halite and crystallizes throughout the year with higher super saturation and higher crystallization rates during winter during summer simultaneous opposing environments coexist an under saturated epilimnion that dissolves halite and a supersaturated hypolimnion that crystallizes halite which results in focusing of halite deposits in the deep hypolimnetic parts of the evaporitic basins and thinning the shallow epilimnetic deposits this article is protected by copyright all rights reserved

alteration and remelting of nascent oceanic crust during continental rupture evidence from zircon geochemistry of rhyolites and xenoliths from the salton trough california abstract rhyolite lavas and xenoliths from the salton sea geothermal field southern california provide insights into crustal compositions and processes during continental rupture and incipient formation of oceanic crust salton buttes rhyolite lavas contain xenoliths that include granophyres fine grained altered rhyolites felsite and amphibole bearing basalts zircon is present in lavas and xenoliths surprisingly even in the basaltic xenoliths where it occurs in plagioclase rich regions interpreted as pockets of crystallized partial melt zircons in the xenoliths are exclusively late pleistocene holocene in age and lack evidence for inheritance u th isochron ages are 20 5 1 2 1 2 ka granophyres 18 3 3 5 3 6 ka felsite 30 1 12 4 14 1 ka and 9 2 6 6 7 0 ka basalts all errors 1 the dominant zircon population in the rhyolite lavas yielded u th ages between 18 and 10 ka with few pre quaternary xenocrysts present 18ozircon values are lower than typical crustal basement values thus ruling out rhyolite genesis by melting of continental crust moreover 18ozircon values are 0 5 1 0 lower than compositions achievable by zircon crystallization from residual melt in equilibrium with unaltered mid ocean ridge basalt suggesting that basaltic crust and silicic plutons in the subsurface of the salton sea geothermal field isotopically exchanged with meteoric waters this is evidence for deep reaching hydrothermal circulation and indicates rhyolite genesis by episodic remelting of altered basalts instead of fractional crystallization of unaltered basaltic magma

comprehensive analysis of earthquake source spectra and swarms in the salton trough california 1 we study earthquakes within california s salton trough from 1981 to 2009 from a precisely relocated catalog we process the seismic waveforms to isolate source spectra station spectra and travel time dependent spectra the results suggest an average p wave q of 340 agreeing with previous results indicating relatively high attenuation in the salton trough stress drops estimated from the source spectra using an empirical green s function egf method reveal large scatter among individual events but a low median stress drop of 0 56 mpa for the region the distribution of stress drop after applying a spatial median filter indicates lower stress drops near geothermal sites we explore the relationships between seismicity stress drops and geothermal injection activities seismicity within the salton trough shows strong spatial clustering with 20 distinct earthquake swarms with at least 50 events they can be separated into early mmax and late mmax groups based on the normalized occurrence time of their largest event these swarms generally have a low skew value of moment release history ranging from 9 to 3 0 the major temporal difference between the two groups is the excess of seismicity and an inverse power law increase of seismicity before the largest event for the late mmax group all swarms exhibit spatial migration of seismicity at a statistical significance greater than 85 a weighted l1 norm inversion of linear migration parameters yields migration velocities from 0 008 to 0 8 km hour to explore the influence of fluid injection in geothermal sites we also model the migration behavior with the diffusion equation and obtain a hydraulic diffusion coefficient of approximately 0 25 m2 s for the salton sea geothermal site which is within the range of expected values for a typical geothermal reservoir the swarms with migration velocities over 0 1 km hour cannot be explained by the diffusion curve rather their velocity is consistent with the propagation velocity of creep and slow slip events these variations in migration behavior allow us to distinguish among different driving processes

salt dissolution and sinkhole formation results of laboratory experiments the accepted mechanism for the formation of thousands of sinkholes along the coast of the dead sea suggests that their primary cause is dissolution of a salt layer by groundwater undersaturated with respect to halite this is related to the drop in the dead sea level which caused a corresponding drop of the freshwater saltwater interface resulting in fresher groundwater replacing the brines that were in contact with the salt layer in this study we used physical laboratory experiments to examine the validity of this mechanism by reproducing the full dynamic natural process and to examine the impact of different hydrogeological characteristics on this process the experimental results show surface subsidence and sinkhole formation the stratigraphic configurations of the aquifer together with the mechanical properties of the salt layer determine the dynamic patterns of the sinkhole formation instantaneous versus gradual formation laboratory experiments were also used to study the potential impact of future stratification in the dead sea if and when the red sea dead sea canal project is carried out and the dead sea level remains stable the results show that the dissolution rates are slower by 1 order of magnitude in comparison with a nonstratified saltwater body and therefore the processes of salt dissolution and sinkhole formation will be relatively restrained under these conditions

depth of seismicity in the imperial valley region 1977 1983 and its relationship to heat flow crustal structure and the october 15 1979 earthquake focal depths from over 1000 earthquakes occuring between 1977 and 1983 in the imperial valley southern peninsular ranges are used to study relationships between the depth of seismicity heat flow and crustal structure this study used relocated a and b quality events from the california institute of technology catalog that were carefully selected to insure focal depth precision of 2 km regional variations in focal depth appear to be related to regional heat flow variation whereas local variations in focal depth especially in the central imperial valley may be related to crustal structure these variations are studied by rheologic modeling a comparison of focal depths of earthquakes occurring before and after the october 15 1979 m 6 6 earthquake indicates that aftershocks during the first 2 months of the sequence were 2 3 km deeper than earthquakes occurring in other time periods the deepest earthquakes in imperial valley are spatially associated with a subbasement dome near the northern end of the imperial fault this dome coincides with the region where the imperial fault undergoes a transition from stick slip behavior to aseismic fault creep models of slip during the 1979 mainshock are also compared with premainshock and postmainshock seismicity a relocation of the 1940 m 7 1 mainshock suggests that this sequence began by rupturing the same portion of the fault that experienced maximum slip during the 1979 mainshock

sedimentation and crustal recycling along an active oblique rift margin salton trough and northern gulf of california transtensional basins embedded in the san andreas fault system of southern california united states and northwestern mexico are fi lled with sediment derived from the colorado river which drains a large area of the western u s interior the sediment is rapidly buried heated and mingled with intrusions in the deep basins to form a new generation of recycled crust along the active plate boundary using a range of values for total basin depth relative volume of mantle derived intrusions and composition of early rift deposits the volume of colorado river derived sediment in the basins is bracketed between 2 2 and 3 4 10 5 km 3 similar to the volume of rock that likely was eroded from the colorado river catchment over the past 5 6 m y the volumetric rate of crustal growth by sedimentation is 80 130 km 3 m y km comparable to growth rates in subductionrelated island arcs and slow seafl oor spreading centers sedimentary and basinal processes thus play a major role in crustal evolution and recycling in this setting and may be important at other rifted margins where a large river system is captured following tectonic collapse of a prerift orogenic highland

seismic imaging of source region in the 1976 ms 7 8 tangshan earthquake sequence and its implications for the seismogenesis of intraplate earthquakes

forest changes in the amazon basin during the last glacial maximum we report here the discovery of forest beds in the amazon basin radiocarbon dated to the wisconsin wurm glaciation these are the first dates from the last glaciation determined on amazonian samples the locality is in ecuador at 1 100 m elevation near the upper limit of the present amazonian rainforest both pollen spectra and podocarpus wood in the deposits suggest that vegetation comparable to the present andean forest grew at least 700 m lower than it does now suggesting a temperature depression of at least 4 5 c for the amazon lowlands

coprecipitation of trace and minor elements in modern authigenic halites from the hypersaline dead sea brine abstract modern halite samples were collected from the dead sea post 1983 and analyzed for their minor br mn k ca and trace cd pb zn ni element concentrations the halites collected include sedimentary halites with different morphologies and halites which crystallized on ropes suspended in the water body rope halites the mechanisms of minor and trace element coprecipitation with these halites are discussed and their apparent distribution coefficients are calculated dmn 0 09 dk 3 6 10 4 dca 5 10 5 dbr 0 011 dcd 9 3 dpb 3 5 dzn 0 041 dni 0 11 mainly based on the sedimentary halites which represent the slowest crystallization rates and are therefore crystallized at or closest to equilibrium with the brine several types of halites which crystallized at different crystallization rates exhibit large variations in coprecipitated mn and to a lesser degree of coprecipitated k and ca the wide range of calculated dbr and dk values in halites precipitated from the dead sea brine and from evaporated seawater are probably due to kinetic factors and not to differences in the parent brine compositions the present study apparent distribution coefficient values probably best represent both the dead sea brine and evaporated seawater at similar ionic strengths the continuous precipitation of halite since 1983 played a major role in the removal of cd and pb from the dead sea brine and only a minor role in the removal of zn and ni based on estimates of inventories in the dead sea the removal flux of cd and pb are discussed

seismic imaging of the metamorphism of young sediment into new crystalline crust in the actively rifting imperial valley california plate boundary rifting between transform faults is opening the imperial valley of southern california and the rift is rapidly filling with sediment from the colorado river three 65 90 km long seismic refraction profiles across and along the valley acquired as part of the 2011 salton seismic imaging project were analyzed to constrain upper crustal structure and the transition from sediment to underlying crystalline rock both first arrival travel time tomography and frequency domain full waveform inversion were applied to provide p wave velocity models down to 7 km depth the valley margins are fault bounded beyond which thinner sediment has been deposited on preexisting crystalline rocks within the central basin seismic velocity increases continuously from 1 8 km s sediment at the surface to 6 km s crystalline rock with no sharp discontinuity borehole data show young sediment is progressively metamorphosed into crystalline rock the seismic velocity gradient with depth decreases approximately at the 4 km s contour which coincides with changes in the porosity and density gradient in borehole core samples this change occurs at 3 km depth in most of the valley but at only 1 5 km depth in the salton sea geothermal field we interpret progressive metamorphism caused by high heat flow to be creating new crystalline crust throughout the valley at a rate comparable to the 2 km myr sedimentation rate the newly formed crystalline crust extends to at least 7 8 km depth and it is shallower and faster where heat flow is higher most of the active seismicity occurs within this new crust

three dimensional basin and fault structure from a detailed seismic velocity model of coachella valley southern california the coachella valley in the northern salton trough is known to produce destructive earthquakes making it a high seismic hazard area knowledge of the seismic velocity structure and geometry of the sedimentary basins and fault zones is required to improve earthquake hazard estimates in this region we simultaneously inverted first p wave travel times from the southern california seismic network 39 998 local earthquakes and explosions 251 land sea shots from the 2011 salton seismic imaging project to obtain a 3 d seismic velocity model earthquakes with focal depths 10 km were selected to focus on the upper crustal structure strong lateral velocity contrasts in the top 3 km correlate well with the surface geology including the low velocity 5 km s sedimentary basin and the high velocity crystalline basement rocks outside the valley sediment thickness is 4 km in the southeastern valley near the salton sea and decreases to 2 km at the northwestern end of the valley eastward thickening of sediments toward the san andreas fault within the valley defines coachella valley basin asymmetry in the peninsular ranges zones of relatively high seismic velocities 6 4 km s between 2 and 4 km depth may be related to late cretaceous mylonite rocks or older inherited basement structures other high velocity domains exist in the model down to 9 km depth and help define crustal heterogeneity we identify a potential fault zone in lost horse valley unassociated with mapped faults in southern california from the combined interpretation of surface geology seismicity and lateral velocity changes in the model

late quaternary spatio temporal limnological variations in the altiplano of bolivia and peru abstract between the western and eastern andean cordilleras in peru and bolivia there are three main lacustrine basins lake titicaca lake poopo and the group of coipasa uyuni for the past few millennia highly variable environmental conditions have been recorded in their sediments today a latitudinal meteorological gradient influences the lakes status leading to specific deposits and ostracod communities lake titicaca in the north is oligohaline whereas lake poopo further south is polyhaline in the south the coipasa uyuni depression is characterized by a 12 000 km2 surficial salt crust during the late pleistocene ca 40 000 to 25 000 yr b p the water depth and salinity in paleolake poopo fluctuated widely and paleolake titicaca was slightly larger than at present sedimentation was mostly biocarbonate in the shallower areas and it was detrital organic in the deepest zones during the holocene a dry period transformed lake poopo into a salar with evaporite precipitation lake titicaca registered a large decline in water level 8100 3600 yr b p initially inducing gypsum precipitation followed by short influxes of water with an ostracod faunal composition similar to that of the modern brines of lake poopo lake titicacas present condition only appeared between 2200 and 1500 yr b p

how much salt precipitates from the brines of a hypersaline lake the dead sea as a case study abstract the actual density salinity relation gb s of the post 1983 supersaturated dead sea brine is not a fixed thermodynamic constant as it would be in undersaturated brines but rather a combination of two different thermodynamic constants one of them nacl is the brine s expansion coefficient to sodium chloride and relates to the process of halite precipitation and the other is the brine s expansion coefficient to total salts and relates to the dilution evaporation process for every particular period under study the actual density salinity relation gb must be evaluated separately the long term gb for the years 1983 1990 as estimated from climatological data is about 3 u kg g roughly 3 5 times larger than either or nacl a new approach based on the difference between nacl and is applied to the 1983 1990 density record it reveals that salts precipitate from the dead sea brines at a rate of 1 9 10 3 g cm3 y about 77 of which precipitate at the periphery of the lake mostly at the southern tip and only the remaining 23 in the interior of the lake

epitaxial salt reefs and mushrooms in the southern dead sea salt usually accumulates in shallow ephemeral brines as simple flat beds however in permanent brines deepening in solar evaporation ponds in the southern dead sea salt accumulation is complicated by the growth of isolated vegetable like salt structures

astronomical theory of paleoclimates and the last glacial interglacial cycle in the 19th century croll and pilgrim stressed the importance of severe winters as a cause of quaternary ice ages later on mainly during the first half of the 20th century koppen spitaler and milankovitch regarded high winter and low summer insolation as favoring glaciation after koppen and wegener related the milankovitch new radiation curve to penck and bruckner s subdivision of the quaternary there was a long lasting debate whether or not such changes in the insolation can explain the quaternary glacial interglacial cycles in the 1970s with the improvements of radiometric dating and of acquiring and interpreting the long continuous geological records with the advent of computers and with the development of more sophisticated astronomical and climate models the astronomical theory and in particular its milankovitch version were revived over the last 5 years most geological astronomical and climatological obstacles have been overcome and the causal role of the orbital variations in long term variation of climate is taken almost universally for granted models of different categories of complexity from conceptual ones to 3 d atmospheric general circulation models and 2 d time dependent models of the whole climate system have now been astronomically forced in order to test the physical reality of the astronomical theory for example experiments with both low and high resolution gcms show that the increased seasonality at 9 000 bp leads to intensified summer monsoon circulation of africa and southern asia on the other hand seasonal models for simulating the transient response of the climate system to astronomical forcing are also developed and the output of these most recent modeling efforts compares favorably with data of the past 400 000 years accordingly the model predictions for the next 100 000 years are used as a basis for forecasting how climate would evolve when forced by orbital variations in the absence of anthropogenic disturbances the long term cooling trend which began some 6 000 years ago will continue for the next 5 000 years this first temperature minimum will be followed by an amelioration around 15 000 ap after present by a cold interval centered al 23 000 ap and by a major glaciation at around 60 000 ap

a late quaternary diatom record of tropical climatic history from lake titicaca peru and bolivia abstract a composite high resolution diatom stratigraphy from three piston cores and one box core in the deep sub basin of lake titicaca reveals large moisture variations during the past 30 kyr in the altiplano region diatom sequences indicate orbital and millennial scale variability in water level and salinity the pelagic freshwater diatom species cyclotella andina and cyclotella stelligera dominate glacial age sediments suggesting that the lake was above its present outlet generally wet conditions continued until 11 000 cal yr bp as indicated by high percentages of freshwater planktonic diatoms large pulses of benthic diatom species between about 11 000 and 10 000 cal yr bp suggest brief intervals of large amplitude declines in lake level during the early holocene 10 000 8500 cal yr bp a freshwater diatom assemblage suggests overflowing conditions pelagic freshwater diatoms are replaced ca 8500 cal yr bp by the salinity indifferent species cyclotella meneghiniana and by benthic taxa indicating the beginning of lake regression during the mid holocene 6000 3500 cal yr bp the abundance of the saline taxon chaetoceros muelleri coupled with high abundances of epiphytic and epipelic diatoms indicates maximum salinity and lowest lake levels in the entire 30 000 year record lake transgression began ca 4000 cal yr bp and the lake achieved modern levels by about 1500 cal yr bp these water level changes imply changes in effective moisture most likely resulting from large precipitation changes precipitation was high throughout the last glacial maximum 21 000 18 000 cal yr bp likely due to an enhanced south american summer monsoon during peak summer insolation in the southern hemisphere in contrast the mid holocene transition was dryer than today in association with an austral summer insolation minimum and the subsequent weakening of the summer monsoon

glacial and postglacial pollen records from the ecuadorian andes and amazon abstract a long pollen record is derived from sediments of a lake dammed behind a low moraine of the last glaciation at 3 s latitude in the ecuadorian andes and is compared with a glacial age pollen record from the amazon rainforest immediately below lake surucucho llaviucu lies at 3180 m on the amazonian flank of the andes and above the glacial age pollen record from san juan bosco at 970 m the surucucho pollen record is interpreted as showing treeless vegetation in glacial times advance of treeline in late glacial time and holocene development of modern andean forests combining the surucucho and san juan bosco records shows that andean vegetation was affected by glacial cooling at all elevations vegetation did not move up and down slope as belts rather plant associations were reformed as temperature sensitive species found different centers of distribution with changing temperature

waveform relocated earthquake catalog for southern california 1981 to june 2011 we determine a new relocated catalog hys catalog 2011 for southern california from 1981 through june 2011 about 75 3 of the hypocenters are calculated with absolute and differential travel time picks and 24 7 could be relocated only by using absolute travel time picks with 3d or 1d velocity models the total catalog consists of more than 502 000 earthquakes in the region extending from baja california in the south to coalinga and owens valley in the north the catalog consists of three m 7 1 m 7 2 and m 7 3 mainshocks their foreshocks and aftershocks and background seismicity caused by tectonic and other processes in the southern california crust hypocenters in the new relocated catalog exhibit tighter spatial clustering of seismicity than does the routinely generated catalog and the depth distribution is tighter and reflects the thickness of the seismogenic zone more accurately compared to the standard catalog the relocated hypocenters are more easily related to other data sets such as mapped late quaternary faults

san andreas fault dip peninsular ranges mafic lower crust and partial melt in the salton trough southern california from ambient noise tomography we use ambient noise tomography to improve cvm h11 9 a community velocity model of southern california our new 3d shear velocity model with 0 05 x0 05 lateral and 1 km vertical blocks reveals new structure beneath the san andreas fault saf peninsular ranges batholith prb southern sierra nevada batholith snb and the salton trough st we use four years of data recorded on 849 broadband stations vastly more than previous studies and including our own broadband salton seismic imaging project a 40 station transect across the st as well as other campaign stations in both mexico and the u s a mean lower crust and upper mantle wavespeeds 3 6 km s 20km 4 2 km s 40km are low by global standards across the saf southeast of san gorgonio pass we observe vertical to steeply dipping lateral velocity contrasts that extend beneath the moho beneath the western prb and westernmost southern snb we observe relatively high shear velocities 3 8 km s in the lower crust that we interpret as the mafic roots of the overlying arc relatively high velocity upper mantle up to 4 5 km s may be part of the intact arc or possibly a remnant of the farallon plate beneath the st we observe zones of low shear velocity in the lower crust and upper mantle which permit up to 4 5 melt in the lower crust and up to 6 melt in the upper mantle depending on the assumed composition and pore geometry our results preclude the existence of older continental crust beneath the st and support the creation of new crust beneath the st this article is protected by copyright all rights reserved

three dimensional seismic velocity structure and precise earthquake relocations in the salton trough southern california abstract i present a new 3d seismic velocity model and high precision earthquake relocations between 1981 and 2010 near the salton trough and the san jacinto fault zone the simul2000 tomography algorithm is applied to derive the 3d v p and v p v s models using first arrivals of a composite event data set the final v p model correlates with geological features at shallow depths and is more consistent with the refraction studies than the starting 3d regional scale model the v p v s model shows strong variations in the upper crust and is dominated by relatively low values below 1 7 in the middle crust except for the salton trough and the imperial valley the newly resolved model is used to relocate all the seismicity in the study area i then apply the similar event cluster analysis and differential time relocation approach based on waveform cross correlation data to the 3d relocated events a dramatic sharpening of seismicity patterns is obtained after using these methods the new locations are more tightly clustered than the previous catalogs mainly due to the different absolute locations the depth distribution along a basal surface may suggest the existence of a detachment fault from the north end of the salton trough to united states mexico border the fine scale velocity structure and precise earthquake relocations will be helpful for investigating the fault geometry seismicity stress interaction and other seismological studies for southern california online material figures of model resolution tests cross sectional comparisons of different p velocity models and earthquake depth distributions

solubilities of gypsum and halite in the dead sea and in its mixtures with seawater1 the solubilities of gypsum cas04 2h 0 and halite nacl in aqueous solutions with ionic strengths between 3 and 13 were studied under ambient conditions mixtures of mediterranean seawater and dead sea brines evaporated to various degrees served as experimental solutions the practical solubility constant of gypsum k mca x vlso eq was found to be related to the ionic strength i of the solution by the empirical expression lox 5 498 0 3769z this relationship was then applied to calculate the degree of saturation with respect to gypsum dsg of the present dead sea water column calculations indicate that the entire dead sea water column ionic strength 9 10 is saturated or even slightly oversaturated with respect to both minerals studied

tropical climate changes at millennial and orbital timescales on the bolivian altiplano tropical south america is one of the three main centres of the global zonal overturning circulation of the equatorial atmosphere generally termed the walker circulation1 although this area plays a key role in global climate cycles little is known about south american climate history here we describe sediment cores and down hole logging results of deep drilling in the salar de uyuni on the bolivian altiplano located in the tropical andes we demonstrate that during the past 50 000 years the altiplano underwent important changes in effective moisture at both orbital 20 000 year and millennial timescales long duration wet periods such as the last glacial maximum marked in the drill core by continuous deposition of lacustrine sediments appear to have occurred in phase with summer insolation maxima produced by the earth s precessional cycle short duration millennial events correlate well with north atlantic cold events including heinrich events 1 and 2 as well as the younger dryas episode at both millennial and orbital timescales cold sea surface temperatures in the high latitude north atlantic were coeval with wet conditions in tropical south america suggesting a common forcing

abrupt aridities and salt deposition in the post glacial dead sea and their north atlantic connection abstract abrupt arid events in the post glacial 17 4 10 kyr bp dead sea basin dsb were recorded by significant lake level declines in lake lisan and massive deposition of gypsum and salt between 17 4 and 16 kyr cal bp the lake level dropped from its late mis2 stand of 260 m below mean sea level m bmsl to 330 m bmsl depositing a thick sequence of gypsum between 16 and 15 kyr cal bp the lake level recovered but dropped abruptly again at 14 kyr cal bp to below 465 m bmsl probably the lowest late pleistocene stand then between 13 and 11 kyr cal bp the younger dryas time interval the lake rose above 400 m bmsl and declined at 11 10 kyr cal bp depositing a thick sequence of salt the abrupt lake level drops and salt deposition coincided with times of ice and meltwater discharges into the north atlantic na heinrich event h1 and meltwater pulse mwp1a similar coincidence between ice and meltwater discharges in the na e g h events and arid episodes at the levant was recorded during the colder last glacial period demonstrating a persistent effect of the north atlantic hydrology and sea ice advances on the levant climate the climatically turmoil post glacial period was accompanied by significant developments in human culture the collapse of the natufian culture during the bolling allerod and the rise of the pre pottery neolithic cultures ppn a and b around the 11 10 kyr cal bp salt deposition interval marking the initiation of the neolithic revolution in the region

reassessment of the 1892 laguna salada earthquake fault kinematics and rupture patterns we present the results of intensive field investigations of the scarp associated with the 23 february 1892 earthquake in northern baja california newly recognized additional offsets suggest the rupture was about 58 km in length twice as long as previous estimates slip produced in the 1892 event varied from purely dextral slip near the international border to roughly 1 1 oblique normal slip farther south along the 2 4 km deep portion of the laguna salada basin the portion of the 1892 rupture with oblique normal slip comprises a number of short poorly organized and discontinuous fault scarps with heights that vary in concert with their strike slip was linked farther south to a short purely normal fault that forms a large releasing bend at the southern termination of the fault zone given the distribution of slip along the earthquake and a likely range of locking depths we conclude the 1892 earthquake was between m w 7 1 7 3 in magnitude consistent with previous estimates from macroseismic observations the length of the laguna salada fault that ruptured in 1892 also accommodated minor normal sense displacement along much of its length in the recent 2010 m w 7 2 el mayor cucapah earthquake which guided the remapping effort online material table of displacement measurements with uncertainty location waypoint number soil unit designation and the strike dip and type of feature measured

the el abra stadial a younger dryas equivalent in colombia abstract a survey of radiocarbon dated palynological stratigraphical and glacio morphological evidence from colombia is presented showing a cold climatic fluctuation most likely between 10 900 and 10 100 bp immediately preceding the initiation of the holocene this fluctuation called the el abra stadial is characterized by lower temperatures and less precipitation and occurs after the late glacial guantiva interstadial average annual temperature during the guantiva interstadial may have been 2 c lower than today and during the el abra stadial from 4 to 6 c lower than today the upper forest line during the el abra stadial was some 400 to 500 m lower than during the guantiva interstadial and some 600 to 800 m lower than today the guantiva interstadial el abra stadial early holocene sequence is radiocarbon dated by some 45 dates and evidence is shown from 14 areas mostly located at high elevations 2000 4000 m in the eastern and central cordillera and in the sierra nevada de santa marta but some from the tropical low lands although more precise dating of the boundaries is desirable we interpret the guantiva el abra climatic fluctuations as equivalents in time and climatic phenomena to the allerod younger dryas sequence in europe

isotopic evidence for late quaternary climatic change in tropical south america the tropical hydrologic cycle affects atmospheric trace gases and global climate change and thus records of hydrologic change encompassing a variety of time scales from the low latitudes are important in paleoclimatology isotopic analysis of calcite from lake junin peru provides a record of hydrologic variability that spans the last glacial interglacial transition in the southern tropics the record reveals a 6 enrichment in 18 o calcite during the late glacial followed by a gradual depletion during the holocene which can be interpreted as a decrease followed by a long term increase in effective moisture close agreement between 18 o calcite and rainy season insolation indicates that long term changes in tropical hydrology were linked to orbital variations furthermore hydrologic change was out of phase in the northern and southern tropics over this time period

complementary slip distributions of the largest earthquakes in the 2012 brawley swarm imperial valley california we investigate the finite rupture processes of two m 5 earthquakes in the 2012 brawley swarm by joint inversion of nearby strong motion and high rate gps data waveform inversions up to 3 hz were made possible by using a small event m w3 9 for path calibration of the velocity structure our results indicate that the first m w5 3 event ruptured a strong concentrated asperity with offsets of 20 cm centered at a depth of 5 km the subsequent m w5 4 event occurred 1 5 h later with a shallower slip distribution that surrounds and is complementary to that of the earlier event the second event has a longer rise time and weaker high frequency energy release compared to the m w5 3 event both events display strong rupture directivity toward the southwest and lack of very shallow 2 km coseismic slip the hypocenters for these events appear to be near or in the bedrock but most of the slip is distributed at shallower depths 6 km and can explain a large part of the gps offsets for the swarm the complementary slip distributions of the two events suggest a triggering relationship between them with no significant creep needed to explain the various data sets

early local last glacial maximum in the tropical andes the local last glacial maximum in the tropical andes was earlier and less extensive than previously thought based on 106 cosmogenic ages from beryllium 10 dating from moraines in peru and bolivia glaciers reached their greatest extent in the last glacial cycle 34 000 years before the present and were retreating by 21 000 years before the present implying that tropical controls on ice volumes were asynchronous with those in the northern hemisphere our estimates of snowline depression reflect about half the temperature change indicated by previous widely cited figures which helps resolve the discrepancy between estimates of terrestrial and marine temperature depression during the last glacial cycle

paleotemperatures from fluid inclusions in halite method verification and a 100 000 year paleotemperature record death valley ca abstract maximum homogenization temperatures of fluid inclusions thmax in halite laboratory grown crystals and modern samples death valley ca match maximum brine temperatures during halite precipitation maximum brine temperatures during halite precipitation in death valley late april 1993 34 4 c agree with thmax 34 c and correlate well with average maximum air temperatures in april 31 3 c and may 37 6 c thmax may be used for paleoclimate interpretations based on the close relationship between saline lake temperatures and average air temperatures from modern settings lower homogenization temperatures demonstrably below the temperatures at which halite grew are interpreted to reflect collapse of some fluid inclusion walls due to the pressure difference between the inside and outside of inclusions by only using thmax the problems of anomalously low homogenization temperatures due to possible collapse of fluid inclusions are avoided halite samples from 30 stratigraphic intervals 90 to 0 m 100 to 0 ka core dv93 1 death valley ca were used to measure homogenization temperatures of fluid inclusions virtually all homogenization temperatures from core dv93 1 are below the modern thmax of 34 c halite precipitation late april 1993 lacustrine halites deposited in a perennial saline lake 35 to 10 ka have thmax between 19 c and 30 c which suggests brine temperatures approximately 4 c to 15 c below modern late april values ephemeral saline lake halites precipitated 60 to 35 ka have thmax between 23 c and 28 c 6 to 11 c below modern values the highest thmax value in the 100 ka record up to 35 c is from a halite sample formed approximately 100 ka in a climate regime somewhat colder than the modern

fault zone characteristics and basin complexity in the southern salton trough california ongoing oblique slip at the pacific north america plate boundary in the salton trough produced the imperial valley california usa a seismically active area with deformation distributed across a complex network of exposed and buried faults to better understand the shallow crustal structure in this region and the connectivity of faults and seismicity lineaments we used data primarily from the salton seismic imaging project to construct a three dimensional p wave velocity model down to 8 km depth and a velocity profile to 15 km depth both at 1 km grid spacing a vp 5 65 5 85 km s layer of possibly metamorphosed sediments within and crystalline basement outside the valley is locally as thick as 5 km but is thickest and deepest in fault zones and near seismicity lineaments suggesting a causative relationship between the low velocities and faulting both seismicity lineaments and surface faults control the structural architecture of the western part of the larger wedge shaped basin where two deep subbasins are located we estimate basement depths and show that high velocities at shallow depths and possible basement highs characterize the geothermal areas

geochemical evolution and residence time of porewater in low permeability rocks of the michigan basin southwest ontario abstract drill cores collected from an 860 m thick paleozoic cambrian to devonian sedimentary sequence of the michigan basin in southwest ontario canada were used to develop vertical profiles of natural tracers in porewater from the sedimentary sequence and build a conceptual model regarding processes and timing of solute migration in this paper the conceptual model is quantitatively assessed with numerical simulations of diffusion dominated solute transport cl and 18o the conceptual model suggests that the tracer profiles result from mixing between a deep shield brine with isotopic characteristics consistent with water rock interaction over a long period of geologic time ordovician seawater at intermediate depth and an overlying hypersaline brine formed by evaporation of seawater in a restricted basin during the silurian between the peak of basin consolidation at 300 ma bp and the pleistocene 2 6 ma bp salinity and isotopic concentration gradients are thought to have driven mixing dominantly by diffusion water isotope data indicate that in the pleistocene melt water infiltrated to a maximum depth of 330 m in the silurian salina formation likely in response to transient glacial loading and elevated sub glacial hydraulic pressures also in the pleistocene over pressured conditions in deep regions of the basin drove high salinity brine eastward in the basal cambrian aquifer interrupting pre existing tracer diffusion profiles a base case set of boundary and initial conditions provides a good fit between simulated and measured tracer profiles but requires effective diffusion coefficients de in the ordovician limestones that are lower than the average values obtained in laboratory measurements by as much as a factor of 10 the base case values are still within the overall range of measured values at the formation scale relatively low in situ de values are attributed to the intermittent occurrence of gas and liquid hydrocarbons in the ordovician carbonate units and the effect of lithostatic confining pressure neither of which are accounted for in the laboratory measurements but both would have the effect of decreasing de for aqueous solutes the numerical model is most sensitive to the formation specific de values and geologically reasonable variations in initial and boundary conditions have a relatively small influence on the results additional simulations indicate that hydraulic disturbance and ingress of meltwater during the pleistocene can explain second order features observed in the measured tracer profiles this work provides supporting evidence for previous research indicating that the porewater residence time in the ordovician sequence approaches the age of the rocks

constraints on evaporation and dilution of terminal hypersaline lakes under negative water balance the dead sea israel abstract the response of hypersaline terminal lakes to negative water balance was investigated by studying brines evaporating to extreme salinities in sinkholes along the western coast of the dead sea and during on site evaporation experiments of the dead sea brine density and temperature were determined in the field and all samples were analyzed for their major and a few minor solutes the activity of h 2 o a h2o in the brines was calculated and the degree of evaporation de was established using sr 2 as a conservative solute the relations between density and water activity were obtained by polynomial regression and the relation between the lake s volume and level was established using hall s 1996 hypsographic model for the dead sea basin relating the results to the modern long term relative humidity rh over the basin shows that a the lowermost attainable level of a terminal lake undergoing evaporation with no inflow is dictated by the median rh this level represents equilibrium between the brine s a h2o and rh b small saline water bodies with high surface to volume ratios a v such as the hypersaline brines in the sinkholes are very sensitive to short term changes in rh in these the brines a h2o closely follows the seasonal changes c the level decline of the dead sea due to evaporation under present climatic conditions and assuming no inflow to the lake may continue down to 516 537 m below mean sea level bmsl corresponding to a water activity range of 0 46 0 39 in its brine in equilibrium with the overlying relative air humidity this suggests that the lake level cannot drop more than 100 m from its present level and d the maximum rh values that existed over the precursor lake of the dead sea lake lisan during geologically reconstructed minima levels can be similarly calculated

a 24 700 yr paleolimnological history from the peruvian andes abstract a new paleolimnological dataset from lake pacucha 13 s 3095 m elevation in the peruvian andes provides evidence of changes in lake level over the past 24 700 yr a late glacial highstand in lake level gave way to an early holocene lowstand this transition appears to have paralleled precessional changes that would have reduced insolation during the wet season the occurrence of benthic salt tolerant diatoms and caco3 deposition suggest that the lake had lost much of its volume by c 10 000 cal yr bp pronounced holocene oscillations in lake level included a second phase of low lake level and heightened volatility lasting from c 8300 to 5000 cal yr bp while a polymictic lake formed at c 5000 cal yr bp these relatively wet conditions were interrupted by a series of drier events the most pronounced of which occurred at c 750 cal yr bp paleolimnological changes in the holocene were more rapid than those of either the last glacial maximum or the deglacial period

anthropogenic seismicity rates and operational parameters at the salton sea geothermal field geothermal power is a growing energy source however efforts to increase production are tempered by concern over induced earthquakes although increased seismicity commonly accompanies geothermal production induced earthquake rate cannot currently be forecast on the basis of fluid injection volumes or any other operational parameters we show that at the salton sea geothermal field the total volume of fluid extracted or injected tracks the long term evolution of seismicity after correcting for the aftershock rate the net fluid volume extracted injected provides the best correlation with seismicity in recent years we model the background earthquake rate with a linear combination of injection and net production rates that allows us to track the secular development of the field as the number of earthquakes per fluid volume injected decreases over time