a late glacial high resolution site and source temperature record derived from the epica dome c isotope records east antarctica the timing and synchronisation of greenland and antarctic climate events that occurred during the last glacial period are still under debate as is the magnitude of temperature change associated with these events here we present detailed records of local and moisture source temperature changes spanning the period 27 45 kyr bp from water stable isotope measurements deltad and delta 18 o in the recently drilled epica dome c ice core east antarctic plateau using a simple isotopic model site deltat site and source deltat source temperatures are extracted from the initial 50 yr high resolution isotopic records taking into account the changes in seawater isotopic composition the deuterium isotope variability is very similar to the less precise deltad record from the vostok ice core and the site temperature inversion leads to a temperature profile similar to the classical palaeothermometry method due to compensations between source and ocean water corrections the reconstructed deltat site and deltat source profiles show different trends during the glacial the former shows a decreasing trend from the warm al event 38 kyr bp toward the last glacial maximum while the latter shows increasing values from 41 to 28 kyr bp the low frequency deuterium excess fluctuations are strongly influenced by obliquity fluctuations controlling the low to high latitude temperature gradients and show a remarkable similarity with a high resolution southeast atlantic sea surface temperature record a comparison of the temperature profiles site and source and temperature gradient deltat source deltat site with the non sea salt calcium and sodium records suggests a secondary influence of atmospheric transport changes on aerosol variations

magma mixing in boninite sequence of chichijima bonin islands abstract boninite from chichijima can be divided into two major types a porphyritic type phenocryst mode exceeds 1 and b aphyric type phenocryst mode is less than 1 both types are further subdivided by means of microphenocryst assemblages into five subtypes i olivine ol clinoenstatite cen bronzite brz ii ol brz iii brz iv brz pigeonite pig augite aug v cen brz there is a systematic correlation between these rock types and the bulk composition of aphyric boninites the most magnesian boninites are of type i and the least magnesian ones are of types iii and v type ii is slightly higher in cao than type i at a given feo mgo ratio type iv is distinct from the others for its high cao and low incompatible element contents at a given feo mgo ratio type iv cannot be derived from the others by crystallization differentiation compositional data for the other types of boninite define rectilinear compositional variations which lie on a tie line connecting fe rich bronzite and primitive boninite microphenocrysts in equilibrium with boninite magma are more magnesian so it would appear that the fe rich bronzite was in equilibrium not with boninite magma but with some evolved descendant e g bronzite andesite magma the variations of aphyric boninites are then best explained by a combination of mixing of primitive boninite and evolved descendants together with equilibrium crystallization processes in order to account for this combination of processes a density stratified open system magma chamber of the type proposed for oceanic ridge systems seems appropriate the upper part of the magma chamber is composed of differentiated bronzite andesite magma and the lower part consists of hot dense and primitive boninite magma crystallization and sporadic overturn and mixing give rise to the spectrum of magma types erupted at the surface

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

record of middle pleistocene climate change from buck lake cascade range southern oregon evidence from sediment magnetism trace element geochemistry and pollen comparison of systematic variations in sediment magnetic properties to changes in pollen assemblages in middle pleistocene lake sediments from buck lake indicates that the magnetic properties are sensitive to changes in climate buck lake is located in southern oregon just east of the crest of the cascade range lacustrine sediments from 5 2 to 19 4 m in depth in core contain tephra layers with ages of 300 400 ka at 9 5 m and 400 470 ka at 19 9 m in these sediments magnetic properties reflect the absolute amount and relative abundances of detrital fe oxide minerals titanomagnetite and hematite the lacustrine section is divided into four zones on the basis of magnetic properties two zones 19 4 17 4 m and 14 5 10 3 m of high magnetic susceptibility contain abundant fe oxides and correspond closely to pollen zones that are indicative of cold dry environments two low susceptibility zones 17 4 14 5 m and 10 3 5 3 m contain lesser amounts of fe oxides and largely coincide with zones of warm climate pollen transitions from cold to warm climate based on pollen are preceded by sharp changes in magnetic properties this relation suggests that land surface processes responded to these climate changes more rapidly than did changes in vegetation as indicated by pollen frequencies magnetic properties have been affected by three factors 1 dissolution of fe oxides 2 variation in heavy mineral content and 3 variation in abundance of fresh volcanic rock fragments trace element geochemistry employing fe and the immobile elements ti and zr is utilized to detect postdepositional dissolution of magnetic minerals that has affected the magnitude of magnetic properties with little effect on the pattern of magnetic property variation comparison of ti and zr values proxies for heavy mineral content to magnetic properties demonstrates that part of the variation in the amount of magnetite and nearly all of the variation in the amount of hematite are due to changes in heavy mineral content variation in the quantity of fresh volcanic rock fragments is the other source of change in magnetite content magnetic property variations probably arise primarily from changes in peak runoff at low to moderate flows magnetic properties reflect only the quantities of heavy minerals derived from soil and highly weathered rock in the catchment at high flows however fresh volcanic rock fragments may be produced by breaking of pebbles and cobbles and such fragments greatly increase the magnetite content of the resulting sediment climatically controlled factors that would affect peak runoff levels include the accumulation and subsequent melting of winter snow pack the seasonality of precipitation and the degree of vegetation cover of the land surface our results do not distinguish among the possible contributions of these disparate factors

high resolution particle size analysis of naturally occurring very fine grained sediment through laser diffractometry abstract in this paper we present results from a large number of experiments aimed at quantifying method and instrument uncertainty associated with laser diffraction analysis we analyzed the size distribution of fine grained sediment 24 hours prior to analysis and using 60 seconds of ultrasonication during analysis 2 obscuration a measure of the concentration of the suspension during analysis produced the most reproducible results at about 20 3 variations in refractive index settings can significantly alter estimated grain size distributions 4 assumed values for absorption the degree to which sediment grains absorb the light can have a profound effect on grain size results absorption settings near 0 resulted in unexpected bimodal grain size distributions for sediments in the 10 m size fraction and significantly skewed the fine grained tail of coarser samples probably because of sub optimal diffraction by particles with a diameter similar in size to the laser wavelength absorption settings closer to 1 produced very reproducible results and unimodal grain size distributions over a wide range of refractive indexes our study has shown that laser diffraction can measure very fine grained sediments 10 m quickly with high precision 5 at 2 standard deviations and without the need for extensive mineralogical determinations these results make possible a new generation of studies in which high resolution time series data sets of sediment grain size can be used to infer subtle changes in paleohydrology

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

present day south american climate abstract this paper documents the main features of the climate and climate variability over south america on the basis of instrumental observations gathered during the 20th century it should provide a modern reference framework for paleoclimate research in south america targeting high resolution proxies over the past few centuries several datasets suitable for present day climate research are first described highlighting their advantages as well as their limitations we then provide a basic physical understanding of the mean annual cycle of the precipitation and atmospheric circulation over the continent and the adjacent oceans in particular the diversity of precipitation temperature and wind patterns is interpreted in terms of the long meridional extent of the continent and the disruption of the large scale circulation caused by the andes cordillera the contrasting oceanic boundary conditions and the landmass distribution similarly the intensity and timing of the interannual and interdecadal climatic fluctuations exhibit considerable geographical dependence as some regions are more influenced by large scale phenomena rooted in the tropical oceans while others are more influenced by high latitude phenomena the impact of these large scale phenomena over south america is documented by a regression analysis between selected atmospheric indices and the precipitation and temperature fields we have included a discussion on the seasonality and long term stability of such impacts and complemented our general description by an updated review of the literature on climate variability over specific regions

glacier fluctuations in the southern peruvian andes during the late glacial period constrained with cosmogenic 3he the occurrence of pronounced climate reversals during the last glacial termination has long been recognised in palaeoclimate records from both hemispheres and from high to low latitudes accurate constraint of both the timing and magnitude of events such as the younger dryas and antarctic cold reversal is vital in order to test different hypotheses for the causes and propagation of abrupt climate change however in contrast to higher latitude regions well dated records from the tropics are rare and the structure of late glacial tropical climate remains uncertain as a step toward addressing this problem we present an in situ cosmogenic 3 he surface exposure chronology from nevado coropuna southern peru documenting a significant fluctuation of the ice margin during the late glacial period ten tightly clustered ages from a pair of moraines located halfway between the modern glacier and the last glacial maximum terminus range from 11 9 to 13 9ka and give an arithmetic mean age of 12 8 0 7ka 1s these data constitute direct evidence for a readvance or prolonged stillstand of glaciers in the arid andes of southwestern peru copyright 2011 john wiley sons ltd

clinoenstatite bearing lava from nepoui new caledonia the lava consists mainly of clinoenstatite phenocrysts 29 sometimes enclosing euhedral chromite a lesser amount of microphenocryst bronzite 20 and a glassy mesostasis clinoenstatite phenocrysts are compositionally homogeneous en 89 fs sub 10 5 wo sub 0 5 with polysynthetic twins on 100 a feature which is believed to indicate inversion from protoenstatite bronzite is variable in composition with en sub 74 84 fs sub 14 22 wo sub 1 5 4 hypersthene en sub 43 61 fs sub 36 52 wo sub 3 4 calcic and subcalcic augite and iron rich hornblende occur as overgrowths on phenocrysts and as quench microlites the new caledonian clinoenstatite boninite is similar chemically mineralogically texturally and in terms of age eocene oligocene and tectonic setting with ophiolite complexes to the three other known clinoenstatite boninite localities cape vogel papua new guinea bonin islands and mariana trench clinoenstatite boninite magmas are believed to result from extensive partial melting of depleted mantle peridotite under hydrous conditions and an abnormally high geothermal gradient modified journal abstract

metal fluxes during magmatic degassing in the oceanic crust sulfide mineralisation at odp site 786b izu bonin forearc volcanogenic massive sulfide deposits are enriched in metals that are either derived from hydrothermal alteration of the basement rocks or supplied by exsolution of metal rich volatiles during magmatic differentiation the extent to which each process contributes to metal enrichment in these deposits varies between different tectonic settings ocean drilling program hole 786b recovered 800 m of upper oceanic crust from a supra subduction zone setting and includes a 30 m thick mineralised zone in situ s isotopic compositions of pyrite decrease from 5 9 2 9 in the upper mineralised zone down to 3 3 2 1 in the extensively altered central mineralisation zone potentially indicating strong magmatic fluid input in this area whole rock data and in situ trace element analyses in sulfide minerals show enrichment of ag as au bi mo s se sb and te in the mineralised zone evaluation of metal behaviour during magmatic differentiation and primary metal fertility of basement rocks suggests that degassing melt is the main source for the high au se and s enrichment observed in the mineralised zone magmatic volatile exsolution occurred late during the magmatic differentiation 2 wt mgo concomitant with oxide crystallisation and metal depletion in the melt comparison of ocean drilling program hole 786b with volcanogenic massive sulfide deposits hosted by boninitic volcanic successions such as in the semail ophiolite the newfoundland appalachians and the flin flon belt suggests that magmatic fluid exsolution could be a common mechanism for au enrichment in bimodal mafic volcanogenic massive sulfide deposits

oxygen isotope constraints on the petrogenesis of volcanic arc magmas from martinique lesser antilles abstract volcanic rocks from the island of martinique in the lesser antilles island arc are highly diverse isotopically values of 18o smow in lavas erupted over the last 5 ma from five stratigraphically discrete and geochemically distinct volcanic centers are morne jacob 7 5to 7 9 pitons du carbet 8 0to 8 9 diamant 6 3to 7 4 piton mt conil 7 2to 7 3 andmt pelee 6 5to 7 4 13 of the 27 samples have been corrected for variable amounts of secondary alteration and low temperature hydration the least18o rich andesites on martinique have 18o values similar to those of the northern lesser antilles 18o 6 0 to 7 3 and other intra oceanic arcs like the marianas 18o 5 5 to 6 8 o isotope ratios are compositionally dependent correlations between 18o and radiogenic isotope ratios 87sr 86sr 143nd 144nd 206pb 204pb and indices of fractionation show that modification of isotopic compositions occurred during magmatic differentiation rather than at source a two stage model is proposed for the origin and differentiation of magmas on martinique primary basaltic melts which are broadly similar in composition to primitive island arc magmas elsewhere e g marianas aleutians south sandwich islands are generated from the subduction modified asthenospheric mantle wedge these magmas ascend into the arc crust and differentiate on martinique crystal fractionation is accompanied by contamination with isotopically distinct crust including a component of terrigenous sediments thus subduction zone processes at the lesser antilles and other island arcs are similar involving only a small albeit significant isotopically volumetric contribution from subducted sediment

the evolution of the patagonian ice sheet from 35 ka to the present day patice abstract we present patice a gis database of patagonian glacial geomorphology and recalibrated chronological data patice includes 58 823 landforms and 1 669 geochronological ages and extends from 38 s to 55 s in southern south america we use these data to generate new empirical reconstructions of the patagonian ice sheet pis and subsequent ice masses and ice dammed palaeolakes at 35 ka 30 ka 25 ka 20 ka 15 ka 13 ka synchronous with the antarctic cold reversal 10 ka 5 ka 0 2 ka and 2011 ad at 35 ka the pis covered of 492 6 x103 km2 had a sea level equivalent of 1 496 mm was 350 km wide and 2090 km long and was grounded on the pacific continental shelf edge outlet glacier lobes remained topographically confined and the largest generated the suites of subglacial streamlined bedforms characteristic of ice streams the pis reached its maximum extent by 33 28 ka from 38 s to 48 s and earlier around 47 ka from 48 s southwards net retreat from maximum positions began by 25 ka with ice marginal stabilisation then at 21 18 ka which was then followed by rapid irreversible deglaciation by 15 ka the pis had separated into disparate ice masses draining into large ice dammed lakes along the eastern margin which strongly influenced rates of recession glacial readvances or stabilisations occurred at least at 14 13 ka 11 ka 6 5 ka 2 1 ka and 0 5 0 2 ka we suggest that 20th century glacial recession a 1 is occurring faster than at any time documented during the holocene

geochemistry of a komatiitic boninitic and tholeiitic basalt association in the mesoarchean koolyanobbing greenstone belt southern cross domain yilgarn craton implications for mantle sources and geodynamic setting of banded iron formation abstract komatiite basalt magmatism and algoma type banded iron formation bif of archean greenstone terranes have common time series but there are few constraints on the geodynamic setting in which bif were precipitated the 3 0 ga koolyanobbing greenstone belt kgb southern cross domain yilgarn craton exhibits an greenschist to lower amphibolite facies metamorphosed lithostratigraphic series including four predominantly mafic to ultramafic volcanic sequences s1 s4 with prominent bif horizons and local basal pyrite dominated massive sulfide lenses in between petrography xrd high precision major trace high field strength and ree element chemistry of representative ultramafic and mafic rocks from s1 s2 and s3 are consistent with a komatiitic boninitic and tholeiitic basalt association komatiites are al depleted and al undepleted al2o3 tio2 12 28 and gd yb n 1 endorsing a zoned plume and or melting over a range of depths the boninite series rocks al2o3 tio2 28 45 and gd yb n pearce 2008 implying a depleted mildly heterogeneous source for the mantle plume from which komatiites erupted boninites lie parallel to and above the mantle array in the field of intraoceanic arcs in keeping with their inferred oceanic convergent margin setting ratios of nb yb extend to lower and higher values than komatiites implying a more heterogeneous upper mantle source of the subarc wedge the kgb exhibits the first reported boninite suite rocks in the southern cross domain yilgarn craton conclusively the komatiitic boninitic and tholeiitic basalt association suggests that bif and basal massive pyrite lenses of the koolyanobbing greenstone belt were precipitated from low temperature submarine discharge of a seawater dominated hydrothermal system driven by magmatic systems of a mantle plume erupting in a forearc convergent margin suprasubduction ophiolite

a record from lake cardiel of climate change in southern south america southern south america the only continental land mass lying between 38 s and the antarctic circle presents a rare opportunity to reconstruct terrestrial records of palaeoclimate in an area that is subject to shifts of polar and mid latitude wind and pressure belts in the bulk of this region patagonia are many hydrographically closed lakes which despite the palaeoclimatic significance of the region and the proven utility of lake level records in reconstructing past climates1 2 have escaped detailed study using sedimentary and geomorphic evidence together with 14c dating we present here a detailed lake level record for lake cardiel fig 1 the highest level of the past 21 000 years occurred at about 9 780 bp reminiscent of tropical lakes rather than those in northern mid latitudes1 2 the lake cardiel record corroborates and clarifies the timing of the wetness record inferred from pollen studies in patagonia

mid and late holocene limnogeology of laguna del negro francisco northern chile and its palaeoclimatic implications lacustrine sediments from the high elevation endorheic saline lake negro francisco 27 28 s 69 14 w 4125 m provide a detailed mid and late holocene environmental history of the southern chilean altiplano mineralogy chemical composition and sedimentary facies analyses of the deposits confirm the regional significance of mid holocene aridity between 6000 and 3800 bp precipitation rates were signifi cantly lower than the c 250 mm yr 1 of today fully arid conditions were interrupted by short term moist spells with an average return period of about 200 years effective moisture increased after 3800 bp and peaked between 3000 and 2600 bp and between 2200 and 1800 bp in two phases with conditions more humid than today comparison with regional palaeodata suggest that these two late holocene humid spells were most likely related to pacific moisture sources salinity levels increased again in laguna del negro francisco after 1800 bp the onset of modern climatic conditions was a stepwise nonlinear proce

storm tracks in the southern hemisphere abstract from 1979 to 1989 global european centre for medium range weather forecasts ecmwf analyses of many meteorological variables important in baroclinic storms have been bandpass filtered to highlight fluctuations on 2 to 8 day time scales in order to illuminate the relationships among the variables in baroclinic storm track regions because of the greater zonal symmetry in the southern hemisphere sh versus the northern hemisphere nh it is possible to examine these relationships over a zonal sector without being dominated by local effects associated with jet stream entrance and exit regions of the storm tracks the bandpassed variance of geopotential height is used to define the storm track and its meridional profile has a pronounced midlatitude maximum in the sh the locations of the jet stream and the variance maxima of meridional and zonal velocity components vorticity vertical motion specific humidity and temperature all bear a distinctive relationship to the storm track but the lat

climate variability over the last 9900 cal yr bp from a swamp forest pollen record along the semiarid coast of chile abstract we present a fossil pollen analysis from a swamp forest in the semiarid coast of chile 32 05 s 71 30 w at the northern influence zone of southern westerly wind belt a 10 000 cal yr bp calendar years before 1950 palynological sequence indicates a humid phase characterized by dense swamp forest taxa dated between 9900 and 8700 cal yr bp the presence of pollen starved sediments with only scant evidence for semiarid vegetation indicates that extreme aridity ensued until 5700 cal yr bp the swamp forest recovered slowly afterwards helped by a significant increase in moisture at 4200 cal yr bp a new swamp forest contraction suggests that another slightly less intense drought occurred between 3000 and 2200 cal yr bp the swamp forest expansion begins again at 2200 cal yr bp punctuated by a highly variable climate comparisons between the record presented here with other records across the region imply major variations in the extent of the southern westerlies during the holocene this variability could have been caused either by latitudinal displacements from the present mean position of southern westerlies wind belt or by changes in the intensity of the south pacific subtropical anticyclone both of which affect winter precipitation in the region

late pleistocene early holocene paraglacial and fluvial sediment history in the turbio valley semiarid chilean andes abstract the transitional character of climatic conditions confers great relevance to paleoclimate studies in the semiarid region where glacial and holocene geomorphologic records are scarce here we present the paraglacial and fluvial evolution of the turbio valley 30 s using both field observations and 14 c ams chronology two key sites at the uppermost turbio valley show glacial margins which likely formed during the 17 12 ka central andean pluvial event and earlier 37 27 ka episodes associated with glacial advances reported elsewhere in the semiarid andes likewise two episodes of subsequent paraglacial response are identified a first episode corresponds to early holocene fine grained deposits 11 500 7800 cal yr bp extending far downstream 40 km from the glacial margins these deposits and coeval debris cones 11 000 5500 cal yr bp are the result of arid conditions with occasional runoffs that were unable to export sediments along the trunk valley the second episode corresponds to disconformably overlying fluvial gravels extending 70 km downstream from the glacial margin indicative of an increase in the fluvial transport capacity occurring not long after 5500 cal yr bp fluvial transport increase resulted from a late holocene shift to wetter climate conditions representing a forcing factor which enhanced the paraglacial response

stable isotope compositions and water contents of boninite series volcanic rocks from chichi jima bonin islands japan measurements of stable isotope compositions and water contents of boninite series volcanic rocks from the island of chichi jima bonin islands japan confirm that a large amount 1 6 2 4 wt of primary water was present in these unusual magmas an enrichment of 0 6 in18o during differentiation is explained by crystallization of18o depleted mafic phases silicic glasses have elevated 18o values and relatively low d values indicating that they were modified by low temperature alteration and hydration processes mafic glasses on the other hand have for the most part retained their primary isotopic signatures since eocene time primary d values of 53 for boninite glasses are higher than those of morb and suggest that the water was derived from subducted oceanic lithosphere

origin of waters responsible for serpentinization of the izu ogasawara mariana forearc seamounts in view of hydrogen and oxygen isotope ratios many serpentinite seamounts occur over a region 20 120 km west of the trench axis in the izu ogasawara mariana forearc regions the hydrogen and oxygen isotopic compositions of serpentine from these regions indicate that there are at least two kinds of waters responsible for serpentinization seawater and water derived from dehydration of the descending slab serpentine from two mariana and two torishima samples with microscopically ductile and sheared texture sheared type have lower d 63to 52 and slightly higher 18o values 6 1 to 8 2 than that of other nine ogasawara samples with mesh texture mesh type d 43to 49 and 18o 5 8to 6 7 this suggests that the sheared type serpentine with lower d and slightly higher 18o values was formed within the wedge mantle by interaction with water derived from a descending slab the sheared texture is likely to have been produced during diapiric uplift the unaltered portion of the ultramafic bodies later interacted with seawater after emplacement at or near the seafloor resulting in formation of the mesh type serpentine with higher d values

late glacial history of lago argentino argentina and age of the puerto bandera moraines in the west central part of lago argentino the puerto bandera moraines are clearly detached from longer more prominent moraines of the last glaciation and from shorter and smaller neoglacial moraines scientists have long speculated about the age of the puerto bandera moraines detailed geomorphologic studies in the western area of lago argentino including stratigraphic profiles at bahia del quemado in the northern branch brazo norte indicate that the puerto bandera moraines were deposited by three pulses of ice each of the three pulses is represented by single moraine ridges and belts of tightly arranged ridges the timing of the three glacier advances was established by radiocarbon dating including data published by john mercer the oldest moraine system formed during the puerto bandera i substade was deposited ca 13 000 14c yr b p moraines of the puerto bandera ii substade were deposited ca 11 000 14c yr b p the youngest moraine system was deposited during a minor readvance shortly before 10 390 c14 yr b p and thus appears to have occurred some time during the european younger dryas interval after this third substade the ice tongues retreated into the interior branches of lago argentino and have remained there since evidence found at bahia del quemado together with data provided by other authors attests to a significant climatic change by the middle holocene which we believe occurred during the herminita advance the first holocene glacial readvance recognized within the area

ferric ferrous ratios h 2 o contents and d h ratios of phlogopite and biotite from lavas of different tectonic regimes complete chemical analyses including ferric and ferrous iron h2o contents and dd values for 16 phlogopite and biotite and 2 hornblende separates are presented samples were obtained from volcanic rocks from four localities 1 phlogopite phenocrysts from minette lavas from the western mexico continental arc 2 biotite and hornblende phenocrysts from andesite lavas from mono basin california 3 phlogopite and biotite from clinopyroxenite nodules entrained in potas sic lavas from the east african rift uganda and 4 phlogopite phenocrysts from a wyomingite lava in the leucite hills wyoming the fe 2 o 3 contents in the mi cas range from 0 8 to 10 5 wt corresponding to 0 09 to 1 15 fe 31 per formula unit pfu water contents vary from 1 6 to 3 0 wt corresponding to 1 58 to 3 04 oh pfu significantly less than would be expected for a site fully occupied by hydroxyl cation and anion based normalization procedures provide accurate mineral for mulae with respect to most cations and anions but are unable to generate accurate estimates of fe 31 yfe t a nd overestimate oh at the expense of o on the hydroxyl site these inaccuracies are present despite acceptable adjust ed totals and stoichiometric calculated site occupancies the phlogopite and biotite phenocrysts in arc related lavas from western mexico and eastern california have the highest fe 31 yfe t ratios 56 87 reflecting high magmatic oxygen fugacities dnno 51 2t o 15 in contrast to those from uganda 25 40 and the leucite hills 23 there is no correlation between the oh content and the fe 31 yfe t ratio in the micas values of k mgyfe 21 d 2s errors were calculated for three phlogo pite olivine pairs 0 12 0 12 0 26 0 14 0 09 0 12 two biotite hornblende pairs 0 73 0 08 and 1 22 0 10 and a single phlogopite augite pair 1 15 0 12 values of k fyoh d for two biotite and hornblende pairs could not be determined without significant error because of the extremely low f contents 0 2 wt of the four phases the dd values obtained in this study encompass a large range 2137 to 243 the phlogo pite and biotite separates from uganda have dd values of 270 to 249 which overlap those believed to represent primary mantle there is a larger range in dd values 2137 to 243 for phlogopite phenocrysts from west ern mexico minette lavas although their range in d 18 o values 5 2 6 2 is consistent with normal mantle it is unlikely therefore that the variable dd values reflect heterogeneity in the mantle source region of the minette magmas nor can the extremely low dd values reflect degassing of h2 or h2o since almost 100 loss of dis solved water in the magma is required an unrealistic scenario given the stability of the hydrous phenocrysts the very low dd values of the mascota minette phlogo pites require that the hydrogen be introduced from an external source e g meteoric water whatever the pro cess responsible for the observed hydrogen isotope com position it had no effect on the d 18 o value fo2 ah2o or bulk composition of the host magmas

oxygen isotope systematics of eclogite mineral phases from south africa abstract eleven eclogite xenoliths from the bobbejaan and roberts victor mines south africa have been characterized by a variety of geochemical techniques the samples include nine bimineralic eclogites and two grospydites that span the range of mantle eclogite major element compositions primary phase end member compositions range from py 75 al 16 gr 09 jd 18 di 82 caes 0 to py 28 al 21 gr 51 jd 49 di 36 caes 15 oxygen isotope analyses of mineral separates were performed for clinopyroxene and garnet isotopic values 18 o range from 4 0 to 7 8 for clinopyroxene and 3 6 to 7 2 for garnet differences in isotopic values between the primary phases clinopyroxene minus garnet range in value from 0 6 to 0 6 although oxygen isotopes are not expected to fractionate at mantle temperatures the anion electrostatic site potential values determined by smyth 1989 are consistent with small degrees of fractionation in the mantle oxygen isotope fractionation between minerals may be calculated by the equation of smyth and clayton f a 10 6 t 2 where a 0 7911 ev fractionation values at 1300 k range from 0 6 jd pyr to 0 03 cats grs while at 1600 k these values are between 0 39 and 0 02 respectively the re equilibration temperatures of the studied eclogite suite are 1050 to 1250 c at 30 kbar therefore the obtained differences between the mineral phases are consistent with the calculated isotope fractionation values the data obtained for eclogite oxygen isotopes suggest that 18 o may fractionate to a small extent at mantle pt conditions

evidence from the rio bayo valley on the extent of the north patagonian icefield during the late pleistocene holocene transition abstract this paper presents data on the extent of the north patagonian icefield during the late pleistocene holocene transition using cosmogenic nuclide exposure age and optically stimulated luminescence dating we describe geomorphological and geochronological evidence for glacier extent in one of the major valleys surrounding the north patagonian icefield the rio bayo valley geomorphological mapping provides evidence for the existence of two types of former ice masses in this area i a large outlet glacier of the north patagonian icefield which occupied the main rio bayo valley and ii a number of small glaciers that developed in cirques on the slopes of the mountains surrounding the valley cosmogenic nuclide exposure age dating of two erratic boulders on the floor of the rio bayo valley indicate that the outlet glacier of the icefield withdrew from the rio bayo valley after 10 900 1000 yr the mean of two boulders dated to 11 400 900 yr and 10 500 800 yr single grain optically stimulated luminescence osl dating of an ice contact landform constructed against this glacier indicates that this ice mass remained in the valley until at least 9700 700 yr the agreement between the two independent dating techniques osl and cosmogenic nuclide exposure age dating increases our confidence in these age estimates a date obtained from a boulder on a cirque moraine above the main valley indicates that glaciers advanced in cirques surrounding the icefield some time around 12 500 900 yr this evidence for an expanded north patagonian icefield between 10 900 1000 yr and 9700 700 yr implies cold climatic conditions dominated at this time

an organic geochemical record of sierra nevada climate since the lgm from swamp lake yosemite abstract sediment records from swamp lake sl in the central sierra nevada california provide evidence of climatic change on millennial and centennial timescales over the last 20 000 years total organic carbon toc abundance varied in concert with elemental and isotopic tracers of organic matter c n 13 c org 15 n biogenic silica content total magnetic susceptibility and sediment lithology we interpret the down core proxy records as representing the response of the lake environment in terms of temperature seasonal ice cover mixing regimes runoff and in situ om and nutrient cycling to shifting climate states these environmental factors in turn drove changes in algal productivity om sources microbial om regeneration and secondary production and detrital input the late pleistocene 19 7 10 8 cal kyr bp was dominated by fluctuations between relatively warm dry intervals with high toc 17 4 16 5 15 8 15 0 13 9 13 2 11 4 11 0 cal kyr bp and cold wet intervals 16 5 15 8 14 8 13 9 13 1 11 6 11 0 10 7 cal kyr bp characterized by low toc and high detrital input the holocene 10 7 cal kyr bp present was characterized by three abrupt increases in toc after 10 8 8 0 and 3 0 cal kyr bp and numerous century scale fluctuations toc increases reflected enhanced lake productivity and om recycling and reduced detrital input in response to changing winter temperature and hydrologic regimes inferred environmental changes at sl correlate with other sierra nevada paleorecords and with reconstructed sea surface temperatures along the california margin parallel changes in the sl and sst records over the past 20 000 years provide new evidence that continental climate in the sierra nevada and the california current system have responded on multiple timescales to common drivers in north pacific ocean atmospheric circulation

early holocene climate change and human occupation along the semiarid coast of north central chile the brief terminal pleistocene archaeological site at santa julia sj 318 50 0 s 718 45 0 w is the only one with fluted projectile preforms and megafauna consumption known from the chilean semiarid coastline here we present the climatic history at sj during the early holocene reconstructed from pollen and charcoal analyses spanning 13 2 8 6 ka 10 3 calibrated 14 c yr bp elevated charcoal concentrations confirm human activity by 13 2 ka human occupation decreased in intensity and charcoal practically disappears from the record after 10 6 ka followed by wetland expansion at sj between 10 5 and 9 5 ka local dominance of coastal shrubland reveals that dry phases occurred between 11 2 10 5 and 9 5 9 0 ka overall these findings imply that by modulating available resources at both local and landscape levels climate change may have played an important role in explaining the peopling of semiarid coastal chile copyright 2010 john wiley sons ltd

the younger dryas cold interval as viewed from central greenland abstract greenland ice core records provide an exceptionally clear picture of many aspects of abrupt climate changes and particularly of those associated with the younger dryas event as reviewed here well preserved annual layers can be counted confidently with only 1 errors for the age of the end of the younger dryas 11 500 years before present ice flow corrections allow reconstruction of snow accumulation rates over tens of thousands of years with little additional uncertainty glaciochemical and particulate data record atmospheric loading changes with little uncertainty introduced by changes in snow accumulation confident paleothermometry is provided by site specific calibrations using ice isotopic ratios borehole temperatures and gas isotopic ratios near simultaneous changes in ice core paleoclimatic indicators of local regional and more widespread climate conditions demonstrate that much of the earth experienced abrupt climate changes synchronous with greenland within thirty years or less post younger dryas changes have not duplicated the size extent and rapidity of these paleoclimatic changes

the chronology of the last glacial maximum and deglacial events in central argentine patagonia this paper evaluates the chronology of the last glacial cycle and deglaciation in the lago pueyrredon valley of central patagonia 47 5 s argentina the valley was a major outlet of the former patagonian ice sheet and the moraines that record its fluctuations are an important proxy record of climate change in southern south america such moraines are well preserved in the lago pueyrredon valley owing in part to the semi arid environment east of the mountain front here we provide the first direct chronology for the age of the rio blanco moraine system by utilizing cosmogenic nuclide surface exposure ages boulders on the moraines give 10be exposure ages that indicate the last glacial maximum lgm maximum extent occurred by 27 25 ka subsequent advances occurred at 23 22 ka 20 18 ka and ca 18 17 ka initial deglaciation began after ca 18 17 ka and was interrupted as evidenced by the lago columna moraines up valley subsequently the outlet glaciers occupying both the lago pueyrredon basin chilean name lago cochrane and the lago buenos aires basin chilean name lago general carrera to the north rapidly retreated more than 80 km at around 16 5 15 ka the timing of the lgm maximum extent and the onset of deglaciation occurred broadly synchronously throughout patagonia deglaciation resulted in a series of interconnected glacier dammed lakes in the region that initially drained toward the atlantic ocean and later drained to the pacific ocean as a consequence of disintegrating ice in the andes

patagonian glacier response during the late glacial holocene transition whether cooling occurred in the southern hemisphere during the younger dryas yd is key to understanding mechanisms of millennial climate change although southern hemisphere records do not reveal a distinct climate reversal during the late glacial period many mountain glaciers readvanced we show that the puerto bandera moraine 50 s which records a readvance of the southern patagonian icefield spi formed at or shortly after the end of the yd the exposure age 10 8 0 5 thousand years ago is contemporaneous with the highest shoreline of lago cardiel 49 s which records peak precipitation east of the andes since 13 thousand years ago absent similar moraines west of the andes these data indicate an spi response to increased amounts of easterly sourced precipitation reflecting changes in the southern westerly circulation rather than regional cooling

latest pleistocene to holocene hydroclimates from lake elsinore california abstract the hydroclimate of the southwestern united states us region changed abruptly during the latest pleistocene as the continental ice sheets over north america retreated from their most southerly extent to investigate the nature of this change we present a new record from lake elsinore located 36 km inland from the pacific ocean in southern california and evaluate it in the context of records across the coastal and interior southwest united states including northwest mexico the sediment core recovered from lake elsinore provides a continuous sequence with multi decadal resolution spanning 19 9 ka bp sedimentological and geochemical analyses reveal hydrologic variability in particular sand and carbonate components indicate abrupt changes at the oldest dryas od bolling allerod ba and younger dryas yd transitions consistent with the timing in greenland hydrogen isotope analyses of the c28 n alkanoic acids from plant leaf waxes dwax reveal a long term trend toward less negative values across 19 9 ka bp dwax values during the od suggest a north pacific moisture source for precipitation consistent with the dipping westerlies hypothesis we find no isotopic evidence for the north american monsoon reaching as far west as lake elsinore therefore we infer that wet dry changes in the coastal southwest were expressed through winter season precipitation consistent with modern climatology comparing lake elsinore to other southwest records notably cave of bells and fort stanton we find coincident timing of the major transitions od to ba ba to yd and hydrologic responses during the od and ba the hydrologic response however varied during the yd consistent with a dipole between the coastal and interior southwest the coherent pattern of hydrologic responses across the interior southwest us and northwest mexico during the od wet the ba drier and yd wet follows changes in the atlantic meridional overturning circulation presumably via its combined influence on north pacific winter storm tracks and the extent magnitude of the north american monsoon in contrast lake elsinore and the coastal southwest experiences a deglacial drying trend punctuated by abrupt change at the od to ba and ba to yd transitions this trend tracks rising greenhouse gases through the deglacial with an apparent southward shift in westerly moisture sources adjusting to the retreating ice sheet

south pacific split jet itcz shifts and atmospheric north south linkages during abrupt climate changes of the last glacial period abstract a number of key paleoclimate records in the southern hemisphere midlatitudes exhibit climate changes synchronous with abrupt climate changes in the north atlantic we advance a hypothesis argued from consideration of model evidence observational climate diagnostics and atmospheric dynamics that attributes said climate changes in the southern hemisphere to a modulation in the strength of the south pacific split jet a pronounced zonally asymmetric feature of the wintertime southern hemisphere westerlies north atlantic cooling is associated with a weaker split jet characterized by weaker south pacific subtropical and subpolar jets and a strengthened midlatitude jet it leads to climate impacts over the south pacific sector that coincides with regions with observed paleoclimate changes timed to the north atlantic these circulation changes are envisioned to operate in addition to the climate impacts resulting from the oceanic bipolar seesaw a proposed global atmospheric teleconnection links north atlantic cooling to the weakening of the split jet north atlantic cooling induces a southward shift of the marine intertropical convergence zone and weakening of the asian monsoon the resulting hadley circulation change weakens the wintertime south pacific subtropical jet and which in turn leads to a weaker south pacific split jet a weaker split jet leads to a southward shift of the zero wind stress curl line implying a shift in the same sense for the south pacific subtropical front over land it leads to winter warming over new zealand winter cooling over subtropical south america drying over western patagonia and winter warming and wetting of southernmost patagonia our hypothesis also predicts reduced storminess over west antarctica similar changes but of opposite sign occur in the northern hemisphere where a stronger wintertime north pacific subtropical jet increases precipitation over the western united states

the isotopic composition of hydrogen in nominally anhydrous mantle minerals the common nominally anhydrous minerals of the earth s mantle are an important reservoir for hydrogen in the earth s interior due to their ability to incorporate hydroxyl in trace quantities we present measurements of the isotopic composition d h ratio of hydrogen from upper mantle derived garnet enstatite and augite employing a two step extraction procedure with infrared spectroscopic monitoring of oh removal from the samples raw d values of all samples range from 80 to 130 and blank corrected d of high purity separates with 50 blank contribution to the measured gas lie in the range 92 to 113 these d values together with predictions of fractionation behavior from ir spectroscopic systematics suggest that the d h ratio of the nominally anhydrous mineral reservoir may differ from that of other mantle hydrogen in being relatively depleted in deuterium to the extent that nominally anhydrous minerals control the distribution of water between the earth s hydrosphere and mantle isotopic fractionations between oh in these minerals and hydrous melts or fluids may contribute to the large d h fractionation between the mantle and the hydrosphere

a 9170 year record of decadal to multi centennial scale pluvial episodes from the coastal southwest united states a role for atmospheric rivers abstract a well dated 9170 calendar year before present cal yr bp paleohydrologic reconstruction is presented from lower bear lake in the san bernardino mountains of the coastal southwest united states this new multi proxy record is characterized by alternating organic rich carbonate rich sediment units interpreted to reflect hydrologically forced changes in the lake s depositional environment our interpretation of the proxy data indicates nine decadal to multi centennial pluvial episodes pe over the past 9170 cal yr bp of these nine inferred pluvials five are interpreted as more pronounced based on their combined proxy interpretations pe v 9170 8250 pe iv 7000 6400 pe iii 3350 3000 pe ii 850 700 and pe i 500 476 top of core cal yr bp the lower bear lake record indicates that the san bernardino mountains source region for the mojave river and its terminal playa was wet during the same periods within dating errors to several of the major pluvials proposed from the lakes in the sink of the mojave river our comparison extends north also to tulare lake which drains the southcentral western sierra nevada mountains this temporally and spatially coherent signal indicates that a similar climate forcing acted to increase regional wetness at various times during the past 9170 cal yr bp as originally proposed by enzel ely and colleagues e g enzel et al 1989 enzel 1992 ely et al 1994 enzel and wells 1997 we too contend that holocene pluvial episodes are associated with changing the frequency of large winter storms that track across a broad region at decadal to multi centennial timescales we build upon their hypothesis through the addition of new and better dated site comparisons recent advances in the understanding of atmospheric rivers and improved knowledge of the ocean atmosphere dynamics that caused the early 20th century western united states pluvial

radiocarbon chronology of the late glacial puerto bandera moraines southern patagonian icefield argentina abstract we report radiocarbon dates that constrain the timing of the deposition of the late glacial puerto bandera moraine system alongside the western reaches of lago argentino adjacent to the southern patagonian icefield close maximum limiting radiocarbon ages n 11 for glacier advance into the outer moraines with a mean value of 11 100 60 14 c yrs bp 12 990 80 cal yrs bp were obtained from wood in deformation soft till exposed beneath flow and lodgment till in bahia del quemado on the northeast side of brazo norte north branch of western lago argentino other exposures of this basal deformation till in bahia del quemado reveal incorporated clasts of peat along with larger inclusions of deformed glaciofluvial and lacustrine deposits radiocarbon dates of wood included in these reworked peat clasts range from 11 450 45 14 c yrs bp to 13 450 150 14 c yrs bp 13 315 60 to 16 440 340 cal yrs bp the implication is that during this interval glacier fronts were situated inboard of the puerto bandera moraines with the peat clasts and larger proglacial deposits being eroded and then included in the basal till during the puerto bandera advance minimum limiting radiocarbon ages for ice retreat come from basal peat in cores sampled in spillways and depressions generated during abandonment of the puerto bandera moraines glacier recession and subsequent plant colonization were initiated close behind different frontal sectors of these moraines prior to 10 750 75 14 c yrs bp 12 660 70 cal yrs bp east of brazo rico 10 550 55 14 c yrs bp 12 490 80 cal yrs bp in peninsula avellaneda and 10 400 50 14 c yrs bp 12 280 110 cal yrs bp in bahia catalana in addition a radiocarbon date indicates that by 10 350 45 14 c yrs bp 12 220 110 cal yrs bp the brazo norte lobe or former upsala glacier had receded well up the northern branch of lago argentino to a position behind the herminita moraines furthermore glacier termini had receded to just outboard of the outer holocene moraines at lago frias and lago pearson anita prior to 10 400 40 14 c yrs bp 12 270 100 cal yrs bp and 9040 45 14 c yrs bp 10 210 50 cal yrs bp respectively the most extensive recession registered during the early holocene was in agassiz este valley where the upsala glacier had pulled back behind the outer holocene moraine reaching close to the present day glacier terminus before 8290 40 14 c yrs bp 9300 80 cal yrs bp the radiocarbon dated fluctuations of the lago argentino glacier in late glacial time given here are in accord with changes in ocean mixed layer properties predominately temperature derived from the isotopic record given here of odp core 1233 taken a short distance off shore of the chilean lake district it also matches recently published chronologies of late glacial moraines in the southern alps of new zealand on the opposite side of the pacific ocean from lago argentino finally the timing of the late glacial reversal of the lago argentino glacier fits the most recent chronology for the culmination of the antarctic cold reversal acr in the deuterium record of the epica dome c ice core from high on the east antarctic plateau therefore we conclude that the climate signature of the acr was widespread in both the ocean and the atmosphere over at least the southern quarter of the globe

alteration and mineralization of an oceanic forearc and the ophiolite ocean crust analogy mineralogical chemical and isotopic o c s and sr analyses were performed on minerals and bulk rocks from a forearc basement section to understand alteration processes and compare with mid ocean ridges mor and ophiolites ocean drilling program hole 786b in the izu bonin forearc penetrates 103 m of sediment and 725 m into volcanic flows breccias and basal dikes the rocks comprise boninites and andesites to rhyolites most of the section was affected by low temperature 100 c seawater alteration with temperatures increasing downward the rocks are partly 5 25 altered to smectite fe oxyhydroxide calcite and phillipsite and exhibit gains of k rb and p loss of ca variable changes in si na mg fe sr and y and elevated 18o and 87sr 86sr higher temperatures 150 c in the basal dikes below 750 m led to more intense alteration and formation of chlorite smectite corrensite albite k feldspar and quartz chlorite a 5 m thick hydrothermally altered and pyritized zone at 815 m in the basal dikes reacted with mixtures of seawater and hydrothermal fluids to mg chlorite albite and pyrite and gained mg and s and lost si and ca focused flow of hydrothermal fluids produced serialization halos na k sericite quartz pyrophyllite k feldspar and pyrite along quartz veins at temperatures of 200 250 c high 87sr 86sr ratios of chloritized 0 7055 and sericitized 0 7065 rocks indicate involvement of seawater via mixing with hydrothermal fluids low 34s of sulfide 2 to 5 5 and sulfate 12 5 are consistent with input of magmatic so2 into hydrothermal fluids and disproportionation to sulfide and sulfate alteration processes were generally similar to those at mors but the arc section is more intensively altered in part because of the presence of abundant glassy rocks and mafic phases the increase in alteration grade below 750 m and the mineralization in the basal dikes are analogous to changes that occur near the base of the volcanic section in mor and the troodos ophiolite

hydrogen isotope systematics of submarine basalts the d h ratios and water contents in fresh submarine basalts from the mid atlantic ridge the east pacific rise and hawaii indicate that the primary d h ratios of many submarine lavas have been altered by processes including 1 outgassing 2 addition of seawater at magmatic temperature and 3 low temperature hydration of glass decreases in d and h2o from exteriors to interiors of pillows are explained by outgassing of water whereas inverse relations between d and h2o in basalts from the galapagos rise and the famous area are attributed to outgassing of ch4 and h2 a good correlation between d values and h2o is observed in a suite of submarine tholeiites dredged from the kilauea east rift zone where seawater added directly to the magma affected only the isotopic compositions of hydrogen and argon analyses of some glassy rims indicate that the outer millimeter of the glass can undergo lowtemperature hydration by hydroxyl groups having d values as low as 100 d values vary with h2o contents of subaerial transitional basalts from molokai hawaii and subaerial alkali basalts from the society islands indicating that the primary d values were similar to those of submarine lavas extrapolations to possible unaltered d values and h2o contents indicate that the primary d values of most thoteiite and alkali basalts are near 80 5 the weight percentages of water are variable 0 15 0 35 for mor tholeiites about 0 25 for hawaiian tholeiites and up to 1 1 for alkali basalts the primary d values of 80 for most basalts are comparable to those measured for deep seated phlogopites these results indicate that hydrogen in marked contrast to other elements such as sr nd pb and o has a uniform isotopic composition in the mantle this uniformity is best explained by the presence of a homogeneous reservoir of hydrogen that has existed in the mantle since the very early history of the earth

the 8k event cause and consequences of a major holocene abrupt climate change abstract a prominent abrupt climate event about 8200 years ago brought generally cold and dry conditions to broad northern hemisphere regions especially in wintertime in response to a very large outburst flood that freshened the north atlantic changes were much larger than typical climate variability before and after the event with anomalies up to many degrees contributing to major displacement of vegetative patterns this 8k event provides a clear case of cause and effect in the paleoclimatic realm and so offers an excellent opportunity for model testing the response to north atlantic freshening has the same general anomaly pattern as observed for older events associated with abrupt climate changes following north atlantic freshening and so greatly strengthens the case that those older events also reflect north atlantic changes the north atlantic involvement in the 8k event helps in estimating limits on climate anomalies that might result in the future if warming caused ice melt and hydrologic cycle intensification at high latitudes lead to major changes in north atlantic circulation few model experiments have directly addressed the 8k event and most studies of proxy records across this event lack the time resolution to fully characterize the anomalies so much work remains to be done

ferropigeonite quartz dacites from chichi jima bonin islands latest differentiates from boninite forming magma chichi jima bonin islands consists of dominant eocene submarine volcanic rocks comprising boninites andesites and dacites and subordinate sedimentary rocks the dacites occur frequently in breccias and pillows overlying a boninite pillow lava sequence the boninite pillows are intruded by a multiple dike in which a core boninite is chilled against outer dacites a density stratified chamber may have been capped by a dacite magma the dacites which can be divided into quartz dacite and quartz free dacite are differentiates from the boninite forming magmas because they vary continuously in composition from boninites through andesites the quartz dacites corresponding to rhyolite in sio2 are lower in na2o and k2o than most orogenic dacites some of the dacites are characterized by ferropigeonite wo7 16en23 39fs68 54 phenocrysts and are clearly ferrodacite producing variable amounts of fs rich normative pyroxenes the relation of sio2 to total feo mgo ratio indicates that many of both types of dacites with glasses in boninites are enriched in total feo despite the strong calc alkalic affinity of boninites the crystallization temperature of ferropigeonite with mg value 30 in a quartz dacite is estimated to be 900 c and that in a quartz free dacite to be 1050 c which are unusually high for differentiated silicic rocks some chichi jima rocks are fresh having a low ratio of fe2o3 to feo on the basis of the experimental study of magmatic ferric ferrous equilibria at 1 bar the oxygen fugacities are calculated as 10 13 6 bars at 900 c for a ferropigeonite quartz dacite and 10 8 9 bars at 1200 c for a boninite with the lowest fe3 fe2 both values lie below the quartz fayalite magnetite buffer line the boninite series volcanic rocks have preserved low oxygen fugacities as well as high temperatures until the latest differentiation stage the ferropigeonite phenocrysts have crystallized from the dacite magmas under the conditions of moderately high temperatures very low oxygen fugacities and high total feo and sio2 concentrations

the last glacial holocene transition in southern chile warming at the last glacial termination in the north atlantic region was interrupted by a period of renewed glacial activity during the younger dryas chronozone ydc the underlying mechanism of this cooling remains elusive but hypotheses turn on whether it was a global or a north atlantic phenomenon chronological sedimentological and palaeoecological records from sediments of small lakes in oceanic southern chile demonstrate that there was no ydc cooling in southern chile it is therefore likely that there was little or no cooling in southern pacific surface waters and hence that ydc cooling in the north atlantic was a regional rather than global phenomenon

tracking abrupt climate change in the southern hemisphere a seismic stratigraphic study of lago cardiel argentina 49os lake sediments from a closed basin in southern patagonia argentina provide a continental archive with which to reconstruct climate change and to test the interhemispheric synchroneity of abrupt events high resolution sub bottom seismic profiles of lago cardiel indicate substantial lake level changes since the late pleistocene which were identified and dated in a series of long piston cores these data allow the reconstruction of the regional water balance at 49 s since the late glacial the seismic stratigraphy reveals a dry late glacial climate with a desiccation of the basin around 11 220 yr bp 14 c lake level rapidly increased by 135 m at the holocene transition following the early holocene highstand at 55 m lake level never dropped significantly below modern level the palaeoclimate changes implied by the lago cardiel record are out of phase with those implied by records from tropical south america and demonstrate considerable latitudinal asynchroneity in the climate evolution of this continent

major hydrological regime change along the semiarid western coast of south america during the early holocene water availability in the semiarid western coast of chile 30 32 s is conditioned by high interannual precipitation variability reflecting the transition between arid subtropical and moist mid latitude climates in the southeastern pacific ocean a paleoclimate reconstruction based on the latest pleistocene holocene geological record from the quebrada santa julia archeological site in chile 31 50 s and on modern meteorological mechanisms producing alluvial episodes in this region indicates a major change in the rainfall regime shortly after 8600 cal yr bp this together with other paleoclimate proxies along the west coast of south america 34 14 s suggests la nina like conditions 13 000 8600 cal yr bp based on sedimentological and geomorphologic evidence we hypothesized that the absence of heavy rainfall events in northern chile and the new hydrological regime that prevailed ca 8600 5700 cal yr bp in north central chile resulted from an increase in the large scale westerly flow over central chile as expected in near neutral enso conditions this atmospheric circulation anomaly is compatible with an equatorward shift of the influence of the southeast pacific subtropical anticyclone relative to the early holocene prior to the onset of modern enso variability

mineralogy and stable isotope geochemistry of hydrothermally altered oceanic rocks mineralogical and isotopic variations observed in altered glassy and crystalline rocksfrom the east pacific rise and the mid atlantic ridge provide information about the temperatures of alteration and seawater rock ratios for various hydrothermal regimes within the oceanic crust a systematic increase in alteration temperature is evident for the glassy rocksin the sequence 1 nontronite and celadonite vesicle fillings 35 c 2 saponite rich pillow breccias 130 170 c 3 calcite rich greenstone breccias and epidote rich greenstone 200 350 c theseresults include the highest temperatures thus far reported for saponite formation the seawater dominated hydrothermal alteration process that formed the saponite rich pillow breccias is characterized by high water rock ratios 0 1 low to moderate temperatures a seawater origin of most of the carbon in vein calcites 13 c 0 and the predominance of fe rich saponite and calcite as secondary phases greenstones chlorite quartz epidote and greenstone breccias chlorite quartz albite calcite are altered in a rock dominated system with lower water rock ratios 50 1 to 13 c 4 the crystalline rocks diabase gabbro and metagabbro are affected to varying degrees by pervasive high temperature seawater interactions that commence soon after solidification producing varying proportions of fine grained secondary minerals including talc smectite chlorite vermiculite actinolite and sodicplagioclase hydrothermal solutions derived from alteration of the crystalline rocks are of the appropriate temperature and isotopic composition to alter the overlying glassy rocks to the observed mineralogies as well as being the source of metal rich deposits associated with the oceanic spreading centers

a seismic stratigraphic analysis of mariana forearc basin evolution new seismic data collected in the 14 5 18 5 n mariana segment of the izu bonin mariana island arc system image six seismic stratigraphic sequences that can be mapped throughout the inner forearc these sediments were most likely deposited from 35 ma to the present the oldest stratigraphic units 1 2 and 3 are syn rift volcaniclastic deposits unit 4 deposits accumulated during a period of mild structural inversion which resulted in several isolated reverse faulted anticlines within the forearc sedimentary basin a late period of extensional deformation began near the end of unit 5 deposition and continued through unit 6 sedimentation to the present seismic lines show that the basement of the forearc is composed of large rotated fault blocks and half grabens with ne nw and nne trends fault offset calculations show that basement faults with dips between 45 and 50 account for only 4 total extension in the forearc south of 16 3 n normal growth faults initiated during basement extension offset the frontal arc high from a deep forearc basin from correlations with the known geologic history we hypothesize that extension during deposition of units 1 through 3 corresponds to rifting of the eo oligocene arc between 35 ma and 29 ma older deposits being too thin to be seismically resolvable localized compression during unit 4 accumulation occurred some time after eo oligocene rifting in the early miocene late stage normal faulting near the end of deposition of unit 5 and throughout unit 6 accumulation may be associated with the opening of the mariana trough backarc basin from 8 ma years to the present there is a higher density of these later faults in the inner forearc between 15 5 and 17 n and in the outer forearc between 14 n and 18 n recent extension is at least partially accommodated by reactivation of older basement faults with the same ne nw and nne trends stratigraphic relationships indicate that the inner forearc south of 16 3 n has differentially subsided and tilted trenchward possibly as a result of a recent change in subducting slab geometry or subducted relief under the forearc

petrology and geochemistry of boninite series volcanic rocks from the mariana trench boninite series volcanic rocks have been recovered from three dredge hauls on the inner slope of the mariana trench these hauls included olivine boninites boninites boninitic andesites and boninitic dacites as well as island arc tholeiitic basalts and andesites the boninite series volcanics range from 52 to 68 sio2 and are characterized by very low abundances of high field strength cations and heavy rare earth elements boninites and olivine boninites have phenocrysts of olivine and orthopyroxene the andesites phenocrysts of orthopyroxene and clinopyroxene and the dacites orthopyroxene clinopyroxene and plagioclase most of the major and trace element variation in the series from boninite to boninitic dacite can be modelled by fractionation of olivine orthopyroxene clinopyroxene and plagioclase in the proportions 2 5 4 1 2 leaving 47 residual liquid the fractionation must be in part open system reverse zoned phenocrysts resorbed olivine and plagioclase xenocrysts and bulk rock compositions which cannot be fit by simple closed system crystallization indicate some magma mixing and phenocryst accumulation two boninitic magma stems can be identified with similar high field strength element abundances but different amounts of ca na al and light rare earth elements there is also evidence for a magma stem transitional in chemistry from the boninites to arc tholeiites the compositions of these boninites are consistent with hypotheses for boninite formation by partial melting of a depleted mantle mixed with an incompatible element enriched fluid the mariana forearc boninite series lacks a strong iron enrichment but produces andesites with lower ti al and y zr and higher mg ni and cr than typical calcalkaline arc andesites and dacites boninites in the mariana system were erupted only in the earliest phases of subduction zone activity

antarctic timing of surface water changes off chile and patagonian ice sheet response marine sediments from the chilean continental margin are used to infer millennial scale changes in southeast pacific surface ocean water properties and patagonian ice sheet extent since the last glacial period our data show a clear antarctic timing of sea surface temperature changes which appear systematically linked to meridional displacements in sea ice westerly winds and the circumpolar current system proxy data for ice sheet changes show a similar pattern as oceanographic variations offshore but reveal a variable glacier response time of up to 1000 years which may explain some of the current discrepancies among terrestrial records in southern south america

flood stratigraphies in lake sediments a review abstract records of the frequency and magnitude of floods are needed on centennial or millennial timescales to place increases in their occurrence and intensity into a longer term context than is available from gauged river flow and historical records recent research has highlighted the potential for lake sediment sequences to act as a relatively untapped archive of high magnitude floods over these longer timescales abyssal lake sediments can record past floods in the form of coarser grained laminations that reflect the capacity for river flows with greater hydrodynamic energy to transport larger particles into the lake this paper presents a framework for investigating flood stratigraphies in lakes by reviewing the conditioning mechanisms in the lake and catchment outlining the key analytical techniques used to recover flood records and highlighting the importance of appropriate field site and methodology selection the processes of sediment movement from watershed to lake bed are complex meaning relationships between measureable sedimentary characteristics and associated river discharge are not always clear stratigraphical palaeoflood records are all affected to some degree by catchment conditioning fluvial connectivity sequencing of high flows delta dynamics as well as within lake processes including river plume dispersal sediment focussing re suspension and trapping efficiency with regard to analytical techniques the potential for direct e g laser granulometry and indirect e g geochemical elemental ratios measurements of particle size to reflect variations in river discharge is confirmed we recommend care when interpreting fine resolution geochemical data acquired via micro scale x ray fluorescence xrf core scanning due to variable down core water and organic matter content altering x ray attenuation we also recommend accounting for changes in sediment supply through time as new or differing sources of sediment release may affect the hydrodynamic relationship between particle size and or geochemistry with stream power where these processes are considered and suitable dating control is obtained discrete historical floods can be identified and characterised using palaeolimnological evidence we outline a protocol for selecting suitable lakes and coring sites that integrates environmental setting sediment transfer processes and depositional mechanisms to act as a rapid reference for future research into lacustrine palaeoflood records we also present an interpretational protocol illustrating the analytical techniques available to palaeoflood researchers to demonstrate their utility we review five case studies of palaeoflood reconstructions from lakes in geographically varied regions these show how lakes of different sizes and geomorphological contexts can produce comprehensive palaeoflood records these were achieved by consistently applying site validated direct and proxy grain size measurements well established chronologies validation of the proxy process interpretation and calibration of the palaeoflood record against instrumental or historical records

asynchronous glacier dynamics during the antarctic cold reversal in central patagonia abstract we present 14 new 10be cosmogenic nuclide exposure ages quantifying asynchronous readvances during the antarctic cold reversal from glaciers in the baker valley region of central patagonia we constrain glacier and ice dammed palaeolake dynamics using a landsystems approach concentrating on outlet glaciers from the eastern northern patagonian icefield npi and monte san lorenzo msl soler glacier npi produced lateral moraines above lago bertrand from 15 1 0 7 to 14 0 0 6 ka when it dammed the drainage of lago general carrera buenos aires through rio baker at a bedrock pinning point at this time soler glacier terminated into the 400 m deseado level of the ice dammed palaeolake later calluqueo glacier msl deposited subaerial and subaqueous moraines in the salto valley near cochrane at 13 0 0 6 ka these moraines were deposited in an ice dammed palaeolake unified through the baker valley lago chalenko 350 m asl the salto valley glaciolacustrine landsystem includes subaqueous morainal banks ice scoured bedrock glacial diamicton plastered onto valley sides perched delta terraces kame terraces ice contact fans palaeoshorelines and subaerial push and lateral moraines boulders from the subaqueous salto moraine became exposed at 12 1 0 6 years indicating palaeolake drainage these data show an asynchronous advance of outlet glaciers from the northern patagonian icefield and monte san lorenzo during the antarctic cold reversal these advances occurred during a period of regional climatic cooling but differential moraine extent and timing of advance was controlled by topography and calving processes

timing of past glaciation at the sierra de aconquija northwestern argentina and throughout the central andes abstract advances in cosmogenic nuclide exposure dating have made moraines valuable terrestrial recorders of palaeoclimate a growing number of moraine chronologies reported from the central andes show that tropical glaciers responded sensitively to past changes in precipitation and temperature over timescales ranging from 103 to 105 years however the causes of past glaciation in the central andes remain uncertain explanations have invoked insolation modulated variability in the strength of the south american summer monsoon teleconnections with the north atlantic ocean and or cooling in the southern hemisphere the driver for these past climate changes is difficult to identify partly due to a lack of dated moraine records especially in climatically sensitive areas of the southern central andes moreover new constraints are needed on precisely where and when glaciers advanced we use cosmogenic 10be produced in situ to determine exposure ages for three generations of moraines at the sierra de aconquija situated at 27 s on the eastern flank of the southern central andes these moraines record glacier advances at approximately 22 ka and 40 ka coincident with summer insolation maxima in the sub tropics of the southern hemisphere as well as at 12 5 ka and 13 5 ka during the younger dryas and the antarctic cold reversal respectively we also identify minor glaciation during bond event 5 also known as the 8 2 ka event these moraines register past climate changes with high fidelity and currently constitute the southernmost dated record of glaciation on the eastern flank of the central andes to contextualise these results we compile 10be data reported from 144 moraines in the eastern central andes that represent past glacier advances we re calculate exposure ages from these data using an updated reference production rate and we re interpret the moraine ages by taking the oldest clustered boulder age after the exclusion of outliers attributed to nuclide inheritance as closest to the timing of glacier advance an approach for which we provide empirical justification this compilation reveals that central andean glaciers have responded to changes in temperature and precipitation we identify cross latitude advances in phase with insolation cycles the last global glacial maximum and episodes of strengthened monsoonal moisture transport including the younger dryas and heinrich stadials 1 and 2 our results from the sierra de aconquija allow us to constrain the southerly limit of enhanced precipitation associated with heinrich stadials at 25 s more broadly our findings demonstrate at both local and regional scales that moraines record past climate variability with a fine spatial and temporal resolution

lake levels for the past 19 000 years from the tl05 4 cores tulare lake california usa geophysical and geochemical proxies abstract geochemical and geophysical proxy data from the tl05 4 lake plain cores of tulare lake california are reported on here representing most of the past 19 000 years the new record consists of carbon nitrogen ratios total organic carbon toc nitrogen n total inorganic carbon tic grain size and magnetic susceptibility analyses from samples taken at 1 cm intervals 45 yr sample age control is provided by 22 radiocarbon dates the first part of the record 19 0 14 5 cal ka bp consists of elevated sand and silt percentages and higher sedimentation rates interpreted as elevated runoff associated with melting of the tioga age sierra nevada ice cap the tic was undetectable and toc and n were low suggesting low productivity in a relatively sterile freshwater lake from 14 5 to 10 3 cal ka bp the deposits consisted of 50 clay and 50 silt with tic and toc extremely low which is consistent with a stable low productivity lake from 10 3 to 7 5 cal ka bp an initial pulse of fining upward sand gave way to increased clay deposition that suggests a lake transgression to a stable highstand coeval with the deep water event found in previously published records of tulare lake and other lakes from central and southern california including owens lake and lake elsinore a few hundred year duration spikes in tic centered at 8 0 cal ka bp is suggestive of evaporating lake conditions toward the end of this early holocene highstand tulare lake dropped quickly to a relative low at 7 5 cal ka bp but then lake level increased steadily until 3 0 cal ka bp high amplitude fluctuation in almost all proxies occurs from 2 5 to 1 8 cal ka bp at the end of the record suggesting that this time interval was characterized by rapid fluctuations in lake level tulare lake levels during the holocene vary in conjunction with sea surface temperature sst records from the ocean drilling program odp site 1017 located off the coast of central california which suggests that variations in ssts throughout the holocene drove changes in precipitation in the sierra nevada and hence tulare lake level since historic lake level histories have been shown to be directly related to stream discharge from the sierra nevada this observation will be integral in forecasting future decadal scale changes in southern san joaquin valley water supply due to anticipated climate change

early and mid holocene age for the tempanos moraines laguna san rafael patagonian chile data about the nature and timing of holocene events from the southern hemisphere especially in southern south america are required to provide insight into the extent and nature of past climate change in a region where land based records are restricted here we present the first use of single grain optically stimulated luminescence osl dating of a moraine sequence recording glacial advance along the western side of the patagonian icefields dates from the tempanos moraines at laguna san rafael lsr show that the san rafael glacier srg advanced to maximum holocene positions during the period 9 3 to 9 7 ka and at 5 7 ka outwash lying beneath the moraine in its northern portion dated to 7 7 ka indicates that the glacier front was also advanced at this time since these advances span both the regional early holocene warm dry phase 11 5 ka to 7 8 ka and the subsequent cooling and rise in precipitation in the mid late holocene since 6 6 ka we infer that the advances of the srg are not simply climate driven but that the glacier has also probably responded strongly to non climatic stimuli such as internal ice dynamics and the transition between calving and non calving many westwards flowing glaciers in patagonia were probably calving during much of the late pleistocene and holocene so we conclude that establishing robust glacial chronologies where climatic and non climatic factors cannot be distinguished is likely to remain a challenge

high resolution paleomagnetic secular variations and relative paleointensity since the late pleistocene in southern south america abstract paleomagnetic inclination declination and relative paleointensity were reconstructed from the sediments of laguna potrok aike in the framework of the international continental scientific drilling program icdp potrok aike maar lake sediment archive drilling project pasado here we present the u channel based full vector paleomagnetic field reconstruction since 51 2 ka cal bp the relative paleointensity proxy rpi was built by normalising the natural remanent magnetisation with the anhysteretic remanent magnetisation using the average ratio at 4 demagnetisation steps part of the chrm interval nrm arm 10 40 mt a grain size influence on the rpi was removed using a correction based on the linear relationship between the rpi and the median destructive field of the natural remanent magnetisation mdf nrm the new record is compared with other lacustrine and marine records and stacks from the mid to high latitudes of the southern hemisphere revealing consistent millennial scale variability the identification of the laschamp and possibly the mono lake geomagnetic excursions and a direction swing possibly associated to the hilina pali excursion at 20 ka cal bp nonetheless a global scale comparison with other high resolution records located on the opposite side of the earth and with various dipole field references hint at a different behaviour of the geomagnetic field around southern south america at 46 ka cal bp

summer precipitation events over the western slope of the subtropical andes abstractsummertime december february djf precipitation over the western slopes of the subtropical andes 32 36 s accounts for less than 10 of the annual accumulation but it mostly occurs as rain and may trigger landslides leading to serious damages based on 13 year of reanalysis in situ observations and satellite imagery a synoptic climatology and physical diagnosis reveal two main weather types lead to distinct precipitation systems the most frequent type 80 of the cases occurs when a short wave midlevel trough with weak winds and thermally driven mountain winds favor the development of convective precipitation during the daytime the trough progresses northwest of a long lasting warm ridge which produces low level easterly airflow that enhances its buoyancy as it moves over the arid land of western argentina toward the andes the weak winds aloft facilitate the penetration of the moist easterly flow into the andes midlevel flow coming from the west side of the andes is decoupled from

southern westerlies during the holocene deduced from geomorphological and pedological studies in the norte chico northern chile 27 33 s abstract in the norte chico precipitation is controlled by atmospheric perturbations and frontal systems associated with the belt of westerly wind circulation the holocene climatic history of the region can be reconstructed from geomorphic and pedologic investigations in comparison to modern climatic conditions increased influence of the westerlies is deduced for the time periods prior to 7300 yr b p between 5000 3700 yr b p 3000 1800 yr b p and around 270 yr b p it remains uncertain whether the increased influence of the westerlies was the consequence of northward shifts of the westerlies as a whole of a meridional expansion of the westerly belt or only of intensity changes of the atmospheric dynamics almost synchronous with changes in the westerlies the coastal fogs in the region were apparently reduced or the fog belt in the coastal range was elevated probably due to a weakened upwelling and warmer water conditions in the eastern pacific in general the climate of the norte chico has become more variable since 5000 yr b p especially since 3000 yr b p with frequent changes of the geoecological conditions

early to mid holocene aridity in central chile and the southern westerlies the laguna aculeo record 34 s abstract central chile 32 35 s lies at the northern border of strong westerly influence and thus exhibits a steep precipitation gradient therefore the palaeoclimatic archives in the region are suitable for detecting past moisture changes the study of laguna aculeo 33 50 s 70 54 w presents a multiproxy holocene lake record including sedimentology geochemistry mineralogy pollen diatoms and radiocarbon dating 17 dates results indicate an arid early to mid holocene period about 9500 5700 cal yr b p after 5700 cal yr b p effective moisture increased progressively and around 3200 cal yr b p modern humid conditions were established numerous intercalated clastic layers reflect flood deposition during rainy winters a fluvial unit was deposited shortly before 9000 cal yr b p subsequently flood events were absent until 5700 but have become frequent since 3200 cal yr b p the frequency of flood layers possibly points to weak or no el nino activity during the early and mid holocene with a subsequent increase during the late holocene during the early and mid holocene the westerlies were probably blocked and hence deflected southward by the subtropical high pressure cell higher precipitation during the last 3200 yr seems strongly related to a weakened subtropical high pressure cell with intensified westerlies and possibly increased el nino activity

mid holocene paleoenvironments in northwestern argentina main patterns and discrepancies abstract this paper summarizes the available paleoenvironmental information for the mid holocene in northwestern argentina in order to systematize a multi scale scenario for human adaptation in the area the main results of the studies carried out by several research teams that have studied the conditions during this period in the tropical andean region are described and compared taking into account their geographical setting the proxies involved and their particular space time resolution the paleoenvironmental situation prior to the onset of mid holocene conditions i e starting at the late glacial maximum is summarized to estimate the nature and extent of the changes occurred during this period paleoenvironmental results their characteristics and interpretation are also considered a general trend towards an aridization process that fostered a hydrologic stress process is traceable along the mid holocene in northwestern argentina and the tropical andes however several localities seem to have retained wetter conditions increasing the contrast between highly productive environments and the generally dry landscape this paper is only a first step towards a full understanding of the diversity and complexity of the mid holocene in different space time scales but a necessary one in order to start to model the resources structure available for human groups in the past in the andes

an integrated analysis of the march 2015 atacama floods in march 2015 unusual ocean and atmospheric conditions produced many years worth of rainfall in a 48 h period over northern chile s atacama desert one of earth s driest regions resulting in catastrophic flooding here we describe the hydrologic and geomorphic drivers of and responses to the 2015 atacama floods in the salado river we estimated a flood peak discharge of approximately 1000 m3 s which caused widespread damage and high sediment loads that were primarily derived from valley fill erosion hillslopes remained surprisingly intact despite their lack of vegetation in the coastal city of chanaral flooding of the salado river produced maximum water depths over 4 5 m meters thick mud deposition in buildings and along city streets and coastal erosion the atacama flooding has broad implications in the context of hazard reduction erosion of contaminated legacy mine tailings and the atacama s status as a terrestrial analog for mars

comment on absence of cooling in new zealand and the adjacent ocean during the younger dryas chronozone barrows et al reports 5 october 2007 p 86 presented cosmogenic exposure dates and data from an ocean sediment core that challenge evidence for glacier advance in new zealand during the younger dryas event we use modeling of geomorphic processes to argue that their cosmogenic exposure dates are inconclusive

on the functioning of the southern oscillation in the south american sector part i surface climate abstract the functioning of the southern oscillation so over south america and the surrounding tropical atlantic and eastern pacific oceans is studied through analyses of bimonthly patterns of correlation between an so index and the fields of pressure wind temperature and rainfall hydrometeorological anomalies being further ascertained from river discharge and lake level records and measurements of outgoing longwave radiation most pronounced is the anomalously low pressure over the eastern pacific during the negative so phase defined by anomalously low high pressure at tahiti darwin consistently positive so pressure correlations over the eastern tropical pacific extend eastward into the north atlantic region and southern south america during the respective winter semester during the austral winter the tendency for anomalously abundant rainfall in central chile during the negative so phase appears related to an anomalously weak and northward displaced south pacific subtropical high while relativ

halogens of bushveld complex south africa δ37cl and cl f evidence for hydration melting of the source region in a back arc setting abstract the bushveld complex is one of only a few layered intrusions anomalously enriched in chlorine this study presents the first chlorine stable isotope analyses of bushveld and associated rocks designed to constrain the source of bushveld cl most samples overlap the range of values for pristine morb and altered seafloor samples 37 cl 4 relative to sea water this contrasts with distal metasedimentary floor rocks 37 cl 0 with little evidence of contamination away from the marginal rocks the cl isotope composition and high cl f ratio is therefore a fundamental characteristic of the lower and critical zone magmas and not derived from infiltration from the country rock these results the high cl f ratio and the boninitic arc like character of bushveld magma are consistent with hydration partial melting of a depleted source in a subduction related setting with cl supplied either by the dehydration of a subducted slab with a heavy cl signature or an overridden wet mantle hotspot

are bushveld u type parent magmas boninites or contaminated komatiites three distinct categories of magmas bushveld u type parent magmas boninites and siliceous high magnesium basalts from archaean greenstone belts share the distictive geochemical characteristics of high mgo 9 19 low tio2 less than 1 and high sio2 greater than 52 boninites are generally thought to form by hydrous melting of metasomatized previously depleted upper mantle while siliceous high magnesium basalts shmb in greenstone belts have recently been recognized as the products of combined fractionation and crustal contamination of komatiites both these mechanisms can apparently give rise to similar end products and both mechanisms have been proposed for the petrogenesis of bushveld u type magmas

carbonate and organic matter sedimentation and isotopic signatures in lake chungara chilean altiplano during the last 12 3 kyr abstract sediments in lakes in the andean volcanic setting are often made up of diatomaceous ooze together with volcaniclastics and small amounts of carbonates despite their scarcity carbonates along with organic matter provide significant paleoenvironmental information about lake systems this study focuses on the carbonates in lake chungara their morphologies distribution and origin deduced from the isotopic markers these markers reflected changes in the water and the biomass between the onset of the holocene and around 9 6 cal kyr bp these changes are marked by general increases in toc tn and tn 15nair and by fluctuating values of toc 13cvpdb in its sediments and are probably related to major shifts in the lake surface volume associated with rises in lake level an increase in salinity around 10 cal kyr bp is thought to be linked to a short dry period giving rise to the onset of carbonate production the mid holocene arid period between 7 3 and 3 5 cal ka bp with a maximum of aridity around 6 0 cal kyr bp was deduced from 18ovpdb values in the endogenic carbonates these results match the reconstructions in lake titicaca based on benthic diatoms and paleoshore levels offshore sediments mainly consist of a diatomaceous ooze laminated in the lower half unit 1 and banded massive with tephra layers in the upper half of the sequence unit 2 toc 13cvpdb and the c n ratio confirm that phytoplankton was the main source of organic matter in these sediments shallower sediments units 3 to 5 developed in platform and littoral settings providing evidence of subaqueous macrophytes and to a lesser extent land plants carbonate content ranges between 0 1 and 6 wt in offshore settings 30 to 40 m water depth and reaches the maximum values in the lower part of unit 2 carbonate minerals low magnesium calcite and minor amounts of high magnesium calcite and aragonite are scarce and are arranged in mm thick layers commonly forming cm thick levels or bioclasts carbonate layers are made up of euhedral to subhedral spindle shaped calcite crystals and to a lesser extent aragonite needles all in the m range aragonite spheroids coexist in littoral sediments with other carbonate shapes and charophyte remains where carbonate reaches locally up to 20 wt co2 photosynthetic depletions related to seasonal phytoplankton blooms were responsible for the high frequency deposition of mm thick carbonate layers the average values for 13cvpdb in lake water plankton and sediments of lake chungara as organic matter or as carbonate are around 15 higher than commonly reported values in other lakes this 13c enrichment is attributed to carbon assimilation from a dic affected by methanogenesis in which hco3 is the dominant species the 13cvpdb and 18ovpdb variations and their covariation in endogenic carbonates suggest that lake water volume and lake level increased along the holocene

helium 3 and deuterium in back arc basalts lau basin and the mariana trough samples of fresh basalt glass from the mariana trough and the lau basin were analyzed for their isotopic composition of water and helium in order to identify the sources of the volatiles in back arc basin basalts in the mariana trough basalts the concentration 0 64 2 1 wt and d h ratio d 46 to 32 of the water provide important evidence for a water rich component from the subducting lithosphere extrapolation to infinite water content gives an end member d h ratio of d 25 3he 4he ratios are in general similar to morb values 8 ra and indicate that mariana trough basalts represent a mixture of a morb type mantle and an alkali and water rich component from the descending slab in contrast the lau basin produces both hydrous 1 3 wt h2o and relatively anhydrous 0 12 0 35 wt basalts the d h ratio d 43 in the hydrous lau basin basalt resembles those of mariana trough lavas the low water contents 0 12 0 35 wt and morb like d h ratios d 63 to 70 in three of five lau basin samples show that the water rich component observed in all mariana trough lavas is absent in some lau basin lavas and not essential for the production of back arc basalts the high3he 4he ratio of rochambeau bank in the northern lau basin 11 ra confirms an earlier analysis by lupton and craig and provides evidence for an enriched mantle source region beneath the lau basin which is perhaps related to the high 3he samoan hotspot

boninite petrogenesis and alteration history constraints from stable isotope compositions of boninites from cape vogel new caledonia and cyprus 18o values of unaltered olivine and pyroxene phenocrysts in boninites from several areas range from 5 8 to 7 4 and indicate that the source for most boninites is more 18o rich than morbs and other oceanic basalts the source for oxygen and other major elements is most likely a refractory portion of the mantle having a 18o value of up to 7 0 to which must be added a small amount of h2o rich fluid to induce partial melting this fluid which is derived from subducted crust is the vehicle for lrees including nd the variable normally low nd values typical of boninites do not correlate with the 18o values post eruptive exchange of oxygen in the glass of boninites with that of sea water at low temperatures 150 c produces 18o values of 10 in optically fresh glass hydration of the glass has increased the water contents of most boninites from estimated magmatic values of 1 2 wt to 2 4 wt and produced d values of 80 which may be lower than the original magmatic d values in contrast to most submarine pillow basalts the magmatic volatile composition of boninite lavas has been extensively modified as a result of post eruptive interaction with seawater

late and postglacial vegetation and fire history in southern patagonia and tierra del fuego abstract two 17 000 yr old peat bog records from low elevation sites in tierra del fuego harberton 54 54 s and southern patagonia rio rubens 52 4 48 s and one c 14 000 cal yr bp record from the upper treeline in tierra del fuego paso garibaldi 54 43 s were analyzed for pollen charcoal and plant macrofossils to reconstruct changes in regional and local vegetation fire frequency and bog hydrology respectively past environmental changes in both lowland records and in the upper treeline record are interpreted in terms of variations in effective moisture during the late glacial period effective moisture changes at both low and high elevation sites were interpreted from comparable shifts between mesic herb rich grasslands and arid empetrum heath or shrub grassland with abundant disturbance indicators the late glacial effective moisture changes were primarily driven by temperature changes during the early holocene expansion of open nothofagus woodlands in the lowlands in present day areas of dense forest was related to a marked precipitation increase however precipitation must have remained highly variable with century long periods of increased summer drought as evidenced by repeated intervals when bogs dried out and fire frequency was high up slope shifts of the nothofagus forest andean tundra ecotone at 11 000 and 9000 cal yr bp also appear to reflect precipitation increases precipitation variability however must not have affected the upper treeline environments as no fires were recorded and the present day nothofagus forest had become established after 9000 cal yr bp upper treeline apparently was below present from 8000 to 7000 and 2500 to c 400 cal yr bp during those times low elevation environments did not register change which suggests that the upper treeline may have been affected by lower temperatures after c 5000 cal yr bp fires became rare in the lowlands suggesting a shift to an equable precipitation regime with only minor intervals of summer drought no simultaneous change was recorded at the upper treeline thus for the late glacial and early holocene the upper and lower treeline environments apparently responded similarly to primarily moisture changes only during the mid and late holocene environmental changes at high and low elevations differed suggesting responses to different climate signals precipitation in the lowlands and temperature at high elevation

radiocarbon reservoir effect and the timing of the late glacial early holocene humid phase in the atacama desert northern chile we revise substantially the regional chronology of lake level fluctuations from the late glacial early holocene humid phase along a high altitude transect 3500 to 4500 m between 18 s and 28 s in the southwestern altiplano of northern chile radiocarbon dates and 210pb profiles for limnic and terrestrial materials allow us to estimate and justify reservoir correction values for conventional 14c dates our chronology suggests that the latest pleistocene early holocene humid phase started between 13 000 and 12 000 14c yr b p and that maximum lake levels were reached between 10 800 and 9200 14c yr b p this is significantly younger than what has been established so far for the titicaca uyuni basin in bolivia the paleolakes disappeared sometime between 8400 and 8000 14c yr b p our revised chronology agrees with the regional history of human occupation and is broadly synchronous with vegetation changes in subtropical continental south america and with the onset of wetland expansion in the northern hemisphere tropics

absence of cooling in new zealand and the adjacent ocean during the younger dryas chronozone as the climate warmed at the end of the last glacial period a rapid reversal in temperature the younger dryas yd event briefly returned much of the north atlantic region to near full glacial conditions the event was associated with climate reversals in many other areas of the northern hemisphere and also with warming over and near antarctica however the expression of the yd in the mid to low latitudes of the southern hemisphere and the southwest pacific region in particular is much more controversial here we show that the waiho loop advance of the franz josef glacier in new zealand was not a yd event as previously thought and that the adjacent ocean warmed throughout the yd

what do the hirm and s ratio really measure in environmental magnetism the hard isothermal remanent magnetization hirm and the s ratio are widely used in environmental magnetism to quantify the absolute and relative concentrations respectively of antiferromagnetic minerals hematite and goethite in mineral mixtures we demonstrate that synthetic al substituted hematite and goethite exhibit a wide range of coercivities which significantly influences the hirm and s ratio these parameters are therefore not necessarily straightforward indicators of the absolute and relative concentrations of hematite goethite to circumvent this problem we propose a new parameter the l ratio which is the ratio of two remanences after alternating field af demagnetization of an irm imparted in a 1 t field with a peak af of 100 mt and 300 mt irmaf 300mt irmaf 100mt these parameters are easily measured using modern vibrating sample or alternating gradient magnetometers changes in hirm only reflect changes in the absolute concentration of hematite and or goethite if the l ratio is relatively constant conversely l ratio fluctuations indicate variable coercivities that possibly reflect changes in the source of hematite goethite corresponding hirm and s ratio variations should be interpreted with caution in such cases the l ratio can be determined using equivalent terms depending on available instrumentation and measurement protocols for example the hirm is equivalent to irmaf 300mt likewise 0 5 sirm irm 100mt where irm 100mt represents the remanent magnetization obtained by first saturating the sample in a high field and then applying a back field of 100 mt is equivalent to irmaf 100mt the hirm 0 5 sirm irm 100mt ratio is therefore a suitable substitute for the l ratio when measurements are made with a long core magnetometer the newly proposed l ratio is straightforward to measure on a wide range of instruments and can provide significant new insights and reduce ambiguities associated with interpretation of two widely used parameters in environmental magnetism the hirm and s ratio

melting of the shallow upper mantle a new perspective detailed examination of liquidus phase relationships in binary and ternary joins of the cfmas cr system has permitted a rigorous determination of the dry melting path of an initially fertile spinel peridotite composition resembling bulk silicate earth or morb pyrolite it is demonstrated that it is impossible to model mantle melting accurately using only one set of ratios of phases entering the melt this implies that the melting process is primarily controlled by solid solution rather than eutectic behaviour the proportions of phases entering a melt depend on whether a phase reacts and or disappears from a system and on the choice of the initial and final peridotite compositions four discrete domains in the melting regime of upper mantle peridotites are distinguished each characterized by different phase melting coefficients relating to the melting of 1 lherzolites 2 clinopyroxene bearing harzburgites i e free clinopyroxene 3 clinopyroxene saturated harzburgites i e clinopyroxene in solid solution in orthopyroxene and 4 clinopyroxene free harzburgites i e no clinopyroxene the proposed non linear fashion in which mantle lithologies melt explains the inadequacy of all previous models to reproduce the observed compositions of upper mantle peridotite melting residues it is suggested that 1 olivine and orthopyroxene will melt cotectically 2 clinopyroxene and spinel will lose most of their aluminous component after 8 melting within the first 4 kb 12 km of ascent from the dry solidus and that 3 clinopyroxene will disappear completely from a morb pyrolite mantle after 42 melting although such a number is significantly higher than that dictated by the position of the clinopyroxene out curves from peridotite isobaric equilibrium melting experiments 22 it is emphasized that the latter are a gross oversimplification of the natural melting process and are not equivalent to melting during adiabatic upwelling it is concluded that the commonly postulated disappearance of clinopyroxene from fertile peridotite compositions at 22 melting is greatly in error if melting in an adiabatically rising mantle is considered thus providing an explanation for many unsuccessful attempts by various authors to model the behaviour of transition elements in sub oceanic and supra subduction zone mantle and derivative magmas

deglacial changes of the southern margin of the southern westerly winds revealed by terrestrial records from sw patagonia 52 s much of the ongoing discussion regarding synchrony or bipolar asynchrony of paleoclimate events has centered on the timing and structure of the last glacial termination in the southern mid latitudes in particular the southwestern patagonian region 50 e55 s its location adjacent to the drake passage and near the southern margin of the southern westerly winds sww allows examining the postulated links between the southern oceanesww coupled system and atmospheric co2 variations through the last glacial termination results from two sites located in the ultima esperanza area 52

covariability of the southern westerlies and atmospheric co2 during the holocene a suite of mechanisms has been proposed to account for natural variations in atmospheric co 2 during the holocene all of which have achieved limited success in reproducing the timing direction and magnitude of change recent modeling studies propose that changes in the latitudinal position and strength of the southern hemisphere westerly winds sww can greatly influence large scale ocean circulation and degassing of the deep ocean via changes in wind driven upwelling in the southern ocean the extent to which the hypothesized sww southern ocean coupled system could account for changes in atmospheric co 2 is uncertain because of a lack of observations on the behavior of the sww in the past the paucity of appropriate records of productivity changes in the southern ocean and our limited understanding of the sensitivity of the southern ocean biological and or physical system to sww forcing here we report a reconstruction of the behavior of the sww during the past 14 k y based on terrestrial ecosystem proxies from western patagonia south america the reconstructed variations in the intensity of zonal flow correspond to the timing and structure of atmospheric co 2 changes and are consistent with the modeled magnitude of co 2 changes induced by varying strengths of the sww the close match between data and models supports the view that the sww southern ocean coupled system underpins multimillennial co 2 variations during the current interglacial and possibly during glacial cycles over the past 800 k y

holocene palaeoclimates of southern patagonia limnological and environmental history of lago cardiel argentina multiproxy palaeoenvironmental and palaeolimnological analyses of two holocene age sediment cores from the margin of lago cardiel a 76 m deep closed basin lake in southern patagonia latitude 49 s provide information on lake level changes that can be related to regional palaeoclimate scenarios sedimentol ogic magnetic susceptibility organic and inorganic carbon content and environmental indicators pollen dia toms ostracodes and stable isotopes on ostracodes show lake levels markedly higher than today during the early holocene following a rapid lake level rise after a desiccation phase prior to 11 000 bp after about 6000 bp lake levels were generally lower but underwent repeated e uctuations these inferred changes support the previously proposed view that the southern westerly stormtracks were focused zonal north of latitude 50 s during the early holocene allowing for antarctic cold fronts to bring easterly moisture to southern patagonia whereas during the late holocene the stormtracks shifted seasonally with an overall more meridional behaviour resulting in less and more variable moisture at these latitudes

hydrochemical and isotopic patterns in a calc alkaline cu and au rich arid andean basin the elqui river watershed north central chile abstract the geochemistry of surface water and groundwater from the elqui river basin north central chile was studied in spring 2007 and fall 2008 to obtain a general understanding of the factors and mechanisms controlling the water chemistry of steep rivers located in mineral rich arid to semi arid zones besides its uniform intermediate igneous lithology this basin is known for acid drainage and high as contents in the el indio au cu as district in its andean head abundant tailings deposits are present in the middle part of the basin where agricultural activities are important according to the results the chemical and isotopic composition of the elqui basin surface water and groundwater is related to uniform calc alkaline lithology and the major polluting system of the chemically reactive but closed el indio mining district the resulting compositional imprints in surface and ground water are a high so4 levels reaching about 1000 mg l in the toro river water directly draining the mining area b a major depletion of fe and pollutant metals in surface water after the confluence of the toro and la laguna rivers c similar chemical composition of surface and ground waters that differ in h and o isotopic composition reflecting the effect of differential evaporation processes downstream of the puclaro dam and d seasonal variations of fe mn cu and zn in surface water in contrast the groundwater chemistry exhibits moderate seasonal changes mainly in hco 3 content in spite of the acid drainage pollution water quality is adequate for human consumption and irrigation this is a consequence of both the dominant calc alkaline lithology and the existing arid climate resulting in neutral to moderately alkaline ph values that are responsible for the precipitation of metal hydroxides and as sorption by fe oh 3

enrichment of h2o and fluid soluble trace elements in the troodos ophiolite evidence for a near trench origin abstract the troodos ophiolite on the island of cyprus is a cretaceous supra subduction zone ophiolite it formed by seafloor spreading in the vicinity of a subduction zone but the exact tectonic setting in which it formed is debated we determined h2o contents together with other volatiles s cl and co2 and sr nd and pb isotope compositions of fresh troodos volcanic glasses previously measured for major and trace element contents glass compositions range from boninite to tholeiitic andesite the least degassed glasses have h2o contents of 1 7 to 2 7 wt and h2o ce ratios of 4400 to 33 600 the most depleted glasses with low zr yb have the highest fractionation corrected h2o contents and h2o ce and the highest subduction zone input highest th la ba zr and 87sr 86sr the high h2o contents enrichment in fluid mobile elements and depletion in zr hf and heavy rare earth elements are consistent with formation above a subduction zone very close to a trench in a fore arc position likely at water depths of 5000 m the enrichment in both fluid mobile e g rb cs and melt soluble e g th elements indicate that the troodos ophiolite formed by propagation of a back arc rift into the fore arc region of an active subduction zone

seasonality of the enso related rainfall variability in central chile and associated circulation anomalies the seasonality of the enso rainfall relationship in central chile 308 418s and associated circulation anomalies are studied using correlation and compositing techniques during el nino episodes there is a tendency for the occurrence of above average precipitation between 308 and 358s in winter june july august jja and from 358 to 388s in late spring october november on while rainfall deficit is typically observed from around 388 to 418s during the following summer january february march jfm when el nino reaches its maximum development opposite rainfall anomalies are characteristic during la nina events this study confirms results from previous investigations indicating that enhanced blocking activity over the amundsen bellings hausen seas area in the southeastern se pacific during el nino is a key feature explaining the wet conditions in winter it is also shown that the same circulation anomaly explains the relatively wet conditions in late spring in the 358 388s region during el nino episodes furthermore the southward displacement from winter to late spring of the area with significant enso related rainfall anomalies seems associated with the seasonal migration of the boundary separating the region under the influence of the subtropical domain from the extratropical domain where the westerly regime and associated disturbances prevail blocking episodes in the se pacific during el nino seem to be part of a wave structure particularly intense during spring characterized by a sequence of positive and negative quasi barotropic height anomalies stretching southeastward from the equator toward the se pacific and back to the southwestern atlantic on the other hand anomalously dry conditions in winter and late spring during la nina are favored by long lasting and intense ridges at subtropical latitudes over the se pacific and south america resulting in a southward migration of the midlatitude storm tracks in summer a higher frequency of ridges in the southern tip of the south america during el nino episodes presumably contributes to reinforcement of the southern edge of the subtropical anticyclone in the se pacific which at this time of the year reaches its southernmost position resulting in the annual rainfall minimum on the other hand an increased frequency of cyclonic circulation anomalies crossing the southern tip of the continent is associated with relatively wet conditions in southern central chile particularly during la nina events

fluctuations of outlet and valley glaciers in the southern andes argentina during the past 13 000 years abstract in the southern argentine andes ten advances of valley glaciers were used to reconstruct the late glacial and holocene glacier history the accumulation areas of these glaciers lie in the precordillera and are thus independent of fluctuations of the south patagonian icefield like the viedma outlet glacier the valley glaciers advanced three times during late glacial time 14 000 10 000 yr b p the youngest advance correlates with the younger dryas stade based on two minimum ams 14 c dates of 9588 and 9482 yr b p the second oldest advance occurred before 11 800 yr b p during the first half of the holocene ca 10 000 5000 yr b p advances culminated about 8500 8000 7500 and 5800 5500 yr b p during the second half of the holocene advances occurred between ca 4500 and 4200 yr b p as well as between 3600 and 3300 yr b p in the rio condor valley three subsequent advances have been identified