global climatic anomalies associated with extremes in the southern oscillation abstract composite temperature and precipitation anomalies during various stages of an event in the southern oscillation so have been computed for several hundred stations across the globe large regions of coherent significant signals are shown to exist for both extremes of the so with warm event signals generally opposite to those during cold events in addition during the year preceding the development of an event in the so year 1 climatic anomalies tend to be opposite to those during the following year year 0 this confirms that the biennial tendency of the so over the pacific indian ocean sectors is also present in more remote regions with climatic signals related to the so many of the signals are consistent enough from event to event to be useful for extended range forecasting purposes

fission track analysis reveals character of collisional tectonics in new zealand during the late cenozoic the pacific plate has been obliquely converging with the australia plate in south island new zealand this has resulted in westward obduction of continental crust of the pacific plate and consequently a major mountain range the southern alps has formed east of the alpine fault and within the leading edge of the pacific plate we have applied the apatite and zircon fission track dating technique to a suite of outcrop samples from three transects across the southern alps starting at the alpine fault to better understand the uplift age and structure of the continental collision the results show the following 1 uplift was underway at 7 ma in the south at haast pass and by 5 ma in the north at arthur s pass 2 profiles of the total amount of late cenozoic uplift show an exponential increase toward the alpine fault adjacent to the alpine fault there has been 14 5 to 21 5 km of uplift in the vicinity of haast pass 14 5 to 21 km near mt cook and 12 5 to 15 5 km in the arthur s pass transect adjacent to the alpine fault in the mount cook region the average uplift rate from 5 5 ma to 1 ma was 2 3 to 2 5 mm yr between 1 ma and the present it has averaged 6 2 mm yr the strongly asymmetric uplift pattern is responsible for the exposure of a 13 25 km wide belt of greenschist to midamphibolite facies rocks immediately east of the alpine fault known as the alpine schists 3 late cenozoic uplift of torlesse greywackes and alpine schists was preceeded during the jurassic early cretaceous by 5 8 km of uplift the otago schist belt to the south was uplifted much more during this interval and in addition western parts of the otago schists were uplifted 5 6 km during the late cretaceous 4 the fission track data do not support the notion of significant late cenozoic shear heating about the alpine fault as previously suggested from spatial variations in k ar ages of the otago and alpine schists

a physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins rift flank uplifts and the breakup or postrift unconformity are characteristic features of many rifted passive or atlantic type continental margins but are not predicted as primary features of simple lithospheric stretching models the explanations that have been proposed for their origin remain controversial either because they call upon special circumstances or because they are difficult to test plane strain finite element models are used in this paper to explore the dynamics of lithospheric necking during rifting and rupture the results agree with the conceptual interpretation that uplift of the rift boundaries to form flank mountains and uplift of the basin responsible for the breakup unconformity are related consequences of regional isostatic compensation of mass that is redistributed during the necking and rupture phases although the amplitudes of these uplifts depend on the model parameter values the relations between and relative signs of these two effects appear to be fundamental the explanation we propose may have been missed in recent studies because there has been a tendency to concentrate on kinematic stretching models which assume local isostatic equilibrium through out the rifting process such an approach is predicated on the assumption that the lithosphere has an insignificant strength or flexural rigidity during extension which is not true if our explanation is correct

sea level pressure variability around antarctica since a d 1750 inferred from subantarctic tree ring records a tree ring chronology network recently developed from the subantarctic forests provides an opportunity to study long term climatic variability at higher latitudes in the southern hemisphere fifty long 1911 1985 homogeneous records of monthly mean sea level pressure mslp from the southern latitudes 15 65 s were intercorrelated on a seasonal basis to establish the most consistent long term trans polar teleconnections during this century variations in summer mslp between the south america antarctic peninsula and the new zealand sectors of the southern ocean are significantly correlated in a negative sense r 0 53 p 0 001 climatically sensitive chronologies from tierra del fuego 54 55 and new zealand 39 47 were used to develop verifiable reconstructions of summer november to february mslp for both sectors of the southern ocean these reconstructions which explain between 37 and 43 of the instrumentally recorded pressure variance indicate that inverse trends in mslp from diametrically opposite sides of antarctica have prevailed during the past two centuries however the strength of this relationship varies over time differences in normalized mslp between the new zealand and the south america antarctic peninsula sectors were used to develop a summer trans polar index stpi which represents an index of sea level pressure wavenumber one in the southern hemisphere higher latitudes tree ring based reconstructions of stpi show significant differences in large scale atmospheric circulation between the nineteenth and the twentieth centuries predominantly negative stpi values during the nineteenth century are consistent with more cyclonic activity and lower summer temperatures in the new zealand sector during the 1800s in contrast cyclonic activity appears to have been stronger in the mid twentieth than previously for the south american sector of the southern ocean recent variations in mslp in both regions are seen as part of the long term dynamics of the atmosphere connecting opposite sides of antarctica a detailed analysis of the mslp and stpi reconstructions in the time and frequency domains indicates that much of the interannual variability is principally confined to frequency bands with a period around 3 3 3 6 y cross spectral analysis between the stpi reconstruction and the southern oscillation index suggests that teleconnections between the tropical ocean and extra tropical mslp variations may be influencing climate fluctuations at southern latitudes

multiproxy summer and winter surface air temperature field reconstructions for southern south america covering the past centuries we statistically reconstruct austral summer winter surface air temperature fields back to ad 900 1706 using 22 20 annually resolved predictors from natural and human archives from southern south america ssa this represents the first regional scale climate field reconstruction for parts of the southern hemisphere at this high temporal resolution we apply three different recon struction techniques multivariate principal component regression composite plus scaling and regularized expectation maximization there is generally good

a promising location in patagonia for paleoclimate and paleoenvironmental reconstructions revealed by a shallow firn core from monte san valentin northern patagonia icefield chile the study of past climate variability from ice core investigations has been largely developed both in polar areas over the past decades and more recently in tropical regions specifically along the south american andes between 0 and 20 s however a large gap still remains at mid latitudes in the southern hemisphere in this framework a 15 3 m long shallow firn core has been extracted in march 2005 from the summit plateau of monte san valentin 3747 m 46 35 s 73 19 w in the northern patagonia icefield to test its potential for paleoclimate and paleoenvironmental reconstructions the firn temperature is 11 9 c at 10 m depth allowing to expect well preserved both chemical and isotopic signals unperturbed by water percolation the dating of the core on the basis of a multi proxy approach combining annual layer counting and radionuclide measurements shows that past environment and climate can be reconstructed back to the mid 1960s a mean annual snow accumulation rate of 36 3 cm year 1 i e 19 2 g cm 2 year 1 is inferred with a snow density varying between 0 35 and 0 6 g cm 3 which is much lower than accumulation rates previously reported in patagonia at lower elevations here we present and discuss high resolution profiles of the isotopic composition of the snow and selected chemical markers these data provide original information on environmental conditions prevailing over southern patagonia in terms of air masses trajectories and origins and biogeochemical reservoirs our main conclusion is that the san valentin site is not only influenced by air masses originating from the southern pacific and directly transported by the prevailing west winds but also by inputs from south american continental sources from the e ne sometimes mixed with circumpolar aged air masses the relative influence of these two very distinct source areas changing at the interannual timescale thus this site should offer a wealth of information regarding south pacific argentinian ne e areas and antarctic climate variability

southern hemisphere circulation features associated with el nino southern oscillation events abstract composite seasonal mean and anomaly fields prepared from operational numerical analyses have been used to describe the southern hemisphere sh circulation features associated with el nino southern oscillation enso events the period of analyses available 1972 83 has limited the composites to include only three enso events the reliability and stability of the composites has been tested using multiple permutation methods and by comparison with the results obtained using a longer period 1950 79 of sh rawinsonde station data in the sh winter a weak equivalent barotropic wavetrain pattern of anomalies extends over australia and the south pacific ocean to south america this wavetrain pattern is quite variable in amplitude and location between enso events although it is more stable over the subtropical pacific in the sh summer the circulation anomalies are more zonally symmetric with increased height at low and high latitudes and decreased height in middle latitudes the circulation anoma

consequences of foreland basin development on thinned continental lithosphere application to the aquitaine basin sw france abstract we present an analysis of the consequences of foreland basin development on thinned continental lithosphere inherited from pre orogenic phases of extension bathymetry at the transition from pre orogenic extensional basin to foreland basin and compaction of pre orogenic sediments contribute to the accommodation space for foreland basin sediments and thrust loads in addition the extension induced transient thermal state of the lithosphere results in ongoing thermal subsidence and a flexural rigidity which changes through time quantitative modelling of the phase of extension and the foreland basin stage of the aquitaine basin southern france shows that the inherited transient thermal state of the lithosphere contributes significantly to 1 the total foreland basin depth and width 2 the post compressional subsidence history and 3 the cratonward onlap pattern accounting for the thermo mechanical effects of pre orogenic extension significantly reduces the estimates of both the flexural rigidity 30 43 for the aquitaine basin and the required topographic or thrust load 40 for the aquitaine basin at foreland basins emplacement of thrust loads below sea level as expected in a pre orogenic extensional basin setting further reduces the required topographic load this sheds light on the wide range of flexural rigidity values reported for continental lithosphere from foreland basin modelling studies and explains in many instances the inferred hidden load or subsurface load in flexural modelling studies at foreland basins the present study has shown that pre orogenic extension phases significantly affect the record of vertical motion and the stratigraphy of the aquitaine basin and is probably important for foreland basin evolution in general

modern pollen climate calibration for southern south america abstract using the response surface technique a modern pollen climate calibration is presented for the mid latitudes in southern south america between latitudes 39 s and 44 s extending from the west coast in chile across the andes into the patagonian steppe region the climate parameters identified that relate to the present day pollen distribution of the nine most important pollen types nothofagus dombeyi type nothofagus obliqua type podocarpus weinmannia caldcluvia eucryphia type cupressaceae myrtaceae misodendrum and steppe types are summer precipitation summer and winter temperatures using the modern pollen climate data set three fossil pollen records mallin aguado and lago moreno east of the andes and caunahue west of the andes are interpreted in terms of these three seasonal climate parameters despite intervals of no analog fossil pollen assemblages the reconstruction shows similar climate trends on both sides of the andes during the last 21 000 cal yr bp 17 000 yr bp with summer precipitation as low or markedly lower than today prior to 17 000 cal yr bp 14 500 yr bp as high or higher than today between 15 000 and 12 500 cal yr bp 12 500 and 10 500 yr bp and again lower than today between 12 500 and 8000 cal yr bp 10 500 and 7200 yr bp summer and winter temperatures were low or high when summer precipitation was high or low

some consequences of compressional tectonics for extensional models of basin subsidence changes in intraplate stress levels have important consequences for the stratigraphy of rifted basins and provide a tectonic explanation for the generation of sequence boundaries late stage compressional phases during the post rift evolution of basins produce unconformities with offlap phases that increase in magnitude with the age of the rifted basin late stage compression has not only a strong bearing on the generation of unconformities but also induces significant downbending of the centre of a basin ignorance of the vertical motions of the lithosphere induced by late stage compression during post rift evolution can therefore give rise to substantial errors in the estimates of crustal extension derived from analysis of basement subsidence using stretching models consequently late stage compression can be of great significance in estimates of depth and timing of the hydrocarbon window inferred from extensional models of basin subsidence quantification of the subsidence induced by post rift compression has important implications for integrated models of basin subsidence and hydrocarbon generation

towards a mechanical model for the formation of the pannonian basin abstract new maps showing crustal and lithospheric thickness variations in the pannonian basin and the surrounding east alpine carpathian and dinaric mountains have been prepared on the basis of recent seismic seismologic and electromagnetic data a map presenting miocene faults of regional significance has been also constructed for the same region by using a wealth of recently available national and or more local studies it is suggested that observed crustal and lithospheric structural contrasts have been controlled primarily by neogene kinematic history of the region kinematic history is characterized by the following main patterns 1 1 indentation by adria and large scale backthrusting in the southern alps 2 2 eastward escape and extension of the eastern alps 3 3 extensional collapse in the pannonian basin area 4 4 formation of broad wrench fault systems along strike in the dinarides and southern carpathians and the western carpathians with dextral and sinistral shear respectively 5 5 compression and accretion of the external thrust and fold belt in the eastern carpathians these kinematic patterns are thought to be interrelated and all are manifestations of the late stage evolution of an overthickened orogenic wedge in order to arrive at a better understanding of the mechanism of extension which formed the pannonian basin deep crustal seismic profiles hydrocarbon exploration reflection lines and borehole data have been analyzed in the little hungarian plain this plain represents the transition zone between the alps and the pannonian lowlands and the results are illustrated by eight interpreted cross sections one result of regional importance is the clear recognition that the transdanubian central range at the southeastern flank of the little hungarian plain is composed of alpine pre senonian thrust sheets this finding marks the end of a century of debate the allochthony of the substrata of the pannonian basin can be now considered proven another result of more general interest is that these cross sections document the mode of lithospheric extension preexisting compressional detachment planes reactivate as low angle normal faults and lead to tectonic unroofing of deeply buried metamorphic terranes characterized by ductile flow along subhorizontal lineation

blocking in the southern hemisphere abstract the focus of this paper is on the frequency and spatial distributions of blocking and persistent anomalies of geopotential height over the southern hemisphere the analysis is based upon daily height fields at 1000 and 500 mb for both summer and winter histogram frequency distributions of height anomalies and maps of the skewness and kurtosis have been computed blocking events are objectively defined by requiring a large positive anomaly to exist for 5 days or more composite flow and anomaly fields for several cases are presented and examined in detail the geographical distribution of the frequency of lame amplitude 150 gpm anomalies at 500 mb that persist for only 1 3 days is very similar to that of the high frequency band 2 8 day period variances that identity the storm tracks in the southern hemisphere the primary location for blocking in the southern hemisphere is in the new zealand sector and blocking occurs through a local enhancement of the climatological split in the mean westerli

thrust tectonics along the north western continental margin of sabah borneo widely accepted plate tectonic models suggest that an inactive subduction zone lies along the north west continental margin of sabah in contrast interpretation of reflection seismic data acquired by bgr shows an autochthonous continental terrane comprising an oligocene to early miocene carbonate platform being progressively overthrust by an allochthonous rock complex progressive compression resulted in the development of four structural zones imbricated thrust sheets zone iii two thrust sheet systems one on top of the other zone iv a complex zone with multiphase deformation zone v and piercement ridges zone vi

relation between salt diapirism and the tectonic history of the sverdrup basin arctic canada the sverdrup basin is a pericratonic sedimentary trough in northern canada containing up to 13 km of carboniferous to tertiary strata the basin formed by late paleozoic continental rifting and was subsequently affected by a series of alternating tectonic settings evaporite diapirs are well exposed at the present erosion level and occur mainly along the basin axis the diapiric source layer consists of about 400 m of anhydrite underlain by salt of unknown stratigraphic thickness deposited during the initial permo carboniferous synrift phase of basin subsidence large salt anhydrite diapirs rose into the sedimentary overburden when the overburden had reached a thickness of several kilometres they grew during a relatively long period of modest horizontal compression from the permo triassic to early cretaceous much smaller tabular anhydrite diapirs were rapidly emplaced during periods of high horizontal compression in the middle cretaceous when large flexural stresses were induced by sedimentary loadi

potential for water table excursions induced by seismic events at yucca mountain nevada the possibility that 100 200 m changes in water table elevation can be mechanically induced by earthquakes is a consideration in site studies of a potential high level nuclear waste repository at yucca mountain nevada however numerical simulations of tectonohydrologic coupling involving earthquakes typical of the basin and range province produce 2 3 m excursions of a water table that is 500 m below the land surface even displacements corresponding to extraordinary seismic events drive water table excursions of less than 20 m flow resulting from earthquake induced pore pressure fields below the water table tends to be mainly horizontal vertical flows that cause changes of the level of the water table are secondary strongly anisotropic permeability intended to enhance vertical flow within fault zones only doubles water table rise in the models considered these simulations of water table rise compare well with observations following large earthquakes in the basin and range the authors models suggest that exceptional hydrologic and or tectonic conditions would be required to produce substantially larger water table rises

early cenozoic crust at the norwegian continental margin and the conjugate jan mayen ridge multichannel seismic profiles at the voring plateau margin off norway and the northern jan mayen ridge have provided a framework for the early tertiary evolutionary history of these areas which were adjacent prior to the opening of the norwegian sea we propose that their paleogene evolution is quite similar and that the two acoustic basement reflectors ee and jo were formed in the early eocene by extrusion of flow basalts from the time of opening to about anomaly 23 time oceanic seafloor was generated by icelandic type spreading during that time the central jan mayen fracture was the main transform the seaward dipping reflector sequences are flow basalts generated by the icelandic spreading the existence of less well developed dipping sequences seaward of the primary ones probably reflects that these regions submerged later because of higher initial elevation during the early eocene subaerial spreading episode which is related to the north atlantic volcanic province basalt flows also covered the adjacent thinned and heavily intruded continental crust it is proposed that the continent ocean boundary is located just landward of anomaly 24b a short distance seaward of the voring plateau escarpment reflector k is only recognized landward of this boundary in a region of transitional crust the escarpment experienced syndepositional faulting and the most elevated parts of the voring marginal high did not subside below shallow water depths before oligocene miocene time we suggest that the voring margin and the jan mayen ridge represent volcanic passive margins the evolution of this margin type may relate to initial uplift due to rifting in previously thinned crust

andradite skarn garnet records of exceptionally low δ 18 o values within an early cretaceous hydrothermal system sierra nevada ca skarn garnets in the mineral king roof pendant of the south central sierra nevada within sequoia national park california usa reveal variable fluid chemistry with a significant component of meteoric water during metasomatism in the early cretaceous sierra nevada batholith we focus on andradite garnet associated with pb zn mineralization in the white chief mine laser fluorination oxygen isotope analyses of 18o of garnet 18o grt from sites along the skarn show a large range of values 8 8 to 4 6 vsmow ion microprobe sims analyses elucidate that individual andradite crystals are strongly zoned in 18o grt up to 7 of variation total rare earth element concentrations ree across individual garnets show progressive depletion of skarn forming fluids in these elements during garnet growth these findings support a skarn model of earliest red high 18o grandite garnet consistent with a magmatic dominated equilibrium fluid 18o h2o as high as 8 later green andradite crystallized in equilibrium with a low 18o fluid indicating a significant influx of meteoric fluid 18o h2o 6 to 5 following a hiatus in garnet growth associated with late stage pb zn mineralization latest orange overprint rims have higher 18o values 18o h2o 0 2 and depleted total rees suggesting influx of high 18o trace element depleted fluid derived from regional metamorphism of the carbonate host remarkably low 18o grt values in the white chief canyon skarn require a significant proportion of meteoric fluid available during 400 c andradite forming metasomatism fluid flow was channelized at the pluton wallrock contact evidenced by the narrow extent of skarn

late cretaceous and cenozoic intra plate compressional deformations in the alpine foreland a geodynamic model abstract the mesozoic grabens and wrench induced troughs of western and central europe developed in response to triassic early cretaceous intra plate tensional stresses which affected the arctic north atlantic and the tethys borderlands during the rifting phase preceding the opening of the respective oceans this resulted in the fragmentation of the continental crust of the alpine foreland during the late cretaceous and tertiary alpine orogeny collision related compressive stresses exerted on the foreland induced the reactivation of these fracture systems causing the inversion of mesozoic grabens and the uplifting of major basement blocks at distances up to 1300 km to the north of the present alpine deformation front the structural style of these inverted basins and basement uplifts is indicative of compressional and transpressional deformations the total amount of crustal shortening associated with these deformations is unlikely to exceed a few tens of kilometres these displacements require a coupling between the foreland and the orogen at the alpine a subduction zones and within the foreland a decoupling at intra crustal levels between the crust and mantle and or at deeper lithospheric levels the example of the alpine foreland indicates that compressive stresses inducing major deformations can be transmitted from a collisional plate boundary through continental lithosphere over distances of up to 1300 km circumstantial evidence suggests that collision related compressive stresses not large enough to give rise to significant deformations can be transmitted through continental lithosphere over even greater distances

crustal structure and the mechanical properties of extended continental lithosphere in the valencia trough western mediterranean seismic refraction and reflection gravity and well data have been used to constrain the structure and evolution of the valencia trough a young extensional basin in the western mediterranean seismic refraction data reveal the present day crustal structure while backstripping of seismic reflection and well data reveal the structure at the time of rifting by comparing the seismically constrained crustal structure to that inferred from backstripping we have been able to evaluate whether the moho is in the expected position given the tectonic subsidence uplift and sediment loading history of the trough the best overall fit between the predicted and seismically constrained crustal structure in the trough is for a model in which the extended continental crust and lithosphere has acquired little or no strength following rifting a low strength is in accord with the observed free air gravity anomaly as well as results from other types of rift basins such as the north sea and the continental margin off the east coast of the usa there are discrepancies between the observed and predicted moho depths beneath the flanks of the valencia trough but they are attributed to either the removal of crustal material during or following rifting iberian peninsula or to orogenic loading of previously extended continental crust mallorca the largest discrepancy up to 10 km correlates with the ebro delta which has prograded into the trough by more than 60 km since the pliocene the discrepancy cannot be explained by the same large scale processes that modified the moho beneath the trough flanks and requires that the lithosphere beneath the ebro delta region is associated with a high 60 t c

tectonic and geodynamic setting of oil and gas basins of the soviet union within the territory of the soviet union and its offshore economic zone are about 70 sedimentary basins containing oil and gas the basins include almost all basin types described in present day plate tectonic classifications namely 1 intracontinental and pericontinental rifts suprarift syneclises and zones of pericratonic downwarps 2 ancient passive margins of continents with adjacent overthrust fold system 3 modern passive margins of continents 4 zones of convergence of lithospheric plates i e zones of subduction of oceanic plates below continental plates and 5 zones of collision of continental lithospheric plates basins of the first type include the pripyat dnieper donets aulacogen the viluy aulacogen of siberia the huge west siberian supra aulacogen basin the analogous yenisei khatanga basin and others the second type includes the volga urals basin with the ural foredeep azov kuban basin and terek caspian basin with the greater caucasus foredeeps and others the difference between these two types is rather arbitrary because the passive margins of continents also undergo the rift stage of development though their main stage of oil and gas accumulation corresponds to the post rift stage the third type is represented by the poorly studied prospective basins of the arctic margin of the soviet union the fourth includes numerous but relatively small basins of the far eastern and northe stern soviet union of which the east sakhalin west kamchatka and anadyr basins have proved to contain oil and gas rifting also played a role in the formation of the back arc group of these basins basins in central asia fergana south tadjik and the transcaucasia region south caspian belong to the fifth basin type the central asian basins lie within the area of secondary epiplatform orogenesis whereas the transcaucasian basins are with the area of primary epigeosynclinal orogenesis so far the only type of basin not identified within the territory of the soviet union is the pull apart basin the location and distribution of oil and gas deposits in the section of a basin prevailing types of traps and scale of potential resources are all features influenced by the geodynami type of the basin

the origin of sedimentary basins a status report from the task force of the international lithosphere program abstract better insights into the mechanisms of basin formation have a direct bearing on the predictive power of forward models for basin fill models that link flexure normal faulting and thrusting on a subbasin scale provide important constraints on the tectonic control of the sedimentary record enabling a quantitative comparsion with eustatic contributions to the basin architecture thus of special importance is the need to link processes with different spatial and temporal scales involved in the evolution of extensional and compressional basins by numerical modelling a new generation of basin modelling concepts and techniques is one of the main objectives of the task force origin of sedimentary basins of the international lithosphere program the focus of this work is on the quantification of the effects of the thermomechanical structure of the lithosphere and its interplay with regional and local stress changes other important developments include the step towards three dimensional modelling and the full integration of rapidly expanding fission track and other data sets to constrain vertical motions in basins as natural laboratories for the interactive testing and development of new basin modelling techniques a number of basins with high quality data from industry government and academia have been selected on the basis of specific testable problems

drought vegetation change and human history on rapa nui isla de pascua easter island abstract stratigraphic records from lake sediment cores and slope deposits on rapa nui document prehistoric human impacts and natural environmental changes a hiatus in sedimentation in rano raraku suggests that this lake basin dried out sometime after 4090 4410 cal yr bp and refilled only decades to centuries before ad 1180 1290 widespread ecosystem changes caused by forest clearance by polynesian farmers began shortly after the end of this drought terrestrial sections show a chronology of burning and soil erosion similar to the lake cores although changing sediment types and shifts in the pollen rain suggest that droughts occurred earlier in the holocene as yet there is no evidence for droughts occurring after ad 1180 1290 the timing of the agricultural colonization of rapa nui now seems well established at ca ad 1200 and it was accompanied by rapid deforestation that was probably exacerbated by the island s small size its droughty climate and the rarity of primeval fires detailed records of a large interval of rapa nui s ecological history remain elusive due to the drought hiatus in the rano raraku sediment record we find no evidence for a rat outbreak impact on rapa nui s vegetation preceding anthropogenic forest clearance

tree ring based reconstructions of northern patagonia precipitation since ad 1600 long term reconstructions 400 years of seasonal and annual precipitation variations were developed for northern patagonia east of the andes using a new set of 16 tree ring width chronologies from austrocedrus chilensis d don endl reconstructions which capture between 41 and 50 of the precipitation variance show that the twentieth century contains the most extreme long periods of wetness and dryness in the past 400 years since about ad 1910 the reconstructions are also characterized by an increase in interannual variability and one of the highest rates of extreme events within the last 400 years a prominent oscillation on the order of 2 2 1 years in length has been identified in the reconstructions using spectral analysis quasi biennial oscillations have been shown to be very marked in some circulation indices of the southern hemisphere although significant oscillations within the preferred frequency domain of el nino southern oscillation enso are present in the reconstructions no clear trod consistent responses to enso have been observed correlations of reconstructions with mean sea level pressure around south america for the interval ad 1912 1984 reveal the influence of subtropical and high latitude features of the atmospheric circulation on precipitation variations in northern patagonia droughts result from an intensification of the subtropical pacific anticyclone off the chilean coast and the deepness of the circum antarctic trough over the south orkney antarctic peninsula sector mean sea level pressure reconstructions for the south atlantic sector of the southern oceans were used to evaluate the temporal stability of the relationships between northern patagonia precipitation and high latitude climatic variations since ad 1750 the influence of high latitude circulation on precipitation appears to be more significant during the twentieth century which in turn may respond to an intensification of wavenumbers 3 on the mean planetary wave structure over the southern hemisphere recent increase of precipitation variability in northern patagonia may reflect stronger interactions between middle and high latitude atmospheric circulation in the southern hemisphere during the twentieth century

climatic fluctuations in northern patagonia during the last 1000 years as inferred from tree ring records abstract millennium old alerce trees fitzroya cupressoides mol johnst have been used to develop a 1120 year reconstruction of the summer temperature departures for the andes of northern patagonia in argentina four main climatic episodes can be distinguished in this proxy paleoclimatic record the first a cold and moist interval from a d 900 to 1070 was followed by a warm dry period from a d 1080 to 1250 correlative with the medieval warm epoch of europe afterward a long cold moist period followed from a d 1270 to 1670 peaking around a d 1340 and 1650 these cold maxima are contemporaneous with two principal little ice age events registered in the northern hemisphere warmer conditions then resumed between a d 1720 and 1790 these episodes are supported by glaciological and palynological data in patagonia following a cold period in the early 1800s tree ring indices have oscillated around the long term mean except for a warmer period from a d 1850 to 1890 correlations between the rio alerce reconstruction and the regional weather stations indicate that the tree ring variations are correlated with a homogeneous summer weather pattern covering patagonia east of the andes from 38 to 50 s

dominant enso frequencies during the little ice age in northern patagonia the varved record of proglacial lago frias argentina abstract the global character of the time interval known as the little ice age lia is at present relatively well established however the forcing mechanisms behind this cooling interval are still elusive investigations in annually laminated sediments have shown that varved sediments are among the best climate archives to tackle these questions proglacial lago frias in northern patagonia is fed by the tronador ice cap 3554 m previous investigations have shown that this glacier has reacted sensitively to climate change during the lia with well identified major glacial advances between ad 1800 1850 results of a multiproxy study of lago frias sediments reflect variations in the transport of glacially derived clay and silt to the basin that can be directly linked to changes in climate sedimentological evidence combined with a chronological model indicate variations in varve thicknesses showing two frequencies centered at 16 4 and 10 5 years that have been previously attributed to the solar cycles and the tropical atlantic sea surface dipole tad respectively the main frequency is however located between 2 5 and 3 0 years pointing towards a dominant el nino southern oscillation enso signal thus the lago frias record provides new insights about the complexity of the various forcing mechanisms behind the cooling during the lia in an area with a paucity of high resolution climate records

on a tectonic mechanism for regional sealevel variations abstract no satisfactory tectonic explanations have yet been offered for the apparent sealevel fluctuations of about 1 cm 1000 years and a magnitude of up to a few hundred meters that have been proposed by vail et al 1 we propose a mechanism that does appear to be able to explain these changes if horizontal stresses of the order of a few kilobars occur in the lithosphere and if changes in these stress fields occur on geological time scales the proposed model is one of an interaction between these stresses and the deflections of the lithosphere caused by sedimentary loading apparent sealevel changes of up to 100 m can be produced at the flanks of the sedimentary basins by this interaction the mechanism is most effective for young margins that are subject to rapid sediment loading by its nature the tectonic model can explain contemporaneous fluctuations in apparent sealevel in neighbouring depositional environments in principle it implies the possibility of regional correlations in different basinal settings

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

dendroclimatological reconstructions in south america a review abstract recent years have seen a consolidation and expansion of tree ring sample collection across south america most collections are concentrated in the temperate forests along the eastern and western slopes of the southern andes 32 s to 55 s however important advances in the reconnaissance and collection of new woody species useful for dendrochronology have recently been documented in new regions the development of chronologies in tropical and subtropical arid regions of the cordillera and in particular the bolivian altiplano is probably one of the most important recent advances in south american dendrochronology polylepis tarapacana growing at 4000 4500 m elevation on the altiplano has yielded more than ten chronologies spanning the past 700 years these records are highly correlated with summer variations in climate the development of chronologies in the humid subtropics and tropics remains a major challenge the number of tree ring chronologies built up using species from these regions ca 40 is comparatively low in relation to the extent of tropical forests the recognition of strong climate signals in tree rings from cedrela species provides a unique opportunity to develop a tree ring network in subtropical and tropical south america the future of dendroclimatology in south american tropical regions is perceived as extremely promising reconstructions of temperature rainfall streamflow snow and regional atmospheric circulation based on ring width density and stable isotopes have been conducted using tree ring chronologies from subtropical and temperate forests these chronologies have also been used in studies relating south american tree rings to high resolution proxies from other continents and studies analyzing past changes in atmospheric circulation the comparison of climatic reconstructions based on tree rings with projected atmospheric circulation patterns provides a useful bridge between past and future trends in global climate change and its implications for human welfare and socio economic development some examples of this bridging are presented in this review future research should continue the development of long tree ring chronologies to improve detection of decadal to centennial climatic variations and to distinguish between natural and human induced climatic changes in south america efforts to develop new tree ring chronologies in the tropical lowlands should also be encouraged collaboration among south american countries in training young scholars is crucial to maintain and increase the progress of dendroclimatology in the region initiatives facilitating the interaction between scientists from the americas and overseas such as done by the iai and pages projects should be broadened and their long term continuation assured

development of the north viking graben inferences from laboratory modelling abstract the north viking graben is a classic sedimentary basin in the north sea that has been thoroughly studied over the last decade despite the amount and quality of seismic and well data now available the processes of extension remain unclear and the relationship between sedimentation and deformation is still a matter of debate we present the results of small scale laboratory modelling the models are made with sand and silicone putty to simulate brittle and ductile behaviour on a crustal scale the experiments were designed to study the effects of a the degree of coupling between brittle and ductile layers b the obliquity of extension and c the reactivation of inherited crustal scale structures the results are used to discuss the symmetry of extensional processes on crustal and lithospheric scales as well as the relationship between sedimentation and deformation it is proposed that the asymmetry of faulting in the upper crust and the nearly symmetric thinning of the whole crust are not mutually exclusive a model involving nearly pure shear on the lithospheric scale is used to explain the development of an asymmetrical basin at shallow level in addition this model accounts for the nearly horizontal stratification of lower cretaceous sediments the basal cretaceous unconformity which caps many of the normal faults and the localization of deformation to the west of the graben during the lower cretaceous

long term glacier variations in the central andes of argentina and chile inferred from historical records and tree ring reconstructed precipitation abstract snow and ice in the central andes of chile and argentina 33 36 s are the major source of water for the highly populated regions near the cities of santiago and mendoza however our knowledge of the forces driving the general glacier retreat in the region is limited in order to obtain a long term perspective of glacier fluctuations and their relationships with climate in the central andes historical glacier variations were documented and compared with a tree ring precipitation reconstruction based upon austrocedrus chilensis trees a multi proxy approach historical documents old aerial photographs and satellite imagery was used to map the fluctuations of eight glaciers including the cipreses glacier which provides the oldest record of glacier variations in the region starting in ad 1842 all the studied glaciers exhibited a negative trend during the 20th century with mean frontal retreats between 50 and 9 m y 1 thinning rates between 0 76 and 0 56 m y 1 and a mean ice area reduction of 3 since 1955 more than 350 tree ring cores were combined into three tree ring chronologies which strongly correlate with the instrumental precipitation in santiago de chile 33 26 s 70 41 w 520 m asl based on these records a 712 year precipitation reconstruction was developed this reconstruction is characterised by a centennial oscillation indicating marked dry conditions around the years 1440 and 1600 ad wet conditions were prevalent in the years 1500 1650 and particularly around 1850 ad since this precipitation maximum the reconstruction shows a clear secular decreasing trend the reduction in precipitation indicated by this reconstruction for the last 150 yr in combination with a significant warming recorded in central chile are the main causes of the observed current glacier retreats

decadal variation of the annual cycle in the australian dataset abstract during the 1970s and 1980s elements of the atmospheric circulation over the southern hemisphere changed markedly from their state in the two previous decades the change was evident in the zonal asymmetry especially in the zonal harmonic wave 3 at higher latitudes and in the semiannual wave in pressure and wind the semiannual wave changed in the same sense in all three southern oceans but by the largest amount in the south pacific ocean the second harmonic in a 12 month series by which we describe the semiannual wave dominates the shape of the long term mean annual curve of sea level pressure in mid and high latitudes this harmonic weakened during the period and its midlatitude peak disappeared in the south pacific ocean as part of the low frequency changes during the 18 years from 1972 to 1988 the central pressure in the subantarctic trough fell the trough moved northward and the subtropical ridge moved south the meridional movement of the trough and the ridge and the concurrent

a quasi biennial signal in western us hydroclimate and its global teleconnections on interannual time scales quasi cyclic activity in the troposphere is generally thought to arise from chaotic feedback processes and therefore to be unpredictable in nature here evidence is presented for periodic clockwork climate behavior seen as a stable quasi biennial qb oscillation in western us winter precipitation estimated at a period of 2 16 0 05 years in the western us the qb precipitation mode has an influence comparable to that of enso with strongest effects observed at central latitudes of the region the oscillation displays systematic phase shifting with respect to the annual cycle signifying a stable nonseasonal and strongly periodic qb mechanism the cycle in precipitation results proximally from a meridional standing pressure wave over the north american pacific coast analysis of monthly pressure data confirms the nonseasonal periodic character of the oscillation which appears to have maintained phase from the mid 20th century to recent years the regional qb pressure cycle is traced to a quasi synchronous pulsation of meridional pressure waves in the extratropics of both hemispheres termed a biennial annular mode oscillation bamo the bamo oscillates in quadrature with a weaker 26 month signal in the tropical southern oscillation due to a shorter period both oscillations operate independently of the stratospheric quasi biennial oscillation qbo

documentary sources from south america potential for climate reconstruction abstract this overview demonstrates the potential of historical documents from ecuador peru bolivia chile and argentina for developing continuous and precise reconstructions of past climatic variations in south america during past centuries we provide an extensive list of the major historical sources of paleoclimatic information including regional archives magazine and newspaper libraries in south america and spain we also discuss the type of information required to develop homogeneous climatic series and the differences in the quality of records between the historical colonial and republican periods we examine the spatial and temporal distributions of historical records in south america the period of analysis varies depending on the date of spanish arrival to each region finally we briefly discuss the limitations in the use of historical records in south america and their future perspectives what information is presently available and what research is still needed to provide consistent reconstructions of past climates based on historical documents

instrument and tree ring based estimates of the antarctic oscillation abstract an estimate of the strength of the austral summer antarctic oscillation using station sea level pressure records for the period 1878 2000 is presented the first to the authors knowledge the reconstruction was obtained by relating the antarctic oscillation aao intensity derived from ncep ncar reanalysis data to the leading principal components of station records using multiple regression analysis particular effort has been made to fit the model in a way that is robust to the questionable trends in the ncep ncar data in the southern hemisphere the trends in the reconstruction are derived from the station data not from the ncep data cross validation with the ncep data and comparison with other analyses of the aao over the late instrumental period give confidence that this station based reconstruction can be regarded as trustworthy with regard to the whole reconstruction period some unquantifiable uncertainty stems from potential instability of the statistical relationships to extend this

discharge trends and flow dynamics of south american rivers draining the southern atlantic seaboard an overview summary river discharge time series in southern south america between 15 and 50 s show dissimilar historical trends in the rio de la plata drainage basin rpdb the record shows a runoff trend change from decreasing to increasing around the mid 20th century independently of the seasonal variation currently observed discharge change in the region is mainly accounted for by increased discharge during low flow periods in contrast most patagonian rivers show a negative discharge trend which mainly occurs in some austral summer months and is particularly significant in the negro river when considering the historical discharge variability in the southern part of south america the spectral analysis produced evidence of interannual quasi decadal and quasi bidecadal periodicities most rivers in the region show el nino like interannual periodicities with the exceptions of the bermejo and pilcomayo rivers in the rpdb during the 20th century interannual periodicity changed from the 2 to 5 year band to the 5 to 7 year band between 1935 and 1970 in patagonia the interannual oscillation showed maximum power 1930 and 1980 in the colorado whereas further south negro and chubut rivers maximum power appears 1950 the quasi decadal signal is strong in the rpdb in general and particularly in patagonia s colorado which runs close to the so called arid diagonal and bears this signal presumably due to the influence of the low level jets lljs this periodicity is conspicuously absent in other patagonian rivers finally a quasi bidecadal signature appears to be restricted to the bermejo and iguacu rivers in the rpdb and in patagonia s colorado and santa cruz rivers

glacial to holocene climate changes in the se pacific the raraku lake sedimentary record easter island 27 s abstract easter island se pacific 27 s provides a unique opportunity to reconstruct past climate changes in the south pacific region based on terrestrial archives although the general climate evolution of the south pacific since the last glacial maximum lgm is coherent with terrestrial records in southern south america and polynesia the details of the dynamics of the shifting westerlies the south pacific convergence zone and the south pacific anticyclone during the glacial interglacial transition and the holocene and the large scale controls on precipitation in tropical and extratropical regions remain elusive here we present a high resolution reconstruction of lake dynamics watershed processes and paleohydrology for the last 34 000 cal yrs bp based on a sedimentological and geochemical multiproxy study of 8 cores from the raraku lake sediments constrained by 22 ams radiocarbon dates this multicore strategy has reconstructed the sedimentary architecture of the lake infilling and provided a stratigraphic framework to integrate and correlate previous core and vegetation studies conducted in the lake high lake levels and clastic input dominated sedimentation in raraku lake between 34 and 28 cal kyr bp sedimentological and geochemical evidences support previously reported pollen data showing a relatively open forest and a cold and relatively humid climate during the glacial period between 28 and 17 3 cal kyr bp including the lgm period colder conditions contributed to a reduction of the tree coverage in the island the coherent climate patterns in subtropical and mid latitudes of chile and eastern island for the lgm more humid conditions suggest stronger influence of the antarctic circumpolar current and an enhancement of the westerlies the end of glacial period occurred at 17 3 cal kyr bp and was characterized by a sharp decrease in lake level conducive to the development of major flood events and erosion of littoral sediments deglaciation termination 1 between 17 3 and 12 5 cal kyr bp was characterized by an increase in lake productivity a decrease in the terrigenous input and a rapid lake level recovery inaugurating a period of intermediate lake levels dominance of organic deposition and algal lamination the timing and duration of deglaciation events in easter island broadly agree with other mid and low latitude circum south pacific terrestrial records the transition to the holocene was characterized by lower lake levels the lake level dropped during the early holocene ca 9 5 cal kyr bp and swamp and shallow lake conditions dominated till mid holocene partially favored by the infilling of the lacustrine basin during the mid to late holocene drought phases led to periods of persistent low water table subaerial exposure and erosion generating a sedimentary hiatus in the raraku sequence from 4 2 to 0 8 cal kyr bp the presence of this dry mid holocene phase also identified in low andean latitudes and in patagonian mid latitudes suggests that the shift of storm tracks caused by changes in the austral summer insolation or forced by el nino like dominant conditions have occurred at a regional scale the palm deforestation of the easter island attributed to the human impact could have started earlier during the 4 2 0 8 cal kyr bp sedimentary gap our paleoclimatic data provides insights about the climate scenarios that could favor the arrival of the polynesian people to the island if it occurred at ca ad 800 it coincided with the warmer conditions of the medieval climate anomaly whereas if it took place at ca ad 1300 it was favored by enhanced westerlies at the onset of the little ice age changes in land uses farming intensive cattle during the last century had a large impact in the hydrology and limnology eutrophication of the lake

influence of large scale teleconnection patterns on methane sulfonate ice core records in dronning maud land records of methane sulfonate ms in ice cores from the high plateau of dronningmaud land dml antarctica drilled in the framework of the european project for icecoring in antarctica are investigated for their potential as an environmental andclimate archive for the atlantic sector of the southern ocean despite postdepositionalchanges years of extraordinary ms concentrations can be clearly detected in the icecore records we use composite anomaly maps of atmospheric parameters from thenational centers for environmental prediction national center for atmospheric researchreanalysis fields for years of extreme ms concentration to detect atmospheric patternscausing ms variability changing atmospheric transport is shown to be an important but not exclusive parameter being conserved in the ms record in dml the oftenhypothesized direct link between high ms concentrations and el nino events is notsupported for the observed region whereas the antarctic dipole adp which ismodulated by el nino southern oscillation conditions exerts significant influence aclear 13 9 year cycle can be found throughout a 2000 year ms record that can be relatedto variations in the adp over the last 300 years a 4 6 year cycle is revealed in thems and sea salt record which vanishes in the deeper part of the ice core as aconsequence of diffusion processes from the long term perspective periods of high msconcentrations are connected to on average higher sea salt aerosol as well reflecting aseasonally independent influence of transport on both species a distinctive period ofefficient atmospheric transport probably due to a pronounced adp could be foundfrom 1200 to 1600 a d

regional patterns of tectonic stress in europe nearly 1500 stress orientation determinations are now available for europe the data come from earthquake focal mechanisms overcoring measurements well bore breakouts hydraulic fracturing measurements and young fault slip studies and sample the stress field from the surface to seismogenic depths three distinct regional patterns of maximum compressive horizontal stress shmax orientation can be defined from these data a consistent nw to nnw shmax stress orientation in western europe a wnw ese shmax orientation in scandinavia similar to western europe but with a larger variability of shmax orientations and a consistent e w shmax orientation and n s extension in the aegean sea and western anatolia the different stress fields can be attributed to plate driving forces acting on the boundaries of the eurasian plate locally modified by lithospheric properties in different regions on average the orientation of maximum stress in western europe is subparallel to the direction of relative plate motion between africa and europe and is rotated 17 clockwise from the direction of absolute plate motion the uniformly oriented stress field in western europe coincides with thin to medium lithospheric thickness approximately 50 90 km and high heat flow values 80 m w m2 in western europe a predominance of strike slip focal mechanisms implies that the intermediate principal stress is vertical the more irregular horizontal stress orientations in scandinavia coincide with thick continental lithosphere 110 170 km and low heat flow 50 m w m2 the cold thick lithosphere in this region may result in lower mean stresses associated with far field tectonic forces and allow the stress field to be more easily perturbed by local effects such as deglaciation flexure and topography the stress field of the aegean sea and western anatolia is consistent with n s extension in a back arc setting behind the hellenic trench subduction zone the stress field is influenced in places by regional geologic structures e g in the western alps where shmax directions show a slight tendency toward a radial stress pattern not all major geologic structures however appear to affect the shmax orientation e g in the vicinity of the rhine rift system horizontal stress orientations are continuous

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