isotopic age constraints and metamorphic history of the talladega belt new evidence for timing of arc magmatism and terrane emplacement along the southern laurentian margin abstract u pb and 40ar 39ar dates from the talladega belt southernmost appalachians provide insight into the timing and nature of pre alleghanian tectonism in this region low grade metasedimentary rocks of the talladega belt represent the outermost preserved portions of the southern laurentian margin thus recording the earliest orogenic events that affected the margin in addition to later overprinting events these rocks are structurally overlain by the hillabee greenstone metavolcanic sequence from which metadacite yields an age of 470 4 ma ion microprobe u pb zircon age hillabee geochemistry indicates formation in an arc or back arc setting we suggest correlation of the hillabee greenstone with 460 470 ma arc related rocks in the dahlonega gold belt which extends along strike with the hillabee through georgia and into north carolina and interpret the hillabee as the southernmost volcanic expression of an early middle ordovician arc that formed outboard of laurentia rocks of the talladega be

teleconnection stationarity variability and trends of the southern annular mode sam during the last millennium the southern annular mode sam is the leading mode of atmospheric interannual variability in the southern hemisphere sh extra tropics here we assess the stationarity of sam spatial correlations with instrumental and paleoclimate proxy data for the past millennium the instrumental period shows that temporal non stationarities in sam teleconnections are not consistent across the sh land areas this suggests that the influence of the sam index is modulated by regional effects however within key regions with good proxy data coverage south america tasmania new zealand teleconnections are mostly stationary over the instrumental period using different stationarity criteria for proxy record selection we provide new austral summer and annual mean sam index reconstructions over the last millennium our summer sam reconstructions are very robust to changes in proxy record selection and the selection of the calibration period particularly on the multi decadal timescale in contrast the weaker performance and lower agreement in the annual mean sam reconstructions point towards changing teleconnection patterns that may be particularly important outside the summer months our results clearly portend that the temporal stationarity of the proxy climate relationships should be taken into account in the design of comprehensive regional and hemispherical climate reconstructions the summer sam reconstructions show no significant relationship to solar greenhouse gas and volcanic forcing with the exception of an extremely strong negative anomaly following the ad 1257 samalas eruption furthermore reconstructed pre industrial summer sam trends are very similar to trends obtained by model control simulations we find that recent trends in the summer sam lie outside the 5 95 range of pre industrial natural variability

zonal asymmetry of the antarctic oscillation 1 in this research the zonal asymmetry of the southern annular mode or the antarctic oscillation aao is studied it is indicated that apparent zonal asymmetry exists in the normalized sea level pressure differences between the middle and high latitudes during the boreal summer among different longitudes especially between the western and eastern hemispheres results show that the southern oscillation so is responsible for part of the zonal asymmetry in aao the western hemisphere and the eastern hemisphere parts of aao are correlated at 0 23 and 0 52 respectively for the period of 1959 1998 before and after the linear regressions on the southern oscillation index soi have been removed from the time series the paper also discusses the relationship between the precipitation in the east asia and the aao before and after removing the linear regressions on so index soi indicating the stable relationship between the east asian precipitation and the zonal symmetric component of aao

analysis of a regional change in the sign of the sam temperature relationship in antarctica this study examines regional atmospheric circulation changes associated with a reversal in the sign of the relationship between the southern annular mode sam and near surface temperatures at halley station east antarctica during the 1980s we show that the key factor affecting the regional sam temperature relationship str is the relative magnitude of two climatological low pressure centres to the west and east of the area which determines the source region of air masses advected into the locality the principal difference affecting the str is shown to be a trend towards a significantly weaker climatological low higher pressure at 20 e during a positive phase of the sam specifically it is variations in the phase and magnitude of the wave number three patterns of atmospheric circulation the non annular component of the sam which are the principal factors governing the regional str a similar reversal is observed in the sign of the correlation between the sam and oxygen isotope values from an ice core located some 1 200 km east of halley this relationship is examined throughout the 20th century by comparing the isotope data to sam reconstructions and demonstrates marked decadal variability thus these data suggest that switches in the str are more likely to reflect natural variability in the long wave patterns over the southern ocean rather than the influence of an anthropogenic forcing this finding is important when considering the potential utility of antarctic isotope data as a proxy for the sam

annual changes in sea ice and phytoplankton in polynyas of the amundsen sea antarctica abstract two coastal polynyas in the amundsen sea amundsen polynya and pine island polynya were studied as part of the dynalife project because of their unusually high rates of biological production and close association with melting ice shelves in this component of the study satellite imagery of ocean color using reprocessing r2009 1 and passive microwave sea ice distributions were used to characterize interannual changes in polynya dynamics and phytoplankton bloom development between 1997 and 2010 interannual differences in sea ice cover were large in both polynyas but especially so in the smaller pine island polynya and were related to synoptic scale wind patterns rather than climate state enso or sam open water season lasted 10 days longer in the amundsen polynya 132 days than in the pine island polynya 122 days the phytoplankton bloom in the amundsen polynya lasted approximately two weeks longer and was 30 more productive per unit area than the bloom in the pine island polynya because pine island polynya was lower in both mean open water area and annual net primary production npp per unit area total annual npp averaged over the 13 year time series was only 60 of that in the amundsen polynya 1 96 and 3 26 tg c yr 1 respectively given the high interannual variability and the short time series duration we did not observe a secular trend in primary production or any relationship with climate indices such as the southern annular mode however with increased iron addition from melting ice shelves into the surface waters of the polynyas we expect that primary production could be enhanced in the future

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

spatial patterns of variability in antarctic surface temperature connections to the southern hemisphere annular mode and the southern oscillation 1 the 17 year 1982 1998 trend in surface temperature shows a general cooling over the antarctic continent warming of the sea ice zone with moderate changes over the oceans warming of the peripheral seas is associated with negative trends in the regional sea ice extent effects of the southern hemisphere annular mode sam and the extrapolar southern oscillation so on surface temperature are quantified through regression analysis positive polarities of the sam are associated with cold anomalies over most of antarctica with the most notable exception of the antarctic peninsula positive temperature anomalies and ice edge retreat in the pacific sector are associated with el nino episodes over the past two decades the drift towards high polarity in the sam and negative polarity in the so indices couple to produce a spatial pattern with warmer temperatures in the antarctic peninsula and peripheral seas and cooler temperatures over much of east antarctica

a predominant reversal in the relationship between the sam and east antarctic temperatures during the twenty first century abstractthe scientific literature portrays a temporally invariant spatial relationship between the phase of the southern annular mode sam and the sign of surface air temperature sat anomalies across antarctica however here the authors describe a predominant switch from a negative to positive sam temperature relationship str across east antarctica in austral summer autumn during the first decade of the twenty first century when the sam was generally weakly positive of the nine years that had a positive regional str from 1957 to 2010 seven occurred during the last decade this reversal appears to be a response to anomalous high pressure over east antarctica resulting from variability in the phase and amplitude of the local component of the zonal wavenumber 3 pressure pattern in years when a reversed positive regional str exists the anomalous circulation is such that there is greater energy flux into the region while enhanced katabatic drainage across the continental interior disrupts the sur

systematics of chlorite alteration at the phelps dodge massive sulfide deposit matagami quebec hydrothermal alteration at the phelps dodge archcan volcanogenic massive sulfide deposit has converted rhyodacite and rhyolite footwall rocks into the following mineral assemblages quartz chlorite albite epidote or sericite quartz chlorite or sericite chlorite or sericite and chlorite talc or stilpnomelane alteration at constant al was initiated by hydration addition of fe mg silicification and leaching of ca na which produced al saturated chlorites with a wide range of fe fe mg ratios within the assemblage quartz chlorite albite epidote or sericite with continued addition of fe and less mg combined with extensive leaching of quartz the chlorite became al undersaturated quartz chlorite talc assemblage and ultimately formed a rock composed essentially of chlorite the chlorite talc or stilpnomelane assemblage is stable in late crosscutting veinlets and in the ore zone chlorites in the si al mg fe system form a rectangular solid solution plane with limited substitution of al for si and extensive substitution of fe for mg in si al space the solid solution plane is outlined by al saturation presence of other al rich mineral and al undersaturation presence of al poor or al free mineral boundaries al iv substitution for si in the chlorites increases from 2 3 to 3 01 formula units based on 8 si al iv with fe fe mg whereas al iv occupancy decreases from 2 88 to 2 65 the valence charge balance is compensated by octahedral site vacancies or by the conversion of fe super 2 to fe super 3 the al iv content of chlorite also increases with temperature chlorites on the al saturated boundary of the solid solution field form a potentially useful geothermometer t degrees c 106 al iv 18 al iv is corrected for changes with the fe fe mg ratio as al iv corrected al iv 0 7 fe fe mg the fe fe mg ratios of bulk rock and contained chlorite correlate well birefringence colors of the chlorite change from green to brown violet and berlin blue as fe fe mg changes from 0 18 to 0 64 the fe fe mg variation apparently depends largely on the proportions of mg rich seawater and fe rich hydrothermal fluid in the altering brine

a comparative analysis of pre silurian crustal building blocks of the northern and the southern appalachian orogen the new york promontory serves as the divide between the northern and southern segments of the appalachian orogen antiquated subdivisions distinct for each segment implied that they had lithotectonic histories that were independent of each other using new lithotectonic subdivisions we compare first order features of the pre silurian orogenic building blocks in order to test the validity of the implication of independent lithotectonic histories for the two segments three lithotectonic divisions termed here the laurentian iapetan and the peri gondwanan realms characterize the entire orogen the laurentian realm composed of native north american rocks is remarkably uniform for the length of the orogen it records the multistage neoproterozoic early paleozoic rift drift history of the appalachian passive margin formation of a taconic seaway and the ultimate demise of both in the middle ordovician the iapetan realm encompasses mainly oceanic and magmatic arc tracts that once lay within the iapetus ocean between laurentia and gondwana in the northern segment the realm is divisible on the basis of stratigraphy and faunal provinciality into peri laurentian and peri gondwanan tracts that were amalgamated in the late ordovician south of new york stratigraphic and faunal controls decrease markedly rock associations are not inconsistent with those of the northern appalachians although second order differences exist exposed exotic crustal blocks of the peri gondwanan realm include ganderia avalonia and meguma in the north and carolinia in the south carolinia most closely resembles ganderia both in early evolution and late ordovician silurian docking to laurentia our comparison indicates that to a first order the pre silurian appalachian orogen developed uniformly starting with complex rifting and a subsequent drift phase to form the appalachian margin followed by the consolidation of iapetan components and ending with accretion of the peri gonwanan ganderia and carolinia this deduction implies that any first order differences between northern and southern segments post date late ordovician consolidation of a large portion of the orogen

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

petrogenesis and structure of the buck creek mafic ultramafic suite southern appalachians constraints on ophiolite evolution and emplacement in collisional orogens integration of detailed field petrological structural and geochemical observations of the buck creek mafic ultramafic suite which is among the larger southern appalachian ultramafic exposures points to an igneous origin as a mid ocean ridge cumulate massif with subsequent emplacement in a deep subduction zone setting these results help to clarify the unresolved role of alpine type ultramafic bodies in the southern appalachians a problem complicated by their generally small and fragmented nature and by significant tectonic overprinting as an ophiolite fragment the buck creek rocks are unusual in their preservation of relatively high pressure anhydrous conditions and thus they provide constraints on mechanisms of ophiolite emplacement field support for a cumulate origin for the buck creek suite includes centimeter to meter scale interlayering of dunite troctolite anorthosite and spinel rich layers and local gradation between buck creek troctolitic rocks and surrounding amphibolites relict anorthitic plagioclase forsteritic olivine and augitic clinopyroxene define a cumulate triangle on an mgo versus al 2 o 3 diagram meta troctolite and meta dunite compositions define a linear array between olivine and plagioclase compositions and many amphibolites fall within this triangle reflecting gabbroic protoliths the relatively abundant troctolite cumulates scarce pyroxene in the ultramafic rocks and the high al 2 o 3 tio 2 and low cr numbers in spinel best match lot or l type lherzolite ophiolites consistent with crystallization in a slow spreading mid ocean ridge setting sapphirine bearing spinel symplectites in the metatroctolites suggest that buck creek rocks remained anhydrous to 800 c and 0 9 1 1 gpa representing conditions atypical of ophiolite emplacement comparisons to the zermatt saas ophiolite and bergen eclogite suggest rapid subduction of buck creek rocks to depths of 30 km where partial hydration perhaps facilitated by pro grade dehydration reactions in surrounding rocks caused strain softening that permitted ductile disaggregation and aided in their emplacement into the overlying accretionary complex alternatively emplacement might have resulted from a switch in subduction polarity with hydration following emplacement uplift shortening and hydration within the accretionary sequences are responsible for the dominant structural features

variability of marine 14c reservoir ages in the southern ocean highlighting circulation changes between 1910 and 1950 abstract recent changes in the southern ocean overturning circulation have been attributed either to natural variability or to anthropogenic forcing the 14c analyses of mollusk shells from kerguelen islands evidence a high decadal variability of the sea surface radiocarbon reservoir ages in the southern south indian ranging from 832 to 1005 30 years between 1910 and 1930 such high variability is common to the different sectors of the southern ocean southern south pacific and atlantic at inter annual and decadal timescales between 1901 and 1950 notably a decrease of 14 c of 40 increased r of 290 years occurred between 1901 and 1940 followed by an increase of 30 between 1940 and 1958 using a simple box model of ocean atmosphere 14co2 exchange this aging is attributed to increased upwelling of cold and 14c depleted subsurface seawaters due to intensified poleward southern westerlies the sea surface 14c aging is indeed well correlated to a positive phase of the southern hemisphere annular mode and to a cooling of the sea surface temperatures in the southern ocean between 1901 and 1940 these pre 1950 sea surface 14c changes highlight the importance of natural changes in wind intensities and ocean dynamics

a 277 year cool season dam inflow reconstruction for tasmania southeastern australia seasonal variability is a significant source of uncertainty in projected changes to precipitation across southeastern australia sea while existing instrumental records provide seasonal data for recent decades most proxy records e g tree rings corals speleothems offer only annual reconstructions of hydroclimate we present the first cool season july august reconstruction of dam inflow lake burbury for western tasmania in sea based on tree ring width athrotaxis selaginoides and mean latewood cell wall thickness phyllocladus aspleniifolius chronologies the reconstruction produced using principal component regression verifies back to 1731 and is moderately skillful explaining around 23 of the variance according to the reconstruction relatively low inflow periods occurred around 1860 the early 1900s and 1970 while relatively high inflows occurred in the 1770s and 1810s highest reconstructed inflows occurred in 1816 and lowest in 1909 comparison with available documentary and instrumental records indicates that the reconstruction better captures high rather than low flow events there is virtually no correlation between our reconstruction and another for december january inflow for the same catchment a result consistent with the relationship between seasonal instrumental data this suggests that conditions in one season have not generally reflected conditions in the other season over the instrumental record or for the past 277 years this illustrates the value of obtaining reconstructions of regional hydroclimatic variability for multiple individual seasons in regions where dry and wet seasons are not strongly defined the results also indicate that the hydroclimate of the southeastern australian region cannot be adequately represented by a single regional reconstruction

ophiolite genesis and global tectonics geochemical and tectonic fingerprinting of ancient oceanic lithosphere ophiolites and discussions on their origin and significance in earth s history have been instrumental in the formulation testing and establishment of hypotheses and theories in earth sciences the definition tectonic origin and emplacement mechanisms of ophiolites have been the subject of a dynamic and continually evolving concept since the nineteenth century here we present a review of these ideas as well as a new classification of ophiolites incorporating the diversity in their structural architecture and geochemical signatures that results from variations in petrological geochemical and tectonic processes during formation in different geodynamic settings we define ophiolites as suites of temporally and spatially associated ultramafic to felsic rocks related to separate melting episodes and processes of magmatic differentiation in particular tectonic environments their geochemical characteristics internal structure and thickness vary with spreading rate proximity to plumes or trenches mantle temperature mantle fertility and the availability of fluids subduction related ophiolites include suprasubduction zone and volcanic arc types the evolution of which is governed by slab dehydration and accompanying metasomatism of the mantle melting of the subducting sediments and repeated episodes of partial melting of metasomatized peridotites subduction unrelated ophiolites include continental margin mid ocean ridge plume proximal plume distal and trench distal and plume type plume proximal ridge and oceanic plateau ophiolites that generally have mid ocean ridge basalt morb compositions subduction related lithosphere and ophiolites develop during the closure of ocean basins whereas subduction unrelated types evolve during rift drift and seafloor spreading the peak times of ophiolite genesis and emplacement in earth history coincided with collisional events leading to the construction of supercontinents continental breakup and plume related supermagmatic events geochemical and tectonic fingerprinting of phanerozoic ophiolites within the framework of this new ophiolite classification is an effective tool for identification of the geodynamic settings of oceanic crust formation in earth history and it can be extended into precambrian greenstone belts in order to investigate the ways in which oceanic crust formed in the archean

deep in the heart of dixie pre alleghanian eclogite and hp granulite metamorphism in the carolina terrane south carolina usa the central part of the carolina terrane in western south carolina comprises a 30 to 40 km wide zone of high grade gneisses that are distinct from greenschist facies metavolcanic rocks of the carolina slate belt to the se and amphibolite facies metavolcanic and metaplutonic rocks of the charlotte belt to the nw this region termed the silverstreet domain is characterized by penetratively deformed felsic gneisses granitic gneisses and amphibolites mineral assemblages and textures suggest that these rocks formed under high pressure metamorphic conditions ranging from eclogite facies through high p granulite to upper amphibolite facies mafic rocks occur as amphibolite dykes as metre scale blocks of coarse grained garnet clinopyroxene amphibolite in felsic gneiss and as residual boulders in deeply weathered felsic gneiss inferred omphacite has been replaced by a vermicular symplectite of sodic plagioclase in diopside consistent with decompression at moderate to high temperatures and a change from eclogite to granulite facies con ditions all samples have been partially or wholly retrograded to amphibolite assemblages we infer the following p t t history 1 eclogite facies p t conditions at 1 4 gpa 650 730 c 2 high p granulite facies p t conditions at 1 2 1 5 gpa 700 800 c 3 retrograde amphibolite facies p t conditions at 0 9 1 2 gpa and 720 660 c this metamorphic evolution must predate intrusion of the 415 ma newberry granite and must postdate formation of the charlotte belt and slate belt arcs 620 to 550 ma comparison with other medium temperature eclogites and high pressure granulites suggests that these assemblages are most likely to form during collisional orogenesis eclogite and high p granulite facies metamorphism in the silverstreet domain may coincide with a 570 535 ma event documented in the western charlotte belt or to a late ordovician early silurian event the occurrence of these high p assemblages within the carolina terrane implies that prior to this event the western carolina terrane charlotte belt and the eastern carolina terrane carolina slate belt formed separate terranes the collisional event represented by these high pressure assemblages implies amalgamation of these formerly separate terranes into a single composite terrane prior to its accretion to laurentia

development of a globally applicable model for near real time prediction of seismically induced landslides substantial effort has been invested to understand where seismically induced landslides may occur in the future as they are a costly and frequently fatal threat in mountainous regions the goal of this work is to develop a statistical model for estimating the spatial distribution of landslides in near real time around the globe for use in conjunction with the u s geological survey usgs prompt assessment of global earthquakes for response pager system this model uses standardized outputs of ground shaking from the usgs shakemap atlas 2 0 to develop an empirical landslide probability model combining shaking estimates with broadly available landslide susceptibility proxies i e topographic slope surface geology and climate parameters we focus on four earthquakes for which digitally mapped landslide inventories and well constrained shakemaps are available the resulting database is used to build a predictive model of the probability of landslide occurrence the landslide database includes the guatemala 1976 northridge 1994 chi chi 1999 and wenchuan 2008 earthquakes performance of the regression model is assessed using statistical goodness of fit metrics and a qualitative review to determine which combination of the proxies provides both the optimum prediction of landslide affected areas and minimizes the false alarms in non landslide zones combined with near real time shakemaps these models can be used to make generalized predictions of whether or not landslides are likely to occur and if so where for earthquakes around the globe and eventually to inform loss estimates within the framework of the pager system

drought reconstructions for the continental united states abstract the development of a 2 lat 3 long grid of summer drought reconstructions for the continental united states estimated from a dense network of annual tree ring chronologies is described the drought metric used is the palmer drought severity index pdsi the number of grid points is 154 and the reconstructions cover the common period 1700 1978 in producing this grid an automated gridpoint regression method called point by point regression was developed and tested in so doing a near optimal global solution was found for its implementation the reconstructions have been thoroughly tested for validity using pdsi data not used in regression modeling in general most of the gridpoint estimates of drought pass the verification tests used in addition the spatial features of drought in the united states have been faithfully recorded in the reconstructions even though the method of reconstruction is not explicitly spatial in its design the drought reconstructions show that the 1930s dust bow

synoptic activity in the seas around antarctica abstract the recent ncep department of energy doe reanalysis 2 update of the original ncep ncar dataset provides what is arguably the highest quality analyses spanning two decades available for the high southern latitudes it therefore offers an excellent starting point from which to assemble a modern comprehensive and reliable picture of synoptic activity in the subantarctic region this set covering the modern satellite era from january 1979 to february 2000 is used herein in addition the exploration in this study has been conducted with sophisticated feature tracking and trajectory analysis software it is shown that the high southern latitude cyclone system density is greatest in the indian ocean and to the south of australia near or to the south of 60 s the numbers in winter exceed those in summer except over a few but important regions such as the bellingshausen sea the antarctic coastal region is confirmed as one of high cyclonicity as is that in the northern part of the antarctic

projection of climate change onto modes of atmospheric variability two possible interpretations of forced climate change view it as projecting either linearly or nonlinearly onto the dominant modes of variability of the climate system an evaluation of these two interpretations is performed using annual mean sea level pressure slp and surface air temperature sat fields obtained from integrations of the geophysical fluid dynamics laboratory coupled general circulation model forced with varying concentrations of greenhouse gases the dominant modes of slp both represent much of the total variability and remain important in warmer climates with sat however the dominant modes are often related to variations in the sea ice edge and so do not remain important once the ice has retreated those unrelated to sea ice remain dominant in the warmer climates but represent smaller fractions of the total variability in general climate change tends to project most strongly onto the more dominant modes the change in slp projects partially onto the top two modes in the northern hemisphere reflecting both an overall decrease in hemispheric slp as well as the pattern of change in the southern hemisphere the change projects negligibly onto the dominant patterns between equilibrium climates but very strongly onto the antarctic oscillation like mode in the transient integrations changes in sat project partially onto the dominant modes but relate more to the mean warming rather than the pattern of change in general the change projects most strongly onto the more dominant modes in all slp domains the projection of climate change overwhelmingly manifests itself as a linear translation in the mode consistent with the linear interpretation in sat domains related to sea ice variability the projection reflects an increased tendency toward ice free regimes consistent with the nonlinear perspective however this nonlinear projection represents only a small portion of the overall climate change

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

chloritization of the hydrothermally altered bedrock at the igarape bahia gold deposit carajas brazil the igarape bahia gold deposit has developed from weathering of a near vertical hydrothermal cu au mineralization zone the unweathered bedrock composed of chlorite schists is mainly metamorphosed basalts pyroclastic and clastic sedimentary rocks and iron formation contents and fe fe mg ratios of chlorites increase from distal country rock towards the mineralization zone which can be attributed to different water rock ratios and locations in a hydrothermal system in the hydrothermal system high salinity fluids convected through basin floor rocks stripping metals from the recharge zones with precipitation in discharge zones the chlorite with lower fe fe mg ratios indicates alteration by relatively unreacted mg rich fluids occurring within recharge zones by contrast the chlorite with higher fe fe mg ratios in the mineralization zone formed from solutions rich in fe mn au cu h2s and sio2 within a discharge zone the iron formation could also be formed within the discharge zone or on the basin floor from the fe rich fluids the distal country rock with less chlorite content is a hydrothermal product at low water rock ratios whereas the proximal country rock and the host rock with more chlorite content formed at high water rock ratio conditions the al iv contents of chlorites indicate that the formation temperatures of these rocks range from 204 to 266 c with temperatures slightly increasing from distal country rock towards the mineralization zone

comparing trends in the southern annular mode and surface westerly jet abstractthis paper examines trends in the southern annular mode sam and the strength position and width of the southern hemisphere surface westerly wind jet in observations reanalyses and models from phase 5 of the coupled model intercomparison project cmip5 first the period over 1951 2011 is considered and it is shown that there are differences in the sam and jet trends between the cmip5 models the hadley centre gridded slp hadslp2r dataset and the twentieth century reanalysis the relationships between these trends demonstrate that the sam index cannot be used to directly infer changes in any one kinematic property of the jet the spatial structure of the observed trends in slp and zonal winds is shown to be largest but also most uncertain in the southeastern pacific to constrain this uncertainty six reanalyses are included and compared with station based observations of slp the cmip5 mean slp trends generally agree well with the direct observations despite some climatological biases

the early twentieth century arctic high fact or fiction reconstructions of monthly mean sea level grid point pressure from station pressure data over the arctic region using an objective technique have revealed two serious errors in the gridded data first all gridded data from the u s historical weather map series for the arctic ocean area away from the north atlantic sector appears to be between 4 and 6 mb too high before about 1931 the semi permanent arctic high produced in the early historical map series was the result of a lack of basic station data and the belief amongst many north american meteorologists of the 1920s and 1930s of the existence of a polar or glacial anticyclone the second error affects only north western north america for the years 1899 1909 here pressure is again too high compared with reconstructed data the cause of this error is not immediately apparent but is probably the result of an erroneous correction to sea level for stations in the region both errors seriously affect the homogeneity of the gridded arctic series the objective scheme used to reveal the errors can also be used to derive correction factors for the gridded data prior to 1931

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

the leading modes of decadal sst variability in the southern ocean in cmip5 simulations the leading modes of sea surface temperature variability in the southern ocean on decadal and even larger time scales are analysed using coupled model intercomparison project 5 cmip5 model simulations and observations the analysis is based on empirical orthogonal function modes of the cmip5 model super ensemble we compare the modes from the cmip5 super ensemble against several simple null hypotheses such as isotropic diffusion red noise and a slab ocean model to investigate the sources of decadal variability and the physical processes affecting the characteristics of the modes the results show three main modes in the southern ocean the first and most dominant mode on interannual to decadal time scales is an annular mode with largest amplitudes in the pacific which is strongly related to atmospheric forcing by the southern annular mode and el nino southern oscillation the second mode is an almost basin wide monopole pattern which has pronounced multi decadal and longer time scales variability it is firstly inducted by the wave 3 patterns in the atmosphere and further developed via ocean dynamics the third mode is a dipole pattern in the southern pacific that has a pronounced peak in the power spectrum at multi decadal time scales all three leading modes found in the cmip5 super model have distinct patterns and time scale behaviour that can not be explained by simple stochastic null hypothesis thus all three leading modes are ocean atmosphere coupled modes and are likely to be substantially influenced or driven by ocean dynamical processes

an altimetry based gravest empirical mode south of africa 2 dynamic nature of the antarctic circumpolar current fronts 1 swart et al 2010 applied altimetry data to the gravest empirical mode south of africa to yield a 16 year time series of temperature and salinity sections in this study we use these thermohaline sections to derive weekly estimates of heat content hc and salt content sc at the goodhope meridional transect of the antarctic circumpolar current acc these estimates compare favorably to observed data the resulting 16 year time series of hc and sc estimates are used to explain the subsurface thermohaline variability at each acc front and frontal zone the variability at the subantarctic zone saz is principally driven by the presence of agulhas rings which occur in this region approximately 2 7 times per annum and are responsible for the longest and highest scales of observed variability the variability of the saz is responsible for over 50 and 60 of the total acc hc and sc variability respectively poleward of the saz the variability is largely determined by the influence of the local topography on the fronts of the region and can be explained by the conservation of potential vorticity wavelet analysis is conducted on the time series of meridionally integrated hc and sc in each acc front and frontal zone revealing a consistent seasonal mode that becomes more dominant toward the southern limit of the acc the lower frequency signals are compared with two dominant modes of variability in the southern ocean the southern annular mode correlates well with the hc and sc anomaly estimates at the antarctic polar front while the southern oscillation index appears to have connections to the variability found in the very southern domains of the acc

hydrothermal alteration and cu ni pge mobilization in the charnockitic rocks of the footwall of the south kawishiwi intrusion duluth complex usa in the neoarchean 2 7 ga contact metamorphosed charnockitic footwall of the mesoproterosoic 1 1 ga south kawishiwi intrusion of the duluth complex the primary metamorphic mineral assemblage and cu ni pge sulfide mineralization is overprinted by an actinolite chlorite cummingtonite prehnite pumpellyite quartz calcite hydrothermal mineral assemblage along 2 3 cm thick veins in calcite hosted by the hydrothermal alteration zones and in a single recrystallized quartz porphyroblast four different fluid inclusion assemblages are documented the composition of these fluid inclusions provide p t conditions of the fluid flow and helps to define the origin of the fluids and evaluate their role in the remobilization and reprecipitation of the primary metamorphic sulfide assemblage pure co2 fluid inclusions were found as early inclusions in recrystallized quartz porphyroblast these inclusions may have been trapped during the recrystallization of the quartz during the contact metamorphism of the footwall charnockite in the footwall of the ski the estimated trapping pressure 1 6 2 0 kbar and temperature 810 920 c conditions correspond to estimates based on felsic veins in the basal zones of the south kawishiwi intrusion fluid inclusion assemblages with co2 h2o nacl and ch4 n2 h2o nacl compositions found in this study along healed microfractures in the recrystallized quartz porphyroblast establish the heterogeneous state of the fluids during entrapment the estimated trapping pressure and temperature conditions 240 650 bar and 120 150 c for co2 h2o nacl inclusions and 315 360 bar and 145 165 c for ch4 n2 h2o nacl inclusions are significantly lower than the p t conditions 700 c and 1 6 2 kbar during the contact metamorphism indicating that this fluid flow might not be related to the cooling of the duluth complex and its contact aureole the presence of chalcopyrite inclusions in these fluid inclusions and in the trails of these fluid inclusion assemblages confirms that at least on local scale these fluids played a role in base metal remobilization no evidences have been observed for pge remobilization and transport in the samples the source of the carbonic phase in the carbonic assemblages co2 ch4 could be the graphite present in the metasedimentary hornfelsed inclusions in the basal zones of the south kawishiwi intrusion the hydrothermal veins in the charnockite can be characterized by an actinolite cummingtonite chlorite prehnite pumpellyite calcite i ii quartz mineral assemblage chlorite thermometry yields temperatures around 276 308 c during the earliest phase of the fluid flow in the late calcite ii phase high salinity 21 6 28 8 nacl cacl2 equiv wt low temperature 90 160 c primary aqueous inclusions were found chalcopyrite sphalerite millerite replacing and intersecting the early hydrothermal phases are associated to the late calcite ii phase the composition of the formational fluids in the canadian shield is comparable with the composition of the studied fluid inclusions this suggests that the composition of the fluids did not change in the past 2 ga and base metal remobilization by formational fluids could have taken place any time after the formation of the south kawishiwi intrusion sulfur isotope studies carried out on the primary metamorphic 34s 7 4 8 9 and the hydrothermal sulfide mineral assemblage 34s 5 5 5 7 proves that during the hydrothermal fluid flow the primary metamorphic ores were remobilized

relations between annular modes and the mean state southern hemisphere winter in a zonally symmetric climatology with a single eddy driven jet such as prevails in the southern hemisphere summer the midlatitude variability is dominated by fluctuations of the jet around its mean position as described by the southern hemisphere annular mode sam to study whether this result holds for a zonally asymmetric climatology the observed variability of the southern hemisphere winter is analyzed the mean state in this case is characterized by relatively weak stationary waves yet there exist significant zonal variations in the mean strength and meridional structure of the subtropical jet stream as in summer the winter sam signature is annular in shape and the corresponding wind anomalies are dipolar but it is associated with two different behaviors of the eddy driven jet in different longitudinal ranges over the indian ocean the sam is associated primarily with a latitudinal shift of the jet around its mean position over the pacific sector it is instead characterized by a seesaw in the wind speed between two distinct latitudes corresponding to the positions of the midlatitude and subtropical jets composites of eddy forcing and baroclinicity over both sectors appear consistent with the two different behaviors as in the zonal mean case high frequency eddies both force and maintain the low frequency wind anomalies associated with the sam the positive feedback by eddies is however not local changes in the eddy forcing are influenced most strongly by zonal wind anomalies located upstream

accumulation variability in the antarctic peninsula the role of large scale atmospheric oscillations and their interactions abstracta new ice core drilled in 2010 to bedrock from the bruce plateau bp on the antarctic peninsula ap provides a high temporal resolution record of environmental conditions in this region the extremely high annual accumulation rate at this site facilitates analysis of the relationships between annual net accumulation an on the bp and large scale atmospheric oscillations over the last 45 years an on the bp has been positively correlated with both the southern annular mode sam and southern oscillation index soi extending this analysis back to 1900 reveals that these relationships are not temporally stable and they exhibit major shifts in the late 1940s and the mid 1970s that are contemporaneous with phase changes in the pacific decadal oscillation pdo these varying multidecadal characteristics of the an oscillation relationships are not apparent when only data from the post 1970s era are employed analysis of the longer ice core record reveals that the influence of the sam on an depends

seasonal zonal asymmetries in the southern annular mode and their impact on regional temperature anomalies abstractthe southern hemisphere annular mode sam is the dominant mode of climate variability in the extratropical southern hemisphere representing variations in pressure and the corresponding changes to the circumpolar zonal flow it is typically thought of as an annular or ringlike structure however on seasonal time scales the zonal symmetry observed in the sam in monthly or annual mean data is much less marked this study further examines the seasonal changes in the sam structure and explores temperature signals across the southern hemisphere that are strongly tied to the asymmetric sam structure the sam asymmetries are most marked in the pacific sector and in austral winter and spring related to changes in the jet entrance and exit regions poleward of 30 s depending on the season the asymmetric sam structure explains over 25 of the variance in the overall sam structure and has strong connections with enso or zonal wavenumber 3 in austral summer and autumn the sam has been becoming more zona

antarctic station based seasonal pressure reconstructions since 1905 1 reconstruction evaluation seasonal mean antarctic pressures at 17 stations are reconstructed based on the method of principal component regression employing midlatitude pressure data as predictors several reconstruction methods were performed in order to assess the stability and reliability of the reconstructions obtained including performing the reconstructions over a shorter 30 year window and withholding the remaining data for an independent validation generally there were small differences between the various approaches but typically reconstructions conducted on data with the trends still present and over the full period of observations achieved the highest skill seasonally reconstruction skill was high in austral summer across the entire antarctic continent reconstructions that employed gridded pressure data over oceans as well as the observations here termed pseudoreconstructions also performed remarkably well in austral winter spatially the reconstruction skill was highest near the antarctic peninsula in all seasons and weakest in coastal east antarctica and the antarctic interior during austral spring and autumn the spatial variability of the skill in part reflects the distance to the nearest midlatitude predictor nonetheless for nearly all seasons and locations the observed trends since 1957 were well captured by the reconstructions as was the low frequency decadal scale variability these results suggest antarctic pressure observations can be extended throughout the twentieth century with high confidence especially in summer allowing for a more precise understanding of the role and magnitude of natural atmospheric circulation variability across antarctica

coupled ocean atmosphere ice response to variations in the southern annular mode abstract the coupled ocean atmosphere ice response to variations in the southern annular mode sam is examined in the national center for atmospheric research ncar community coupled climate model version 2 the model shows considerable skill in capturing the predominantly zonally symmetric sam while regional deviations between model and observation sam winds go a long way in explaining the generally small differences between simulated and observed sam responses in the ocean and sea ice systems vacillations in the position and strength of the circumpolar winds and the ensuing variations in advection of heat and moisture result in a dynamic and thermodynamic forcing of the ocean and sea ice both meridional and zonal components of ocean circulation are modified through ekman transport which in turn leads to anomalous surface convergences and divergences that strongly affect the meridional overturning circulation and potentially the pathways of intermediate water ventilation a heat budget analysis de

spatial variability of sea level pressure and 500 mb height anomalies over the southern hemisphere abstract the spatial variability of mean sea level pressure slp and 500 mb height anomalies over the southern hemisphere during summer djf and winter jja is determined using eigenvector analysis based on daily synoptic maps from 1972 to 1979 the patterns of spatial distribution of pressure and height anomalies are further verified and examined by means of station data and the eigenvectors are compared between the seasons and to those found for the northern hemisphere the first eigenvector shows that midlatitude anomalies of slp and 500 mb height are of an opposite sign to those found over and around antarctica the pattern is highly barotropic and suggests strengthening and weakening of the zonal wind in alternating latitude belts the 500 mb height differences are calculated for five midlatitude to antarctic station pairs using data from the late 1950 s onward these latitudinal height differences are also used to describe the association between the hemispheric westerlies and the southern oscil

a century of climate variability in central dronning maud land east antarctica and its relation to southern annular mode and el nino southern oscillation stable isotope records of oxygen and hydrogen were studied from a 65 m long ice core retrieved from the central dronning maud land east antarctica in order to reconstruct the coastal antarctic climate variability during the last century and its relation to the southern annular mode sam and el nino southern oscillation enso the 18 o records showed a significant relation to the sam with a dominant 4 years variability except during specific periods 1918 1927 19381947 1989 2005 when enso teleconnection was established through the in phase relation between sam and southern oscillation index soi the combined influence of enso and sam was seen on surface air temperatures in this region mainly during the austral summer season from 1989 to 2005 further a significant relationship between 18 o and sam was observed on a decadal scale which overrides the intermittent influence of enso major shifts in the deuterium excess record were observed during periods of enso teleconnections which support a shift in moisture source regions during the periods of stronger enso teleconnections surface air temperatures estimated using the 18 o t spatial slope for this region depicted a significant warming of 1 c for the past century the study reveals that throughout the last century sam was the dominant mode of climatic variability in the coastal region of central dronning maud land on a decadal scale

formation of high pressure metabasites in the southern appalachian blue ridge via taconic continental subduction beneath the laurentian margin 1 tectonic models that account for the occurrence of eclogite retrograde eclogite peridotite and migmatitic basement gneisses in the southern blue ridge invoke closure of a small ocean basin between the eastern blue ridge ebr and western blue ridge wbr in this obducted ophiolite model franciscan type eastward subduction of oceanic crust beneath the piedmont arc occurred prior to obduction of the arc onto the laurentian margin the discovery of kilometer scale eclogite bodies near the ebr wbr boundary are cited as evidence for obducted ophiolite accreted island arc models however thermobarometric estimates based on mineral chemistry from hp metabasites of the western central and eastern blue ridge indicate that eclogites and granulites are medium temperature type 550 900 c inconsistent with the obducted ophiolite model mid ocean ridge basalt subducted beneath continental margins and island arcs rarely reaches temperatures in excess of 550 c thermobarometric comparisons of the present study and a reexamination of deep seismic profiles from the blue ridge allow for a model of westward subduction of continental material beneath laurentia during the taconic orogeny that produced a megamelange now preserved in the central and eastern blue ridge tectonic provinces p t paths determined from blue ridge hp metabasites are similar to p t paths determined previously from caledonian and variscan eclogites thermobarometric similarities imply a common tectonic history of continental collision subduction of continental crust to depths of 50 65 km followed by rapid eduction

the soapstone ridge complex southern appalachians petrographic mineral compositional and oxygen isotope investigation samples of the soapstone ridge complex ssr in the southern appalachians examined for this study are composed of megacrystic orthopyroxenites amphibole schists and talc chlorite amphibole schists the mineralogy of the ssr samples studied consists of varying proportions of amphibole chlorite talc orthopyroxene and fe ti oxides amphibole is the domi nant mineral in almost all ssr samples studied the amphiboles display zoning whereby cores that are composed of magne siohornblende and edenite consistent with amphibolite facies conditions are rimmed by tremolite actinolite consistent with greenschist facies conditions oxygen isotope compositions of ssr amphiboles investigated show a wide range in 18o values from a low value of 1 8 to a high value of 6 1 such wide ranges in 18oamphibole values occur in ophiolite complexes and oceanic crustal rocks relict orthopyroxene from the ssr has a 18o value of 3 4 a value lower than those from layered intrusions but comparable to some pyroxene 18o values from ophiolites equilibration temperatures calculated for actinolite chlorite yield a temperature of 227 c consistent with greenschist facies conditions it is proposed that the ssr amphibole cores were metamorphosed probably during terrane terrane collision under amphibolite facies conditions with the actinolite rims possibly being formed during thrusting of the ssr rocks onto the continental margin

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

historical sam variability part i century length seasonal reconstructions seasonal reconstructions of the southern hemisphere annular mode sam index are derived to extend the record before the reanalysis period using station sea level pressure slp data as predictors two reconstructions using different predictands are obtained one jones and widmann jw based on the first principal component pc of extratropical slp and the other fogt on the index of marshall a regional based sam index visbeck is also considered these predictands agree well post 1979 correlations decline in all seasons except austral summer for the full series starting in 1958 predictand agreement is strongest in spring and summer hence agreement between the reconstructions is highest in these seasons the less zonally symmetric sam structure in winter and spring influences the strength of the sam signal over land areas hence the number of stations included in the reconstructions reconstructions from 1865 were therefore derived in summer and autumn and from 1905 in winter and spring this paper examines the skill of each reconstruction by comparison with observations and reanalysis data some of the individual peaks in the reconstructions such as the most recent in austral summer represent a full hemispheric sam pattern while others are caused by regional slp anomalies over the locations of the predictors the jw and fogt reconstructions are of similar quality in summer and autumn while in winter and spring the marshall index is better reconstructed by fogt than the pc index is by jw in spring and autumn the sam shows considerable variability prior to recent decades

relation between annular modes and the mean state southern hemisphere summer abstract the annular modes emerge as the leading mode of extratropical month to month climate variability in both hemispheres here the influence of the background state on the structure and dynamics of the southern hemisphere annular mode sam during the austral summer when the climatology is characterized by a single well defined eddy driven jet is studied subsets of the climatology are constructed for early and late summer and for contrasting polarities of the enso cycle the analysis is based both on observations and on perpetual state gcm experiments the main differences between the subsets involve variations of the latitude of the mean jet it is found that in all the cases the sam is characterized by latitudinal shifts of the jet about its mean position reinforced by a positive momentum flux feedback from baroclinic waves this result is consistent with previous studies of the dynamics of the zonally averaged circulation but is found here to hold over all longitudes and for different positi

wave maintained annular modes of climate variability abstract the leading modes of month to month variability in the northern and southern hemispheres are examined by comparing a 100 yr run of the geophysical fluid dynamics laboratory gcm with the ncep ncar reanalyses of observations the model simulation is a control experiment in which the ssts are fixed to the climatological annual cycle without any interannual variability the leading modes contain a strong zonally symmetric or annular component that describes an expansion and contraction of the polar vortex as the midlatitude jet shifts equatorward and poleward this fluctuation is strongest during the winter months the structure and amplitude of the simulated modes are very similar to those derived from observations indicating that these modes arise from the internal dynamics of the atmosphere dynamical diagnosis of both observations and model simulation indicates that variations in the zonally symmetric flow associated with the annular modes are forced by eddy fluxes in the free troposphere while

inferences on late stage evolution of the russell lake allochthon and the soapstone ridge complex in georgia southern appalachians based on chlorite geothermometry

synchronous variability in the southern hemisphere atmosphere sea ice and ocean resulting from the annular mode zonally symmetric fluctuations of the midlatitude westerly winds characterize the primary mode of atmospheric variability in the southern hemisphere during all seasons this is true not only in observations but also in an unforced 15 000 yr integration of a coarse resolution r15 coupled ocean atmosphere model here it is documented how this mode of atmospheric variability known as the southern annular mode sam generates ocean circulation and sea ice variations in the model integration on interannual to centennial timescales that are tightly in phase with the sam the positive phase of the sam is associated with an intensification of the surface westerlies over the circumpolar ocean around 608s and a weakening of the surface westerlies farther north this induces ekman drift to the north at all longitudes of the circumpolar ocean and ekman drift to the south at around 308s through mass continuity the ekman drift generates anomalous upwelling along the margins of the antarctic continent and downwelling around 458s the anomalous flow diverging from the antarctic continent also increases the vertical tilt of the isopycnals in the southern ocean so that a more intense circumpolar current is also closely associated with positive sam in addition the anomalous divergent flow advects sea ice farther north resulting in an increase in sea ice coverage finally positive sam drives increases in poleward heat transport at about 308s while decreases occur in the circumpolar region ocean and sea ice anomalies of the opposite sign occur when the sam is negative the ocean and sea ice fluctuations associated with the sam constitute a significant fraction of simulated ocean variability poleward of 308s year round the robustness of the mechanisms relating the sam to oceanic variability suggests that the sam is likely an important source of large scale variability in the real southern hemisphere ocean

u pb geochronologic nd isotopic and geochemical evidence for the correlation of the chopawamsic and milton terranes piedmont zone southern appalachian orogen abstract we report u pb crystallization ages from four metavolcanic rocks and two granitic gneiss samples as well as whole rock chemical analyses and sm nd isotopic ratios from 25 metaigneous and metasedimentary rocks from the chopawamsic and milton terranes southern appalachian orogen a metarhyolite sample from the chopawamsic formation and a metabasalt sample from the ta river formation in the chopawamsic terrane have indistinguishable u pb crystallization ages of documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 471 4 pm 1 3

definition of antarctic oscillation index following walker s work about his thmous three oscillations published during the 1920 30s many papers were written about atmospheric oscillations a iburth atmospheric oscillation in the middle and high southern latitudes was lbund and nanted the grotarctic oscillation ao a refiers to a large scale alternation of atmospheric mass between the mid latitudes and high latitudes surthce pressure in order to understand the spatial structure of sea level pressure variation in detail empirical orthogonal fitnction analysis is applied an objective index of the antarctic oscillation index aoi is defined as the diffierence of zonal mean sea level pressure between 40os and 65os the aoi has the potential tbr clarifying climate regimes in the southern hemisphere similar to how the na and the npo has been used in the northern hemisphere were there other oscillation s besides nao npo and s especially in the southern hemisphere it had been supposed that there might be other atmospheric oscillation s in the high southern latitudes although as early as in the first quarter of this century walker 1928 had stated that just as in the north atlantic there is a pressure opposition between the azores and iceland there is an opposition between the high pressure belt across chile and the argentine on the one hand and the low pressure area of weddell sea and the bellingshausen sea on the other the scarcity of data in the southern hemisphere hindered the search tbr new oscillation s during the last two decades more comprehensive data over the southern hemisphere became available and more analyses were carried out see kidson 1975 rogers and van loon 1982 mo and l 7 ite 1985 2 4o 1986 connolley 1997 gong and wang 1998 a tburth atmospheric oscillation in the middle and high southern latitudes was tbund and nanted as the antarctic oscillation a wang 1992 gong and wang 1998 the term ao relrs to a large scale alternation of atmospheric mass between the mid latitude sur hce pressure

parallel decadal variability of inferred water temperatures for northern and southern hemisphere intermediate water masses we use a novel proxy growth rates of long lived deep water fish orange roughy to reconstruct inferred water temperatures of intermediate water masses in both northern and southern hemispheres since the mid 1800s the data are consistent with instrumental records showing long term warming in the northern hemisphere but also indicate decadal variability of intermediate depth temperatures that is coherent across the two hemispheres this variability correlates with the dominant subpolar annular mode in each hemisphere and implies a bihemispheric oceanic response to external forcing that influences the properties of intermediate depth water masses

twentieth century sea ice variability in the weddell sea and its effect on moisture transport evidence from a coastal east antarctic ice core record high resolution study of deuterium excess d excess sea salt sodium ss na and methane sulfonic acid msa in an ice core from coastal dronning maud land cdml east antarctica revealed the

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

influence of the southern annular mode on the sea ice ocean system 1 the global sea ice ocean model orca2 lim driven by the ncep ncar national centers for environmental prediction national center for atmospheric research reanalysis daily 2 m air temperatures and 10 m winds and by monthly climatologies for precipitation cloud cover and relative humidity is used to investigate the impact of the southern annular mode sam on the antarctic sea ice ocean system our results suggest that the response of the circumpolar southern ocean consists of an annular and a nonannular component for the sea ice cover the non annular component seems to be the most important the annular component strongly affects the overall patterns of the upper ocean circulation when the sam is in its positive phase a northward surface ekman drift a downwelling at about 45 degreess and an upwelling in the vicinity of the antarctic continent are simulated the non annular component has a significant impact at the regional scale especially in the weddell ross amundsen and bellingshausen seas in those regions the pressure pattern associated with the sam induces meridional winds which advect warmer air in the weddell sea and around the antarctic peninsula and colder air in the amundsen and ross seas this implies a dipole response of sea ice to the sam with on average a decrease in ice area in the weddell sea and around the antarctic peninsula and an increase in the ross and amundsen seas during years with a high sam index the long term trend in the observed sea ice area does not appear to be related to the trend in the sam index

blocking over the south pacific and rossby wave propagation abstract atmospheric blocking events over the south pacific are investigated using a 39 yr record of 500 hpa height fields from the ncep ncar reanalysis dataset the analysis extends earlier work using a 16 yr record and confirms that the occurrence of blocking over the southeast pacific is strongly modulated by the enso cycle during austral spring and summer comparison of results at 500 hpa with the 300 hpa meridional wind component showed that blocking events are associated with large scale wave trains lying across the south pacific from the region of australia to southern south america similar wave trains are evident in both hemispheres in singular value decomposition analyses between 300 hpa meridional wind components and tropical pacific outgoing longwave radiation olr anomalies the hypothesis that the divergence associated with tropical olr anomalies forces an extratropical wave response that results in enhanced blocking over the southeast pacific was tested using a linearized barotropic vorti

synoptic variability in the ross sea region antarctica as seen from back trajectory modeling and ice core analysis 1 synoptic variability in the ross sea region antarctica over the last thirty years is investigated using back trajectory modeling and cluster analysis we identify two dominant air mass trajectory clusters oceanic west antarctic and continental east antarctic our analysis shows that the oceanic west antarctic trajectories have an annual cycle similar to the semiannual oscillation and on average peak in frequency during april while continental east antarctic trajectories reach their annual maximum during december we demonstrate a causal association between the el nino southern oscillation enso and the frequency of oceanic west antarctic trajectories originating from the ross sea and amundsen sea regions in contrast we find that the southern annular mode sam has little influence on the trajectory cluster frequencies we then develop proxy records for synoptic variability using a shallow firn core from gawn ice piedmont in southern victoria land continental east antarctic trajectory frequency correlates with concentrations of nitrate no3 which is sourced from stratospheric air masses descending over the antarctic interior at seasonal to inter annual scales the frequency of oceanic west antarctic trajectory clusters strongly correlate with deuterium excess which is sensitive to changes in relative humidity and sea surface temperature in the ross and amundsen seas inter annual variability in the frequency of oceanic west antarctic trajectories is discussed with respect to enso and changes in sst and sea ice extent

a station based southern annular mode index from 1884 to 2005 atmospheric pressure observations from the southern hemisphere are used to estimate monthly and annually averaged indexes of the southern annular mode sam back to 1884 this analysis groups all relevant observations in the following four regions one for antarctica and three in the subtropical zone continuous surface pressure observations are available at a number of locations in the subtropical regions since the end of the nineteenth century however year round observations in the subpolar region near the antarctic continent began only during the 1940 60 period the shorter antarctic records seriously compromise the length of a traditionally estimated sam index to improve the situation proxy estimates of antarctic sea level pressure anomalies are provided based on the concept of atmospheric mass conservation poleward of 208s this allows deriving a longer sam index back to 1884 several aspects of the new record its statistical properties seasonal trends and the regional pressure anomaly correlations are presented

persistent positive anomalies in the southern hemisphere circulation abstract long time series of reanalyses from ncep ncar and from ecmwf are used to investigate the occurrence of persistent positive anomalies ppas in the 500 hpa geopotential height field over the southern hemisphere extratropics during 1958 2001 defining persistent anomalies as those of at least 100 m in magnitude lasting for at least 5 days it is found that the region of most frequent occurrence is over the south pacific a cluster analysis of monthly ppa counts shows two distinct patterns one a zonal wavenumber 1 zw1 pattern centered over the southeast pacific near 60 s and the other a zonal wavenumber 3 zw3 pattern with centers near new zealand and over the southern atlantic and indian oceans results were insensitive to the choice of dataset and to the removal of a linear trend from the daily height fields the southeast pacific ppa region is strongly modulated by enso while the zw3 pattern appears only weakly related to enso variability a strong upward trend is apparent in occurrence o