ice cores record significant 1940s antarctic warmth related to tropical climate variability although the 20th century warming of global climate is well known climate change in the high latitude southern hemisphere sh especially in the first half of the century remains poorly documented we present a composite of water stable isotope data from high resolution ice cores from the west antarctic ice sheet this record representative of west antarctic surface temperature shows extreme positive anomalies in the 1936 45 decade that are significant in the context of the background 20th century warming trend we interpret these anomalies previously undocumented in the high latitude sh as indicative of strong teleconnections in part driven by the major 1939 42 el nino these anomalies are coherent with tropical sea surface temperature mean sh air temperature and north pacific sea level pressure underscoring the sensitivity of west antarctica s climate and potentially its ice sheet to large scale changes in the global climate

paleosol carbonates from the omo group isotopic records of local and regional environmental change in east africa abstract pliocene and pleistocene sedimentary rocks from the omo turkana basin in east africa are well known for fossil and archeological evidence of human evolution and provide a unique opportunity to study four million years of environmental change in a rift basin this study uses carbon and oxygen isotope ratios of pedogenic carbonates to examine environmental variability across 5000 km 2 within the omo turkana basin an expanded isotopic dataset including the first isotopic data on pedogenic carbonates from the shungura formation and new data from the nachukui and koobi fora formations is compared to published isotopic records from both the omo turkana basin and the lower awash basin ethiopia regionally the carbon isotope record indicates a steady increase of c 4 vegetation in floodplain environments for the past 4 million years the oxygen isotopic record indicates that the isotopic composition of rainfall was depleted in 18 o relative to today s waters and that both basins likely received more rainfall in the pliocene than today a shift to higher 18 o values in paleosol carbonate after 2 ma in the omo turkana basin but not in the lower awash basin suggests that the ecology and hydrology in these two rift basins were influenced by different climatic regimes in addition to regional trends pedogenic carbonates sampled from different parts of the basin show that the distribution of c 4 vegetation and soil water 18 o values varied with proximity to the axial river system and specifically that c 3 vegetation was more dominant in soils of the shungura formation compared with coeval sediments downstream in the nachukui and koobi fora formations this large isotopic dataset from pedogenic carbonates provides the opportunity to examine how terrestrial systems responded to global climate change during the last 4 million years from both local and regional perspectives the isotopic data indicate that local basin and climate dynamics strongly influenced the impact of large scale environmental change in east african rift basins

dynamical response of equatorial indian ocean to intraseasonal winds zonal flow nonlinear and linear 4 layer ocean models are used to explore the dynamics of intraseasonal 20 90 day periods zonal flow in the equatorial indian ocean the model simulations suggest that the observed 40 60 day zonal surface current is forced primarily by wind associated with the madden julian oscillation mjo which peaks at 40 60 days the strongest spectral peak of zonal flow however occurs at 90 day period in the model and a corresponding 90 day peak appears in the observed sea level data the 90 day current results from the preferential excitation of kelvin and rossby waves by the lower frequency component of intraseasonal wind and from the enhancement by rossby waves reflected from the eastern ocean boundary

the role of amundsen bellingshausen sea anticyclonic circulation in forcing marine air intrusions into west antarctica persistent positive 500 hpa geopotential height anomalies from the ecmwf era interim reanalysis are used to quantify amundsen bellingshausen sea abs anticyclonic event occurrences associated with precipitation in west antarctica wa we demonstrate that multi day minimum 3 day duration anticyclones play a key role in the abs by dynamically inducing meridional transport which is associated with heat and moisture advection into wa this affects surface climate variability and trends precipitation rates and thus wa ice sheet surface mass balance we show that the snow accumulation record from the roosevelt island climate evolution rice ice core reflects interannual variability of blocking and geopotential height conditions in the abs ross sea region furthermore our analysis shows that larger precipitation events are related to enhanced anticyclonic circulation and meridional winds which cause pronounced dipole patterns in air temperature anomalies and sea ice concentrations between the eastern ross sea and the bellingshausen sea weddell sea as well as between the eastern and western ross sea

origins and dynamics of the 90 day and 30 60 day variations in the equatorial indian ocean abstract sea level observations in the equatorial indian ocean show a dominant spectral peak at 90 days and secondary peaks at 30 60 days over an intraseasonal period 20 90 days a detailed investigation of the origins and dynamics of these variations is carried out using an ocean general circulation model namely the hybrid coordinate ocean model hycom two parallel experiments are performed in the tropical indian ocean basin for the period 1988 2001 one is forced by ncep 3 day mean forcing fields together with the climate prediction center cpc merged analysis of precipitation cmap pentad precipitation and the other is forced by monthly mean fields to help to understand the role played by the wind driven equatorial wave dynamics a linear continuously stratified ocean model is also used both the observed and modeled 90 day sea level anomaly fields and hycom surface current clearly show equatorial kelvin and first meridional mode rossby wave structures that are forced by the 90 day winds the

detection of temperature and sea ice extent changes in the antarctic and southern ocean 1949 96 abstract some global climate models indicate that future global warning from increased atmospheric concentrations of greenhouse gases may be greatest in the polar regions over areas where the sea ice cover is reduced the reduction of sea ice area in the models also gives rise to a strong positive feedback to the warming from the increase of atmospheric greenhouse gas concentration to date and the results of transient climate models an estimate of the expected change in the antarctic temperatures and sea ice extent can be made the existing data for observed changes in temperatures of the antarctic and southern ocean extending back to approx 1956 and approx 1945 respectively are analyzed along with the data of sea ice cover commencing in 1973 to examine the extent to which the anticipated warming trends and sea ice decrease are being realized in spite of high temporal and spatial variability the data does support small significant trends of temperature increase and sea ice cover decrease compatible in magnitude to those expected as a consequence of atmospheric greenhouse gas increase the seasonal cycle shows a delayed period of autumn winter sea ice growth with a longer period of open water this supports a mechanism for positive feedback between decreasing sea ice cover and increasing temperature

origins of wind driven intraseasonal sea level variations in the north indian ocean coastal waveguide 1 in this paper we show that a linear continuously stratified ocean model reproduces observed wind driven intraseasonal sea level variability in the coastal waveguide of the northern indian ocean nio sensitivity experiments with intraseasonal wind forcing selectively applied in the equatorial region bay of bengal and arabian sea show that a large part of the basin scale sea level variations are driven by zonal wind fluctuations along the equator within the nio coastal waveguide the contribution of remote equatorial forcing decreases from 80 90 in the andaman sea to 50 northeast of sri lanka and then increases to 60 70 along the west coast of india during the southwest monsoon intraseasonal wind variations become stronger over the nio resulting in a larger contribution of local wind forcing to sea level variability along the west up to 60 and east up to 40 coasts of india

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

the influence of the amundsen sea low on the winds in the ross sea and surroundings insights from a synoptic climatology the amundsen sea low asl is an area of climatologically low atmospheric pressure situated over the southern ocean the depth and location of this feature have significant effects on winds temperature moisture transport and sea ice in its vicinity in this article we quantify the modulating effect of this feature on winds over the ross sea and ross ice shelf we examine composites of surface winds sampled according to extrema in asl depth longitude and latitude we employ the output of a previously developed synoptic climatology to identify the explanatory synoptic scale forcings in autumn winter and spring aws we find that the impact of the depth of the asl is smaller than that of its location the asl moves eastward when it is deep thereby reducing its influence on ross sea winds when the asl is northward we find strongly enhanced southerly flows over the ross sea and ice shelf forced by greater cyclonic activity in the north of the ross sea in summer we find increased cyclonic flow coinciding with a deeper asl despite the asl being located in the bellingshausen sea at this time the responses to the asl longitude and latitude are profoundly different to those in aws suggesting that relationships are strongly dependent on the varying seasonal location of the low we examine two metrics of the asl depth and identify that the absolute mean sea level pressure mslp has a more widespread response than that of the relative mslp

intraseasonal to semiannual variability of sea surface height in the astern equatorial indian ocean and southern bay of bengal intraseasonal to semiannual variability of sea surface height ssh in the eastern equatorial indian ocean eeio and southern bay of bengal bob is investigated using altimetric data and solutions to 1 layer first baroclinic mode and linear continuously stratified lcs multi baroclinic mode models the amplitude and dominant period of ssh variability differ regionally large amplitude variability is found along the west coast of sumatra in a zonal band across the bob centered along 5 n east of sri lanka and in the northwestern bob respectively along the sumatran west coast ssh variability peaks at 30 60 days 90 days and 180 days along 5 n and east of sri lanka the 30 60 day variability is dominant sensitivity experiments using a nonlinear version of the 1 layer model forced by realistic winds reproduce the observed patterns of intraseasonal variability in the southern bob at 30 60 days the solutions show that eddies nonlinear rossby waves propagating from the east rather than local wind forcing account for most of the variance east of sri lanka furthermore they demonstrate that the variance is significantly enhanced by the nonlinear transfer of 90 120 day energy into the intraseasonal band of 30 60 days the lcs solutions show that the first two baroclinic modes explain most of the ssh variance at 90 180 days the second baroclinic mode dominates the ssh variance at 180 days a consequence of basin resonance and strong wind forcing

the linearity of the el nino teleconnection to the amundsen sea region el nino southern oscillation enso drives interannual variability in west antarctic climate through altering atmospheric circulation in the amundsen sea region asr the el nino asr teleconnection is known to be strongest in austral winter and spring but its variation with el nino amplitude is underexplored this study uses experiments from the hadgem3 a climate model to investigate the el nino asr teleconnection for a range of imposed sst perturbations spanning weak 0 75 k to strong 3 k amplitudes in austral winter the el nino asr teleconnection behaves linearly for el nino amplitudes up to 2 25 k but is found to weaken for stronger forcing 3 k the anomalous rossby wave source in the subtropical south pacific increases monotonically with el nino amplitude however a rossby wave reflection surface originally located in the western south pacific sector extends progressively eastward with increasing el nino amplitude reducing wave propagation into the asr the wave reflection surface is associated with curvature in the upper tropospheric zonal winds which intensifies as the subtropical jet strengthens under el nino forcing in contrast the el nino asr teleconnection in austral summer which more closely resembles the southern annular mode is found to increase linearly for el nino amplitudes up to 3 k the results explicitly demonstrate that a linear approximation of the el nino teleconnection to the asr is reasonable based on the range of el nino amplitudes observed in recent history

freshening of the ross sea during the late 20th century ocean measurements in the ross sea over the past four decades one of the longest records near antarctica reveal marked decreases in shelf water salinity and the surface salinity within the ross gyre these changes have been accompanied by atmospheric warming on ross island ocean warming at depths of 300 meters north of the continental shelf a more negative southern oscillation index and thinning of southeast pacific ice shelves the freshening appears to have resulted from a combination of factors including increased precipitation reduced sea ice production and increased melting of the west antarctic ice sheet

hemispheric atmospheric variations and oceanographic impacts associated with katabatic surges across the ross ice shelf antarctica numerical simulations and surface based observations show that katabatic winds persistently converge toward and blow across the siple coast part of west antarctica onto the ross ice shelf about 14 of the time during winter april to august 1988 thermal infrared satellite images reveal the horizontal propagation of this negatively buoyant katabatic airstream for about 1000 km across the ice shelf to its northwestern edge a trajectory that nearly parallels the transantarctic mountains this takes place when the pressure field supports such airflow and is caused by synoptic scale cyclones that decay near and or over marie byrd land the northwestward propagation of the katabatic winds is accompanied by other changes in the hemispheric long wave pattern an upper level ridge develops over wilkes land resulting in an enhancement of the split jet in the pacific ocean then more frequent and or intensified synoptic scale cyclones are steered toward marie byrd land where they become nearly stationary to the northeast of the climatological location the resulting isobaric configuration accelerates the katabatic winds crossing siple coast and supports their horizontal propagation across the ross ice shelf an immediate impact of this katabatic airflow that crosses from the ice shelf to the ross sea is expansion of the persistent polynya that is present just to the east of ross island this polynya is a conspicuous feature on passive microwave images of antarctic sea ice and plays a central role in the salt budget of water masses over the ross sea continental shelf the impact of this katabatic airflow upon mesoscale cyclogenesis over the south pacific ocean is also discussed

influence of an island on hysteresis of a western boundary current flowing across a gap abstractwe investigate impact of an island on hysteresis of a western boundary current wbc flowing across a gap using a nonlinear 1 5 layer ocean model the results of hysteresis curves show the

sedimentology and isotope geochemistry of lacustrine carbonates of the oligocene campins basin north east spain the non marine campins basin developed in the oligocene during a period of early rifting of the catalan coastal ranges lacustrine deposits interbedded between two alluvial units comprise shallow and deep lacustrine facies the lower shallow lacustrine facies are made up of microbialite buildups and thin limestone beds in the studied area these facies are overlain by deep lacustrine facies which consist of alternations of several metre thick carbonate and mudstone dominated intervals in addition to calcite which is characteristic of the shallow lacustrine facies aragonite and abundant dolomite are present in the deep lacustrine facies this mineralogical change in the sequence reflects an overall increase in the mg ca ratio of the lake waters the deep lacustrine sequences are interpreted as having formed in a hydrologically closed basin that was subject to changes in the mg ca ratio of the water probably related to variations in the evaporation precipitation rate the sedimentological mineralogical and isotopic characteristics of the campins basin dolomites suggest that in general they are primary in origin the stable isotope data show an approximate covariance between 13c and 18o in the lower shallow lacustrine carbonates calcite which suggests that they formed during the onset of closure of the lake the 13c and 18o values of the deep lacustrine carbonates display three different clusters that are roughly related to the carbonate mineralogy normalisation with respect to calcite of the isotopic compositions of dolomite and aragonite from the deep lacustrine carbonates allows the integration of all these isotope values into one covariant trend the sequential appearance of different carbonate minerals and the isotopic covariant trend may indicate an overall evaporative concentration of the lake waters the change in slope of the covariant trend for the isotope values between the shallow and the deep lacustrine carbonates might reflect the change in the waterbody morphology recorded in the basin fill sequence

δ18o in mollusk shells from pliocene lake hadar and modern ethiopian lakes implications for history of the ethiopian monsoon abstract two of the five lacustrine intervals in the largely fluvial hadar formation afar ethiopia occur in the sidi hakoma member deposited 3 4 3 2 ma in a perspective of the 18o of 11 modern ethiopian lakes and their shells the 18o of the hadar fossil shells provide a snapshot of the nature of ancient lake hadar and ethiopia s climate in the pliocene ethiopia s modern lakes both in the rift and on the western plateau are fed by drainage of plateau rain with its well established barely negative 18osmow of 1 3 except for the man made lake koka reservoir all other ethiopian lakes are isotopically quite positive ranging from 5 4 to 16 0 indicating how significant evaporation is in their water budget shells from lakes with extant mollusk populations are mostly in isotopic equilibrium with the 18o and temperature of their lake water the upper transgressive interval in the sidi hakoma member is the largest one in the formation beginning at its base with the gastropod beds beach deposits mollusks from shell beds other than the gastropod beds show more positive and more variable 18o between shells with internal variations within shells as much as 7 at these times the site must have been underlain by a shallow partially isolated embayment of lake hadar which underwent rapid expansions and then contractions by evaporation within the few year lifetimes of the individual mollusks the results from the gastropod beds are of most significance for interpreting the overall paleoclimate at hadar their uniformly negative 18opdb shell values that average 6 7 represent a much less evaporated stage of lake hadar when its 18osmow was 8 lower than the spectrum of modern lakes in ethiopia and indeed even 3 or more lower than average modern plateau rain to explain such negative values we hypothesize that the atlantic derived air mass component to the ethiopian monsoon was persistently strengthened during pliocene summers which intensified the amount and the negative isotopic character of rainfall onto both the afar and the ethiopian plateaus that drained to lake hadar a similar phenomenon characterized the brief periodic pluvial episodes of the quaternary including the latest in the early holocene known as the african humid period in contrast to the hot semi desert steppe conditions of today s western afar the diverse abundant terrestrial fossil fauna at hadar including the early hominid australopithecus afarensis is explained by the wetter and probably cooler summers that persisted throughout the late pliocene

a prolonged high salinity event in the northern arabian sea during 2014 17 abstracta prolonged high salinity event in the northern arabian sea to the east of the gulf of oman during 2014 17 was identified based on argo datasets the prolonged event was manifested as enh

generation of the north equatorial undercurrent jets by triad baroclinic rossby wave interactions abstractformation processes responsible for the north equatorial undercurrent neuc jets that appear across the tropical north pacific ocean near 9 13 and 18 n are explored both theoretically and using numerical models with different complexities analyses of an eddy resolving global ocean general circulation model output reveal that the neuc jets have a mode 1 baroclinic vertical structure and are spatially persistent on the interannual and longer time scales this ogcm simulated vertical structure prompts the authors to adopt the simpler nonlinear layer reduced gravity model as well as the baroclinic rossby wave triad interaction theory to unravel the essential processes underlying the neuc jets the seed for the neuc jets originates in annual baroclinic rossby waves driven by the large scale surface wind stress forcing emanating from the ocean basin s eastern boundary these wind forced primary waves are subject to nonlinear triad interactions and break down offshore where the e folding tim

evolution of the tropospheric split jet over the south pacific ocean during the 1986 89 enso cycle abstract a case study investigation into the meridional and horizontal circulation over the south pacific ocean is presented for the 1986 89 el nino southern oscillation enso cycle using the european centre for medium range weather forecasts ecmwf analyses annual average fields are created for the years before and after the 1987 minimum warm phase and 1989 maximum cold phase in the southern oscillation index the analyses reveal a shift in the split jet stream over the south pacific sector 180 120 w from a strong subtropical jet stj and weak polar front jet pfj during the warm phase to a weak stj and strong pfj during the cold phase analysis of the momentum budget reveals how the split jet in the upper troposphere over south pacific ocean evolved during the 1986 89 enso cycle during the warm phase the strong stj is associated with advection of the mean flow momentum flux from the australian sector which is approximately balanced by a large negative ageostrophic term the pfj is primaril

isotopic evidence for plio pleistocene environmental change at gona ethiopia abstract a 4 5 ma record of fluvial and lacustrine deposits is well exposed at gona in the afar depression of ethiopia we use isotopic values of pedogenic carbonate and fossil teeth to reconstruct plio pleistocene environmental change at gona an increase in 13c values of pedogenic carbonates since 4 5 ma points to a shift from woodlands to grassy woodlands in the early pliocene 10 4 to 3 9 vpdb to more open but still mixed environments in the late pleistocene 3 0 to 1 4 vpdb this pattern is also seen in isotopic records elsewhere in east africa however at 1 5 ma the higher proportion of c4 grasses at gona is largely a result of a local facies shift to more water limited environments the wide range of 13c values of pedogenic carbonate within single stratigraphic levels indicates a mosaic of vegetation for all time intervals at gona that depends on depositional environment elements of this mosaic are reflected in 13c values of both modern plants and soil organic matter and plio pleistocene soil carbonate indicating higher amounts of c4 grasses with greater distance from a river channel in both the modern and ancient awash river systems 18o values of pedogenic carbonates increase up section from 11 9 in the early pliocene to 6 4 vpdb in the late pleistocene the wide range of 18o values in paleovertisol carbonates from all stratigraphic levels probably reflects short term climate changes and periods of strong evaporation throughout the record based on the comparison between 18o values of plio pleistocene pedogenic carbonates and modern waters we estimate that there has been a 6 5 increase in mean annual 18o values of meteoric water since 4 5 ma 18o values of pedogenic carbonate from other east african records indicate a similar shift increasing aridity and fluctuations in the timing and source of rainfall are likely responsible for the changes in 18o values of east african pedogenic carbonates through the plio pleistocene

improved satellite altimetry in coastal systems case study of the corsica channel mediterranean sea 1 the fidelity of corrections and processing are critical for a realistic use of official altimetric products close to the coast a new processing strategy which starts from the topex poseidon gdrs with the addition of improved corrective terms is proposed and evaluated in the area of the corsica channel sea level anomalies agree with the coincident sea truth bottom pressure and tide gauge within 2 3 cm rms for seasonal and longer time scales analysis for almost ten years of coincident mooring and altimetric velocities shows that a substantial reduction of uncertainty to 4 cm s 1 may be possible after reasonable filtering of the noise introduced by more variable coastal sea surface states the conclusion is that the altimetry success is still limited to seasonal time scales and provided that the oceanographic signal ensures an adequate signature to be isolated from background noise

shear wave splitting observations in the chinese tianshan orogenic belt 1 a linear array of 26 3 component broadband digital stations across the chinese tianshan orogenic belt ctob was deployed for 13 months to measure the shear wave splitting fast direction of teleseismic shear waves beneath the southern ctob is nww see and gradually turns into nee sww in the north delay times are 0 65 1 48s with average value of 0 97 0 15s and the maximum delay time is observed in the middle mountain and decrease in the south and the north fast directions are generally parallel to the strike of the orogenic belt indicating that more than one hundred kilometers of upper mantle is involved in collisional deformation compared to other stations change in fast direction for stations in the south and north ends of the array is probably resulted from subduction of the tarim block and the junggar block into the tianshan range respectively

a coastal transect of mcmurdo dry valleys antarctica snow and firn marine and terrestrial influences on glaciochemistry samples of snow and firn from accumulation zones on clark commonwealth blue and victoria upper glaciers in the mcmurdo dry valleys 77 788 s 161 1648 e antarctica are evaluated chemically and isotopically to determine the relative importance of local site specific factors vs regional scale influences in defining glaciochemistry spatial variation in snow and firn chemistry confirms documented trends within individual valleys regarding major ion deposition relative to elevation and to distance from the coast sodium and methylsulfonate ms for example follow a decreasing gradient with distance from the coast along the axis of victoria valley 350 119 gl 1 for na 33 14 gl 1 for ms a similar pattern exists between commonwealth and newall glaciers in the asgaard range when comparing major ion concentrations e g na m s c a 2 or trace metals e g al fe among different valleys however site specific exposures to marine and local terrestrial chemical sources play a dominant role because chemical signals at all sites respond to particulates with varying mixtures of marine and terrestrial sources each of these influences on site glaciochemistry must be considered when drawing temporal climate inferences on regional scales

transport and deposition of heavy metals in the ross sea region antarctica emissions and long range transport of toxic metals and metalloids pose a global threat to ecosystems and human health global industrialization occurring from the late nineteenth century releases large quantities of pollutants into the earth s atmosphere despite international efforts to mitigate emissions accumulation of metals is still observed in the most remote regions of the planet new baseline studies are needed to determine i natural background concentration of pollutants ii contributions of anthropogenic emissions and iii potential remobilization of previously deposited metals constructing such records requires distinguishing source strength from transport efficiency to the recording site and accounting for local depositional effects here we investigate the sensitivity and representation of southern hemisphere atmospheric concentrations of heavy metals fe al mn pb tl and as in the roosevelt island climate evolution rice ice core a new coastal antarctic ice core site concentration variability with precipitation is explored in daily surface snow samples collected over 70 days while seasonal deposition is investigated through snow pit sampling we find that snow sample concentrations increase with particular snow precipitation types rime and fog and enhanced meridional atmospheric transport to the site snow pit heavy metals peak in summer and also show variable intraannual peaks seasonal airmass modeling based on era interim reanalysis data indicates a synoptic shift during the spring and summer months we conclude that modern heavy metal concentrations are influenced by transport efficiency and scavenging behavior and thus time series records from rice have the potential to provide representative data of regional changes in heavy metals

assessing the link between coastal morphology wave energy and sea ice throughout the holocene from antarctic raised beaches post glacial rebound has preserved beaches across many ice free parts of the antarctic coastline these beaches typically contain gravel to boulder sized deposits and are built by high magnitude waves five new ages from the western antarctic peninsula were added to a compilation of 282 published ages from antarctic beaches a reduced compilation based solely on those ages that date beach formation is used to assess variations in beach formation throughout the holocene around antarctica we suggest the clustering of beach ages centered at 0 8 and 2 4 ka in the antarctic peninsula 1 5 3 6 and 6 0 ka in the ross sea and a broad peak from 2 7 to 6 3 ka in east antarctica indicates periods of heightened wave exposure leading to increased beach formation measurements of clast roundness from raised beaches show more rounded material is coincident with periods of heightened beach formation providing an independent means of assessing wave climate a comparison of periods of increased beach formation with available sea ice proxies suggests beach formation is synchronous with reduced sea ice conditions and thus higher wave climate as the presence or absence of sea ice determines open water conditions the factors that control sea ice directly influence antarctic coastal evolution

solute and isotope geochemistry of subsurface ice melt seeps in taylor valley antarctica the mcmurdo dry valleys of antarctica are a polar desert region with watersheds dominated by glacial melt recent ground exploration reveals unusual surface fl ow seep features not directly supplied by glacial melt much of this seep water is potentially derived from permafrost snow patches refrozen precipitation accumulated in the subsurface buried glacier ice or even groundwater from the deep subsurface flow features that lack obvious glacier melt sources were identifi ed in archived aerial photographs of taylor valley this valley was surveyed for extant and extinct seeps and the locations of geomorphic features in fi active seeps were documented water samples from seeps were analyzed for major ions and stable isotopes of hydrogen and oxygen solute chemistry and isotopic signatures of seeps are distinct from those of nearby streams and glaciers with the seeps having elevated solute concentrations all but one seep had water isotopically heavier than water from nearby glaciers and streams suggesting that seep waters have been substantially modifi ed if they had been derived originally from the same meteoric sources that supply local glaciers and streams the seeps are important because they compose a previously overlooked component of the desert hydrological cycle seep features in the dry valleys are potential terrestrial analogs for the geologically young gullies observed on mars which are thought to be evidence of groundwater seepage and surface runoff

cold conditions in antarctica during the little ice age implications for abrupt climate change mechanisms abstract the little ice age lia is one of the most prominent climate shifts in the past 5000 yrs it has been suggested that the lia might be the most recent of the dansgaard oeschger events which are better known as abrupt large scale climate oscillations during the last glacial period if the case then according to broecker 2000a 2000b antarctica should have warmed during the lia when the northern hemisphere was cold here we present new data from the ross sea antarctica that indicates surface temperatures were 2 c colder during the lia with colder sea surface temperatures in the southern ocean and or increased sea ice extent stronger katabatic winds and decreased snow accumulation whilst we find there was large spatial and temporal variability overall antarctica was cooler and stormier during the lia although temperatures have warmed since the termination of the lia atmospheric circulation strength has remained at the same elevated level we conclude that the lia was either caused by alternative forcings or that the sea saw mechanism operates differently during warm periods

snow chemistry across antarctica un updated compilation of published and new data of major ion ca cl k mg na no3 so4 and methylsulfonate ms concentrations in snow from 520 antarctic sites is provided by the national itase international trans antarctic scientific expedition programmes of australia brazil china germany italy japan korea new zealand norway united kingdom the united states and the national antarctic programme of finland the comparison shows that snow chemistry concentrations vary by up to four orders of magnitude across antarctica and exhibit distinct geographical patterns the antarctic wide comparison of glaciochemical records provides a unique opportunity to improve our understanding of the fundamental factors that ultimately control the chemistry of snow or ice samples this paper aims to initiate data compilation and administration in order to provide a framework for facilitation of antarctic wide snow chemistry discussions across all itase nations and other contributing groups the data are made available through the itase web page http www2 umaine edu itase content syngroups snowchem html and will be updated with new data as they are provided in addition recommendations for future research efforts are summarized

isotopic hydrology and paleohydrology of the madagi kenya natron tanzania basin during the late quaternary abstract three generations of stromatolites mark the recent extension of paleolakes in the magadi natron basin on the border between tanzania and kenya the last two generations are observed some 50 m above the modern lakes level they are respectively attributed to the beginning of the last interglacial and to the pleistocene holocene transition analysis of the morphology and texture of the stromatolites reveals an ecological zonation between 0 and 10 14 m below the shoreline their relatively high 18o and 13c values reflect a long residence time for the paleolake water which would have been favorable to the establishment of an isotopic equilibrium between atmospheric co2 and the dissolved inorganic carbon despite deep carbon inputs in relation to carbonititic volcanism a study of the 18o 2h and 13c contents in the hydrothermal springs perennial rivers and lacustrine brines indicates that during the last period of significant renewal of the deep saline groundwater precipitation was depleted in heavy isotopes when compared to modern precipitation this difference corresponds to a drop of about 600 1000 m in altitudinal hydroclimatic zones finally a comparison between the modern and paleohydrological data leads us to believe that the stabilization of the paleolake shorelines at the same altitude can be attributed to control by the water table level in the aquifer of the basaltic plateaus east of the basin

the international trans antarctic scientific expedition itase an overview from its original formulation in 1990 the international trans antarctic scientific expedition itase has had as its primary aim the collection and interpretation of a continent wide array of environmental parameters assembled through the coordinated efforts of scientists from several nations itase offers the ground based opportunities of traditional style traverse travel coupled with the modern technology of gps crevasse detecting radar satellite communications and multidisciplinary research by operating predominantly in the mode of an oversnow traverse itase offers scientists the opportunity to experience the dynamic range of the antarctic environment itase also offers an important interactive venue for research similar to that afforded by oceanographic research vessels and large polar field camps without the cost of the former or the lack of mobility of the latter more importantly the combination of disciplines represented by itase provides a unique multidimensional space and time view of the ice sheet and its history itase has now collected 20 000 km of snow radar recovered more than 240 firn ice cores total length 7000 m remotely penetrated to 4000 m into the ice sheet and sampled the atmosphere to heights of 20 km

oceanographic mechanisms and penguin population increases during the little ice age in the southern ross sea antarctica abstract the adelie penguin is a well known indicator for climate and environmental changes exploring how large scale climate variability affects penguin ecology in the past is essential for understanding the responses of southern ocean ecosystems to future global change using ornithogenic sediments at cape bird ross island antarctica we inferred relative population changes of adelie penguins in the southern ross sea over the past 500 yr and observed an increase in penguin populations during the little ice age lia 1500 1850 ad we used cadmium content in ancient penguin guano as a proxy of ocean upwelling and identified a close linkage between penguin dynamics and atmospheric circulation and oceanic conditions during the cold period of 1600 1825 ad a deepened amundsen sea low asl led to stronger winds intensified ocean upwelling enlarged ross sea and mcmurdo sound polynyas and thus higher food abundance and penguin populations we propose a mechanism linking antarctic marine ecology and atmospheric oceanic dynamics which can help explain and predict responses of antarctic high latitudes ecosystems to climate change

a relationship between dunes fire and climate recorded in the holocene deposits of quebec during the past 5 000 yr bp the tropics have experienced an increase in aridity and aeolian activity in both maritime and continental areas1 4 in contrast the onset and subsequent development of post hypsithermal climates in northern latitudes were primarily conducive to global cooling it is suggested here that aeolian activity in cold environments represents a direct response to this long term cooling trend that began after 6 000 5 000 yr bp at the end of the climatic optimum5 9 this study establishes the holocene chronology of sand dunes near the outer forest limit in northern quebec fig 1 i show here that fires initiate the aeolian activity and that the fire dune relationship is typical of cooling period on this basis a palaeoclimatic reconstruction since the climatic optimum is proposed

shear wave velocity structure of upper mantle under taiwan from the array analysis of surface waves 1 a one dimensional shear wave velocity structure in the top 200 km of upper mantle under the central range cr of taiwan was proposed from inversion of fundamental mode rayleigh wave phase velocity which is determined from array analysis crust under cr has relatively low velocities with the thickness of 40 50 km when comparing with other regions in taiwan this might imply the existence of a mountain root upper mantle low velocity zone with s wave velocities of about 4 25 4 4 km sec is also derived the thin lid 30 km with a relatively high velocity of 4 90 km sec reveals the probable connection with the lithosphere of the eurasian plate the overall thickness of lithosphere under cr is about 80 km which is approximate to those under the adjacent sea areas of china in other words the upper mantle beneath cr is a part of the eurasian plate

reply to comment by doran et al on el nino suppresses antarctic warming 1 doran et al commented on our recent paper el nino suppresses antarctic warming bertler et al 2004 suggesting that our interpretation of their article antarctic climate cooling and terrestrial ecosystem response doran et al 2002 was incorrect instead they assert that their paper does not state that 1 antarctica as whole is cooling since 1966 nor that 2 the mcmurdo dry valleys data were used to verify this finding or represent this longer term cooling 2 we are especially pleased that doran et al agree with us that the dry valleys do not show a longer term cooling however we cannot find any fault in our interpretation of their original paper owing to

the medieval climate anomaly in antarctica abstract the medieval climate anomaly mca is a well recognized climate perturbation in many parts of the world with a core period of 1000 1200 ce here we are mapping the mca across the antarctic region based on the analysis of published palaeotemperature proxy data from 60 sites in addition to the conventionally used ice core data we are integrating temperature proxy records from marine and terrestrial sediment cores as well as radiocarbon ages of glacier moraines and elephant seal colonies a generally warm mca compared to the subsequent little ice age lia was found for the subantarctic islands south of the antarctic convergence the antarctic peninsula victoria land and central west antarctica a somewhat less clear mca warm signal was detected for the majority of east antarctica mca cooling occurred in the ross ice shelf region and probably in the weddell sea and on filchner ronne ice shelf spatial distribution of mca cooling and warming follows modern dipole patterns as reflected by areas of opposing temperature trends main drivers of the multi centennial scale climate variability appear to be the southern annular mode sam and el nino southern oscillation enso which are linked to solar activity changes by nonlinear dynamics

austral summer foehn winds over the mcmurdo dry valleys of antarctica from polar wrf foehn winds are a prominent feature of the mcmurdo dry valleys mdvs climate and are responsible for periods of strong winds and warming the foehn mechanism determined from a case study presented in earlier work is shown here to be robust for a set of the mdvs summer foehn events over the 1994 2009 period using output from the polar weather research and forecasting model polar wrf gap flow south of the mdvs is evidenced by the positive relationship between the pressure gradient and near surface wind speed along the gap subsequently mountain waves are generated and result in adiabatic warming and the downward transport of warm air into the mdvs and differences in mountain wave characteristics depend on the ambient wind direction and the degree of flow nonlinearity pressure driven channelling then brings warm foehn air downvalley although a large range of synoptic scale circulation patterns can drive foehn events the warmest foehn events are typically associated with blocking highs over the australian sector of the southern ocean leading to warm air advection over continental antarctica the episodic nature of foehn events and the tenuous connections between such events and interannual modes of climate variability suggests that intraseasonal variability may be more important for determining their frequency and magnitude the extraordinarily warm austral summer of 2001 2002 across antarctica shows that advection of warm maritime air into the continental interior and strong flow aloft result in warm foehn conditions and significant melt for the mdvs

critical frequencies at ocean boundaries past theoretical work has shown that for low frequency flow at a given ocean boundary location a critical frequency c exists such that for c unforced motion is trapped to the coast while for c energy leaves the coast alternatively for motion of a given frequency on the boundary there exists a critical latitude such that the motion is trapped to the coast poleward of that latitude but equatorward it is not this theory is discussed physically for both meridional and nonmeridional boundaries the simple formula for critical frequency along a nonmeridional boundary is used to document critical periods for the eastern and western atlantic pacific and indian ocean boundaries the theory occasionally breaks down when boundary curvature is too large

central west antarctica among the most rapidly warming regions on earth the west antarctic ice sheet is contributing to sea level rise but temperature trends in the region have remained uncertain a complete temperature record for byrd station in central west antarctica spanning from 1958 to 2010 establishes west antarctica as one of the fastest warming regions globally

intraseasonal response of the northern indian ocean coastal waveguide to the madden julian oscillation a new observational record of upper ocean currents at 15 n on the western coast of india is dominated by intraseasonal 55 110 day variations of alongshore currents whereas sea level at the same location has a clear seasonal signal these observations can be interpreted within the framework of linear wave theory at 15 n the minimum period for planetary waves is 90 day meaning that intraseasonal energy is largely trapped at the coast in the form of poleward propagating kelvin waves while lower frequency signals associated with the annual cycle can radiate offshore as planetary waves this dynamical difference results in a steeper offshore slope of sea level at intraseasonal timescale and thus stronger geostrophic alongshore currents a consequence is that the alongshore currents are in phase with intraseasonally filtered sea level near the coast and a gridded satellite product is shown to reproduce the current variations reasonably well the intraseasonal current variations along the west coast of india are part of basin scale sea level fluctuations of the northern indian ocean equatorial and coastal waveguides the wind forcing associated with this basin scale circulation closely matches surface wind signals associated with the madden julian oscillation copyright 2009 by the american geophysical union

high resolution palaeoclimatology of the last millennium a review of current status and future prospects this review of late holocene palaeoclimatology represents the results from a pages clivar intersection panel meeting that took place in june 2006 the review is in three parts the principal high resolution proxy disciplines trees corals ice cores and documentary evidence emphasizing current issues in their use for climate reconstruction the various approaches that have been adopted to combine multiple climate proxy records to provide estimates of past annual to decadal timescale northern hemisphere surface temperatures and other climate variables such as large scale circulation indices and the forcing histories used in climate model simulations of the past millennium we discuss the need to develop a framework through which current and new approaches to interpreting these proxy data may be rigorously assessed using pseudo proxies derived from climate model runs where the answer is known the article concludes with a list of recommendations first more raw proxy data are required from the diverse disciplines and from more locations as well as replication for all proxy sources of the basic raw measurements to improve absolute dating and to better distinguish the proxy climate signal from noise second more effort is required to improve the understanding of what individual proxies respond to supported by more site measurements and process studies these activities should also be mindful of the correlation structure of instrumental data indicating which adjacent proxy records ought to be in agreement and which not third large scale climate reconstructions should be attempted using a wide variety of techniques emphasizing those for which quantified errors can be estimated at specified timescales fourth a greater use of climate model simulations is needed to guide the choice of reconstruction techniques the pseudo proxy concept and possibly help determine where given limited resources future sampling should be concentrated

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

an isotopic study of a fluvial lacustrine sequence the plio pleistocene koobi fora sequence east africa stable isotopic analyses of plio pleistocene and modern sediments in the fluvial lacustrine system occupying the turkana basin east africa provide constraints on the paleoenvironmental and diagenetic histories of the pliocene through the recent sediments in the basin the 13c values for carbonates in lacustrine sediments range from 15 to 22 relative to pdb depending on the varying proportions of co2 from the atmospheric reservoir and from various metabolic sources the 18o values of carbonates in lacustrine sediments indicate that the isotopic composition of paleolake water varied by over 10 from the pliocene to the present the 13c values for pedogenic carbonates record paleoccologic variations and suggest that c4 plants did not become well established in the preserved depositional parts of the basin until about 1 8 myr ago the 18o values pedogenic carbonates suggest a range of over 10 for the isotopic composition of soil water during this interval they also suggest a period of major climatic instability from about 3 4 to 3 1 myr and at about 1 8 myr together the 13c and 18o values of pedogenic carbonates indicate that the present conditions are as arid and hot as any that had prevailed during deposition of these plio pleistocene sediments

geometry and dynamics of an east antarctic ice sheet outlet glacier under past and present climates 1 the behavior of east antarctic ice sheet eais outlet glaciers both at present and during the recent geological past is of considerable interest both from the point of view of understanding the mechanics of contemporary glacier dynamics and also with regard to epoch scale ice sheet stability during plio pleistocene climate transitions here we use a glacier flowline model that incorporates the effects of longitudinal stresses to numerically simulate ferrar glacier first under present day environmental conditions and subsequently under both colder and warmer climate regimes representing the last glacial maximum lgm and mid pliocene peak warmth respectively using airborne radar profiles insar derived surface velocities ice core and geological data for empirical constraint we present a diagnostic simulation that uses an iterative method to closely reproduce observed dynamics our model suggests that the glacier is largely cold based under present conditions flows predominantly by way of internal deformation and cascades over bedrock ridges due to the combined action of changes in cross sectional valley geometry local steepening of the glacier surface and the non local effects of longitudinal coupling time dependent evolutionary simulation of a lower profile glacier under a colder drier lgm climate predicts flow velocities lower than present with minimal bedrock erosion or basal till flux conversely the warmer than present mid pliocene climate produces a more dynamic glacier that is warm based and sliding along much of its bed we propose that eais outlet glaciers such as the ferrar respond dynamically along their length in response to changing environmental forcings with most significant changes taking place in their lower reaches adjustment to perturbations in upper catchments is more muted

paleoenvironments of the earliest stone toolmakers gona ethiopia fluvio lacustrine sediments of the hadar and busidima formations along the northern awash river ethiopia archive almost three million years 3 4 to 0 6 ma of human evolution including the earliest documented record of stone toolmaking at 2 5 2 6 ma this paper brings together sedimentologic and isotopic evidence for the paleoenvironmental context of early hominids from both formations but with particular emphasis on the setting for the early toolmakers the pre 2 92 ma record hadar formation is characterized by low gradient fl uvial paludal and lacustrine deposition in an undissected topography most analogous to reaches of the modern middle awash river near gewane the gona area experienced repeated deep dissection and aggradation by the awash river starting between 2 92 and ca 2 7 ma and continuing through the top of the record at 0 6 ma busidima formation each aggradational succession is 10 20 m in thickness and fi nes upward from wellrounded conglomerates at the base to capping paleosols at the top during this period the ancestral awash represented by these fi ning upward sequences was dominantly meandering and fl owed northeast as it does today smaller channels tributary to the axial awash system are also extensively exposed in the busidima formation compared to the axial system conglomerates the tributary channels transported fi ner less mature volcanic clasts mixed with abundant carbonate nodules reworked from adjacent badlands stone artifacts oldowan 2 6 2 0 ma at the oldest archaeological sites are only associated with the axial awash system in the bedded silts or capping paleosols of the fi ning upward sequences the implements were made from rounded cobbles from the channels but manufacture and use of the tools was always away from the channel bars on the nearby sandy banks and silt dominated fl oodplains archaeological sites higher in the record acheulian 1 7 ma occur in similar axial river contexts as well as along tributary channels further removed from artifact raw material sources mature paleosols in the hadar and busidima formations are mostly pale to darkbrown vertisols typifi ed by abundant clay slickensides pseudo anticlinal and vertical fracturing and carbonate nodules such calcic vertisols are common in the region today demonstrating that the paleoclimate over the past 3 4 m y has been semi arid and strongly seasonal carbon isotopic results from pedogenic carbonates in the vertisols allow reconstruction of the proportion of c 3 plants trees and shrubs to c 4 plants grasses through time the 13

state of the antarctic and southern ocean climate system this paper reviews developments in our understanding of the state of the antarctic and southern ocean climate and its relation to the global climate system over the last few millennia climate over this and earlier periods has not been stable as evidenced by the occurrence of abrupt changes in atmospheric circulation and temperature recorded in antarctic ice core proxies for past climate two of the most prominent abrupt climate change events are characterized by intensification of the circumpolar westerlies also known as the southern annular mode between 6000 and 5000 years ago and since 1200 1000 years ago following the last of these is a period of major trans antarctic reorganization of atmospheric circulation and temperature between ad1700 and 1850 the two earlier antarctic abrupt climate change events appear linked to but predate by several centuries even more abrupt climate change in the north atlantic and the end of the more recent event is coincident with reorganization of atmospheric circulation in the north pacific improved understanding of such events and of the associations between abrupt climate change events recorded in both hemispheres is critical to predicting the impact and timing of future abrupt climate change events potentially forced by anthropogenic changes in greenhouse gases and aerosols special attention is given to the climate of the past 200 years which was recorded by a network of recently available shallow firn cores and to that of the past 50 years which was monitored by the continuous instrumental record significant regional climate changes have taken place in the antarctic during the past 50 years atmospheric temperatures have increased markedly over the antarctic peninsula linked to nearby ocean warming and intensification of the circumpolar westerlies glaciers are retreating on the peninsula in patagonia on the sub antarctic islands and in west antarctica adjacent to the peninsula the penetration of marine air masses has become more pronounced over parts of west antarctica above the surface the antarctic troposphere has warmed during winter while the stratosphere has cooled year round the upper kilometer of the circumpolar southern ocean has warmed antarctic bottom water across a wide sector off east antarctica has freshened and the densest bottom water in the weddell sea has warmed in contrast to these regional climate changes over most of antarctica near surface temperature and snowfall have not increased significantly during at least the past 50 years and proxy data suggest that the atmospheric circulation over the interior has remained in a similar state for at least the past 200 years furthermore the total sea ice cover around antarctica has exhibited no significant overall change since reliable satellite monitoring began in the late 1970s despite large but compensating regional changes the inhomogeneity of antarctic climate in space and time implies that recent antarctic climate changes are due on the one hand to a combination of strong multi decadal variability and anthropogenic effects and as demonstrated by the paleoclimate record on the other hand to multi decadal to millennial scale and longer natural variability forced through changes in orbital insolation greenhouse gases solar variability ice dynamics and aerosols model projections suggest that over the 21st century the antarctic interior will warm by 3 4 1oc and sea ice extent will decrease by 30 ice sheet models are not yet adequate enough to answer pressing questions about the effect of projected warming on mass balance and sea level considering the potentially major impacts of a warming climate on antarctica vigorous efforts are needed to better understand all aspects of the highly coupled antarctic climate system as well as its influence on the earth s climate and oceans

precursory accelerating seismic moment release amr in a synthetic seismicity catalog a preliminary study 1 a power law like acceleration of seismic moment release amr has been proposed as a precursor to large earthquakes because of problems with real world data we have used a synthetic seismicity model of 256 interacting faults embedded in a 3 d elastic half space to search for periods of amr preceding the largest events mw 7 1 in only 5 of 18 cases does the amr model fit the data significantly better than a linear moment release and then only weakly so this proportion or higher occurs in 8 of 1000 randomized catalogs we conclude that either amr is unlikely to be a common precursor or that factors contributing to the amr pattern in the real world are missing from the synthetic model

improving the quality of satellite altimetry data over continental shelves 1 satellite altimetry has proven to be a useful tool to study oceanic processes in the deep ocean over continental shelves however the aliasing of unresolved high frequency signals of tidal and wind induced origin is the source of long wavelength errors that corrupt altimetry measurements and limit their use in shallow waters in 2005 ssalto duacs performed a complete reanalysis of altimeter data to accommodate the latest tidal model got2000 and a correction for the aliased high frequency signals using a hydrodynamic model mog2d g this paper examines the quality and the performance of the newly released altimetry data over the northwest european shelf this region is known for complex tides and for frequent storm surges the newly corrected maps of sea level anomalies were compared with a previous altimetry product residual tidal aliasing was analyzed and the impact of mog2d g and got2000 models was assessed altimeter records were compared with tide gauge measurements this research showed a significant reduction in the contamination of data by high frequency aliasing achieved through the use of the aforementioned models however aliased shallow water tidal constituents pose a serious problem and it is obvious that future tidal corrections should feature local tides nonaliased physical sea level variability was also studied focusing on interannual seasonal and intra annual periods from 20 days to 1 year modes the magnitudes and the contributions of each mode to the total variance were estimated it was demonstrated that the newly corrected data can successfully be used to study the variability of sea level over continental shelves

a dynamical ocean feedback mechanism for the madden julian oscillation composite analysis is applied to study the dynamical ocean response to madden julian mj events measured by anomalies in sea surface height from the merged topex poseidon european remote sensing satellite altimetry dataset in each of the tropical ocean basins significant equatorial waves are forced which are shown to modulate the sea surface temperature sst by 0 2 0 3 degc in the absence of strong surface heat fluxes in the indian ocean there is a clear dynamical response which may play a significant role in generating later mj events surface westerly winds associated with the active phase of the madden julian oscillation mjo force an eastward propagating oceanic downwelling equatorial kelvin wave which on reaching the eastern boundary at sumatra forces reflected downwelling equatorial rossby waves and coastal kelvin waves the coastal kelvin waves propagate southwards towards northern australia and northwards into the bay of bengal and will be important for local physical chemical and biological processes the equatorial rossby waves propagate westward across the indian ocean arriving in the western indian ocean approximately 80 100 days after the initial kelvin wave was generated the arrival of these waves generates positive sst anomalies which leads to convection and may trigger the next but one mj event or amplify the low frequency tail of the mjo this constitutes a coupled feedback mechanism from the ocean dynamics onto the mjo somewhat similar to the delayed oscillator mechanism for the el nino southern oscillation

14 c and th u dating of pleistocene and holocene stromatolites from east african paleolakes during recent humid episodes stromatolites were built along paleolake margins some 60 m above the modern water level of lakes natron and magadi southern gregory rift valley three generations of stromatolites are observed the more recent ones frequently covering pebbles and boulders eroded from the older ones the youngest one yielded 14c ages ranging from approximately 12 000 to 10 000 yr b p their 13c values 2 6 suggest isotopic equilibrium between the paleolake total inorganic dissolved carbon and the atmospheric co2 thereby lending credence to the reliability of the 14c an initial 230th232th ratio in the detrital component was determined by thu measurements on the 14c dated stromatolites using this value a 230th234u chronology for the older stromatolites was calculated ages of 240 000 and 135 000 10 000 yr were obtained for the first and second generations respectively a humid episode apparently characterized eastern africa during each glacial interglacial transition 18o and 13c measurements on stromatolites when compared to values on modern waters and carbonates provide paleohydrological information long residence time of the paleolake waters and less seasonally contrasted regimes are inferred

atmospheric teleconnections involving the southern ocean 1 i review the characteristic patterns of low frequency interannual and subdecadal variation in atmospheric circulation over the southern hemisphere sh extratropics and their climatic associations e g temperature precipitation winds sea surface temperatures ssts and sea ice conditions for the southern ocean the considerable spatial and temporal limitations of the observational database have strongly conditioned the pace of our understanding of sh teleconnections particularly for the pacific sector where the tropical el nino southern oscillation enso exerts a dominant influence an enso signal appears in the intensity interannual variations of the amundsen sea mean low pressure asl jet streams and long waves these variations comprise the so called pacific south america psa teleconnection patterns of low frequency variability in sh circulation that are mostly extratropical in origin but which can interact with enso are dominated by the zonally symmetric high latitude mode or antarctic oscillation aao the aao involves an alternation of atmospheric mass between middle and high southern latitudes a zonally asymmetric mode of wave number 1 is represented by an oscillation in pressure height between australian and south american sectors depicted by a trans polar circulation index a significant wave number 2 oscillation in the coupled atmosphere ocean ice system or antarctic circumpolar wave acw has a similar periodicity to enso and is strongest in the pacific sw atlantic sectors atmospheric teleconnections involving the southern ocean including those to enso show evidence of recent changes and the climatic implications of these are discussed

dynamics of wind forced intraseasonal zonal current variations in the equatorial indian ocean 1 this study examines the structure and dynamics of wind forced intraseasonal zonal current variability in the equatorial indian ocean we take advantage of a variety of satellite and in situ data sets including unprecedented 4 8 year long velocity time series records from the research moored array for african asian australian monsoon analysis and prediction rama program spectral analysis reveals prominent intraseasonal zonal currents variations along the equator with periods of 30 70 days these oscillations are vertically in phase above the thermocline and propagate eastward with the local zonal winds in the thermocline intraseasonal zonal velocity variations also propagate eastward across a broad range of phase speeds expected for low baroclinic equatorial kelvin waves amplitudes decrease with depth with deeper levels leading those near surface collectively these results suggest that the near surface layer responds directly to intraseasonal zonal wind stress forcing and that subsequently energy radiates downward and eastward in the thermocline in the form of wind forced equatorial kelvin waves in addition intraseasonal zonal current variability on the equator is coherent with off equatorial sea surface height fluctuations in the eastern and central of the basin this coherence is primarily due to the fact that equatorial zonal wind variations are associated with off equatorial wind stress curls that can generate local ekman pumping and westward propagating rossby waves

twentieth century surface temperature trends in the western ross sea antarctica evidence from a high resolution ice core abstracta 125 yr ice core record of climate from the whitehall glacier ice divide provides exceptionally high resolution stable isotope data from the northwest margin of the ross sea antarctica this is the only proxy data available to extend the instrumental record of temperature in this region where little is known about climate variability over the past two centuries using ecmwf interim re analysis era interim data this study develops a precipitation weighted 18o temperature transfer function of 0 62 c 1 which is comparable to other proximal ice cores such as taylor talos and law domes reconstructed mean annual temperatures show no significant change between 1882 and 2006 however a decrease in cold season april september amjjas temperatures of 1 59 0 84 c decade 1 at 90 confidence is observed since 1979 this cooling trend is in contrast to a surface temperature record from ross island scott base where significant spring warming is observed it is also coincident with a pos

an antarctic circumpolar wave in surface pressure wind temperature and sea ice extent the southern ocean is the only oceanic domain encircling the globe it contains the strong eastward flow of the antarctic circumpolar current and is the unifying link for exchanges of water masses at all depths between the world s major ocean basins1 as these exchanges are an important control on mean global climate the southern ocean is expected to play an important role in transmitting climate anomalies around the globe interannual variability has been often observed at high southern latitudes and observations of sea ice extent suggest that such features propagate eastwards around the southern ocean2 3 here we use data from a variety of observational techniques to identify significant interannual variations in the atmospheric pressure at sea level wind stress sea surface temperature and sea ice extent over the southern ocean these anomalies propagate eastward with the circumpolar flow with a period of 4 5 years and taking 8 10 years to encircle the pole this system of coupled anomalies which we call the antarctic circumpolar wave is likely to play an important role in climate regulation and dynamics both within and beyond the southern ocean

a 1 2 myr record of isotopic changes in a late pliocene rift lake ethiopia the hadar fluvio lacustrine formation ethiopia contains an original hominid fossil australopithecus afarensis and an abundant vertebrate faunal assemblage1 2 the formation3 4 consists of a 150 300 m thick sequence of fine to coarse detrital sediments originating from the ethiopian plateau escarpment with some interbedded pyroclastic layers the three lower members of the formation were formed in a lacustrine environment which was occasionally interrupted by fluvial drainage the upper member is quite distinct and formed as an alluvial fan delta this sedimentary sequence was deposited at the end of the pliocene between 3 9 and 2 7 myr as indicated by magnetostratigraphy5 the palaeomagnetic record spans the gilbert gauss transition period k ar dating6 7 and biostratigraphy8 we consider here the oxygen and carbon isotope variations observed throughout the formation and their palaeo hydrological implications

intraseasonal variability of sea surface height in the bay of bengal intraseasonal variability isv of sea surface height ssh over the bay of bengal bob is studied using altimetry data and an eddy resolving ocean model in both the model hindcast and satellite observations large ssh isv is found along the eastern and northern coasts of the bob in the western bob and in a zonal band across the bay centered near 5 degrees n the isv displays a clear seasonality in the western bob it reaches its annual maximum in spring whereas it does so in summer and autumn southeast of sri lanka driven by equatorial intraseasonal winds equatorial kelvin waves propagate eastward reach the western coast of sumatra and reflect there to propagate around the perimeter of the bob as coastally trapped waves two distinct bands of high eddy activity are detected in the western and central bob respectively in both bands isolated eddies propagate southwestward eddy formation in the eddy train in the central bay is linked to the coastal wave as it bends around the corner of the irrawaddy delta off myanmar eddy activity contributes to the high isv in the central bay to some extent an energetics analysis indicates that high total eddy energy in the western bob is due to barotropic baroclinic instability of the mean current citation cheng x s p xie j p mccreary y qi and y du 2013 intraseasonal variability of sea surface height in the bay of bengal j geophys res oceans 118 816 830 doi 10 1002 jgrc 20075

characterizing the zonally asymmetric component of the sh circulation much research concerning the southern hemisphere sh zonally asymmetric circulation has focused on the pacific south american mode psa or the major zonal waves however these large scale decompositions may mask important local variability in this paper the month to month variability explained by the zonal waves 1 and 3 is examined and an alternative representation of the sh circulation is presented based on two quasi stationary anticyclones in the sub antarctic western hemisphere these anticyclones are related to the zonal waves but features of their variability are masked by the zonal wave decomposition in particular the anticyclones strengths are not positively covariant they are also compared with the leading principal components of the sh atmosphere we show that they capture variance independent of the southern annular mode additionally they explain a generally greater fraction of the variability than the psa and in a manner that also includes information regarding spatial variability these results have implications for analysis of the atmospheric forcing of western antarctic climate

multidecadal sea level and gyre circulation variability in the northwestern tropical pacific ocean abstractsea level rise with the trend 10 mm yr 1 has been observed in the tropical western pacific ocean over the 1993 2009 period this rate is 3 times faster than the global mean value of the sea level rise analyses of the satellite altimeter data and repeat hydrographic data along 137 e reveal that this regionally enhanced sea level rise is thermosteric in nature and vertically confined to a patch in the upper ocean above the 12 c isotherm dynamically this regional sea level trend is accompanied by southward migration and strengthening of the north equatorial current nec and north equatorial countercurrent necc using a 1 layer reduced gravity model forced by the ecmwf reanalysis wind stress data the authors find that both the observed sea level rise and the nec necc s southward migrating and strengthening trends are largely attributable to the upper ocean water mass redistribution caused by the surface wind stresses of the recently strengthened atmospheric walker circulation based on the lo

origins of eddy kinetic energy in the bay of bengal by analyzing satellite observational data and ocean general circulation model experiments this study investigates the key processes that determine the spatial distribution and seasonality of intraseasonal eddy kinetic energy eke within the bay of bengal bob it is revealed that a complicated mechanism involving both local and remote wind forcing and ocean internal instability is responsible for the generation and modulation of eke in this region high level eke mainly resides in four regions east of sri lanka region 1 the western bob region 2 northwest of sumatra region 3 and the coastal rim of the bob region 4 the high eke levels in regions 1 and 2 are predominantly produced by ocean internal instability which contributes 90 and 79 respectively prominent seasonality is also observed in these two regions with higher eke levels in boreal spring and fall due to enhanced instability of the east indian coast current and the southwest monsoon current respectively in contrast ocean internal instability contributes 49 and 52 of the total eke in regions 3 and 4 respectively whereas the atmospheric forcing of intraseasonal oscillations isos also plays an important role isos produce eke mainly through wind stress involving both the remote effect of equatorial winds and the local effect of monsoonal winds equatorial origin wave signals significantly enhance the eke levels in regions 3 and 4 in the form of reflected rossby waves and coastal kelvin waves respectively the local wind forcing effect through ekman pumping also has a significant contribution in regions 3 and 4 24 and 22 respectively

monsoonal circulation of the mcmurdo dry valleys ross sea region antarctica signal from the snow chemistry mcmurdo dry valleys mdv ross sea region antarctica precipitation exhibits extreme seasonality in ion concentration 3 5 orders of magnitude between summer and winter precipitation to identify aerosol sources and investigate causes for the observed amplitude in concentration variability four snow pits were sampled along a coast polar plateau transect across the mdv the elevation of the sites ranges from 50 to 2400m and the distance from the coast from 8 to 93 km average chemistry gradients along the transect indicate that most species have either a predominant marine or terrestrial source in the mdv empirical orthogonal function analysis on the snow chemistry time series shows that at least 57 of aerosol deposition occurs concurrently a conceptual climate model based on meteorological observations is used to explain the strong seasonality in the mdv our results suggest that radiative forcing of the ice free valleys creates a surface low pressure cell during summer which promotes air mass flow from the ross sea the associated precipitating air mass is relatively warm humid and contains a high concentration of aerosols during winter the mdv are dominated by air masses draining off the east antarctic ice sheet that are characterized by cold dry and low concentrations of aerosols the strong differences between these two air mass sources create in the mdv a polar version of the monsoonal flow with humid warm summers and dry cold winters

interannual variability of tehuantepec eddies 1 topex poseidon satellite altimeter observations and the naval research laboratory layered ocean model simulations show interannual variability in the number and intensity of tehuantepec eddies off the mexican southwest coast analysis of the results illustrates that downwelling coastally trapped waves which are generated in the equatorial pacific play a crucial role in the modulation and generation of tehuantepec eddies and a dominant role in tehuantepec eddy interannual variability this introduces a new paradigm in which the generation and modulation of tehuantepec eddies is not exclusively explained in terms of the strong and intermittent tehuantepec wind events in fact the results show anticyclonic eddy formation during periods of calm tehuantepec winds that is specifically exemplified by the formation of two anticyclonic tehuantepec eddies during a 5 month period of weak gulf of tehuantepec winds during summer of 1997 furthermore the satellite observed and nlom simulated proliferation of tehuantepec eddies during el nino years is explained by the corresponding increase in downwelling coastally trapped waves and a lack of increase in the number and strength of tehuantepec wind events during el nino years

a pleistocene lacustrine episode in southeastern libya fossiliferous lacustrine deposits of middle pleistocene age have been found in central fezzan libya 1 on each side of the east west depressions of the wadi shati south of the precambrian qarqaf anticline1 8 they represent the shoreline of a former brackish water lake fig 1 which some 130 000 yr bp covered an area about 100km long and 10 20 km wide at present the area may be classified as hyperarid since 1978 a collaborative study of the fossil assemblages has been undertaken it included macro and micropalaeontological determination th u dating stable isotope and chemical analyses in parallel with sedimentological and archaeological studies of the sites here we consider the th u dating and the isotopic palaeohydrology of the lacustrine episode

el nino suppresses antarctic warming here we present new isotope records derived from snow samples from the mcmurdo dry valleys antarctica and re analysis data of the european centre for medium range weather forecasts era 40 to explain the connection between the warming of the pacific sector of the southern ocean jacka and budd 1998 jacobs et al 2002 and the current cooling of the terrestrial ross sea region doran et al 2002a our analysis confirms previous findings that the warming is linked to the el nino southern oscillation enso kwok and comiso 2002a 2002b carleton 2003 ribera and mann 2003 turner 2004 and provides new evidence that the terrestrial cooling is caused by a simultaneous enso driven change in atmospheric circulation sourced in the amundsen sea and west antarctica

seasonality of airmass pathways to coastal antarctica ramifications for interpreting high resolution ice core records abstractunderstanding airmass pathways is critical for ice core interpretation and the ability to determine the broadscale characteristics and seasonality of synoptic scale flow using paleoclimate records offers great potential to improve the understanding of past atmospheric circulation the dominant airmass pathways to a coastal antarctic ice core site at the whitehall glacier in the ross sea are modeled using snowfall and high resolution stable isotope data between 1979 and 2006 combined with back trajectories produced from both ncep ncar and ecmwf interim re analysis era interim data back trajectories generated from both datasets produce comparable results they show that high snowfall is associated with cyclonic airflow in the ross sea with a strong meridional component along the western ross sea coast over a 28 yr time frame trajectories also reveal a clear distinction between flow paths associated with above and below average annual temperatures high and low d in the ice core record in

new cnes cls09 global mean dynamic topography computed from the combination of grace data altimetry and in situ measurements 1 an accurate knowledge of the ocean mean dynamic topography mdt is mandatory for the optimal use of altimetric data including their assimilation into operational ocean forecasting systems a new global 1 4 resolution mdt was computed for the 1993 1999 time period with improved data and methodology compared to the previous rio05 mdt field first a large scale mdt is obtained from the cls01 altimetric mean sea surface and a recent geoid model computed from 4 5 years of grace gravity recovery and climate experiment data altimetric sea level anomalies and in situ measurements are then combined to compute synthetic estimates of the mdt and the corresponding mean currents while the rio05 mdt was based on 10 years of in situ dynamic heights and drifting buoy velocities the new field benefits from an enlarged data set of in situ measurements ranging from 1993 to 2008 and includes all hydrological profiles from the argo array moreover the processing of the in situ data has been updated a new ekman model was developed to extract the geostrophic velocity component from the drifting buoy measurements the handling of hydrologic measurements has also been revisited compared to the previous rio05 solution the new global mdt resolves much stronger gradients in western boundary currents with mean velocities being doubled in some places moreover in comparison to several other recent mdt estimates we find that the new cnes cls09 mdt is in better agreement with independent in situ observations

synoptic controls on precipitation pathways and snow delivery to high accumulation ice core sites in the ross sea region antarctica 1 dominant storm tracks to two ice core sites on the western margin of the ross sea antarctica skinner saddle sks and evans piedmont glacier are investigated to establish key synoptic controls on snow accumulation this is critical in terms of understanding the seasonality source regions and transport pathways of precipitation delivered to these sites in situ snow depth and meteorological observations are used to identify major accumulation events in 2007 2008 which differ considerably between sites in terms of their magnitude and seasonal distribution while snowfall at evans piedmont glacier occurs almost exclusively during summer and spring skinner saddle receives precipitation year round with a lull during the months of april and may cluster analysis of daily back trajectories reveals that the highest accumulation days at both sites result from fast moving air masses associated with synoptic scale low pressure systems there is evidence that short duration pulses of snowfall at sks also originate from mesocyclone development over the ross ice shelf and local moisture sources changes in the frequency and seasonal distribution of these mechanisms of precipitation delivery will have a marked impact on annual accumulation over time and will therefore need careful consideration during the interpretation of stable isotope and geochemical records from these ice cores

links between the amundsen sea low and sea ice in the ross sea seasonal and interannual relationships previous studies have shown that sea ice extent in the southern ocean is influenced by the intensity and location of the amundsen sea low asl through their effect on the meridional winds however the inhomogeneous nature of the influence of the asl on sea ice as well as its influence during critical periods of the sea ice annual cycle is not clear in this study we do a spatio temporal analysis of links between the asl and the sea ice during the advance and retreat periods of the ice over the period 1979 2013 focusing on the role of the meridional and zonal winds we use the era interim monthly averaged 500 mb geopotential height and 10 m wind data along with monthly passive microwave sea ice concentrations sic to examine the seasonal and interannual relationships between the asl and sic in the ross amundsen sea ice sector to characterize the state of the asl we use indices that describe its location and its intensity we show that the asl has preferred locations and intensities during ice advance and retreat seasons the strength and direction of the influence of the asl are not spatially homogeneous and can change from advance to retreat season and there are strong significant relationships between the characteristics of the asl and sic within and across seasons and interannually

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

basin resonances in the equatorial indian ocean abstractprevious studies have investigated how second baroclinic mode n 2 kelvin and rossby waves in the equatorial indian ocean io interact to form basin resonances at the semiannual 180 day and 90 day periods this paper examines unresolved issues about these resonances including the reason the 90 day resonance is concentrated in the eastern ocean the time scale for their establishment and the impact of complex basin geometry a hierarchy of ocean models is used an idealized one dimensional 1d model a linear continuously stratified ocean model lcsm and an ocean general circulation model ogcm forced by quick scatterometer quikscat wind during 2000 08 results indicate that the eastern basin concentration of the 90 day resonance happens because the westward propagating rossby wave is slower and thus is damped more than the eastward propagating kelvin wave results also indicate that superposition with other baroclinic modes further enhances the eastern maximum and weakens sea level