thickness and extent of the subglacial till layer beneath an antarctic paleo ice stream fast flowing ice streams and outlet glaciers currently account for as much as 90 of the discharge from the antarctic and greenland ice sheets although the deformation of subglacial material has been proposed as the mechanism for this rapid motion such sediment is usually hidden under several kilometers of ice marine geophysical records have allowed reconstruction of the three dimensional thickness of the sedimentary bed beneath a large antarctic paleo ice stream for the first time fast flow is indicated by streamlined seafloor lineations that form the surface of a layer of low shear strength unsorted sediment averaging 4 6 m thick rapid motion of the paleo ice stream was a result of subglacial deformation within this layer

rossby waves mediate impacts of tropical oceans on west antarctic atmospheric circulation in austral winter recent studies link climate changearound antarctica to the sea surface temperature of tropical oceans with teleconnections from the pacific atlantic and indian oceans making different contributions to antarctic climate in this study the impacts of each ocean basin on the wintertime southern hemisphere circulation are identified by comparing simulation results using a comprehensive atmospheric model an idealized dynamical core model and a theoretical rossby wave model the results herein show that tropical atlantic ocean warming indian ocean warming and eastern pacific cooling are all able to deepen the amundsen sea low located adjacent to west antarctica while western pacific warming increases the pressure to the west of the international date line encompassing the ross sea and regions south of the tasman sea in austral winter these tropical ocean basins work together linearly to modulate the atmospheric circulation around west antarctica further analyses indicate that these teleconnections critically depend on stationary rossby wave dynamics and are thus sensitive to the background flow particularly the subtropical midlatitude jet nearthesejets wind shearis amplified which strengthens the generation of rossby waves on the other hand near the edges of the jets the meridional gradient of the absolute vorticity is also enhanced as a consequence of the rossby wave dispersion relationship the jet edge may reflect stationary rossby wave trains serving as a waveguide the simulation results not only identify the relative roles of each of the tropical ocean basins in the tropical antarctica teleconnection but also suggest that a deeper understanding of teleconnections requires a better estimation of the atmospheric jet structures

calcrete profile development in quaternary alluvial sequences southeast spain implications for using calcretes as a basis for landform chronologies a detailed study of the morphology and micro morphology of quaternary alluvial calcrete profiles from the sorbas basin shows that calcretes may be morphologically simple or complex the simple profiles reflect pedogenesis occurring after alluvial terrace formation and consist of a single pedogenic horizon near the land surface the complex profiles reflect the occurrence of multiple calcrete events during terrace sediment aggradation and further periods of pedogenesis after terrace formation these complex calcrete profiles are consequently described as composite profiles the exact morphology of the composite profiles depends upon 1 the number of calcrete forming events occurring during terrace sediment aggradation 2 the amount of sediment accretion that occurs between each period of calcrete formation and 3 the degree of pedogenesis after terrace formation simple calcrete profiles are most useful in establishing landform chronologies because they represent a single phase of pedogenesis after terrace formation composite profiles are more problematic pedogenic calcretes that form within them may inherit carbonate from calcrete horizons occurring lower down in the terrace sediments in addition erosion may lead to the exhumation of older calcretes within the terrace sediment calcrete inheritance may make pedogenic horizons appear more mature than they actually are and produce horizons containing carbonate embracing a range of ages calcrete exhumation exposes calcrete horizons whose morphology and radiometric ages are wholly unrelated to terrace surface age composite profiles are therefore only suitable for chronological studies if the pedogenic horizon capping the terrace sequence can be clearly distinguished from earlier calcrete forming events thus a detailed morphological micro morphological study is required before any chronological study is undertaken this is the only way to establish whether particular calcrete profiles are suitable for dating purposes copyright 2003 john wiley sons ltd

a telemetric system for measuring electrotelluric variations in greece and its application to earthquake prediction abstract a detailed description of the telemetric system that records variations in the earth s electrical field from sixteen field stations in greece is presented each field station measures potential differences between eight pairs of electrodes inserted into the ground in two orthogonal directions n s and e w two techniques have been applied the first one is real time where the field station takes the information digitizes it and transmitts it via telephone line to a central station in athens which decodes the information offsets it automatically and displays on chart recorders the small variations in the telluric current the resolution of the system is 0 1 mv for a total gain of 200 the second technique uses dataloggers where the information is digitized and stored in the datalogger memory the central station has a commercial personal computer which communicates with the datalogger takes the information via a standard telephone line and plots the recordings every 4 h the data are stored in compressed mode on a tape back up streamer for future reference the system works unattended

fast recession of a west antarctic glacier satellite radar interferometry observations of pine island glacier west antarctica reveal that the glacier hinge line position retreated 1 2 0 3 kilometers per year between 1992 and 1996 which in turn implies that the ice thinned by 3 5 0 9 meters per year the fast recession of pine island glacier predicted to be a possible trigger for the disintegration of the west antarctic ice sheet is attributed to enhanced basal melting of the glacier floating tongue by warm ocean waters

late twentieth century northern hemisphere sea ice record from u s national ice center ice charts 1 arctic sea ice plays a key role in the climate system by acting as the interface between a warm ocean and a cold atmosphere establishing the true pattern of recent behavior of the sea ice in this region is critical to simulating the role of sea ice in future climate recently released operational ice charts from the u s national ice center provide insight into the late twentieth century behavior of northern hemisphere sea ice providing more reliable ice concentrations during summer and freeze up than those available from the passive microwave record the major winter and summer modes of ice concentration variability observed from empirical orthogonal function analysis covering the period 1972 1994 are shown to indicate respectively the 1 year lagged response of the sea ice to the north atlantic oscillation and the winter preconditioning of summer sea ice coverage in the eastern arctic by the north atlantic oscillation feedback to the atmosphere is suggested in each case by zero lag cyclone frequency relationships to these two sea ice modes of variability

sedimentation associated with antarctic peninsula ice shelves implications for palaeoenvironmental reconstructions of glacimarine sediments abstract recent disintegration of a number of antarctic peninsula ice shelves has given us a unique opportunity to investigate sub ice shelf sediments we characterize three sediment facies associations of two antarctic peninsula ice shelves larsen a and larsen inlet subglacial facies consist mainly of basal till diamicton with high shear strengths deposited under a grounded ice sheet progressive upward decrease in shear strength reflects a gradual decrease in the confining vertical effective pressure of grounded ice during till deposition proximal ice shelf glacimarine facies diamicton gravel rich and sand rich facies gravelly mud dropstone mud and sandy muds were deposited by sub ice shelf rain out bottom current activity and sediment gravity flows following decoupling of grounded ice from the sea floor distal ice shelf glacimarine and or open marine facies comprise terrigenous and diatom bearing bioturbated muds and gravelly muds that contain limited ice rafted debris these accumulated after recession of the grounding line to the coast with coarse grained surface sediments possibly documenting most recent ice shelf break up antarctic peninsula ice shelf sediments are more heterogeneous than ice shelf facies deposited elsewhere in antarctica cold polar antarctic ice shelves can be differentiated from temperate and sub polar marine terminated glacial sedimentary systems by the dominance of coarse grained proximal ice shelf glacimarine facies and an absence of subaqueous outwash meltwater sediment facies

on the extraordinary katabatic winds of adelie land the winds observed in adelie land eastern antarctica are the strongest observed anywhere on earth close to sea level e g cape denison measured a mean annual wind speed of about 20 m s 1 some historic data from the area are available however such measurements were carried out at different places for different time periods hence in december 1992 we placed four automatic weather stations along the coast of adelie land two in the maximum wind jet port martin and cape denison and one on each side of this jet d 10 close to dumont d urville and penguin point respectively we obtained about three months of good data as on march 25 1993 a strong storm destroyed three of the four wind sensors wind velocities are discussed as a function of other meteorological parameters further the interrelationships between the stations are described some of the findings are 1 the very high wind speeds reported earlier this century are in agreement with our measurements the wind directional constancy is high 2 historic measurements reported cape denison to be the windiest station not only for antarctica but also close to sea level for planet earth again our measurements are in agreement 3 very strong wind speeds have a more down slope direction than weaker ones 4 the general atmospheric pressure gradient enhanced or inhibited the gravity flow this is especially well pronounced in summer and 5 in summer above normal pressure is correlated with above normal temperatures in fall the opposite holds true

warm ocean is eroding west antarctic ice sheet 1 satellite radar measurements show that ice shelves in pine island bay have thinned by up to 5 5 m yr 1 over the past decade the pattern of shelf thinning mirrors that of their grounded tributaries the pine island thwaites and smith glaciers and ocean currents on average 0 5 c warmer than freezing appear to be the source the synchronised imbalance of the inland glaciers is the result of reduced lateral and basal tractions at their termini and the drawdown of grounded ice shows that antarctica is more sensitive to changing climates than was previously considered

esr dating in quaternary geology abstract electron spin resonance esr a relatively new dating technique was first suggested by zeller et al 1967 zeller 1968 and levy 1968 it has made substantial progress in frequent applications in the last few years esr dating is based on the direct measurement of the amount of radiation induced paramagnetic electrons trapped in crystal defects these free electrons were generated by alpha beta and gamma radiation of natural radioelements e g u th k and have accumulated in the minerals over geologic time the esr age is obtained by dividing the total amount of accumulated radiation dose archaeological dose ad by the dose per year annual dose this review comprises four major parts the principles of the method the determination of the archaeological dose ad the determination of the annual dose and a compilation of datable materials several questions remain the evaluation of the ad the determination of the annual dose and particularly with respect to the nature and stability of the electron traps used for dating

modelling circumpolar deep water intrusions on the amundsen sea continental shelf antarctica results are presented from an isopycnic coordinate model of ocean circulation in the amundsen sea focusing on the delivery of circumpolar deep water cdw to the inner continental shelf around pine island bay the warmest waters to reach this region are channeled through a submarine trough accessed via bathymetric irregularities along the shelf break temporal variability in the influx of cdw is related to regional wind forcing easterly winds over the shelf edge change to westerlies when the amundsen sea low migrates west and south in winter spring this drives seasonal on shelf flow while inter annual changes in the wind forcing lead to inflow variability on a decadal timescale a modelled period of warming following low cdw influx in the late 1980 s and early 1990 s coincides with a period of observed thinning and acceleration of pine island glacier

the timing of quaternary calcrete development in semi arid southeast spain investigating the role of climate on calcrete genesis quaternary aged calcrete horizons are common weathering products in arid and semi arid regions it is however unclear how calcrete forming processes respond to the major oscillations in climate that occur over the quaternary period this paper presents a u series based calcrete age database from the sorbas basin southeast spain the study constructs an age frequency distribution of these ages which is consequently compared to a range of palaeoenvironmental records from the mediterranean the age distribution presented here suggests that the formation of pedogenic calcrete horizons in the sorbas basin primarily occurs during warm isotope stages mis 1 and 5 with very few calcrete ages occurring during cold glacial stadial stages mis 2 3 and 4 it is suggested that this is a function of the environments that existed during warm isotope stages being more conducive to calcrete development than those that existed during cold climate episodes in a semi arid region such as the sorbas basin it is likely that increased aridity during glacial stages coupled with reduced vegetation and accelerated landscape instability was crucial in reducing rates of calcrete formation in a semi arid region such as southeast spain calcrete formation during the quaternary therefore oscillates with climate change but is primarily a warm episode phenomenon it is suggested that further studies are required to see how calcrete genesis responds to environmental change in more humid parts of the mediterranean

ice stream retreat and ice shelf history in marguerite trough antarctic peninsula sedimentological and foraminiferal signatures the timing nature and causes of grounded ice sheet retreat following the last glacial maximum lgm in marguerite trough west antarctic peninsula and subsequent early holocene ice shelf decay are presented in this paper we use sedimentological foraminiferal geotechnical and accelerator mass spectrometer ams radiocarbon data from marine cores from the mid continental shelf together with previously published ams dates to establish a sedimentological and chronological model initial ice sheet retreat through the outer and mid shelf sectors of marguerite trough was under way by ca 14 ka b p was rapid and coincided with the sea level rise of meltwater pulse 1a an ice shelf formed during this retreat and fine grained laminated muds reflecting meltwater derived suspension settling and or tidal pumping were deposited during this time the ice sheet remained grounded on the inner shelf ice shelf breakup and retreat of the calving front from ca 13 2 to 12 5 ka b p was slow 100 m a 1 across the outer and mid shelf with calving bay conditions remaining for at least 3 5 ka we interpret this ice shelf decay to have been driven by an incursion of weddell sea transitional water onto the shelf in contrast grounding line and ice shelf retreat in the inner bay occurred from ca 9 3 ka b p and was driven by circumpolar warm deep water encroaching onto the continental shelf at this time the mid shelf was an open marine environment characterized by hemipelagic deposition these findings highlight the importance of oceanographic controls in the breakup of antarctic peninsula ice shelves during the holocene

investigation on age and genesis of silcretes in queensland australia preliminary results silcretes from queensland australia were dated by means of the electron spin resonance dating technique the results range from 1 5 to 10 8 million years therefore these silcretes were formed between the upper miocene and the early pleistocene for a conclusive interpretation of the data geochemical and thin section analyses were also carried out esr dating of silcretes for the first time offers a direct approach to a chronostratigraphic framework of the genesis of these duricrusts and of the palaeoclimatic events attributed to them

physical properties of the variations of the electric field of the earth preceding earthquakes ii determination of epicenter and magnitude abstract as reported in the preceding paper a transient change of the electric field of the earth seismic electric signal hereafter called ses appears many hours before an earthquake eq by measuring this change in a given direction and dividing it with a suitable relative effective resistivity one obtains a quantity that reflects the current density in this direction measurements in two directions e w and n s give the relative signal intensity jrel at the station under consideration by measuring jrel at a number of stations and considering that it attenuates according to a 1 r law the epicenter can be determined with an accuracy usually around 100 km once the epicenter has been determined the product jrel r can be evaluated so that the magnitude m can be estimated by resorting to an empirical log jrel r versus m plot the uncertainty of m is around 0 5 units following sobolev 1975 and for the statistics to be beyond any doubt predictions were officially documented before the eq occurrence for 23 earthquakes with a magnitude equal or greater than ms 5 0 two events were missed the present method is compared to other electrical methods used in china japan and soviet union a number of problems concerning the origin of the effect its directivity and the attenuation with distance remain open for further studies

foraminiferal assemblages and caco3 dissolution since the last deglaciation in the maxwell bay king george island antarctica abstract three sediment cores a10 01 02 and 08 from the maxwell bay king george island antarctica were quantitatively analyzed for foraminiferal fauna planktonic foraminifera of three cores are rare due to the special antarctica environment benthic foraminifera is mainly composed of globocassidulina biora globocassidulina crassa rossensis cassidulinoides parkerianus and miliammina arenacea g biora and g crassa rossensis show high percentages in the shallower core a10 08 while m arenacea displays obviously high percentage in deeper core a10 02 the lower parts of the cores have a lower abundance of foraminifera while the upper parts have a relatively higher abundance the down core variations of benthic foraminifera reflect the contrast of surface water environment between the last deglaciation and post glacial during the last deglaciation lower parts of the cores the lower abundant foraminifera was consistent with the lower toc which reflected that the extensive sea ice prevented the production of primary organisms and therefore lower flux of organic particles was delivered to the sea floor abundant foraminifera together with higher toc in the upper parts of the cores suggested a higher primary productivity after the glaciation the shallowest water depth core a10 08 45 m displayed a better carbonate preservation than the other two cores a10 01 and 02 from the depths of 85 and 105 m respectively the disparity in carbonate dissolution reflected the remarkable shallow lysocline and carbonate compensation depth ccd in the antarctic area and also reflected significant variations in water properties even within such a difference only about 60 m in water depth down core variations of benthic foraminifera dissolution index bdi and caco 3 content indicated the existence of stronger carbonate dissolution in the upper parts than those in the lower parts of the cores the down core variations of carbonate dissolution suggested changes of water properties linked to the shallow ccd in this area it was supposed that the less influence of the saline shelf water during the last deglaciation enhanced the carbonate preservation with the sea level increasing and retreat of the coastal ice after the glacial erosive water masses and the higher co 2 accumulated by the increased flux of organic material led to severe dissolution of caco 3 and foraminiferal shells in the sediment

oceanic heat transport onto the amundsen sea shelf through a submarine glacial trough glaciers which drain the west antarctic ice sheet wais into the amundsen sea are accelerating and thinning rapidly these observations have been attributed to the regional oceanography whereby heat contained within circumpolar deep water cdw drives the basal melting of floating glaciers on the basis of new data we calculate that 2 8 terra watts 1012 of oceanic heat flow onto the continental shelf and toward the glaciers via a submarine glacial trough this is enough to account for most of the basal melting in the entire region suggesting the ocean is supplying an excess of heat toward the antarctic continent

tufas and travertines of the mediterranean region a testing ground for freshwater carbonate concepts and developments actively forming travertine and tufa sites are widespread in temperate and warm climates such as the mediterranean region but also develop in other climatic regimes from the arctic to equatorial latitudes the terms travertine and tufa are sometimes applied indiscriminately today however each has a specific definition most studied deposits are active or of quaternary especially holocene age there are fewer tertiary and even less late mesozoic examples on record in part this is because of a recognition problem as these deposits commonly preserve as fragmentary erosional remnants physico chemical precipitation of calcium carbonate is commonly considered to be the main mechanism contributing to tufa and travertine deposition rapid cooling of waters further aids the process in thermal travertine sites however biomediation of calcium carbonate associated with prokaryote microphyte biofilms is now recognized to be equally important in slow flowing and near static sites much of this precipitation occurs in close association with cyanobacterial heterotrophic bacterial and diatoms the mediterranean region figures significantly in the development of travertine and tufa research consequently this article employs key literature on mediterranean examples to illustrate developments and concepts in freshwater carbonate research modern work started in the 1950s and defined many previously unknown outcrops many such sites became the targets for early radiocarbon dating studies since the late 1970s a number of laboratory based and field based classification schemes have been proposed some schemes were based on associated macrovegetation types others were based on petrological characteristics or on geometry and sedimentary facies characteristics of late the sedimentological modelling has benefited greatly from the use of shallow geophysical techniques in order to better define the internal geometries of the deposits two distinct research strands were developed during the 1990s both aimed at a better understanding of environmental change the first considered biocomponents the research was multifaceted and ranged from exploring the role of micro organisms in cement and lime mud precipitation to biostratigraphic analysis of contained pollen and invertebrate remains these provided proxy environmental information which has helped to define past climate variability in the region the second research strand focussed on geochemical signatures as a proxy tool for defining environmental change this definition was made possible by new petrological studies which have greatly aided the recognition of primary depositional fabrics this improved knowledge has reduced the sampling dangers of diagenetic contamination inherent in earlier geochemical studies lithofacies modelling has also brought to light important early post depositional neomorphic changes which obscure primary fabrics and complex diagenetic histories have been revealed stable isotope signatures of carbon and oxygen have also been used to define palaeo water temperature fine tuning of depositional time frames has also been achieved from absolute dating techniques employing radiocarbon and uranium thorium

genesis and climatic interpretation of paleosols and calcretes in a plio pleistocene alluvial fan of the costa blanca se spain abstract a plio pleistocene alluvial fan near la regia in the southeast coast of spain contains a vertical series of 7 fossil soils and 7 calcrete complexes the soil stratigraphy reflects recurring alternation of sedimentation and soil formation suggesting numerous pedogenically effective cyclical climatic changes during the late pliocene and early pleistocene the differentiated composition of calcretes near la regia is a polygenetic product surface erosion and sedimentary fossilization were followed by secondary carbonatization and subsequent induration at least 15 stages of soil formation are reconstructed red paleosols and pedogenic calcretes are well developed and reflect humid subtropical and mediterranean conditions during soil genesis with geomorphodynamic stability in contrast the accumulation of sediments and synsedimentary calcretes correlates with geomorphodynamic activity under considerably drier mediterranean conditions

latest aspects of earthquake prediction in greece based on seismic electric signals ii abstract since 1983 continuous monitoring of the electrotelluric field has been carried out using an array of measuring stations located at various sites in greece the basic physical properties of the transient changes seismic electric signals ses in the electrotelluric field that are forerunners of earthquakes were first described six years ago since then a large body of data has been collected resulting in new insight into various aspects of the method the present paper reviews the latest developments in ses based earthquake prediction and describes the current procedures used to predict the epicenter and magnitude of an impending earthquake a detailed list of the predictions officially issued in greece during the past 3 years january 1 1987 november 30 1989 is also given public warnings were issued well before the most destructive seismic activity

the diel cycle of water vapor in west greenland we present a study of the dynamics of small scale 100 km atmospheric circulation in west greenland which is dominated by interactions of marine and continental air masses water vapor concentration and isotopic ratios measured continuously over a 25 day period in kangerlussuaq greenland were used to monitor the convergence of easterly katabatic winds and westerly sea breezes that form a front between the dry isotopically depleted glacial air mass and the moist isotopically enriched marine air mass during the latter 16 days of the measurement period an interval with no large scale synoptic interference the inland penetration of the sea breeze controlled the largest day to day humidity and vapor isotopic variations kangerlussuaq experienced sea breezes in the afternoon on 9 days consistent with the long term average of such occurrences on 56 of days in july and august the inland position of the sea breeze front is controlled by the katabatic wind strength which is stronger during times of reduced cloud coverage and or higher pressure gradient between the coast and the greenland ice sheet the position and movement of the front will likely respond to changes in the general atmospheric circulation and regional radiation balance resulting from global warming which will in turn impact the local hydrological cycle and ecosystem processes

the landsat image mosaic of antarctica abstract the landsat image mosaic of antarctica lima is the first true color high spatial resolution image of the seventh continent it is constructed from nearly 1100 individually selected landsat 7 etm scenes each image was orthorectified and adjusted for geometric sensor and illumination variations to a standardized almost seamless surface reflectance product mosaicing to avoid clouds produced a high quality nearly cloud free benchmark data set of antarctica for the international polar year from images collected primarily during 1999 2003 multiple color composites and enhancements were generated to illustrate additional characteristics of the multispectral data including the true appearance of the surface discrimination between snow and bare ice reflectance variations within bright snow recovered reflectance values in regions of sensor saturation and subtle topographic variations associated with ice flow lima is viewable and individual scenes or user defined portions of the mosaic are downloadable at http lima usgs gov educational materials associated with lima are available at http lima nasa gov

observations reveal external driver for arctic sea ice retreat 1 the very low summer extent of arctic sea ice that has been observed in recent years is often casually interpreted as an early warning sign of anthropogenic global warming for examining the validity of this claim previously ipcc model simulations have been used here we focus on the available observational record to examine if this record allows us to identify either internal variability self acceleration or a specific external forcing as the main driver for the observed sea ice retreat we find that the available observations are sufficient to virtually exclude internal variability and self acceleration as an explanation for the observed long term trend clustering and magnitude of recent sea ice minima instead the recent retreat is well described by the superposition of an externally forced linear trend and internal variability for the externally forced trend we find a physically plausible strong correlation only with increasing atmospheric co2concentration our results hence show that the observed evolution of arctic sea ice extent is consistent with the claim that virtually certainly the impact of an anthropogenic climate change is observable in arctic sea ice already today

recent breakdown of the seasonal linkage between the winter north atlantic oscillation northern annular mode and summer northern annular mode abstractthe summer northern annular mode nam and the winter north atlantic oscillation nao winter nam have a positive correlation from the mid 1960s to the 1980s namely when the winter nao na

the mechanisms of the atlantic meridional overturning circulation slowdown induced by arctic sea ice decline abstractwe explore the mechanisms by which arctic sea ice decline affects the atlantic meridional overturning circulation amoc in a suite of numerical experiments perturbing the arctic sea ice ra

multi model assessment of the late winter extra tropical response to el nino and la nina el nino southern oscillation enso is known to affect the northern hemisphere tropospheric circulation in late winter january march but whether el nino and la nina lead to symmetric impacts and with the same underlying dynamics remains unclear particularly in the north atlantic three state of the art atmospheric models forced by symmetric anomalous sea surface temperature sst patterns mimicking strong enso events are used to robustly diagnose symmetries and asymmetries in the extra tropical enso response asymmetries arise in the sea level pressure slp response over the north pacific and north atlantic as the response to la nina tends to be weaker and shifted westward with respect to that of el nino the difference in amplitude can be traced back to the distinct energy available for the two enso phases associated with the non linear diabatic heating response to the total sst field the longitudinal shift is embedded into the large scale rossby wave train triggered from the tropical pacific as its anomalies in the upper troposphere show a similar westward displacement in la nina compared to el nino to fully explain this shift the response in tropical convection and the related anomalous upper level divergence have to be considered together with the climatological vorticity gradient of the subtropical jet i e diagnosing the tropical rossby wave source in the north atlantic the enso forced slp signal is a well known dipole between middle and high latitudes different from the north atlantic oscillation whose asymmetry is not indicative of distinct mechanisms driving the teleconnection for el nino and la nina

understanding the interdecadal variability of east asian summer monsoon precipitation joint influence of three oceanic signals abstracteast asian summer monsoon precipitation easmp features complicated interdecadal variability with multiple time periods and spatial patterns using century long datasets of hadisst cru precipitation and era 20c reanalysis this study examines the joint influence of three oceanic interdecadal signals i e pacific decadal oscillation pdo atlantic multidecadal oscillation amo and indian ocean basin mode iobm on the easmp which however is found not to be simply a linear combination of their individual effects when pdo and amo are out of phase the same sign sst anomalies occur in north pacific and north atlantic and a zonally orientated teleconnection wave train appears across the eurasian mid high latitudes propagating from north atlantic to northern east asia along the asian westerly jet waveguide correspondingly the interdecadal precipitation anomalies are characterized by a meridional tripole mode over eastern china when pdo and amo are in phase with opposite sign sst anomal

changes in the west antarctic ice sheet since 1963 from declassified satellite photography comparison of declassified satellite photography taken in 1963 with more recent satellite imagery reveals that large changes have occurred in the region where an active ice stream enters the ross ice shelf ice stream b has widened by 4 kilometers at a rate much faster than suggested by models and has decreased in speed by 50 percent the ice ridge between ice streams b and c has eroded 14 kilometers these changes along with changes in the crevassing around crary ice rise imply that this region s velocity field shifted during this century

transient electric variations associated with large intermediate depth earthquakes in south aegean abstract a telluric station was installed on crete in the south aegean in order to investigate the existence of transient electric variations before large near intermediate depth earthquakes during the experiment two transient electric variations not correlated with geomagnetic variations were recorded and associated with two time isolated intermediate depth earthquakes with local magnitude m l 5 8 and 4 8 respectively finally a qualitative discussion on the form of the electric signal based on the charge dislocation model is presented

official earthquake prediction procedure in greece abstract since jan 19 1983 the authors have been operating a telemetric network of electrotelluric stations in greece the real time observation of specific pre seismic variations in the electric field of the earth seismic electric signals ses allows us to predict the time epicenter and magnitude of an impending earthquake eq initially the predictions were announced by expediting telegrams prior to the event after the ministry of public works established the earthquake prediction council epc in september 1985 predictions were dealt with in special sessions of the council prior to the occurrence of an earthquake it was decided to announce only eq s with an expected magnitude ms 4 8 for epicenters predicted within or near the perimeter surrounding the network of measuring stations and ms 5 for eq s predicted outside the perimeter this procedure was followed from september 1985 to march 18 1986 with the following results 1 1 within the network only one eq with ms 4 9 occurred during the period mentioned the prediction of the magnitude was accurate to within a few tenths of a magnitude unit while the epicenter was predetermined to within some tens of kilometers no predictions were made that were not followed by earthquakes 2 2 outside the network three eq s with ms 5 4 5 2 and 5 3 occurred on nov 9 dec 18 and dec 23 1985 respectively the first was missed the magnitudes of the other two were predicted to be ms 5 2 and 5 5 respectively the corresponding epicentral coordinates were forecast with an accuracy of 150 and 160 km respectively the sessions were discontinued on march 18 1986 on march 24 1986 a ms 6 1 eq was predicted and directly announced to the ministry of public works the event occurred on march 29 with the predicted magnitude and less than 50 km from the predicted epicenter

seasonal and regional manifestation of arctic sea ice loss abstractthe arctic ocean is currently on a fast track toward seasonally ice free conditions although most attention has been on the accelerating summer sea ice decline large changes are also occu

ice sheet grounding line dynamics steady states stability and hysteresis 1 the ice sheet ice shelf transition zone plays an important role in controlling marine ice sheet dynamics as it determines the rate at which ice flows out of the grounded part of the ice sheet together with accumulation this outflow is the main control on the mass balance of the grounded sheet in this paper we verify the results of a boundary layer theory for ice flux in the transition zone against numerical solutions that are able to resolve the transition zone very close agreement is obtained and grid refinement in the transition zone is identified as a critical component in obtaining reliable numerical results the boundary layer theory confirms that ice flux through the grounding line in a two dimensional sheet shelf system increases sharply with ice thickness at the grounding line this result is then applied to the large scale dynamics of a marine ice sheet our principal results are that 1 marine ice sheets do not exhibit neutral equilibrium but have well defined discrete equilibrium profiles 2 steady grounding lines cannot be stable on reverse bed slopes and 3 marine ice sheets with overdeepened beds can undergo hysteresis under variations in sea level accumulation rate basal slipperiness and ice viscosity this hysteretic behavior can in principle explain the retreat of the west antarctic ice sheet following the last glacial maximum and may play a role in the dynamics of heinrich events

clay mineral provenance of sediments in the southern bellingshausen sea reveals drainage changes of the west antarctic ice sheet during the late quaternary the belgica trough and the adjacent belgica trough mouth fan in the southern bellingshausen sea pacific sector of the southern ocean mark the location of a major outlet for the west antarctic ice sheet during the late quaternary the drainage basin of an ice stream that advanced through belgica trough across the shelf during the last glacial period comprised an area exceeding 200 000 km 2 in the west antarctic hinterland previous studies mainly based on marine geophysical data from the continental shelf and slope focused on the bathymetry and seafloor bedforms and the reconstruction of associated depositional processes and ice drainage patterns in contrast there was only sparse information from seabed sediments recovered by coring in this paper we present lithological and clay mineralogical data of 21 sediment cores collected from the shelf and slope of the southern bellingshausen sea most cores recovered three lithological units which can be attributed to facies types deposited under glacial transitional and seasonally open marine conditions the clay mineral assemblages document coinciding changes in provenance the relationship between the clay mineral assemblages in the subglacial and proglacial sediments on the shelf and the glacial diamictons on the slope confirms that a grounded ice stream advanced through belgica trough to the shelf break during the past thereby depositing detritus eroded in the west antarctic hinterland as soft till on the shelf and as glaciogenic debris flows on the slope the thinness of the overlying transitional and seasonally open marine sediments in the cores suggests that this ice advance occurred during the last glacial period clay mineralogical acoustic sub bottom and seismic data furthermore demonstrate that the palaeo ice stream probably reworked old sedimentary strata including older tills on the shelf and incorporated this debris into its till bed the geographical heterogeneity of the clay mineral assemblages in the sub and proglacial diamictons and gravelly deposits indicates that they were eroded from underlying sedimentary strata of different ages these strata may have been deposited during either different phases of the last glacial period or different glacial and interglacial periods additionally the clay mineralogical heterogeneity of the soft tills recovered on the shelf suggests that the drainage area of the palaeo ice stream flowing through belgica trough changed through time c 2009 elsevier b v all rights reserved

wavelet analysis of polar vortex variability over the twentieth century recent increases in extreme weather events in the northern hemisphere have been linked to amplified planetary waves changes in planetary wave properties are linked to changes in climate hence finding a mechanism that links the planetary wave variability under climatic forcing and midlatitude blocking events has engendered a great deal of interest in this study wavelet analysis is applied to time series of planetary wave phase speeds at high latitudes as a first step to assessing the potential for identifying these mechanisms in the observational record a circumpolar multiannual cycle increase is found but signals also demonstrate a complex westward propagation pattern with periods of intense wave variability significant correlations between wavelet power at all time scales and albedo snow cover atmospheric ozone levels and surface air temperature are demonstrated

provenance of lgm glacial till sand fraction across the ross embayment antarctica abstract the provenance of late quaternary ross embayment till was investigated by comparing the coarse sand composition of east and west antarctic source area tills with till samples from across the ross sea the west antarctic samples from beneath the whillans b and kamb c ice streams are petrologically distinct from samples of lateral moraines flanking several east antarctic outlet glaciers the characteristic assemblage of four west antarctic samples includes felsic intrusive and detrital sedimentary lithic fragments plagioclase and abundant quartz in contrast most of the ten east antarctic till samples contains abundant mafic intrusive and detrital sedimentary lithic fragments as well as less abundant quartz the distinctive composition of these source areas can be linked to 33 samples from 20 cores of last glacial maximum lgm age till distributed across the ross sea western ross sea till samples exhibit mineralogic and lithological similarities to east antarctic till samples although these western ross sea tills contain higher percentages of felsic intrusive and extrusive lithic fragments eastern ross sea till samples are compositionally similar to west antarctic till particularly in their abundance of quartz and dearth of mafic and extrusive lithic components central ross sea till exhibits compositional similarities to both east and west antarctic source terranes including a mafic lithic component and marks the confluence of ice draining from east and west antarctica during the lgm thus west antarctic derived ice streams did not advance into the western ross sea this indicates that even if pre lgm equivalents of the present siple coast ice streams existed they did not simply expand allowing west antarctic derived ice to dominate the lgm ross ice sheet

deglacial history of the west antarctic ice sheet in the western amundsen sea embayment abstract the amundsen sea embayment ase drains approximately 35 of the west antarctic ice sheet wais and is one of the most rapidly changing parts of the cryosphere in order to predict future ice sheet behaviour modellers require long term records of ice sheet melting to constrain and build confidence in their simulations here we present detailed marine geological and radiocarbon data along three palaeo ice stream tributary troughs in the western ase to establish vital information on the timing of deglaciation of the wais since the last glacial maximum lgm we have undertaken multi proxy analyses of the cores core description shear strength x radiographs magnetic susceptibility wet bulk density total organic carbon nitrogen carbonate content and clay mineral analyses in order to 1 characterise the sedimentological facies and depositional environments and 2 identify the horizon s in each core that would yield the most reliable age for deglaciation in accordance with previous studies we identify three key facies which offer the most reliable stratigraphies for dating deglaciation by recording the transition from a grounded ice sheet to open marine environments these facies are i subglacial ii proximal grounding line and iii seasonal open marine in addition we incorporate ages from other facies e g glaciomarine diamictons deposited at some distance from the grounding line such as glaciogenic debris flows and iceberg rafted diamictons and turbates into our deglacial model in total we have dated 78 samples mainly the acid insoluble organic aio fraction but also calcareous foraminifers which include 63 downcore and 15 surface samples through careful sample selection prior to dating we have established a robust deglacial chronology for this sector of the wais our data show that deglaciation of the western ase was probably underway as early as 22 351 calibrated years before present cal yr bp reaching the mid shelf by 13 837 cal yr bp and the inner shelf to within c 10 12 km of the present ice shelf front between 12 618 and 10 072 cal yr bp the deglacial steps in the western ase broadly coincide with the rapid rises in sea level associated with global meltwater pulses 1a and 1b although given the potential dating uncertainty additional more precise ages are required before these findings can be fully substantiated finally we show that the rate of ice sheet retreat increased across the deep up to1600 m basins of the inner shelf highlighting the importance of reverse slope and pinning points in accelerated phases of deglaciation

coastal water vapor isotopic composition driven by katabatic wind variability in summer at dumont d urville coastal east antarctica abstract dumont d urville station located on the east coast of antarctica in adelie land is in one of the windiest coastal region on earth due to katabatic winds downslope from the east antarctic ice sheet in summer the season of interest in this study coastal weather is characterized by well marked diel cycles in temperature and wind patterns our study aims at exploring the added value of water vapor stable isotopes in coastal adelie land to provide new information on the local atmospheric water cycle and climate an important application is the interpretation of water isotopic profiles in snow and ice cores recently drilled in adelie land we present the first continuous measurements of 18 o and d excess in water vapor over adelie land during our measurements period 26 12 2016 to 03 02 2017 we observed clear diel cycles in terms of temperature humidity and isotopic composition the cycles in isotopic composition are particularly large given the muted variations in temperature when compared to other antarctic sites where similar monitoring have been performed based on data analyses and simulations obtained with the regional mar model on the coastal adelie land we suggest that the driver for 18 o and d excess diel variability in summer at dumont d urville is the variation of the strength of the wind coming from the continent the periods with strong wind are associated with the arrival of relatively dry air with water vapor associated with low 18 o and high d excess from the antarctic plateau finally in addition to the interpretation of snow and ice core isotopic profiles in the coastal regions our study has implications for the evaluation of atmospheric models equipped with water isotopes

dynamical constraints on katabatic wind cessation in adelie land antarctica the katabatic wind events observed in the coastal zone of adelie land antarctica on 27 november and 3 december 1985 are simulated with a hydrostatic mesoscale atmospheric model coupled to a snow moder the diurnal cycle of insolation is strong the main difference in the forcing between the two events is the large scale wind which is weak on 27 november and moderate on 3 december in both cases temperature and wind are characterized by well marked diurnal cycles in particular katabatic winds blow during nighttime and upslope winds during daytime in both cases the katabatic airstream slows down progressively over the ocean consequently continental air piles up and this generates a pool of cold air responsible for a pressure gradient force opposing the katabatic wind an amplification of the slowing down results when in the morning insolation increases the surface inversion weakens but the influence of the cold air pool increases the katabatic how starts to decay over the coastal zone and then retreats progressively toward the ice sheet interior when the large scale wind is weak the surface warming is sufficient for generating an additional upslope bouyancy force and anabatic flow develops over the ice sheet in the afternoon when the large scare wind is moderate and downslope the pilling up of cold air is important and this has a dramatic impact on the flow a sharp spatial transition is generated between downslope and upslope winds over the ocean this discontinuity moves toward the ice sheet interior in the morning and is responsible for the sudden cessation of the katabatic flow seen by static observers the results of the simulations are used in order to refine a simple parameterization of antarctic katabatic winds

snow accumulation variability over the west antarctic ice sheet since 1900 a comparison of ice core records with era 20c reanalysis this study uses a set of 37 firn core records over the west antarctic ice sheet wais to test the performance of the twentieth century from the european centre for medium range weather forecasts era 20c reanalysis for snow accumulation and quantify temporal variability in snow accumulation since 1900 the firn cores are allocated to four geographical areas demarcated by drainage divides i e antarctic peninsula ap western wais central wais and eastern wais to calculate stacked records of regional snow accumulation our results show that the interannual variability in era 20c precipitation minus evaporation p e agrees well with the corresponding ice core snow accumulation composites in each of the four geographical regions suggesting its skill for simulating snow accumulation changes before the modern satellite era pre 1979 snow accumulation experiences significantly positive trends for the ap and eastern wais a negative trend for the western wais and no significant trend for the central wais from 1900 to 2010 the contrasting trends are associated with changes in the large scale moisture transport driven by a deepening of the low pressure systems and anomalies of sea ice in the amundsen sea low region

recent dramatic thinning of largest west antarctic ice stream triggered by oceans a growing body of observational data suggests that pine island glacier pig is changing on decadal or shorter timescales these changes may have far reaching consequences for the future of the west antarctic ice sheet wais and global sea levels because of pig s role as the ice sheet s primary drainage portal we test the hypothesis that these changes are triggered by the adjoining ocean specifically we employ an advanced numerical ice flow model to simulate the effects of perturbations at the grounding line on pig s dynamics the speed at which these changes are propagated upstream implies a tight coupling between ice sheet interior and surrounding ocean

interaction of katabatic flow with local thermal effects in a coastal region of adelie land east antarctica katabatic flows largely dominate the climate of the adelie land coastal region a detailed climatological data analysis of dumont d urville has been conducted results of this study support the idea that katabatic flow can be locally enhanced by the diurnal cycle of solar insolation and the temperature contrast between the continent and the ocean the interaction between katabatic wind and local thermal effects is expressed in terms of scale analysis except for surface stress all terms in the momentum equation for a katabatic flow in a coastal region of antarctica can reach the same order of magnitude the local circulation then is the result of a relatively tenuous force balance which can be disrupted even by a weak perturbation of any term to estimate the effect of the temperature contrast between the ocean and the continent on the katabatic flow two numerical experiments have been conducted the simulations consider an ocean free of sea ice representative of the summer months and another winter case with the ocean covered by thick sea ice these simulations show that with the ocean free of sea ice the katabatic flows extend only a limited distance over the open ocean during the day due to the local thermal effects with the ocean covered by sea ice the katabatic winds are not constrained and extend a considerable distance offshore

observations beneath pine island glacier in west antarctica and implications for its retreat thinning ice in west antarctica is currently contributing about 10 of the observed rise in global sea level observations obtained from an autonomous underwater vehicle operating beneath pine island glacier west antarctica reveal that the glacier was recently grounded on a transverse ridge in the sea floor but now warm sea water flows through the widening gap above the ridge thinning ice in west antarctica resulting from acceleration in the flow of outlet glaciers is at present contributing about 10 of the observed rise in global sea level1 pine island glacier in particular has shown nearly continuous acceleration2 3 and thinning4 5 throughout the short observational record the floating ice shelf that forms where the glacier reaches the coast has been thinning rapidly6 driven by changes in ocean heat transport beneath it as a result the line that separates grounded and floating ice has retreated inland7 these events have been postulated as the cause for the inland thinning and acceleration8 9 here we report evidence gathered by an autonomous underwater vehicle operating beneath the ice shelf that pine island glacier was recently grounded on a transverse ridge in the sea floor warm sea water now flows through a widening gap above the submarine ridge rapidly melting the thick ice of the newly formed upstream half of the ice shelf the present evolution of pine island glacier is thus part of a longer term trend that has moved the downstream limit of grounded ice inland by 30 km into water that is 300 m deeper than over the ridge crest the pace and ultimate extent of such potentially unstable retreat10 are central to the debate over the possibility of widespread ice sheet collapse triggered by climate change11 12

antarctic sediment chronology by programmed temperature pyrolysis methodology and data treatment 1 we report a detailed programmed temperature pyrolysis combustion methodology for radiocarbon 14c dating of antarctic sub ice shelf sediments the method targets the autochthonous organic component in sediments that contain a distribution of acid insoluble organic components from several sources of different ages the approach has improved sediment chronology in organic rich sediments proximal to antarctic ice shelves by yielding maximum age constraints significantly younger than bulk radiocarbon dates from the same sediment horizons the method proves adequate in determining isotope ratios of the pre aged carbon end member however the isotopic compositions of the low temperature measurements indicate that no samples completely avoided mixing with some proportion of pre aged organic material dating the unresolved but desired young end member must rely on indirect methods but a simple mixing model cannot be developed without knowledge of the sedimentation rate or comparable constraints a mathematical approach allowing for multiple mixing components yields a maximum likelihood age a first order approximation of the relative proportion of the autochthonous component and the temperature at which allochthonous carbon begins to volatilize and mix with the autochthonous component it is likely that our estimation of the cutoff temperature will be improved with knowledge of the pyrolysis kinetics of the major components chronology is improved relative to bulk acid insoluble organic material ages from nine temperature interval dates down to two but incorporation of inherently more pre aged carbon in the first division becomes more apparent with fewer and larger temperature intervals

understanding the climatic signal in the water stable isotope records from the neem shallow firn ice cores in northwest greenland 1 samples of precipitation and atmospheric water vapor were collected together with shallow firn ice cores as part of the new deep drilling project in northwest greenland the neem project these samples were analyzed for their isotope composition to understand the processes affecting the climatic signal archived in the water stable isotope records from the neem deep ice core the dominant moisture source for the snow deposited at the neem site may be originating as far south as 35 n from the western part of the atlantic ocean the surface atmospheric water vapor appears in isotopic equilibrium with the snow surface indicating a large water exchange between the atmosphere and snowpack the interannual variability of neem shallow firn ice cores stable isotope data covering the last 40 years shows an unexpectedly weak nao signal regional to global atmospheric models simulate a dominant summer precipitation in the neem area suggesting that the intermittency of modern winter precipitation is responsible for the lack of a strong nao imprint the interannual variability of neem isotope data however shows a strong correlation with interannual variations of baffin bay sea ice cover a relationship consistent with air mass trajectories neem deep ice core isotopic records may therefore provide detailed information on past baffin bay sea ice extent neem stable water isotope content increasing trend points to a local warming trend of 3 0 c over the last 40 years

causes of the large warm bias in the angola benguela frontal zone in the norwegian earth system model we have investigated the causes of the sea surface temperature sst bias in the angola benguela frontal zone abfz of the southeastern atlantic ocean simulated by the norwegian earth system model noresm similar to other coupled models noresm has a warm sst bias in the abfz of up to 8 c in the annual mean our analysis of noresm reveals that a cyclonic surface wind bias over the abfz drives a locally excessively strong southward 0 05 m s relative to observation angola current displacing the abfz southward a series of uncoupled stand alone atmosphere and ocean model simulations are performed to investigate the cause of the coupled model bias the stand alone atmosphere model driven with observed sst exhibits a similar cyclonic surface circulation bias while the stand alone ocean model forced with the reanalysis data produces a warm sst in the abfz with a magnitude approximately half of that in the coupled noresm simulation an additional uncoupled sensitivity experiment shows that the atmospheric model s local negative surface wind curl generates anomalously strong angola current at the ocean surface consequently this contributes to the warm sst bias in the abfz by 2 c compared to the reanalysis forced simulation there is no evidence that local air sea feedbacks among wind stress curl sst and sea level pressure slp affect the abfz sst bias turbulent surface heat flux differences between coupled and uncoupled experiments explain the remaining 2 c warm sst bias in noresm ocean circulation upwelling and turbulent heat flux errors all modulate the intensity and the seasonality of the abfz errors

clay mineral distribution in surface sediments of the south atlantic sources transport and relation to oceanography abstract surface samples mostly from abyssal sediments of the south atlantic from parts of the equatorial atlantic and of the antarctic ocean were investigated for clay content and clay mineral composition maps of relative clay mineral content were compiled which improve previous maps by showing more details especially at high latitudes large scale relations regarding the origin and transport paths of detrital clay are revealed high smectite concentrations are observed in abyssal regions primarily derived from southernmost south america and from minor sources in southwest africa near submarine volcanoes of the antarctic ocean south sandwich bouvet island smectite contents exhibit distinct maxima which is ascribed to the weathering of altered basalts and volcanic glasses the illite distribution can be subdivided into five major zones including two maxima revealing both south african and antarctic sources a particularly high amount of mg and fe rich illites are observed close to east antarctica they are derived from biotite bearing crystalline rocks and transported to the west by the east antarctic coastal current chiorite and well crystallized dioctaedral illite are typical minerals enriched within the subantarctic and polarfrontal zone but of minor importance off east antarctica kaolinite dominates the clay mineral assemblage at low latitudes where the continental source rocks west africa brazil are mainly affected by intensive chemical weathering surprisingly a slight increase of kaolinite is observed in the enderby basin and near the filchner ronne ice shelf the investigated area can be subdivided into ten large scale clay facies zones with characteristic possible source regions and transport paths clay mineral assemblages of the largest part of the south atlantic especially of the western basins are dominated by chlorite and illite derived from the antarctic peninsula and southernmost south america and supported by advection within the circumantarctic deep water flow in contrast the east antarctic provinces are relatively small assemblages of the eastern basins north of 30 s are strongly influenced by african sources controlled by weathering regimes on land and by a complex interaction of wind river and deep ocean transport the strong gradient in clay mineral composition at the brazilian slope indicate a relatively low contribution of tropically derived assemblages to the western basins

electron spin resonance esr dating abstract esr dating has been systematically applied in earth sciences and archaeology since 1975 when ikeya dated a stalactite from the akiyoshi cave in japan in the meantime this new technique has been successfully applied to the dating of materials such as speleothems spring deposited travertines mollusc shells corals and tooth enamel the present research focuses on the dating of quartz which allows the age assessment of heated ceramics volcanic rocks intrafault material or windblown sediments esr dating is based on the measurement of the number of paramagnetic centers in a mineral these centers are generated by alpha beta and gamma radiation of the matural radioelements such as u th and k and have accumulated over time two parameters have to be determined the accumulated dose ad and the dose rate d to which the sample was exposed this review comprises three major parts a introduction into esr dating b application of the method and c appendices giving detailed description of dose rate calculation physical basis of electron spin resonance the esr spectrometer and esr lines the major emphasis lies on the outline of the application of esr dating this includes the discussion of the esr signals of the various materials sampling sample preparation and measurement techniques

observations on the suitability of the signal at g 2 0040 for esr dating of secondary carbonates abstract most secondary carbonates display a broad esr signal at g 2 0040 but the characteristics of this signal vary from observations using a variety of australian and chinese secondary carbonates it appears that the signal may often be suitable for the estimation of accumulated doses provided certain precautions are taken

sea level fingerprinting as a direct test for the source of global meltwater pulse ia the ice reservoir that served as the source for the meltwater pulse ia remains enigmatic and controversial we show that each of the melting scenarios that have been proposed for the event produces a distinct variation or fingerprint in the global distribution of meltwater we compare sea level fingerprints associated with various melting scenarios to existing sea level records from barbados and the sunda shelf and conclude that the southern laurentide ice sheet could not have been the sole source of the meltwater pulse whereas a substantial contribution from the antarctic ice sheet is consistent with these records

modeling ocean cryosphere interactions off adelie and george v land east antarctica abstractocean cryosphere interactions along the adelie and george v land agvl coast are investigated using a coupled ocean sea ice ice shelf model the dominant feature of the mertz glacier tongue mgt located at approximately 145 e was a highly productive winter coastal polynya system until its calving in february 2010 dramatically changed the regional icescape this study examines the annual mean seasonal and interannual variabilities of sea ice production basal melting of the mgt ice shelves large icebergs and fast ice dense shelf water dsw export and bottom water properties on the continental slope and rise and assesses the impacts of the calving event the interannual variability of the winter coastal polynya regime is dominated by the regional offshore winds and air temperature which are linked to activity of the amundsen sea low pressure system this is the main driver of the interannual variability of dsw exported from the agvl region the calving event led to a decrease in sea

mechanisms of interannual to decadal scale winter labrador sea ice variability the variability of the winter sea ice cover of the labrador sea region and its links to atmospheric and oceanic forcing are investigated using observational data a coupled ocean sea ice model and a fully coupled model simulation drawn from the cmip5 archive a consistent series of mechanisms associated with high sea ice cover are found amongst the various data sets the highest values of sea ice area occur when the northern labrador sea is ice covered this region is found to be primarily thermodynamically forced contrasting with the dominance of mechanical forcing along the eastern coast of baffin island and labrador and the growth of sea ice is associated with anomalously fresh local ocean surface conditions positive fresh water anomalies are found to propagate to the region from a source area off the southeast greenland coast with a 1 month transit time these anomalies are associated with sea ice melt driven by the enhanced offshore transport of sea ice in the source region and its subsequent westward transport in the irminger current system by combining sea ice transport through the denmark strait in the preceding autumn with the greenland blocking index and the atlantic multidecadal oscillation index strong correlation with the labrador sea ice area of the following winter is obtained this relationship represents a dependence on the availability of sea ice to be melted in the source region the necessary atmospheric forcing to transport this offshore and a further multidecadal scale link with the large scale sea surface temperature conditions

pre bomb radiocarbon and the reservoir correction for calcareous marine species in the southern ocean four antarctic marine mollusc shells which were collected alive between 1917 and 1940 were analyzed by accelerator mass spectrometry to provide the first pre bomb radiocarbon measurements of biogenic carbonates from the southern ocean after correcting for the impact of fossil fuel combustion suess effect radiocarbon activities of the pre bomb shells averaged 149 8 10 4 in contrast the 14c values for post bomb molluscs echinoderms brachiopods and foraminifera averaged 96 1 25 2 these biogenic carbonate 14c values are nearly identical to pre bomb estimates 148 to 152 and post bomb measurements 98 4 22 0 of the surface waters in the southern ocean average radiocarbon ages of the biogenic carbonates before and after 1950 1303 84 years and 811 205 years respectively along with those from seals and penguins indicate that the antarctic marine radiocarbon reservoir has decreased in age by nearly 500 years during the second half of the 20th century marine species and seawater measurements firmly place the radiocarbon reservoir correction at 1300 100 years for calcareous marine fossils which are widespread abundant and well preserved organic materials for interpreting ice sheet climate and sea level impacts on the antarctic marine ecosystem during the holocene

observed sea ice extent in the russian arctic 1933 2006 1 we present a time series of sea ice extent in the russian arctic based on observational sea ice charts compiled by the arctic and antarctic research institute aari these charts are perhaps the oldest operational sea ice data in existence and show that sea ice extent in the russian arctic has generally decreased since the beginning of the chart series in 1933 this retreat has not been continuous however for the russian arctic as a whole in summer there have been two periods of retreat separated by a partial recovery between the mid 1950s and mid 1980s the aari charts combined with air temperature records suggest that the retreat in recent decades is pan arctic and year round in some regions whereas the early twentieth century retreat was only observed in summer in the russian arctic the aari ice charts indicate that a significant transition occurred in the russian arctic in the mid 1980s when its sea ice cover began to retreat along with that of the rest of the arctic summertime sea ice extents derived from the aari data set agree with those derived from passive microwave including the hadley centre s global sea ice coverage and sea surface temperature hadisst data set the hadisst results do not indicate the 1980s transition or the partial recovery that took place before it the aari charts therefore add significantly to our understanding of the variability of arctic sea ice over the last 8 decades and we recommend their inclusion in future historical data sets of arctic sea ice

heat waves in china definitions leading patterns and connections to large scale atmospheric circulation and ssts based on the daily maximum temperatures tmax from 587 surface observation stations in china during 1959 2013 heat waves are detected using both absolute and relative definitions the spatiotemporal variations of heat wave occurrence duration amplitude are compared between the two definitions considering the significant differences in regional climatology relative threshold is more meaningful to detect the local extremes by utilizing the empirical orthogonal function the integral index heat wave total intensity is decomposed into three dominant modes interdecadal id interannual tripole ia tr and interannual dipole ia dp modes the id mode shows uniform anomalies over the whole china with the maximum in north and its corresponding time series depict notable interdecadal variations with a turning point around mid 1990s the ia dp mode exhibits opposite signed anomalies over north and south china the ia tr mode shows an anomalous tripole pattern with negative anomalies over central china and positive anomalies over north and south china in its positive phase both the ia dp and ia tr patterns are more obvious since mid 1990s with mainly year to year variations before that all the three modes are controlled by anomalous high pressure systems which are accompanied by local scale dry land conditions the diabatic heating associated with anomalous convective activities over tropical western pacific triggers rossby wave trains propagating northward along the east asia which causes abnormal heat waves through descending motion over the high pressure nodes in turn the severe convections are generated by enhanced walker circulation in the tropical pacific due to warming and or cooling sea surface temperature sst anomalies in the tropical western and eastern pacific respectively

review the atmospheric boundary layer an overview is given of the atmospheric boundary layer abl over both continental and ocean surfaces mainly from observational and modelling perspectives much is known about abl structure over homogeneous land surfaces but relatively little so far as the following are concerned i the cloud topped abl over the sea predominantly ii the strongly nonhomogeneous and nonstationary abl iii the abl over complex terrain these three categories present exciting challenges so far as improved understanding of abl behaviour and improved representation of the abl in numerical models of the atmosphere are concerned

water isotopes as tools to document oceanic sources of precipitation the isotopic composition of precipitation in deuterium oxygen 18 and oxygen 17 depends on the climatic conditions prevailing in the oceanic regions where it originates mainly the sea surface temperature and the relative humidity of air this dependency applies to present day precipitation but also to past records which are extracted for example from polar ice cores in turn coisotopic measurements of deuterium and oxygen 18 offer the possibility to retrieve information about the oceanic origin of modern precipitation as well as about past changes in sea surface temperature and relative humidity of air this interpretation of isotopic measurements has largely relied on simple rayleigh type isotopic models and is complemented by lagrangian back trajectory analysis of moisture sources it is now complemented by isotopic general circulation models igcm in which the origin of precipitation can be tagged we shortly review published results documenting this link between the oceanic sources of precipitation and their isotopic composition we then present experiments performed with two different igcms the giss model ii and the lmdz model we focus our study on marine water vapor and its contribution to precipitation over antarctica and over the andean region of south america we show how igcm experiments allow us to relate climatic conditions prevailing in the oceanic source of precipitation to its isotopic composition such experiments support at least qualitatively the current interpretation of ice core isotopic data in terms of changes in sea surface temperature additionally we discuss recent studies clearly showing the added value of oxygen 17 measurements key points link between the isotopic content of precipitation and its oceanic origin application of this method to polar ice cores andean precipitation potential of combining deuterium excess and oxygen 17 excess 2013 american geophysical union all rights reserved

characteristics of electromagnetic noise in the ioannina region greece a possible origin for so called seismic electric signal ses the study of electromagnetic noise in the ioannina region nw greece shows the existence of long transient electric signals duration 10 s without measurable correlated magnetic signals as is the case for seismic electric signal ses observed in the van network of short term earthquake prediction our signals have an artificial origin and are emitted by different kinds of transmitters implanted in the ioannina region this origin can be clearly ascertained from simultaneous observation at stations in direct sight of the transmitters of four electromagnetic components two electric and two magnetic in a broad band of frequencies 10 3 10 hz relying on these observations it is proposed that the april 18 and 19 1995 electric signals interpreted by the van group as ses precursors to the may 13 kozani earthquake are due to some transmitter located far to the north of the ioa station of the van network the transmitters of this area would be of digital type as is increasingly common in radio telecommunication networks we believe that careful studies of electromagnetic noise in a broad range of frequencies should precede lengthy discussions of the statistical significance of recorded signals

recent loss of floating ice and the consequent sea level contribution we combine new and published satellite observations and the results of a coupled ice ocean model to provide the first estimate of changes in the quantity of ice floating in the global oceans and the consequent sea level contribution rapid losses of arctic sea ice and small antarctic ice shelves are partially offset by thickening of antarctic sea ice and large antarctic ice shelves altogether 746 127 km 3 yr 1 of floating ice was lost between 1994 and 2004 a value that exceeds considerably the reduction in grounded ice over the same period although the losses are equivalent to a small 49 8 m yr 1 rise in mean sea level there may be large regional variations in the degree of ocean freshening and mixing ice shelves at the antarctic peninsula and in the amundsen sea for example have lost 481 38 km 3 yr 1

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

physical properties of the variations of the electric field of the earth preceding earthquakes i abstract in an earlier paper we described the physical properties of the preseismic transient variations in the electrotelluric field the present letter clarifies a few points that were not properly emphasized in our previous publications furthermore recent results like that of the destructive kalamata earthquake on september 13 1986 indicate that the duration of a preseismic electric signal may reach considerably high values lasting up to several hours

why is it hard to predict the future of ice sheets ice sheet retreat hypotheses of instability could be missing important processes that limit the rate or extent of retreat or conversely ice sheet behavior is strongly influenced by processes at its margin and base observations of rapid changes at these boundaries are helping modelers to improve predictions of future changes

reconstruction of the west antarctic ice sheet in pine island bay during the last glacial maximum and its subsequent retreat history abstract marine geological and geophysical studies were conducted to determine the late quaternary glacial history of the west antarctic ice sheet in pine island bay antarctica the data set includes sea floor imagery in the form of multibeam swath bathymetry and deep tow side scan sonar surveys distribution of sedimentary deposits and basal surface conditions are revealed through intermediate resolution seismic data and chirp 3 5 khz sub bottom profiles sedimentary deposits were sampled with piston cores and calcareous material was dated using ams radiocarbon techniques results from the study indicate the ice sheet was grounded on the outer shelf during its maximum extent sometime in the past thick ice flowing slowly and resting on crystalline bedrock was influenced by significant amounts of subglacial meltwater on the inner shelf thinner but more rapidly flowing ice characterized the seaward extent of the ice sheet which was grounded on a sedimentary substrate deglaciation occurred in two phases beginning soon after the last glacial maximum the outer most extension of the ice sheet retreated gradually pausing on a bathymetric high on the middle shelf by 16 000 14c years ago between 16 000 and 12 000 14c years ago ice sheet retreat resumed and may have proceeded rapidly to reach a present day position by 10 000 14c years ago

whither arctic sea ice a clear signal of decline regionally seasonally and extending beyond the satellite record the arctic sea ice has been pointed to as one of the first and clearest indicators of climate change satellite passive microwave observations from 1979 through 2005 now indicate a significant 8 4 1 5 decade 1 trend 99 confidence level in september sea ice extent a larger trend than earlier estimates due to acceleration of the decline over the past 41 years there are differences in regional trends with some regions more stable than others not all regional trends are significant the largest trends tend to occur in months where melt is at or near its peak for a given region a longer time series of september extents since 1953 was adjusted to correct biases and extended through 2005 the trend from the longer time series is 7 7 0 6 decade 1 99 slightly less than from the satellite derived data that begin in 1979 which is expected given the recent acceleration in the decline

electromagnetic signals generated in the solid earth by digital transmission of radio waves as a plausible source for some so called seismic electric signals abstract claims by the van group varotsos p alexopoulos k 1984 physical properties of the variations of the electric field of the earth preceding earthquakes i tectonophysics 110 73 98 and later works to have developed a short term earthquake prediction technique in greece continue to arouse contentious debates claims of success in using geoelectrical precursors to predict earthquakes are criticized and defended 1998 letters phys today 51 6 15 100 great debates in seismology the van method of earthquake prediction 1998 eos 79 573 580 this is partly because of the unknown origin of the so called seismic electric signals ses precursors their particular characteristics are not those of the usual electromagnetic noise cultural noise or of the natural electromagnetic field magnetotelluric field in this paper we show that transient electric signals looking like ses can be generated by digital transmitters of the radio telecommunication network such signals have been observed in different regions of the world including greece and vietnam their characteristics have been analyzed in a broad band of frequencies 10 3 103 hz in the ioannina greece site which is considered as the most sensitive area of the van network it is concluded that some of the signals recorded at this site and identified as ses are probably of artificial origin and that the criteria used by the van group are not sufficient to guarantee that the so called ses are not man made without an extended and thorough study of the ambient electromagnetic noise in a broad band of frequencies and better information about the electrical properties of the deep structure beneath the monitoring station earthquake predictions issued on the basis of signals recorded by the van network are of dubious significance

the met office hadley centre sea ice and sea surface temperature data set version 2 1 sea ice concentrations we present a new version of the sea ice concentration component of the met office hadley centre sea ice and sea surface temperature data set hadisst 2 1 0 0 passive microwave data are combined with historical sources such as sea ice charts to create global analyses on a 1 grid from 1850 to 2007 climatology was used when no information about the sea ice was available our main aim was to create a homogenous data set by calculating and applying bias adjustments using periods of overlaps between the different data sources used national ice center charts from 1995 to 2007 have been used as a reference to achieve this in particular large bias adjustments have been applied to the passive microwave data in both the antarctic and arctic summers overall hadisst 2 1 0 0 contains more ice than hadisst1 1 with higher concentrations shorter marginal ice zones and larger extents and areas in some regions and periods a new method for estimating the concentrations within the ice pack using the distance from the ice edge has been developed and evaluated this was used when only the extents were known or the original concentration fields were heterogeneous a number of discontinuities in the hadisst1 1 record are no longer found in hadisst 2 1 0 0

influence of large scale atmospheric circulation on marine air intrusion toward the east antarctic coast marine air intrusions into antarctica play a key role in high precipitation events here we use shipboard observations of water vapor isotopologues between australia and syowa on the east antarctic coast to elucidate the mechanism by which large scale circulation influences marine air intrusions the temporal isotopic variations at syowa reflect the meridional movement of a marine air front they are also associated with atmospheric circulation anomalies that enhance the southward movement of cyclones over the southern ocean the relationship between large scale circulation and the movement of the front is explained by northerly winds which in association with cyclones move toward the antarctic coast and push marine air with isotopically enriched moisture into the inland covered by glacial air with depleted isotopic values future changes in large scale circulation may have a significant impact on the frequency and intensity of marine air intrusion into antarctica

problems encountered with absolute dating u series esr of spanish calcretes abstract u series and esr dating techniques were applied to calcretes sampled at locations with a chronostratigraphic framework in spain esr dating considering the organic signal at g 2 0045 leads to an age overestimation up to 200 ka the percentage of error decreases however with increasing age so that this method may be more suitable to the dating of early pleistocene samples despite the unique limitations of the esr method to the dating of calcretes only a differentiation of early middle and late pleistocene calcretes is reasonable