twenty first century warming of a large antarctic ice shelf cavity by a redirected coastal current the redirection of warm water under the filchner ronne ice shelf during the second half of this century could cause the ice shelf base to melt at a rate 20 times higher than at present warm ocean currents are known to erode ice shelves from below but changes in currents can be forced by many different mechanisms leading to uncertain outcomes this study highlights the vulnerability to climate change of a small antarctic coastal region which has potentially severe consequences for the mass balance of a large antarctic ice shelf hellmer et al use climate modelling to show that the projected loss of sea ice in the weddell sea east of the antarctic peninsula leads to an increase in wind stress which in turn accelerates a warm ocean current far underneath the vast filchner ronne ice shelf the authors predict that the increased warmth could increase melt by a factor of 20 with possible consequences for ice stream dynamics in the east antarctic ice sheet the antarctic ice sheet loses mass at its fringes bordering the southern ocean at this boundary warm circumpolar water can override the continental slope front reaching the grounding line1 2 through submarine glacial troughs and causing high rates of melting at the deep ice shelf bases3 4 the interplay between ocean currents and continental bathymetry is therefore likely to influence future rates of ice mass loss here we show that a redirection of the coastal current into the filchner trough and underneath the filchner ronne ice shelf during the second half of the twenty first century would lead to increased movement of warm waters into the deep southern ice shelf cavity water temperatures in the cavity would increase by more than 2 degrees celsius and boost average basal melting from 0 2 metres or 82 billion tonnes per year to almost 4 metres or 1 600 billion tonnes per year our results which are based on the output of a coupled ice ocean model forced by a range of atmospheric outputs from the hadcm35 climate model suggest that the changes would be caused primarily by an increase in ocean surface stress in the southeastern weddell sea due to thinning of the formerly consolidated sea ice cover the projected ice loss at the base of the filchner ronne ice shelf represents 80 per cent of the present antarctic surface mass balance6 thus the quantification of basal mass loss under changing climate conditions is important for projections regarding the dynamics of antarctic ice streams and ice shelves and global sea level rise

hydrological characteristics of the drainage system beneath a surging glacier a rare combination of natural circumstances permits assessment of current theories on water flow beneath glaciers outburst floods from the subglacial lake grimsvotn in iceland took place before during and after surging of skei ararjokull the glacier beneath which the outburst floods drain the observable drainage patterns associated with these floods show the different nature of the basal water conduit system of the glacier during surge and non surge phases during surge conditions basal water is dispersed slowly across the bed in a distributed drainage system but when the glacier is not surging water is transported rapidly through a system of tunnels

a history of jokulhlaups from strandline lake alaska u s a les vidanges brutales du strandline lake se produisent tous les 1 a 5 ans la vidange est precedee par le developpement d un golfe de velage dans le lobe du triumvirate glacier qui barre le lac et par le remplissage de petits lacs sur le glacier on analyse le mecanisme a partir de cartes photogrammetriques dressees avant et apres la vidange

compilation of non annually resolved holocene proxy climate records stacked holocene peatland palaeo water table reconstructions from northern britain abstract the number and range of holocene palaeoclimate reconstructions from various regions of the world have increased dramatically over the last decade the data density for many regions and proxies now offers the potential of robust regional scale reconstructions that avoid the problems of records from individual sites and improve communication between palaeoclimate subdisciplines and climate modellers however there are problems with chronological uncertainties and quantification of proxies which make compilation of multiple records difficult here we explore a stacking and tuning approach to the derivation of regional records from peatland climate proxies to test its applicability to non annually resolved terrestrial records twelve individual records from northern britain based on water table reconstructions from testate amoebae analysis were divided into four regions records were detrended normalised and compared within regions to identify clear correlative events the original chronologies of the records were tuned using both these events and independent age markers the stacked record for northern britain indicates pronounced changes to wet conditions at 3600 2760 and 1600 cal yr bp with more minor changes at 3060 2050 1260 860 550 and 260 cal yr bp the main wet phases are highly correlated with mid european lake highstands wider north atlantic climate change inferred from ocean and ice core records and solar variability tuning and stacking of non annual terrestrial palaeoclimate records is a new approach to the compilation and reconciliation of individual records within coherent climatic regions and provides a tool for upscaling of palaeoclimate records for climate model data comparisons

warming of deep and abyssal water masses along the greenwich meridian on decadal time scales the weddell gyre as a heat buffer abstract the southern ocean renders a significant contribution to the global overturning system through the formation of deep and bottom waters the weddell sea is one of the most prominent regions in this respect data obtained between 1984 and 2008 from eight repeat hydrographic sections moored instruments and profiling floats in the weddell gyre on the greenwich meridian almost all of them collected with rv polarstern were used to identify variations in the weddell system fluctuations in the water mass properties were detected in the warm deep water with a temperature maximum in the 1990s and a minimum in 2005 but also significant variations occurred in the weddell sea deep and bottom waters whereas the warm deep water is dominated by decadal variations the average temperature and salinity of the whole water column is subject to a positive trend over 24 years the variations of the water mass properties are induced by variations of the inflow of circumpolar deep water at the boundary due to asymmetric wind forcing at the northern and the southern limb of the gyre variable in and outflows occur at the open boundaries internal processes redistribute heat and salt in the gyre resulting in a long term increase of the temperature and salinity in the whole water column the transfer of heat to deeper layers assigns to the weddell gyre the role of a buffer with potential impact on the global climate

density driven southern hemisphere subpolar gyres in coupled climate models 1 we investigate the representation of southern hemisphere subpolar gyres in 20 ipcc ar4 climate models the models reproduce three southern subpolar gyres the weddell gyre ross gyre and australian antarctic gyre in agreement with observations some models simulate the presence of a subpolar supergyre with strong connectivity between the three gyres the gyre strengths and structures show a great range across the models it is found that the link between the gyre strengths and wind stress curls is weak indicating that the sverdrup balance does not hold for the modelled southern subpolar gyres instead the simulated gyre strengths are mainly determined by upper layer meridional density gradients which are themselves determined predominantly by the salinity gradients these findings suggest that a correct simulation of salinity is crucial in the simulation of southern subpolar ocean circulation

a three thousand year record of north atlantic climate annual band counting on three radiometrically dated stalagmites from nw scotland provides a record of growth rate variations for the last 3000 years over the period of instrumental meteorological records we have a good historical calibration with local climate mean annual temperature mean annual precipitation regional climate north atlantic oscillation and sea surface temperature sst strongest at 65 70 n 15 20 w although the correlation with the latter breaks down prior to the instrumental record this suggests that the climatic factors that force nw scottish climate and therefore our stalagmite growth varied through time and include winter nao strength the strength of the thermohaline circulation and possibly solar output spectral analysis was performed on the stalagmite growth rate time series a spectral frequency of 50 70 years is predominant in two stalagmites that were deposited from 1000 to 3000 bp a slightly longer frequency of 72 94 years is dominant from 1000 bp to present these are the same as that observed in ocean gcm output for the north atlantic region ssts our stalagmites provide high resolution precisely dated evidence of a similar periodicity predominating over the last 3000 years in a climate proxy record known to be sensitive to changes in forcing functions relevant to the north atlantic sector

a thousand year speleothem proxy record of north atlantic climate from scotland luminescent organic matter in stalagmites may form annual bands allowing growth rate to be precisely determined stalagmite growth rate is controlled by precipitation so annual bands can be used to derive long precipitation records a continuously banded stalagmite from a cave in nw scotland was used to provide a 1100 year high resolution record of precipitation the location of the cave means that precipitation is closely linked to the north atlantic oscillation for which a record is also derived this suggests that changes in the north atlantic oscillation state was an important control on european climate over the past millennium

circumpolar influences on the weddell sea indication of an antarctic circumpolar coastal wave abstract the antarctic circumpolar wave is now a well known feature that can be detected in atmospheric oceanic mixed layer and sea ice data in this coupled ice ocean model driven by 40 yr of daily atmospheric forcing data it represents a significant part of the interannual variability linking the sea ice and water mass formation processes in the weddell sea with other areas in the antarctic water ring in addition these model results show a decadal period wavelike anomaly pattern near the coast of antarctica propagating westward at about 2 cm s 1 this coastally trapped bottom intensified phenomenon likely has important effects on the dense water formation rate in the weddell sea and even the occurrence of the weddell polynya

horizontal circulation and volume transports in the weddell gyre derived from argo float data argo floats provide both hydrographic and trajectory data affording the opportunity to investigate surface to mid depth ocean dynamics here argo float data are used to determine the absolute geostrophic velocity field of the upper 50 2000 m of the weddell gyre from which the overall circulation pattern is investigated the weddell gyre plays a pivotal role in the modification of climate by advecting heat towards the antarctic ice shelves and by modifying the water masses that feed into the lowest limb of the global ocean overturning circulation warm deep water the source water mass that delivers heat to the weddell gyre is conveniently located within the upper 2000 m domain covered by the floats we investigate its volume transport as it circulates the gyre full depth volume transports are estimated by applying a quadratic function to extrapolate the relative dynamic height field component to the full ocean depth using ctd profiles from ship based surveys to determine an extrapolation error major new insights are provided by this study there is an established double gyre structure to the circulation with a strong eastern cell and a weaker western cell regional variation of the baroclinic component of the flow field is revealed indicating a northeast to southwest reduction in the baroclinic flow along with a strong meridional gradient of baroclinic flow along the northern limb of the gyre especially east of 25 w the zonal mean gyre strength away from the shelf edge is 32 5 sv 1 sv 1 106 m3 s 1 of which 13 3 sv are associated with the advection of warm deep water there is a considerable amount of recirculation within the gyre interior where water does not traverse the full zonal extent of the gyre the recirculation is stronger in the eastern cell of the observed double gyre structure the interior circulation cells partly explain the large variations in previous gyre strength estimates we provide an extensive review of previous estimates in context of the new results obtained

on the near bottom variability in the northwestern weddell sea the thermohaline data from the first brazilian hydrographic cruise to the northwestern weddell sea ar xviii revealed significant near bottom changes in water column properties over seasonal and interannual time scales favorable ice conditions in 2000 allowed a dense station coverage of the area including the main pathways for weddell sea deep and bottom waters the new results are compared with the data from the 1998 german cruise ant xv 4 and other historical data a warming of the bottom layer was discovered that was more attributable to short term seasonal or interannual fluctuations in the formation of cold bottom water than to a long term trend there was both consistency and variation between and within seasons invariant bottom water characteristics were observed in different seasons summer winter and variable bottom water characteristics were observed in the same season summer at the same locations this reduces the possibility of a dominant seasonal effect instead we propose that the intermittent behavior of small cold water sources along the weddell sea s periphery causes the variability measured in the deep northwestern weddell sea the observed variability has consequences for the water mass export across the south scotia ridge as the absence of the fresher lighter weddell sea bottom water south of south orkney plateau during ar xviii might be linked to a reduced ventilation of the deep scotia sea the results of this study show the need for ongoing efforts for establishing a long term monitoring of this region with global importance

freshwater transport at fimbulisen antarctica 1 the intricate near circumpolar system of fronts and currents surrounding antarctica isolates much of earth s freshwater from the saline oceans immediately north the antarctic slope front sustains bathymetrically steered flow at the shelf break whereas the shallow coastal current travels rapidly alongside the ice front a hydrographic survey of the southeastern weddell sea finds these two features to have merged near the narrow 40 km wide continental shelf at fimbulisen on the prime meridian its trolltunga ice tongue overshoots the shelf break northward into this slope current observations on either side of the ice tongue demonstrate its retarding effect on the westward flowing waters it overhangs and its contribution to the poorly understood freshwater budget from oxygen isotope ratio measurements and referenced geostrophic shears we find the combined glacial meltwater and sea ice melt transport upstream of trolltunga at 0 6 e to account for 18 0 5 8 msv of the total 1 6 0 2 sv westward transport sv 106 m3 s 1 in trolltunga s lee and downstream at 2 8 w we find this figure to ultimately increase to 23 8 15 5 msv of a total 2 8 0 4 sv transport each of these sections was impeded by sea ice cover so these estimates of westward transport are probably lower limits the westward glacial ice meltwater transport of 10 3 msv at 2 8 w highlights the role that fimbulisen plays in preconditioning shelf waters before they reach broad continental shelves in the southwestern weddell sea where they transform to bottom waters

the circulation and water masses of the antarctic shelf and continental slope between 30 and 80 e abstract the circulation and water masses from the antarctic continental shelf to 62 s between 30 and 80 e are described using hydrographic data collected on seven hydrographic sections during the baseline research on oceanography krill and the environment west broke west experiment the eastern limb of the weddell gyre dominates circulation between 30 and 40 e and is significantly cooler and fresher than the region to the east the antarctic circumpolar current acc extends from the north into the survey region east of 40 e reaching as far south as 65 5 s at 60 e this results in increasing observed maximum temperature and salinities progressively towards the east peaking at 80 e due to the intrusion of the southern acc front saccf to 63 s this southward extension is steered by the southern end of kerguelen plateau causing a horizontal shear of over 0 15 m s 1 between the eastward acc and westward flowing antarctic slope current asc the asc is observed at all six meridional sections immediately north of the shelf break it is strongly barotropic and transports a total of 15 8 7 4 sv westwards while the bottom referenced baroclinic component only contributes 1 3 0 3 sv at each section this current intensifies to a narrow westward jet with absolute velocities up to 0 3 m s 1 over the steepest shelf slope gradients at 70 e a v shape is observed in the asf this and the nearby presence of denser shelf water and ice shelf water is characteristic of antarctic bottom water aabw formation but no new aabw is found on this section instead significantly warmer saltier and less oxygenated aabw to the east and newly formed aabw high on the continental slope immediately to the west suggest a formation region just west of 70 e this newly formed aabw progressively becomes warmer and saltier west of 60 e and is observed extending offshore and moving westward below eastward flowing water masses acc frontal positions are found to be 1 2 farther north in the survey region than suggested by historical climatology

dendrochronological evidence for a lower water table on peatland around 3200 3000 bc from subfossil pine in northern scotland tree ring analysis of subfossil pinus sylvestris l from nine new peatland sites located beyond the species current northern limit in scotland established a regional chronology called wrath 9 the chronology has been provisionally dated against irish pine chronologies and provides the first annual resolution picture of scots pine expansion from c 3200 bc and subsequent demise from c 3000 bc pine germination and growth is suggested to be associated with a widespread fall in bog water tables that indicates a regional climatic control bog pines progressively declined in number rather than died out in a single event reflecting their growth in a marginal habitat close to a critical ecological threshold the use of tree ring sequences from in situ bog pine macrofossils provides a higher resolution insight into past conditions than possible with existing radiocarbon and pollen based chronologies

the antarctic slope current near 30 e the antarctic slope current flows westward above the continental slope of antarctica entering the weddell sea near 30 e and supplying dense water to the deep overturning cell there and contributing to global antarctic bottom water formation observations from the 2008 i6s hydrographic section are used to investigate the strength of the slope current near 30 e a prominent topographic feature the gunnerus bank diverts the slope current upstream of this longitude and has a large effect on the current s structure splitting it into a coastal and offshore component the bank also enhances water mass mixing and lateral exchange across the slope as part of the 2008 occupation an additional line was made along the crest of the bank forming a closed volume over the western side by combining hydrographic and lowered acoustic doppler current profiler measurements in this box using an inverse method the slope current transport is estimated to be 9 6 2 3 sv the transport associated with the antarctic slope front is 4 0 0 3 sv of which 1 8 0 3 sv enters the weddell gyre as recently formed dense water

repeated cfc sections at the greenwich meridian in the weddell sea 1 repeated observations of the tracer chlorofluorocarbon 11 cfc 11 for a section along the greenwich meridian from antarctica 70 s to about 50 s are presented for the period 1984 1998 the cfc sections display a highly persistent pattern a middepth cfc minimum in the central weddell sea is bounded laterally by elevated levels of dissolved cfcs at the southern margin of the weddell basin and by a column of elevated cfc concentrations around 55 s near to the northern margin part of the latter column covers waters of the antarctic circumpolar current which indicates that a moderate portion of these waters was ventilated in the weddell sea deep cfc maxima adjoining the southern and northern margins of the weddell basin indicate advective cores of recently ventilated waters the southern core supports previous notions of deep water import into the weddell sea from the east for all deep and bottom waters the portions ventilated on the cfc timescale 50 years are small effective initial cfc saturations for these portions are estimated to be between 60 and 70 using in part new data from off the filchner ronne ice shelf for various cfc features along the section mostly advective cores ventilated fractions and mean ages of these fractions were obtained with error limits the procedure was to fit an age distribution of a prescribed form to cfc 11 time series for these features constructed from the various realizations of the cfc section the ages are between 3 and 19 years and the ventilated fractions range between 6 and 23 indicating a rather limited ventilation of the interior weddell sea subsurface layer waters on the cfc timescale it is shown that the concurrent cfc 12 data provide little additional information the work demonstrates a high information content of repeated tracer observations and encourages similar approaches also in other ocean regions

modelling the evolution of subglacial tunnels due to varying water input the time evolution ofa subglacial tunnel cross section is examined using a two dimensional finite element ice flow model coupled to an idealized drainage system simulations are driven by physically based calculations of surface water input variations at storglaciaren sweden highlights of the model are its ability to handle unsteady conditions and irregular tunnel shapes agreement between modelled water pressure and borehole water levels is good the following conclusions are reached i tunnels adapt to fluctuating inflow on time scales of days storms during which effective pressure ranges from 0 to 0 9 mpa cause significant adjustments but daily fluctuations due solely to meltwater inflow are minor ii open channel flow may become commonplace late in the ablation season iii initial tunnel shape influences subsequent tunnel evolution and seasonal water pressure variation over the course of a summer tunnels retain some of their initial shape though in all experiments the width to height ratio increased with time iv tunnel contraction forms broad low tunnels however v given two tunnels of equal initial area the higher narrower one expands more rapidly thus more semi circular tunnels may capture flow from broader neighbours early in the summer

high productivity in an ice melting hot spot at the eastern boundary of the weddell gyre 1 the southern ocean so plays a key role in modulating atmospheric co2 via physical and biological processes however over much of the so biological activity is iron limited new in situ data from the antarctic zone south of africa in a region centered at 20 e 25 e reveal a previously overlooked region of high primary production comparable in size to the northwest african upwelling region here sea ice together with enclosed icebergs is channeled by prevailing winds to the eastern boundary of the weddell gyre where a sharp transition to warmer waters causes melting this cumulative melting provides a steady source of iron fuelling an intense phytoplankton bloom that is not fully captured by monthly satellite production estimates these findings imply that future changes in sea ice cover and dynamics could have a significant effect on carbon sequestration in the so

preconditioning and formation of maud rise polynyas in a high resolution earth system model abstractopen ocean polynyas oops in the southern ocean are ice free areas within the winter ice pack that are associated with deep convection potentially contributing to the formation of antarct

on the structure and the transport of the eastern weddell gyre abstract the circulation pattern and volume transports in the eastern weddell gyre are estimated on the basis of hydrographic data collected by r v polarstern between 1989 and 1996 in the northeastern edge of the weddell gyre eastward flowing water masses from the antarctic circumpolar current and the weddell sea converge due to the strong effect of topographic constraints on ocean currents in the weakly stratified waters of high latitudes the wedge like structure of the southwest indian ridge can cause the convergence the increased shear leads to instabilities of the current at the eastern end of the ridge which produce an intense mesoscale eddy field between 15 and 30 e in the eddies water from the weddell cold regime and the antarctic circumpolar current waters mix and form the water masses of the weddell warm regime these waters are advected southward and flow towards the westward southern rim current which is driven by the antarctic eastwind band hence there is not a continous flow from the northern to the southern rim but a decay of the mean flow in the northeast and a reformation in the south volume transports across the greenwich meridian estimated on the basis of a combined ctd adcp data set result in an eastward flow of 61 sv in the northern rim current and a westward return flow of 66 sv in the southern part of the gyre the transport is about twice as high as previous estimates between kapp norvegia and the northern tip of the antarctic pensinsula indicating a significant gyre circulation north of 70 s

architectural analysis of a volcaniclastic jokulhlaup deposit southern iceland sedimentary evidence for supercritical flow the 1918 eruption of the glacially capped katla volcano southern iceland generated a violent jokulhlaup or glacial outburst flood inundating a large area of m rdalssandur the proglacial outwash plain where it deposited ca 1 km3 of volcaniclastic sediment the character of the 1918 jokulhlaup is contentious having been variously categorized as a turbulent water flow a hyperconcentrated flow or as a debris flow based on localized outcrop analysis in this study outcrop based architectural analyses of the 1918 deposits reveal the presence of lenticular and tabular bedsets associated with deposition from quasi stationary antidunes and down current migrating antidunes and from regular based bedsets associated with transient chute and pool bedforms all of which are associated with turbulent transcritical to supercritical water flow conditions antidune wavelengths range from 24 to 96 m corresponding to flow velocities of 6 to 12 m sec 1 and average flow depths of 5 to 19 m this range of calculated flow velocities is in good agreement with estimates made from eyewitness accounts architectural analysis of the 1918 jokulhlaup deposits has led to an improved estimation of flow parameters and flow hydraulics associated with the 1918 jokulhlaup that could not have been achieved through localized outcrop analysis the observations presented here provide additional sedimentological and architectural criteria for the recognition of deposits associated with transcritical and supercritical water flow conditions the physical scale of sedimentary architectures associated with the migration of bedforms is largely dependent on the magnitude of the formative flow events or processes sedimentary analyses must therefore be undertaken at the appropriate physical scale if reliable interpretations regarding modes of deposition and formative flow hydraulics are to be made

cycles and shifts 1 300 years of multi decadal temperature variability in the gulf of alaska the gulf of alaska goa is highly sensi tive to shifts in north pacific climate variability here we present an extended tree ring record of january september goa coastal surface air temperatures using tree ring width data from coniferous trees growing in the mountain ranges along the goa the reconstruction 1514 1999 based on living trees ex plains 44 of the temperature variance although as the number of chronologies decreases back in time this value decreases to and remains around 30 before 1840 verification of the calibrated models is however robust utilizing sub fossil wood we extend the goa reconstruction back to the early eighth century the goa reconstruction correlates significantly 95 cl with both the pacific decadal oscillation index 0 53 and north pacific index 0 42 and therefore likely yields important information on past climate variability in the north pacific region intervention analysis on the goa reconstruction identifies the known twentieth century climate shifts around the 1940s and 1970s al though the mid 1920s shift is only weakly expressed in the context of the full 1 300 years record the well studied 1976 shift is not unique multi taper method spectral analysis shows that the spectral properties of the living and sub fossil data are similar with both records showing significant 95 cl spectral peaks at 9 11 13 14 and 18 19 years singular spectrum analysis identifies in order of importance significant oscillatory modes at 18 7 50 4 38 0 91 8 24 4 15 3 and 14 1 years the amplitude of these modes varies through time it has been suggested minobe in geo phys res lett 26 855 858 1999 that the regime shifts during the twentieth century can be explained by the interaction between pentadecadal 50 4 years and bi decadal 18 7 years oscillatory modes removal of these two modes of variance from our goa time series does indeed remove the twentieth century shifts but many are still identified prior to the twentieth century our analysis suggests that climate variability of the goa is very complex and that much more work is required to understand the underlying oscillatory behavior that is observed in instrumental and proxy records from the north pacific region

persistent positive north atlantic oscillation mode dominated the medieval climate anomaly the medieval climate anomaly mca was the most recent pre industrial era warm interval of european climate yet its driving mechanisms remain uncertain we present here a 947 year long multidecadal north atlantic oscillation nao reconstruction and find a persistent positive nao during the mca supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker nao conditions into the little ice age lia globally distributed proxy data suggest that this nao shift is one aspect of a global mca lia climate transition that probably was coupled to prevailing la nina like conditions amplified by an intensified atlantic meridional overturning circulation during the mca

exchange of water between the ross gyre and acc assessed by lagrangian particle tracking to reach upwelling and downwelling zones deep within the southern ocean seasonal sea ice cover water masses must move across the antarctic circumpolar current and through current systems including the ross gyre weddell gyre and antarctic slope current in this study we focus our attention on the lagrangian exchange between the ross gyre and surrounding current systems we conducted numerical experiments using five day 3 d velocity fields from the southern ocean state estimate with a particle tracking package to identify pathways by which waters move from near the antarctic coastal margins or antarctic circumpolar current into the interior of the ross gyre and to identify the time scales of variability associated with these pathways waters from near the antarctic margins enter the ross gyre along the western and northern boundaries of gyre until the gyre separates from the pacific antarctic ridge near fracture zones at this juncture antarctic circumpolar current derived inflow dominates the across gyre transport up to the antarctic margin transport and exchange associated with different time average components of flow are calculated to determine the relative contributions of high and low frequency and time mean components

circumpolar structure and distribution of the antarctic circumpolar current fronts 2 variability and relationship to sea surface height 1 in part 1 of this study we showed that the antarctic circumpolar current acc consisted of multiple fronts each of which was consistently associated with a particular contour of sea surface height ssh or approximate streamline in part 2 we have used maps of ssh to examine the variability of the acc fronts between 1992 and 2007 the ssh label associated with each frontal branch is nearly constant around the circumpolar belt the front labels are also nearly constant in time the bands of enhanced ssh gradient i e fronts occur along the same streamlines throughout the 15 year period of observations both short and long period changes of the ssh frontal labels of the acc are small based on a tight relationship between dynamic height and cumulative baroclinic transport of the acc the baroclinic transport variability of the individual branches of the acc is also expected to be small the major change in the total acc baroclinic transport occurs in the drake passage the streamline associated with the northern branch of the saf saf n does not pass through drake passage and the waters carried by this branch are not observed there instead the transport of the saf n turns north in the pacific to supply the export of water to the indian ocean north and south of australia strong eddy activity in the southeast pacific acts to dissipate the hydrographic signature of the saf n there in the atlantic the saf n reappears as the same streamline is again associated with enhanced ssh gradients to the east of the brazil malvinas confluence zone while the large changes in ssh have occurred in the southern ocean between 1992 and 2007 there are strong regional differences because the acc fronts are robustly associated with particular ssh contours the changes in ssh reflect shifts in the position of the acc fronts in the circumpolar average each of the acc fronts has shifted to the south by about 60 km the changes in ssh in the southern ocean are largely due to changes in ocean circulation rather than warming and freshening by atmospheric fluxes much larger changes in ssh are observed in some locations of the southern ocean particularly where the fronts interact with large scale topography the northern branch of the pf pf n near the kerguelen plateau is an extreme example where the pf n followed a path around the northern end of kerguelen plateau between 1992 and 1997 passed through the fawn trough after 2003 and oscillated between the two paths between 1997 and 2003

seismicity crisis at the katla volcano iceland signs of a cryptodome abstract katla one of the most active and hazardous icelandic volcanoes has shown signs of unrest since 1999 in july that year a small glacial flood lasting a few hours was observed accompanied by abnormal seismicity it was probably caused by a short lived shallow magma intrusion or possibly a small subglacial eruption in 2002 seismic activity increased dramatically particularly in the go abunga area west of the caldera and earthquakes have occurred continuously ever since a network of four portable seismometers was run at katla in the spring summer 2003 with one station directly at the locus of the go abunga activity these observations are combined with the data of the permanent icelandic digital seismograph network run by the icelandic meteorological office the earthquakes at go abunga are concentrated in a small area with a diameter of 3 to 4 km and the events are shallow mainly within the uppermost 2 km we propose that the unusual pattern of seismicity indicates an intruding hot and acidic cryptodome apparently this dome has been slowly rising for decades but its propagation towards the surface accelerated some time around 1999 possibly triggered by a basaltic intrusion this may lead to a silicic dome building eruption in the go abunga area which should be taken into consideration when estimating the eruption hazard at katla

tornetrask tree ring width and density ad 500 2004 a test of climatic sensitivity and a new 1500 year reconstruction of north fennoscandian summers this paper presents updated tree ring width trw and maximum density mxd from tornetrask in northern sweden now covering the period ad 500 2004 by including data from relatively young trees for the most recent period a previously noted decline in recent mxd is eliminated non climatological growth trends in the data are removed using regional curve standardization rcs thus producing trw and mxd chronologies with preserved low frequency variability the chronologies are calibrated using local and regional instrumental climate records a bootstrapped response function analysis using regional climate data shows that tree growth is forced by april august temperatures and that the regression weights for mxd are much stronger than for trw the robustness of the reconstruction equation is verified by independent temperature data and shows that 63 64 of the instrumental inter annual variation is captured by the tree ring data this is a significant improvement compared to previously published reconstructions based on tree ring data from tornetrask a divergence phenomenon around ad 1800 expressed as an increase in trw that is not paralleled by temperature and mxd is most likely an effect of major changes in the density of the pine population at this northern tree line site the bias introduced by this trw phenomenon is assessed by producing a summer temperature reconstruction based on mxd exclusively the new data show generally higher temperature estimates than previous reconstructions based on tornetrask tree ring data the late twentieth century however is not exceptionally warm in the new record on decadal to centennial timescales periods around ad 750 1000 1400 and 1750 were equally warm or warmer the 200 year long warm period centered on ad 1000 was significantly warmer than the late twentieth century p 0 05 and is supported by other local and regional paleoclimate data the new tree ring evidence from tornetrask suggests that this medieval warm period in northern fennoscandia was much warmer than previously recognized

how iceberg calving and grounding change the circulation and hydrography in the filchner ice shelf ocean system the formation of bottom water in the southern weddell sea is strongly influenced by the flow of ice shelf water isw out of the filchner ronne ice shelf cavity the breakout of three giant icebergs in 1986 and their grounding on the shallow berkner bank modified the circulation and water mass formation in the filchner trough and the adjacent sea areas hydrographic measurements along the filchner ice shelf front carried out with rv polarstern in 1995 show significant changes in the water mass characteristics and flow patterns in the filchner trough in comparison to measurements from the early 1980s changes in the trough will affect the flow over the sill to the deep weddell abyssal plain we combine a three dimensional ocean circulation model with conductivity temperature depth and stable isotope measurements to investigate the details of the circulation in front of and beneath the filchner ice shelf we assess the impact of stranded icebergs and a more southerly ice shelf front position caused by a 1986 iceberg calving event on the circulation and observed water mass properties results indicate variations of the flow pattern in the filchner trough and on berkner bank where high salinity shelf water the feedstock for isw is produced the calving and grounding impacts illustrate the sensitivity of the ice shelf ocean system to perturbations in local bathymetric settings

recent deep water sedimentation trace metal and radioisotope geochemistry across the southern ocean and northern weddell sea antarctica abstract a wide variety of deep water depositional environments were examined across 12 sampling stations in the southern ocean and northern weddell sea antarctica in order to provide a depositional context for the benthic biodiversity studies of andeep antarctic benthic deep sea biodiversity colonisation history and recent community patterns here we present a diverse dataset comprising sub bottom profiles seabed photographs sediment profile images and box and multicore samples in order to investigate the recent depositional environments across the region the sediments were investigated using texture structure trace metal mn fe u mo ba and pb stable 206pb 207pb and radionuclide excess 210pb isotopes the sediments of the agulhas basin are interpreted as siliceous pelagites the product of enhanced surface productivity the eastern weddell continental rise is characterised by diverse depositional environments with hemipelagic turbiditic and contouritic sedimentation in contrast the northern weddell abyssal plain is dominated by hemipelagites with fine grained turbidites a single sampling station from the central powell basin contained hemipelagites and a fine grained turbidite a core from the central bransfield strait recovered hemipelagites with a silt turbidite the seabed photographs display a seabed dominated by biogenic mud balls formed by cirratulid polychaetes trace metal pb isotope and excess 210pb data all reveal the central bransfield strait to be a region of enhanced productivity with a mass accumulation rate of 0 073 g cm2 two stations in the bellingshausen sea recovered hemipelagites and turbidites mn fe and mo data suggest a degradation of organic matter in the sediments leading to redox cycling

multi centennial variability controlled by southern ocean convection in the kiel climate model a quasi oscillatory multi centennial mode of open ocean deep convection in the atlantic sector of the southern ocean in the kiel climate model is described the quasi periodic occurrence of the deep convection causes variations in regional and global surface air temperature southern hemisphere sea ice coverage southern ocean and north atlantic sea surface height the antarctic circumpolar current and the atlantic meridional overturning circulation amoc the deep convection is stimulated by a strong built up of heat at mid depth when the heat reservoir is virtually depleted a coincidental strong freshening event at the sea surface shuts down the convection the heat originates from relatively warm deep water formed in the north atlantic the several decades lasting recharge process of the heat reservoir depends on the amoc and the weddell gyre and sets a minimum delay for the deep convection to recur while the strength of the amoc increases the weddell gyre weakens during the non convective regime convection onset and shutdown also depend on the stochastic occurrence of favorable sea surface conditions which contributes to the multi centennial period of the phenomenon the shutdown triggers a century long deviation in amoc strength caused by significant reductions in bottom water formation and surface salinity in the southern ocean s atlantic sector additional numerical experimentation reveals that sea ice has an important effect on the frequency of occurrence and intensity of the deep convection further we find intriguing similarities to the weddell polynya observed during the 1970s

reconstructing holocene climate from tree rings the potential for a long chronology from the scottish highlands despite promising research in the 1980s showing the potential of scots pine pinus sylvestris l for the reconstruction of past summer temperatures in the scottish highlands little dendroclimatic work has been attempted in this region since this reflects in part the limited number of sparsely distributed remnant natural semi natural pine woodlands in the scottish highlands and the lack of old growth forest therein on average most of the pine trees dated in this region are around 225 years in age here we present the first results of an ongoing interdisciplinary initiative to develop a long scottish chronology through the acquisition of modern historical and subfossil pine material from the native pinewoods historic structures and lakes of the scottish highlands radiocarbon dating of 25 subfossil pine timbers recovered from lake sediments identified the presence of preserved material covering the last 8000 years with initial clusters focused on the last two millennia and early mid holocene alth

reconstructing 800 years of summer temperatures in scotland from tree rings this study presents a summer temperature reconstruction using scots pine tree ring chronologies for scotland allowing the placement of current regional temperature changes in a longer term context living tree chronologies were extended using subfossil samples extracted from nearshore lake sediments resulting in a composite chronology 800 years in length the north cairngorms ncairn reconstruction was developed from a set of composite blue intensity high pass and ring width low pass filtered chronologies with a range of detrending and disturbance correction procedures calibration against july august mean temperature explains 56 4 of the instrumental data variance over 1866 2009 and is well verified spatial correlations reveal strong coherence with temperatures over the british isles parts of western europe southern scandinavia and northern parts of the iberian peninsula ncairn suggests that the recent summer time warming in scotland is likely not unique when compared to multi decadal warm periods observed in the 1300s 1500s and 1730s although trends before the mid sixteenth century should be interpreted with some caution due to greater uncertainty prominent cold periods were identified from the sixteenth century until the early 1800s agreeing with the so called little ice age observed in other tree ring reconstructions from europe with the 1690s identified as the coldest decade in the record the reconstruction shows a significant cooling response 1 year following volcanic eruptions although this result is sensitive to the datasets used to identify such events in fact the extreme cold and warm years observed in ncairn appear more related to internal forcing of the summer north atlantic oscillation

a numerical model of the weddell sea large scale circulation and water mass distribution a circumpolar model for regional studies of the wind driven and thermohaline circulation of the southern ocean including the major sub ice shelf areas is described a first series of numerical experiments focusing on the weddell sea reveals a pronounced and persistent double cell structure of the weddell gyre with a maximum transport of 60 sv in agreement with observations experiments with artificial passive tracers point to the shallow shelf areas off the filchner ronne ice shelf as main locations for bottom water production the trajectories of lagrangian floats are used to determine the pathways and timescales of water mass spreading in the model in addition the effect of sub ice shelf forcing on the water mass characteristics is evaluated it is shown that water modified in the sub ice cavities contributes significantly to the deep and bottom water formation along the continental slope and affects the water mass characteristics throughout the weddell sea by increasing the stability of the near surface stratification and preventing deep convection

sea ice transports in the weddell sea time series of sea ice draft in the weddell sea are evaluated together with hydrographic observations satellite passive microwave data and ice drift for estimation of the freshwater fluxes into and out of the weddell sea ice draft is measured with moored upward looking sonars since 1990 along two transects across the weddell gyre one transect extending from the tip of the antarctic peninsula to kapp norvegia was sampled between 1990 and 1994 and covers the flow into and out of the southern weddell sea the other transect sampled since 1996 and extending from the antarctic continent northward along the greenwich meridian covers the exchange of water masses between the eastern and the western weddell sea in order to relate results obtained during the different time periods empirical relationships are established between the length of the sea ice season derived from the satellite passive microwave data and defined as the number of days per year with the sea ice concentration exceeding 15 and 1 the annual mean ice draft and 2 the annual mean ice volume transport by using these empirical relationships estimates of annual mean ice drafts and ice volume transports are derived at all mooring sites for the period february 1979 through february 1999 wind and current force a westward ice transport in the coastal areas of the eastern weddell sea and a northward ice transport in the west during the 2 year period 1991 1992 the mean ice volume export from the weddell sea is 50 19 103 m3 s 1 this freshwater export is representative for a longer term 20 year mean and exceeds the average amount of freshwater gained by precipitation and ice shelf melt by about 19 103 m3 s 1 yielding an upper bound for the formation rate of newly ventilated bottom water in the weddell sea of 2 6 sv

the transport of the weddell gyre across the prime meridian abstract current meter observations from instruments moored from 1996 to 2001 are used to determine the structure and the volume transport of the weddell gyre on the greenwich meridian the record length mean volume transport is 45 sv to the east within the northern and 56 sv to the west within the southern limb of the weddell gyre thus 11 sv must leave the gyre circulation west of the greenwich meridian and enter it east of it the deficit occurs with 8 sv mainly in the circumpolar deep water cdw warm deep water wdw layer surface waters and weddell sea deep water wsdw contribute 2 and 3 sv respectively in contrast to this 3 sv more of weddell sea bottom water wsbw flow in the northern limb to the east than in the southern limb to the west which suggests a wsbw formation rate of about 3 sv in the western weddell sea in the southern boundary of the antarctic circumpolar current acc a volume transport of 35 16 sv was found using geostrophic calculations adjusted with two measurements of the absolute velocity the large heat content of the northern limb points to an extensive heat exchange between the weddell sea and the world ocean west of the prime meridian hence the heat transport as well as the volume transport suggest that the water masses of the weddell gyre are not exclusively replaced in its eastern part but that there is a significant exchange of water masses to the west of the prime meridian

a well verified multiproxy reconstruction of the winter north atlantic oscillation index since a d 1400 abstract a new well verified multiproxy reconstruction of the winter north atlantic oscillation nao index is described that can be used to examine the variability of the nao prior to twentieth century greenhouse forcing it covers the period a d 1400 1979 and successfully verifies against independent estimates of the winter nao index from european instrumental and noninstrumental data as far back as 1500 the best validation occurs at interannual timescales and the weakest at multidecadal periods this result is a significant improvement over previous proxy based estimates which often failed to verify prior to 1850 and is related to the use of an extended reconstruction model calibration period that reduced an apparent bias in selected proxies associated with the impact of anomalous twentieth century winter nao variability on climate teleconnections over north atlantic sector land areas although twentieth century nao variability is somewhat unusual comparable periods of persistent positive phase

hydrologic and geomorphic effects of temporary ice dammed lake formation during jokulhlaups glacial outburst oods jokulhlaups occur frequently in glaciated environments and the resultant ooding causes geomorphic change and in some instances damage to local infrastructure during some jokulhlaups oodwater is stored temporarily in ice marginal locations in july 1999 a linearly rising jokulhlaup burst from solheimajokull iceland during this remarkable event subglacial oodwater pooled transiently in two relict ice dammed lake basins before draining suddenly back into solheimajokull the signi cance of such rapid formation and attendant drainage of temporary ice dammed lakes during jokulhlaups has not been addressed consequently this paper i assesses the hydrologic and geomorphic effects of temporary ice dammed lake formation caused by lake basin retro lling and ii discusses the impact and signi cance of transient retro lling under jokulhlaup conditions pre and post ood eldwork at solheimajokull enabled the impact and signi cance of lake basin retro lling to be assessed field evidence demonstrates that the july 1999 jokulhlaup had an unusually rapid rise to peak discharge resulting in subglacial oodwater being purged to ice marginal locations the propensity for temporary retro lling was controlled by rapid expulsion of oodwater from solheimajokull coincident with locations suitable for oodwater storage floodwater inundated both ice marginal lake basins permitting signi cant volumes of sediment deposition coarse grained deltas prograding from the ice margin and boulders perched on scoured bedrock provide geomorphic records of sudden retro lling the depositional characteristics of lake basin deposits at solheimajokull are similar to jokulhlaup sediments documented in proglacial settings elsewhere however their depositional setting and association with ice marginal landforms is distinctive findings suggest that temporary ice dammed lake formation and drainage has the capacity to alter the shape of the ood hydrograph especially if drainage of a temporary lake is superimposed on the original jokulhlaup deposits associated with lake basin retro lling have a long term preservation potential that could help to identify temporary ice dammed lake formation in modern and ancient glacial environments copyright 2003 john wiley sons ltd

the three dimensional overturning circulation of the southern ocean during the woce era a box inverse model of the southern ocean during the world ocean circulation experiment is constructed to investigate the three dimensional structure of the regional overturning circulation in that era the model has many features in common with various preceding inverse studies but also contains several novel elements that make it well suited for addressing many of the significant uncertainties that surround the circulation at present the net overturning circulation of the southern ocean is found to consist of two well defined cells of similar strength the upper cell consists of a northward transport of 18 8 5 5 sv of surface mode and intermediate waters lighter than the 27 5 kg m 3 isoneutral and an equivalent southward flow in the approximate 27 5 27 9 kg m 3 neutral density range encompassing the bulk of the upper circumpolar deep water the lower cell involves the northward export of 18 6 0 9 sv of antarctic bottom water and lower circumpolar deep water denser than 28 08 kg m 3 and an opposing transport in the lighter classes of that water mass substantial structural differences between the overturning circulations of the atlantic indian and pacific basins are indicated by the model s solution overall the diagnosed southern ocean circulation shares many qualitative and some quantitative features with previous inverse estimates particularly as regards the large scale depth integrated lateral circulation and associated energy fluxes in the subtropics and in the antarctic circumpolar current and the strength of the upper overturning cell however it also suggests several significant adjustments to current views of the regional circulation most notable amongst these are the subpolar circulation of the southern ocean is more vigorous and zonally interconnected than generally thought the associated lower overturning cell is more intense than indicated by most preceding estimates contrary to common perception sub surface mixing processes play a role of comparable importance to air sea ice exchanges of buoyancy in underpinning the dianeutral closure of the southern ocean overturning even at shallow mode and intermediate water levels and the connection between north atlantic deep water formation and southern ocean upwelling is fundamentally three dimensional such that deep waters from the north atlantic must upwell dianeutrally before being returned to the permanent pycnocline of the northern oceans

frequency and characteristics of glacier floods in the swiss alps damage due to glacier floods in the swiss alps occurs about once every two years at present despite the pronounced retreat of glaciers during the twentieth century and the installation of many water reservoirs which act as flood retention basins over half 60 to 70 of the observed floods are caused by outbursts of marginal glacier lakes or sudden breaks of ice dams and 30 to 40 by ruptures of water pockets in a glacierized mountain region as densely populated as the swiss alps even debris flows triggered by outbursts of very small water masses may be dangerous historical information about glacier floods in the swiss alps although incomplete and heterogeneous is used as an empirical basis for an attempt to recognize potential hazards at an early stage by considering outburst processes volumes of water involved potential peak discharge values lithology and inclination within the reach of glacier streams

response of southern ocean circulation to global warming may enhance basal ice shelf melting around antarctica we investigate the large scale oceanic features determining the future ice shelf ocean interaction by analyzing global warming experiments in a coarse resolution climate model with a comprehensive ocean component heat and freshwater fluxes from basal ice shelf melting ism are parameterized following beckmann and goosse ocean model 5 2 157 170 2003 melting sensitivities to the oceanic temperature outside of the ice shelf cavities are varied from linear to quadratic holland et al in j clim 21 2008 in 1 per year co2 increase experiments the total freshwater flux from ism triples to 0 09 sv in the linear case and more than quadruples to 0 15 sv in the quadratic case after 140 years at which 4 280 ppm 1 120 ppm was reached due to the long response time of subsurface temperature anomalies ism thereafter increases drastically if co2 concentrations are kept constant at 1 120 ppm varying strength of the antarctic circumpolar current acc is crucial for ism increase because southward advection of heat dominates the warming along the antarctic coast on centennial timescales the acc accelerates due to deep ocean warming north of the current caused by mixing of heat along isopycnals in the southern ocean so outcropping regions in contrast to previous studies we find an initial weakening of the acc during the first 150 years of warming this purely baroclinic effect is due to a freshening in the so which is consistent with present observations comparison with simulations with diagnosed ism but without its influence on the ocean circulation reveal a number of ism related feedbacks of which a negative ism feedback due to the ism related local oceanic cooling is the dominant one

modeling giant iceberg drift under the influence of sea ice in the weddell sea antarctica the drift trajectory of giant iceberg c 7 traversing the weddell sea antarctica for 2 years was successfully simulated application of the classical driving forces like wind and ocean currents resulted in a significant discrepancy between modeled and observed iceberg velocities in the western weddell sea the most realistic drift pattern in space and time was achieved by adding a sea ice force which represents the ability of a dense sea ice cover 90 to lock in icebergs and collect the momentum of the wind over an area much larger than the area of the iceberg proper this process was parameterized using a sea ice strength p which depends on sea ice concentration and thickness both having highest values in winter and in the western weddell sea which is covered with multi year sea ice as a consequence of the sensitivity to sea ice the timing of the iceberg drift becomes important revealing the region off brunt ice shelf eastern weddell sea as a location where bergs either continue westward with the coastal current or follow a southern branch onto the shallow continental shelf

fronts transport and weddell gyre at 30 e between africa and antarctica a detailed description of the frontal structure of major currents and estimates of transport between africa and antarctica at 30 e were made on the basis of a finely resolved hydrographic section made during the 1996 civa 2 cruise particular emphasis was put on a refinement of the eastern boundary of the weddell gyre by analyzing also supplementary hydrographic data from the 1993 civa 1 cruise and the best available historical hydrographic data in the weddell and enderby basins contrary to the general belief our results show that the weddell gyre extends far beyond 30 e reaching at least as far east as the enderby land promontory 53 e from this point westward currents along the antarctic continental margin constitute the gyre s southern boundary thus closing the cyclonic circulation of the gyre at its easternmost end as the most convincing evidence for this refined circulation scheme significant westward transport south of 65 s has been identified from the civa 1 acoustic doppler current profiler data we have shown also using an inertial jet model that the blocked feature of the weddell cold regime 57 s to the west of 25 e is due to the topographic control of flow by local bathymetry during the civa 2 cruise 70 of the antarctic circumpolar current acc was concentrated near the polar front 51 s with surface speeds reaching up to 70 cm s 1 the baroclinic current field in the subpolar area south of the weddell front 58 s for civa 2 and 57 s for civa 1 is featureless 3 cm s 1 but yielding a nonnegligible eastward transport of 15 sv 1 sv 106 m3 s 1 this bottom referenced baroclinic transport is entirely compensated by a substantial westward barotropic transport south of 65 s the acc transport across the 30 e section during the civa 2 cruise is estimated to be 160 sv

formation and spreading of antarctic deep and bottom waters inferred from a chlorofluorocarbon cfc simulation 1 the formation of deep and bottom waters along antarctica s perimeter is determined by ocean interaction with the atmosphere sea ice ice shelves and bottom topography it initiates a chain of processes that contribute to the ventilation of the global abyss to identify the formation sites and investigate the combined effects of the local forcing mechanisms on water mass transformation and spreading in the southern ocean chlorofluorocarbon cfc simulations with the regional ocean circulation model brios 1 were performed the model uses terrain following vertical coordinates to better represent both near bottom and mixed layer processes and includes an explicit formulation of the ice shelf ocean interaction in agreement with observations the results show the main deep and bottom water formations sites to be located in the ross sea prydz bay and southwestern weddell sea the ross sea ventilates the south east pacific and australian antarctic basins both ross sea and prydz bay ventilate via the antarctic coastal current the weddell enderby basin the latter signal is overprinted by sources in the weddell sea which ventilate the south scotia sea and also the weddell enderby basin despite the general agreement between observed and simulated quantities like bottom layer cfc distribution and inventories along the greenwich meridian the model tends to underestimate the ventilation of the abyssal ocean like other models with coarse resolution

evidence of a southward eddy corridor in the south west indian ocean mesoscale eddies and meanders have been shown to be one of the dominant sources of flow variability in the world s ocean one example of an isolated eddy hotspot is the south west indian ridge swir several investigations have shown that the swir and the corresponding planetary potential vorticity field f h exert a strong influence on the location and dynamics of the antarctic circumpolar current acc resulting in substantial fragmentation of the jets downstream of the ridge the easterly extension of this eddy corridor appears to be restricted to the deep channel separating the conrad rise from the del cano and crozet plateau however while the fate of eddies formed at the swir has been widely investigated and the frontal character of this eastward extension is well known the zone of diminishing variability that extends southwards to approximately 60 s remains poorly sampled using a combination of argo aviso and ncep ncar datasets the character of this eddy corridor as a conduit for warm core eddies to move across the acc into the antarctic zone is investigated in this study we track a single warm core eddy as it moves southwards from an original position of 31 e 50 20 s to where it dissipates 10 months later in the enderby basin at 56 20 s an argo float entrained within the eddy confirms that its water masses are consistent with water found within the antarctic polar frontal zone north of the apf latent and sensible heat fluxes are on average 8w m2 and 10w m2 greater over the eddy than directly east of this feature it is estimated that the eddy lost an average of 5w m2 of latent heat and 5w m2 of sensible heat over a 1 year period an amount capable of melting approximately 0 92m of sea ice in addition using an eddy tracking algorithm a total of 28 eddies are identified propagating southwards 25 of which are anti cyclonic in rotation based on the new argo float data combined with aviso and ncep ncar datasets these results suggest that the southward passage of warm core eddies act as vehicles transporting heat salt and biota southwards across the acc and into the eastern boundary of the weddell gyre

the role of tides in ocean ice shelf interactions in the southwestern weddell sea near observed weddell sea gyre continental shelf cavity water masses in interactive ocean sea ice tide ice shelf melt simulations tides amplify basal melt refreeze pattern raising net melt by 50 associated with enhanced time varying kinetic energy at the ice base impacts of additional meltwater production on weddell continental shelf sea ice and newly formed bottom water properties are suggested corresponding author u hausmann uhausc at gmail dot com this article has been accepted for publication and undergone full peer review but has not been through the copyediting typesetting pagination and proofreading process which may lead to differences between this version and the version of record please cite this article as

historical storminess and climate see saws in the north atlantic region the existence of a well defined climate see saw across the north atlantic region and surrounding areas has been known for over 200 years the occurrence of severe winters in western greenland frequently coincides with mild winters in northern europe conversely mild winters in western greenland are frequently associated with cold winters across northern europe whereas this see saw is normally discussed in terms of air temperature and pressure differences here we explore how the climate see saw is reflected in records of historic storminess from scotland nw ireland and iceland it is concluded that the stormiest winters in these regions during the last ca 150 years have occurred when western greenland temperatures have been significantly below average in contrast winters of reduced storminess have coincided with winters when air temperatures have been significantly above average in western greenland this reconstruction of winter storminess implies a relationship between chronologies of coastal erosion and the history of north atlantic climate see saw dynamics with sustained winter storminess and hence increased coastal erosion taking place when the icelandic low pressure cell is strongly anchored within the circulation of the northern hemisphere considered over the last ca 2000 years it would appear that winter storminess and climate driven coastal erosion was at a minimum during the medieval warm period by contrast the time interval from ca ad 1420 until present has been associated with sustained winter storminess across the north atlantic that has resulted in accelerated coastal erosion and sand drift d 2004 elsevier b v all rights reserved

carbon dynamics of the weddell gyre southern ocean the accumulation of carbon within the weddell gyre and its exchanges across the gyre boundaries are investigated with three recent full depth oceanographic sections enclosing this climatically important region the combination of carbon measurements with ocean circulation transport estimates from a box inverse analysis reveal that deep water transports associated with warm deep water wdw and weddell sea deep water dominate the gyre s carbon budget while a dual cell vertical overturning circulation leads to both upwelling and the delivery of large quantities of carbon to the deep ocean historical sea surface pco2 observations interpolated using a neural network technique confirm the net summertime sink of 0 044 to 0 058 0 010 pg c yr 1 derived from the inversion however a wintertime outgassing signal similar in size results in a statistically insignificant annual air to sea co2 flux of 0 002 0 007 pg c yr 1 mean 1998 2011 to 0 012 0 024 pg c yr 1 mean 2008 2010 to be diagnosed for the weddell gyre a surface layer carbon balance independently derived from in situ biogeochemical measurements reveals that freshwater inputs and biological drawdown decrease surface ocean inorganic carbon levels more than they are increased by wdw entrainment resulting in an estimated annual carbon sink of 0 033 0 021 pg c yr 1 although relatively less efficient for carbon uptake than the global oceans the summertime weddell gyre suppresses the winter outgassing signal while its biological pump and deep water formation act as key conduits for transporting natural and anthropogenic carbon to the deep ocean where they can reside for long timescales

a comparison of two recent jokulhlaups from an ice dammed lake sondre stromfjord west greenland the hydro graphs of two jokulhl aups resulting from the sudden drainage of an ice d ammed lake in west greenland in 1984 and 1987 are compared the first flood had a similar peak discharge to the second but drained only two thi rds of the total volume of the 1987 event which amounted to 32 36 x 106 m3 in 36 h calcula tions based on the lake refill time suggest that it drains every 2 3 years but that peak flows may be variable from flood to flood the timing of the joku lhlaups in relation to the melt season may reflect variations of water pressure within the subglacial drainage networks and changes in the

shallow remineralization in the weddell gyre 1 the region influenced by the polar front in the southern ocean is characterized by relatively high productivity which is mirrored in strong depletions of 234th in the surface water a good tracer of export production and by high accumulation rates on the underlying seabed farther south the weddell sea is generally considered a low productivity region with very low export fluxes this finding is based on satellite observations sediment accumulation rates trap deployments and phytoplankton distribution if this would be true 234th should be close to equilibrium with its parent however in a series of high resolution transects of 234th 238u across the antarctic circumpolar current acc 234th was found to be depleted by 10 15 throughout the clear weddell gyre only to reach equilibrium in sea ice covered regions of the coastal zone vertical profiles showed that the depletion was limited to the upper mixed layer and was balanced by an enrichment of similar magnitude at 100 250m depth this implies that the export of particles below 250 m is negligible such shallow remineralization is in line with the discrepancies between biogenic silica production rates and sediment trap data observed in the weddell and ross seas these observations in the weddell sea are fully consistent with our inverse modeling results for both organic carbon and opal and they are not inconsistent with tco2 and oxygen sections that show a tco2 enriched oxygen reduced shallow subsurface layer this blue ocean characterized by upwelling of co2 enriched deep waters supports sufficient productivity to be a net sink for co2 to abyssal depths hoppema et al 1999 no record of this productivity and export is stored in the underlying sediment which has important palaeoceanographic consequences

the contribution of the weddell gyre to the lower limb of the global overturning circulation the horizontal and vertical circulation of the weddell gyre is diagnosed using a box inverse model constructed with recent hydrographic sections and including mobile sea ice and eddy transports the gyre is found to convey 42 8 sv 1 sv 106 m3 s 1 across the central weddell sea and to intensify to 54 15 sv further offshore this circulation injects 36 13 tw of heat from the antarctic circumpolar current to the gyre and exports 51 23 msv of freshwater including 13 1 msv as sea ice to the mid latitude southern ocean the gyre s overturning circulation has an asymmetric double cell structure in which 13 4 sv of circumpolar deep water cdw and relatively light antarctic bottom water aabw are transformed into upper ocean water masses by mid gyre upwelling at a rate of 2 2 sv and into denser aabw by downwelling focussed at the western boundary 8 2 sv the gyre circulation exhibits a substantial throughflow component by which cdw and aabw enter the gyre from the indian sector undergo ventilation and densification within the gyre and are exported to the south atlantic across the gyre s northern rim the relatively modest net production of aabw in the weddell gyre 6 2 sv suggests that the gyre s prominence in the closure of the lower limb of global oceanic overturning stems largely from the recycling and equatorward export of indian sourced aabw

contourite deposits in the central scotia sea the importance of the antarctic circumpolar current and the weddell gyre flows abstract new swath bathymetry with multichannel and high resolution seismic profiles shows a variety of contourite drift sediment wave morphologies and seismic facies in the central scotia sea the deposits are to be found at the confluence between the two most important bottom current flows in the southern ocean the eastward flowing antarctic circumpolar current acc and the northward outflow of the weddell sea deep water wsdw the contourite drifts are wedge like deposits up to 1 km thick that exhibit aggradational reflectors along axis thinning towards the margins the contourite drifts occur in areas of weaker flows along the margins of contourite channels and in areas protected by obstacles the elongate mounded drifts are best developed along the left hand margins of channelized bottom current flows due to the coriolis force a contourite fan has a main channel and two distributary channels that expand over a gentle seafloor the proximal fan exhibits sediment waves with the distal fan incised by furrows sediment wave fields are well developed in areas of intensified bottom flows without channels particularly at the confluence of the acc and the wsdw small sediment waves occur where unidirectional bottom current flows predominate sediment waves may develop under the influence of internal waves produced by the interaction of the flows and sea bottom relief the stratigraphic sequence above the oceanic crust of early to middle miocene age contains six seismic units separated by major reflectors all the units were shaped under the influence of strong bottom current flows although they exhibit distinct seismic facies changes that record the variations of the bottom current pathways over time the age of the units was calculated based on the age of the oceanic crust and sedimentation rates of deep sea deposits in the region the oldest units vi iv are of early to middle miocene age and developed under the influence of the acc they are characterized by a southward progradational pattern of the seismic units and sedimentation rates of 5 8 cm ky unit iii with an estimated middle miocene age evidences the first incursion of wsdw into the central scotia sea when plate movement caused openings in the south scotia ridge and allowed the connection with the northern weddell sea through jane basin and gaps in the ridge unit ii estimated to be of late miocene to early pliocene age extends over the area and is characterized by internal unconformities a major unconformity at the base of unit ii records an important reorganization of bottom current flows that may predate the onset of grounded ice sheets on the antarctic peninsula shelf unit i of late pliocene to quaternary age shows intensified bottom currents the unconformity at the base of unit i probably predates the onset of major northern hemisphere glaciations and the greater expansion of antarctic ice sheets during the late pliocene the extensive distribution of contourite deposits above the oceanic crust testifies to the long term production of antarctic bottom water cold deep water was swept northward from the weddell gyre interacting with the acc and possibly exerting profound influences on the global circulation system and the onset of major glaciations

summer temperatures in the canadian rockies during the last millennium a revised record we present a significant update to a millennial summer temperature reconstruction 1073 1983 that was originally published in 1997 utilising new tree ring data predominantly picea engelmannii the reconstruction is not only better replicated but has been extended 950 1994 and is now more regionally representative calibration and verification statistics were improved with the new model explaining 53 of may august maximum temperature variation compared to the original 39 of april august mean temperatures the maximum latewood density data which are weighted more strongly in the regression model than ringwidth were processed using regional curve standardisation to capture potential centennial to millennial scale variability the reconstruction shows warm intervals comparable to twentieth century values for the first half of the eleventh century the late 1300s and early 1400s the bulk of the record however is below the 1901 1980 normals with prolonged cool periods from 1200 to 1350 and from 1450 to the late 19th century the most extreme cool period is observed to be in the 1690s these reconstructed cool periods compare well with known regional records of glacier advances between 1150 and the 1300s possibly in the early 1500s early 1700s and 1800s evidence is also presented of the influence of solar activity and volcanic events on summer temperature in the canadian rockies over the last 1 000 years although this reconstruction is regional in scope it compares well at multi decadal to centennial scales with northern hemisphere temperature proxies and at millennial scales with reconstructions that were also processed to capture longer timescale variability this coherence suggests that this series is globally important for the assessment of natural temperature variability over the last 1 000 years

seasonal cycle of hydrography on the eastern shelf of the filchner trough weddell sea antarctica new two year long records from three moorings located at 76 s along the eastern flank and shelf of the filchner trough give insight in the seasonal cycle of hydrography to a region where modified warm deep water mwdw enters the southern weddell sea continental shelf possibly reaching the filchner ronne ice shelf the biggest ice shelf by volume in antarctica a persistent northward flow of ice shelf water isw is found along the slope of the trough at 600 m depth while the data on the shelf indicate a seasonal cycle characterized by four phases a distinct warm inflow period separated in two phases with maximum temperatures of 1 c appears to be related to the seasonal heaving of the antarctic slope front thermocline along the continental shelf break further north and a seasonal extension of the isw layer onto the eastern shelf the density gradients between the isw in the trough and the mwdw on the adjacent shelf drive the southward flow during these phases a flow reversal is found in winter ceasing the southward flow along the eastern flank of the trough weaker density gradients between the trough and the shelf during winter allow a westward flow partly driven by a n s density gradient existing across the eastern shelf during this time from spring through to summer the isw layer in the trough extends onto the eastern shelf where it occupies the bottom layer at our moorings and it is associated with northward flow

temperature sensitive tien shan tree ring chronologies show multi centennial growth trends two millennia length juniper ring width chronologies processed to preserve multi centennial growth trends are presented for the alai range of the western tien shan in kirghizia the chronologies average the information from seven near timberline sampling sites and likely reflect summer temperature variation for comparison chronologies are also built using standard dendrochronological techniques we briefly discuss some qualities of these inter decadal records and show the low frequency components removed by the standardization process include a long term negative trend in the first half of the last millennium and a long term positive trend since about ad 1800 the multi centennial scale alai range chronologies where these trends are retained are both systematically biased but in an opposite sense in their low frequency domains nevertheless they represent the best constraints and estimates of long term summer temperature variation and reflect the medieval warm period the little ice age and a period of warming since about the middle of the nineteenth century

lithofacies variations within sandur deposits the role of runoff regime flow dynamics and sediment supply characteristics abstract the icelandic sandur plains have for long acted as classic sites for models of braided river behaviour and of associated lithofacies assemblages however many of the icelandic sandurs are subject to repeated catastrophic flood events or jokulhlaups which are likely to have played a significant role in sandur construction established lithofacies models based on the icelandic sandurs have failed to take account of the varying runoff regimes which characterise the different sandur environments in addition sediment inputs to sandur channel systems are highly variable fluctuating in response both to varying runoff patterns and to advance and retreat of the source glacier that affect sediment availability within the proglacial zone this paper describes the main lithofacies types and vertical profiles that characterize the sandurs of south iceland and demonstrates that they can largely be attributed to extreme runoff events with few deposits typical of braided river facies occurring within the sedimentary record a preliminary qualitative model is developed that allows interpretation and prediction of vertical lithofacies profiles derived from glacial outwash in terms of i the drainage mechanism which in turn controls the dominant runoff population ii sediment availability and iii the spatial variability in flow dynamics

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

the fate of the southern weddell sea continental shelf in a warming climate abstractwarm water of open ocean origin on the continental shelf of the amundsen and bellingshausen seas causes the highest basal melt rates reported for antarctic ice shelves with severe consequences for the ice shelf ice sheet dynamics ice shelves fringing the broad continental shelf in the weddell and ross seas melt at rates orders of magnitude smaller however simulations using coupled ice ocean models forced with the atmospheric output of the hadcm3 sres a1b scenario run co2 concentration in the atmosphere reaches 700 ppmv by the year 2100 and stays at that level for an additional 100 years show that the circulation in the southern weddell sea changes during the twenty first century derivatives of circumpolar deep water are directed southward underneath the filchner ronne ice shelf warming the cavity and dramatically increasing basal melting to find out whether the open ocean will always continue to power the melting the authors extend their simulations applying twentieth century atmospheric

integrated hydrologic and hydrochemical observations of hidden creek lake jokulhlaups kennicott glacier alaska 1 hidden creek lake hcl an ice marginal lake impounded by kennicott glacier wrangell mountains alaska fills annually to 20 to 30 106 m3 and then drains subglacially within 2 to 3 days during the 1999 and 2000 jokulhlaups we carried out a series of planned observations around the lake and in the kennicott river which drains the glacier approximately 20 of the lake volume was contained within a subglacial water wedge beneath the ice dam the entire volume of the lake drains through the wedge hydraulic head loss through this constriction may be responsible for the fairly symmetrical shape of the hcl outflow hydrographs deduced from lake level records basin hypsometry and collapse of the ice dam the flood hydrographs in the kennicott river are similar in shape to the outflow hydrographs and within error lake volume matched the river flood volume in both years up to 12 106 m3 of water was temporarily stored within the glacier during the 2000 jokulhlaup during the 2000 jokulhlaup the background flow in the kennicott river shifted to a dilute chemical composition as the hcl jokulhlaup progressed donoho falls lake filled with water whose chemistry was closer to that of the background flow in kennicott river than to hcl water comparison of these chemical signals with typical summer variations in kennicott river chemistry suggests that the jokulhlaup created high subglacial water pressure that impeded normal drainage of solute rich water from a distributed drainage system into a conduit system at the glacier bed and even caused flow direction locally to reverse

scotia sea regional tectonic evolution implications for mantle flow and palaeocirculation abstract the scotia sea and surrounding scotia arc have evolved over the past 40 ma by extension behind an east migrating subduction zone at the boundary between the south american sam and antarctic ant plates the considerable data set now available regional geology and geophysics earthquake seismology satellite altimetry global plate analyses suggest why east migrating subduction began what has been the driving force that has sustained it and what other processes have controlled the mode of back arc extension in the scotia sea a suite of six reconstructions has been developed based on this data set the reconstruction to 40 ma creates a compact cuspate continental connection between south america and the antarctic peninsula at the subducting pacific margin with fragments now dispersed around the scotia arc occupying positions within it compatible with their known geology the driving force has been subduction of south american ocean floor which began as a result of southward migration of the pole of south american antarctic plate rotation and a key modulator of back arc extension has been collision of ridge crest sections of the south american antarctic plate boundary with the east advancing trench cenozoic regional tectonic evolution has two other likely consequences which greatly increase its importance firstly this region saw the tectonic disruption of the final barrier to complete circum antarctic deep water flow that may have had a profound effect on palaeoclimate secondly it is possible that the rapid roll back of the hinge of subduction is related to shallow eastward flow in the sub lithospheric mantle both of these consequences are explored the reconstructions show that rapid roll back of the subduction hinge averaging 50 mm a over the last 40 ma with respect to the south american plate has been a feature of all of scotia sea evolution and provide a history of motion of several oceanic microplates most of which are now welded together within the scotia sea this will guide the location of seismometers and or dredge hauls to test the hypothesis of shallow mantle flow and help interpret the results the reconstructions also allow an assessment of the creation of deep water pathways that would have permitted the development of the present day antarctic circumpolar current acc an early miocene onset within the period 22 17 ma seems likely for the acc depending on the structure and palaeo elevation of davis bank and aurora bank sections of the north scotia ridge however the study shows there was a delay of one or more million years between initial provision of a deep water pathway and the major mid miocene change in global climate involving the general level of antarctic glaciation that may have been related if these changes were related then the delay suggests that other factors possibly rough elevated ocean floor but also non tectonic factors such as atmospheric co2 were important in determining palaeoclimate

volcanic cooling signal in tree ring temperature records for the past millennium the authors acknowledge the national science foundation for funding much of the research presented herein rw s scottish work is currently funded through the uk leverhulme trust and natural environment research council nerc projects relic reconstructing 8000 years of environmental and landscape change in the cairngorms f 00 268 bg and scot2k reconstructing 2000 years of scottish climate from tree rings ne k003097 1

an unusual jokulhlaup resulting from subglacial volcanism solheimajokull iceland jokulhlaups glacial outburst floods are frequent in glaciated terrain jokulhlaups exhibiting a sudden rise to peak discharge have not been subject to detailed investigation a volcanically generated flood burst from solheimajokull iceland in july 1999 this paper accounts for the causes characteristics and impacts of this flood pre and post flood fieldwork was carried out at solheimajokull allowing the reconstruction of mean flow velocities and peak discharge flood onset was rapid rising to a peak discharge of 4 4 x 103 m3s 1 1 2 x 103 m3s 1 within one hour high basal water pressures resulted in floodwater bursting through the glacier surface ice rip up clasts containing glacial diamict provided evidence of floodwater contact with the glacier bed within the glacier jokulhlaup sedimentation occurred within hydrofractures and conduits generating complex hydrofracture fills and esker ridges in the proglacial zone regions of flow expansion associated with rapid reductions in sediment transport capacity controlled the locations of major jokulhlaup sedimentation a large fan composed of material of up to boulder size was deposited at the glacier snout two ice marginal basins filled and drained during the jokulhlaup one of the basins jokulsargil emptied rapidly during the flood via ice dam flotation accentuating peak jokulhlaup discharge high rates of downstream peak discharge attenuation during the july 1999 jokulhlaup provides an analogy with flash flood hydrographs in semi arid regions and the catastrophic failure of man made dams the july 1999 jokulhlaup was initially triggered by the subglacial volcanic eruption but the characteristics of the flood were accentuated by within event meltwater storage and release this unusual jokulhlaup provides an important addition to our understanding of the spectrum of distinctive jokulhlaup characteristics

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

a 1052 year tree ring proxy for alpine summer temperatures a june august alpine temperature proxy series is developed back to ad 951 using 1 527 ring width measurements from living trees and relict wood the reconstruction is composed of larch data from four alpine valleys in switzerland and pine data from the western austrian alps these regions are situated in high elevation alpine environments where a spatially homogenous summer temperature signal exists in an attempt to capture the full frequency range of summer temperatures over the past millennium from inter annual to multi centennial scales the regional curve standardization technique is applied to the ring width measurements correlations of 0 65 and 0 86 after decadal smoothing with high elevation meteorological stations since 1864 indicate an optimal response of the rcs chronology to june august mean temperatures the proxy record reveals warm conditions from before ad 1000 into the thirteenth century followed by a prolonged cool period reaching minimum values in the 1820s and a warming trend into the twentieth century this latter trend and the higher frequency variations compare well with the actual high elevation temperature record the new central alpine proxy suggests that summer temperatures during the last decade are unprecedented over the past millennium it also reveals significant similarities at inter decadal to multi centennial frequencies with large scale temperature reconstructions however deviating during certain periods from h h lamb s european north atlantic temperature history

summer temperature variations in the european alps a d 755 2004 abstract annually resolved summer temperatures for the european alps are described the reconstruction covers the a d 755 2004 period and is based on 180 recent and historic larch larix decidua mill density series the regional curve standardization method was applied to preserve interannual to multicentennial variations in this high elevation proxy dataset instrumental measurements from high low elevation grid boxes back to 1818 1760 reveal strongest growth response to current year june september mean temperatures the reconstruction correlates at 0 7 with high elevation temperatures back to 1818 with a greater signal in the higher frequency domain r 0 8 low elevation instrumental data back to 1760 agree with the reconstruction s interannual variation although a decoupling between warmer instrumental and cooler proxy data before 1840 is noted this offset is larger than during any period of overlap with more recent high elevation instrumental data even though the proxy time series

on the transport variability and origin of dense water masses crossing the south scotia ridge abstract the deep scotia sea is filled with ventilated weddell sea deep water this in turn is an essential contributor to the ventilation of the world ocean abyss depending on the formation process and or its location along the weddell sea periphery deep and bottom water masses follow different routes to cross the south scotia ridge a primitive equation hydrostatic terrain following coordinate ocean general circulation model brios 1 is used to investigate the water mass export from the weddell sea the model is circumpolar focusing on the weddell sea with particularly high resolution 20 km in the dovetail area eastward weddell sea deep water transport of 24 106 m3 s 1 is found in the northern limb of the weddell gyre across 44 w export rates of weddell sea deep water through gaps in the south scotia ridge are estimated to be 6 4 106 m3 s 1 with a semi annual cycle of 0 6 106 m3 s 1 which can be correlated to atmospheric cyclone activity and weddell gyre strength sensitivity studies considering extreme sea ice conditions in the weddell sea show higher lower exports in years of minimum maximum winter sea ice extent lagrangian particle trajectories illustrate the pathways of water masses from the inner weddell sea into the scotia sea through various gaps in the south scotia ridge they highlight the existing flow divergence on the northwestern continental shelf with one branch entering bransfield strait and the other continuing eastwards subsequently filling the deep weddell and scotia seas water masses flowing through the major gaps originate from the southwestern and southeastern weddell sea continental shelves however water masses formed east of the weddell sea e g prydz bay also seem to feed the deep scotia sea since a large portion of floats flowing northward through the gaps of the south scotia ridge have been in contact with the mixed layer processes outside the inner weddell sea

late holocene pinewoods persistence in the gredos mountains central spain inferred from extensive megafossil evidence macro and megafossil studies are of great value in palaeoecology because such evidence is spatially precise directly radiocarbon dated and usually taxon specific here we present new macro and megafossil data from ten sites from the gredos mountains central iberian peninsula that suggest persistent forest cover through the late holocene with a widespread belt of pinewoods in the highlands of the central iberian mountains well preserved pine cones found at several sites revealed that both pinus sylvestris and pinus nigra were present in the area during the middle and late holocene at locations of important biogeographical interest the p sylvestris forests represent one of the southernmost locations of its entire range p nigra was not known to have occurred in central spain during the holocene it was found at the westernmost edge of its range in siliceous soils a rare environment compared with the rest of its distribution finally we explored the potential for obtaining a long pine chronology from central iberia using tree ring measurements and radiocarbon dating of pine subfossil logs

the late holocene kauri chronology assessing the potential of a 4500 year record for palaeoclimate reconstruction abstract millennial and multi millennial tree ring chronologies can provide useful proxy records of past climate giving insight into a more complete range of natural climate variability prior to the 20th century since the 1980s a multi millennial tree ring chronology has been developed from kauri agathis australis from the upper north island new zealand previous work has demonstrated the sensitivity of kauri to the el nino southern oscillation enso here we present recent additions and extensions to the late holocene kauri chronology lhkc and assess the potential of a composite master chronology agauc13 for palaeoclimate reconstruction the updated composite kauri chronology now spans 4491 years 2488 bce 2002 ce and includes data from 18 modern sites 25 archaeological sites and 18 sub fossil swamp kauri sites consideration of the composition and statistical quality of agauc13 suggests the lhkc has utility for palaeoclimate reconstruction but there are caveats these include a differences in character between the three assemblages including growth rate and sensitivity b low sample depth and low statistical quality in the 10th 13th century ce when the record transitions from modern and archaeological material to the swamp kauri c a potential difference in amplitude of the signal in the swamp kauri d a westerly bias in site distribution prior to 911 ce e variable statistical quality across the entire record associated with variable replication and f complex changes in sample depth and tree age and size which may influence centennial scale trends in the data further tree ring data are required to improve statistical quality particularly in the first half of the second millennium ce

actinium 227 as a deep sea tracer sources distribution and applications abstractactinium is one of the rarest naturally occurring elements on earth we measured its longest lived isotope 227ac half life 21 77 years for the first time in the water column of the southeast pacific the central arctic the antarctic circumpolar current acc and the weddell gyre besides the profile in the southeast pacific which confirms earlier findings about the role of diapycnal mixing for 227ac distribution we found three other different types of vertical profiles these profiles point to a prominent role of advection for 227ac distribution especially in the southern ocean depending on the type of profile found 227ac is proposed as a tracer for different oceanographic questions in the southern ocean up to 4 93 0 32 dpm m 3 227acex 227ac in excess of its progenitor 231pa are found close to the sea floor which are the highest concentrations ever observed in the ocean close to the sea surface in the weddell gyre wg 0 46 0 05 dpm m 3 227acex are detected we use 227acex there to determine the upwelling velocity in the eastern weddell gyre to be about 55 m y 1 in the acc upper and lower circumpolar deep water ucdw and lcdw are found to differ clearly in their 227acex activity high 227acex activities are therefore a promising tracer for recent inputs of lcdw to the sea surface which may help to understand the role of deep upwelling for iron inputs into antarctic surface waters the expected release of 227ac is compared with 228ra to make sure that the large near surface excess in the water column of the southern ocean is not due to lateral inputs by isopycnal mixing results of a model indicate that the 227ac 228ra flux ratio is about 50 times lower on shelves than in the deep sea data from the central arctic and from a transect across the acc confirm that 228ra and 227acex differ strongly in their sources the first measurements of 227ac on suspended matter less than 1 7 of total 227ac close to the sea floor indicate that the particle reactivity of 227ac is negligible in the open ocean in agreement with earlier findings nozaki 1984 despite the extremely low concentrations of 227ac new measurement techniques moore and arnold 1996 point to a comfortable and comparably simple determination of 227ac in the future finally 227acex may become a widely used deep sea specific tracer

a 7500 year peat based palaeoclimatic reconstruction and evidence for an 1100 year cyclicity in bog surface wetness from temple hill moss pentland hills southeast scotland analyses of plant macrofossils peat humification and testate amoebae were used to reconstruct a proxy climate record spanning the last 7500 years from an ombrotrophic bog temple hill moss in southeast scotland the plant macrofossil data were subjected to detrended correspondence analysis dca which modelled effectively the significant wet shifts within the record a mean water table depth transfer function was applied to the testate amoebae data to provide quantifiable changes the three proxy records show coherent phase changes which are interpreted as variability in past effective precipitation two tephra horizons glen garry and lairg a were used in conjunction with radiocarbon dates to construct an age depth model producing a robust geochronology from which a time series was calculated the palaeoclimatic reconstruction identified major wet shifts throughout the holocene with specific events occurring around cal 6650 5850 5300 4500 3850 3400 2800 2450 1450 1350 and 250 150 bp spectral analysis of the plant macrofossil dca and colorimetric humification data produced a millennial scale periodicity of 1100 years the same periodicity has also been found in a palaeoclimatic reconstruction from a site in cumbria walton moss and may be linked with millennial scale periodicities found in oceanic palaeoclimatic records

combined measurements of subglacial water pressure and surface velocity of findelengletscher switzerland conclusions about drainage system and sliding mechanism interpretation des mesures de pression dans les forages et des vitesses superficielles la comparaison avec les modeles suggere que l on a neglige le frottement du aux debris dans les modeles et qu il n existe jamais de chenaux cylindriques rectilignes

an eddy permitting southern ocean state estimate abstract an eddy permitting general circulation model of the southern ocean is fit by constrained least squares to a large observational dataset during 2005 06 data used include argo float profiles ctd synoptic sections southern elephant seals as oceanographic samplers seaos instrument mounted seal profiles xbts altimetric observations envisat geosat jason 1 and ocean topography experiment topex poseidon and infrared and microwave radiometer observed sea surface temperature an adjoint model is used to determine descent directions in minimizing a misfit function each of whose elements has been weighted by an estimate of the observational plus model error the model is brought into near agreement with the data by adjusting its control vector here consisting of initial and meteorological boundary conditions although total consistency has not yet been achieved the existing solution is in good agreement with the great majority of the 2005 and 2006 southern ocean observations and better repr