climate variability along latitudinal and longitudinal transects in east antarctica in the framework of the international trans antarctic scientific expedition itase programme france and italy carried out a traverse along one west east and two north south transects in east antarctica from november 2001 to january 2002 eighteen shallow snow firn cores were drilled and surface snow samples were collected every 5 km along the traverse firn temperatures were measured in boreholes down to 30 m the cores were analyzed forradioactivity to obtain snow accumulation rate data the surface snow samples were analyzed for d 18 o to correlate isotopic values with borehole temperatures multiple regression analysis shows a global near dry adiabatic lapse rate and a latitudinal lapse rate of 1 05 c lat s 1 in the dome c drainage area analysis of firn temperatures reveals a super adiabatic lapse rate along the ice divide between talos dome and the southern ocean coast and in some sectors along the ice divide between the astrolabe basin and d59 snow accumulation rates and firn temperatures show warmer temperatures and higher accumulation values close to the ice divides extending from talos dome and dome c to the southern ocean the spatial pattern of data is linked with a katabatic wind source basin and moisture source region

accumulation variability over a small area in east dronning maud land antarctica as determined from shallow firn cores and snow pits some implications for ice core records we investigate and quantify the variability of snow accumulation rate around a medium depth firn core 1160 m drilled in east dronning maud land antarctica 75 degrees 00 s 15 degrees 00 e 3470 m h a e ellipsoidal height we present accumulation data from five snow pits and five shallow 20 m firn cores distributed within a 3 5 7 km distance retrieved during the 2000 01 nordic epica european project for ice coring in antarctica traverse snow accumulation rates estimated for shorter periods show higher spatial variance than for longer periods accumulation variability as recorded from the firn cores and snow pits cannot explain all the variation in the ion and isotope time series other depositional and post depositional processes need to be accounted for through simple statistical analysis we show that there are differences in sensitivity to these processes between the analyzed species oxygen isotopes and sulphate are more conservative in their post depositional behaviour than the more volatile acids such as nitrate and to some degree chloride and methanesulphonic acid we discuss the possible causes for the accumulation variability and the implications for the interpretation of ice core records

snow density along the route traversed by the japanese swedish antarctic expedition 2007 08 during the japanese swedish antarctic traverse expedition of 2007 08 we measured the surface snow density at 46 locations along the 2800 km long route from syowa station to wasa station in east antarctica the mean snow density for the upper 1 or 0 5 m layer varied from 333 to 439 kg m 3 over a region spanning an elevation range of 365 3800 m a s l the density variations were associated with the elevation of the sampling sites the density decreased as the elevation increased moving from the coastal region inland however the density was relatively insensitive to the change in elevation along the ridge on the antarctic plateau between dome f and kohnen stations because surface wind is weak in this region irrespective of elevation the wind speed was suggested to play a key role in the near surface densification the results of multiple regression performed on the density using meteorological variables were significantly improved by the inclusion of wind speed as a predictor the regression analysis yielded a linear dependence between the density and the wind speed with a coefficient of 13 5 kg m 3 m s 1 1 this relationship is nearly three times stronger than a value previously computed from a dataset available in antarctica our data indicate that the wind speed is more important to estimates of the surface snow density in antarctica than has been previously assumed

the june july 1993 seismo acoustic event at coaxial segment juan de fuca ridge evidence for a lateral dike injection the coaxial segment juan de fuca ridge was the site of an intense swarm of earthquakes that began at 21 43 gmt on june 26 1993 julian day 177 the swarm started near 46 15 n and migrated northward over the next 40 hours to 46 36 n where the majority of 676 events occurred during the following 3 weeks of activity the earthquakes propagated nne at a velocity of 0 3 0 1 m s 1 from the southern to northern swarm sites the activity went undetected by land based seismic networks along the oregon and washington coasts suggesting that the earthquakes were all m 4 0 the character of this earthquake swarm is very similar to dike injections observed at krafla and kilauea volcanoes the earthquake activity and subsequent migration probably represent a lateral dike injection into faults and fissures comprising the coaxial segment the reservoir acting as the dike s source likely resides beneath or to the south of the initial southern swarm of earthquakes the large magma supply at axial volcano cannot be ruled out as the source for the coaxial dike even though axial volcano exhibited no earthquake activity related to the coaxial swarm the t wave earthquake swarm reported here is the first deep ocean observation of volcanic seismicity associated with what most likely was a mid ocean ridge dike injection event

deficiencies in the diatom evidence for a pliocene reduction of the east antarctic ice sheet evidence for pliocene reduction of the east antarctic ice sheet eais has been inferred from the presence of pliocene planktic marine diatoms in tills of the sirius group now exposed along the slopes of the transantarctic mountains we highlight deficiencies in this diatom evidence for a pliocene reduction of the eais first we examine what diatom habitats are left behind by a retreating ice sheet in this case the fennoscandian ice sheet fis and find that diatoms should occur in planktic and benthic marine brackish water freshwater and terrestrial habitats we expect that during former reexpansions these diverse diatom assemblages were picked up by the advancing fis and deposited in tills this is shown to be the case and diatoms found in tills from sweden and finland reflect the many habitats over which the fis passed if there was a reduction of the eais during the pliocene followed by renewed glaciation diatoms from many different habitats should be found in the resulting tills of the sirius group this is not the case only marine planktic diatoms and a few freshwater forms are reported similarly vertical downsection distribution of diatoms in sirius group and fennoscandian tills differ while in the sirius group diatoms appear restricted to surface and near surface sediments in fennoscandia they are found throughout the tills such data do not support a pliocene reduction model for the eais

p and t wave detection thresholds pn velocity estimate and detection of lower mantle and core p waves on ocean sound channel hydrophones at the mid atlantic ridge since 1999 six sound fixing and ranging sofar hydrophones have been moored along the mid atlantic ridge mar 15 35 n these hydrophones 8 bit data resolution are designed for long term monitoring of mar seismicity using the acoustic t waves of seafloor earthquakes the completeness level of the mar t wave earthquake catalog estimated from size frequency constraints is mb 3 0 a significant improvement in detection compared to the mb 4 6 completeness level estimated from national earthquake information center magnitude frequency data the hydrophones also detect the acoustic phase of converted upper mantle p arrivals from regional earthquakes at epicentral distances of 374 1771 km and from events as small as mb 3 6 these regional p waves are used to estimate a pn velocity of 8 0 0 1 km sec 1 along the east and west mar flanks an unexpected result was the identification of p arrivals from earthquakes outside the atlantic ocean basin the hydrophones detected p waves from global earthquakes with magnitudes of 5 8 8 3 at epicentral distances ranging from 29 6 to 167 2 examination of travel times suggests these teleseismic p waves constitute the suite of body wave arrivals from direct mantle p to outer and inner core reflected refracted phases the amplitudes of the teleseismic p waves also exhibit the typical solid earth wave field phenomena of a p shadow zone and caustic at d 144 these instruments offer a long term relatively low cost alternative to ocean bottom seismometers that allows for obser vation of pn velocities and mantle core phases arriving at normally inaccessible deep sea locations

trends and patterns in the recent accumulation and oxygen isotopes in coastal dronning maud land antarctica interpretations from shallow ice cores to investigate recent variability in accumulation and d 18 o we synthesize data from five snowcores covering the period1932 96 fromthe sector16 38 w 4 48 e in coastal dronning maudland dml antarctica the d 18 orecords fromthe differentsites areremarkablysimilarand suggestacommon stablemoisturesourceforthis coastal section of dml while the accumulation pattern is local and specific features restricted to the individual sites the overall accumulation pattern is related to the temperature variability as indicated by coastal instrumental records accumulation and d 18 o correlate between 1955 and1985 but deviate thereafter with the proxy temperature record showing a positive trend while accumulation decreased this occurs at the same time as an increase in sea ice extentinthearea whichmayhaveresultedincirculationchangesandmorenortherlystorm paths both stacked accumulation and d 18 o records show that large scale atmospheric sig nals aswellas some pronounced individualevents arerecorded in dmlcoastal ice cores

oxygen carbon and u series isotopes of aragonites from vestfold hills antarctica clues to geochemical processes in subglacial environments aragonites occurring in situ on the gneissic bedrock at vestfold hills an ice free coastal antarctic oasis possess morphologic and petrographic characteristics typical of subglacial carbonate precipitates the sup 14 c chronology of the samples is invalidated by modern carbon contamination and a sup 14 c sup 12 c reservoir correction of unknown magnitude in contrast u and th isotope analyses suggest that the subglacial deposits can be treated as closed datable systems if allowance is made for the excess sup 230 th derived from the small and variable detrital silicate fraction coexisting with the aragonites the mean sup 230 th depositional age of 35 000 plus minus 2 000 yrs correlates with late isotope stage 3 of deep sea glacial chronology and represents the time when the vestfold hills were partially or completely buried under the advancing east antarctic ice sheet the survival of the aragonites following the ice sheet retreat during the holocene is attributed to the extreme arid climate of the area the aragonites are anomalously depleted in sup 18 o and slightly depleted in sup 13 c relative to smow and pdb standards respectively delta sup 18 o 15 7 plus minus 0 9 per thousand delta sup 13 c minus 3 6 plus minus 0 4 per thousand the melt water with which the aragonitesmore would have equilibrated at 0 degree c is about 7 to 9 per thousand more depleted in sup 18 o relative to the extant basal ice source delta sup 18 o minus 41 per thousand part of this enhanced sup 18 o deficiency i e 4 to 6 per thousand is ascribed to temporal shifts in delta sup 18 o of the antarctic ice the rest to isotope effects of the subglacial hydrology a model of subglacial aragonite precipitation is proposed on the basis of water flow between warm melting zones and cold freezing zones at the ice sheet sole less

characterization and formation of melt layers in polar snow observations and experiments from west antarctica author posting international glaciological society 2005 this article is posted here by permission of international glaciological society for personal use not for redistribution the definitive version was published in journal of glaciology 51 2005 307 312 doi 10 3189 172756505781829395

a new surface accumulation map for western dronning maud land antarctica from interpolation of point measurements as a result of intensive field activities carried out by several nations over the past 15 years a set of accumulation measurements for western dronning maud land antarctica was collected based on firn core drilling and snow pit sampling this new information was supplemented by earlier data taken from the literature resulting in 111 accumulation values using geographical information systems software a first region wide mean annual snow accumulation field was derived in order to define suitable interpolation criteria the accumulation records were analyzed with respect to their spatial autocorrelation and statistical properties the resulting accumulation pattern resembles well known characteristics such as a relatively wet coastal area with a sharp transition to the dry interior but also reveals complex topographic effects furthermore this work identifies new high return shallow drilling sites by uncovering areas of insufficient sampling density

extreme wind ice interaction over recovery ice stream east antarctica surface snow accumulation over east antarctica is an important climate indicator but a difficult parameter to constrain surface mass ablation dominates over persistent wind scour zones as near surface katabatic winds accelerate over locally steeper ice surface topography and sublimate and redistribute snow here we quantify ablation rates and downwind redeposition of snow over wind scour zones in the upper recovery ice stream catchment airborne radio echo soundings show a gradual ablation of 16 18 m of firn corresponding to 200 years of accumulation over these zones and ablation rates of 54 kg m 2 a 1 54 mm water equivalent a 1 we conclude that mass loss is dominated by sublimation and mass is transported downwind as water vapor because snow redeposition downslope of the wind scour zones constitutes only a small fraction 10 of the cumulative mass loss key points widespread wind scour zones impact surface mass balance over recovery ice stream catchment radiostratigraphy shows gradual ablation of 200 years of accumulation in east antarctica the mass loss over the wind scour zones is mostly by sublimation with little redeposition

firn accumulation records for the past 1000 years on the basis of dielectric profiling of six cores from dronning maud land antarctica this paper presents an overview of firn accumulation in dronning maud land dml antarctica over the past 1000 years it is based on a chronology established with dated volcanogenic horizons detected by dielectric profiling of six medium length firn cores in 1998 the british antarctic survey retrieved a medium length firn core from western dml during the nordic epica european project for ice coring in antarctica traverse of 2000 01 a 160 m long firn core was drilled in eastern dml together with previously published data from four other medium length ice cores from the area these cores yield 50 possible volcanic horizons all six firn cores cover a mutual time record until the 29th eruption this overlapping period represents a period of approximately 1000 years with mean values ranging between 43 and 71 mm w e the cores revealed no significant trend in snow accumulation running averages over 50 years averaged over the six cores indicate temporal variation in the order of 5 all cores display evidence of a minimum in the mean annual firn accumulation rate around ad 1500 and maxima around ad 1400 and 1800 the mean increase over the early 20th century was the strongest increase but the absolute accumulation rate was not much higher than around ad 1400 in eastern dml a 13 increase is observed for the second half of the 20th century

early pliocene marine sediments coastline and climate of east antarctica we record the first onshore late tertiary fossiliferous marine deposit from the 8000 km long coastline of east antarctica glaciomarine sediments containing abundant diatoms and molluscs were deposited in shallow waters off an open coast during the early pliocene 4 5 3 5 ma and are now exposed less than 15 m above sea level on marine plain in the vestfold hills lat 68 359s long 78 009e marine diatoms suggest early pliocene as the most probable age of the sediments fossil sand wedges show that the deposit was above sea level at least briefly before it was covered with water and subsequently capped with glaciomarine till the coastline at the time of deposition of the marine sediments is inferred to have been close to but farther inland than that of today the ice margin may have been 50 km farther inland considerably reducing the ice volume of antarctica climate at the time of deposition was interglacial and perhaps warmer than the present

paleodepth determination from antarctic benthic diatom assemblages abstract analysis of modern surface sediments from fjords in the vestfold hills antarctica indicates that 58 of the variation in benthic diatom assemblages can be attributed to changes in environmental parameters with water depth attenuation of light through the water column is suggested to account for 45 of the variation and the decrease in substrate grain size with depth possibly accounts for a further 13 cluster analysis and principal component analysis were used to objectively circumscribe five floral zones between the surface and 35 m depth the depth distribution of the benthic diatoms was then used to interpret the paleodepth of relict fjord holocene sediments exposed around deep lake in the death valley vestfold hills paleodepths measured from the sea ice bench around deep lake combined with data from grain size analysis indicate that the relict fjord sediments have no analogue amongst the modern fjord sediments sampled in the vestfold hills without a comparable modern habitat on which to model the diatom depth zones however this study was unable to accurately determine the paleowater depth at deep lake using diatoms paleodepth determination will be possible using grain size analysis and diatom data when the substrate and light requirements of benthic diatoms are understood

climate variables along a traverse line in dronning maud land east antarctica temperature density and accumulation data were obtained from shallow firn cores drilled during an overland traverse through a previously unknown part of dronning maud land east antarctica the traverse area is characterised by high mountains that obstruct the ice flow resulting in a sudden transition from the polar plateau to the coastal region the spatial variations of potential temperature near surface firn density and accumulation suggest that katabatic winds are active in this region proxy wind data derived from firn density profiles confirm that annual mean wind speed is strongly related to the magnitude of the surface slope the high elevation of the ice sheet south of the mountains makes for a dry cold climate in which mass loss owing to sublimation is small and erosion of snow by the wind has a potentially large impact on the surface mass balance a simple katabatic wind model is used to explain the variations of accumulation along the traverse line in terms of divergence convergence of the local transport of drifting snow the resulting wind and snowdrift patterns are closely connected to the topography of the ice sheet ridges are especially sensitive to erosion while ice streams and other depressions act as collectors of drifting snow

an empirical relation between overburden pressure and firn density two empirical equations for firn densification have been obtained considering firn porosity as a function of overburden pressure in the first equation thereduction ratio of porosity in firn is assumed to be proportional to the increasing ratioof overburden pressure and the mth power of the porosity the porosity exponent m should be close to 2 so as to have a best fit with 14 depth density profiles fromgreenland and antarctica in the second equation the reduction ratio of porosity wasassumed to increase proportionally to the increment of overburden pressure and thenth power of the porosity the most satisfactory values of the exponent range from 1 to 1 it has been suggested that firn density determined primarily by overburdenpressure and firn temperature contribute to a lesser degree

factors controlling the near surface wind field in antarctica abstract using data from the regional atmospheric climate model racmo ant1 the momentum budget of the antarctic atmospheric surface layer sl taken as the lowest model layer located at 6 7 m above the surface is presented in july winter the katabatic pressure gradient force pgf dominates the sl momentum budget over the steep coastal slopes which results in strong 10 15 m s 1 and directionally constant katabatic winds farther inland where surface slopes are more gentle the large scale pgf may become equally important with the circumpolar pressure trough north of the antarctic coastline the large scale pgf acts along with the katabatic pgf in the downslope direction in wilkes land dronning maud land and on the western ross ice shelf the large scale pgf causes equivalent geostrophic winds in excess of 10 m s 1 thermal wind effects that oppose the downslope acceleration are especially strong in areas where large scale forcing is weak which allows cold air to pile up over the flat ice she

t wave generation and propagation a comparison between data and spectral element modeling t waves are underwater acoustic waves generated by earthquakes modeling of their generation and propagation is a challenging problem using a spectral element code specfem2d this paper presents the first realistic simulations of t waves taking into account major aspects of this phenomenon the radiation pattern of the source the propagation of seismic waves in the crust the seismic to acoustic conversion on a non planar seafloor and the propagation of acoustic waves in the water column the simulated signals are compared with data from the mid atlantic ridge recorded by an array of hydrophones the crust water interface is defined by the seafloor bathymetry different combinations of water sound speed profiles and sub seafloor seismic velocities and frequency content of the source are tested the relative amplitudes main arrival times and durations of simulated t phases are in good agreement with the observed data differences in the spectrograms and early arrivals are likely due to too simplistic source signals and environmental model these examples demonstrate the abilities of the specfem2d code for modeling earthquake generated t waves

characteristics of accumulation around the epica deep drilling site in dronning maud land antarctica based on ground penetrating radar profiles we analyze area wide spatial and temporal characteristics of accumulation rate in the vicinity of the epica european project for ice coring in antarctica deep drilling site in dronning maud land antarctica edml an area of 1600 km 2 is covered by 500 km of radar profiles organized in a star like pattern with eight 20 25 km legs and a 10 km grid with 1 3 km spacing each pattern being centred on the edml drilling location distributions of density cumulative mass age and the electromagnetic wave speed with depth are available from physical ice core records nine internal reflection horizons are continuously tracked within the upper 110 m of ice over the whole area yielding a spatial picture of accumulation rate history over 1000 years the mean accumulation rate over the last 153 years varies between 50 and 75 kg m 2 a 1 over 50 km perpendicular to the ice divide the spatial average is 61 kg m 2 a 1 this general pattern is overlain by small scale variations of accumulation rate on the order of 10 of the mean maximum local gradients in accumulation rate are 2 3 kg m 2 a 1 km 1 about five times the regional accumu lation rate gradient comparison of topography and accumulation rate along a 20 km profile in the direction of the mean winds indicates that variations in accumulation rate over short distances are linked to surface undulations our results show that advected spatial variations of accumulation rate are on the same order and even exceed temporal changes over the investigated periods ice flow and upstream effects therefore might influence accumulation rates reconstructed from the edml ice core

derived constituents in the glacial sediments of the vestfold hills east antarctica abstract sediment derived from pre existing marine deposits and weathered surfaces is a common consituent of glacial drift in the vestfold hills east antarctica ninety seven samples of glacial drift were examined for marine macrofossils and weathered clasts and 41 were examined for foraminifera fragments or whole specimens of shells worm tubes sponge spicules and foraminifera were recovered from 25 samples clasts that exhibited evidence of subaerial weathering such as tafoni and weathering rinds were found in 53 samples derived sediment was found in 62 of all samples these data indicate that the last advance of ice derived much of its sediment locally the incorporation of marine fauna in the glacial deposits makes the identification of in situ interglacial sequences difficult

a 1500 year record of accumulation at amundsenisen western dronning maud land antarctica derived from electrical and radioactive measurements on a 120 m ice core during the nordic epica pre site survey in dronning maud land in 1997 1998 a 120 m long ice core was retrieved 76 00 s 08 03 w 2400 m above sea level the whole core has been measured using the electric conductivity measurement ecm and dielectric profiling dep techniques and the core chronology has been established by detecting major volcanic eruptions in a nearby shallow core radioactive traces from nuclear tests conducted during the 1950s and 1960s have been identified altogether 13 ecm and dep peaks in the long core are identified as originating from specific volcanic eruptions in addition two peaks of increased total activity are identified in the short core accumulation is calculated as averages over the time periods between these dated events accumulation rate is 62 millimetres w eq yr for the last 181 years 1816 a d to present and 61 mm w eq yr for the last 1457 years 540 a d to present our record shows an 8 decrease in accumulation between 1452 and 1641 a d i e part of the little ice age compared to the long term mean

long term seismicity of the reykjanes ridge north atlantic recorded by a regional hydrophone array summary the seismicity of the northern mid atlantic ridge was recorded by two hydrophone networks moored in the sound fixing and ranging sofar channel on the flanks of the mid atlantic ridge north and south of the azores during its period of operation 05 2002 09 2003 the northern sirena network deployed between latitudes 40 20 n and 50 30 n recorded acoustic signals generated by 809 earthquakes on the hotspot influenced reykjanes ridge this activity was distributed between five spatio temporal event clusters each initiated by a moderate to large magnitude 4 0 5 6 m earthquake the rate of earthquake occurrence within the initial portion of the largest sequence which began on 2002 october 6 is described adequately by a modified omori law aftershock model although this is consistent with triggering by tectonic processes none of the reykjanes ridge sequences are dominated by a single large magnitude earthquake and they appear to be of relatively short duration 0 35 4 5 d when compared to previously described mid ocean ridge aftershock sequences the occurrence of several near equal magnitude events distributed throughout each sequence is inconsistent with the simple relaxation of mainshock induced stresses and may reflect the involvement of magmatic or fluid processes along this deep 2000 m section of the reykjanes ridge

thickening of the ice stream catchments feeding the filchner ronne ice shelf antarctica 1 earlier ice sheet mass balance estimates disagree with satellite altimeter measured thickening of the catchment area that feeds the filchner ronne ice shelf antarctica in an effort to reconcile these differences we generated a new flux gate mass balance estimate using improved elevation and velocity data our results show a 39 26 gton yr thickening whereas earlier flux gate results indicated minor thinning our results are consistent with altimeter derived estimates of elevation change this suggests that altimeter observed thickening on the east antarctic plateau may be the result of some combination of a 20th century accumulation increase and a continuing response to the 50 accumulation increase that began in the early holocene

accumulation and proxy temperature variability in dronning maud land antarctica determined from shallow firn cores during 1996 97 a european project for ice coring in antarctica epica pre site surveying traverse worked in the area between 70 s 5 e and 75 s 15 e in dronning maud land we present data obt

antarctic surface and subsurface snow and ice melt fluxes abstract this paper presents modeled surface and subsurface melt fluxes across near coastal antarctica simulations were performed using a physical based energy balance model developed in conjunction with detailed field measurements in a mixed snow and blue ice area of dronning maud land antarctica the model was combined with a satellite derived map of antarctic snow and blue ice areas 10 yr 1991 2000 of antarctic meteorological station data and a high resolution meteorological distribution model to provide daily simulated melt values on a 1 km grid covering antarctica model simulations showed that 11 8 and 21 6 of the antarctic continent experienced surface and subsurface melt respectively in addition the simulations produced 10 yr averaged subsurface meltwater production fluxes of 316 5 and 57 4 km3 yr 1 for snow covered and blue ice areas respectively the corresponding figures for surface melt were 46 0 and 2 0 km3 yr 1 respectively thus demonstrating the dominant role of subsurface ov

spatial and temporal variation of sublimation on antarctica results of a high resolution general circulation model in this paper we use output of a high resolution general circulation model echam 3 t106 resolution 1 1 x 1 1 to study the spatial and temporal variation of sublimation on antarctica first we compare model results with available observations of sublimation rates the yearly cycle with small latent heat fluxes during the winter is well reproduced and the agreement with sparsely available spot observations is fair the model results suggest that a significant 10 15 of the annual precipitation over antarctica is lost through sublimation and that sublimation plays an important role in the formation of blue ice areas a preliminary analysis of the atmospheric boundary layer moisture budget shows that the spatial variation of sublimation in the coastal zone of east antarctica can be explained by variations of horizontal advection of dry air dry air advection and thus surface sublimation is enhanced in areas where katabatic winds are strong and have a large downslope component and where the antarctic topography drops suddenly from the plateau to the coastal zone in areas where horizontal advection is small like the plateau and the large ice shelves special conditions must be met to make significant sublimation at the surface possible

paraglacial redistribution of glacial sediments in the vestfold hills east antarctica abstract the vestfold hills landscape is dominated by bare rock slopes and unconsolidated deposits form a minor component of the surficial geology the principal objectives of the study were to explain the distribution of unconsolidated deposits determine the nature and timing of sedimentary processes during and after deglaciation and the impact of these processes on landscape development observations of late quaternary glaciation and deglaciation of the area and contemporary depositional processes are reported and a conceptual model of geomorphological change since deglaciation is presented the model attempts to reconcile the types and rates of contemporary depositional processes with the distribution of deposits and landforms and to explain why unconsolidated deposits cover less than 20 of the hills despite the effects of recent glaciation the lack of unconsolidated deposit in the landscape can be attributed to the combined effects of low debris volumes in the ice and the redistribution of debris during and after deglaciation redistribution of debris can be explained by paraglacial processes which are non glacial sedimentary processes that are directly conditioned by glaciation paraglacial sedimentation is a response to rapid adjustment of the debris system after the dominance of glacial conditions and is characterized by disequilibrium between sediment supply and transportation of sediment by nonglacial processes evidence from the vestfold hills suggests paraglacial sedimentary processes are dominated by mass movement of glacial debris from slopes and the formation of stable valley fills and that the main sediment transfers occur within a few thousand years of deglaciation

toggling of seismicity by the 1997 kagoshima earthquake couplet a demonstration of time dependent stress transfer 1 two m 6 well recorded strike slip earthquakes struck just 4 km and 48 days apart in kagoshima prefecture japan in 1997 providing an opportunity to study earthquake interaction aftershocks are abundant where the coulomb stress is calculated to have been increased by the first event and they abruptly stop where the stress is dropped by the second event this ability of the main shocks to toggle seismicity on and off argues that static stress changes play a major role in exciting aftershocks whereas the dynamic coulomb stresses which should only promote seismicity appear to play a secondary role if true the net stress changes from a sequence of earthquakes might be expected to govern the subsequent seismicity distribution however adding the stress changes from the two kagoshima events does not fully capture the ensuing seismicity such as its rate change temporal decay or migration away from the ends of the ruptures we therefore implement a stress transfer model that incorporates rate state friction in which seismicity is treated as a sequence of independent nucleation events that are dependent on the fault slip slip rate and elapsed time since the last event the model reproduces the temporal response of seismicity to successive stress changes including toggling decay and aftershock migration nevertheless the match of observed to predicted seismicity is quite imperfect due perhaps to inadequate knowledge of several model parameters however to demonstrate the potential of this approach we build a probabilistic forecast of larger earthquakes on the expected rate of small aftershocks taking advantage of the large statistical sample the small shocks afford not surprisingly such probabilities are highly time and location dependent during the first decade after the main shocks the seismicity rate and the chance of successive large shocks are about an order of magnitude higher than the background rate and are concentrated exclusively in the stress triggering zones

a snow sensor experiment in dronning maud land antarctica in january 2000 nine snow sensors were deployed in dronning maud land antarctica along a 355 km transect from kvitkuven near the shelf edge via the finnish research station aboa to the amundsenisen plateau the purpose was to test a sensor system for spatio temporal variations in temperature across the snow air interface and snow accumulation ablation which includes atmos pheric net balance and migrating snow dunes in the dry snow conditions environmental static electricity interfered with data transfer several sensors were disabled early while the longest record reached 6 months along the main transect the year 2000 mass balance ranged from 52 to 221 mm w e largely following spatial patterns seen by other researchers the level increased toward the edge of the ice sheet unloading of drifting snow as the slope flattens rather than increased snowfall as previously thought may be responsible for this at the hogisen ice dome site the mass balance was 897 mm w e possibly due to unloading of wind blown snow as katabatic winds are locally forced uphill this mechanism is important to maintain such topographic features along the antarctic ice sheet margin major precipitation events occurred at 3 5 week intervals and much of the precipitation fell before mid june the daily signal in temperature disappeared after the autumn equinox then the spectrum displayed a broad peak at synoptic frequencies potential temperature decreased towards the shelf edge displaying a pattern consistent with strong inversions and suggesting that strong evaporative cooling is associated with the katabatic winds

global change over the last climatic cycle from the vostok ice core record antarctica abstract the study of ice cores provides the opportunity of access to numerous parameters which are related to climate or environmental changes many of these variables are of regional or even global geographical significance there are now several ice cores which penetrate into ice which has formed at the surface of polar ice sheets during the last ice age and the recently obtained vostok antarctica record provides detailed information over the last climatic cycle 160 ka in comparison with current holocene conditions the last glacial maximum 20 ka bp is characterized by much colder conditions up to 10 c and reduced precipitation 1 2 a large increase of continental and marine aerosols is explained by a more vigorous large scale atmospheric circulation associated with changing continental deserts and shelves as well as changes in sea ice extent the drastic climatic change occurring at the last glacial termination is correlated with a large increase of atmospheric co 2 from about 200 to 270 ppmv the isotopic temperature record from the vostok ice core depicts two drastic glacial interglacial terminations around 15 and 140 ka bp and a long glacial period 110 15 ka bp which includes two interstadials full glacial stages are characterized by larger aerosol loadings the co 2 record of global significance is well correlated with the isotope temperature profile with high 270 ppmv during interglacials and low 200 ppmv during full glacial conditions spectral analysis of the yostok temperature record supports the existence of a relationship between the pleistocene climate and orbital forcing on the other hand the existence of a co 2 climate correlation suggests that co 2 changes have had an important climatic role in amplifying the relatively weak orbital forcing

accumulation variability and mass budgets of the lambert glacier amery ice shelf system east antarctica at high elevations the temporal and spatial variability of the annual accumulation rate and the mass budgets of five sub basins of the lambert glacier amery ice shelf system las east antarctica at high elevations are assessed using a variety of datasets derived from field measurements and modeling the annual temporal variations of the accumulation rate for four cores from the west and east sides of the las are around 34 decadal fluctuation of the accumulation from the dt001 firn core drops to 10 and the 30 year fluctuation to 5 which is assumed to contain the information about the regional and long term trend in accumulation the 15 point running mean of the annual accumulation rate derived from stake measurements can remove most of the high frequency spatial variation so as to better represent the local accumulation model simulations show that the spatial variability of erosion deposition of snow by the wind has a noticeable impact on the surface mass balance at the higher parts of the las mass budget estimates at high elevation sub basins of the las suggest drainage 9 has a negative imbalance of 0 7 0 4 gt a 1 lambert and mellor glaciers have a positive imbalance of 3 9 2 1 and 2 1 2 4 gt a 1 respectively and fisher glacier and drainage 11 are approximately in balance the higher elevation region as a whole has a positive mass imbalance of 4 4 6 3 gt a 1 which is consistent with the most recent radar altimetry assessment that shows an overall thickening over this region

spatial and temporal variability of snow accumulation in east antarctica from traverse data recent snow accumulation rate is a key quantity for ice core and mass balance studies several accumulation measurement methods stake farm fin core snow radar profiling surface morphology remote sensing were used compared and integrated at eight sites along a transect from terra nova bay to dome c east antarctica to provide information about the spatial and temporal variability of snow accumulation thirty nine cores were dated by identifying tritium b marker levels 1965 66 and non sea salt nss so4 2 spikes of the tambora indonesia volcanic event 1816 in order to provide information on temporal variability cores were linked by snow radar and global positioning system surveys to provide detailed information on spatial variability in snow accumulation stake farm and ice core accumulation rates are observed to differ significantly but isochrones snow radar correlate well with ice core derived accumulation the accumulation ablation pattern from stake measurements suggests that the annual local noise metre scale in snow accumulation can approach 2 years of ablation and more than four times the average annual accumulation with no accumulation or ablation for a 5 year period in up to 40 of cases the spatial variability of snow accumulation at the kilometre scale is one order of magnitude higher than temporal variability at the multi decadal secular scale stake measurements and firn cores at dome c confirm an approximate 30 increase in accumulation over the last two centuries with respect to the average over the last 5000 years

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

bulk friction modeling of afterslip and the modified omori law abstract afterslip data from the superstition hills fault in southern california a creep event on the same fault the modified omori law and cumulative moments from aftershocks of the 1957 aleutian islands earthquake all indicate that the original formulation by dieterich 1981 constitutive properties of faults with simulated gouge agu geophys monogr 24 103 120 for friction evolution is more appropriate for systems far from instability than the commonly used approximation developed by ruina 1983 slip instability and state variable friction laws j geophys res 88 10359 10370 to study instability the mathematical framework we use to test the friction models is a one dimensional massless spring slider under the simplifying assumption proposed by scholz 1990 the mechanics of earthquakes and faulting cambridge university press and used by marone et al 1991 on the mechanics of earthquake afterslip j geophys res 96 8441 8452 that the state variable takes on its velocity dependent steady state value throughout motion in response to a step in stress this assumption removes explicit state variable dependence from the model obviating the need to consider state variable evolution equations anti derivatives of the modified omori law fit our data very well and are very good approximate solutions to our model equations a plausible friction model with omori law solutions used by wesson 1988 dynamics of fault creep j geophys res 93 8929 8951 to model fault creep and generalized by rice 1983 constitutive relations for fault slip and earthquake instabilities pure appl geophys 121 443 475 to a rate and state variable friction model yields exactly omori s law with exponents greater than 1 but yields unstable solutions for omori exponents less than 1 we estimate from the dieterich formulation the dimensionless parameter a which is equal to the product of the nominal coefficient of friction and the more commonly reported friction parameter a we find that a is typically positive qualitatively consistent with laboratory observations although our observations are considerably larger than laboratory values however we also find good model fits for a when data correspond to omori exponents less than 1 a modification of the stability analysis by rice and ruina 1983 stability of steady frictional slipping j appl mech 50 343 349 indicates that a is not a consequence of our assumption regarding state variable evolution a consistent interpretation of a in terms of laboratory models appears to be that the data are from later portions of processes better characterized by two state variable friction models a is explained by assuming that our data cannot resolve the co seismic evolution of a short length scale state variable to a velocity weakening state our parameterization leads to an apparent negative instantaneous viscosity we estimate the largest critical slip distance associated with afterslip to be 1 10 cm consistent with other estimates for near surface materials we assume that our observed large values for a reflect the fact that our model ignores the geometrical complexities of three dimensional stresses in fractured crustal materials around a fault zone with frictional stresses that vary on a fault surface our one dimensional model parameters reflect spatially averaged bulk stress and frictional properties of a fault zone where we clearly cannot specify the details of the averaging process our analysis of omori s law suggests that bulk frictional properties of a fault zone are well described by our simple laboratory based models but they would need to change during the seismic cycle for a mainshock instability to recur unless a mainshock aftershock sequence were characterized by a process similar to the arrested instabilities possible in two state variable systems

recent surface mass balance from syowa station to dome f east antarctica comparison of field observations atmospheric reanalyses and a regional atmospheric climate model stake measurements at 2 km intervals are used to determine the spatial and temporal surface mass balance smb in recent decades along the japanese antarctic research expedition traverse route from syowa station to dome f to determine smb variability at regional scales this traverse route is divided into four regions i e coastal lower katabatic upper katabatic and inland plateau we also perform a regional evaluation of large scale smb simulated by the regional atmospheric climate model versions 2 1 and 2 3 racmo2 1 and racmo2 3 and the four more recent global reanalyses large scale spatial variability in the multi year averaged smb reveals robust relationships with continentality and surface elevation in the katabatic regions smb variability is also highly associated with surface slope which in turn is affected by bedrock topography stake observation records show large inter annual variability in smb but did not indicate any significant trends over both the last 40 years for the coastal and lower katabatic regions and the last 20 years record for the upper katabatic and inland plateau regions the four reanalyses and the regional climate model reproduce the macro scale spatial pattern well for the multi year averaged smb but fail to capture the mesoscale smb increase at the distance interval 300 to 400 km from syowa station thanks to the updated scheme in the cloud microphysics racmo2 3 shows the best spatial agreement with stake measurements over the inland plateau region era interim jra 55 and merra exhibit high agreement with the inter annual variability of observed smb in the coastal upper katabatic and inland plateau regions and moderate agreement in the lower katabatic region while ncep2 and racmo2 1 inter annual variability shows no significant correlation with the observations for the inland plateau region

a comparison of volcanic edifices at the reykjanes ridge and the mid atlantic ridge at 24 30 n a detailed analysis of high resolution side scan sonar data shows that the volcanic edifices built within the axial zones of the slow spreading 20 mm yr reykjanes ridge and the slow spreading 25 mm yr mid atlantic ridge are remarkably similar in fact individual seamounts hummocks rounded mounds and hummocky ridges at the reykjanes ridge have nearly identical morphological counterparts at the mid atlantic ridge mar arguing that commonly eruptive conditions are similar at the two ridges the construction of these volcanic edifices typical of slow spreading ridges occurs at the reykjanes ridge despite its proximity to the iceland hot spot and the influence of the hot spot on other characteristics of the ridge axis such as its overall shape an axial high north of about 59 n its shallow axial depths and its thicker crustal section the volume of magma that goes into constructing volcanic edifices at each of 12 segments of the mar and four regions of the reykjanes ridge is calculated using multibeam bathymetry data our results indicate that edifice volume per unit seafloor area equivalent to a uniform thickness over the area of interest is larger at the mar than at the reykjanes ridge on average taking into account spreading rate we then estimate b the average building rate per unit length along the axis which is also larger at the mar we conclude that the same volcanic edifices build the crust at the reykjanes ridge and mar but that their emplacement is more frequent at the mar to explain our results and reconcile them with those of magde and smith 1995 who documented that seamounts are taller and more abundant at the reykjanes ridge than at the mar we consider the controls on diking and eruption within the axial zones of the two ridges we suggest that the combination of slower spreading rate and the oblique geometry of spreading at the reykjanes ridge leads to fewer eruptions which are more widely dispersed across the axial zone than at the mar if this hypothesis is correct the proportion of seamounts modified by subsequent eruptions will be less this might also explain the taller heights of the seamounts if there is less overlap and infilling between edifices

changes in antarctic temperature wind and precipitation in response to the antarctic oscillation output of a 14 year integration with a high resolution 55 km 55 km regional atmospheric climate model is used to study the response of antarctic near surface climate to the antarctic oscillation aao the periodical strengthening and weakening of the circumpolar vortex in the southern hemisphere in spite of the relatively short record wind temperature and precipitation show widespread and significant aao related signals when the vortex is strong high aao index northwesterly flow anomalies cause warming over the antarctic peninsula ap and adjacent regions in west antarctica and the weddell sea in contrast cooling occurs in east antarctica the eastern ross ice shelf and parts of marie byrd land most of the annual temperature signal stems from the months march august the spatial distribution of the precipitation response to changes in the aao does not mirror temperature changes but is in first order determined by the direction of flow anomalies with respect to the antarctic topography when the vortex is strong high aao index the western ap becomes wetter while the ross ice shelf parts of west antarctica and the lambert glacier basin east antarctica become drier

monitoring pacific ocean seismicity from an autonomous hydrophone array since may 1996 an array of autonomous hydrophone moorings has been continuously deployed in the eastern equatorial pacific to provide long term monitoring of seismic activity including low level volcanic signals along the east pacific rise between 20 n and 20 s and the galapagos ridge the instruments and moorings were designed to continuously record low frequency acoustic energy in the sofar channel for extended periods and produce results comparable to those previously derived by using the u s navy sound surveillance system sosus in the northeast pacific the technology and methodology developed for this experiment including instrument design mooring configuration analysis software location algorithms with an analysis of errors and a predicted error field are described in detail volcanic activity is observed throughout the pacific along with seismicity along transform faults subduction zones and intraplate regions comparison data sets indicate detection thresholds and accuracy better than the land networks for open ocean areas and results comparable to or better than sosus volcanic seismicity along the fast spreading east pacific rise appears similar to documented examples in the northeast pacific but with much shorter durations one example from the intermediate spreading galapagos ridge is comparable to northeast pacific examples and several episodes of activity were observed in the wilkes transform fault zone a site of continuing off axis seismicity is located near 18 s and 116 w isolated intraplate earthquakes are observed throughout the study area earthquake information from this experiment and future observations will be provided through the world wide web and earthquake data centers

momentum budget of the east antarctic atmospheric boundary layer results of a regional climate model output of a regional atmospheric climate model is used to quantify the average january and july momentum budget of the atmospheric boundary layer abl over the east antarctic ice sheet and the surrounding oceans results are binned in nine elevation intervals over the ice sheet and six distance intervals over the ocean in january when surface cooling is weak the large scale pressure gradient force dominates the abl momentum budget in july under conditions of strong surface cooling a shallow katabatic jet develops over the gentle slopes of the interior ice sheet and a strong deep jet over the steep coastal slopes in the coastal regions the abl thickens considerably caused by the piling up of cold air over the adjacent sea ice and ice shelves this represents the main opposing force for the katabatic winds horizontal and vertical advection are generally small in the cross slope direction the momentum budget represents a simple balance between surface drag and coriolis turning intraseasonal variability of the large scale wind field in the abl can be explained in terms of the strength of the polar vortex the background baroclinicity and the topography of the ice sheet subsidence is found over the interior ice sheet and rising motion in the coastal zone reflecting the acceleration and deceleration of the katabatic circulation however vertical velocities are generally small because the downslope mass flux in the abl is confined to a shallow layer below the wind speed maximum

till stratigraphy and glacial history of the vestfold hills area east antarctica abstract the formation properties and stratigraphy of glacigenic deposits were studied at the marginal zone of the east antarctic ice sheet during the 1988 1989 australian national antarctic research expedition anare samples 132 were collected for granulometric geochemical heavy mineral and various dating analysis fabric analyses 27 were performed from glacial till and debris rich basal ice three test pits were excavated through frozen sediments to solid bedrock at a depth of 4 2 m the whole ice free area of 410 km2 was studied by stereo interpretation of aerial photographs and reconnaissance field survey a small outlet glacier the sorsdal glacier flows gently to the sea at the southern part of the vestfold hills area its terminus is floating the glacier was previously much larger and a majority of the moraine ridges in the vestfold hills area are probably lateral moraines of its former extensions radial and lateral flow of the glacier was observed from till fabric and striation data the present ice flow pattern and debris fabric in the glacier sole is similar to the one observed from till fabric and striations tills deposited by earlier phases of the sorsdal glacier cover an interglacial deposit of shelly gravel near the australian davis station shelly gravel represents clearly an ice free period when the climate was warmer and sea level higher than at present and this stage is named the davis interglacial according to the thermoluminescence tl datings and amino acid analyses of the shelly gravel deposits it seems that the davis interglacial is over 300 000 or over 1 000 000 years old the glacial stratigraphy of the vestfold hills shows at least two similar pleistocene outlet glacier floodings during which the sorsdal glacier had drained the vast ice masses of the continental ice sheet beyond the vestfold hills antarctic oasis

a study of the surface mass balance in dronning maud land antarctica using automatic weather stations we use data from four automatic weather stations awss in dronning maud land east antarctica to study the surface mass balance and its components distinct differences were found between the moisture climates of the high plateau the katabatic wind zone and the coastal ice shelves significant undersaturation occurs year round in the katabatic wind zone while on the high plateau and on the coastal ice shelf the air is usually close to saturation in summer absorption of shortwave radiation at the snow surface enhances surface sublimation at all sites removing 3 9 of the annual solid precipitation significant summer melting is an equally important ablation term near the coast but vanishes inland vertically integrated column drifting snow sublimation was estimated using two different methods this process appears to be similar to or greater in magnitude than surface sublimation because intervals between significant precipitation events may last as long as several months sublimation and melt cause extended periods of surface ablation in summer in summer all ablation processes together remove 15 56 of the solid precipitation or 6 27 on an annual basis

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

using in situ cosmogenic 10be to identify the source of sediment leaving greenland we use the concentration of in situ 10be in quartz isolated from fluvial and morainal sand to trace sediment sources and to determine the relative contribution of glacerized and deglaciated terrain to greenland s sediment budget we sampled along the western eastern and southern margins of the greenland ice sheet and collected sediment sourced from glacerized n 19 and non glacerized terrain n 10 from channels where sediment from glacerized and non glacerized terrain is mixed n 28 from holocene glacial fluvial terraces n 4 and from one sand dune in situ 10be concentrations in sediment range from 1600 to 34 000 atoms g 1 the concentration of in situ 10be in sediment sourced from non glacerized terrain is significantly higher than in sediment sourced from glacerized areas in mixed channel sediment and in terrace sediment that was deposited during the holocene to constrain the timing of landscape exposure for the deglaciated portion of the narsarsuaq field area in southern greenland we measured in situ 10be concentration in bedrock n 5 and boulder n 6 samples paired bedrock and boulder ages are indistinguishable at 1 uncertainty and indicate rapid exposure of the upland slopes at 10 5 ka the isotope concentration in sediment sourced from non glacerized terrain is higher than in sediment sourced from glacerized terrain because the non glacerized landscape has been exposed to cosmic radiation since early holocene deglaciation sediment from glacerized areas contains a low but measurable concentration of 10be that probably accumulated at depth during a prolonged period of exposure probably before the establishment of the greenland ice sheet the concentration of 10be in mixed fluvial sediment and in terrace sediment is low and similar to the concentration in sediment from glacerized areas which indicates that the greenland ice sheet is the dominant source of sediment moving through the landscape outside the glacial margin in the areas we sampled copyright 2014 john wiley sons ltd

aminostratigraphy of european marine interglacial deposits molluscan fossils collected from shallow water marine sediment across nw europe and nearby arctic regions have been analysed for the extent of isoleucine epimerization dl ratio in indigenous protein residues the dl ratios confirm that essentially all classical eemian sites from nw europe are of the same age and are correlative with the type locality near amersfoort in the netherlands shells from interglacial marine sediment beneath the type weichselian till in poland also correlate with the type eemian site dl ratios in holsteinian marine shells 0 29 are substantially higher than in their eemian counterparts 0 17 late cromerian shells yield even higher ratios 0 46 dl ratios in late glacial shells 0 06 and middle weichselian shells 0 09 permit differentiation from modern 0 01 and last interglacial material based on the position of the matuyama brunhes boundary and the differences in dl ratios the eemian must correlate with isotope substage 5e whereas the holsteinian is most likely substage 7c possibly stage 9 but certainly younger than stage 11 intra saalian warm periods may be terrestrial equivalents of the younger substages of stage 7 extensive pre eemian marine sediments along the sw coast of denmark previously correlated with the holsteinian are shown to be of late cromerian age the underlying till there is the first widespread evidence of a pre elsterian till in nw europe dl ratios in molluscs from last interglacial sites along the arctic coast of the ussr the arctic islands and eastern greenland are substantially lower than in their european counterparts due to their low thermal histories the combined mid and high latitude data are used to develop a predictive model for the expected dl ratio in any of several moderate epimerization rate taxa for last interglacial sites with mean temperatures between 20 and 15 c not all sites could be unambiguously assigned to an established interglacial the fjosanger norway and margareteberg sweden sites previously thought to be eemian yield dl ratios higher than in secure nearby eemian material it is yet unresolved whether these are aberrant sites or if they predate the last interglacial in situ shoreline deposits encountered in borings in sw belgium and in exposures on the belgium coastal plain contain molluscs that yield dl ratios intermediate between secure eemian and late weichselian ratios raising the possibility that a late stage 5 high sea level event attained near modern levels in the southern north sea basin resolution of these uncertainties is the focus of future work

new observations of local seismicity by the sn 1 seafloor observatory in the ionian sea off shore eastern sicily italy summary seismicity in eastern sicily as recorded by the submarine network 1 seafloor observatory sn1 in the period from 2002 october to 2003 may is examined with the aim of identifying the as yet poorly known seismogenic zones placed in the ionian basin where some of the strongest earthquakes have occurred a comparison between the seismic recordings of land networks and the seafloor station has allowed us to focus on low magnitude seismicity only recorded by sn 1 we have analysed 239 high quality events from among a total of 485 seismic signals not included in the land based network bulletins the waveform features and the possible source zones for those events are investigated by means of polarization and particle motion techniques most of the 239 events 213 are characterized by high values of rectilinearity typical of p and s arrival particle motions while the remaining 26 events have different polarization features with an emergent first phase and prevalently planar polarization we have interpreted the latter signals as being associated to submarine landslides from particle motion analysis we have determined the azimuthal distribution of the events and the incidence angles of p waves in respect to the observatory with the aim of determining their distribution in relation to the active but scarcely known structural setting of the off shore area moreover the integrated locations of some earthquakes occurring in the study area and recorded by sn 1 and land stations was performed to determine the apparent p wave velocity necessary to calculate source station distances as an additional result of the integration we have obtained more accurate locations of earthquakes occurring in the coastal and off shore areas of eastern sicily associated with reduced horizontal and vertical errors and significantly lower values of azimuthal gaps lastly a location distribution of the 213 analysed events was obtained by setting two conditions 1 a maximum epicentral distance to a fixed depth coinciding with the depth of the seafloor station and 2 a minimum epicentral distance associated to the maximum depth of events accordingly two patterns of seismicity were determined for the maximum and the minimum expected spread of the hypocentres the main features of both patterns are a diffuse seismicity in the western ionian basin with a major epicentre density se of sn 1 and a depth of most of the events within 60 km local magnitude determination was also performed taking into account an attenuation law proposed for southeastern sicily despite the uncertainties in the location distribution using single station recordings the results show diffuse seismicity all around sn 1 and in particular in the off shore area

numerical models of faulting at oblique spreading centers obliquely spreading mid ocean ridges such as the reykjanes ridge display two distinct fault sets distinguishable by orientation and position on axis faults are oriented oblique to both the trend of the axis and the normal to the relative plate separation vector while faults on the flanks strike approximately parallel to the ridge axis numerical modeling techniques are used here to simulate the development of faulting on the reykjanes ridge stresses acting in a cross section through the lithosphere at a slow spreading ridge are investigated using the fast lagrangian analysis of continua flac explicit difference modeling software the predicted stresses from the cross sectional models are imposed as a condition in boundary element models of fracture propagation and linkage on axis fault simulations run under conditions similar to the reykjanes ridge successfully reproduce the mapped distribution of faults and predict the observed orientation of the axial volcanic ridges simulations of fractures away from the axis show the development of axis parallel faults by the interaction and linkage of fractures which have been rafted off axis also in accord with observations stresses modeled in cross section favor downdip displacement on faults dipping toward the ridge axis

spatiotemporal distribution of the seismicity along the mid atlantic ridge north of the azores from hydroacoustic data insights into seismogenic processes in a ridge hot spot context 1 the seismicity of the north atlantic was monitored from may 2002 to september 2003 by the sirena array of autonomous hydrophones the hydroacoustic signals provide a unique data set documenting numerous low magnitude earthquakes along the section of the mid atlantic ridge mar located in a ridge hot spot interaction context during the experiment 1696 events were detected along the mar axis between 40 n and 51 n with a magnitude of completeness level ofmb 2 4 inside the array location errors are in the order of 2 km and errors in the origin time are less than 1 s from this catalog 15 clusters were detected the distribution of source level sl versus time within each cluster is used to discriminate clusters occurring in a tectonic context from those attributed to non tectonic i e volcanic or hydrothermal processes the location of tectonic and non tectonic sequences correlates well with regions with positive and negative mantle bouguer anomalies mbas indicating the presence of thinner colder and thicker warmer crust respectively at the scale of the entire array both the complete and declustered catalogs derived from the hydroacoustic signals show an increase of the seismicity rate from the azores up to 43 30 n suggesting a diminishing influence of the azores hot spot on the ridge axis temperature and well correlated with a similar increase in the along axis mbas the comparison of the mar seismicity with the residual mba rmba at different scales leads us to think that the low magnitude seismicity rates are directly related to along axis variations in lithosphere rheology and temperatures

regional seismicity of the mid atlantic ridge observations from autonomous hydrophone arrays summary autonomous hydrophones arrays are an excellent tool for monitoring mid ocean ridge seismic activity the major advantage of using arrays of autonomous hydrophones for recording deep ocean ridge earthquakes is its low magnitude detection thresholds achievable using hydroacoustic techniques regional analysis of the detection thresholds of the different autonomous hydrophones arrays deployed along the mid atlantic ridge reveals the strong influence of the detection threshold in the number of recorded events and it must be taken into account in any further analysis in this study the analysis of both autonomous hydrophones and teleseismically detected mid atlantic ridge seismicity reveals that the background seismicity from the relatively short recording periods of the autonomous hydrophones mimic the results of the much longer teleseismic recording it also reveals that seismicity generally cluster at both the segment scale and on mantle bouguer anomaly maxima the big majority of these clusters seem to be related to dyke intrusions and propagation along the mid atlantic ridge these dyke intrusions interact with the mainshock aftershock sequences the seismic sequences mainshock aftershock analysis reveals that the strength of the faults is highly influenced by the mode or style of faulting detachment faults which are ubiquitous along the mid atlantic ridge can produce more prolific shorter duration seismic sequences revealing faster and reduced strain releases in comparison to higher angle normal faults this reduced strain release is most likely to occur due to the presence of higher levels of serpentinization on detachment faults higher levels of serpentenisation can also promote an aseismic transient slip on the mainshock aftershock sequences

the northern mid atlantic and reykjanes ridges spreading center morphology between 55 50 n and 63 00 n seamarc ii and hydrosweep acoustic imagery and bathymetry reveal that the northern mid atlantic ridge mar and reykjanes ridge between 55 50 n and 63 00 n are segmented seafloor spreading centers that exhibit structural morphologies that vary with distance from iceland the northern 100 km of the mar 55 50 n 56 47 n is oriented 005 perpendicular to the spreading azimuth and contains four third order spreading segments separated along strike by right and left stepping axial discontinuities the boundary between mar and reykjanes ridge occurs at 56 47 n where the bight transform fault offsets the neo volcanic axis 15 km right laterally across a single linear fault oriented 092 this is the only transform fault between 55 50 n and 63 00 n and is inferred to have generated the bight fracture zone the reykjanes ridge lies between the bight transform and iceland s reykjanes peninsula and is oriented 30 oblique to the spreading orthogonal direction axial faults and volcanic systems on the reykjanes ridge are arranged in a right stepping en echelon pattern and display strikes intermediate between the spreading orthogonal direction and the strike of the ridge which is compatible with experimental models of oblique extension spreading segments on the northern mar and reykjanes ridge are defined structurally and bathymetrically at the smallest scale the volcanic axis is segmented into individual volcanic systems 4 45 km long which are separated along strike by intervolcano gaps or offsets these features are analogous to fourth order spreading segments documented elsewhere on the mar axial volcanic systems are superimposed on intermediate wavelength 13 65 km axial topographic highs that constitute third or second order spreading segments segment boundaries occur at axial depth maxima which correspond to offsets in the volcanic axis four primary characteristics of the spreading axis axial valley depth axial boundary fault throw relief along the neovolcanic axis and degree of inter segment structural discontinuity decrease toward the north this variation is consistent with higher crustal temperatures near iceland due to either thicker crust or elevated mantle temperatures

surface mass balance and stable oxygen isotope ratios from shallow firn cores on fimbulisen east antarctica the mass balance of antarctica is one of the crucial factors for determining sea level change in a warming climate the marginal zones of the continent namely the ice shelves are most sensitive to climate change during the 2009 10 austral summer an extensive glaciological field campaign was carried out on fimbulisen an ice shelf in east antarctica to investigate its recent surface mass balance shallow 10 18 m firn cores were drilled and accumulation rates and stable isotope ratios determined for firn core dating two different methods were compared 1 seasonal variations of stable oxygen isotope ratios d 18 o and 2 dielectric profiling including using the volcanic eruptions of pinatubo philippines 1991 and el chichon mexico 1982 as time markers the mean annual accumulation for the period 1992 2009 ranges from 298 to 349 mm w e a 1 the interannual variability at the drilling sites is 30 accumulation rates show a weak decreasing trend during the past 20 30 years which is statistically significant only for one of the cores stable isotope ratios were compared to the snowfall temperature of neumayer station neither the temperatures nor the d 18 o values show any trend for the investigated time period

aftershock sequences in the mid ocean ridge environment an analysis using hydroacoustic data abstract hydroacoustic data from autonomous arrays and the u s navy s sound surveillance system sosus provide an opportunity to examine the temporal and spatial properties of seismicity along portions of the slow spreading mid atlantic ridge mar intermediate spreading juan de fuca ridge jdfr and fast spreading east pacific rise epr aftershock and foreshock events are selected from the hydroacoustic earthquake catalog using single link cluster slc analysis with a combined space time metric in the regions examined hydroacoustic data improve the completeness level of the earthquake catalog by 1 5 2 0 orders of magnitude allowing the decay constant p of the modified omori law mol to be determined for individual sequences a non parametric goodness of fit test indicates six of the seven sequences examined are described well by a mol model the p values obtained for individual ridge and transform sequences using hydroacoustic data are larger than that previously estimated from the analysis of a stacked sequence generated from teleseismic data for three sequences along the siqueiros discovery and western blanco transforms p values are estimated to be 0 94 1 29 the spatial distribution of aftershocks suggests that the mainshock rupture is constrained by intra transform spreading centers at these locations an aftershock sequence following a 7 1 m s thrust event near the northern edge of the easter microplate exhibits p 1 02 0 11 within the sequence aftershocks are located to the north of a large topographic ridge which may represent the surface expression of the shallow dipping fault that ruptured during the mainshock two aftershock sequences near 24 25 n and 16 35 n on the mar exhibit higher p values 1 74 0 23 and 2 37 1 65 although the latter estimate is not well constrained because of the small number of aftershocks larger p values along the ridge crest might reflect a hotter thermal regime in this setting additional monitoring however will be needed to determine if p value differences between the ridge and transform sequences are robust a 1999 sequence on the endeavour segment of the jdfr which has been correlated with changes in the hydrothermal system is described poorly by the mol model the failure of the mol model the anomalously large number of earthquakes within the sequence and absence of a clearly dominant mainshock are inconsistent with aftershock activity and the simple tectonic origin that has been proposed previously for this sequence

accumulation variability derived from an ice core from coastal dronning maud land antarctica a 100 m long ice core was retrieved from the coastal area of dronning maud land dml antarctica in the 2000 01 austral summer the core was dated to ad 1737 by identification of volcanic horizons in dielectrical profiling and electrical conductivity measurement records in combination with seasonal layer counting from high resolution oxygen isotope d 18 o data a mean long term accumulation rate of 0 29 m a 1 w e was derived from the high resolution d 18 o record as well as accumulation rates during periods in between the identified volcanic horizons a statistically significant decrease in accumulation was found from about 1920 to the present a comparison with other coastal ice cores from dml suggests that this is a regional pattern

amino acid geochronology resolution and precision in carbonate fossils changes in indigenous proteins preserved in carbonate skeletons can be used to estimate the time elapsed since death of the organism racemization the most widely used reaction in amino acid geochronology refers to the inversion of l amino acids to their d configuration for the protein amino acid l isoleucine racemization occurs about only one of the two chiral carbon atoms this reaction epimerization proceeds from an initial dl ratio near zero to an equilibrium ratio of about 1 30 the reaction rate is controlled primarily by temperature and to a lesser degree by the nature of the proteins themselves a variable related to taxonomy and the extent of protein degradation analyzing monospecific samples minimizes the taxonomic variable the resolving power of dl ratios as relative age indices is a function of the reaction rate degree of natural variability and analytical uncertainty natural variability is defined as the spread in ratios in five well preserved shells of the same age from a single stratum and is primarily related to taxonomy it can range from 20 or more in taxa of low reliability to 1 in taxa of greatest integrity 5 to 10 is to be expected analytical uncertainty within a single laboratory is relatively insignificant amounting to no more than 2 but interlaboratory comparisons suggest caution in comparing ratios determined at different laboratories or by different techniques sampling appropriate portions of a shell is essential to minimize variability in dl ratios site temperature exerts the greatest control on reaction rate hence resolving power for tropical sites 25 c age differences 1 ka can be resolved within the holocene and ca 5 to 10 ka for older samples as the rate decreases equilibrium is attained after 150 to 300 ka the reaction rate is substantially lower at mid latitude sites ca 10 c where equilibrium requires about 2 ma and resolution within the last glacial cycle is no better than 10 to 20 ka arctic sites 10 c show almost no measurable racemization within the holocene and in extreme cases even within the last 100 ka equilibrium is not attained in 10 ma the extent of amino acid racemization epimerization in carbonate fossils provides chronological information for the critical time period beyond radiocarbon dating dl ratios can be used directly as relative age indices and with suitable calibration can provide reasonable estimates of absolute age and or effective diagenetic temperature improving the accuracy of racemization based age estimates requires a better understanding of racemization kinetics in carbonate systems

detailed distribution of microearthquakes along the northern reykjanes ridge off sw iceland we have obtained a snapshot image of the earthquake activity along the northern reykjanes ridge rr using a dense ocean bottom seismometer obs array the earthquakes are narrowly concentrated along the ne sw trending ridge crest the seismicity is segmented into clusters by the en echelon nne ssw trending axial volcanic systems which characterize the obliquely spreading ridge the hypocenters are concentrated at somewhat greater depths 3 7 km than on the reykjanes peninsula rp where the crust is thicker normal faulting dominates at the ridge crest the focal planes are oriented more ne sw than nne ssw i e parallel to the ridge crest and its peripheral faults rather than the trend of individual axial volcanic systems and associated faults

spatial variability at shallow snow layer depths in central dronning maud land east antarctica spatial variability at swallow snow layer depths in central dronning maud land east antarctic

firnification and the effects of wind packing on antarctic snow using firn core data from ten widely spread antarctic sites the depen dence of firnification on temperature wind and accumulation rate has been examined with two empirical models one model relates the square of the porosity to the logarithm of the overburden pressure and yields good fit to data through the first stage of firnifica tion up to around 0 70 0 75 mg m 3 beyond which it severely overestimates density all three meteorological factors enter into this model with higher temperatures and stronger winds increasing firnification rates whilst higher accumulation rates have the opposite effect at any given depth a temperature increase of looe has the equivalent effect to a wind speed increase of 5 m s i or an accumulation rate decrease of 0 10 m a w e a sec ond model equates the logarithm of the porosity to overburden pressure and gives a much better fit to field data at higher densities where values asymptote to the bubble free density of pure ice this model generally yields a poor match to field data in the upper layers with surface densities generally overestimated annual mean wind speed appears to be the least important of the local variables in this case consistent with the success of the model at greater depth in matching data profiles

generation of hydroacoustic signals by oceanic subseafloor earthquakes a mechanical model summary for more than 15 yr the recording of hydroacoustic signals with hydrophones moored in a minimum sound velocity channel called the sofar sound fixing and ranging channel has allowed for detection and localization of many small magnitude earthquakes in oceanic areas however the interpretation of these hydroacoustic signals fails to provide direct information on the magnitudes focal mechanisms or focal depths of the causative earthquakes these limitations result in part from an incomplete understanding of the physics of the conversion across the seafloor interface from seismic waves generated by subseafloor earthquakes to hydroacoustic t waves to try and overcome some of these limitations we have developed a 2 d finite element mechanical model of the conversion process by computing an exact solution of the velocity field of the waterborne t waves our model shows that a double couple source mechanism of a subseafloor earthquake generates t waves whose take off angles are adequate to allow penetration into the sofar channel and efficient trapping by this waveguide furthermore our model confirms that a double couple source with a high s wave content produces higher amplitude t waves than a simple explosive source which only generates p waves

the interaction of katabatic winds and the formation of blue ice areas in east antarctica blue ice areas bias are an extreme example of a local mass balance gradient and are furthermore reasonably stable in time and space owing to local feed back mechanisms a meteorological experiment performed in and around a blue ice area in dronning maud land east antarctica showed that during driftingsnow conditions surface wind speed over the blue ice behind the mountain barrier is equal to that away from the mountains when corrected for surface roughness and stability this implies that use of diagnostic katabatic wind models to estimate divergence of drifting snow can be extended to the situation where nunataks are involved in preventing the drifting snow from passing which is the case for most bias a diagnostic model is tested for a two dimensional profile in terre adelie after which it is applied to entire east antarctica the present order of magnitude estimate shows that areas sensitive to blue ice formation appear where precipitation is low and mean annual wind speed is high i e in dronning maud land and the drainage basin of lambert glacier the results appeared to be especially sensitive to a change in inversion strength a decrease in inversion strength weakens the katabatic flow and thus the amount of snowdrift transport reducing the area where bias can develop

identification of antarctic ablation areas using a regional atmospheric climate model the occurrence of antarctic ablation areas in dronning maud land the lambert glacier basin victoria land the transantarctic mountains and the antarctic peninsula is realistically predicted by the regional atmospheric climate model racmo2 ant with snowdrift related processes calculated offline antarctic ablation areas are characterized by a low solid precipitation flux in combination with strong sublimation snowdrift erosion and or melt the strong interaction between atmospheric circulation and topography plays a decisive role in the precipitation distribution and hence that of ablation areas three types of antarctic ablation areas can be distinguished all occurring in dry regions type 1 is the erosion driven ablation area caused by 1 d and or 2 d divergence in the katabatic wind field at high elevations 2000 3200 m asl type 2 is the sublimation driven ablation area this type occurs at lower elevations

importance of aeolian processes in the origin of the north polar chasmata mars abstract a detailed examination of the location and orientation of sand dunes and other aeolian features within the north polar chasmata indicates that steep scarps strongly influence the direction and intensity of prevailing winds these steep scarps are present at the heads and along the margins of the north polar chasmata topographic profiles of the arcuate head scarps and equator facing wall of chasma boreale reveal unusually steep polar slopes ranging from 6 30 the relatively steep sloped 8 sinuous scarp at the head of two smaller chasmata located west of chasma boreale exhibits an obvious resistant cap forming unit scarp retreat is occurring in places where the cap unit is actively being undercut by descending slope winds low albedo surfaces lacking sand dunes or dust mantles are present at the base of the polar scarps a 100 300 m deep moat located at the base of the scarps corresponds with these surfaces and indicates an area of active aeolian scour from descending katabatic winds small local dust storms observed along the equator facing wall of chasma boreale imply that slope wind velocities in chasma boreale are sufficient to mobilize dust and sand sized particles in the polar layered deposits pld two amphitheater forms located above the cap forming unit of the sinuous scarp and west of chasma boreale may represent an early stage of polar scarp and chasma formation these two forms are developing within a younger section of polar layered materials the unusually steep scarps associated with the polar chasmata have developed where resistant layers are present in the pld offering resistance during the headward erosion and poleward retreat of the scarps steep slopes that formed under these circumstances enhance the flow of down scarp katabatic winds on the basis of these observations we reject the fluvial outflood hypothesis for the origin of the north polar chasmata and embrace a wind erosion model for their long term development in the aeolian model off pole katabatic winds progressively remove materials from the steep slopes below chasmata scarps undermining resistant layers at the tops of scarps and causing retreat by headward erosion assuming a minimum age for the onset of formation of chasma boreale 105 yr results in a maximum volumetric erosion rate of 0 35 km 3 yr 1 removal of this volume of material from the equator facing wall and head scarps of chasma would require a rate for scarp retreat of 0 5 m yr 1

balance velocities and measured properties of the antarctic ice sheet from a new compilation of gridded data for modelling this paper presents a new compilation of gridded data sets for three dimensional modeling of the antarctic ice sheet these are for surface elevation icethickness bedrock elevation and accumulation rate as interpolated on a 281 x 281 mesh with 20 km spacing and encompass all of the ice sheet and thesurrounding continental shelf data sources include the bamber digital elevation model from ers 1 radar altimeter data a redigitization of available ice thicknessdata the giovinetto accumulation data recent ice thickness data from british and german expeditions as well as accumulation data from german and norwegianexpeditions in particular new data were incorporated for the filchner ronne schelfeis and for dronning maud land arising from the epica pre site survey special attention was devoted to carefully match the various data sources both among themselves as across the grounding line and below the ice shelves toenable ice sheet expansion and retreat in dynamic situations as an application the balance flow is calculated over the entire ice sheet using a two dimensionalfinite difference scheme and compared with a previous assessment this brought to light the existence of ice streaming features extending well inland of the icesheet a detailed zoom over dronning maud land exhibits the general flow characteristics of interest for locating a future deep drilling site as a by product anupdated value of 26 4 x 106 km3 was obtained for the total volume of the ice sheet and ice shelves or equivalent to 61 1 m of global sea level rise after removalof the ice sheet and subsequent oceanic invasion and isostatic rebound the total accumulation over the grounded ice sheet including the antarctic peninsula is1924 gta 1 or between 5 and 20 higher than earlier estimates including all of the ice shelves the value is 2344 gta 1

seafloor seismicity antarctic ice sounds cetacean vocalizations and long term ambient sound in the indian ocean basin this paper presents the results from the deflo hydroacoustic experiment in the southern indian ocean using three autonomous underwater hydrophones complemented by two permanent hydroacoustic stations the array monitored for 14 months from november 2006 to december 2007 a 3000 x 3000 km wide area encompassing large segments of the three indian spreading ridges that meet at the indian triple junction a catalogue of 11 105 acoustic events is derived from the recorded data of which 55 per cent are located from three hydrophones 38 per cent from 4 6 per cent from five and less than 1 per cent by six hydrophones from a comparison with land based seismic catalogues the smallest detected earthquakes are m b 2 6 in size the range of recorded magnitudes is about twice that of land based networks and the number of detected events is 5 16 times larger seismicity patterns vary between the three spreading ridges with activity mainly focused on transform faults along the fast spreading southeast indian ridge and more evenly distributed along spreading segments and transforms on the slow spreading central and ultra slow spreading southwest indian ridges the central indian ridge is the most active of the three with an average of 1 9 events 100 km month along the sunda trench acoustic events mostly radiate from the inner wall of the trench and show a 200 km long seismic gap between 2 degrees s and the equator the array also detected more than 3600 cryogenic events with different seasonal trends observed for events from the antarctic margin compared to those from drifting icebergs at lower up to 50 degrees s latitudes vocalizations of five species and subspecies of large baleen whales were also observed and exhibit clear seasonal variability on the three autonomous hydrophones whale vocalizations dominate sound levels in the 20 30 and 100 hz frequency bands whereas earthquakes and ice tremor are a dominant source of ambient sound at frequencies 20 hz

stable isotope records from dronning maud land antarctica the european project for ice coring in antarctica epica includes a comprehensive pre site survey on the inland ice plateau of dronning maud land this paper focuses on the investigation of the o 18 content of shallow firn and ice cores these cores were dated by profiles derived from dielectric profiling and continuous flow analysis measurements the individual records were stacked in order to obtain composite chronologies of o 18 contents and accumulation rates with enhanced signal to noise variance ratios these chronologies document variations in the last 200 and 1000 years the o 18 contents and accumulation rates decreased in the 19th century and increased during the 20th century using the empirical relationships between stable isotopes accumulation rates and the 10 in firn temperature the variation of both parameters can be explained by the same temperature history but other causes for these variations such as the build up of the snow cover cannot be excluded a marked feature of the 1000 year chronology occurs during the period ad 1180 1530 when the o 18 contents remains below the long term mean cross correlation analyses between five cores from the weddell sea region and dronning maud land show that o 18 records can in some periods be positively correlated and in others negatively correlated indicating a complex climatic history in time and space

seamount volcanism at the reykjanes ridge relationship to the iceland hot spot the axial zone of the reykjanes ridge is covered with small 0 5 3 km in diameter volcanoes that pile together to form larger axial volcanic ridges this style of volcanism is similar to that at the mid atlantic ridge mar and may be common to slow spreading ridges despite proximity of the reykjanes ridge to the iceland hot spot in this study we quantitatively investigate the population of seamounts in three study areas at the reykjanes ridge areas a and b are centered at 62 n and 60 n respectively area c is centered at 58 n and is located south of the transition in ridge morphology from an axial high to an axial graben using multibeam bathymetry data 541 seamounts summit height h 50 m were identified in the three areas and their size and shape statistics were compiled additionally 105 seamounts in areas b and c were recognized in deep towed side scan images and their surface morphologies hummocky or smooth were recorded on the basis of estimated population parameters we find that seamounts at the reykjanes ridge are more abundant 310 20 per 103 km2 on average than at the mar between 24 and 30 n 200 10 per 103 km2 significant along axis variations exist at the reykjanes ridge however which are not simply related to distance from the hot spot area b has nearly twice the abundance of seamounts as either area a or area c variation in the characteristic height of the seamount population is also observed between the reykjanes ridge 68 2 m and the mar 58 2 m but no significant variation is found between our three study areas a dramatic change in seamount surface morphology occurs between areas b and c there are no side scan data from area a area c has 78 hummocky seamounts similar to the proportion observed at the mar while area b has 83 smooth seamounts on the basis of these results we present a conceptual model for building the shallow crust at the slow spreading reykjanes ridge that takes into account the possible influence of the iceland hot spot on the crustal melt delivery system and its influence on variables that control seamount abundances sizes shapes and surface morphologies in this model we suggest that the increased seamount production and proliferation of smooth seamounts in area b may be associated with a pulse of hot spot material in the form of asthenosphere of higher temperature that has recently affected area b

the epica ice core from dronning maud land first results from stable isotope measurements the european project for ice coring in antarctica epica focuses on the drilling of two deep ice cores the first at dome c and the second at kohnen station 75 00 s 0 04 e in dronning maud land dml this paper deals with stable isotope records from ice cores drilled in dml in the first season the deep epica dml core reached a depth of 450 m recovering ice approximately 7000 years old generally the d 18 o record indicates a stable holocene climate and shows low variability however during the last 4000 years based on a preliminary time scale the d 18 o values decrease continuously by about 0 6 and the deuterium excess values increase by about 0 5 t he correlation between d 18 o and the deuterium excess d is investigated for a 50 m long core section and the near surface snow high pass filtered profiles are positively correlated whereas the correlation between low pass filtered profiles is negative a post depositional effect due to diffusion processes can be seen in a sub annually resolved profile from snow pit samples changes in the seasonality of the evolution of the snow cover and the consequences for stable isotope content are demonstrated with data from ice core b31

a century of accumulation and temperature changes in dronning maud land antarctica a mass balance program was initiated in the vestfjella heimefrontfjella area of western dronning maud land during the austral summer of 1988 1989 as a part of this program spatial and temporal variations in snow accumulation and temperature stable isotopes are measured using shallow firn cores in this paper we present surface accumulation data and discuss the climatic implications of the stable isotope records from two shallow firn cores one 30 m deep core obtained about 200 km from the coast at 700 m asl 73 36 s 12 26 w covers the period 1932 1991 the other core was drilled at about 500 km from the coast at 2900 m asl 75 00 s 2 00 e and covers the period 1865 1991 the recent accumulation increase that has been reported from several areas of the antarctic continent is not present in either of these records instead our coastal record suggests a significant decrease in accumulation with the strongest trend from about 1975 there is a positive trend in the oxygen isotope signal in both cores which in the coastal core corresponds to a temperature increase of about 1 8 c since the early 1930s and in the high altitude core to about 0 8 c since 1865 however it is likely that part of this increase in 18o is due to a change of moisture source

spatial distribution of snow in western dronning maud land east antarctica mapped by a ground based snow radar spatial distribution of snow in western dronning maud land east antarctica mapped by a ground based snow radar

low frequency seismic signals recorded by obs at stromboli volcano southern tyrrhenian sea 1 five three component broadband ocean bottom seismometers obss were deployed on the seafloor around the aeolian islands southern tyrrhenian sea by comparing obss digital seismograms we found a low frequency seismicity recorded only at obs05 the nearest seafloor station to stromboli volcano this seismicity appears in the form of a continuous seismic signal tremor like signal as well as a considerable number of shock like events we focused on recordings from obs05 to verify their correlation with stromboli volcanic activity from the spectral analysis we observed low frequency events lp events superposed upon the continuous background noise tremor lp events and tremor showing similar energy fluctuations and frequency content appear to be produced by the same dynamic processes we interpret this low frequency seismicity as probably originating from a continuous uprising of gas bubbles from the deeper part of the stromboli magmatic column this could highlight the existence of a deeper source for low frequency seismicity

a benchmark dataset of in situ antarctic surface melt rates and energy balance abstract surface melt on the coastal antarctic ice sheet ais determines the viability of its ice shelves and the stability of the grounded ice sheet but very few in situ melt rate estimates exist to date here we present a benchmark dataset of in situ surface melt rates and energy balance from nine sites in the eastern antarctic peninsula ap and coastal dronning maud land dml east antarctica seven of which are located on ais ice shelves meteorological time series from eight automatic and one staffed weather station neumayer ranging in length from 15 months to almost 24 years serve as input for an energy balance model to obtain consistent surface melt rates and energy balance results we find that surface melt rates exhibit large temporal spatial and process variability intermittent summer melt in coastal dml is primarily driven by absorption of shortwave radiation while non summer melt events in the eastern ap occur during fohn events that force a large downward directed turbulent flux of sensible heat we use the in situ surface melt rate dataset to evaluate melt rates from the regional atmospheric climate model racmo2 and validate a melt product from the quikscat satellite

volcanism and hydrothermalism on a hotspot influenced ridge comparing reykjanes peninsula and reykjanes ridge iceland abstract current estimates indicate that the number of high temperature vents one of the primary pathways for the heat extraction from the earth s mantle at least 1 per 100 km of axial length scales with spreading rate and should scale with crustal thickness but up to present shallow ridge axes underlain by thick crust show anomalously low incidences of high temperature activity here we compare the reykjanes ridge an abnormally shallow ridge with thick crust and only one high temperature vent known over 900 km axial length to the adjacent subaerial reykjanes peninsula rp which is characterized by high temperature geothermal sites confined to four volcanic systems transected by fissure swarms with young holocene volcanic activity multiple faults cracks and fissures and continuous seismic activity new high resolution bathymetry gridded at 60 m of the reykjanes ridge between 62 30 n and 63 30 n shows seven axial volcanic ridges avr that based on their morphology geometry and tectonic regime are analogues for the volcanic systems and fissure swarms on land we investigate in detail the volcano tectonic features of all mapped avrs and show that they do not fit with the previously suggested 4 stage evolution model for avr construction instead we suggest that avr morphology reflects the robust or weak melt supply to the system and two or more eruption mechanisms may co exist on one avr in contrast to 4 stage evolution model our interpretations indicate that unlike on the reykjanes peninsula faults on and around avrs do not cluster in orientation domains but all are subparallel to the overall strike of avrs orthogonal to spreading direction high abundance of seamounts shows that the region centered at 62 47 n and 25 04 w between avr 5 and 6 is volcanically robust while the highest fault density implies that avr 1 and southern part of avr 6 rather undergo period of melt starvation based on our observations and interpretations we expect all of the avrs on reykjanes ridge to be hydrothermally active but morphological and hydrographic settings of this ridge may cause hydrothermal plumes to be quickly dispersed and diluted due to exposure to strong bottom currents therefore combined ctd and autonomous vehicles surveys are probably the most efficient methods for hydrothermal exploration along the reykjanes ridge