integrating palaeocaves into palaeolandscapes an analysis of cave levels and karstification history across the gauteng malmani dolomite south africa abstract the drimolen palaeocave system in the fossil hominid sites of south africa unesco world heritage site is well known for numerous remains of early hominins such as paranthropus robustus and early homo these hominin fossils along with bone tools and notably diverse accumulation of non hominin primates and fauna have all been excavated from the main quarry area of the site where extensive lime mining took place here we report the first radiometric age of 1 712 0 269 ma for hominin bearing deposits associated with the dnh7 paranthropus robustus cranium in the main quarry area of the site which is consistent with recent biochronological estimates this age is similar to recent estimates for swartkrans member 1 hanging remnant somewhere between 2 3 and 1 8 ma which also contains paranthropus and early homo simultaneously we integrate the newly radiometrically dated main quarry deposits with a new fossil deposit the drimolen makondo discovered in 2013 that is situated some 50 m up the hill to the west from the main quarry it has experienced only limited disturbance from mining but much more extensive erosion preliminary excavations and analysis have revealed that the makondo infill is older than the main quarry dating to 2 706 0 428 ma its greater age is confirmed by biochronology the makondo thus overlap with the suggested end of deposition of australopithecus bearing sterkfontein deposits although it is yet to yield any hominin remains these new dates for the two drimolen palaeocave system deposits indicates that contrary to prior age estimates the drimolen site as a whole records the critical hominin and faunal turnover in south african palaeocommunities that occurred around 2 3 1 7 ma finally as the drimolen makondo represents a rare example of a pre 2 ma fossil bearing deposit in the gauteng exposures of the malmani dolomite we also integrate our results into the greater south african record of palaeodeposit formation most of which occur between 2 0 and 1 0 ma an analysis of the age of palaeocave infillings across the malmani dolomite suggests that as is classically the case with karst the height within the dolomite is broadly correlated to their age although with some notable exceptions that are likely related to localised geological features our analysis also indicates that most caves have undergone some form of secondary karstification related to a younger phase of cave formation contrasting with models that suggest the cavities all formed at the same time and that infill is related to erosion and the opening up of cave passages as such the reason that few pre 2 ma deposits have been identified in the gauteng exposures of the malmani dolomite is probably because these older caves have been eroded away identifying such early caves is critical in understanding whether earlier hominins may have once existed in south africa or if erosion of older deposits or an absence of speleogenesis at this time has made such early periods absent from the geological record

wind driven processes controlling oceanic heat delivery to the amundsen sea antarctica variability in the heat delivery by circumpolar deep water cdw is responsible for modulating the basal melting of the amundsen sea ice shelves however the mechanisms controlling the cdw inflow to the region s continental shelf remain little understood here a high resolution regional model is used to assess the processes governing heat delivery to the amundsen sea the key mechanisms are identified by decomposing cdw temperature variability into two components associated with 1 changes in the depth of isopycnals heave hve and 2 changes in the temperature of isopycnals water mass property changes wmp in the dotson getz trough cdw temperature variability is primarily associated with wmp the deeper thermocline and shallower shelf break hinder cdw access to that trough and cdw inflow is regulated by the uplift of isopycnals at the shelf break which is itself controlled by wind driven variations in the speed of an undercurrent flowing eastward along the continental slope in contrast cdw temperature variability in the pine island thwaites trough is mainly linked to hve the shallower thermocline and deeper shelf break there permit cdw to persistently access the continental shelf cdw temperature in the area responds to wind driven modulation of the water mass on shelf volume by changes in the rate of inflow across the shelf break and in ekman pumping induced vertical displacement of isopycnals within the shelf the western and eastern amundsen sea thus represent distinct regimes in which wind forcing governs cdw mediated heat delivery via different dynamics

the earthquake prediction experiment at parkfield california since 1985 a focused earthquake prediction experiment has been in progress along the san andreas fault near the town of parkfield in central california parkfield has experienced six moderate earthquakes since 1857 at average intervals of 22 years the most recent a magnitude 6 event in 1966 the probability of another moderate earthquake soon appears high but studies assigning it a 95 chance of occurring before 1993 now appear to have been over simplified the identification of a parkfield fault segment was initially based on geometric features in the surface trace of the san andreas fault but more recent microearthquake studies have demonstrated that those features do not extend to seismogenic depths on the other hand geodetic measurements are consistent with the existence of a locked patch on the fault beneath parkfield that has presently accumulated a slip deficit equal to the slip in the 1966 earthquake a magnitude 4 7 earthquake in october 1992 brought the parkfield experiment to its highest level of alert with a 72 hour public warning that there was a 37 chance of a magnitude 6 event however this warning proved to be a false alarm most data collected at parkfield indicate that strain is accumulating at a constant rate on this part of the san andreas fault but some interesting departures from this behavior have been recorded here we outline the scientific arguments bearing on when the next parkfield earthquake is likely to occur and summarize geophysical observations to date

glider observations of the dotson ice shelf outflow abstract the amundsen sea is one of the most productive polynyas in the antarctic per unit area and is undergoing rapid changes including a reduction in sea ice duration thinning ice sheets retreat of glaciers and the potential collapse of the thwaites glacier in pine island bay a growing body of research has indicated that these changes are altering the water mass properties and associated biogeochemistry within the polynya unfortunately difficulties in accessing the remote location have greatly limited the amount of in situ data that has been collected in this study data from a teledyne webb slocum glider was used to supplement ship based sampling along the dotson ice shelf dis this autonomous underwater vehicle revealed a detailed view of a meltwater laden outflow from below the western flank of the dis circumpolar deep water intruding onto the shelf drives glacial melt and the supply of macronutrients that along with ample light supports the large phytoplankton blooms in the amundsen sea polynya less well understood is the source of micronutrients such as iron necessary to support this bloom to the central polynya where chlorophyll concentrations are highest this outflow region showed decreasing optical backscatter with proximity to the bed indicating that particulate matter was sourced from the overlying glacier rather than resuspended sediment this result suggests that particulate iron and potentially phytoplankton primary productivity is intrinsically linked to the magnitude and duration of sub glacial melt from circumpolar deep water intrusions onto the shelf

a linear stratified ocean model of the coastal undercurrent the linear stratified ocean model of mccreary 1981 is used to study the wind driven response of the ocean near an eastern coast the model can be regarded as an extension of the inviscid models of lighthill 1969 and of gill clarke 1974 that allows the vertical diffusion of heat and momentum into the deep ocean solutions are still found as expansions of vertical normal modes vertical mixing affects each mode as a linear drag with a drag coefficient that increases rapidly with mode number n a zonally uniform band of steady equatorward winds forces the ocean and the resulting flow field has many features in common with observations at eastern boundaries there is a surface equatorward jet and a poleward coastal undercurrent confined within 10 20 km of the coast both currents extend well poleward of the wind band upwelling does not reach great depths but occurs only above the core of the undercurrent weak downwelling occurs at greater depths there is offshore ekman drift in the surface mixed layer and return flow at a depth slightly above the core of the undercurrent the baroclinic alongshore pressure gradient field and the vertical mixing of heat and momentum are essential elements of the model dynamics but the beta and horizontal mixing are not low order vertical modes n 6 tend toward a two dimensional balance they generate the transverse circulation pattern associated with coastal ekman pumping

antarctic thermocline dynamics along a narrow shelf with easterly winds abstractdetermining the role of southern ocean warm intermediate water for driving melting of the antarctic ice sheet is a major challenge in assessing future sea level rise analysis of 2859 ctd p

geological setting and age of australopithecus sediba from southern africa we describe the geological geochronological geomorphological and faunal context of the malapa site and the fossils of australopithecus sediba the hominins occur with a macrofauna assemblage that existed in africa between 2 36 and 1 50 million years ago ma the fossils are encased in water laid clastic sediments that were deposited along the lower parts of what is now a deeply eroded cave system immediately above a flowstone layer with a u pb date of 2 026 0 021 ma the flowstone has a reversed paleomagnetic signature and the overlying hominin bearing sediments are of normal polarity indicating deposition during the 1 95 to 1 78 ma olduvai subchron the two hominin specimens were buried together in a single debris flow that lithified soon after deposition in a phreatic environment inaccessible to scavengers

seismological monitoring on the 2003 tokachi oki earthquake derived from off kushiro permanent cabled obss and land based observations abstract japan marine science and technology center installed a cabled geophysical observatory system off kushiro hokkaido island in july 1999 this observatory system comprises three ocean bottom seismographs obss two tsunami gauges and a geophysical geochemical monitoring system 4 years and 2 months after the installation a megathrust earthquake the 2003 tokachi oki earthquake 26th september in japan standard time jst mjma 8 0 occurred along a plate boundary underneath a forearc basin where the system is located the system recorded clear unsaturated seismograms just at 28 6 km from the epicenter this paper demonstrates advantages brought by the cabled observatory to record the megathrust earthquake showing how earthquake detectability is improved dramatically combining permanent obs and land based observations around the region and importance of the in situ monitoring on the seismogenic zone in the present study processing obss and land based network together and comparing magnitudes of common observed earthquakes with national authorized network event detection level improved down to m 1 5 which is much lower than the previously designed as down to m 2 comparing detection level before and after installing obss we found dramatic improvement of the earthquake detection level in the interesting region real time continuous observations of microearthquakes since 1999 have brought us tremendous findings first a seismic quiescence started about 10 days before the 2003 tokachi oki earthquake second aftershock distribution is not uniform over the focal area and can be divided into several sub regions which might indicate an existence of several asperities we think that the geophysical observations helped to understand the initiation process of the rupture of the 2003 tokachi oki earthquake and that observations including seismological geodynamic hydrogeological and the other multidisciplinary observations would provide a clue to future understanding of seismogenic processes at subduction zones

is the oceanic heat flux on the central amundsen sea shelf caused by barotropic or baroclinic currents the glaciers that drain the west antarctic ice sheet into the amundsen sea are accelerating and experiencing increased basal melt of the floating ice shelves warm and salty deep water has been observed to flow southward in deep troughs leading from the shelf break to the inner shelf area where the glaciers terminate it has been suggested that the melting induced by this warm water is responsible for the acceleration of the glaciers here we investigate the structure of the currents and the associated heat flow on the shelf using in situ observations from 2008 to 2014 in dotson trough the main channel in the western part of the amundsen sea shelf together with output from a numerical model the model is generally able to reproduce the observed velocities and temperatures in the trough albeit with a thicker warm bottom layer in the absence of measurements of sea surface height we define the barotropic component of the flow as the vertical average of the velocity it is shown that the flow is dominated by warm barotropic inflows on the eastern side and colder and fresher barotropic outflows on the western side the transport of heat appears to be primarily induced by this clockwise barotropic circulation in the trough contrary to earlier studies emphasizing a bottom intensified baroclinic inflow as the main contributor

the interdisciplinary marine system of the amundsen sea southern ocean recent advances and the need for sustained observations the southern ocean exerts a profound influence on the functioning of the earth system in part because its location and unique bathymetric configuration enable direct linkages to the other major ocean basins ganachaud and wunsch 2000 and lumpkin and speer 2007 it is the site of the world s largest current system the antarctic circumpolar current acc which transfers waters and climatically ecologically important tracers between the atlantic indian and pacific oceans rintoul et al 2001 in addition to the strong horizontal connectivity the acc is also characterized by a vigorous overturning circulation which upwells warm nutrient rich waters from intermediate depth to the surface where they are modified by interactions with the atmosphere and cryosphere to form new water masses some of which are lighter and others more dense marshall and speer 2012 this overturning circulation structures the southern ocean both horizontally and vertically dictates the levels of its communication with the rest of the global ocean and is a fundamental control on the sequestration of carbon from the atmosphere into the ocean interior sallee et al 2012 in some locations the upwelled waters can intrude onto the antarctic shelves supplying heat and nutrients to the shallower regions this is believed to be especially effective in west antarctica where the southern edge of the acc moves close to the shelf break martinson 2011 orsi et al 1995 and thoma et al 2008

geomagnetic excursions knowns and unknowns geomagnetic excursions are short lived episodes when earth s magnetic field deviates into an intermediate polarity state understanding the origin frequency amplitude duration and field behavior associated with excursions is a forefront research area within solid earth geophysics recent advances in excursion research are summarized here and key further research is suggested to resolve major unanswered questions improving the global distribution of excursion records particularly from the southern hemisphere obtaining high resolution sedimentary excursion records with good age control from sites with sedimentation rates 10 cm kyr obtaining volcanic excursion records coupled with high precision geochronology and estimating excursion duration with high chronological precision will all facilitate hypothesis testing concerning the deep earth dynamics that generate geomagnetic excursions

geomagnetic excursions and paleointensities in the matuyama chron at ocean drilling program sites 983 and 984 iceland basin 1 we report natural remanent magnetization nrm directions and geomagnetic paleointensity proxies for part of the matuyama chron 0 9 2 2 ma interval from two sites located on sediment drifts in the iceland basin at ocean drilling program sites 983 and 984 mean sedimentation rates in the late matuyama chron are 15 9 and 11 5 cm kyr 1 respectively for the older part of the record 1 2 ma oxygen isotope data are too sparse to provide the sole basis for age model construction the resemblance of the volume susceptibility record and a reference 18o record led us to match the two records to derive the age models this match based on site 983 984 susceptibility is consistent with available site 983 984 benthic 18o data paleointensity proxies were derived from the slope of the nrm versus anhysteretic remanent magnetization plot for alternating field demagnetization in the 30 60 mt peak field range paleointensity lows correspond to polarity reversals at the limits of the jaramillo olduvai cobb mountain and reunion subchrons and to seven excursions in nrm component directions magnetic excursions defined here by virtual geomagnetic polar latitudes crossing the virtual geomagnetic equator are observed at 932 1048 1115 1190 1215 cobb mountain subchron 1255 1472 1480 1567 1575 gilsa subchron and 1977 ka the results indicate that geomagnetic directional excursions associated with paleointensity minima are a characteristic of the matuyama chron and probably of polarity chrons in general

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

modeling ocean processes below fimbulisen antarctica 1 model simulations of circulation and melting beneath fimbulisen antarctica obtained using an isopycnic coordinate ocean model are presented model results compare well with available observations of currents and hydrography in the open ocean to the north of fimbulisen and suggest that warm deep water exists above the level of a sub ice shelf bedrock sill the principal pathway for warm waters to enter the sub ice shelf cavity the model shows a southward inflow of warm deep water over this sill and into the cavity producing a mean cavity temperature close to 1 0 c this leads to high levels of basal melting 10 m a at the grounding line of jutulstraumen and an average melting over the ice shelf base close to 1 9 m a the southward inflow is a compensating flow caused by the northward outflow of fresh cold water produced by the basal melting results on inflow and melting are difficult to validate since no in situ measurements yet exist in the cavity if such high melt rates are realistic the mass balance of fimbulisen must be significantly negative and the ice shelves along dronning maud land must contribute about 4 4 msv of melt water to the weddell sea about 15 of the total antarctic meltwater input to the southern ocean

eddy overturning of the antarctic slope front controls glacial melting in the eastern weddell sea 1 the eastern weddell sea is characterized by narrow continental shelves and warm deep water wdw is located in close proximity to the ice shelves in this region the exchange of wdw across the antarctic slope front asf determines the rate of basal ice shelf melting here we present a unique data set consisting of 2351 vertical profiles of temperature and salinity collected by southern elephant seals mirounga leonina and a profile beneath the fimbul ice shelf fis obtained via drilling through 395 m of ice this data set reveals variations in salinity and temperature through winter and using a conceptual model of the coastal salt budget we quantify the main exchange processes our data show that modified wdw with temperatures below 1 5 c is advected onto the shelf and into the ice shelf cavities by an eddy overturning of the asf the onshore ekman flux of surface waters during summer is the main source of freshwater that leads to the formation of low salinity shelf waters in the region the modified wdw that reaches beneath the ice shelves is too cold for basal ice shelf melting to create such low salinity water a high resolution model of an idealized asf continental shelf ice shelf system supports the conclusions from the data analysis the inflow of wdw onto the continental shelf and into the ice shelf cavity occurs within a bottom boundary layer where the eddy advection in the model is particularly strong in close agreement with the observed vertical profile of temperature beneath the fis citation nost o a m biuw v tverberg c lydersen t hattermann q zhou l h smedsrud and k m kovacs 2011 eddy overturning of the antarctic slope front controls glacial melting in the eastern weddell sea j geophys res 116 c11014 doi 10 1029 2011jc006965

beyond 500ka progress and prospects in the upb chronology of speleothems and their application to studies in palaeoclimate human evolution biodiversity and tectonics abstract this review summarises current research aimed at extending the chronology and thus scientific utility of speleothems beyond the 500 ka limit previously imposed by conventional u th dating methods the u pb decay scheme is familiar to all geoscientists but its application to speleothems is a relatively recent development and one set to revolutionise their use in studies of climate change human evolution and migration biodiversity tectonics and landscape evolution technological advances such as the introduction of multi collector icpms instruments have played a key role in this breakthrough and multiple inter laboratory and inter method comparisons provide evidence that the methodology is now mature and that the ages obtained are robust some impediments remain in particular with respect to corrections for initial isotopic disequilibrium younger samples and the construction of internal chronologies older samples but these are areas of intense research activity and are likely to see significant advances in the near future the coupling of speleothem u pb dating with other nascent technologies offering the prospect of precise palaeotemperature estimation is an exciting development in palaeoclimate science while u pb chronologies of archaeological sites are producing important new insights into human evolution although less well developed at this point the methodology appears equally well suited and significant for future studies of past faunal change and landscape evolution

measurements beneath an antarctic ice shelf using an autonomous underwater vehicle the cavities beneath antarctic ice shelves are among the least studied regions of the world ocean yet they are sites of globally important water mass transformations here we report results from a mission beneath fimbul ice shelf of an autonomous underwater vehicle the data reveal a spatially complex oceanographic environment an ice base with widely varying roughness and a cavity periodically exposed to water with a temperature significantly above the surface freezing point the results of this the briefest of glimpses of conditions in this extraordinary environment are already reforming our view of the topographic and oceanographic conditions beneath ice shelves holding out great promises for future missions from similar platforms

measurements of ice thickness and seabed topography under the fimbul ice shelf dronning maud land antarctica 1 this paper presents results from seismic measurements of the ice and water column thickness of the fimbul ice shelf in the northeastern weddell sea seismic reflection measurements were conducted at 183 stations covering most of the ice shelf seismic velocities in the ice were derived from refraction measurements at 12 stations distributed evenly across the area as well as from temperature and density data from the fimbul ice shelf velocities in the water were derived from temperature and salinity data from beneath the fimbul ice shelf ice thicknesses were found to vary between 160 m and 550 m with uncertainties up to 10 m water column thicknesses up to 900 m were found within the central ice shelf cavity and values exceed 2000 m where the ice shelf overhangs the continental slope uncertainties in water column thickness are estimated to be 60 m and are dominated by the uncertainties in the shape of the seabed ice draft and seabed elevation was derived from ice and water column thickness assuming hydrostatic pressure the resulting map of seabed elevation and water column thickness suggests that the strong westward flowing coastal current will be steered under the ice shelf and thus drive a sub ice shelf flow warm deep water does not have direct access to the ice shelf cavity while relatively cold coastal waters shallower than 500 m will interact closely with the fimbul ice shelf

direct terrestrial marine correlation demonstrates surprisingly late onset of the last interglacial in central europe an interdisciplinary study of a small sedimentary basin at neumark nord 2 nn2 germany has yielded a high resolution record of the palaeomagnetic blake event which we are able to place at the early part of the last interglacial pollen sequence documented from the same section we use this data to calculate the duration of this stratigraphically important event at 3400 350 yr more importantly the neumark nord 2 data enables precise terrestrial marine correlation for the eemian stage in central europe this shows a remarkably large time lag of ca 5000 yr between the mis 5e peak in the marine record and the start of the last interglacial in this region

geoarchaeological and 3d visualisation approaches for contextualising in situ fossil bearing palaeokarst in south africa a case study from the 2 61 ma drimolen makondo abstract south africa contains a wealth of palaeokarst deposits that have yielded hominin fossils and early stone age archaeology despite the complex nature of deposition within many of these caves there has been a dearth of detailed geoarchaeological studies undertaken on these sites many sites in south africa have been interpreted using an overly simplistic member system based on simplified sedimentological attributes rather than chronostratigrahic units many of the defined members thus identify different but contemporary geological processes occurring in the caves this has caused serious confusion in reconstructing the life histories of palaeocaves and the ages of the fossil remains interned within them it is critical to uncover new sites that have not been extensively altered by decades of data collection and destructive mining techniques employed early in their discovery although unmined sites present their own problems with regards to extensive colluvium cover and access to fossil bearing units analysing strata that is found in situ enhances overall confidence of interpretations drawn a wealth of geoarchaeological and 3d visualisation techniques can now be employed to aid in the understanding of cave life histories as well as their excavation in this paper we present the first attempt to integrate and publish data from a range of such methods on south african fossil bearing palaeokarst using the newly discovered drimolen makondo deposit as a case study this includes the use of ground penetrating radar 3d visualisation through photogrammetry and multi scale 3d scanning micromophology and petrography palaeomagnetism mineral magnetism synchrotron radiation electron spin resonance uranium lead dating and biochronology our analysis has allowed us to successfully uncover the full extent of this new 2 61 ma fossil bearing palaeokarst deposit and to visualise and interpret its chronostratigraphy

recent advances and future prospects of the u th and u pb chronometers applicable to archaeology abstract the u th chronometer has revolutionized quaternary science in the last few decades and can now be considered a well established mature technique with growing application in archaeology as an alternative to 14 c dating and osl reaching well beyond the cutoff for both these methods applying the u pb technique to material within a time frame of interest to archaeology is a challenge only recently overcome with enormous potential for future development and use in terms of range u th can generally date material of between a few years and as much as 600 ka while u pb is best suited to material of 1 million years and older u th dating is typically precise with error margins of better than 1 routinely achievable for material of the last interglacial age or younger such precision is possible with u pb dating in the mid quaternary but most ages have uncertainties in the 5 10 range carbonates are the most desirable u series target material with closed system behaviour being particularly important for u th dating making inorganic deposits such as speleothems secondary cave carbonates tufa and calcrete ideal some biogenic carbonates such as coral and eggshell are often amenable to u series dating but less ideal material such as fossil teeth bone and mollusc shell usually continue to gain uranium after deposition meaning accurate ages cannot be calculated in all cases the importance of a thorough understanding of the context of dated material cannot be overstated in this contribution we review u th and u pb dating through an archaeological lens focussing on the methods themselves how to best interpret published data and how best to avoid common pitfalls we highlight the major successes through a number of case studies and provide an overview of what we believe to be the future directions of this field

the lower limb and mechanics of walking in australopithecus sediba the discovery of a relatively complete australopithecus sediba adult female skeleton permits a detailed locomotor analysis in which joint systems can be integrated to form a comprehensive picture of gait kinematics in this late australopith here we describe the lower limb anatomy of au sediba and hypothesize that this species walked with a fully extended leg and with an inverted foot during the swing phase of bipedal walking initial contact of the lateral foot with the ground resulted in a large pronatory torque around the joints of the foot that caused extreme medial weight transfer hyperpronation into the toe off phase of the gait cycle late pronation these bipedal mechanics are different from those often reconstructed for other australopiths and suggest that there may have been several forms of bipedalism during the plio pleistocene

seasonal variations of the antarctic coastal ocean in the vicinity of lutzow holm bay during the period of 1990 1992 year round oceanographic observations were conducted in the vicinity of lutzow holm bay east antarctica it was found that the thickness of the winter water ww layer characterized by a cold fresh oxygen rich water exhibits its maximum in the austral fall typically 500 m and its minimum in the austral summer typically 350 400 m the associated density variation of the water column explains only about one third of the seasonal variations in sea level at the coast which suggests a large seasonal variation in barotropic coastal flow prominent freshening occurs in the ww layer during fall this appears to be caused by the accumulation of ww whose upper portion is freshened in the preceding summer these seasonal variations appear to occur every year we propose that the seasonal variation in the ww layer is mainly caused by the seasonal variation in the wind over the coastal ocean in fall the prevailing easterly wind intensifies which increases the ekman convergence of ww in the coastal ocean while in summer the opposite occurs

high latitude oceanography using the autosub autonomous underwater vehicle a combination of measurements from autosub an autonomous underwater vehicle and ship based instruments are used to describe the oceanographic conditions beneath fimbul ice shelf antarctica the data show an intricate oceanographic regime that is suggestive of variability at seasonal or longer time scales results from a numerical model of the flow beneath the ice shelf lend support to a strong seasonal variability and data from instruments moored beneath the ice shelf show substantial temporal variations the autosub data indicate temperatures within the cavity somewhat lower than our model results would suggest thus our modeled melt rates average of 0 85 m yr21 might be overestimates although they are substantially lower than from previously published model studies 4 9 and 1 9 m yr21 the contribution of ice shelf melt in the freshwater balance of the waters upstream of the climatically important filchner ronne ice shelf needs to be reassessed

borehole image analysis of the nankai accretionary wedge odp leg 196 structural and stress studies electrical images recorded with resistivity at bit rab from two sites drilled during ocean drilling program odp leg 196 were analyzed to study the effects of subduction at the nankai margin for the first time in the history of scientific deep sea drilling in odp in situ complete borehole images of the decollement zone were obtained analyses of all drilling induced fracture data indicated that the maximum horizontal compressive stress shmax axes have an azimuth of 303 and analyses of breakout data from rab images indicated an azimuth of 310 these azimuths approximate the convergence direction of the philippine sea plate towards the eurasian plate the frontal thrust at site 808 was encountered at about 389 mbsf density porosity resistivity and gamma ray data change across the frontal thrust the decollement zone at the deformation front was identified between 937 and 965 mbsf the base of the decollement is sharply defined as the maximum extent of conductive fracturing and is marked by abrupt changes in physical properties mikada h becker k moore j c klaus a austin g l bangs n l bourlange s broilliard j bruckmann w corn e r davis e e flemings p b goldberg d b gulick s s hansen m b hayward n hills d j hunze s ienaga m ishiguro h kinoshita m macdonald r d mcneill l obana s hong o s peacock s pettigrew t l saito s sawa t thaiprasert n tobin h j tsurumi h 2002 proc odp initial rep 196 college station tx ocean drilling program the upper boundary of the decollement is marked by several sets of conductive fractures and by high variability in physical properties the decollement zone is characterized by intense brittle fracturing these fractures are considered to be the consequence of cyclic stresses and high fluid pressures in this zone we analyzed fracture dips and their orientations at both sites and found that they are all consistent with a unique stress field model surrounding the two sites

a new tide model for the antarctic ice shelves and seas we describe a new tide model for the seas surrounding antarctica including the ocean cavities under the floating ice shelves the model uses data assimilation to improve its fit to available data typical peak to peak tide ranges on ice shelves are 1 2 m but can exceed 3 m for the filchner ronne and larsen ice shelves in the weddell sea spring tidal ranges are about twice these values model performance is judged relative to the 5 10 cm accuracy that is needed to fully utilize ice shelf height data that will be collected with the geoscience laser altimeter system scheduled to be launched on the ice cloud and land elevation satellite in late 2002 the model does not yet achieve this level of accuracy except very near the few high quality tidal records that have been assimilated into the model some improvement in predictive skill is expected from increased sophistication of model physics but we also require better definition of ice shelf grounding lines and more accurate water column thickness data in shelf seas and under the ice shelves long duration tide measurements bottom pressure gauge or gps in critical data sparse areas particularly near and on the filchner ronne and ross ice shelves and pine island bay are required to improve the performance of the data assimilation model

eddy generation and jet formation via dense water outflows across the antarctic continental slope along various stretches of the antarctic margins dense antarctic bottom water aabw escapes its formation sites and descends the continental slope this export necessarily raises the isopycnals associated with lighter density classes over the continental slope resulting in density surfaces that connect the near freezing waters of the continental shelf to the much warmer circumpolar deep water cdw at middepth offshore in this article an eddy resolving process model is used to explore the possibility that aabw export enhances shoreward heat transport by creating a pathway for cdw to access the continental shelf without doing any work against buoyancy forces in the absence of a net alongshore pressure gradient the shoreward cdw transport is effected entirely by mesoscale and submesoscale eddy transfer eddies are generated partly by instabilities at the pycnocline sourcing their energy from the alongshore wind stress but primarily by instabilities at the cdw aabw interface sourcing their energy from buoyancy loss on the continental shelf this combination of processes induces a vertical convergence of eddy kinetic energy and alongshore momentum into the middepth cdw layer sustaining a local maximum in the eddy kinetic energy over the slope and balancing the coriolis force associated with the shoreward cdw transport the resulting slope turbulence self organizes into a series of alternating along slope jets with strongly asymmetrical contributions to the slope energy and momentum budgets cross shore variations in the potential vorticity gradient cause the jets to drift continuously offshore suggesting that fronts observed in regions of aabw down slope flow may in fact be transient features

phosphor imaging as a tool for in situ mapping of ppm levels of uranium and thorium in rocks and minerals abstract phosphor imaging is a type of digital autoradiography that has been widely used in biochemistry to examine radioactively tagged proteins we used phosphor imaging to map in situ u and th in polished slabs of geological materials including carbonates phosphates and silicate rich rocks we examined samples containing between 2 and 500 ppm u and 700 ppm th to evaluate the applicability of the technique to geological samples resolution of 1 mm or better was obtained even for low concentration 10 ppm samples these analyses are routine and only require a light box phosphor screen and access to a phosphor imager the technique is nondestructive relatively inexpensive and requires very little processing time we used this technique to identify u and th enriched carbonates and phosphates and to find hot spots of u and th rich minerals in a granodiorite these high resolution maps of u and th allow us to effectively sample for geochronology and identify potentially interesting samples for synchrotron x radiation studies the maps produced by phosphor imaging also have great potential for investigating the details of adsorption of radionuclides to rocks and minerals in contaminated areas

a model for the structure of the antarctic slope front the antarctic slope front is an oceanic front that appears to be a semi permanent feature situated above or near long sections of the shelf break of the antarctic continental shelf these sections include the shelf break of the ross and weddell seas it is distinguished by a v shaped structure unique to coastal antarctica in which isopycnals slope downward from near the surface on both the shallow continental shelf and the deep continental slope sides toward the bottom near the upper part of the slope in the regions where it is observed the overflow of dense water from the shelf down the slope is observed or presumed to occur such overflows entrain fluid from the overlying stratified environment into the downflow and this entrainment acts as a distributed sink of the overlying fluid a model of this frontal structure is constructed here consisting of the downslope flow modelled as a plume and the overlying fluid governed by quasi geostrophic dynamics with the effect of the plume on the latter being represented by a suitable distribution of sinks the alongslope currents follow from geostrophy and potential vorticity conservation two distinct flow regimes are found in the first regime a realistic depiction of the two sided v shaped structure is obtained where most of the fluid flowing off the shelf enters the downflow at the top of the slope constituting the shallow side of the v and fluid from offshore enters the deep side of the v alongslope flow in this region is mostly eastward in the second regime where most of the fluid flowing off the shelf passes over the downflow only the shallow side of the v is present and alongslope flow is westward near the shelf break and eastward further offshore

the endocast of mh1 australopithecus sediba the virtual endocast of mh1 australopithecus sediba obtained from high quality synchrotron scanning reveals generally australopith like convolutional patterns on the frontal lobes but also some foreshadowing of features of the human frontal lobes such as posterior repositioning of the olfactory bulbs principal component analysis of orbitofrontal dimensions on australopith endocasts mh1 sts 5 and sts 60 indicates that among these mh1 orbitofrontal shape and organization align most closely with human endocasts these results are consistent with gradual neural reorganization of the orbitofrontal region in the transition from australopithecus to homo but given the small volume of the mh1 endocast they are not consistent with gradual brain enlargement before the transition

low frequency currents and continental shelf waves in the southern weddell sea abstract the salient features of low frequency current fluctuations obtained from an analysis of eight current meter records from the continental shelf and slope of the southern weddell sea are compared to baroclinic and barotropic theories a simple baroclinic theory of internal waves is used successfully to predict high frequency spectral cutoff values from low frequency velocity ellipse calculations made from the continental slope mooring data the success of this theory indicates that the higher spectral energy levels observed over the slope compared to the shelf are probably due to baroclinic motions a barotropic model of free continental shelf waves probably by saint guily 1976 is adapted for the local topography and the predictions of the model compared to observations coherences and phases between moorings separated by 10 and 160 km in the along shelf direction provide substantial evidence of the existence of shelf waves as predicted by the theory for periods of 3 60 days and for the lowest

termites and necrophagous insects associated with early pleistocene gelasian australopithecus sediba at malapa south africa abstract this study focuses on two early pleistocene australopithecus sediba hominin specimens and associated fauna from malapa south africa these specimens have been interpreted as having fallen through a shaft opening into a cave where they died and likely mummified before being washed into a lower chamber in order to better understand the taphonomy of the fossils and to identify the invertebrate agent s responsible for damage we examined the fossils using high resolution imagery and studied the site and associated breccia blocks in the laboratory for traces of invertebrate activity we also conducted bone modification experiments with termites and hide beetles results show the presence of blowfly puparia within the cranium of the juvenile male mh1 indicating that flies visited the facial orifices of the freshly decomposing corpse blowflies which have a requirement to oviposit in daylight imply that the body was exposed to sunlight for part of the day a shaft opening that admitted sunlight is supported by the presence of a fossil fungus garden associated with mh2 fungus gardens occur subsurface and sprout mushrooms in areas with dappled light analysis of the fossil surfaces revealed a pattern comprising 14 damage types that were made on relatively fresh bone a bone modification experiment conducted with resident termites at the site showed that they created the same suite of microscopic surface features as those observed on the fossils the features are mostly the result of harvesting symbiotic fungi from fresh bones and mineral rich coatings from fossils damage resulting from the activity of hide beetles is similar to that of termites apart from invasive edge gnawing produced by the beetles this research highlights the importance of insect activity in the modification of fossils in the cradle of humankind world heritage site area and calls for consideration of this agent at other fossil sites in the region

wind forced downwelling slope currents a numerical study abstract a study is made of the dynamics of slope currents that arise from a steady constant alongshore wind over a uniform shelf over the first 10 20 days the evolution of the downwelled system on an f plane is qualitatively described by linear coastal trapped wave dynamics after this time the thermal wind shear associated with the bottom mixed layer becomes important in the evolution of the undercurrent uc which is shown to be driven by the alongshore pressure gradient due to sea level as the uc over the slope evolves the bottom ekman transport becomes small and negative leading to the detachment of flow near the shelf break localized spreading of isopycnals and further intensification of the uc in contrast to results obtained without bottom drag bottom friction and boundary layer transport are shown to lead to a two to threefold increase in cross shelf interior transport downwelling and thermal wind shear by day 60 the resultant uc has speeds of up to 15 cm s 1 and a net transport of

contemporary flowstone development links early hominin bearing cave deposits in south africa abstract the cradle of humankind cave sites in south africa preserve fossil evidence of four early hominin taxa australopithecus africanus australopithecus sediba paranthropus robustus and early homo in order to integrate this record into a pan african scenario of human evolutionary history it is critical to have reliable dates and temporal ranges for the southern african hominins in the past a lack of precise and accurate chronological data has prevented the evaluation of the temporal relationships between the various sites here we report new uranium lead u pb radiometric ages obtained from sheets of calcium carbonate flowstone inter bedded between clastic cave sediments at the site of swartkrans providing bracketing ages for the fossiliferous deposits the fossil bearing units of swartkrans specifically the hanging remnant and lower bank of member 1 are underlain by flowstone layers dated to 2 25 0 05 ma and 2 25 0 08 ma and capped by layers of 1 8 0 01 ma and 1 7 0 07 ma the age bracket of the member 1 deposits is therefore between 2 31 and 1 64 ma however by combining the u pb with biostratigraphic data we suggest that this can be narrowed down to between 1 9 and 1 8 ma these data can be compared with other recently dated sites and a radiometrically dated u pb age sequence formed sterkfontein member 4 swartkrans member 1 malapa and cooper s d from this new u pb dataset a pattern of contemporary flowstone development emerges with different caves recording the same flowstone forming event specifically overlapping flowstone formation takes place at swartkrans and sterkfontein at 2 29 ma and 1 77 ma and at sterkfontein and malapa at 2 02 ma this suggests a regional control over the nature and timing of speleothem development in cave deposits and these flowstone layers could assist in future correlation both internal to specific deposits and regionally between sites

u pb dated flowstones restrict south african early hominin record to dry climate phases the cradle of humankind cradle in south africa preserves a rich collection of fossil hominins representing australopithecus paranthropus and homo1 the ages of these fossils are contentious2 4 and have compromised the degree to which the south african hominin record can be used to test hypotheses of human evolution however uranium lead u pb analyses of horizontally bedded layers of calcium carbonate flowstone provide a potential opportunity to obtain a robust chronology5 flowstones are ubiquitous cave features and provide a palaeoclimatic context because they grow only during phases of increased effective precipitation6 7 ideally in closed caves here we show that flowstones from eight cradle caves date to six narrow time intervals between 3 2 and 1 3 million years ago we use a kernel density estimate to combine 29 u pb ages into a single record of flowstone growth intervals we interpret these as major wet phases when an increased water supply more extensive vegetation cover and at least partially closed caves allowed for undisturbed semi continuous growth of the flowstones the intervening times represent substantially drier phases during which fossils of hominins and other fossils accumulated in open caves fossil preservation restricted to drier intervals thus biases the view of hominin evolutionary history and behaviour and places the hominins in a community of comparatively dry adapted fauna although the periods of cave closure leave temporal gaps in the south african fossil record the flowstones themselves provide valuable insights into both local and pan african climate variability climate driven periodicity of flowstone accretion between 3 2 and 1 3 million years ago in cradle of humankind caves reveals that the presence of hominin fossils reflects accumulation in open caves during intermittent substantially drier phases

acceleration and overturning of the antarctic slope current by winds eddies and tides all exchanges between the open ocean and the antarctic continental shelf must cross the antarctic slope current asc previous studies indicate that these exchanges are strongly influenced by mesoscale and tidal variability yet the mechanisms responsible for setting the asc s transport and structure have received relatively little attention in this study the roles of winds eddies and tides in accelerating the asc are investigated using a global ocean sea ice simulation with very high resolution 1 48 grid spacing it is found that the circulation along the continental slope is accelerated both by surface stresses ultimately sourced from the easterly winds and by mesoscale eddy vorticity fluxes at the continental shelf break the asc exhibits a narrow 30 50 km swift 0 2 m s 1 jet consistent with in situ observations in this jet the surface stress is substantially reduced and may even vanish or be directed eastward because the ocean surface speed matches or exceeds that of the sea ice the shelfbreak jet is shown to be accelerated by tidal momentum advection consistent with the phenomenon of tidal rectification consequently the shoreward ekman transport vanishes and thus the mean overturning circulation that steepens the antarctic slope front asf is primarily due to tidal acceleration these findings imply that the circulation and mean overturning of the asc are not only determined by near antarctic winds but also depend crucially on sea ice cover regionally dependent mesoscale eddy activity over the continental slope and the amplitude of tidal flows across the continental shelf break

australopithecus sediba at 1 977 ma and implications for the origins of the genus homo newly exposed cave sediments at the malapa site include a flowstone layer capping the sedimentary unit containing the australopithecus sediba fossils uranium lead dating of the flowstone combined with paleomagnetic and stratigraphic analysis of the flowstone and underlying sediments provides a tightly constrained date of 1 977 0 002 million years ago ma for these fossils this refined dating suggests that au sediba from malapa predates the earliest uncontested evidence for homo in africa

antarctic ice rises and rumples their properties and significance for ice sheet dynamics and evolution locally grounded features in ice shelves called ice rises and rumples play a key role buttressing discharge from the antarctic ice sheet and regulating its contribution to sea level ice rises typically rise several hundreds of meters above the surrounding ice shelf shelf flow is diverted around them on the other hand shelf ice flows across ice rumples which typically rise only a few tens of meters above the ice shelf ice rises contain rich histories of deglaciation and climate that extend back over timescales ranging from a few millennia to beyond the last glacial maximum numerical model results have shown that the buttressing effects of ice rises and rumples are significant but details of processes and how they evolve remain poorly understood fundamental information about the conditions and processes that cause transitions between floating ice shelves ice rises and ice rumples is needed in order to assess their impact on ice sheet behavior targeted high resolution observational data are needed to evaluate and improve prognostic numerical models and parameterizations of the effects of small scale pinning points on grounding zone dynamics

refining the image of the san andreas fault near parkfield california using a finite difference travel time computation technique abstract the parkfield area seismic observatory paso was a dense telemetered seismic array that operated for nearly 2 years in a 15 km aperture centered on the san andreas fault observatory at depth safod drill site the main objective of this deployment was to refine the locations of earthquakes that will serve as potential targets for safod drilling and in the process develop a high for passive seismological techniques resolution image of the fault zone structure a challenging aspect of the analysis of this data set was the known existence of large 20 25 contrasts in seismic wavespeed across the san andreas fault the resultant distortion of raypaths could challenge the applicability of approximate ray tracing techniques in order to test the sensitivity of our hypocenter locations and tomographic image to the particular ray tracing and inversion technique employed we compare an initial determination of locations and structure developed using a coarse grid and an approximate ray tracer thurber c roecker s roberts k gold m powell m l and rittger k 2003 earthquake locations and three dimensional fault zone structure along the creeping section of the san andreas fault near parkfield ca preparing for safod geophys res lett 30 3 10 1029 2002gl016004 with one derived from a relatively fine grid and an application of a finite difference algorithm hole j a and zelt b c 1995 3 d finite difference reflection traveltimes geophys j int 121 2 427 434 in both cases we inverted arrival time data from about 686 local earthquakes and 23 shots simultaneously for earthquake locations and three dimensional vp and vp vs structure included are data from an active source seismic experiment around the safod site as well as from a vertical array of geophones installed in the 2 km deep safod pilot hole drilled in summer 2002 our results show that the main features of the original analysis are robust hypocenters are located beneath the trace of the fault in the vicinity of the drill site and the positions of major contrasts in wavespeed are largely the same at the same time we determine that shear wave speeds in the upper 2 km of the fault zone are significantly lower than previously estimated and our estimate of the depth of the main part of the seismogenic zone decreases in places by 100 m tests using virtual earthquakes borehole receiver gathers of picks for surface shots indicate that our event locations near the borehole currently are accurate to about a few tens of meters horizontally and vertically

a window into africa s past hydroclimates the sisal_v1 database contribution africa spans the hemispheres from temperate region to temperate region and has a long history of hominin evolution although the number of quaternary palaeoclimatic records from the continent is increasing much of the history of spatial and temporal climatic variability is still debated speleothems as archives of terrestrial hydroclimate variability can help reveal this history here we review the progress made to date with a focus on the first version of the speleothem isotopes synthesis and analysis sisal database the geology of africa has limited development of large karst regions to four areas along the northern coast bordering the mediterranean eastern africa and the horn of africa southwestern africa and southern africa exploitation of the speleothem palaeoclimate archives in these regions is uneven with long histories of research e g in south africa but large areas with no investigations such as west africa consequently the evidence of past climate change reviewed here is irregularly sampled in both time and space nevertheless we show evidence of migration of the monsoon belt with enhanced rainfall during interglacials observed in northeast africa southern arabia and the northern part of southern africa evidence from eastern africa indicates significant decadal and centennial scale rainfall variability in northwestern and southern africa precession and eccentricity influence speleothem growth largely through changing synoptic storm activity

coastal upwelling onshore offshore circulation equatorward coastal jet and poleward undercurrent over a continental shelf slope abstract the onshore offshore circulation equatorward coastal jet and poleward undercurrent associated with coastal upwelling are studied with numerical models the model ocean has a continental shelf slope uniform in the longshort direction and is forced by the wind stress with a limited longshore extent the thermocline intersects the shelf slope and the internal radius of deformation is smaller than the width of the shelf slope this may be a typical situation for coastal upwelling regions such as those off oregon and northwest africa as the initial response to the onset of the winds the ekman offshore flow and the compensating onshore flow are induced and the equatorward flow develops over the shelf slope when the first mode coastal trapped wave from the equatorward edge of the forcing region arrives the onshore compensating flow offshore of the coastal area begins to decrease in strength and eventually offshore flow accompanied by downwelling dominates thus the upwelling tends to be confined t

introduction to special section preparing for the san andreas fault observatory at depth 7209 seismology earthquake dynamics andmechanics 7230seismology seismicityandseismotectonics 8010structural geology fractures and faults citation hickman s m zoback and w ellsworth 2004 introduction to specialsection preparing for the san andreas fault observatory atdepth geophys res lett 31 l12s01 doi 10 1029 2004gl020688

using u pb ages of miocene tufa for correlation in a terrestrial succession barstow formation california sedimentary rocks and associated fossils are the direct record of past life and its environmental context few methods allow direct and precise dating of this important archive making it diffi cult to correlate climate biologic and tectonic events preserved in terrestrial records we sampled lacustrine tufa calcite from the middle member of the miocene barstow formation to further test the feasibility of uranium lead dating of terrestrial carbonates five samples yield u pb ages 2 of 14 81 0 39 ma 15 30 0 25 ma 15 39 0 15 ma 16 14 0 40 ma and 16 24 0 23 ma these precise ages are consistent with existing ages from k ar and 40 ar 39 ar dating of intercalated volcanic ashes our most precise u pb age on tufa has an uncertainty of 1 150 ka which is equivalent to uncertainties for k ar ages from the same time period our results indicate that u pb dating of carefully sampled and screened sedimentary carbonates provides much needed age constraints in purely terrestrial sequences and can be a powerful tool for correlation even in deposits with structural complexity and rapid facies changes

connecting antarctic cross slope exchange with southern ocean overturning previous idealized investigations of southern ocean overturning have omitted its connection with the antarctic continental shelves leaving the influence of shelf processes on antarctic bottom water aabw export unconsidered in particular the contribution of mesoscale eddies to setting the stratification and overturning circulation in the antarctic circumpolar current acc is well established yet their role in cross shelf exchange of water masses remains unclear this study proposes a residual mean theory that elucidates the connection between antarctic cross shelf exchange and overturning in the acc and the contribution of mesoscale eddies to the export of aabw the authors motivate and verify this theory using an eddy resolving process model of a sector of the southern ocean the strength and pattern of the simulated overturning circulation strongly resemble those of the real ocean and are closely captured by the residualmean theory over the continental slope baroclinic instability is suppressed and so transport by mesoscale eddies is reduced this suppression of the eddy fluxes also gives rise to the steep v shaped isopycnals that characterize the antarctic slope front in aabw forming regions of the continental shelf furthermore to produce water on the continental shelf that is dense enough to sink to the deep ocean the deep overturning cell must be at least comparable in strength to wind driven mean overturning on the continental slope this results in a strong sensitivity of the deep overturning strength to changes in the polar easterly winds

oceanographic observations at the shelf break of the amundsen sea antarctica the part of the west antarctic ice sheet that drains into the amundsen sea is currently thinning at such a rate that it contributes nearly 10 of the observed rise in global mean sea level acceleration of the outlet glaciers appears to be caused by thinning at their downstream ends where the ice goes afloat indicating that the changes are probably being forced from the ocean observations made since the mid 1990s on the amundsen sea continental shelf have revealed that the deep troughs carved by previous glacial advances are flooded by almost unmodified circumpolar deep water cdw with temperatures around 3 4 c above the freezing point and that this water mass drives rapid melting of the floating ice here we report observations of water properties and currents made in the region where one of those troughs reaches the continental shelf edge we estimate the absolute circulation within the trough from a combination of detided acoustic doppler current profiler data and geostrophic shear derived from conductivity temperature depth sections the shelf edge region is characterised by a landward deepening of the pycnocline separating cdw from the overlying colder and fresher surface waters this feature the so called antarctic slope front asf is almost circumpolar in extent and is typically a full depth feature the pycnocline intersecting the seabed over the upper continental slope however the asf is weaker in the amundsen sea where it is rarely a full depth feature geostrophic shear associated with the asf leads to a weakening of the associated westward current with depth and an eastward undercurrent of varying strength has been reported at other locations at the time of our amundsen sea observations the westward surface flow was weak giving rise to a strong eastward undercurrent flowing along the continental shelf edge and upper slope at the upstream western side of the trough the undercurrent turns south driving a net on shelf flow of cdw in the western part of the trough and leaving a weakened shelf edge flow that re establishes itself on the downstream eastern side of the trough an analogous feature was captured albeit crudely in an earlier coarse resolution model of the circulation on the amundsen sea shelf and variability in its strength associated with variability in the surface wind stress was the main cause of variations in the heat content of the waters on the inner continental shelf our observations thus lend support to the earlier hypothesis that changes in atmospheric forcing over the continental shelf edge could be the ultimate driver of changes in the west antarctic ice sheet outlet glaciers that drain into the amundsen sea

observations of the antarctic slope undercurrent in the southeastern weddell sea 1 the antarctic slope front presents a dynamical barrier between the cold antarctic shelf waters in contact with ice shelves and the warmer subsurface waters offshore two hydrographic sections with full depth current measurements were undertaken in january and february 2009 across the slope and shelf in the southeastern weddell sea southwestward surface intensified currents of 30 cm s 1 and northeastward undercurrents of 6 9 cm s 1 were in thermal wind balance with the sloping isopycnals across the front which migrated offshore by 30 km in the time interval between the two sections a mid depth undercurrent on february 23 was associated with a 130 m uplift of the main pycnocline bringing warm deep water closer to the shelf break this vertical displacement comparable to that caused by seasonal variations in wind speed implies that undercurrents may affect the exchanges between coastal and deep waters near the antarctic continental margins

the gibraltar arc seismogenic zone part 2 constraints on a shallow east dipping fault plane source for the 1755 lisbon earthquake provided by tsunami modeling and seismic intensity the great lisbon earthquake has the largest documented felt area of any shallow earthquake and an estimated magnitude of 8 5 9 0 the associated tsunami ravaged the coast of sw portugal and the gulf of cadiz with run up heights reported to have reached 5 15 m while several source regions offshore sw portugal have been proposed e g gorringe bank marquis de pombal fault no single source appears to be able to account for the great seismic moment as well as all the historical tsunami amplitude and travel time observations a shallow east dipping fault plane beneath the gulf of cadiz associated with active subduction beneath gibraltar represents a candidate source for the lisbon earthquake of 1755 here we consider the fault parameters implied by this hypothesis with respect to total slip seismic moment and recurrence interval to test the viability of this source the geometry of the seismogenic zone is obtained from deep crustal studies and can be represented by an east dipping fault plane with mean dimensions of 180 km n s 210 km e w for 10 m of co seismic slip an mw 8 64 event results and for 20 m of slip an mw 8 8 earthquake is generated thus for convergence rates of about 1 cm yr an event of this magnitude could occur every 1000 2000 years available kinematic and sedimentological data are in general agreement with such a recurrence interval tsunami wave form modeling indicates a subduction source in the gulf of cadiz can partly satisfy the historical observations with respect to wave amplitudes and arrival times though discrepancies remain for some stations a macroseismic analysis is performed using site effect functions calculated from isoseismals observed during instrumentally recorded strong earthquakes in the region m7 9 1969 and m6 8 1964 the resulting synthetic isoseismals for the 1755 event suggest a subduction source possibly in combination with an additional source at the nw corner of the gulf of cadiz can satisfactorily explain the historically observed seismic intensities further studies are needed to sample the turbidites in the adjacent abyssal plains to better document the source region and more precisely calibrate the chronology of great earthquakes in this region

impacts of open ocean deep convection in the weddell sea on coastal and bottom water temperature a high resolution global ocean sea ice model is employed to investigate the impacts of open ocean deep convection on coastal and bottom water temperature in the weddell sea the imposed strong and persistent cyclonic wind forcing and the large loss of bottom water weaken the stratification and eventually trigger the occurrence of open ocean deep convection in the southern limb of the weddell gyre in this model the production rate of the bottom water induced by the deep convection is estimated to be about 5 sv 1 sv 106 m3 s for a polynya with a similar size to that of the observed weddell polynya in the mid 1970s the cooling induced by deep convection at mid depth is transported towards the shelf regions by standing meanders or eddies to affect the basal melting of ice shelves and is transported westward by an intensified slope current interior coastal temperature in regions with a broader continental shelf is less affected by the deep convection as the intensified slope current acts to suppress heat exchanges across the shelf break also the deep convection causes warming in the weddell bottom water around the convection site when the simulated polynya size is similar to that of the observed weddell polynya in the mid 1970s this finding sheds light on the observed non monotonic decadal change cooling between 1984 1992 and warming between 1998 2008 in the weddell bottom water temperature when the simulated polynya further develops into a large size across the weddell sea the sustained broad deep convection causes large cooling in the bottom water in the western weddell sea and warming in the eastern weddell sea with the bottom water temperature also being strongly modulated by a greatly intensified weddell gyre

physiographic influences on dense shelf water cascading down the antarctic continental slope abstract predicting the source areas for antarctic bottom water aabw requires knowledge of how cold dense water masses form and move from the antarctic shelves to the continental slope here we use a review of nearly 50 years of direct hydrographic observations to infer the main broad scale influences on the distribution of dense shelf water dsw overflows that cascade down the continental slope around antarctica the dynamics and distribution of large ice shelves coastal polynyas and the physiography of the antarctic continental shelves are each considered the catalogue we present increases the number of dsw observations to 27 adds 20 additional stations where this process is likely to have occurred and identifies 41 areas where dsw appears to be absent our pan antarctic multi decadal review enhances the understanding of the formation and export of dsw and highlights the variability and complexity of ice ocean systems on high latitude continental margins the study also provides a context for understanding recent episodes of antarctic ice shelf instability and how the relationship between dsw and aabw may evolve with climatic and oceanographic changes

rapid subsurface warming and circulation changes of antarctic coastal waters by poleward shifting winds the southern hemisphere westerly winds have been strengthening and shifting poleward since the 1950s this wind trend is projected to persist under continued anthropogenic forcing but the impact of the changing winds on antarctic coastal heat distribution remains poorly understood here we show that a poleward wind shift at the latitudes of the antarctic peninsula can produce an intense warming of subsurface coastal waters that exceeds 2 c at 200 700 m depth the model simulated warming results from a rapid advective heat flux induced by weakened near shore ekman pumping and is associated with weakened coastal currents this analysis shows that anthropogenically induced wind changes can dramatically increase the temperature of ocean water at ice sheet grounding lines and at the base of floating ice shelves around antarctica with potentially significant ramifications for global sea level rise

the gibraltar arc seismogenic zone part 1 constraints on a shallow east dipping fault plane source for the 1755 lisbon earthquake provided by seismic data gravity and thermal modeling the great lisbon earthquake of 1755 with an estimated magnitude of 8 5 9 0 is the most destructive earthquake in european history yet the source region remains enigmatic recent geophysical data provide compelling evidence for an active east dipping subduction zone beneath the nearby gibraltar arc marine seismic data in the gulf of cadiz image active thrust faults in an accretionary wedge above an east dipping decollement and an eastward dipping basement tomographic and other data support subduction and rollback of a narrow slab of oceanic lithosphere beneath the westward advancing gibraltar block although no instrumentally recorded seismicity has been documented for the subduction interface we propose the hypothesis that this shallow east dipping fault plane is locked and capable of generating great earthquakes like the nankai or cascadia seismogenic zones we further propose this east dipping fault plane to be a candidate source for the great lisbon earthquake of 1755 in this paper we use all available geophysical data on the deep structure of the gulf of cadiz gibraltar region for the purpose of constraining the 3 d geometry of this potentially seismogenic fault plane to this end we use new depth processed seismic data have interpreted all available published and unpublished time sections examine the distribution of hypocenters and perform 2 d gravity modeling finally a finite element model of the forearc thermal structure is constructed to determine the temperature distribution along the fault interface and thus the thermally predicted updip and downdip limits of the seismogenic zone

high precision slip distribution of the 1944 tonankai earthquake inferred from tsunami waveforms possible slip on a splay fault abstract inversion of tsunami waveforms is a well established technique for estimating the slip distributions of subduction zone earthquakes with some of the most detailed results having been obtained for earthquakes in the nankai trough sw japan the present study although it uses a method and tsunami waveform data set almost identical to previous study aims to improve on previous work by using a more precise specification of initial conditions for the calculation of tsunami green s functions specifically we incorporated four improvements in the present study 1 we used a realistic plate model based only on seismic survey results and assumed it to be the fault plane of the 1944 tonankai earthquake 2 the smallest subfaults consistent with the long wavelength approximation were used in the tsunami inversion analysis 3 we included the effect of horizontal displacement of the ocean bottom on tsunami generation and 4 we performed a checkerboard resolution test as obtained in previous studies a zone of high slip 2 0 m was resolved off the shima peninsula however the more precise calculation of tsunami green s functions has revealed additional detail that was not evident in previous studies which we demonstrate is resolvable and correlates with the position of known faults in the accretionary prism while there was little or no slip near the trench axis in the eastern part of the rupture zone there was up to 1 5 m of slip resolved within 30 km of the trough axis in the western part along the coast of the kii peninsula this troughward slip zone coincides with the position of a large splay fault mapped in multichannel reflection surveys furthermore it is also clear that the upper edge of the enshu fault off shima and atsumi peninsulas is consistent with the up dip limit of slip in the eastern part of our model we tested the possibility that slip occurred on the former splay fault instead of on the plate interface during the 1944 tonankai earthquake and find that slip on this splay fault is also consistent with the data although we cannot distinguish whether slip was dominant on the splay fault or on the plate interface we further suggest that the position of the enshu fault may be determined by the subduction of topographic highs and that such faults may have an important influence on the up dip rupture limit of the 1944 tonankai and potentially other subduction zone earthquakes

the antarctic slope current in a changing climate the antarctic slope current asc is a coherent circulation feature that rings the antarctic continental shelf and regulates the flow of water towards the antarctic coastline the structure and variability of the asc influences key processes near the antarctic coastline that have global implications such as the melting of antarctic ice shelves and water mass formation that determines the strength of the global overturning circulation recent theoretical modeling and observational advances have revealed new dynamical properties of the asc making it timely to review earlier reviews of the asc focused largely on local classifications of water properties of the asc s primary front here we instead provide a classification of the current s frontal structure based on the dynamical mechanisms that govern both the along slope and cross slope circulation these two modes of circulation are strongly coupled similar to the antarctic circumpolar current highly variable motions such as dense overflows tides and eddies are shown to be critical components of cross slope and cross shelf exchange but understanding of how the distribution and intensity of these processes will evolve in a changing climate remains poor due to observational and modeling limitations results linking the asc to larger modes of climate variability such as el nino show that the asc is an integral part of global climate an improved dynamical understanding of the asc is still needed to accurately model and predict future antarctic sea ice extent the stability of the antarctic ice sheets and the southern ocean s contribution to the global carbon cycle

taphonomic interpretations of the haasgat hgd assemblage a case study in the impact of sampling and preparation methods on reconstructing south african karstic assemblage formation abstract the haasgat fossil bearing karstic system is situated within the skurweberg mountain range in the northeastern portion of the fossil hominids of south africa unesco world heritage site in south africa as is the case for the nearby gondolin hominin locality haasgat occurs in an area of substantial modern topographic relief that contrasts with the low relief landscape of the southwestern extent of the world heritage site surrounding the blauubank stream valley sites e g sterkfontein swartkrans kromdraai bolt s farm this suggests differential landscape formation processes during the neogene and potentially novel palaeoecosystems and taphonomic processes governing karstic fossil assemblage composition across even a small geographic region this is particularly critical given the overall paucity of taphonomic data from the region the substantial cercopithecoid primate assemblage that is uniquely dominated by the basal baboon species papio angusticeps and the recent announcement of the first hominin specimen from haasgat here we provide the first comprehensive taphonomic analysis of the haasgat hgd faunal assemblage that was developed from ex situ calcified sediment blocks in the 1990s there is direct evidence for biotic activity e g large bodied carnivores and porcupines mediating the formation of parts of the hgd faunal assemblage including at least part of the primate craniodental and postcranial sample there is minimal evidence for pre depositional element uv exposure and weathering or winnowing of the assemblage but there is abiotic distortion and crushing of elements our analysis has equally found that taphonomic data from the hgd assemblage is compromised by a modern overprint of damage through mechanical preparation and a lack of documentation generated during sampling processing and initial curation nearly half the cortical surfaces and many dental specimens in the assemblage exhibit evidence of substantial preparation damage rendering many purported biotic modifications ambiguous or suspect element proportions may be artificially skewed towards craniodental specimens and more reflective of block selection and or selective processing rather than original deposition composition as a result the haasgat hgd sample provides only limited data on the depositional processes mediating karstic assemblage formation in the region and ultimately serves as a cautionary tale of the impacts of palaeontological sampling strategies on subsequent analysis and research

a flying start then a slow slip the human tragedy caused by the sumatra andaman earthquake moment magnitude 9 3 on 26 december 2004 and its companion nias earthquake moment magnitude 8 7 on 28 march 2005 is difficult to comprehend these earthquakes the largest in 40 years have also left seismologists searching for the words and tools to describe the enormity of the geological processes involved four papers in this issue discuss aspects of a rupture process of surprising complexity the first such event to test the sensitivity and range of many new technologies a surprising feature of the earthquake is that after the initial rapid rupture subsequent slip of the plate interface occurred with decreasing speed toward the north

seasonality of warm water intrusions onto the continental shelf near the totten glacier warm modified circumpolar deep water mcdw from the southern ocean drives rapid basal melt of the totten ice shelf on the sabrina coast east antarctica affecting the mass balance of the grounded totten glacier recent observations show that mcdw intrudes onto the continental shelf through a depression at the shelf break here we investigate such intrusions by combining 1 new oceanographic and bathymetric observations collected for two consecutive years by profiling floats in the depression south of the shelf break 2 oceanographic measurements collected by conductivity temperature depth instrumented seals on continental slope and 3 an ocean model the depression provides a pathway for persistent inflow of warm 0 1 c mcdw to the inner shelf in austral autumn and early winter mcdw intrusions were up to 0 5 c warmer and were are 75 m thicker than in spring and summer the seasonality of the flow on the continental slope explains the seasonality of the intrusions the mcdw layer on the continental slope is warmer and thicker to the east of the depression than to the west in autumn and early winter a strong top to bottom westward current antarctic slope current transports the warmer and thicker mcdw layer along the slope and is diverted poleward at the eastern entrance of the depression a bottom intensified eastward current antarctic slope undercurrent develops in other months allowing cooler and thinner intrusions to enter the depression from the west our study illustrates how circulation on the antarctic slope regulates the ocean heat delivery to the continental shelf and ultimately to the ice shelves

seasonal variability of water masses and transport on the antarctic continental shelf and slope in the southeastern weddell sea 1 an array of five moorings was deployed from february 2009 to february 2010 across the antarctic shelf and slope in the southeastern weddell sea 18 w observations demonstrate the key processes responsible for variability in water masses and transport in the region rapid fluctuations in temperature and salinity throughout the year are linked with variability in wind stress over the array this causes the deepening or shoaling of the pycnocline past the depth of the moorings in the upper 500 m the seasonal cycle in salinity shows freshening in autumn with the strongest freshening at the shallowest mooring 250 m furthest on shelf the sea ice concentration over the array exceeds 90 during this period and contributes a positive salt flux into the ocean during autumn freshening begins during strong along shore easterly winds in late april 2009 this demonstrates that variations in ekman transport and wind driven mixing play a key role in determining the salinity of shelf waters around antarctica transport of the antarctic slope current also shows a seasonal cycle with a maximum during late april model simulations show the importance of along shore advection as the arrival of a fresh anomaly from upstream determines the timing of the salinity minimum at the array these processes are likely to be important for other regions around the antarctic continent

revised ages for tuffs of the yellowstone plateau volcanic field assignment of the huckleberry ridge tuff to a new geomagnetic polarity event 40 ar 39 ar ages were determined on the three major ash flow tuffs of the yellowstone plateau volcanic field in the region of yellowstone national park in order to improve the precision of previously determined ages total fusion and incremental heating ages of sanidine yielded the following mean ages huckleberry ridge tuff 2 059 0 004 ma mesa falls tuff 1 285 0 004 ma and lava creek tuff 0 639 0 002 ma the huckleberry ridge tuff has a transitional magnetic direction and has previously been related to the reunion normal polarity subchron dating of the reunion event has been reviewed and its ages have been normalized to a common value for mineral standards the age of the huckleberry ridge tuff is significantly younger than lava flows of the reunion event on re union island supporting other evidence for a normal polarity event younger than the reunion event