cosmogenic nuclides constrain surface fluctuations of an east antarctic outlet glacier since the pliocene understanding past changes in the antarctic ice sheets provides insight into how they might respond to future climate warming during the pliocene and pleistocene geological data show that the east antarctic ice sheet responded to glacial and interglacial cycles by remaining relatively stable in its interior but oscillating at its marine based margin it is currently not clear how outlet glaciers which connect the ice sheet interior to its margin responded to these orbitally paced climate cycles here we report new ice surface constraints from skelton glacier an outlet of the east antarctic ice sheet which drains into the ross ice shelf our multiple isotope 10be and 26al cosmogenic nuclide data indicate that currently ice free areas adjacent to the glacier underwent substantial periods of exposure and ice cover in the past we use an exposure burial model driven by orbitally paced glacial interglacial cycles to determine the probable ice surface history implied by our data this analysis shows that 1 the glacier surface has likely fluctuated since at least the pliocene 2 the ice surface was 200 m higher than today during glacial periods and the glacier has been thicker than present for 75 90 of each glacial interglacial cycle and 3 ice cover at higher elevations possibly occurred for a relatively shorter time per pliocene cycle than pleistocene cycle our multiple nuclide approach demonstrates the magnitude of ice surface fluctuations during the pliocene and pleistocene that are linked to marine based ice margin variability

dynamics of wind forced coherent anticyclones in the open ocean we numerically study the dynamics of coherent anticyclonic eddies in the ocean interior for the hydrostatic rotating stably stratified turbulence we use a high resolution primitive equation model forced by small scale winds in an idealized configuration many properties of the horizontal motions are found to be similar to those of two dimensional and quasi geostrophic turbulence major differences are a strong cyclone anticyclone asymmetry linked to the straining field exerted by vortex rossby waves which is also found in shallow water flows and the complex structure of the vertical velocity field which we analyze in detail locally the motion can become strongly ageostrophic and vertical velocities associated with vortices can reach magnitudes and levels of spatial complexity akin to those reported for frontal regions transport and mixing properties of the flow field are further investigated by analyzing lagrangian trajectories particles released in the pycnocline undergo large vertical excursions because of the vertical velocities associated to the vortices with potentially important consequences for marine ecosystem dynamics

estimation of the agulhas ring impacts on meridional heat fluxes and transport using argo floats and satellite data 1 a method that combines vertical profiles from the argo floats program and satellite sea surface height ssh data is used to reconstruct the vertical structure of the agulhas rings all eddies shed by the agulhas retroflection in the period between january 2005 and december 2008 were successfully reconstructed the velocity structures obtained are tilted and phase shifted in relation to the temperature anomalies resulting in an annual mean eddy meridional heat flux across the ring paths of 0 062 0 012 pw northward a first order estimate indicates 0 07 pw entering the atlantic from the indian ocean through agulhas rings the volume transport by agulhas rings is believed to play a central role in the overturning circulation being the main process responsible for the leakage of indian ocean waters to the atlantic the new estimates of the time mean ring volume transport of 9 8 sv from the indian to the atlantic ocean fall in the range obtained by previous works these estimates include a better representation of the trapped water region in the eddies a large inter annual variability in the volume transport was observed with a maximum of 11 21 sv in 2007 this variability is related to the number of structures shed by the agulhas retroflexion per year the ring shapes play a secondary though important role

the cosmogenic 21ne production rate in quartz evaluated on a large set of existing 21ne 10be data abstract based on a compilation of published combined 10 be and 21 ne cosmogenic nuclide data sets from quartz samples obtained at eth zurich we assess the 21 ne 10 be p21 p10 production rate ratio with the goal to determine the 21 ne production rate p21 in quartz a variety of sliding erosion islands in a 21 ne 10 be versus 10 be diagram were evaluated to find the one that fits the data best which in turn yields the most probable p21 if the 10 be production rate is known the approach minimizes the influence of samples with a complex exposure history a best fit value for p21 p10 sp sp the 10 be fraction being produced by spallation as opposed to production by muons of 4 23 0 17 is obtained for a 10 be half life of 1 39 ma adopting a p10 sp value in quartz of 4 41 0 52 at g 1 yr 1 this yields a p21 of 18 7 2 3 at g 1 yr 1 it is possible that 2 of the 21 ne is produced by fast muons

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

holocene dust in east antarctica provenance and variability in time and space in this paper we provide a comprehensive overview of the state of knowledge of dust flux and variability in time and space in different sectors of east antarctica during the holocene by integrati

denudation rates and a topography driven rainfall threshold in northern chile multiple cosmogenic nuclide data and sediment yield budgets abstract the quantification of geomorphic process rates on the outcrop and the orogen scale is important to describe accurately the interaction between the relative effects of erosion tectonics and climate on landscape evolution we report single and paired cosmogenic nuclide 10 be 26 al and 21 ne derived erosion rates and exposure ages on hillslope interfluves from the tectonically active western central andes that show a distinct spatial variation a positive correlation of erosion rates with elevation and present day rainfall rates is observed erosion rates at lower altitudes the hyperarid coastal cordillera and the western escarpment with the northern part of the atacama desert are extremely low and of the order of 10 100 cm my nominal exposure ages 1 6 my in contrast erosion rates at higher altitudes the semiarid western cordillera range up to 4600 cm my nominal exposure ages 0 02 0 1 my this latter average long term bedrock erosion rate record suggested to be coupled to an orographically controlled pattern of rainfall is also reflected in the pattern of denudation rates derived from a short term decadal record of limited sediment yield data specifically denudation rates calculated from sediment flux data are of a similar order of magnitude as erosion rates deduced from long lived cosmogenic nuclides from bedrock hillslope interfluves of the western cordillera nevertheless the production and the supply of sediment from the western andean slope are very limited analysis of multiple cosmogenic nuclides allows simultaneous determination of erosion rates and exposure ages but also reveals complex exposure histories of non bedrock samples such as boulders or amalgamated clast samples notably this study shows that saturation of nuclides usually assumed in studies where only a single nuclide is analyzed is rather the exception than the rule as revealed by erosion island plots constant erosion that started much later than the formation age of the rocks or episodic erosion by spalling can partially explain non steady state concentrations and more complicated exposure scenarios furthermore the use of multiple nuclides with different half lives allowed us to infer that no significant variations in long term erosion rates have occurred and that at the western escarpment erosion rates have been low and constant for most of the late neogene nevertheless the time intervals necessary to reach steady state concentrations for cosmogenic nuclides can be quite different from those needed for landscapes to reach steady state

cosmogenic 3he concentrations in ancient flood deposits from the coombs hills northern dry valleys east antarctica interpreting exposure ages and erosion rates abstract in situ produced cosmogenic 3 he analyses provide independent support for the model of a stable hyper arid polar climate persisting in east antarctica since the mid miocene and provide quantitative constraints on long term rates of erosion within the dry valleys in the coombs hills area a series of cobble size boulders form mega ripples with wavelengths of approximately 50 m their topographic position and association with features characteristic of scabland such as stripped corrugated bedrock surfaces indicate the boulders were deposited by subglacial floodwaters such outburst flooding could only have occurred during overriding of the northern dry valleys by a greatly expanded east antarctic ice sheet timing of the overriding episode has been previously assigned to 14 8 to 13 6 ma by correlation with volcanic ash deposits dated by 40 ar 39 ar in the asgard range of the dry valleys cosmogenic 3 he concentrations in clinopyroxene from ferrar dolerite boulders are consistent with 8 6 to 10 4 ma exposure calculated using scaling factors appropriate for antarctica and assuming zero erosion these are among the oldest surface exposure dates yet measured on earth but are not however consistent with the 40 ar 39 ar chronology used to define the age of the landscape due to unconstrained levels of erosion erosion rates of 0 03 0 06 m ma 1 are necessary to have produced the measured boulder exposure age if they were deposited at 14 8 ma these are less than half the steady state erosion rate derived from cosmogenic 3 he in the nearby bedrock surfaces 0 17 m ma 1 and testify to the extreme stability of the landscape

implications of quartz grain microtextures for onset eocene oligocene glaciation in prydz bay odp site 1166 antarctica abstract this paper presents the results of the scanning electron microscopic sem analysis of quartz grains from a selection of samples at site 1166 ocean drilling program leg 188 drilled site 1166 on the prydz bay continental shelf antarctica to document onset and fluctuations of east antarctic glaciation this site recovered upper pliocene holocene glacial sediments directly above cretaceous through lower oligocene sediments recording the transition from preglacial to early glacial conditions sem analysis of quartz grains at site 1166 was used to characterize the glacial and preglacial sediments by their diagnostic textures angular edges edge abrasion as well as arcuate to straight steps are the most frequent features in glacial deposits the highest frequency of grains with round edges is present in middle late eocene fluvio deltaic sands however angular outlines fractured plates with subparallel linear fractures and edge abrasion indicating glacier influence are also present preglacial carbonaceous mudstone and laminated gray claystone show distinctive high relief quartz grains and some chemical weathering on grain surfaces the results of the microtextural analysis of quartz grains are used to verify some critical periods of ice sheet evolution such as the transition from the east antarctic preglacial to glacial conditions on the continental shelf from middle late eocene to late eocene early oligocene time

the 21ne production rate in quartz revisited abstract i have revised our earlier production rate determination of 21ne in terrestrial quartz s niedermann th graf j s kim c p kohl k marti and k nishiizumi 1994 earth planet sci lett 125 341 355 taking account of improved knowledge about the exposure age of samples used in that work and applying distinct procedures for scaling to sea level and high latitudes the corrected value of 19 0 3 7 atoms g 1 a 1 is in excellent agreement with expectations based on nuclear properties j masarik and r c reedy 1995 earth planet sci lett 136 381 395 and closely corresponds to the present day production rate in the case of substantial variations of the geomagnetic field in the past as proposed by several studies the revised value can consistently be used with suitable correction methods

underground gravity survey in alpine regions an underground gravity study was carried out under extreme conditions of the alpine regions the lead zinc mine bleiberg carinthia was selected as an example to show the possibilities and limitations of the subsurface gravity method for in situ density determinations gravity measurements were made in two vertical mine shafts passing through triassic sedimentary rocks of the bleiberg unit the main prblem in gravity data reduction in extremely rugged topography is the accurate calculation of the terrain effect on underground stations a general discussion of the various corrections required for the gravity measurements in the mine is presented the mean interval densities in the two shafts in limestone dolomite and schists formations were determined as 2 76 and 2 77 g cm 3 respectively with an accuracy of better than 0 01 g cm 3 for a depth interval of 50 m the interval densities provide valuable information about the lithological and structural changes in the shaft surroundings and also agree well with the representative hand sample densities in the second part the applications of subsurface horizontal gravity surveys in exploration are discussed since the influence of topography is less underground because of the greater distance to the surface subsurface surveys have definite advantages over surface surveys and can be very helpful in locating anomalous density zones in the mines an example of gravity survey with a station spacing of 10 m at a depth of about 540 m is presented

dating of sirius group tillites in the antarctic dry valleys with cosmogenic3he and21ne we measured in situ produced cosmogenic3he and21ne in boulder and bedrock surface samples in and near sirius group tillites from two localities in southern victoria land antarctica pyroxene quantitatively retains cosmogenic3he for millions of years the deposit at mt fleming has a minimum exposure age of 6 5 ma while 6 ma is a probable minimum age for the table mountain tillite these lower limits not taking into account erosion of the sampled surfaces are based on the samples with the highest concentrations of cosmogenic noble gases and currently accepted production rates since the plagioclase bearing mt fleming samples almost certainly lost part of their cosmogenic ne the minimum exposure age at this location is presumably even 50 higher than the stated value the concentrations of cosmogenic ne in our samples constrain uplift rates of the transantarctic mountains to 170 m ma these data contradict the hypothesis of a collapse of the east antarctic ice sheet in the pliocene coupled with high uplift rates and support the model of a stable ice sheet since the middle miocene

fluvial origin of the valley system in northern victoria land antarctica from quantitative geomorphic analysis a network of sinuous valleys with typical dendritic pattern characterizes northern victoria land nvl in antarctica subparallel to parallel and angular to rectangular patterns are also present quantitative geomorphic analysis of the valley network has been carried out utilizing gis spatial analysis while drainage densities and drainage frequencies show low values segments of the nvl valley network are substantially well organized as indicated by bifurcation ratio r b and direct bifurcation ratio r bd parameters all basins faithfully adhere to horton s laws of drainage network composition quantitative geomorphic analysis suggests that the valley system can be ascribed to fl uvial origin and that consequently a morphoclimatic system completely different from that of present day must have driven its carving the resulting data provide indications about the origin of the valley network and this invaluable information can be used for the reconstruction of earlier phases of glacial history and climatic and tectonic evolution of this signifi cant antarctic region fluvial erosion enhanced the denudation of the transantarctic mountains from at least 55 ma to at least the eocene oligocene boundary ca 34 ma fluvial basins adapted to the tectonic structure following the main regional fault systems a well developed alpine topography postdates the fl uvial morphology temperate glaciers were responsible for denudation until the late miocene parasitic glaciers presently mantle the previously sculpted topography present day glacial erosion is negligible and denudation has been exceedingly slow since 7 5 ma

late cenozoic deposits at reedy glacier transantarctic mountains implications for former thickness of the west antarctic ice sheet abstract deposits corresponding to multiple periods of glaciation are preserved in ice free areas adjacent to reedy glacier southern transantarctic mountains glacial geologic mapping supported by 10be surface exposure dating shows that reedy glacier was significantly thicker than today multiple times during the mid to late cenozoic longitudinal surface profiles reconstructed from the upper limits of deposits indicate greater thickening at the glacier mouth than at the head during these episodes indicating that reedy glacier responded primarily to changes in the thickness of the west antarctic ice sheet surface exposure ages suggest this relationship has been in place since at least 5 ma the last period of thickening of reedy glacier occurred during marine isotope stage 2 at which time the glacier surface near its confluence with the west antarctic ice sheet was at least 500 m higher than today

past and future grounding line retreat of the west antarctic ice sheet the history of deglaciation of the west antarctic ice sheet wais gives clues about its future southward grounding line migration was dated past three locations in the ross sea embayment results indicate that most recession occurred during the middle to late holocene in the absence of substantial sea level or climate forcing current grounding line retreat may reflect ongoing ice recession that has been under way since the early holocene if so the wais could continue to retreat even in the absence of further external forcing

multiple cosmogenic nuclides document complex pleistocene exposure history of glacial drifts in terra nova bay northern victoria land antarctica geomorphological and glacial geological surveys and multiple cosmogenic nuclide analyses 10be 26al and 21ne allowed us to reconstruct the chronology of variations prior to the last glacial maximum of the east antarctic ice sheet eais and valley glaciers in the terra nova bay region glacially scoured coastal piedmonts with round topped mountains occur below the highest local erosional trimline they represent relict landscape features eroded by extensive ice overriding the whole coastal area before at least 6 ma pre dating the build up of the mt melbourne volcanic field since then summit surfaces were continuously exposed and well preserved under polar condition with negligible erosion rates on the order of 17 cm ma complex older drifts rest on deglaciated areas above the younger late pleistocene glacial drift and below the previously overridden summits the combination of stable and radionuclide isotopes documents complex exposure histories with substantial periods of burial combined with minimal erosion the areas below rounded summits were repeatedly exposed and buried by ice from local and outlet glaciers the exposure ages of the older drift s indicate multiple pleistocene glacial cycles which did not significantly modify the pre existing landscape

eddy length scales in the north atlantic ocean eddy length scales are calculated from satellite altimeter products and in an eddy resolving model of the north atlantic ocean four different measures for eddy length scales are derived from kinetic energy densities in wave number space and spatial decorrelation scales observational estimates and model simulation agree well in all these measures near the surface as found in previous studies all length scales are in general decreasing with latitude they are isotropic and proportional to the local first baroclinic rossby radius l r north of about 30 n while south of 30 n or for l r 30 km zonal length scales tend to be larger than meridional ones and scalar length scales show no clear relation to l r anymore instead they appear to be related to the local rhines scale in agreement with a recent theoretical prediction by theiss 2004 the observed and simulated pattern of eddy length scales appears to be indicative of two different dynamical regimes in the north atlantic anisotropic turbulence in the subtropics and isotropic turbulence in the subpolar north atlantic both regions can be roughly characterized by the ration between l r and the rhines scales l r with l r l r in the isotropic region and l r l r in the anisotropic region the critical latitude that separates both regions i e where l r l r is about 30 n

significant sink of ocean eddy energy near western boundaries ocean eddies generated through instability of the mean flow are a vital component of the energy budget of the global ocean modelling combined with satellite altimetry data suggests that the energy from westward propagating eddies is scattered and eventually dispersed when they reach the western boundary of an ocean basin

controls on subaerial erosion rates in antarctica erosion rates offer insight on landscape development and the relative importance of chemical and physical processes of weathering minimal chemical weathering makes antarctica an ideal location in which to compare the physical weathering of carbonate rocks to other lithologies here we report the first cosmogenic nuclide derived erosion rates for carbonate rocks in antarctica carbonate samples collected in the southernmost ellsworth mountains reflect a 36cl erosion rate of 0 22 0 02 mm ka this erosion rate is consistent with other reported antarctic erosion rates but is lower than 36cl erosion rates derived from other arid regions in the world these results are integrated with a continent wide reanalysis of 28 erosion rate studies 200 measurements which comprise numerous rock types and other cosmogenic nuclides by combining cosmogenic nuclide derived erosion rates across studies the larger trends provide insight into factors e g lithology glacial history and availability of abrasive material affecting subaerial erosion rates in antarctica statistical analysis of the compiled data set shows differences based on lithology with sandstone having the largest range of erosion rates the compiled data also reveals higher erosion rates in areas with a large potential sediment supply like the dry valleys samples collected from boulders yield lower erosion rates than those collected from bedrock likely due to a combination of physical processes that affect boulders and bedrock differently and glacial history which can affect the apparent cosmogenic nuclide derived erosion rate

plio pleistocene history of ferrar glacier antarctica implications for climate and ice sheet stability abstract the areal distribution and elevation of glacial drifts in vernier valley southern victoria land are used to reconstruct the plio pleistocene history of upper ferrar glacier 21 ne cosmogenic nuclide analyses of surface cobbles on four moraines ferrar 1 2 3 and 4 provide age control a minimum age estimate for ferrar drifts calculated by assuming zero surface erosion indicates that the oldest moraine ferrar 4 was deposited at least 3400 ka our preferred age model which applies a very conservative erosion rate of 5 cm ma 1 in age calculations suggests that ferrar 4 is 4000 ka ferrar 3 is 1200 ka and ferrar 2 is 700 ka based on glacial geologic data ferrar 1 is modern cosmogenic ages for cobbles on this moraine suggest a value for nuclide inheritance of 50 ka the ferrar drifts are most easily interpreted in terms of a progressive reduction in the ice surface elevation of upper ferrar glacier during plio pleistocene time relative to today the surface of upper ferrar glacier was 100 to 125 m higher during the pliocene climatic optimum and 50 m higher during early to mid quaternary time conversely during mis 2 the ice surface elevation of upper ferrar glacier was likely no larger than today and may have stood below modern levels the texture and sedimentology of all ferrar drifts indicate that during ice recession from vernier valley the upper ferrar glacier lacked surface melting ablation zones even during the pliocene climatic optimum results from a simple 2 d glaciological flow band model demonstrate that upper ferrar glacier also lacked basal melting zones during ice recession we show that the development of weathering pits and desert varnish on cobbles exposed at the surface of ferrar drifts varies in accord with cosmogenic age the mean width and depth of the largest surface pits on boulders from ferrar drifts increases by 10 mm ma 1 and 6 7 mm ma 1 respectively the maximum thickness of desert varnish on surface boulders increases by 1 5 mm ma 1 these rates may be used to help calculate ages for dolerite rich drifts elsewhere in the western dry valleys region the general stability of the ice surface elevation of upper ferrar glacier and of the landscape in vernier valley suggests minimal climatic amelioration in the upland region of the dry valleys during the last 4 ma

vertical structure of mesoscale eddies in the eastern south pacific ocean a composite analysis from altimetry and argo profiling floats 1 the mean vertical structure of mesoscale eddies in the peru chile current system is investigated by combining the historical records of argo float profiles and satellite altimetry data a composite average of 420 526 profiles acquired by argo floats that surfaced into cyclonic anticyclonic mesoscale eddies allowed constructing the mean three dimensional eddy structure of the eastern south pacific ocean key differences in their thermohaline vertical structure were revealed the core of cyclonic eddies ces is centered at 150 m depth within the 25 2 26 0 kg m 3 potential density layer corresponding to the thermocline in contrast the core of the anticyclonic eddies aes is located below the thermocline at 400 m depth impacting the 26 0 26 8 kg m 3 density layer this difference was attributed to the mechanisms involved in the eddy formation while intrathermocline ces would be formed by instabilities of the surface equatorward coastal currents the subthermocline aes are likely to be shed by the subsurface poleward peru chile undercurrent in the eddy core maximum temperature and salinity anomalies are of 1 c and 0 1 with positive negative values for aes ces this study also provides new insight into the potential impact of mesoscale eddies for the cross shore transport of heat and salt in the eastern south pacific considering only the fraction of the water column associated with the fluid trapped within the eddies each ce and ae has a typical volume anomaly flux of 0 1 sv and yields to a heat and salt transport anomaly of 1 3 1011 w and 3 8 103 kg s 1 respectively

east antarctic deglaciation and the link to global cooling during the quaternary evidence from glacial geomorphology and 10be surface exposure dating of the sor rondane mountains dronning maud land abstract reconstructing past variability of the antarctic ice sheets is essential to understand their stability and to anticipate their contribution to sea level change as a result of future climate change recent studies have reported a significant decrease in thickness of the east antarctic ice sheet eais during the last several million years however the geographical extent of this decrease and subsequent isostatic rebound remain uncertain in this study we reconstruct the magnitude and timing of ice sheet retreat at the sor rondane mountains in dronning maud land east antarctica based on detailed geomorphological survey cosmogenic exposure dating and glacial isostatic adjustment modeling three distinct deglaciation phases are identified for this sector during the quaternary based on rock weathering and 10 be surface exposure data we estimate that the ice sheet thinned by at least 500 m during the pleistocene this thinning is attributed to the reorganization of southern ocean circulation associated with global cooling into the pleistocene which reduced the transport of moisture from the southern ocean to the interior of eais the data also show that since the last glacial maximum the ice surface has lowered less than ca 50 m and that this lowering probably started after ca 14 ka this suggests that the eais in dronning maud land is unlikely to have been a major contributor to postglacial sea level rise and meltwater pulse 1a

a new holocene relative sea level curve for terra nova bay victoria land antarctica more than 100 radiocarbon dates of penguin guano and remains shells and seal skin afford ages for raised beaches adjacent to terra nova bay antarctica these dates permit construction of a new relative sea level curve that bears on the timing of deglaciation recession of the ross sea ice sheet grounding line from terra nova bay occurred no earlier than 7200 14c yr 8000 cal yr bp retreat along the victoria land coast may have been rapid possibly contributing to eustatic sea level rise centred at ca 7600 cal yr bp the presence of a significant amount of ice remaining in the ross sea embayment in holocene time lessens the chance that antarctica contributed significantly to meltwater pulse 1a several thousand years earlier copyright 2004 john wiley sons ltd

thresholds for cenozoic bipolar glaciation the long standing view of earth s cenozoic glacial history calls for the first continental scale glaciation of antarctica in the earliest oligocene epoch 33 6 million years ago1 followed by the onset of northern hemispheric glacial cycles in the late pliocene epoch about 31 million years later2 the pivotal early oligocene event is characterized by a rapid shift of 1 5 parts per thousand in deep sea benthic oxygen isotope values3 oi 1 within a few hundred thousand years4 reflecting a combination of terrestrial ice growth and deep sea cooling the apparent absence of contemporaneous cooling in deep sea mg ca records4 5 6 however has been argued to reflect the growth of more ice than can be accommodated on antarctica this combined with new evidence of continental cooling7 and ice rafted debris8 9 in the northern hemisphere during this period raises the possibility that oi 1 represents a precursory bipolar glaciation here we test this hypothesis using an isotope capable global climate ice sheet model that accommodates both the long term decline of cenozoic atmospheric co2 levels10 11 and the effects of orbital forcing12 we show that the co2 threshold below which glaciation occurs in the northern hemisphere 280 p p m v is much lower than that for antarctica 750 p p m v therefore the growth of ice sheets in the northern hemisphere immediately following antarctic glaciation would have required rapid co2 drawdown within the oi 1 timeframe to levels lower than those estimated by geochemical proxies10 11 and carbon cycle models13 14 instead of bipolar glaciation we find that oi 1 is best explained by antarctic glaciation alone combined with deep sea cooling of up to 4 c and antarctic ice that is less isotopically depleted 30 to 35 than previously suggested15 16 proxy co2 estimates remain above our model s northern hemispheric glaciation threshold of 280 p p m v until 25 myr ago but have been near or below that level ever since10 11 this implies that episodic northern hemispheric ice sheets have been possible some 20 million years earlier than currently assumed although still much later than oi 1 and could explain some of the variability in miocene sea level records

induced gravity anomalies and rock burst risk in coal mines a case history1 the use of the gravity method to predict rock bursts in mines is based on the relationship between the development of a dilatancy process in the exploited rock mass and the time dependent gravity anomalies induced by this phenomenon the differences between successive observations of anomalies and the time behaviour of their trend amplitudes as precursors of preceding changes of rock stability are interpreted the centres of zones of induced rock density variation are determined by computing the position of singular points of the differences between anomalies two gravity surveys have been carried out in the radbod coal mine germany the first survey took place at the level of the dickebank seam depth 1030 m the second in the sonnenschein seam depth 1090 m the observations were made with worden and lacoste romberg d type gravimeters the differences between successive anomalies were less than 100 gal in the case of the dickebank seam the position of singular points demonstrates the effect of two approaching longwalls on a previously mined out seam and on the gallery in which the gravity observations were made in the case of the sonnenschein seam the trend amplitudes show distinct variations in the formation of the approaching longwall below the edges of all previously mined out seams in particular the effect of a remnant pillar has caused the largest gravity gradients this result corresponds to the existence of a zone of rock burst hazard known from test drilling the computed singular points are grouped together under the remnant pillar indicating two local hazard zones both results the observed development of rock instability with time and the information about the position of the disturbed rock mass relative to the mine workings are of importance subsurface gravity surveying can therefore be a valuable tool for predicting rock bursts

role of in situ cosmogenic nuclides 10be and 26al in the study of diverse geomorphic processes the central premises of applications of the in situ cosmogenic dating method for studying specific problems in geomorphology are outlined for simple and complex exposure settings in the light of these general models we discuss the information that can be derived about geomorphic processes utilizing concentrations of in situ produced cosmogenic radionuclides 10be half life 1 5 ma and 26a1 half life 0 7 ma in a variety of geomorphic contexts glacial polish and tills meteorite impact craters alluvial fans paleo beach ridges marine terraces sand dunes and bedrock slopes we also compare 10be 26al data with results obtained by other dating methods we conclude that the technique of measuring in situ cosmic ray produced nuclides holds promise for quantitative studies of processes and time scales in a wide range of geomorphological problems

cenozoic landscape evolution of the convoy range to mackay glacier area transantarctic mountains onshore to offshore synthesis on the basis of geomorphic mapping we reconstruct the landscape evolution of the convoy range to mackay glacier area of the rifted margin of the transantarctic mountains and compare the land record with that obtained from offshore marine sedimentary rocks in the ross sea three landform assemblages reflect 1 fluvial planation and dissection 2 local glaciation under temperate conditions and 3 overriding by the east antarctic ice sheet overall landscape evolution is typical of a passive continental margin contrasts in morphology between the convoy range and the adjacent dry valleys and royal society mountains reflect the varying location of the initial drainage divide in relationship to the rifted coast in a wider synthesis we draw the following conclusions for the 260 km long mcmurdo sector of the transantarctic mountains denudation since rifting at ca 55 ma has removed a wedge 4 7 km thick at the coast declining inland to 1 km most denudation occurred in the eocene from planation and incision of river valleys near the coast a subsequent pulse of denudation most rapid at 34 31 ma and declining until ca 17 ma coincided with further crustal extension and a change from cool temperate to polar climate during the same interval there was a progressive decrease in landscape modification by warm based glaciers and or rivers between 14 8 and 13 6 ma the maximum overriding antarctic ice sheet flowed northeastward across the mountains leaving meltwater features crossing high altitude saddles and areally scoured bedrock near the coast since 13 6 ma the landscape has seen little change under a hyperarid polar climate either by local glaciers or subaerially fragile middle miocene surficial deposits still survive there has been tectonic stability since the middle miocene

timing of the local last glacial maximum in terra nova bay antarctica defined by cosmogenic dating abstract the jangbogo hills are erratic covered landforms consisting of a series of benches that are parallel to the length of campbell glacier northern victoria land antarctica we sampled 41 erratic cobbles from six benches to reveal the exposure times of glacier erratics using in situ 10be and 26al the erratics from the upper three benches yield exposure ages older than marine isotope stage mis 4 with most exposed since mis 5 however the lower three benches exhibit tight clusters of exposure ages that range from mis 3 to the holocene campbell glacier underwent rapid downwasting during mis 5 centered at 98 3 ka from its maximum position at the penultimate glacial maximum pgm this downwasting continued throughout the last glacial period with a potential minor stagnation around a bench 90 m asl between 35 4 and 17 0 ka our cosmogenic nuclides surface exposure dating results highlight three important points concerning the glacial history of terra nova bay since the penultimate glacial maximum pgm in northern victoria land antarctica 1 campbell glacier was thicker at the pgm than at the global last glacial maximum lgm 2 the local lgm occurred during mis 4 and 3 the extent of campbell glacier during the global lgm 90 m was much smaller than previously assumed 300 400 m hence the previous view that the local lgm mis 4 in victoria land antarctica was synchronous with the global lgm mis 2 should be treated with caution

pleistocene dynamics of the interior east antarctic ice sheet current models describing past configurations of the east antarctic ice sheet are poorly constrained by observations exposure dating of bedrock surfaces using in situ produced cosmogenic nuclides provides an ideal tool for directly constraining former changes in ice sheet elevation we present cosmogenic radionuclide 10 be and 26 al measurements in bedrock surfaces and glacially transported cobbles in the grove mountains a group of nunataks within the slow flowing interior ice sheet dome hundreds of kilometers from the coastal ice margin and from ice streams samples were collected in vertical transects over 500 m of relief minimum bedrock and erratic exposure ages show a trend of increasing age with height above the ice sheet spanning a period from 0 3 to 4 0 ma and 50 900 ka respectively no evidence was found for thicker ice at the last glacial maximum compared to modern ice thickness the older bedrock exposure ages of 2 5 4 0 ma require steady state erosion rates of 1 the measured two isotope bedrock exposure ages are successfully modeled when changes in surface elevation of the ice sheet are described by a combination of linear long term ice surface lowering and shorter term high frequency glacial interglacial oscillations the best fit model requires a long term thinning rate of 50 m m y 1 and an elevation change of 100 m over a 100 k y glacial cycle

an improved experimental determination of cosmogenic 10be 21ne and 26al 21ne production ratios in quartz abstract the confidence in surface exposure dating and related research such as erosion rate studies or burial dating strongly depends on the accuracy and precision of the currently used production rates of in situ produced cosmogenic nuclides reducing the uncertainties of nuclide production rates by more accurate calibrations with independently dated natural rock surfaces is crucial for further improving the quantification of earth surface processes here we use surface samples from the 760 2 ka old bishop tuff in eastern california to quantify the 10 be 21 ne and 26 al 21 ne production rate ratios in quartz our determination is based on 1 measured nuclide concentrations of cosmogenic 10 be 21 ne and 26 al 2 a conservative estimate for the erosion of the tuff in the volcanic tableland area which we base on our previously published 21 ne concentrations goethals m m niedermann s hetzel r fenton c r 2009 determining the impact of faulting on the rate of erosion in a low relief landscape a case study using in situ produced 21 ne on active normal faults in the bishop tuff california geomorphology 103 401 413 and a conservative estimate for the uncertainty of the 21 ne production rate and 3 the assumption of steady state erosion other assumptions such as the applied scaling procedure the muon contribution to nuclide production or the attenuation lengths of neutrons and muons in rock do not substantially affect the results based on 13 samples the following average production rate ratios and conservative uncertainty estimates are obtained for sea level high latitude open sky and rock surface 0 249 0 009 or 0 232 0 009 for 10 be 21 ne using 10 be half lives of 1 51 and 1 39 ma respectively and 1 80 0 09 for 26 al 21 ne for an 26 al half life of 0 72 ma the 10 be 21 ne and the 26 al 21 ne production ratios are consistent with currently used production rates but the ratios are much more precise than previous determinations the resulting 26 al 10 be production ratio of 7 23 0 45 for a 10 be half life of 1 51 ma or 7 76 0 49 for a 10 be half life of 1 39 ma is high when compared to previously published values we discuss reasons for this difference amongst them the possibility that 26 al analyses in general might be compromised by artefacts affecting the stable al concentration measurements when combined with a 10 be production rate of 5 01 at g 1 a 1 for the 1 51 ma half life or 4 61 at g 1 a 1 for the 1 39 ma half life our production ratios convert to 21 ne and 26 al production rates of 20 1 and 36 2 at g 1 a 1 or 19 9 and 35 7 at g 1 a 1 respectively

global surface eddy diffusivities derived from satellite altimetry 1 velocities derived from aviso sea surface height observations adjusted to be nondivergent are used to simulate the evolution of passive tracers at the ocean surface eddy mixing rates are derived from the tracer fields in two ways first the method of nakamura is applied to a sector in the east pacific second the osborn cox diffusivity is calculated globally to yield estimates of diffusivity in two dimensions the results from the east pacific show weak meridional mixing at the surface in the southern ocean 1000 m2 s 1 consistent with previous results but higher mixing rates 3000 5000 m2 s 1 in the tropical ocean the osborn cox diagnostic provides a global picture of mixing rates and agrees reasonably well with the results from the east pacific it also shows extremely high mixing rates 104 m2 s 1 in western boundary current regions the osborn cox diffusivity is sensitive to the tracer initialization which we attribute to the presence of anisotropic mixing processes the mixing rates are strongly influenced by the presence of a mean flow nearly everywhere as shown by comparison with an eddy only calculation with the mean flow absent finally results are compared with other recent estimates of mixing rates using lagrangian and inverse methods

float derived isopycnal diffusivities in the dimes experiment as part of the diapycnal and isopycnal mixing experiment in the southern ocean dimes 210 subsurface floats were deployed west of the drake passage on two targeted density surfaces absolute single particle diffusivities are calculated for the floats the focus is on the meridional component which is less affectedby the meanshear the diffusivitiesare estimatedin severalways including a novelmethodbased on the probability density function of the meridional displacements this allows the determination of the range of possible lateral diffusivities as well as the period over which the spreading can be said to be diffusive the method is applied to the float data and to synthetic trajectories generated with the massachusetts institute of technologygeneral circulationmodel mitgcm becauseof ballastingproblems manyofthefloatsdid not remain on their targeted density surface however the float temperature records suggest that most occupied asmallrangeofdensities sothefloatsweregroupedtogetherfortheanalysis thelatterfocuseson asubsetof 109 of the floats launched near 1058w the different methods yield a consistent estimate for the diffusivity of 800 6 200m 2 s 21 the same calculations were made with model particles deployed on 20 different density surfaces and the result for the particles deployed on the neutral density surface g 5 27 7 surface was the same within the errors the model was then used to map the variation of the diffusivity in the vertical near the core of the antarctic circumpolar current acc the results suggest mixing is intensified at middepths between 1500 and 2000m consistent with several previous studies

production rate of cosmogenic 21ne in quartz estimated from 10be 26al and 21ne concentrations in slowly eroding antarctic bedrock surfaces abstract we estimated the production rate of 21ne in quartz using a set of samples from slowly eroding sandstone surfaces in the antarctic dry valleys geologic evidence as well as cosmogenic 10be and 26al concentrations indicate that i these sites have experienced millions of years of surface exposure at low erosion rates and ii steady erosion has been sustained long enough that surface 10be and 26al concentrations have reached equilibrium with the erosion rate under these conditions surface cosmogenic 21ne concentrations should be a function only of the erosion rate and the 21ne production rate as the erosion rate can be determined from 10be and 26al concentrations this allows an estimate of the 21ne production rate estimating the reference 21ne production rate on this basis with the assumption that all 21ne production is by neutron spallation yields a poor fit to measured 21ne concentrations and a systematic residual that is correlated with the erosion rate of the sample site the same steady erosion assumption with a production model that includes production by deeply penetrating muons yields a good fit both to our measurements and to similar independent measurements from an antarctic bedrock core both data sets together yield a total reference 21ne production rate of 18 3 0 4 atoms g 1 a 1 of which 0 66 0 10 atoms g 1 a 1 is due to muon interactions

constraints on age erosion and uplift of neogene glacial deposits in the transantarctic mountains determined from in situ cosmogenic 10be and 26al 10 be and 26 al data from sandstone boulders in three neogene glacial deposits in the mcmurdo sound dry valleys region of southern victoria land antarctica indicate minimum exposure ages of approx 3 ma and maximum long term erosion rates of approx 5 12 cm m y supporting the suggestion that polar desert conditions have persisted in the dry valleys since at least late pliocene time variation of cosmogenic nuclide production rate with altitude also allows constraints on past uplift rates model calculations employing 10 be data indicate little or no uplift in the dry valleys region in the past 3 m y precluding rapid 1 km m y late pliocene uplift previously suggested for some parts of the transantarctic mountains

mass spectrometric identification of cosmic ray produced neon in terrestrial rocks with multiple neon components studies of cosmic ray produced nuclides in terrestrial rocks are expected to provide important geomorphological and glaciological information such as surface exposure ages erosion rates and extent of glacial cover in the case of the stable nuclide21ne the cosmic ray produced component may represent but one of several components and a component resolution based on three isotope correlations is essential we developed analytical techniques which permit accurate corrections for all interfering ions we show for our modified nier source that corrections for doubly charged species based on constant charge state ratios are not satisfactory the improved techniques permit isotopic studies of 106 atoms of21ne the spallation ratio 22ne 21ne c from si was calibrated using a quartz separate from an allan hills sandstone and yields a value of1 243 0 022 this ratio is expected to be essentially constant for terrestrial quartz samples and should be useful in component resolutions the stepwise release of ne at increasing temperatures shows that cosmic ray produced ne is released from quartz at rather low temperatures this permits an estimate of the activation energy for ne diffusion in quartz 90 10 kj mol

cosmogenic noble gas studies in the oldest landscape on earth surface exposure ages of the dry valleys antarctica extraordinarily high surface exposure ages have been determined for sirius group tillites of mt fleming and mt feather as well as at localities in the inner dry valleys using cosmogenic helium and neon ages of 10 ma at mt fleming 5 3 ma at mt feather and 6 5 ma at insel mountain are among the highest nominal exposure ages published so far these values are minimal ages as they are based on the assumption of zero erosion and uplift the mt feather sample independently confirms the pre pliocene age of the sirius group sediments in the dry valleys as previously determined at mt fleming the insel mountain samples provide evidence for a landscape formation of the inner dry valleys not later than late miocene time assuming conservatively low values of 2 5 cm ma 1 for erosion rate and 50 m ma 1 for uplift rate we infer that the sirius group tillites at mt fleming were deposited earlier than 20 ma ago this indicates that the overriding of the dry valleys block of the transantarctic mountains by the east antarctic ice sheet occurred not later than the early miocene maximum long term erosion rates in the inner dry valleys must be 15 cm ma 1 down to altitudes 1000 m since such low erosion rates require permanently cold and hyperarid conditions the response of antarctica to the pliocene warm climatic episode must have been small cosmogenic nuclide data from both the inner dry valleys and the sirius group sediment localities support the hypothesis of a stable east antarctic ice sheet since at least late miocene time implying that the climate of antarctica was decoupled from that of lower southern latitudes we present also new elemental 21ne production rates of p21 mg 196 atoms g 1 yr 1 and p21 al 55 atoms g 1 yr 1 at sea level and high geomagnetic latitude these figures are consistent with a 3he production rate of p3 110 atoms g 1 yr 1 similar to previously published values this consistency provides evidence that pyroxene is retentive for both helium and neon over at least 10 ma cosmogenic ne in quartz and pyroxene has a 22ne 21ne cos ratio of 1 266 0 040 and 1 159 0 040 respectively

multiple cosmogenic nuclides document the stability of the east antarctic ice sheet in northern victoria land since the late miocene 5 7 ma the timing and amplitude of changes in the antarctic ice level are relevant to understanding past climate fluctuations and ongoing changes in the global climate and sea levels in this study we present surface exposure ages based on in situ produced cosmogenic 10be and 21ne in the bedrock samples of glacially eroded relict surfaces from the deep freeze range northern victoria land the proximity of this region to the east antarctic ice sheet indicates that the area is sensitive to variations in inland ice volume permitting the investigation of the behavioural relationship between the east antarctic ice sheet and the alpine glacial system in northern victoria land dating erosional surfaces provides a precise chronology of northern victoria land paleoclimate evolution and allows us to correlate the east antarctic ice sheet response to global climate events and local ice level variations the 10be and 21ne concentrations from the highest peaks of the deep freeze range strongly indicate that the relict landscape features were continuously exposed for 5 7 ma denudation rates inferred from our data show that the erosion rate of the summits has been extremely low 5 cm ma for at least 5 7 ma along with evidence of persistent climate stability cold and arid conditions from other sectors of the transantarctic mountains our results indicate that the transition from the wet based to the cold based glacial regime in northern victoria land occurred after the creation of the polar east antarctic ice sheet in the middle miocene

on the influence of a lower layer on the propagation of nonlinear oceanic eddies abstract the one layer reduced gravity also called equivalent barotropic model has been widely used in countless applications although its validity is based on the assumption that a second lower layer is sufficiently deep to be dynamically inactive the question of how deep that second layer ought to be has not yet received thorough examination when one considers the importance of the two processes excluded from the reduced gravity model namely barotropic motion and baroclinic instability the conventional choice of a second layer much deeper than the first might be too simplistic a scaling analysis aimed at covering all two layer regimes geostrophic as well as ageostrophic leads to a double criterion requiring that the total depth of fluid be much larger than either of two values these values resulting from f plane and plane dynamics apply to the shorter and longer scales respectively a number of numerical experiments on the propagation of eddies on the plane with various eddy radii a

correction of in situ cosmogenic nuclide production rates for geomagnetic field intensity variations during the past 800 000 years we present integrated relative production rates for cosmogenic nuclides in rock surfaces which take into account reported variations of the geomagnetic field intensity during the past 800 000 yr the calculations are based on the model simulating cosmic ray particle interactions with the earth s atmosphere given by masarik and beer simulation of particle fluxes and cosmogenic nuclide production in the earth s atmosphere j geophys res 104 d10 12099 12111 1999 corrections are nearly independent on altitude between sea level and at least 5000 m the correction factors are essentially identical for all stable and radioactive cosmogenic nuclides with half lives longer than a few hundred thousand years at the equator integrated production rates for exposure ages between 40 000 to 800 000 yr are 10 to 12 higher than the present day values whereas at latitudes 40 geomagnetic field intensity variations have hardly influenced in situ cosmogenic nuclide production correction factors for in situ 14c production rates differ from those of longer lived nuclides they are always smaller than 2 because the magnetic field intensity remained rather constant during the past 10 kyr when the major fraction of the 14c extant today was produced

response of beryllium and radiogenic isotope ratios in northern atlantic deep water to the onset of northern hemisphere glaciation we present time corrected ratios of cosmogenic 10 be to continent sourced 9 be from two fe mn crusts located in the northwest atlantic in the vicinity of the origins of northern atlantic deep water nadw these initial 10 be 9 be ratios represent those of the ambient seawater at the time of crust deposition and are constant through the last 7 ma previously published isotope records of radiogenic nd and pb isotopes in these crusts show a decrease in e nd and an increase in 206 pb 204 pb over the last 5 ma these changes are consistent with a gradual increase in the strength of nadw production an increase in the labrador sea component of nadw or an increased erosional input into the labrador sea since the residence time and thus the advective length scales of dissolved be in deep water lie between those of nd and pb records of 10 be 9 be should contrary to what has been observed vary in phase with those of nd and pb if these variations are accounted for by changes in paleo circulation the observed variations in radiogenic nd and pb isotopes are therefore most likely to be explained with an increase in the flux of terrigenous matter in the area of the labrador sea which was possibly associated with ice rafting and selective leaching of pb isotopes an increase of the labrador sea component that contributes to nadw is also a possibility but based on the 10 be 9 be data presented here large scale changes in the thermohaline circulation can be discounted as cause for the radiogenic tracer variations

interpretation of the propagation of surface altimetric observations in terms of planetary waves and geostrophic turbulence 1 the interpretation of surface altimetric signals in terms of rossby waves is revisited rather than make the long wave approximation the horizontal scale of the waves is adjusted to optimally fit the phase speed predicted by linear theory to that observed by altimetry assuming a first baroclinic mode vertical structure it is found that in the tropical band the observations can be fit if the wavelength of the waves is assumed to be large of order 600 km or so however poleward of 30 it is more difficult to fit linear theory to the observations and the fit is less good than at lower latitudes the required scale of the waves must be reduced to about 100 km somewhat larger than the local deformation wavelength it is argued that these results can be interpreted in terms of rossby wave baroclinic instability and turbulence theory at low latitudes there is an overlap between geostrophic turbulence and rossby wave timescales and so an upscale energy transfer from baroclinic instability at the deformation scale produces waves at high latitudes there is no such overlap and waves are not produced by upscale energy transfer these ideas are tested by using surface drifter data to infer turbulent velocities and timescales that are compared to those of linear rossby waves a transition from a field dominated by waves to one dominated by turbulence occurs at about 30 broadly consistent with the transition that is required to fit linear theory to altimetric observations

a model of the glacial retreat of upper rennick glacier victoria land antarctica the morphology of the lichen hills in the upper section of rennick glacier victoria land antarctica is summarised as follows a a top surface on the volcanic rocks with scattered erratic blocks b an exhumed kukri peneplain sculptured with roches moutonnees with striae and crescentic gouges on which lie moraines and patches of drift of mainly volcanic rocks c a granitic bedrock eroded by glaciers into sharp peaks and cirques on top of which there is a glacial drift attributable to ancient blue ice areas higher than those observed at present and which may be correlated with the terra nova drift late wisconsin d various holocene ice cored moraines that are pushed to the lee side of the nunataks arid are often banded in strips of different lithology the bands of the holocene moraines are related to the rock complexes that became exposed from the ice during the lowering of the surface of the glacier analysis of the lithology and pattern of the supraglacial debris as well as of the blue ice areas allows us to construct a depositional model for the moraines and to relate the glacial drift to blue ice areas existing since the last glacial maximum lgm the proposed model shows the different stages of recession of upper rennick glacier that are also valid for similar situations observed in northern victoria land a surface lowering of upper rennick glacier of several hundred metres shows that significant changes have occurred at the pacific edge of the east antarctic ice sheet since the lgm

mid pleistocene cosmogenic minimum age limits for pre wisconsinan glacial surfaces in southwestern minnesota and southern baffin island a multiple nuclide approach abstract paired 10 be and 26 al analyses n 14 indicate that pre wisconsinan glaciated bedrock surfaces near the northern baffin island and southern minnesota paleo margins of the laurentide ice sheet have long and complex histories of cosmic ray exposure including significant periods of partial or complete shielding from cosmic rays using the ratio 26 al 10 be we calculate that striated outcrops of sioux quartzite in southwestern minnesota southern margin were last overrun by ice at least 500 000 years ago weathered bedrock tors on the once glaciated uplands of baffin island northern margin are eroding no faster than 1 1 m myr 1 the equivalent of at least 450 000 years of surface and near surface exposure our data demonstrate that exposure ages and erosion rates calculated from single nuclides can underestimate surface stability dramatically because any intermittent burial and the resultant lowering of nuclide production rates and nuclide abundances will remain undetected

westward motion of mesoscale eddies abstract since the pioneering work of nof the determination of the westward drift of mesoscale eddies under the planetary beta effect has been a recurrent theme in mesoscale oceanography and several different formulae have been proposed in the literature here recpatiulation is sought and within the confines of a single layer model a generalized formula is derived although it is similar to nof s the present formula is established from a modified definition and with fewer assumptions it also recaptiulates all other formulae for the one layer model and applies to a wide variety of situations including cases when the vortex develops a wake of rossby waves or undergoes axismmetrization following the derivation of the formula a physical interpretation clarifies the migration mechanism which can be divided between a self induced propulsion and a reaction from the displaced ambient fluid numerical simulations with primitive and geostrophic equations validate the formula for a variety of length sc

global observations of large oceanic eddies 1 ten years of sea surface height ssh fields constructed from the merged topex poseidon t p and ers 1 2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean the higher resolution of the merged dataset reveals that more than 50 of the variability over much of the world ocean is accounted for by eddies with amplitudes of 5 25 cm and diameters of 100 200 km these eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies respectively the vast majority of the eddies are found to be nonlinear

the evolution and propagation of quasigeostrophic ocean eddies abstractthe long term evolution of initially gaussian eddies is studied in a reduced gravity shallow water model using both linear and nonlinear quasigeostrophic theory in an attempt to understand westward propagating mesoscale eddies observed and tracked by satellite altimetry by examining both isolated eddies and a large basin seeded with eddies with statistical characteristics consistent with those of observed eddies it is shown that long term eddy coherence and the zonal wavenumber frequency power spectral density are best matched by the nonlinear model individual characteristics of the eddies including amplitude decay horizontal length scale decay and zonal and meridional propagation speed of a previously unrecognized quasi stable state are examined the results show that the meridional deflections from purely westward flow poleward for cyclones and equatorward for anticyclones are consistent with satellite observations examination of the fluid transport properties of the eddies shows that an

a linear stochastic field model of midlatitude mesoscale variability abstracta semiempirical model of midlatitude sea surface height ssh variability is formulated and tested against two decades of weekly global fields of merged altimeter data the model is constrained to match approximately the observed ssh wavenumber power spectrum but it predicts the spatiotemporal ssh field structure as a propagating damped linear response to a stochastic forcing field an objective coherent eddy identification and tracking procedure is applied to the model and altimeter ssh fields with a focus on eddies with lifetimes l 16 weeks the model eddy dataset reproduces the basic global mean characteristics of the altimeter eddy dataset including the structure of mean amplitude and scale life cycles the number distributions versus lifetime and the distributions of all eddy length scale realizations the model underpredicts the numbers of eddy realizations with large amplitudes and large scales overpredicts the growth of mean amplitude and scale with lifetime and modestly overpre

horizontal mixing in the southern ocean from argo float trajectories we provide the first observational estimate of the circumpolar distribution of cross stream eddy diffusivity at 1000 m in the southern ocean using argo float trajectories we show that argo float trajectories from the float surfacing positions can be used to estimate lateral eddy diffusivities in the ocean and that these estimates are comparable to those obtained from rafos floats where they overlap using the southern ocean state estimate sose velocity fields to advect synthetic particles with imposed behavior that is argo like and rafos like diffusivity estimates from both sets of synthetic particles agreed closely at the three dynamically very different test sites the kerguelen island region the southeast pacific ocean and the scotia sea and support our approach observed cross stream diffusivities at 1000 m calculated from argo float trajectories ranged between 300 and 2500 m2 s 1 with peaks corresponding to topographic features associated with the scotia sea the kerguelen plateau the campbell plateau and the southeast pacific ridge these observational estimates agree with previous regional estimates from the diapycnal and isopycnal mixing experiment in the southern ocean dimes near the drake passage and other estimates from natural tracers helium inverse modeling studies and current meter measurements these estimates are also compared to the suppressed eddy diffusivity in the presence of mean flows the comparison suggests that away from regions of strong topographic steering suppression explains both the structure and magnitude of eddy diffusivity but that eddy diffusivities in the regions of topographic steering are greater than what would be theoretically expected and the acc experiences localized enhanced cross stream mixing in these regions

scaling time integrated in situ cosmogenic nuclide production rates using a continuous geomagnetic model abstract spatial and temporal variations in earth s magnetic field affect the corresponding time integrated distribution of in situ cosmogenic nuclide cn production rates these effects can be quantified by the effective vertical cutoff rigidity r c a measure of the energy required for primary cosmic rays to penetrate the geomagnetic field and interact with the atmosphere at a given location recent cn production rate scaling models are based on atmospheric cosmic ray measurements parameterized using r c estimates derived from detailed modern geomagnetic field representations which include both dipole and non dipole field contributions however published methods for quantifying time integrated geomagnetic effects on cn production rate scaling rely on various geocentric dipolar approximations to r c driven by separate records of paleomagnetic pole position and paleointensity therefore applying dipolar paleomagnetic records spanning millennial time scales which explicitly ignore past non dipole effects to scaling models derived using modern geomagnetic field representations may lead to systematic errors in any calculated results a recently published continuous geomagnetic model covering the last 7 kyr cals7k 2 m korte and c g constable continuous geomagnetic field models for the past 7 millennia 2 cals7k 2005 geochem geophys geosyst 6 q02h16 doi 10 1029 2004gc000801 may allow reduction of such errors by bridging the gap between detailed modern geomagnetic and simplified paleomagnetic models we have developed a new model framework describing temporal and spatial variation in r c for 0 7 ka and earlier based on cals7k 2 which explicitly accounts for non dipole field effects while attempting to mitigate systematic scaling biases scaling factors derived using the new r c framework predict significant longitudinal variability in time integrated cn production while predictions using dipolar geomagnetic approximations do not one can test these predictions using in situ cosmogenic 14 c in situ 14 c in quartz due to its short half life 5 73 kyr 14 c attains secular equilibrium between production and decay after approximately 25 kyr of exposure at which point its measured concentration is only a function of its integrated average production rate initial in situ 14 c results from samples at secular equilibrium from 38 n and 3 5 km in tibet and eastern california are consistent with the longitudinal variability predicted by the new framework

exposure ages from mountain dipsticks in mac robertson land east antarctica indicate little change in ice sheet thickness since the last glacial maximum past changes in east antarctic ice sheet eais volume are poorly known and diffi cult to measure yet are critical for predicting the response of the ice sheet to modern climate change in particular it is important to identify the sources of sea level rise since the last glacial maximum lgm and ascertain the present day stability of the world s largest ice sheet we present altitudinal transects of 10 be and 26 al exposure ages across the framnes mountains in mac robertson land that allow the magnitude and timing of eais retreat to be quantifi ed our data show that the coastal eais thinned by at most 350 m in this region during the past 13 k y this reduction in ice sheet volume occurred over a 5 k y period and the present icesheet profi le was attained ca 7 ka in contrast to the west antarctic ice sheet which continues to retreat today combined with regional offshore and terrestrial geologic evidence our data suggest that the reduction in eais volume since the lgm was smaller than that indicated by contemporary ice sheet models and added little meltwater to the global oceans stability of the ice margin since the middle holocene provides support for the hypothesis that eais volume changes are controlled by growth and decay of northern hemisphere ice sheets and associated global sea level changes

rock burst forecasting and genetic research in coal mines by microgravity method microgravity can be used for predicting rock bursts for the first time gravity anomalies related to rock bursts have been recorded the methodology developed has led to the first successful predictions the depth of the rock burst focus might be determined on the basis of analytical downward continuation of related gravity anomalies the focus is treated as a singular point of the gravity potential and its derivatives the rock burst gravity anomalies might be explained on the basis of the assumed dilatancy process that causes the rock burst the mean density change of the rock mass threatened with rock bursts can be estimated from the corresponding rock burst gravity anomalies

eddy kinetic energy in the north atlantic from surface drifters one hundred ten satellite tracked freely drifting buoys measured velocities and trajectories of the near surface currents in the north atlantic mean velocity values and the velocity variance about the mean were calculated for different regions a horizontal map of eddy kinetic energy was prepared on a 2 2 grid between latitudes 20 and 55 n maximum eddy energy 3000 cm2 s 2 coincides with the high speed gulf stream jet where it begins large amplitude meanders near 37 n 67 w a tongue of high eddy energy coincides with the stream s path eastward and around the grand banks into the newfoundland basin where values of 1000 cm2 s 2 are found a weaker tongue extends eastward across the mid atlantic ridge near 45 n a second weak extension reaches southeastward from the stream and crosses the mid atlantic ridge between 30 and 35 n north and south of the stream eddy energy diminishes rapidly reaching an e folding at 300 km from the axis values of 200 cm2 s 2 were observed in the mid gyre region and 100 cm2 s 2 in the eastern north atlantic and north equatorial current although the gross distribution of eddy energy is similar to that determined from ship drift measurements there are significant differences eddy energy from drifters amounts to about twice the value measured by ship drift in the gulf stream and one half the ship drift values in the mid gyre it is suggested that these differences are due to the horizontal averaging of mesoscale motion and the errors in navigation both of which are problems with the ship drift technique

aeolian dust in the talos dome ice core east antarctica pacific ross sea sector victoria land versus remote sources over the last two climate cycles a new ice core taldice drilled at talos dome east antarctica ross sea sector preserves a ca 250 ka long record of palaeoclimate and atmospheric history we investigate dust variability and provenance at the site during glacial periods and the holocene through the sr nd isotopic composition of ice core dust and potential source areas psa we provide new isotopic data on dust sources from victoria land such as regoliths glacial drifts aeolian sands and beach deposits some of these sources are located at high altitude and are known to have been ice free throughout the pleistocene the major features of the taldice dust record are very similar to those from central east antarctica during glacial times south america was the dominant dust supplier for talos dome as well as for the entire east antarctic plateau conversely during the holocene the principal input of mineral dust at talos dome probably derives from proximal sources which are the ice free areas of northern victoria land located at similar altitude with respect to the drilling site atmospheric mobilisation of dust from these neighbouring areas and transport inland to talos dome can be ultimately associated with advection of maritime air masses from the pacific ross sea region copyright 2010 john wiley sons ltd supporting information can be found in the online version of this article

landscape evolution of the dry valleys transantarctic mountains tectonic implications there are different views about the amount and timing of surface uplift in the transantarctic mountains and the geophysical mechanisms involved our new interpretation of the landscape evolution and tectonic history of the dry valleys area of the transantarctic mountains is based on geomorphic mapping of an area of 10 000 km2 the landforms are dated mainly by their association with volcanic ashes and glaciomarine deposits and this permits a reconstruction of the stages and timing of landscape evolution following a lowering of base level about 55 m y ago there was a phase of rapid denudation associated with planation and escarpment retreat probably under semiarid conditions eventually downcutting by rivers aided in places by glaciers graded valleys to near present sea level the main valleys were flooded by the sea in the miocene during a phase of subsidence before experiencing a final stage of modest upwarping near the coast there has been remarkably little landform change under the stable cold polar conditions of the last 15 m y it is difficult to explain the sirius group deposits which occur at high elevations in the area if they are pliocene in age overall denudation may have removed a wedge of rock with a thickness of over 4 km at the coast declining to 1 km at a point 75 km inland which is in good agreement with the results of existing apatite fission track analyses it is suggested that denudation reflects the differences in base level caused by high elevation at the time of extension due to underplating and the subsequent role of thermal uplift and flexural isostasy most crustal uplift 2 4 km is inferred to have occurred in the early cenozoic with 400 m of subsidence in the miocene followed by 300 m of uplift in the pliocene

equatorward energy cascade critical latitude and the predominance of cyclonic vortices in geostrophic turbulence geostrophic turbulence exhibits features similar to those observed in the oceans a movement of energy toward the equator a critical latitude below which are alternating zonal flows and above which the flow is largely isotropic and a predominance of cyclonic vortices above the critical latitude these features arise in geostrophic turbulence when the latitude dependence of the deformation radius is taken into account with the aid of a quasigeostrophic one layer numerical model this paper proposes physical mechanisms giving rise to these features

average circulation seasonal cycle and mesoscale dynamics of the peru current system a modeling approach h isolines the pccc appears to be directly forced by the cyclonic wind stress curl the model is able to produce the upwelling front the cold water tongue which extends toward the equator and the equatorial front as described in the literature model seasonal changes in sst and ssh are compared to measurements for the central pcs model eke is 10 to 30 lower than the observations the model eddy diameters follow a strong equatorward increase the injection length scales derived from the energy spectra strongly correlate to the rossby radius of deformation confirming the predominant role of baroclinic instability at 3 s the model solution appears to switch from a turbulent oceanic regime to an equatorial regime dominated by zonal currents

divergent pathways of cyclonic and anti cyclonic ocean eddies satellite altimetry is used to study the propagation pathways of warm and cold ocean eddies in different ocean basins we consider eddies that have a life span longer than 3 months and we present three regional studies in the southeast indian the southeast atlantic and the northeast pacific oceans the case studies show that simple theories for vortex propagation on a plane work in regions where energetic eddies propagate though a weak background flow under these conditions anticyclonic cyclonic eddies propagate westward and equatorward poleward this divergence in the eddy pathways implies a net equatorward eddy heat flux and has implications for the meridional transport of freshwater carbon nutrients etc