vertical tectonic deformation associated with the san andreas fault zone offshore of san francisco california abstract a new fault map of the shelf offshore of san francisco california shows that faulting occurs as a distributed shear zone that involves many fault strands with the principal displacement taken up by the san andreas fault and the eastern strand of the san gregorio fault zone structures associated with the offshore faulting show compressive deformation near where the san andreas fault goes offshore but deformation becomes extensional several km to the north off of the golden gate our new fault map serves as the basis for a 3 d finite element model that shows that the block between the san andreas and san gregorio fault zone is subsiding at a long term rate of about 0 2 0 3 mm yr with the maximum subsidence occurring northwest of the golden gate in the area of a mapped transtensional basin although the long term rates of vertical displacement primarily show subsidence the model of coseismic deformation associated with the 1906 san francisco earthquake indicates that uplift on the order of 10 15 cm occurred in the block northeast of the san andreas fault since 1906 5 6 cm of regional subsidence has occurred in that block one implication of our model is that the transfer of slip from the san andreas fault to a fault 5 km to the east the golden gate fault is not required for the area offshore of san francisco to be in extension this has implications for both the deposition of thick pliocene pleistocene sediments the merced formation observed east of the san andreas fault and the age of the peninsula segment of the san andreas fault

guyot and seamount morphology and tectonics of the hawaiian emperor elbow by multi beam sonar abstract five guyots and five seamounts are shown from the southernmost end of the emperor chain an area called the hawaiian emperor bend or the milwaukee seamount group in the north central pacific ocean the data are from the u s naval oceanographic office navoceano multi beam survey files the bend is shown to occur over an area encompassing 260 km questions are raised as to the relative proximity of different flat top depths and formational possibilities in the light of the differing geomorphology on the features in addition there are two new features taish and go shirakawa seamounts and four additional new names of features are introduced antoku guyot toba guyot and genji and go sanj seamounts

seamount resolution in satellite derived bathymetry 1 i compare satellite derived global relief data on 13 seamounts in the northeast pacific ocean to echosounder derived multibeam values from the gulf of alaska seamount expeditions and the west coast seamounts and ridges multibeam surveys for peak height latitude longitude and midsection area i find smith and sandwell s 1997 global sea floor topography relatively accurate for peak geoposition but generally deeper than multibeam by 192 m 132 m cell size alone can explain 50 90 of peak height variation suggesting higher resolution geodetic altimetry could improve the accuracy of these estimates nevertheless midsection areas overlap by 80 11 the altimetric technique clearly resolves the presence and general form of numerous unnamed deep seamounts though predicted seamount peak height estimates for small features may vary from their true depth by up to 50 these findings support high end estimates of global seamount abundance since small seamount features 1200 m relief revealed by satellite may in actuality be quite substantial features 2500 m relief

paleogene evolution of the kodiak islands alaska consequences of ridge trench interaction in a more southerly latitude the kodiak islands of alaska are principally composed of a late cretaceous and paleogene complex of accreted deep sea rocks an early paleocene magmatic event invaded the accretionary complex with mid ocean ridge basalt morb andesite and granodiorite geochemical evidence suggests both the andesite and granodiorite are mixtures of morb and sediment the volcanic rocks are interlayered with coarse clastic sediments and deformed with the latter the granodioritic intrusions with k ar ages as old as 62 ma postdate emplacement of the early paleocene sedimentary and volcanic rocks interaction of the subduction complex with the kula farallon ridge most simply explains this early paleocene magmatic episode paleomagnetic studies of the volcanic rocks indicate this interaction occurred at 40 3 6 north latitude which is 25 3 9 south of the expected position of the kodiak islands relative to north america the magmatic arc presently northwest of the kodiak accretionary complex was active during the late cretaceous and early paleocene diminished after the ridge trench interaction and resurged from late eocene into miocene time the magmatic resurgence is coeval with the obductive offscraping of eocene to oligocene submarine fan deposits in the kodiak islands the petrology of these fan deposits indicates they are the most likely proximal equivalent for the zodiac fan thereby limiting its relative motion with respect to the kodiak islands possible models accounting for the northward motion of the kodiak accretionary complex include 1 coupling the accretionary complex and possibly related arc to the northward moving kula plate and closing an ocean basin north of the arc in paleogene time 2 emplacing the kodiak accretionary complex at the northward limit of the paleomagnetic data with subsequent northward motion accomplished by closure of a small back arc basin and or intracontinental shortening and 3 transcurrent faulting and northward motion of the kodiak accretionary complex without the presently adjacent arc

small fluctuations in the density and thickness of a dry firn column it is of practical importance to have a description on time scales of 1 100 years of the relationship between the mass imbalance of an ice sheet and its rate of change of thickness in this paper a linearized treatment off the relationship is described closed form expressions are derived that relate the time variant density in an isothermal firn layer to the fluctuations in accumulation rate and density that occur at the surface these expressions are used to provide a spectral description of the contribution of surface accumulation and surface density fluctuations to the rate of change of thickness of an ice sheet using these the contribution of firn densification to the variability of ice sheet thickness is examined as a function of the time interval over which the ice sheet is observed this contribution is illustrated for sites in antarctica and greenland it is concluded that it is important to give greater attention than hitherto to the spatial scale of accumulation fluctuations if satellite observations of ice sheet elevation change are to be used to estimate ice sheet imbalance over short time intervals

reassessment of net surface mass balance in antarctica abstract recent in situ measurements of surface mass balance and improved calculation techniques are used to produce an updated assessment of net surface mass balance over antarctica a new elevation model of antarctica derived from ers 1 satellite altimetry supplemented with conventional data was used to delineate the ice flow drainage basins across antarctica the areas of these basins were calculated using the recent digital descriptions of coastlines and grounding lines the delineation of drainage basins was achieved using an automatic procedure which gave similar results to earlier hand drawn catchment basins more than 1800 published and unpublished in situ measurements of net surface mass balance from antarctica were collated and then interpolated a net surface mass balance map was derived from passive microwave satellite data being employed as a forcing field to control the interpolation of the sparse in situ observations basinwide integrals of net surface mass balance were calculated using t

basal melting at the ekstrom ice shelf antarctica estimated from mass flux divergence we characterize the basal mass balance of the ekstr om ice shelf dronning maud land antarctica using interferometrically derived surface velocities and ice thickness measurements from radio echo sounding res the surface velocities are based on data from european remote sensing satellites 1 and 2 ers 1 2 during 1994 97 the ice thickness grid consists of 136 res profiles acquired between 1996 and 2006 mass fluxes are calculated along selected res profiles where possible to reduce uncertainties from ice thickness interpolation elsewhere large scale mass fluxes are calculated using interpolated ice thickness data themass flux into the ekstr om ice shelf from themain grounded drainage basins is estimated to be 3 19 0 4gt a 1 the mass flux near the ice shelf front is 2 67 0 3gt a 1 assuming steady state and based on the equation of continuity we interpret the residual mass flux as a combined effect of snow accumulation and subglacial melting refreezing using net snow accumulation rates from previous studies we link the mass flux divergence in irregular shaped polygons to processes beneath the ice shelf the highest subglacial melt rates of 1 1ma 1 are found near the grounding zone of two main inflow glaciers and around the german station neumayer iii the detection of unlikely refreezing in a small area 15 km west of neumayer iii is attributed to both dataset inaccuracies and a possibly past violation of the steady state assumption in general the method and input data allow mapping of the spatial distribution of basal melting and the results are in good agreement with several previous studies

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

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

growth of greenland ice sheet interpretation an observed 0 23 m year thickening of the greenland ice sheet indicates a 25 to 45 excess ice accumulation over the amount required to balance the outward ice flow the implied global sea level depletion is 0 2 to 0 4 mm year depending on whether the thickening is only recent 5 to 10 years or longer term 100 years if there is a similar imbalance in the northern 60 of the ice sheet area the depletion is 0 35 to 0 7 mm year increasing ice thickness suggests that the precipitation is higher than the long term average higher precipitation may be a characteristic of warmer climates in polar regions

relationship between axial morphology crustal thickness and mantle temperature along the juan de fuca and gorda ridges we analyze gravity data over the juan de fuca and northern gorda ridges to understand the lithospheric structure of two ridges with contrasting axial morphologies spreading at the same intermediate rate 28 mm yr half rate the cleft segment at the south end of the juan de fuca ridge has an axial high morphology while the northern segment of the gorda ridge has a rift valley residual mantle bouguer anomalies rmba on the northern gorda ridge are elevated relative to the cleft segment by 10 20 mgal indicating thinner crust and or a colder mantle the minimum value 50 mgal of the rmba along the juan de fuca ridge is over axial seamount and gradually increases south toward the blanco transform the observed rmba are interpreted to result from along axis variations in crustal thickness and mantle density both of which are controlled by temperatures in the upper mantle where decompression melting occurs we estimate that mantle temperatures are elevated by 30 40 c beneath axial seamount resulting in an excess crustal thickness of 1 7 km the cleft segment is associated with crust that is estimated to be only 300 700 m thicker and mantle temperatures are only 10 15 c higher than beneath the northern gorda ridge however even these small differences in crustal thickness and mantle temperature appear to be sufficient to produce a major change in lithospheric strength and axial morphology these results are consistent with the predicted sensitivity of recent thermo mechanical models for rift valley formation to small changes in crustal thickness and mantle temperature at intermediate spreading rates we attribute the systematic differences in axial morphology crustal thickness mantle temperature and lithospheric strength along the juan de fuca gorda ridge system to the presence of the cobb thermal anomaly at axial seamount the hotter mantle beneath the juan de fuca ridge results in greater amounts of decompression melting and the formation of a thicker crust and a thinner weaker lithosphere than along the gorda ridge

the antarctic ice sheet its history and response to sea level and climatic changes over the past 100 million years abstract the development surface form flow and erosive activity of the antarctic ice sheet over the past 100 million years is related to geological evidence that indicates long term trends of global climate the glaciological description of the evolution of the ice sheet covers its interactions with the atmosphere and with the ocean discussion focuses on changes of the equilibrium line altitude ela with time of the accumulation rate with global temperature and basal melting of ice shelves by ocean waters the tendency of global climate to change rapidly or to drift slowly between two near equilibrium states involves two types of changes the former that has been widely recognized is reversible a second type involving ice sheets or ice shelves appears to be almost irreversible since they remain in their changed state unless a much larger reversal of factors driving climate occurs we refer to any rapid but reversible changes as climatic jumps and to the latter as climate ice switches variability of climate in response to changing radiation with the earth s orbital parameters and other causes is included in our model extensive glaciation of east antarctica commenced after 40 m y b p with wide fluctuations until shortly after 20 m y b p a climate ice switch then prevented any major deglaciation a further climate ice switch associated with the ela falling below sea level occurred soon after 10 m y b p this led to rapid formation of ice shelves and the marine ice sheet of west antarctica which advanced as grounded ice to the edge of the continental shelf after 5 m y b p the grounded ice started to retreat extensive ice shelves remained and most glacial debris was then deposited beneath the inner regions of ice shelves response to northern hemisphere glaciation since 2 4 m y b p during glacial periods involved extension of the grounded ice area a large decrease of mass input and decreased melting of outer parts of large ice shelves while the melting rate beneath inner regions was probably similar to the present marine core evidence suggests that retreat caused by global cooling has been dominant since 5 m y b p and that changes in extent due to northern hemisphere glaciation since 2 4 m y b p have had different effects on the major and on smaller northerly ice shelves

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

antarctic temperatures over the past two centuries from ice cores 1 we present a reconstruction of antarctic mean surface temperatures over the past two centuries based on water stable isotope records from high resolution precisely dated ice cores both instrumental and reconstructed temperatures indicate large interannual to decadal scale variability with the dominant pattern being anti phase anomalies between the main antarctic continent and the antarctic peninsula region comparative analysis of the instrumental southern hemisphere sh mean temperature record and the reconstruction suggests that at longer timescales temperatures over the antarctic continent vary in phase with the sh mean our reconstruction suggests that antarctic temperatures have increased by about 0 2 c since the late nineteenth century the variability and the long term trends are strongly modulated by the sh annular mode in the atmospheric circulation

parameterization of the annual surface temperature and mass balance of antarctica this study entails the parameterization by means of a linear multiple regression analysis of the annual surface temperature and mass balance of antarctica the analysis was performed for the entire ice cap as well as for three separate regions ice shelves elevation less than 200 m the interior elevation above 1500 m and the escarpment region in between it was found that temperature can be parameterized very well in terms of elevation and latitude the latitudinal gradient on the ice shelves can be explained by the super adiabatic lapse rate along the surface and latitudinal temperature gradient in the interior assuming adiabatic descent of air in the inversion layer from the interior region towards the coast and an axisymmetric spreading over the ice shelves the surface mass balance can be parameterized reliably only in the interior where it has a strong positive correlation with the saturation vapour pressure of the free atmosphere and a significant correlation with the shape of the dome the convex shape of the dome contributes to the mass balance by inducing subsidence of the relatively moist air of the free atmosphere into the inversion layer this results in precipitation as radiative cooling in the inversion exceeds adiabatic warming an estimate is made of the annual horizontal and vertical advective velocities in the free atmosphere above the interior based on regression results and a physical analysis of the precipitation processes in this region a temperature sensitivity analysis was performed for the current mass balance distribution for a 1 k rise in surface temperature the regression estimate of the increase in accumulation on the grounded ice sheet is equivalent to a rate of sea level lowering of 0 2 mm a 1 this is about 30 less than estimates based on the current mass balance perturbated by the increase in saturation vapour pressure of the free atmosphere

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

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

paleomagnetism of northern cocos seamounts constraints on absolute plate motion paleodeclinations of several small seamounts on the northern cocos plate demonstrate that it rotated approximately 30 counter clockwise about a pole close to its northern boundary during the past 1 to 6 m y paleoinclinations agree with models of absolute plate motion in which the northern component of velocity for the cocos plate is about 50 mm yr the paleomagnetic data dredge samples and seamount morphology either independently or in concert are reasonably reliable for distinguishing fault blocks from central volcanoes and for determining the approximate age of a structure relative to that of the surrounding sea floor

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

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

sediment transport in the san francisco bay coastal system an overview abstract the papers in this special issue feature state of the art approaches to understanding the physical processes related to sediment transport and geomorphology of complex coastal estuarine systems here we focus on the san francisco bay coastal system extending from the lower san joaquin sacramento delta through the bay and along the adjacent outer pacific coast san francisco bay is an urbanized estuary that is impacted by numerous anthropogenic activities common to many large estuaries including a mining legacy channel dredging aggregate mining reservoirs freshwater diversion watershed modifications urban run off ship traffic exotic species introductions land reclamation and wetland restoration the golden gate strait is the sole inlet connecting the bay to the pacific ocean and serves as the conduit for a tidal flow of 8 10 9 m 3 day in addition to the transport of mud sand biogenic material nutrients and pollutants despite this physical biological and chemical connection resource management and prior research have often treated the delta bay and adjacent ocean as separate entities compartmentalized by artificial geographic or political boundaries the body of work herein presents a comprehensive analysis of system wide behavior extending a rich heritage of sediment transport research that dates back to the groundbreaking hydraulic mining impact research of g k gilbert in the early 20th century

dependence of antarctic surface mass balance on temperature elevation and distance to open ocean the latest compilations of surface mass balance mean annual surface temperature and elevation for the antarctic ice sheet derived from data sets of approximately 1500 700 and 105 points respectively have been used to obtain areally integrated means for 24 ice drainage systems and 329 grid point values covering the whole ice sheet monthly summaries of remotely sensed sea ice data for 1973 1976 have been used to obtain mean annual distance to open ocean linear and second order regression analyses of surface balance on 1 temperature for the entire ice sheet 2 elevation for the conterminous grounded ice and 3 distance to the open ocean for the ice shelves including ice rises and attached islands have been made using both system means and grid point values these analyses show correlation coefficients of between 0 63 and 0 81 and they provide bases for descriptive models of the present antarctic ice sheet as well as for predictive models of the response of the ice sheet to air temperature changes and variations in meridional mass and energy transfers extrapolation to other ice sheets past and present may be possible but should be made cautiously linear models are recommended for paleoclimatic reconstructions of ice sheets in upper mid latitudes and second order models are recommended for those in high latitudes system means are shown to be reliable for these purposes incidental results are new estimates of the mean annual surface temperature for the whole ice sheet 36 c and mean surface elevation for the conterminous grounded ice 2290 m

accumulation rates in dronning maud land antarctica as revealed by dielectric profiling measurements of shallow firn cores the european programme for ice coring in antarctica includes a comprehensive pre site survey on the inland ice plateau of dronning maud land antarctica the german glaciological programme during the 1997 98 field season was carried out along a 1200 km traverse on amundsenisen and involved sampling the snow cover in pits and by shallow firn cores this paper focuses on the accumulation studies the cores were dated by dielectric profiling and continuous flow analysis distinct volcanogenic peaks and seasonal signals in the profiles served to establish a depth time scale the eruptions of krakatoa tambora an unknown volcano kuwae and el chichon are well documented in the ice variations of the accumulation rates over different times were inferred from the depth time scales a composite record of accumulation rates for the last 200 years was produced by stacking 12 annually resolved records according to this accumulation rates decreased in the 19th century and increased in the 20th century the recent values are by no means extraordinary as they do not exceed the values at the beginning of the 19th century variations in accumulation rates are most probably linked to temperature variations indicated in 18o records from amundsenisen

shallow firn cores from neumayer ekstromisen antarctica a comparison of accumulation rates and stable isotope ratios since 1979 80 glaciological studies have been carried out at ekstromisen antarctica including accumulation stake measurements snow pit and shallow firn core studies snow stratigraphy chemical properties and stable isotope ratios 18 o were investigated this study focuses on three cores taken between 1982 and 1998 the 1998 core was dated using dielectric profiling 18 o profiles and stake measurements accumulation rates show high interannual and spatial variability due to the extreme wind influence no significant trend was found for the last 50 years during the first half of the 20th century accumulation decreased the high spatial and interannual variability however means that trends must be interpreted with care in spite of the highly irregular accumulation distribution stable isotope ratios show little spatial variability the mean annual 18 o values of cores b04 and fb0198 agree fairly well for the time period 1955 82 covered by both cores 18 o values have increased during most of the 20th century since the late 1980s a decrease is observed this change is not related to air temperature since mean annual air temperatures at neumayer show no significant trend over the last two decades

decadal timescale links between antarctic peninsula ice core oxygen 18 deuterium and temperature the antarctic peninsula region has exprienced a long term warming trend over the twentieth century with the 1971 90 mean at faraday being 1 9 c warmer than the mean over 1903 41 based on expedition reports for the period prior to 1900 there is conflicting evidence from different data sources an initial interpretation of isotopic data from ice cores suggests that the nineteenth century was warmer than the twentieth century in contrast snow accumulation rate data for the nineteenth century from the same ice cores suggest lower temperatures here we investigate these facts by studying the links between atmospheric temperature over the antarctic peninsula circulation parameters and isotopic data over the period of instrumental records we show that the relationships between these variables are complex and highly spatially variable in particular the correlations between temperature and 18o and d are generally of the order r 0 5 or less on timescales of one to five years conflicts between evidenc

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

sea level pressure variability over the southern indian ocean inferred from a glaciochemical record in princess elizabeth land east antarctica 1 a 250 year high resolution multivariate ice core record from lgb65 70 50 07 s 77 04 29 e 1850 m asl princess elizabeth land pel is used to investigate sea level pressure slp variability over the southern indian ocean sio empirical orthogonal function eof analysis reveals that the first eof eof1 of the glaciochemical record from lgb65 represents most of the variability in sea salt throughout the 250 year record eof1 is negatively correlated 95 confidence level and higher to instrumental mean sea level pressure mslp at kerguelen and new amsterdam islands sio on the basis of comparison with ncep ncar reanalysis strong correlations were found between sea salt variations and a quasi stationary low that lies to the north of prydz bay sio comparison with a 250 year long summer transpolar index stpi inferred from sub antarctic tree ring records reveals strong coherency decadal scale slp variability over sio suggests shifting of the polar vortex prominent decadal scale deepening of the southern indian ocean low siol exists circa 1790 1810 1835 1860 1880 1900 and 1940 a d continuously after the 1970s and prominent weakening circa 1750 1795 1825 1850 1870 1890 1910 and 1955 a d the lgb65 sea salt record is characterized by significant decadal scale variability with a strong 21 year periodic structure 99 9 confidence level the relationship between lgb65 sea salt and solar irradiance changes shows that this periodicity is possibly the solar hale cycle 22 years

multi beam sonar surveys of guyots of the gulf of alaska abstract this paper describes in detail the three guyots in the gulf of alaska the form of these features has been charted from total bottom coverage bathymetric surveys using swath mapping sonar data were collected by the u s naval oceanographic office statements and descriptions of the geomorphology of these guyots welker durgin and pratt are used to speculate on the ultimate demise of the juan de fuca hot spot

inferences from stable water isotopes on the holocene evolution of scharffenbergbotnen blue ice area east antarctica we show that it is possible to extract a high resolution annual paleoclimate record from the surface of a blue ice area bia the variability of the surface stable isotope values suggests that almost all the surface ice in scharffenbergbotnen bia east antarctica is of holocene age the isotopic changes across the bia show that the modern climate there is warmer than the climate in the early holocene optimum 11 kyr bp a volume conserving ice flow model for the bia constrained by isotopic variability and layer thicknesses and a series of 14 c ages indicate both that the bia has been smaller than now and that the surface velocities were considerably smaller during the last glacial maximum changes in ice sheet thickness drive the bia towards present day conditions the relatively young age of the majority of the bia also explains the lack of meteorite finds in this area and may be typical for many bias in low elevation nunatak areas

a century of climate variability in central dronning maud land east antarctica and its relation to southern annular mode and el nino southern oscillation stable isotope records of oxygen and hydrogen were studied from a 65 m long ice core retrieved from the central dronning maud land east antarctica in order to reconstruct the coastal antarctic climate variability during the last century and its relation to the southern annular mode sam and el nino southern oscillation enso the 18 o records showed a significant relation to the sam with a dominant 4 years variability except during specific periods 1918 1927 19381947 1989 2005 when enso teleconnection was established through the in phase relation between sam and southern oscillation index soi the combined influence of enso and sam was seen on surface air temperatures in this region mainly during the austral summer season from 1989 to 2005 further a significant relationship between 18 o and sam was observed on a decadal scale which overrides the intermittent influence of enso major shifts in the deuterium excess record were observed during periods of enso teleconnections which support a shift in moisture source regions during the periods of stronger enso teleconnections surface air temperatures estimated using the 18 o t spatial slope for this region depicted a significant warming of 1 c for the past century the study reveals that throughout the last century sam was the dominant mode of climatic variability in the coastal region of central dronning maud land on a decadal scale

spatial distribution of surface mass balance on amundsenisen plateau antarctica derived from ice penetrating radar studies the distribution of surface mass balance on amundsenisen dronning maud land antarctica is investigated along a continous profile line ice penetrating radar is used to map variations in ice layer thickness within the upper 100 m of the ice sheet the route passes several firn and ice core drilling sites over a distance of 320 km dielectric profiling data of ice cores is used to calculate the depths of selected reflection horizons and the cumulative mass of the ice column the local surface mass balance is determined as a temporal average covering a time span of almost two centuries the findings indicate a complex accumulation pattern superimposed on a general low surface mass balance which is related to small scale surface undulations the results of the radar soundings are in general in good agreement with surface mass balance data derived from firn core studies discrepancies between these two datasets can be explained by spatial mismatch or by minor quality of either ice core profiles or radar data for regional comparison of radar based accumulation data we use an accumulation distribution interpolated from point measurements the surface mass balance varies up to 50 over short distances with correlation lengths of 10 km we conclude that the current utilization schemes of point sampling are only capable of reproducing local values and regional trends but provide no information on the small scale variability of surface mass balance

antarctic elevation change from 1992 to 1996 satellite radar altimeter measurements show that the average elevation of the antarctic ice sheet interior fell by 0 9 0 5 centimeters per year from 1992 to 1996 if the variability of snowfall observed in antarctic ice cores is allowed for the mass imbalance of the interior this century is only 0 06 0 08 of the mean mass accumulation rate

an 860 km surface mass balance profile on the east antarctic plateau derived by gpr abstract snow accumulation and its variability on the east antarctic plateau are poorly understoodduetosparseandregionallycon nedmeasurements wepresenta5 3ghz c band ground penetratingradar gpr pro lewith atotal length of860kmrecovered duringthe jointnorwegian us internationalpolar year traverse 2007 08 mean surface mass balance smb over the last 200years was derived fromthe gpr data by identifying the volcanic deposition of the tambora eruption in 1815 it varies between9 1 and 37 7kgm 2 a 1 over the pro le with a mean of 23 7kgm 2 a 1 and a standard deviation of4 7kgm 2 a 1 the 200year smb estimated is signi cantly lower than most of the smb estimates overshorter time periods in this region this can be partly explained by a smb minimum in the vicinity ofthe ice divide however it is more likely that a recent increase in smb observed by several studies islargely responsible for the observed discrepancy introduction many recent studies have concentrated on the surface massbalance smb vaughan and others 1999 arthern andothers 2006 monaghan and others 2006 van de berg andothers 2006 and mass changes davis and others 2005 zwally and others 2005 of the antarctic ice sheet in orderto assess antarctica s contribution to changes in global sealevel new techniques such as radar altimetry have madeit possible to study continent wide elevation changes withhigh accuracy these changes are often related to changesin precipitation on the east antarctic plateau eap davisand others 2005 zwally and others 2005 however thesetechniques only cover short time periods it is important toobtain ground truth over longer time periods to understandhow observed changes relate to the past to date there have been very few in situ measurements ofsmb available from the interior of the eap the present smbestimates are mainly based on remote sensing e g arthernand others 2006 or numerical modelling e g monaghanand others 2006 van de berg and others 2006 calibratedby very sparse in situ measurements for the interior ofthe continent there are also indications that there are anon negligible number of zero accumulation sites so calledglazedareas intheinterioroftheeapthatareoftennottakeninto account by mass balance estimates and can changetheirvalue signi cantly frezzotti andothers 2002 scambosandothers 2008 it isclear that moreaccumulation dataarerequired to study the spatial and temporal variability of smband to improve the spatial resolution and accuracy of large scale accumulation studies the smb is the aggregate of many processes such asprecipitation from clouds and clear skies the formationof hoar frost at the surface and within the snowpack sublimation melting and runoff wind scouring and driftdeposition eisen and others 2008 snow accumulation canbe derived using various methods e g eisen and others 2008 snow pit rn and ice core studies provide valuableinformation about mean smb for a certain point location takahashi and others 1994 isaksson and others 1996 ansch utz and others in press these point measurementscan be spatially extended by ground penetrating radar gpr smb is proportional to the re ector depth withinthe rn pack as variations in vertical strain rates can beneglected in the top tens of metres of the ice sheet nye 1963 gpr has previously been successfully used to followisochronous rn layers providing detailed information aboutthe smb variability across antarctica fujita and others 1999 richardson naslund 2004 rotschky and others 2004 spikes and others 2004 arcone and others 2005a although large regions of the eap still remain uncovered we show smb derived by gpr data collected duringthe rst leg of the norwegian us scienti c traverse ofeastantarctica http traverse npolar no duringthe2007 08austral summer nus07 this joint project is part of thelarger trans antarctic scienti c traverses expeditions icedivideofeast antarctica taste idea andthe internationalpartnerships in ice coringsciences ipics goldman 2008

bedrock geology of the san francisco bay area a local sediment source for bay and coastal systems abstract local watersheds may contribute over half of the sediment load coming into san francisco bay today the bedrock underlying these watersheds is the ultimate source for most of this sediment this paper outlines the geologic history of this bedrock which records the complex tectonic history of the san francisco bay area over the last 200 ma the jurassic to eocene franciscan complex in the bay area is the most widespread bedrock the local franciscan can be broken into nine tectonic terranes that represent pieces of seafloor that were accreted to the north american margin in over a 100 myr period of subduction each terrane has a unique age range sequence of seafloor rocks and metamorphic history the franciscan rocks were thrust eastward under the great valley complex the great valley complex reflects a forearc basin comprised of jurassic ocean crust the coast range ophiolite and overlying jurassic and cretaceous turbidite dominated sedimentary rocks of the great valley group by the beginning of the cenozoic era shallowing of the angle of subduction along the continental margin led to uplift and infilling of the forearc basin to shelf depth recorded at this time are sedimentary sequences governed by eustatic sealevel changes and evidence of the first unroofing of franciscan rocks marine sedimentary rocks dominate the region through the miocene and unconformities within the early tertiary sedimentary record reflect periods of tectonic activity and uplift middle to late miocene sedimentary rocks are extensively deposited throughout the bay area in the late miocene the mendocino triple junction passed northward through the area and transform tectonism commenced a slab window developed behind the triple junction resulted in volcanic activity that produced the sonoma volcanics in the north bay and volcanics of the east bay hills by pliocene time terrestrial sedimentary rocks were being deposited in many parts of the bay area faulting associated with the san andreas system led to the development of small basins the displacement of local bedrock blocks and the transport of the salinian complex from the southern sierra to the western margin of the bay area the modern topography of the region started emerging by about 6 ma to 4 ma when compression across the san andreas system increased and uplift of the coast ranges began the first estuarine influence in san francisco bay is recorded in 600 ka rocks about the same time as the modern sacramento river system started flowing through the san francisco estuary valley today s local san francisco bay watershed is comprised of numerous small stream systems around the bay with headwaters in the surrounding hills and mountains active tectonism produces relief in these watersheds of typically 500 m or more with the ridgelines typically supported by more resistant bedrock units steep topography leads to rapid bedrock erosion particularly of the finer grained sedimentary rocks landslides provide a significant portion of the sediment carried by the streams and several of the bedrock units are more prone to landslides particularly the central and novato quarry terranes of the franciscan complex and finer grained units of both the great valley group and tertiary rocks many of the larger streams have dammed reservoirs that trap much of their sediment load before it can reach the bay

climate variability in west antarctica derived from annual accumulation rate records from itase firn ice cores thirteen annually resolved accumulation rate records covering the last 200 years from the pine island thwaites and ross drainage systems and the south pole are used to examine climate variability over west antarctica accumulation is controlled spatially by the topography of the ice sheet and temporally by changes in moisture transport and cyclonic activity a comparison of mean accumulation since 1970 at each site to the long term mean indicates an increase in accumulation for sites located in the western sector of the pine island thwaites drainage system accumulation is negatively associated with the southern oscillation index soi for sites near the ice divide and periods of sustained negative soi 1940 42 1991 95 correspond to above mean accumulation at most sites correlations of the accumulation rate records with sea level pressure slp and the soi suggest that accumulation near the ice divide and in the ross drainage system may be associated with the mid latitudes the post 1970 increase in accumulation coupled with strong slp accumulation rate correlations near the coast suggests recent intensification of cyclonic activity in the pine island thwaites drainage system

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

northern hess rise extended by multi beam sonar abstract the bathymetry for three of the ridges north of the hess rise is presented from u s naval oceanographic office sass surveys these ridges strike in directions not parallel or perpendicular to any other features in the north pacific ocean they were previously uncharted and presumably undetected they probably predate the emperor guyots and are contemporaries of the musician seamounts

accumulation studies on amundsenisen dronning maud land antarctica by means of tritium dielectric profiling and stable isotope measurements first results from the 1995 96 and 1996 97 field seasons the paper focuses on studies of snow pit samples and shallow firn cores taken during the 1995 96 and 1996 97 field seasons at amundsenisen dronning maud land antarctica the dating of the firn is based on the artificial tritium distribution in the snow cover and on several reference horizons identified by electrical measurements the early 1964 through 1965 horizon is marked by the deposition of sulfate released to the atmosphere during the eruption of the agung volcano in march 1963 this horizon was detected by dielectric profiling and electrical conductivity measurements the proof by chemical analysis has still to be seen at the ten investigated sites on amundsenisen the 1964 65 horizon was identified 4 1 5 7 m below the surface the accumulation rates on amundsenisen are 41 91kg ma the cores are up to 100 years old a relationship between isotope content and the mean air temperature on a regional scale can be based onmeasurements of firn temperature at10m depth at the drilling sites betweenneumayer station at the coast and heimefrontfjella the temperature gradient of the deuterium content is 9 6 k south of heimefrontfjella on the amundsenisen plateau it is only 5 5 k time series of yearly accumulation rates show no significant trend for the isotope records a significant trend to higher values with gradients of 0 1 0 2 dh a can be seen in five of the ten time series

oceanic plateaus the fragmentation of continents and mountain building many anomalous rises in today s oceans may be submerged continental fragments detached from previous continents ancient island arcs or basaltic piles formed by hot spots and spreading centers these rises are embedded in their respective moving oceanic plates and are fated to be consumed at active margins where such rises are being consumed at present e g the nazca ridge they cause cessation of volcanism disruption of the downgoing slab and possible shifts in plate boundary configuration many past rises including numerous continental fragments have been recognized within mountain belts as allochthonous terranes they constitute a large portion of the orogenic belts in the north pacific from mexico through western north america alaska east siberia japan and in new zealand the orogenic deformation in these belts is possibly the result of the accretion of the allochthonous terranes many terranes have been accreted with substantial deformation also in the alpine chain well before major continent continent collisions it is suggested therefore that the accretion of fragments may be the common process of the deformation phase of mountain building subduction of normal oceanic crust may be insufficient for deformation whereas full continent continent collision may not be necessary the general validity of this conclusion depends critically on whether allochthonous terranes caused orogenic deformation in the andes or not most of the accreted fragments with continental affinities in the mesozoic cenozoic orogenic belts of the world can be traced back to the breakup of gondwana beginning with a pacifica domain in the permian through a larger india domain in the early mesozoic and continuing through the separation of the somalia plate in the near future the reasons for this 250 million year breakup process are not known but some kind of thermal process possible of mantle wide scale is implied

guyots of the mid emperor chain mapped with multibeam sonar abstract bathymetry of seven of the middle emperor chain guyots from u s naval oceanographic office multibeam narrow beam swath mapping surveys is presented these data are contoured at a 100 fm interval using different theories on formation juxtaposed with the accurate bathymetry of this chain tectonic possibilities are shown for changes in plate direction and conduit activity fluctuations the range for one complete pulse of this activity is shown to be 280 nm 518 km for the emperor chain

tropical pacific high latitude south atlantic teleconnections as seen in δ18o variability in antarctic coastal ice cores 1 we use a network of eight ice cores from coastal dronning maud land dml antarctica to examine the role of the tropical enso el nino southern oscillation in the temporal variability of 18o in annual accumulation the longest record from the s100 ice core covering the period 1737 1999 is used to analyze the teleconnections between the tropical pacific and coastal dml on decadal scales and longer a shorter stacked coastal dml 18o series spanning 1955 1999 is constructed to assess the variability of enso teleconnection on interannual scales results suggest that on typical enso timescales of 2 6 years the strength of the teleconnection varies in time being stronger for years with generally negative phase of the southern annular mode sam on the timescales of approximately two decades bidecadal positive isotope anomalies are associated with oceanic warming and a westward sea surface temperature sst gradient in the equatorial pacific bidecadal variability in sam forced by the tropical pacific is proposed as a critical element in the teleconnection our analysis suggests that a multidecadal positive trend in the annual mean 18o values from the analyzed cores can be indicative of the atmospheric warming that begun in this part of the dml already in the 1910s the trend in 18o quantified in terms of long term surface air temperature sat changes is consistent with the instrumental data yet we speculate that the accurate estimation of sat trends requires an assessment of the potential role of secular sam and sea ice extent changes in shaping the isotopic signal

snow accumulation variability from seasonal surface observations and firn core stratigraphy eastern wilkes land antarctica annual accumulation records were derived from two firn cores drilled at gd03 69 00 s 115 30 e 1835m and gd15 69 00 s 130 48 e 2155m which are separated by 750 km along the 2000 m contour in eastern wilkes land the accumulation records spanning the period 1930 85 show that annual accumulation has increased by 25 from 1960 to 1985 resulting in the highest accumulation rates in the 55 year records annual accumulation layers were identified in the firn cores using a firn stratigraphic model based on the observed characteristics and variability of the seasonal snow surface layer together with seasonal oxygen isotope ratios the accumulation records support other evidence for a similar recent increase across antarctica the greater increase over the long term mean for 1930 85 in eastern wilkes land was observed at gd15 which is located on a northeast aspect slope near terre adelie it is suggested that the increase is the result of changes in the general atmospheric circulation pattern which have produced a higher annual frequency of precipitation events

the trans pacific chinook trough megatrend abstract the chinook trough is a trans pacific megatrend by using heretofore unpublished bathymetry and geophysical data the trend of the chinook trough megatrend has been determined from the juan de fuca ridge in the gulf of alaska to the izu bonin trench the feature passes through the emperor fracture zone intersects the krusenstern fracture zone at the hess rise passes through the emperor seamounts intersects the mamua fracture zone and several unnamed nnw sse trending fractures at the shatskiy rise after an undetermined passage through nadeshda basin it intersects another nnw sse trending fracture zone kashima fracture zone at nelson guyot and ends as uyeda ridge instead of being a trough the feature is a fracture zone herein called a megatrend the feature is colinear to the mendocino and clipperton fracture zones

sub tidal benthic habitats of central san francisco bay and offshore golden gate area a review abstract deep water potential estuarine and marine benthic habitat types were defined from a variety of new and interpreted data sets in central san francisco bay and offshore golden gate area including multibeam echosounder mbes side scan sonar and bottom grab samples potential estuarine benthic habitats identified for the first time range from hard bedrock outcrops on island and mainland flanks and some bay floor regions to soft very dynamic bedforms consisting of sediment waves and ripples soft sediment ranges from mud and sand to bimodal two or more grain sizes sediment of gravel pebbles and cobbles in addition considerable anthropogenic features i e pipelines bridge abutments dredged channels dump sites were distinguished of the 52 potential benthic habitat types mapped compressed to 14 types for this paper 24 were of unconsolidated sediment with five of these comprised of dynamic bedforms or sediment waves and dunes five of mixed soft over hard substrate type six of hard substrate or rock outcrop 13 of anthropogenically disturbed areas and four hard anthropogenic features rock outcrops and rubble are considered the primary habitat type for rockfish sebastes spp lingcod ophiodon elongatus and in shallow water for herring clupea pallasii spawning dynamic bedforms such as sand waves are considered potential foraging habitat for juvenile lingcod may be sub tidal habitat for the pacific sand lance ammodytes hexapterus forage fish and possibly resting habitat for migratory fishes such as sturgeon acipenser medirostris the potential marine benthic habitats identified in san francisco bay are not unlike those found in other estuaries around the world and this study should contribute significant information that will be of interest to scientists managers and fishers investigating and utilizing bay and estuarine resources as described in the many papers of this special issue the understanding of the interrelationship of geology and ecology is critical to the identification of essential habitats and the sustainability of a healthy ecosystem

observations on gulf of alaska seamount chains by multi beam sonar abstract geomorphic and age data are presented for the dellwood denson dickins giacomini and ely seamounts the tsimshian seachannel and the southern juan de fuca ridge with brown bear bear cub grizzly bear and cobb seamounts formational speculations extrapolated to a regional scale allow the strikes and outer limits of the seamount chains to be interpreted six of these chains are shown in the gulf of alaska none of which conform to the pratt welker or kodiak bowie in the literature different strikes show the chains plate to have rotated 23 about 17 m y ago morphology also shows that there are four less guyots in the gulf than previously thought and that at least in the gulf of alaska guyot heights do not necessarily reflect sealevel during erosion

integration of bed characteristics geochemical tracers current measurements and numerical modeling for assessing the provenance of beach sand in the san francisco bay coastal system abstract over 150 million m3 of sand sized sediment has disappeared from the central region of the san francisco bay coastal system during the last half century this enormous loss may reflect numerous anthropogenic influences such as watershed damming bay fill development aggregate mining and dredging the reduction in bay sediment also appears to be linked to a reduction in sediment supply and recent widespread erosion of adjacent beaches wetlands and submarine environments a unique multi faceted provenance study was performed to definitively establish the primary sources sinks and transport pathways of beach sized sand in the region thereby identifying the activities and processes that directly limit supply to the outer coast this integrative program is based on comprehensive surficial sediment sampling of the san francisco bay coastal system including the seabed bay floor area beaches adjacent rock units and major drainages analyses of sample morphometrics and biological composition e g foraminifera were then integrated with a suite of tracers including 87sr 86sr and 143nd 144nd isotopes rare earth elements semi quantitative x ray diffraction mineralogy and heavy minerals and with process based numerical modeling in situ current measurements and bedform asymmetry to robustly determine the provenance of beach sized sand in the region

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

seamount morphology in the bowie and cobb hot spot trails gulf of alaska full coverage multibeam bathymetric mapping of twelve seamounts in the gulf of alaska reveals that they are characterized by flat topped summits rarely with summit craters and by terraced or step bench flanks these summit plateaus contain relict volcanic features e g flow levees late stage cones and collapse craters and as such must have been constructed by volcanic processes such as lava ponding above a central vent rather than by erosion above sea level the terraced flanks are composed of a sequence of stacked lava deltas and cones probably tube fed from a central lava pond a morphology which is suggestive of long lived stable central lava sources and low to moderate eruption rates indicative of significant time spent above a hot spot outlet most of these seamounts have summit plateaus surrounded and cut into by amphitheater headwall scarps and flanks that are scarred by debris chutes but lack visible debris accumulations at their base we interpret the lack of blocky debris fields as evidence that the slope failures are mainly small scale debris flows rather than large scale flank collapses however we cannot rule out the possibility that large flank collapse blocks from early in the histories of these seamounts are now hidden beneath the thick glacio fluvial fan deposits that cover the gulf of alaska seafloor these slope failure features become smoother and longer and increase in size and abundance with increasing age of a seamount suggesting that slope failure processes continue long after volcanic activity ceases

random fluctuations of snow accumulation over antarctica and their relation to sea level change short term changes in the volume of ice sheets as analyzed by radar altimetry may not be related to long term climatic change indeed the large relaxation time of an ice sheet induces a low frequency response to random fluctuations of snow accumulation however the time scale of the response is big compared to the average human lifetime and the effect of these random fluctuations on sea level change may be important even if they are not linked to climatic change in this study the relaxation time of an ice sheet is expressed with respect to the ice thickness surface slope and ice velocity these parameters are deduced from the precise topography derived from the geodetic cycle of the ers1 radar altimeter the variance of the induced effect on ice elevation is found to be around 3 m over a 30 year scale and with a maximum of 10 m in wilkes land and in the western part of the west antarctic ice sheet near the coast this effect can mask a climatic signal and thus be critical for altimetric mass balance surveys the estimated changes in antarctica s elevation between the seasat 1978 and ers 1993 epochs could be explained at least partially by such processes in terms of sea level change over the 30 year scale the standard deviation of the induced effect is 8 2 8 cm finally we show that the probability of a present day induced sea level rise of between 0 5 and 1 mm year over a 30 year time scale is estimated at 10 10 with coastal areas accounting for half of this signal

ground based measurements of spatial and temporal variability of snow accumulation in east antarctica the east antarctic ice sheet is the largest highest coldest driest and windiest ice sheet on earth understanding of the surface mass balance smb of antarctica is necessary to determine the present state of the ice sheet to make predictions of its potential contribution to sea level rise and to determine its past history for paleoclimatic reconstructions however smb values are poorly known because of logistic constraints in extreme polar environments and they represent one of the biggest challenges of antarctic science snow accumulation is the most important parameter for the smb of ice sheets smb varies on a number of scales from small scale features sastrugi to ice sheet scale smb patterns determined mainly by temperature elevation distance from the coast and wind driven processes in situ measurements of smb are performed at single points by stakes ultrasonic sounders snow pits and firn and ice cores and laterally by continuous measurements using ground penetrating radar smb for large regions can only be achieved practically by using remote sensing and or numerical climate modeling however these techniques rely on ground truthing to improve the resolution and accuracy the separation of spatial and temporal variations of smb in transient regimes is necessary for accurate interpretation of ice core records in this review we provide an overview of the various measurement techniques related difficulties and limitations of data interpretation describe spatial characteristics of east antarctic smb and issues related to the spatial and temporal representativity of measurements and provide recommendations on how to perform in situ measurements

lithospheric age dependence of off ridge volcano production in the north pacific data for numbers of seamounts on north pacific ocean crust of different age indicate that the production rate of new off ridge seamounts volcanoes is proportional to the inverse of the square root of the age of the lithosphere this observation is consistent with several hypotheses which have been offered to explain the origin of off ridge oceanic volcanism and in combination with petrologic and paleomagnetic evidence for small oceanic volcanoes leads to a new self consistent model for off ridge volcanism in this model the production rate of off ridge volcanoes is controlled primarily by the availability of fracture zone conduit systems in the thickening lithosphere in contrast mantle plume or hotspot volcanoes may punch through the oceanic lithosphere decreasing production rate of off ridge volcanoes on old oceanic lithosphere may be associated with decreasing extent of partial melting of chemically and isotopically heterogeneous mantle material

eight centuries of volcanic signal and climate change at talos dome east antarctica 1 during the 1996 programma nazionale di ricerche in antartide international trans antarctic scientific expedition traverse two firn cores were retrieved from the talos dome area east antarctica at elevations of 2316 m td 89 m long and 2246 m st556 19 m long cores were dated by using seasonal variations in non sea salt nss so42 concentrations coupled with the recognition of tritium marker level 1965 1966 and nss so42 spikes due to the most important volcanic events in the past pinatubo 1991 agung 1963 krakatoa 1883 tambora 1815 kuwae 1452 unknown 1259 the number of annual layers recognized in the td and st556 cores was 779 and 97 respectively the d record obtained from the td core has been compared with other east antarctic isotope ice core records dome c epica south pole taylor dome these records suggest cooler climate conditions between the middle of 16th and the beginning of 19th centuries which might be related to the little ice age lia cold period because of the high degree of geographical variability the strongest lia cooling was not temporally synchronous over east antarctica and the analyzed records do not provide a coherent picture for east antarctica the accumulation rate record presented for the td core shows a decrease during part of the lia followed by an increment of about 11 in accumulation during the 20th century at the st556 site the accumulation rate observed during the 20th century was quite stable

little ice age neoglacial paleoenvironmental conditions at siple station antarctica the 550 year records of 18 o and dust concentrations from siple station antarctica suggest warmer and less dusty atmospheric conditions from 1600 to 1830 a d which encompasses much of the northern hemisphere little ice age lia dust and 18 o data from south pole station indicate that the opposite conditions e g cooler and more dusty were prevalent there during the lia meteorological data from 1945 85 show that the lia temperature opposition between amundsen scott and siple inferred from 18 o is consistent with the present spatial distribution of surface temperature there is some observational evidence suggesting that under present conditions stronger zonal westerlies produce a temperature pattern similar to that of the lia these regional differences demonstrate that a suite of spatially distributed high resolution ice core records will be necessary to characterize the lia in antarctica

probing the structure of the deep continental crust old buried deformed crystalline rocks apparently make up most of the 40 kilometer thick continental crust this part of the earth is poorly explored and constitutes a major frontier of modern earth science two techniques seismic reflection profiling and drilling which were developed by industry for other purposes offer special potential for such exploration seismic profiling of the deep crust by cocorp the consortium for continental reflection profiling has already produced important information including evidence for extensive thin skinned thrusting of older rocks over a continental margin as the corresponding ocean basin closed deep drilling of crystalline rocks of the continents for scientific purposes is so far relatively unexploited in the united states but is already being carried on elsewhere in general big science is likely to become more important in basic geology as this frontier is explored

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

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