implications of till deformation on glacier dynamics the dynamics of glacier motion are governed to a large extent by the properties of the basal interface in this paper we address the interaction of a glacier with a layer of till at its bed in an attempt to test whether our physical understanding of till is sufficient to explain general features of the observed flow field and changes in geometry of black rapids glacier alaska u s a we also investigate whether or not a till layer has a clear surface observable signature in the dynamics of the glacier towards this end we use a finite element ice flow model with a coulomb failure criterion within the basal till layer we find that simple till physics can be used to describe decadal seasonal and short term hours to days velocity variations and possibly uplift events mechanisms for each of these variations involve an increase in the extent of till at failure a transfer of shear stress across the bed and a consequent increase in ice deformation effective shape factors are calculated that permit a simple incorporation of this boundary condition into glacier response models our analyses however have not resulted in the identification of a clear and unique signature of a till layer in the surface dynamics of a glacier

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

the calcarenite di gravina formation in matera southern italy new insights for coarse grained large scale cross bedded bodies encased in offshore deposits excellent outcrops of the upper pliocene lower pleistocene calcarenite di gravina around matera southern italy provide continuous exposure of coarse grained clastic basin margin shoreline to offshore facies among these facies the most conspicuous and volumetrically important are the transition slope deposits that form large scale high angle cross bedded lithosomes these are laterally extensive parallel with the paleoshoreline and show seaward progradation we interpret them to represent avalanches of sediment swept out onto a depositional slope below wave base from the shoreface zone by storm waves and wind driven currents three types of building blocks are recognized based on bedding patterns and facies architecture embryonic parasequences mature parasequences and simple sequences parasequences formed during stillstands of sea level and simple sequences during high frequency cycles of relative change of sea level these building blocks are stacked in a backstepping configuration and onlap onto cretaceous limestone substrate backstepping is believed to be due to a tectonically forced transgression that is punctuated by high frequency cycles of sea level modern analogs for these building blocks are the holocene prograding prisms detected in high resolution seismic lines of the mediterranean shelves the reflection patterns of these seismic units resemble the bedding architecture of the matera simple sequences and parasequences and show similarities of shape size position and orientation of coastal setting and direction of progradation comparison of the holocene prisms and the pliocene pleistocene accretional units in matera indicates that they may represent the same begin page 662 genetic process progradation of clastic prisms below the wave base level the matera accretional units also show similarities with other examples of laterally extensive large scale cross bedded sand bodies encased in offshore deposits such as some sandbanks differentiating between these laterally extensive and seaward prograding cross bedded sand bodies and some coarse grained gilbert type deltas is difficult however if interpretations are based only on two dimensional 2 d outcrops in dip section without high resolution data it is also difficult to distinguish between transition slope and prograding shoreface lithosomes this difficulty may be acute where only seismic or well log data are available however certain other architectural characteristics such as stacking and preservation of facies belts and position of bounding surfaces as well as differences in associated sedimentary structures and fossil content may be used for interpretation the matera example provides a mechanism for emplacement in offshore settings of elongate and strandline parallel sand and gravel deposits that prograde seaward and that preserve a coarsening upward internal succession this article offers an interpretation for other ancient examples of large scale cross bedded lithosomes encased in offshore deposits

integrated tephrochronology and magnetostratigraphy for cyclothemic marine strata wanganui basin implications for the pliocene pleistocene boundary in new zealand abstract the middle pliocene to earliest pleistocene part of the rangitikei river section in wanganui basin contains at least six distal tephras five are rhyolitic kowhai eagle hill ohingaiti waipura and vinegar hill tephras and one is andesitic mangamako tephra all tephras occur as macroscopic layers and are enclosed within cyclothemic marine sediments that accumulated in shoreface to outer shelf water depths under conditions of oscillating sea level driven by glacio eustacy the glass and ferromagnesian compositions of the silicic tephras imply derivation from calc alkaline rhyolitic sources either or both of taupo volcanic zone and southern coromandel volcanic zone the waipuru and vinegar hill tephras have isothermal plateau fission track itpft ages of 1 87 0 15 ma and 1 75 0 13 ma respectively paleomagnetic results allow identification of i the gauss matuyama boundary located ca 70 m below the top of the mangaweka mudstone and ii the top of the olduvai subchron placed at the base of the waipuru shellbed the itpft ages of the tephras are consistent with the interpreted magnetostratigraphy and also with astronomically tuned timescales correlation of the rangitikei sequences to the odp site 846 18o record indicates that each sequence corresponds to a glacial interglacial isotope stage couplet and allows ages to be interpolated for tephras not dated directly integration of the new ages for the waipuru and vinegar hill tephras the magnetostratigraphy and the sequence correlations to the astronomically tuned oxygen isotope timescale lead us to place the pliocene pleistocene boundary as defined at the vrica stratotype at the base of the highstand systems tract siltstone of sequence 17 in the rangitikei section 60 m below the vinegar hill tephra

glacier changes in southeast alaska and northwest british columbia and contribution to sea level rise 1 the digital elevation model dem from the 2000 shuttle radar topography mission srtm was differenced from a composite dem based on air photos dating from 1948 to 1987 to determine glacier volume changes in southeast alaska and adjoining canada srtm accuracy was assessed at 5 m through comparison with airborne laser altimetry and control locations measured with gps glacier surface elevations lowered over 95 of the 14 580 km2 glacier covered area analyzed with some glaciers thinning as much as 640 m a combination of factors have contributed to this wastage including calving retreats of tidewater and lacustrine glaciers and climate change many glaciers in this region are particularly sensitive to climate change as they have large areas at low elevations however several tidewater glaciers that had historically undergone calving retreats are now expanding and appear to be in the advancing stage of the tidewater glacier cycle the net average rate of ice loss is estimated at 16 7 4 4 km3 yr equivalent to a global sea level rise contribution of 0 04 0 01 mm yr

episodic reactivation of large scale push moraines in front of the advancing taku glacier alaska 1 taku glacier an advancing former tidewater glacier in alaska has been actively pushing its proglacial sediments along part of its terminus over the last 50 years producing so called push moraines the mobilization of these sediments which were locally lifted more than 20 m above sea level by 2004 has happened episodically rather than steadily the last major event of proglacial sediment deformation occurred in 2001 presumably caused by sliding along a basal detachment layer since then most deformation has been localized within a few meters of the terminus including impressive deformational features of the terminal ice where slabs of ice tens of centimeters in thickness have undercut proglacial sediments and vegetation and lifted them up between 2002 and 2004 surface velocities and horizontal displacements were measured across the terminus and in the proglacial push moraine area sediment displacement was highest between the end of march and mid june a decrease in displacement with distance from the terminus revealed that the sediments were deforming internally rather than along a

a microscopic sedimentary succession of graded sand and microbial mats in modern siliciclastic tidal flats microscopic studies of thin sections from modern siliciclastic tidal flat sediments in the southern north sea demonstrate the significant role of microbial mats in the buildup of sedimentary sequences this is documented by a unit only a few millimetres thick it starts at the base with a fine to medium grained quartz sand often containing secondary pores fenestrae type merging gradually into finer sediments the lower siliciclastic part is superposed by an upper organically dominated layer built by microbial mats within the organic material single quartz grains without any contact to each other are oriented with their long axes parallel to the bedding planes each siliciclastic part in the lower section of the unit indicates the initial deposition of coarser grains in a stronger flow regime followed by gradually decreasing flow velocities each microbial mat in the upper part essentially represents a period of low sedimentation rate during its growth grains still settle down onto the mat and become bound in the organic matrix the orientation of these grains with their long axes parallel to the bedding plane points to an energetically suitable position to gravity achieved by the friction reduction of the soft organic matter repeated depositional events followed by low rate deposition cause the buildup of various units there is no visible reworking of the former surfaces since the microbial mats prevent erosion during periods of increased flow the buildup is characteristic of siliciclastic sediments repeatedly occupied stabilized and fixed by microbial films or mats

lowstand shorefaces transgressive incised shorefaces and forced regressions examples from the viking formation joarcam area alberta abstract in the joarcam beaverhill lake area of alberta there are three long 40 km narrow 5 km sandbodies in the late albian viking formation they are surrounded by offshore open marine mudstones and have previously been interpreted as offshore bars however the sandbodies are both underlain and overlain by erosion surfaces joarcam is the only field with abundant cores and the sandbody shows a sandier upward and coarsening upward succession all three fields have recently been reinterpreted in the literature as lowstand shoreface deposits but the order in which they formed remains controversial our well log cross sections suggest that the lindbrook shoreface was the first to form at a time of maximum lowstand of sea level it was truncated as sea level began to rise and the lindbr ok transgressive surface of erosion tse has been traced into the erosion surface that underlies joarcam joarcam can therefore be interpreted as a shoreface incised during a pause in an overall transgression both the lindbrook and joarcam shorefaces appear to be truncated by the regressive surface of erosion rse that underlies beaverhill lake this suggests that beaverhill lake is the youngest of the shorefaces and implies a second major fall of relative sea level the lowstand shorefaces tend to be thinner because of reduced accommodation space during sea level fall they tend to prograde farther beaverhill lake about 23 km because of abundant sediment supply at lowstand but consist largely of sandstone directly overlying the rse at beaverhill lake the shoreface sediments prograded at least 10 km before any mud in the offshore to shoreface transition was preserved by contrast the transgressive shorefaces tend to be thicker because of accommodation space created during transgression however they tend not to prograde so far joarcam up to 13 km possibly because of reduced supply of sediment to the shoreface during transgression the two proposed episodes of lowering of relative sea level are tentatively correlated with the two separate valley incisions documented at crystal about 90 km to the southwest these incisions represent type 1 sequence boundaries but the boundaries are not continuous regressive surfaces of erosion from crystal to the joarcam beaverhill lake area in both cases the falling stage rses have been eroded by the subsequent tses these tses are the only surfaces preserved between the incised valleys and the lowstand shorefaces

a simple mechanism for irreversible tidewater glacier retreat 1 tidewater glacier retreat is abrupt and typically irreversible the mechanics of abrupt onset are evaluated by considering the behavior of a sliding law that depends inversely upon effective pressure pice pwater for such a law flux can increase with decreasing thickness if the loss of bed traction exceeds the loss of driving stress characteristic values of increased flux and glacier thinning are shown to propagate upstream if ice flux increases with decreasing thickness below an ice thickness threshold determined by the chosen sliding law upstream propagation leads to instability described in earlier literature in which increased flow leads to thinning loss of bed traction and continued acceleration in simplest terms the instability arises when alterations in glacier geometry act to reduce resistive stresses more than driving stresses the effects of diffusion are also analyzed and it is shown that for the form of sliding law considered here diffusion will not necessarily eliminate upstream propagating instabilities application of this theory shows that a transition from stable to unstable conditions occurred at columbia glacier alaska near the time of onset of its retreat in the early 1980s the theory also successfully predicts stable or rapidly retreating states for 12 other alaska tidewater glaciers and its applicability to greenland outlet glaciers is discussed

ring shear studies of till deformation coulomb plastic behavior and distributed strain in glacier beds a ring shear device was used to study the factors that control the ultimate steady strength of till at high shear strains tests at a steady strain rate and at different stresses normal to the shearing direction yielded ultimate friction angles of 26 3 and 18 6 for tills containing 4 and 30 clay sized particles respectively other tests at steady normal stresses and variable shear strain rates indicated a tendency for both tills to weaken slightly with increasing strain rate this weakening may be due to small increases in till porosity these results provide no evidence of viscous behavior and suggest that a coulomb plastic idealization is reasonable for till deformation however viscous behavior has often been suggested on the basis of distributed shear strain observed in subglacial till we hypothesize that deformation may become distributed in till that is deformed cyclically in response to fluctuations in basal water pressure during a deformation event transient dilation ofdiscrete shear zones should cause a reduction in internal pore water pressure that should strengthen these zones relative to the surrounding till a process called dilatant hardening consequent changes in shear zone position when integrated over time may yield the observed distributed strain

groundwater dynamics and arsenic contamination in bangladesh although arsenic contaminated groundwater in bangladesh is a serious health issue little is known about the complex transient patterns of groundwater flow that flush solutes from aquifers and carry solutes into the subsurface hydrologic modeling results for our field site in the munshiganj district indicate that groundwater flow is vigorous flushing the aquifer over time scales of decades to a century and also transporting solute loads into the aquifer with recharge from ponds rivers and rice fields the combined hydrologic and biogeochemical results from our field site imply that the biogeochemistry of the aquifer system may not be in steady state and that the net effect of competing processes could either increase or decrease arsenic concentrations over the next decades modeling results suggest that irrigation has greatly changed the location timing and chemical content of recharge to the aquifer flushing water through the system more quickly and also cycling large fluxes of water through rice fields during the dry season that could mobilize arsenic from oxides in near surface sediments furthermore the hydrologic model reveals that ponds many of which have been excavated over the last 50 years now provide much of the groundwater recharge these ponds receive most of the waste from the villages and thus provide another potential source of organic carbon to the groundwater system

forced regressions and lowstand deltas holocene canadian examples abstract some canadian holocene deltas that formed during and after relative sea level falls of over 100 m are modern examples of forced regressions and lowstand deltas the principal controls on deltaic morphology and stratigraphy are rate of sea level change sediment supply timing type basin physiography and sediment dispersal processes in the receiving basin our observations indicate important alongstrike variability in deposition and erosion that affect facies architecture and stratal geometry during rapid relative sea level fall fluvial channels incise rapidly and do not migrate lateral channel migration which would produce a widespread fluvial unconformity begins once relative sea level fall has slowed and continues through the early part of relative sea level rise parts of he emerging shoreline cut off from the fluvial sediment supply become sites of shoreface incision into prodelta deposits regressive marine erosion and wave cut terraces are developed where sandy sediment is then supplied to the shoreface by rivers or updrift sources sharp based littoral sandbodies directly overlie the shoreface erosion surface other parts of the deltas below wave base that become abandoned through lobe switching can also be eroded by tidal currents deltas that have prograded into deep water show evidence of submarine slope instability such as submarine channel development base of slope turbidites and thick and thin skinned failures that disrupt clinoforms isopach trends reflect the existence of underlying structure with holocene sediments locally either thi ning or pinching over bedrock highs

application of image cross correlation to the measurement of glacier velocity using satellite image data abstract image to image cross correlation software is applied to pairs of digital satellite images to map the velocity field of moving ice this technique uses small scale glacial surface features such as crevasse scars and snow dunes as markers on the surface of the moving ice displacements of the surface features are mapped by selecting small image areas centered on distinct features or by dividing a large area of densely featured glacial surface into a grid of areas and searching a subsequent image for matching areas using a cross correlation algorithm interpolation of the peak correlation values allows the displacements to be measured to subpixel accuracy resulting in very precise velocity measurements cross correlation is also applied to provide image coregistration in areas devoid of bedrock exposures in such areas subtle large scale topographic undulations in the ice surface related to underlying bedrock structure may be correlated by using large image areas and low pass filtered images both types of applications are demonstrated using ice stream d and ice stream e in west antarctica as test areas a high resolution map of the velocity field of the central portion of ice stream e generated by the displacement measuring technique is presented the use of cross correlation software is a significant improvement over previous manually based photogrammetric methods for velocity measurement and is far more cost effective than in situ methods in remote polar areas

sedimentary and structural evolution of a pleistocene small scale push moraine in eastern poland new insight into paleoenvironmental conditions at the margin of an advancing ice lobe abstract recent studies of push moraines have focused on the interplay between the dynamics of ice margins and the environmental variables of the foreland into which they advance these studies showed that the spatial distribution geometry and style of the glaciotectonic deformation of push moraines are controlled by ice induced stresses the strain rate the rheology of the deposits and hydraulic conductivity in this work we provide new insight into this interplay at a small spatio temporal scale specifically the ancient glacial system of the liwiec ice lobe within the younger saalian ice sheet in eastern poland the paleoenvironmental variables that are analysed here refer to the dynamics of the hydrological processes that affected the patterns and sediment deposition rate on the terminoglacial fan and the resulting mechanical stratigraphy and hydraulic conductivity of the foreland we document the progradational sequence of the fan deposits that developed as a result of the ice lobe thickening and the steepening of its stationary front the sedimentary features of the fan the lithology of its basement and the hydraulic conductivity of the foreland strongly influenced the geometry and kinematics of fold growth during the advance of the ice lobe the predominance of flexural slip and the development of fractures including fold accommodation faults were interpreted to be an effect of buckle folding due to horizontal shortening induced by ice advance the partial overriding of the push moraine by the ice lobe and thus the submarginal conditions for deformation were inferred from the significant hinge migration and internal deformation of the strata under undrained conditions in one of the folds the synfolding deposition pattern of the fan growth strata allowed us to suggest that the push moraine was probably formed by a sustained advance rather than surge

satellite derived volume loss rates and glacier speeds for the juneau icefield alaska we provide a high resolution map of elevation change rates dh dt at the juneau icefield jif southeastern alaska in order to quantify its contribution to sea level rise between 2000 and 2009 2013 we also produce the first high resolution map of ice speeds at the jif which we use to constrain flux and look for acceleration we calculate dh dt using stacked digital elevation models dems from the advanced spaceborne thermal emission and reflection radiometer aster instrument and the shuttle radar topography mission srtm taking into account srtm c band penetration via comparison with srtm x band elevations overall the jif is losing mass less rapidly 0 13 0 12mw e a than other alaskan icefields 0 79mw e a we determine glacier speeds using pixel tracking on optical image pairs acquired from 2001 to 2010 by aster from radar image pairs acquired between 2007 and 2011 and from radar interferometry in 1995 we detect seasonal speed variations but no interannual acceleration ruling out dynamics as the cause of the observed thinning thinning must therefore be due to the documented warming in the region flux measurements confirm this for mendenhall glacier showing that calving constitutes only 2 5 5 of mass loss there

tectonic and sea level controls on nontropical neogene limestones in new zealand modern shelf carbonates and neogene on land equivalents have formed upon and adjacent to the new zealand sector of the convergent australia pacific plate boundary they are exclusively skeletal hashes dominated by bryozoans bivalves barnacles and foraminifers typical of nontropical foramol carbonates tectonism has influenced carbonate formation by determining terrigenous sediment supply rates and therefore the dilution factor and has affected the structure of the sea floor by forming imbricate thrust ridges and fault bounded platforms that support the carbonates the neogene limestones are more abundant closer to the plate boundary than their modern counterparts reflecting an increase in tectonism with time in the late pliocene sea level movements combined with uplift of the forearc and transform basins to form widespread limestones only during the glacials

the stratigraphic architecture of late pliocene 2 8 2 4 ma asymmetrical shelf sequences western wanganui basin new zealand abstract the western wanganui basin in the vicinity of parikino contains a 410 m thick succession of thirteen sequences that accumulated between 2 8 and 2 4 ma traditional facies analysis of the succession indicates accumulation of the sequences in shoreface to mid shelf depositional palaeoenvironments the late pliocene sequences have been correlated with oxygen isotope stages g10 to g92 and each of 41 ka glacial interglacial stage couplets is represented by an individual depositional sequence comprising transgressive tst highstand hst and regressive rst systems tracts most sequence boundaries are unconformable and coincide with transgressive surfaces of erosion tse ravinement surface with ophiomorpha burrows extending down into underlying sandstone one sequence boundary at the base of the wilkies shellbed is a correlative conformity two types of shellbed occur within tsts and are associated with key sequence stratigraphic surfaces onlap and backlap shellbed onlap shellbeds onlap the tse and sequence boundary backlap shellbeds result from stratigraphic condensation at the top of the tst and are overlain by the downlap surface dls in most of the sequences the onlap and backlap shellbeds are superposed forming compound shellbeds rarely a downlap shellbed overlies the dls within the base of hsts hsts are composed typically of massive aggradational mid shelf siltstone that grades up into sandstone which forms thick progradational inner shelf to shoreface lithofacies attributed to regressive systems tracts rst lensoidal toplap shellbeds comprised of reworked nearshore storm emplaced fauna occur within the upper part of rsts all of the parikino sequences have asymmetrical architectures with thin tsts this arises because of the very low rates of non tropical carbonate accumulation during the transgressions that is about half of the 41 ka period of each cycle amounting to a few metres at most of shellbed followed by very high rates of terrigenous sediment accumulation during the latter half of cycles an implication of this work is that marked 40 60 m eustatic sea level changes occurred repeatedly during the interval 2 8 to 2 4 ma this implies substantial and successive continental glaciations from at least 2 8 ma probably in the northern hemisphere

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

sedimentary successions formed by fifth order glacio eustatic cycles in the middle to upper quaternary formations of the oga peninsula northeast japan abstract the northern coast of the oga peninsula is a type locality for quaternary sedimentary exposures on the sea of japan side of northeast japan middle to late pleistocene shallow marine to nonmarine sediments are continuously exposed on sea cliffs along the anden coast these sediments have been mapped and classified into nine sedimentary facies based on grain size sedimentary structures intensity of bioturbation and associated fossils the depositional environments and paleo water depths of each facies have been estimated based on comparison with the present sub bottom sedimentary features observed in coastal systems around the oga peninsula on the basis of sedimentary facies analysis variations in the depositional depth through time have been reconstructed and correlated with the specmap 18o curve using four marker tephras as time controls the two curves generally agree between approximately 80 and 450 ka suggesting that the sedimentary cycles at the anden coast faithfully record 5th and 6th order glacio eustatic sea level changes peak to peak comparison between the reconstructed depositional depth curve and the 18o curve reveals that 1 unconformities are formed during the late eustatic sea level falls and or the following lowstands 2 transgressive lag deposits are mainly formed below wave base 3 deepening upward successions which sometimes occur below the ravinement surfaces are formed in the inner part of estuary or barrier island environments where wave action was minor 4 shoaling upward successions formed during eustatic sea level falls are deposited under the influence of intense wave action in a strand plain coastal plain system and 5 the characteristic combination of thinner deepening upward successions and thicker shoaling upward successions reflects the asymmetric pattern of glacio eustatic sea level changes and or lower sediment supply during transgression

basin physiography and tectonic influence on sequence architecture and stacking pattern pleistocene succession of the canoa basin central ecuador facies shell bed features and sequence stratigraphic framework for the shallow marine pleistocene upper canoa and tablazo formations are presented based on outcrop data from the southern coast of cabo san lorenzo ecuador sediments of this succession exhibit a distinct cyclic pattern consisting of a stack of eight depositional sequences cyclothems likely developed under the main control of orbitally induced sea level changes as a rule within the studied interval an idealized cyclothem is composed of a transgressive systems tract tst and a highstand systems tract hst whereas deposits attributable to the lowstand and falling stage systems tracts are not present transgressive lithosomes may be defined by estuarine deposits interposed between the sequence boundary and the ravinement surface back barrier wedge and by upward fining shoreface to inner shelf facies successions above the ravinement backstepping shelf wedge separated by an expanded siliciclastic core hiatal shell concentrations occur at the base onlap shell beds and the top backlap shell beds of the transgressive shelf wedges and some occur at the base of highstand systems tracts downlap shell beds on the basis of sedimentary facies geometry taphonomy and paleoecology of shell beds and the nature of the transition between siliciclastic and mollusk bearing sediments cyclothems were classified into two main types that show dependence upon paleoshoreline morphological configuration sheltered in the upper canoa formation and exposed in the tablazo formation notwithstanding the different synsedimentary tectonic and climatic regimes the ecuadorian cyclothems share basic patterns of condensation and facies assemblages with other roughly coeval cyclothemic successions around the world this suggests that 1 hiatal shell bed development is not just a temperate latitude phenomenon 2 a global process such as glacio eustatic sea level change is the primary mechanism of control for the general architecture of sequences and 3 specific paleogeographic settings play an important role by determining the taphonomic and paleoecologic characteristics of key shell beds the nature of their contacts with the encasing sediments and the type of the component set of facies at a multicycle time scale tectonics influenced the long term trend of the relative sea level changes and consequently the large scale stratigraphic organization owing to the continued tectonic uplift of the area successive high frequency depositional sequences are nested to form a longer order falling stage sequence set

strong feedbacks between hydrology and sliding of a small alpine glacier 1 we report the spatial and temporal pattern of sliding on the 7 km long bench glacier alaska using five continuously recording gps antennas following motion of the surface ice distributed at 1 km spacing along the glacier center line we documented surface ice motion over 50 days during summer 2002 surface speeds in two previous winters constrain the motion component associated with ice deformation allowing isolation of the sliding speed history we observed two speedup events bracketing 2 weeks of steady slow sliding the first event was not associated with a meteorological trigger was more subtle than the second and propagated up glacier at a rate of several hundred meters per day the second event coincided with a warm up valley wind which triggered considerable melt of the glacier surface sliding speeds in this event reached 0 3 m d 1 and began almost simultaneously at all sites in the ablation area both the horizontal and vertical displacement time series can be explained by growth and collapse of cavities in the lee of bumps in the bedrock bed cavities grow during rapid sliding and decay by viscous creep we posit that effective pressure averaged over some large area of the bed is inversely proportional to the sliding speed this effective pressure then controls the collapse rate of cavities whose dimensions are estimated from a plausible stepped bed geometry this model explains well the horizontal and vertical surface displacement history through the first event and beginning of the second event the vertical record demands a substantial and abrupt drop in water pressure that departs from the posited sliding effective pressure relationship we argue that this pressure drop reflects establishment of efficient subglacial drainage also manifested in a nearly simultaneous step increase in water discharge in the exit stream the establishment of an efficient conduit system terminates sliding its maintenance inhibits further sliding over the remainder of the summer

dynamic controls on glacier basal motion inferred from surface ice motion 1 current heuristic laws that relate the motion of glaciers due to sliding along the bed to the subglacial water pressure fail to reproduce variations in sliding speed on timescales of specific hydrologic events such as lake drainage rainfall or surging this may be due to the importance of subglacial cavity evolution and shifts in the glacier stress field both of which are not accounted for in typical sliding laws we use multiple time series of surface motion over a 66 day period at brei amerkurjokull iceland to infer changes in bed separation and longitudinal force budget we observe multiple distinct periods of increased surface motion and uplift corresponding to periods of rainfall and or increased temperatures we find consistent hysteresis and lags between motion and variations in both the bed separation and longitudinal stress gradient that we attribute to the redistribution of normal stresses at the bed during cavity growth increases in the longitudinal stress gradient suggest a downglacier stress transfer during increased basal motion that is consistent with increased drainage system efficiency toward the terminus our results suggest that the transient evolution of the subglacial drainage system and shifts in the glacier stress field are important controls on basal motion

arsenic mobility in groundwater surface water systems in carbonate rich pleistocene glacial drift aquifers michigan abstract within the lower peninsula of michigan groundwaters from the marshall formation mississippian contain as derived from as rich pyrites often exceeding the world heath organization drinking water limit of 10 g l many michigan watersheds established on top of pleistocene glacial drift derived from erosion of the underlying marshall formation also have waters with elevated as the huron river watershed in southeastern lower michigan is a well characterized hydrogeochemical system of glacial drift deposits proximate to the marshall fm subcrop which hosts carbonate rich groundwaters streams and wetlands fens and well developed soil profiles aqueous and solid phase geochemistry was determined for soils soil waters surface waters streams and fens and groundwaters from glacial drift aquifers to better understand the hydrogeologic and chemical controls on as mobility soil profiles established on the glacial drift exhibit enrichment in both fe and as in the oxyhydroxide rich zone of accumulation the amounts of fe and as present as oxyhydroxides are comparable to those reported from bulk marshall fm core samples by previous workers however the as host in core samples is largely unaltered pyrite and arsenopyrite this suggests that the transformation of fe sulfides to fe oxyhydroxides largely retains as and fe at the oxidative weathering site groundwaters have the highest as values of all the waters sampled and many were at or above the world health limit most groundwaters are anaerobic within the zones of fe3 and as v reduction although reduction of fe iii oxyhydroxides is the probable source of as there is no correlation between as and fe concentrations the as fe mole ratios in drift groundwaters are about an order of magnitude greater than those in soil profiles suggesting that as is more mobile than fe this is consistent with the dominance of as iii in these groundwaters and with the partitioning of fe2 into carbonate cements soil waters have very low as and fe contents consistent with the stability of oxyhydroxides under oxidizing vadose conditions when co2 charged groundwaters discharge in streams and fens dissolved as is effectively removed by adsorption onto fe oxides or carbonate marls although fe does not display conservative behavior with as in groundwaters a strong positive correlation exists between as and sr concentrations as water rock interactions proceed the as fe and sr ca ratios would be expected to increase because both as and sr behave as incompatible elements comparisons with groundwater chemistries from other drift hosted aquifers proximate to the marshall sandstone are consistent with these relations thus the sr content of carbonate rich groundwaters may provide useful constraints on the occurrence origin and evolution of dissolved as in such systems

rapid erosion of soft sediments by tidewater glacier advance taku glacier alaska usa 2 0 0 1 m a 1 1940 2005 at l 3 km h 350 m and 1 5 0 2 m a 1 1952 2005 at l 1 5 km h 250 m detailed mapping over a 4 km 2 area of the terminus revealed a deeply incised channel in line with a major outlet stream glaciofluvial processes must play the dominant role in the subglacial erosion and removal of these unlithified sediments citation motyka r j m truffer e m kuriger and a k bucki 2006 rapid erosion of soft sediments by tidewater glacier advance taku glacier alaska usa geophys res lett 33 l24504 doi 10 1029 2006gl028467

pleistocene unconformity bounded shelf sequences wanganui basin new zealand correlated with global isotope record abstract eleven successive unconformity bound sequences in the castlecliff section wanganui basin each typically composed of a lower variably conglomeratic 0 1 2 m thick shell bed and an upper 5 20 m thick barren siltstone are identified in the stratotype of the local new zealand middle pleistocene castlecliffian stage based on magnetostratigraphy the section is correlated with the published benthonic oxygen isotope curve for dsdp core 552a from the north atlantic each of the sequences accumulated during one of the odd numbered interglacial isotope stages in the interval 31 to 11 inclusive the unconformities developed during intervening glacial ages when the shelf was exposed through glacio eustatic lowering the correlation provides a geochronologic framework for assessment of the eustatic contribution to the generation of the sequences in a situation where the paleoshorelines and related shelf sequences are preserved and for which an independent approximation of the sea level history is available in the form of an oxygen isotope curve

astronomic timescale for the pliocene atlantic δ18o and dust flux records of ocean drilling program site 659 high resolution benthic oxygen isotope and dust flux records from ocean drilling program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the atlantic from 2 85 ma back to 5 ma spectral analysis of the 18o record indicates that the 41 kyr period of earth s orbital obliquity dominates the pliocene record this is shown to be true regardless of fundamental changes in the earth s climate during the pliocene however the cycles of sahelian aridity fluctuations indicate a shift in spectral character near 3 ma from the early pliocene to 3 ma the periodicities were dominantly precessional 19 and 23 kyr and remained strong until 1 5 ma subsequent to 3 ma the variance at the obliquity period 41 kyr increased the timescale tuned to precession suggests that the pliocene was longer than previously estimated by more than 0 5 m y

isotope and minor element geochemistry of high arsenic groundwater from hangjinhouqi the hetao plain inner mongolia abstract high as groundwater is widely distributed in the northwestern hetao plain an arid region with slow groundwater flow arsenic concentration in groundwater ranges from 1 to 1000 g l most water samples have elevated salinities with cl and or hco 3 as the dominant anions and na as the dominant cation high concentrations of as in shallow aquifers are associated with strongly reducing conditions as evidenced by high concentrations of dissolved organic c doc nh 4 dissolved sulfide arsenite and dissolved ch 4 and relatively low concentrations of no 3 and so 4 2 results of the hydrochemical and h and o isotope geochemical studies indicate that evapotranspiration is an important process controlling the enrichment of na and cl as well as trace elements such as as b f and br in groundwater in na hco 3 dominated groundwaters as b and f were enriched decades of irrigation using yellow river water has resulted in elevation of the groundwater level which has accelerated salt accumulation in shallow groundwater and surface soil in addition irrigation is responsible for the release of some components from aquifer materials and mixing with saline groundwaters as indicated by minor element and isotope geochemical data used to trace groundwater flow paths sr isotope composition also indicates that bedrock weathering is one of the primary sources of as in groundwater in the study area

geochemical controls on arsenic and rare earth elements approximately along a groundwater flow path in the shallow aquifer of the hetao basin inner mongolia article i nfo groundwaters and sediments were sampled approximately along a groundwater flow path in the shallow aquifer of the hetao basin inner mongolia along a flow path with a length of about 9 km groundwater evolves from ca hco3 so4 through mg ca hco3 cl to na cl hco3 from the recharge zone to the discharge

terminus dynamics at an advancing glacier taku glacier alaska taku glacier alaska usa is currently in the advance stage of the tidewater glacier cycle we investigated the near terminus dynamics by measuring surface velocities surface elevation changes ice thickness and ablation velocities vary on sub daily diurnal seasonal and interannual timescales flowline modeling shows that the modeled surface velocities are sensitive to changes in till yield strength and thus effective basal pressures the glacier bed deepens in the up glacier direction and this imposes a minimum subglacial water pressure necessary for water to drain along the bed in a simple model we impose water pressure gradients based on phreatic surfaces of constant slopes to simulate the winter summer transitions this proves sufficient to explain an observed early season switch from compressional to block flow velocities also vary between years changing basal conditions can result in lower horizontal velocities which decrease the ice supply to the terminus and result in temporary surface lowering but a decrease in ice flux to the terminus must lead to ice storage further upstream and that ice mass will eventually reach the terminus this can explain the observed episodic nature of terminus advance

rheological nonlinearity and flow instability in the deforming bed mechanism of ice stream motion contrary to what has recently been assumed in modeling the proposed deforming bed mechanism for the rapid motion of antarctic ice streams the rheology of water saturated till is probably highly nonlinear according to information from soil mechanics and preliminary experiments on till from the base of ice stream b the equivalent flow law exponent n is probably as high as 100 and the nonlinearities of the shear stress and effective pressure dependences are closely linked the high nonlinearity has important consequences for the deforming bed mechanism a flow system operating by this mechanism can be unstable as a result of feedback from the generation of basal water by shear heating of basal till the short term feedback effect is analyzed for a perturbation in a model ice stream in which the basal meltwater is transported through a distributed system of narrow gap conduits at the ice till interface although the analysis is approximate and some of the system parameters are poorly known the results suggest that the deforming bed mechanism is unstable for n 20 the apparent lack of such an instability in the currently active ice streams implies that their motion is controlled not by the deforming bed mechanism but by some other as yet unidentified mechanism

sequence stratigraphy of a condensed low accommodation succession lower upper cretaceous dakota sandstone henry mountains southeastern utah cretaceous low accommodation deposits have been extensively studied in the subsurface of the western interior of north america because of their prolific hydrocarbon production and remaining potential understanding the stratigraphic complexities of these deposits in the subsurface relies strongly on detailed outcrop analogs in this study the dakota sandstone was examined along 100 km 62 mi of semicontinuous outcrop between the towns of hanksville and ticaboo in the henry mountains of southeastern utah this region represented a low accommodation setting located over the forebulge of the cretaceous western interior basin during accumulation of the unit the dakota sandstone is 0 to 38 m 125 ft thick of cenomanian age and records multiple cycles of sediment accumulation the dakota sandstone is subdivided into two condensed top truncated stratigraphic sequences the upper of which contains two parasequences the basal parts of both sequences are composed of braided fluvial conglomerates and sandstone overlain by tidally influenced fluvial sandstone inclined heterolithically stratified estuarine mudstone carbonaceous shale and coal the overlying parasequences consist of coarsening upward lower to upper shoreface mudstone sandstone tidal inlet deposits and oyster shell concentrations these facies define tripartite subdivisions of depositional environments typical of wave dominated estuaries the fluvial deposits may represent lowstand deposits but overall sediments accumulated during transgressive systems tracts tst the parasequences recorded in the henry mountains are similar to the dakota sandstone of northwestern new mexico and to high frequency sequences identified in the kaiparowits plateau approximately 80 km 50 mi to the southwest which suggests eustatic driving mechanisms the best potential for hydrocarbon reservoirs occurs in fluvial sandstones and conglomerates

cool water shell bed taphofacies from miocene pliocene shelf sequences in new zealand utility of taphofacies in sequence stratigraphic analysis

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

growth and collapse of the distributed subglacial hydrologic system of kennicott glacier alaska usa and its effects on basal motion nearly 100 days of hourly glacier motion hydrology and hydrochemistry measurements on kennicott glacier alaska usa demonstrate the complicated relationship between water and motion at the glacier bed our observations capture the transient glacier response to seasonal and daily melt cycles and to a jokulhlaup that prompts a sixfold increase in glacier speed sliding is promoted whenever the water inputs to the glacier exceed the capacity of the subglacial hydrologic system to transmit the water sensitivity of sliding to daily meltwater inputs varies strongly through the season implying that the state of the hydrologic system governs the sensitivity of basal sliding a numerical model constructed to explore these relationships reveals the roles of the effective pressure the exponent to which this is taken in the sliding law 0 1 0 6 glacier macroporosity 2 and the cavity generating capacity of the glacier bed which encapsulates the sizes and spacing of bed roughness elements temporal changes in the effective pressure associated with evolution of both water inputs and subglacial water transmission capacity can explain the varying strength of diurnal velocity fluctuations of kennicott glacier spatial patterns of glacier macroporosity and of basal roughness govern variation in sensitivity of sliding to water inputs

a review of wanganui basin new zealand global reference section for shallow marine plio pleistocene 2 5 0 ma cyclostratigraphy abstract wanganui basin new zealand contains one of the most complete late neogene marine stratigraphic records in the world the ca 2 km thick basin fill for the last ca 2 5 ma comprises 47 superposed cyclothems which correspond to successive 5th 100 ka and 6th 41 ka order glacio eustatic sea level fluctuations on the palaeo new zealand shelf since oxygen isotope stage 100 stages 100 to 5 are represented by marine cyclothems whereas stages 17 to 3 are represented by a suite of coeval and younger uplifted marine terrace sequences additionally a predominantly glacial loess stratigraphy exists for isotope stages 12 2 the presence of interbedded tephras and an established paleomagnetic stratigraphy allows the development of an integrated cyclostratigraphy for wanganui basin which correlates closely with the global oxygen isotope scale in all except two cases cycles 12 and 36 individual unconformity bound cyclothems sequences represent a single glacial interglacial couplet of milankovitch frequency lithologic and faunal variation within the cyclothems corresponds closely to that predicted by the sequence stratigraphic model each cyclothem generally contains a transgressive systems tract a mid cycle condensed shellbed a highstand systems tract and often a regressive systems tract six common cyclothem motifs are inferred to represent deposition in shelf locations between the highstand and lowstand shorelines viz the hawera maxwell turakina seafield castlecliff and rangitikei motifs a seventh type the nukumaru motif includes coquina limestone and represents deposition in shoreface and very shallow water marine environments

observations of a reversal in vertical and horizontal strain rate regime during a motion event on unteraargletscher bernese alps switzerland during a motion event on unteraargletscher bernese alps switzerland in spring 1996 surface velocities were measured up to eight times a day at four different locations along the central flowline using global positioning system equipment in addition accumulated vertical strains over the uppermost 50 and 100 m were measured at a location where the total ice thickness is 260 m the motion event was accompanied by high horizontal and vertical strain rates as compared to annual mean values a reversal in strain regime was observed with horizontal strain rates changing to extension while vertical strain rates became compressive this strain rate reversal coincided within the temporal resolution of the data with a maximum in vertical ice displacement at the surface within a day variations in vertical strain from 0 04 a 1 to 0 06 a 1 were observed over the uppermost 100 m vertical stretching is estimated to have contributed to at least 20 of the anomalous vertical ice movement at the surface there were significant differences between measured longitudinal strain averaged over a distance corresponding to a few ice thicknesses and measured vertical strain in spring 1997 a similar but more detailed set of measurements was collected at the same measuring site and vertical strain rates were found to vary non uniformly with depth with the largest values closest to the surface

high resolution sequence stratigraphy of early transgressive deposits viking formation joffre field alberta canada the lower cretaceous viking formation of the joffre field is characterized by complex reservoir architecture deposits of three discrete sequences were delineated using high resolution sequence stratigraphy the coarse grained deposits of sequence 3 lying between bd 2 and an overlying open marine flooding surface comprise the main reservoir interval within the viking formation of the joffre field this succession has previously been interpreted as an incised conglomeratic shoreface stranded in a basinal position during transgression however sequence 3 displays characteristics difficult to reconcile with a shoreface interpretation including an abundance of brackish mudstone interbeds and rip up clasts dominance of trough cross stratification in the coarse clastics and large scale interfingering of the coarse clastics with fine grained marginal marine deposits despite the incised basal contact and brackish water characteristics of the deposits the succession does not reflect an estuarine incised valley complex as conventional sequence stratigraphic wisdom might suggest the shore parallel orientation of the deposit the lack of a convincing valley margin to the northeast and parasequence orientations lying parallel to the strike of the deposit are inconsistent with an incised valley interpretation instead the succession is interpreted as a broad brackish water embayment of the shoreline into which coarse clastic bayhead delta and distributary channel complexes were deposited during incremental transgression such lagoonal or brackish bay complexes are ubiquitous in modern transgressive shorelines but previously have been recognized only rarely in the ancient record

forward modelling of the sequence stratigraphic architecture of shelf cyclothems application to late pliocene sequences wanganui basin new zealand we demonstrate a procedure for forward modelling of the sequence stratigraphic architecture i e positions of systems tract boundaries of shelf cyclothems as observed at outcrop sites or in well logs the 1 d model is based on the fact that the deposition of facies within shelf sequences and those defining the key stratigraphic surfaces between systems tracts respond directly to changes in depth between the sea surface and seafloor this accommodation bathymetry model incorporates three reference surfaces sea surface seafloor and lower sequence boundary each of which varies independently as a result of changes in the rates of eustatic sea level sedimentation and subsidence the model input and boundary conditions are an eustatic sea level curve i e late cenozoic deep sea 18o record an independent chronology for the outcrop or well section and a subsidence curve the model outputs are changes in accommodation and palaeobathymetry throughout the sequence and the time missing at erosional sequence boundaries the main variable in the model i e sedimentation rate is established by comparison of a model output bathymetry with the model target palaeobathymetry established from the faunal and facies content of the sequence being modelled when the model output and target are compatible the model sedimentation rate curve is adopted and the theoretical positions of the systems tract boundaries can be read off the model in relation to the lower sequence boundary and compared with independent field based interpretations of their stratigraphic position the model is designed to predict the architecture of sequences as they appear at particular outcrop sites or in well sections its usefulness lies in establishing the timing of accumulation of systems tracts in relation to stages in a eustatic sea level cycle in particular distinguishing between units deposited during highstand versus regressive systems tracts the model is applied to 6th order 41 ka plio pleistocene cyclothems in wanganui basin new zealand where it distinguishes the boundary between highstand systems tracts hst and regressive systems tracts rst the modelling has implications for the definition of systems tracts especially in late cenozoic successions for which the record of eustatic sea level changes is known independently

arsenic movement and traces in the groundwater from the hetao area inner mongolia in the hetao area of inner mongolia quaternary alluvial aquifers used for the water supply are contaminated by naturally occurring arsenic which heavily affects the health of 200 000 local residents this study on the isotopes of strontium and relevant elements contained in the groundwater as well as the arsenic in the groundwater and residents hair indicates that the arsenic originally derives from the upper reaches of this area where arsenic levels are high in groundwater rock and soil over respectively 44 km work line aa and 36 km work line bb away from there the levels of arsenic in the water corresponding to the trend of the residents arseniasis decrease along the direction of the flow from 0 251 to 0 05 mg l and 0 232 to 0 036 mg l the result of this research suggests that long term strategies to deal with this arseniasis should involve finding hydrous terrains uncontaminated by water from the upper reaches and developing routes to prevent water from taking arsenic

modeling the evolution of the juneau icefield between 1971 and 2100 using the parallel ice sheet model pism we study the evolution of the juneau icefield one of the largest icefields in north america 3700 km 2 using the parallel ice sheet model pism we test two climate datasets 20 km weather research and forecasting model wrf output and data from the scenarios network for alaska planning snap derived from spatial interpolation of observations good agreement between simulated and observed surface mass balance was achieved only after substantially adjusting wrf precipitation to account for unresolved orographic effects while snap s climate pattern is incompatible with observations of surface mass balance using the wrf data forced with the rcp6 0 emission scenario the model projects a decrease in ice volume by 58 68 and a 57 63 area loss by 2099 compared with 2010 if the modeled 2070 99 climate is held constant beyond 2099 the icefield is eliminated by 2200 with constant 1971 2010 climate the icefield stabilizes at 86 of its present day volume experiments started from an ice free state indicate that steady state volumes are largely independent of the initial ice volume when forced by identical scenarios of climate stabilization despite large projected volume losses the complex high mountain topography makes the juneau icefield less susceptible to climate warming than low lying alaskan icefields

where glaciers meet water subaqueous melt and its relevance to glaciers in various settings glacier change is ubiquitous but the fastest and largest magnitude changes occur in glaciers that terminate in water this includes the most rapidly retreating glaciers and also several advancing ones often in similar regional climate settings furthermore water terminating glaciers show a large range in morphology particularly when ice flow into ocean water is compared to that into freshwater lakes all water terminating glaciers share the ability to lose significant volume of ice at the front either through mechanical calving or direct melt from the water in contact here we present a review of the subaqueous melt process we discuss the relevant physics and show how different physical settings can lead to different glacial responses we find that subaqueous melt can be an important trigger for glacier change it can explain many of the morphological differences such as the existence or absence of floating tongues subaqueous melting is influenced by glacial runoff which is largely a function of atmospheric conditions this shows a tight connection between atmosphere oceans and lakes and glaciers subaqueous melt rates even if shown to be large should always be discussed in the context of ice supply to the glacier front to assess its overall relevance we find that melt is often relevant to explain seasonal evolution can be instrumental in shifting a glacier into a different dynamical regime and often forms a large part of a glacier s mass loss on the other hand in some cases melt is a small component of mass loss and does not significantly affect glacier response

high resolution magnetostratigraphy of mid pliocene 3 3 3 0 ma shallow marine sediments whanganui basin new zealand

groundwater flow in an arsenic contaminated aquifer mekong delta cambodia abstract to advance understanding of hydrological influences on as concentrations within groundwaters of southeast asia the flow system of an as rich aquifer on the mekong delta in cambodia where flow patterns have not been disturbed by irrigation well pumping was examined monitoring of water levels in a network of installed wells extending over a 50 km2 area indicates that groundwater flow is dominated by seasonally variable gradients developed between the river and the inland wetland basins while the gradient inverts annually net groundwater flow is from the wetlands to the river hydraulic parameters of the aquifer k 10 4 ms 1 and overlying clay aquitard k 10 8 ms 1 were determined using grain size permeameter and slug test analyses when coupled with observed gradients they indicate a net groundwater flow velocity of 0 04 0 4 ma 1 downward through the clay and 1 13 ma 1 horizontally within the sand aquifer producing aquifer residence times on the order 100 1000 a the results of numerical modeling support this conceptual model of the flow system and when integrated with observed spatial trends in dissolved as concentrations reveal that the shallow sediments upper 2 10 m of fine grained material are an important source of as to the underlying aquifer

an examination of spatial variability in the timing and magnitude of holocene relative sea level changes in the new zealand archipelago holocene relative sea level rsl changes have been reconstructed for four regions within the new zealand archipelago the northern north island including northland auckland and the coromandel peninsula the southwest coast of the north island the canterbury coast south island and the otago coast south island in the north island the rsl highstand commenced c 8100 7240 cal yr bp when present mean sea level pmsl was first attained this is c 600 1400 years earlier than has been previously indicated for the new zealand region as a whole and is consistent with recent holocene rsl reconstructions from australia in north island locations the early holocene sea level highstand was quite pronounced with rsl up to 2 75 m higher than present in the south island the onset of highstand conditions was later with the first attainment of pmsl being between 7000 6400 cal yr bp in the mid holocene the northern north island experienced the largest sea level highstand with rsl up to 3 00 m higher than present this is demonstrably higher than the highstand recorded for the southwest north island and otago regions a number of different drivers operating at a range of scales may be responsible for the spatial and temporal variation in the timing and magnitude of rsl changes within the new zealand archipelago one possible mechanism is the north south gradient in rsl that would arise in the intermediate field around antarctica in response to the reduced gravitational attraction of the antarctic ice sheet ais as it lost mass during the holocene this gradient would be enhanced by the predicted deformation of the lithosphere in the intermediate field of the southern ocean around antarctica due to hydro isostatic loading and mass loss of the ais however no such long wavelength signals in sea surface height or solid earth deformation are evident in glacial isostatic adjustment gia model predictions for the new zealand region while research from australia has suggested that north south variations in holocene rsl changes due to hydro isostatic influences are limited or non existent at the regional to local scale post glacial meltwater loading on the continental shelf around new zealand is predicted by gia modelling to have a significant effect on the timing and magnitude of rsl changes through the phenomenon of continental levering the spatial variation in continental levering is controlled by the configuration of the coast and the width of the adjacent continental shelf with continental levering providing a robust explanation for the observed spatial and temporal variations in rsl changes further research is required to characterise the regional and local effects of different tectonic regimes wave climates and sediment regimes these are potentially very significant drivers of rsl variability at the regional to local scale however the magnitude of their potential effects remains equivocal

the source and transport of arsenic in a bedrock aquifer new hampshire usa the geographic distribution of elevated groundwater as concentrations in a fractured silicate bedrock aquifer in central new hampshire correlates with the presence of pegmatites which border late devonian granites and intrude metasedimentary rocks as concentrations in the pegmatites averaged 9 6 mg kg which is much higher than the associated granites 0 24 mg kg and metasedimentary rocks 0 8 mg kg as was concentrated in these pegmatites by partial melting of calcareous metapelites and subsequent recrystallization as granites with low as concentrations and pegmatites with high as concentrations arsenic behaves similarly to b which was also concentrated into these late stage fluids arsenopyrite feass with an oxidation reaction rim of scorodite feaso4 2h2o was observed in aquifer materials elevated as concentrations have been observed to occur in other new england locations in pelitic metasediments intruded by anatectic plutons it is proposed that pegmatite formation from partial melting of pelitic metasediments may be an important mechanism for concentrating as in crystalline aquifer materials which can then cause local as enrichment of groundwaters groundwater as concentrations ranged from 26 nmol l to 5300 nmol l with a median value 210 nmol l that is more than 30 times higher than the median for groundwaters from all of new hampshire 6 5 nmol l high chloride concentrations 1 mmol l resulting from road salt contamination of recharge waters suggest that groundwaters are most likely young 670 nmol l or 50 g l have very low fe concentrations 7 samples with low as 7 fe oxyhydroxides form rapidly and have a neutral or negative net surface charge that does not readily adsorb as at ph 7 fe oxyhydroxide formation is slow and depends on dissolved o2 availability however the resultant fe oxyhydroxides have a positive net surface charge and appear to adsorb as readily

sequence stratigraphy of sixth order 41 k y pliocene pleistocene cyclothems wanganui basin new zealand a case for the regressive systems tract this study is based on a late pliocene and early pleistocene approximately 2 6 1 7 ma succession about 1 km thick of 20 sixth order 41 k y duration cyclothems of shelf origin exposed in the rangitikei river valley in the eastern part of wanganui basin the cyclothems correlate with 18 o isotope stages 100 58 and each 41 k y glacialinterglacial stage couplet is represented by an individual depositional sequence comprising transgressive highstand and regressive systems tracts unlike most examples inferred from the stratigraphic record these systems tracts were deposited during phases of known sea level cycles indicated by the contemporary oxygen isotope ice volume curve because of the high rate of subsidence of wanganui basin glacioeustatic sea level falls during most cycles were not of sufficient magnitude to expose the outer shelf thus the rangitikei section provides an exceptional example of regressive strata deposited landward of the contemporary shelf break simple one dimensional modeling shows that moderate to high rates of basin subsidence 1 2 mm yr and low rates of sedimentation 0 2 mm yr during transgressions combined to produce an accommodation surplus at the relative highstand this surplus accommodation was infilled during the late highstand and ensuing fall partly by aggradational highstand systems tract shelf siltstone and chiefly by strongly progradational shoreface sediments of the regressive systems tract rangitikei regressive systems tracts are distinguished from forced regressive systems tracts sensu hunt and tucker 1992 by their different stratal geometry by definition forced regressive systems tracts display an erosional contact with the underlying highstand systems tracts and typically occur as a series of downstepped disjunct shoreline wedges stranded on the shelf and or slope in contrast regressive systems tracts exhibit a gradational lower contact above which parasequences are stacked in a strongly progradational pattern terminated by the superjacent sequence boundary cyclothems display two types of motif termed rangitikei dt depositional transgression and rangitikei nt nondepositional transgression which include the following architectural elements in ascending stratigraphic order 1 a basal sequence boundary that is coincident with either the transgressive surface of erosion which displays small scale up to 50 cm erosional relief and may be penetrated by the ichnofossil ophiomorpha or its deeper water correlative conformity 2 either a thick 5 30 m transgressive systems tract comprising a deepening upward nearshore to inner shelf mixed carbonate siliciclastic lithofacies succession depositional transgression or a thin 2 m transgressive systems tract comprising condensed fossiliferous facies deposited on the sediment starved offshore shelf nondepositional transgression 3 a sharp downlap surface separating condensed fossiliferous facies of the transgressive systems tract from terrigenous siltstone of the superjacent highstand systems tract 4 a highstand systems tract comprising a 10 20 m thick interval of aggradational shelf siltstone and 5 a thick up to 45 m progradational inner shelf to shoreface lithofacies assemblage ascribed to the regressive systems tract condensed shell beds are associated with intrasequence and sequence bounding discontinuities and together with the sedimentological and stratal characteristics of the sequences are important indicators of stratigraphic architecture four types of shell bed are associated with surfaces formed by four different types of stratal termination onlap backlap downlap and flooding surface shell beds cf kidwell 1991 are associated respectively with the transgressive surface of erosion apparent truncation at the top of the transgressive systems tract the downlap surface and local marine flooding surfaces a fifth shell bed type termed a compound shell bed forms in offshore environments where the downlap surface converges with the sequence boundary and elements of both the downlap and the backlap shell beds become mixed or superposed the shell beds mark zones of stratal attenuation and can be used as surrogates for seismic discontinuities when applying sequence stratigraphic concepts at outcrop scale

the initiation of northern hemisphere glaciation for well over a century scientists have speculated that variations in the atmospheric concentration of radiatively important trace gases such as carbon dioxide could control the earth s climate e g arrhenius 1 896 recent observations of significant glacial interglacial variation in atmo spheric co2 in ice cores put this idea on a firm observational as well as theoretical footing e g barnola et ai1 987 in this century as atmospheric co2 levels creep steadily upwards in response to the burning of fossil fuels and forests the specter of manmade global climate change looms before us ipcc 1990 a possibility that has heightened interest in the natural variability of climate in the past in particular the 3 c warming pre dicted for the next century has stimulated interest in past warm climates such as the middle pliocene around 3 0 million years ma ago an interval that has often been invoked as a greenhouse world budyko et al 1985 in this paper the climate transition from the warm mid pliocene around 3 2 ma to the onset of northern hemisphere ice ages around 2 4 ma is examined evidence for the initiation of significant northern hemisphere glaciation is examined as well as how this event affected climate around the globe while the cause of individual glacial interglacial oscillations is tied to milankovitch variations in the earth s orbit around the sun e g imbrie et ai 1 992 these insolation changes cannot account for the long term cooling trend which culminated in northern hemisphere glaciation in the final section of this paper mechanisms of long term climate change

cyclostratigraphy of middle pliocene mid shelf to upper slope strata eastern wanganui basin new zealand correlations to the deep sea isotope record abstract rangitikei valley in eastern wanganui basin contains a well exposed 750 m thick middle pliocene succession that accumulated during the gauss chron traditional facies analysis involving laboratory grain size determinations and benthic foraminiferal census on a suite of closely spaced 5 m samples show that the utiku group lower 350 m accumulated predominantly in a mid shelf environment the overlying mangaweka mudstone 400 m thick accumulated in an outer shelf to upper slope environment combined with the identification of sequence stratigraphic surfaces sequence boundary transgressive surface of erosion and downlap surface four sequences have been identified in the utiku group in the outwardly massive mangaweka mudstone there is no outcrop evidence for sequences seven sedimentary cycles are nevertheless defined by changes in grain size and by variations in foraminiferal paleobathymetry the utiku group sequences show mostly asymmetric sequence architecture with comparatively thin tsts rapid deepening across the utiku group mangaweka mudstone boundary at 3 0 ma involving an increase in water depth of at least 100 m that persisted until 2 55 ma orignated tectonically probably as a result of plate boundary interactions this is the second of two known rapid deepening tectono sedimentary events each separated by about 1 5 my higher order sea level cyclicity involving 11 sedimentary cycles as presently defined are superimposed upon this second tectono sedimentary cycle independent magnetostratigraphies allow the sedimentary cycles to be correlated to the astronomically tuned oxygen isotope stratigraphy for odp site 846 for the interval 3 55 3 0 ma the sedimentary cyclicity reflects the periodicities of the more major enriched 18 o peaks which range from 41 ka mg2 to m2 to 210 ka mg6 to mg2 thus the duration of cyclicty in the utiku group closely corresponds to the duration between significant sea level lowering events which are marked by glacial 18 o shifts of 0 4 on the odp site 846 benthic 18 o curve

naturally occurring arsenic mobilization at a landfill in maine and implications for remediation abstract elevated levels of dissolved arsenic 300 g l 1 have been detected beneath and in groundwater plumes extending away from a closed landfill in southern maine this study sought to determine the source of arsenic to the aquifer the processes responsible for arsenic mobilization and to evaluate the effectiveness of remediation efforts that have occurred at this site the as appears to originate in the natural glacial aquifer solids which contain 5 mg kg 1 as on a dry weight basis this conclusion is supported by the relatively uniform distribution of as in sediment samples results of laboratory batch incubation experiments and comparisons with groundwaters in nearby wetlands which also have high levels of dissolved as that do not appear to originate within the landfill the as is mobilized in the subsurface by strongly reducing conditions beneath the landfill and in nearby wetlands in the aquifer beneath the landfill the average oxidation reduction potential orp is 95 mv eh 105 mv and these reducing conditions were primarily induced by landfill leachate remediation efforts at this site have included installation of a low permeability clay cap groundwater extraction oxidation and re injection and subsurface oxidation by injection of magnesium peroxide the natural source of arsenic within the aquifer solids coupled with widespread reducing conditions has severely limited the effectiveness of these interventions on groundwater arsenic concentrations

milankovitch 41000 year cycles in lithofacies and molluscan content in the tropical middle miocene nyalindung formation jawa indonesia abstract nine cyclothems based on changes in sedimentary facies and molluscan fossil associations are identified in the middle miocene 12 ma lower part of nyalindung formation cijarian river section sukabumi west jawa province indonesia molluscan associations were studied in 75 blocks collected through the succession 47 species of autochthonous molluscs belonging to 38 genera were separated from the blocks five molluscan associations were recognized through comparison of these species with their closest living analogues a sedimentary cycle consists of two conformable lithologic units in ascending order a gravelly shellbed or gravelly conglomeratic sandstone and a muddy fine to medium grained sandstone the exception is the basal cycle which has an intercalation of limestone the systematic change in the molluscan fossil associations within individual cycles indicates that lithological changes correspond to changes in water depth with an amplitude of about 30 m the short time period represented by the section and the thin units many not more than 2 m thick indicates that the main cause of the cyclicity was orbitally induced climate change representing milankovitch scale cycles of 41 000 years this appears to be the first time milankovitch sea level cycles have been reported from the tropical regions of the earth

time dependent basal stress conditions beneath black rapids glacier alaska usa inferred from measurements of ice deformation and surface motion observations of surface motion and ice deformation from 2002 03 were used to infer mean stress fields in a cross section of black rapids glacier alaska usa over seasonal timescales basal shear stresses in a well defined zone north of the center line orographic left were approximately 7 and 16 lower in spring and summer respectively than in winter correspondingly higher stresses were found near the margins these changes in the basal shear stress distribution were sufficiently large to cause mean surface velocities to be 1 2 and 1 5 times larger in spring and summer than in winter these results were inferred with a simple inverse finite element flow model that can successfully reproduce bulk surface velocities and tiltmeter data stress redistribution between the well defined zone and the margins may also occur over much shorter time periods as a result of rapidly changing basal conditions ice bed decoupling or enhanced till deformation thereby causing large variations in surface velocity and strongly influencing the glacier s net motion during summer

the aquatic geochemistry of arsenic in volcanic groundwaters from southern italy abstract this paper discusses the abundance speciation and mobility of as in groundwater systems from active volcanic areas in italy using literature data and new additional determinations the main geochemical processes controlling the fate of as during gas water rock interaction in these systems are examined arsenic concentrations in the fluids range from 0 1 to 6940 g l with wide differences observed among the different volcanoes and within each area the dependence of as content on water temperature ph redox potential and major ions is investigated results demonstrate that as concentrations are highest where active hydrothermal circulation takes place at shallow levels i e at vulcano island and the phlegrean fields in both areas the dissolution of as bearing sulphides is likely to be the main source of as mature cl rich groundwaters representative of the discharge from the deep thermal reservoirs are typically enriched in as with respect to so4 rich steam heated groundwaters in the hco3 groundwaters recovered at vesuvius and etna aqueous as cycling is limited by the absence of high temperature interactions and by high fe content of the host rocks resulting in oxidative as adsorption thermodynamic modelling suggests that reducing h2s rich groundwaters are in equilibrium with realgar whereas in oxidising environments over saturation with respect to fe oxy hydroxides is indicated under these oxidising conditions as solubility decreases controlled by as co precipitation with or adsorption on fe oxy hydroxides consistent with thermodynamic considerations as mobility in the studied areas is enhanced in intermediate redox environments where both sulphides and fe hydroxides are unstable

variational methods for glacier flow over plastic till we investigate the mechanics of ice streams and glaciers flowing over a bed consisting of coulomb plastic subglacial sediment or more generally of channel flows with coulomb or solid friction laws at the boundary sliding is assumed to occur if shear stress at the glacier bed attains a prescribed locally defined yield stress while no sliding is assumed possible below that yield stress importantly the location of regions of slip and no slip at the bed is not known a priori but forms part of the solution by analogy with friction problems in elasticity we derive a weak formulation as a semi coercive variational inequality which admits a unique solution provided a solvability condition ensuring force balance is satisfied the variational formulation is then exploited to calculate numerical solutions and we investigate the effect of variations in subglacial water pressure ice thickness and surface slope on the discharge of a valley glacier with a plastic bed significant differences are found between the behaviour of wide and narrow as well as steep and shallow angled glaciers and our results further indicate the need to develop models capable of accounting for longitudinal stresses

active seismic studies in valley glacier settings strategies and limitations subglacial tills play an important role in glacier dynamics but are difficult to characterize in situ amplitude variation with angle ava analysis of seismic reflection data can distinguish between stiff tills and deformable tills however ava analysis in mountain glacier environments can be problematic reflections can be obscured by rayleigh wave energy scattered from crevasses and complex basal topography can impede the location of reflection points in 2 d acquisitions we use a forward model to produce challenging synthetic seismic records in order to test the efficacy of ava in crevassed and geometrically complex environments we find that we can distinguish subglacial till types in moderately crevassed environments where moderate depends on crevasse spacing and orientation the forward model serves as a planning tool as it can predict ava success or failure based on characteristics of the study glacier applying lessons from the forward model we perform ava on a seismic dataset collected from taku glacier in southeast alaska in march 2016 taku glacier is a valley glacier thought to overlay thick sediment deposits a near offset polarity reversal confirms that the tills are deformable

rapid retreat and acceleration of helheim glacier east greenland 1 a significant amount of the measured coastal thinning of the greenland ice sheet may be due to recent acceleration of outlet glaciers using remote sensing we measured two major periods of speedup on helheim glacier between 2000 and 2005 that increased peak speeds from approximately 8 to 11 km yr these speedups coincided with rapid retreats of the calving front totaling over 7 5 km the glacier also thinned by over 40 m from 2001 to 2003 retreat of the ice front appears to decrease resistance to flow and concentrates the gravitational driving force over a smaller area farther up glacier acceleration may be a delayed response to surface draw down and steepening of the glacier s main trunk if the 2005 speedup also produces strong thinning then much of the glacier s main trunk may un ground leading to further retreat citation howat i m i joughin s tulaczyk and s gogineni 2005 rapid retreat and acceleration of helheim glacier east greenland geophys res lett 32 l22502 doi 10 1029 2005gl024737

speciation and enrichment of arsenic in strongly reducing shallow aquifers at western hetao plain northern china high arsenic as groundwater is widely distributed in northwestern hetao plain an arid region with sluggish groundwater flow observed as concentration in groundwater from wells ranges from 76 to 1 093 g l most water samples have high total dissolved solids with cl and hco3 as the dominant anions and na as the dominant cation the major hydrochemical types of most saline groundwaters are na mg cl hco3 and na mg cl by contrast fresh groundwaters generally belong to the na mg hco3 type high concentrations of arsenic in shallow aquifers are associated with strongly reducing conditions as evidenced by high concentrations of dissolved organic carbon ammonium as well as dissolved sulfide and fe dominance of arsenite relatively low concentrations of nitrate and sulfate and occasionally high content of dissolved methane ch4 high as groundwaters from different places at hetao plain experienced different redox processes fluoride is also present in high as groundwater ranging between 0 40 and 3 36 mg l although fluorosis poses an additional health problem in the region it does not correlate well with as in spatial distribution geochemical analysis indicates that evapotranspiration is an important process controlling the enrichment of na and cl as well as trace elements such as as b and br in groundwater

effect of indigenous bacteria on geochemical behavior of arsenic in aquifer sediments from the hetao basin inner mongolia evidence from sediment incubations abstract incubation studies were carried out using 5 freshly collected sediments from shallow aquifers of the hetao basin inner mongolia the aquifer sediments covering a range of redox conditions as indicated by their deep grey to yellow color were mixed with degassed artificial as solution or degassed deionized water at a ratio of solid to water of about 1 10 wt wt suspensions which were either amended with glucose or autoclaved were incubated in parallel with unamended suspensions five microcosm cultures of unamended sediments gradually release the equivalent of 0 03 0 30 g g as to the dissolved phase the addition of glucose as a potential electron donor results in a marked stimulation in the mobilization of as 0 71 3 81 g g in the amended incubations for all sediments the quantity of as released accounts for 60 70 of as bound to fe mn oxides in the original sediments the microbially mediated mobilization of as with the organic nutrient as an electron donor is strongly associated with the as bound to fe mn oxides as well as the exchangeable as during the incubations amended with glucose 2 4 of the sediment fe is released the results suggest that the introduction of labile dissolved organic c into the yellowish sediment aquifers with as free groundwater would reduce a significant proportion of the fe iii oxyhydroxides mediated by anaerobic bacteria respiration and increase groundwater as concentrations

rapid wastage of alaska glaciers and their contribution to rising sea level we have used airborne laser altimetry to estimate volume changes of 67 glaciers in alaska from the mid 1950s to the mid 1990s the average rate of thickness change of these glaciers was 0 52 m year extrapolation to all glaciers in alaska yields an estimated total annual volume change of 52 15 km 3 year water equivalent equivalent to a rise in sea level sle of 0 14 0 04 mm year repeat measurements of 28 glaciers from the mid 1990s to 2000 2001 suggest an increased average rate of thinning 1 8 m year this leads to an extrapolated annual volume loss from alaska glaciers equal to 96 35 km 3 year or 0 27 0 10 mm year sle during the past decade these recent losses are nearly double the estimated annual loss from the entire greenland ice sheet during the same time period and are much higher than previously published loss estimates for alaska glaciers they form the largest glaciological contribution to rising sea level yet measured

ice thickness measurements of taku glacier alaska u s a and their relevance to its recent behavior using radio echo soundings and seismic reflections we measured cross sections of taku glacier near juneau alaska to resolve inconsistencies in previous measurements and to understand better the glacier s dynamics the maximum thickness is about 1477 m and the minimum bed elevation is about 600 m below sea level which establishes taku glacier as the thickest and deepest temperate glacier yet measured our data indicate that during the 19th century the terminus of taku glacier may have begun its rapid advance at a position where the ice bed was greater than 300 m below sea level and more than 25 km from the inland end of its submarine trough this behavior is uncharacteristic of temperate tide water glaciers the glacier which no longer calves has eroded a sediment layer 100 m thick since 1890 at an average rate of about 3 m a 1 since 1948 this high erosion rate retards advance by entrenching the glacier into the terminal moraine calculations based on ice deformation theory indicate significant basal ice motion near the terminus and high basal shear stress 140 220 kpa along much of its length estimated differences between ice flux and balance flux are consistent with observed thickening and positive net mass balance these data indicate that ice volume is increasing and that further advance is likely

hydraulic and mechanical properties of glacial sediments beneath unteraargletscher switzerland implications for glacier basal motion the force on a ploughmeter and subglacial water pressure have been measured in the same borehole at unteraargletscher switzerland in order to investigate ice sediment coupling and the motion at the base of a soft bedded glacier a strong inverse correlation of the recorded pressure and force fluctuations in conjunction with a significant time lag between the two signals suggests that pore water pressures directly affect the strength of the subglacial sediment the lag is interpreted to reflect the time required for the water pressure wave to propagate through the pores of the sediment to the depth of the ploughmeter analysis of the propagation velocity of this pressure wave yielded an estimate of the hydraulic diffusivity a key parameter necessary to characterize transient pore water flow furthermore the inferred inverse relationship between pore water pressure and sediment strength implies that coulomb plastic deformation is an appropriate rheological model for the sediment underlying unteraargletscher however the sediment strength as derived from the ploughmeter data was found to be one order of magnitude smaller than that calculated for a coulomb frictional material using the water pressure measurements this significant discrepancy might result from pore water pressures in excess of hydrostatic down glacier from the ploughmeter as the ploughmeter is dragged through the sediment sediment is compressed if the rate of this compression is large relative to the rate at which pore water can drain away excess pore water pressures will develop that have the potential to weaken the sediment the same process could lead to highly fluid sediment down glacier from clasts that protrude into the glacier sole and thus would otherwise provide the roughness to couple the glacier to its bed iverson 1999 rapidly sliding glaciers overlying sediments might therefore move predominantly by ploughing which tends to focus basal motion near the glacier sole rather than at depth in the bed

rigorous gps data processing strategies for glaciological applications global positioning system gps data are now routinely used for many glaciological applications in some common cases systematic errors are unmodelled at the data processing stage although they are often presumed insignificant in this paper i investigate these assumptions for three different scenarios 1 measurements on a moving glacier 2 measurements on a floating ice shelf and 3 precise height determination over large elevation ranges such as for aircraft positioning in lidar laser altimeter missions in each case systematic errors are shown to be present in the coordinate solutions that have a far greater magnitude than the formal error estimates produced by the gps processing software under certain conditions if these coordinate biases go undetected short and long term measurements of horizontal ice velocity or rates of ice thickness change may be erroneous and the coordinates could not be expected to match rigorously processed data or results from different processing techniques more rigorous processing strategies are discussed that allow for bias free parameter estimation

fast tidewater glaciers some iceberg calving outlet glaciers flow continuously at speeds normally associated with surging glaciers arid exhibit dramatic instability scenarios related to those suggested for marine ice sheets no temperate tidewater glaciers are known to have floating termini but many polar and subpolar tidewater glaciers do the fast flow of temperate calving glaciers is almost entirely due to basal sliding and appears to be a function of the effective pressure on the bed which may approach zero and the longitudinal back stress on the terminus the terminus boundary condition the calving relation is imperfectly known yet is vital to the dynamics of these glaciers calving relations for grounded tidewater glaciers have been suggested on empirical grounds but have not been rigorously tested the calving relations for floating termini are virtually unknown this together with the imperfect understanding of basal sliding inhibits confidence in our understanding of the stability of these glaciers columbia glacier alaska is an instructive example because observations have been made on the major changes in its geometry calving rate and dynamics that have occurred in less than 10 years the calving flux has increased more rapidly than the glacier flux causing thinning and retreat as a result the ice velocity has increased markedly the short term velocity changes relate to changes in back pressure ice recession tidal changes and the flux of water injected to the bed these results have relevance to the mechanisms of basal sliding glacier surges and the stability of marine ice streams

geochemical modeling approach to predicting arsenic concentrations in a mine pit lake abstract between 1968 and 1983 the north pit at the getchell mine humboldt county nv filled with water to form a lake in 1983 water quality data were collected with the following results as concentrations of 0 29 to 0 59 mg l ph of 7 1 to 7 9 so 4 concentrations of 1490 to 1640 mg l and tds of 2394 to 2500 mg l using geochemical modeling techniques presented here pit lake waters have been theoretically allowed to react for 8 5 a the approximate time that the north pit had been completely full by 1983 modeling results predict ph of 7 9 to 8 2 so 4 concentrations of 1503 to 1644 mg l tds of 2054 to 2366 mg l and as concentrations ranging from 0 57 in the hypolimnion to 96 mg l in the epilimnion in the epilimnion model results do not match observed as concentrations suggesting that mechanisms such as precipitation of arsenate salts or adsorption to mineral surfaces may control as levels in an actual pit lake system adsorption to fe oxyhydroxide surfaces is questioned by the authors because of the low fe content in the getchell system but adsorption to al oh 3 gibbsite and clay mineral surfaces may be important in controlling natural as concentrations

taku glacier alaska u s a on the move again active deformation of proglacial sediments taku glacier is one of the few glaciers in alaska u s a that has advanced over the last century 7 km since 1890 this advance slowed substantially during the past decade but in summer 2001 the glacier terminus began to readvance at a rate of 30 cm d 1 the advance produced dramatic proglacial sediment deformation up to 200 m in from of the terminus two to three large bulges and several secondary bulges developed in the proglacial sediments as a result of glacial compression along a 1 km wide portion of the terminus the bulge nearest the terminus was 10 m high and 65 m wide the middle bulge 7 m high advanced at 15 cm d 1 and the distal bulge 3 m high and 50 m wide at 9 cm d 1 crenulations and prominent fractures developed in the overlying vegetation layer the frontal lobes of the bulges were steep and overlaid a shear zonc where sediments were being thrust up and over the ground surface ice proximal push moraines 1 10 m high formed along much of the 9 km wide terminus although deformation was minimal at some locations

arsenic associations in sediments from the loess aquifer of la pampa argentina groundwater from the quaternary loess aquifer of la pampa central argentina has significant problems with high concentrations of as up to 5300 g l 1 as well as other potentially toxic trace elements such as f b mo u se and v total as concentrations in 45 loess samples collected from the aquifer have a range of 3 18 mg kg 1 with a mean of 8 mg kg 1 these values are comparable to world average sediment as concentrations five samples of rhyolitic ash from the area have as concentrations of 7 12 mg kg 1 chemical analysis included loess sediments and extracted porewaters from two specially cored boreholes results reveal a large range of porewater as concentrations being generally higher in the horizons with highest sediment as concentrations the displaced porewaters have as concentrations ranging up to 7500 g l 1 as well as exceptionally high concentrations of some other oxyanion species including v up to 12 mg l 1 the highest concentrations are found in a borehole located in a topographic depression which is a zone of likely groundwater discharge and enhanced residence time comparison of sediment and porewater data does not reveal unequivocally the sources of the as but selective extract data acid ammonium oxalate and hydroxylamine hydrochloride suggest that much of the as and v is associated with fe oxides primary oxides such as magnetite and ilmenite may be partial sources but given the weathered nature of many of the sediments secondary oxide minerals are probably more important extract compositions also suggest that mn oxide may be an as source the groundwaters of the region are oxidising with dissolved o2 no3 and so4 normally present and as v usually the dominant dissolved as species under such conditions the solubility of fe and mn oxides is low and as mobilisation is strongly controlled by sorption desorption reactions desorption may be facilitated by the relatively high ph conditions of the groundwaters in the region 7 0 8 8 and high concentrations of potential competitors e g v p hco3 phreeqc modelling suggests that the presence of v at the concentrations observed in the pampean porewaters can suppress the sorption of as to hydrous fe iii oxide hfo by up to an order of magnitude bicarbonate had a comparatively small competitive effect oxalate extract concentrations have been used to provide an upper estimate of the amount of labile as in the sediments a near linear correlation between oxalate extractable and porewater as in one of the cored boreholes investigated has been used to estimate an approximate kd value for the sediments of 0 94 l kg 1 this low value indicates that the sediments have an unusually low affinity for as