basal conditions and ice dynamics inferred from radar derived internal stratigraphy of the northeast greenland ice stream we analyze the internal stratigraphy in radio echo sounding data of the northeast greenland ice stream to infer past and present ice dynamics in the upper reaches of the ice stream we propose that shear margin steady state folds in internal reflecting horizons irhs form due to the influence of ice flow over spatially varying basal lubrication irhs are generally lower in the ice stream than outside likely because of greater basal melting in the ice stream from enhanced geothermal flux and heat of sliding strain rate modeling of irhs deposited during the holocene indicates no recent major changes in ice stream vigor or extent in this region downstream of our survey irhs are disrupted as the ice flows into a prominent overdeepening when combined with additional data from other studies these data suggest that upstream portions of the ice stream are controlled by variations in basal lubrication whereas downstream portions are confined by basal topography

coherent radar ice thickness measurements over the greenland ice sheet we developed two 150 mhz coherent radar depth sounders for ice thickness measurements over the greenland ice sheet we developed one of these using connectorized components and the other using radio frequency integrated circuits rfics both systems are designed to use pulse compression techniques and coherent integration to obtain the high sensitivity required to measure the thickness of more than 4 km of cold ice we used these systems to collect radar data over the interior and margins of the ice sheet and several outlet glaciers we operated both radar systems on the nasa p 3b aircraft equipped with gps receivers radar data are tagged with gps derived location information and are collected in conjunction with laser altimeter measurements we have reduced all data collected since 1993 and derived ice thickness along all flight lines flown in support of program for regional climate assessment parca investigations and the north greenland ice core project radar echograms and derived ice thickness data are placed on a server at the university of kansas http tornado rsl ukans edu greenlanddata htm for easy access by the scientific community we obtained good ice thickness information with an accuracy of 10 m over 90 of the flight lines flown as a part of the parca initiative in this paper we provide a brief description of the system along with samples of data over the interior along the 2000 m contour line in the south and from a few selected outlet glaciers

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

the different diffusive transport behaviours of some metals in layers of peru basin surface sediment abstract diffusion experiments with a duration of 90 days were carried out with radio tracers in an oxic and a suboxic sediment layer from two deep sea sediment cores diffusion coefficients breakthrough and time lag values were determined and the results checked by modelling only small differences of diffusive transport were observed for na and cs during the four experiments na behaved as a perfect conservative tracer and the somewhat stronger uptake of cs in one sample was caused by preferential absorption by illite that was enriched in this sample the significant differences between the four experiments for the diffusion parameters of mn zn co and cd correlate with the differing chemical compositions of the sediment layers higher mn oxide concentrations in the sample led to slower diffusion through the sediment sample and to significant sorption of the diffusing heavy metals this result confirms the dominating role of mn oxide phases in controlling the diffusive exchange of heavy metals between deep sea sediment and bottom water sediment resuspension of the oxic surface layer such as during potential ferromanganese nodule mining in the deep sea would be followed by increased diffusive flux of dissolved heavy metals especially mn from suboxic sediment layers to the new disturbed sediment bottom water interface according to our modelling the mn flux from the oxic sediment surface of 0 3 mg m 2 yr 1 in the undisturbed state would increase to up to several mg m 2 yr 1 within the first few weeks after disturbance depending on the time necessary until a stable oxic and mn oxide rich layer is again re established a total mn2 release of 54 mg m 2 was calculated if the original state is reached within 100 yr in contrast to only 3 5 mg m 2 for 5 yr of re establishment the fluxes of the other heavy metals would be smaller corresponding to their lower pore water concentrations in the suboxic layer compared to mn

greenland ice sheet surface properties and ice dynamics from ers 1 sar imagery c band synthetic aperture radar sar imagery from the european space agency s ers 1 satellite reveals the basic zonation of the surface of the greenland ice sheet the zones have backscatter signatures related to the structure of the snowpack which varies with the balance of accumulation and melt at various elevations the boundaries of zones can be accurately located with the use of this high resolution imagery the images also reveal a large flow feature in northeast greenland that is similar to ice streams in antarctica and may play a major role in the discharge of ice from the ice sheet

paleoclimate and precipitation seasonality of the early eocene mcabee megaflora kamloops group british columbia early eocene fossil floras from british columbia are a rich resource for reconstructing western north american early cenozoic climate the best known of these floras reflect cooler mat 15 c upland forest communities in contrast to coeval mat 18 c forests in lowland western north american sites of particular interest is whether early eocene climates were monsoonal highly seasonal precipitation the mcabee site is a 52 9 0 83 ma 0 5 km outcrop of bedded lacustrine shale interbedded with volcanic ash in this report two historical megaflora collections that were collected independently from different stratigraphic levels and or laterally separated by 100 200 m in the 1980s university of saskatchewan and 2000s brandon university are investigated to i assess whether they represent the same leaf population ii assess whether a combined collection yields more precise climate estimates and iii reconstruct paleoclimate to assess the character of regional early eocene precipitation seas

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

flow of ice sheets in the vicinity of subglacial peaks although changes of surface slope across a subglacial peak can be explained at least semi quantitatively on a two dimensional basis in terms of gradients of longitudinal and shear stresses along a flow line we lack appreciation of flow in the third dimension which may tend to cause lower layers to flow around rather than over a sharp peak this paper collects and surveys evidence relevant to flow in the third dimension and discusses the processes involved particularly the evidence from radio echo layering and also discusses possible reasons for the lack of radio echo layers near the base of the antarctic ice sheet

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

analysis of deep penetrating radar surveys of west antarctica us itase 2001 1 we collected 1850 km of ground based radio echo sounding res data in west antarctica along the 2001 us leg of the international trans antarctic scientific expedition traverse us itase these data represent the first high resolution measurements of ice thickness and internal stratigraphy for portions of this area that bear on questions about the stability of the west antarctic ice sheet wais internal layers depicting isochrones have been traced continuously for much of the profile length and a date from the byrd deep core is ascribed to one of these isochrones from which we estimate vertical velocities across the traverse route comparison of our ice thickness measurements with bedmap show good agreement in regions where the database is well constrained by data coverage where the bedmap dataset was forced to interpolate differences are as high as 45 of the ice thickness

inference of accumulation rate patterns from deep layers in glaciers and ice sheets the spatial pattern of accumulation rate can be inferred from internal layers in glaciers and ice sheets non dimensional analysis determines where finite strain can be neglected shallow layer approximation or approximated with a local one dimensional flow model local layer approxima tion and where gradients in strain rate along particle paths must be included deep layers we develop a general geophysical inverse procedure to infer the spatial pattern of accumulation rate along a steady state flowband using measured topography of the ice sheet surface bed and a deep layer a variety of thermomechanical ice flow models can be used in the forward problem to calculate surface topography and ice velocity which are used to calculate particle paths and internal layer shapes an objective tolerance criterion prevents over fitting the data after making site specific simplifications in the thermomechanical flow algorithm we find the accumulation rate along a flowband through taylor mouth a flank site on taylor dome antarctica using a layer at approximately 100 m depth or 20 of the ice thickness accumulation rate correlates with ice surface curvature at this site gradients along flow paths critically impact inference of both the accumulation pattern and the depth age relation in a 100 m core

kinetic and thermodynamic factors controlling manganese concentrations in oceanic waters abstract data are presented describing the changes in the distribution of dissolved and particulate mn observed over a 16 month period in the periodically anoxic waters of saanich inlet a fjord located on the coast of vancouver island british columbia during the spring and summer when the bottom waters were anoxic a dense cloud of particulate mn was found at mid depths where mn 2 enriched anoxic bottom waters were mixing with oxygenated waters then during the autumn aand winter following an intrusion which reoxygenated the bottom water an intense precipitation of mn was observed throughout the entire water column during this latter period dissolved mn concentrations in the bottom water which exceeded 1000 nmol l under anoxic conditions decreased towards a lower limit of 1 6 nmole l a value comparable to that observed in pacific ocean waters of similar ph and dissolved oxygen content mn in the particulate matter collected just above the oxic anoxic interface was found to have an average oxidation number of 3 05 and on this basis it is proposed that dissolved mn concentrations in oceanic waters are controlled by the precipitation of the metastable oxide mineral manganite mnooh a hypothesis consistent with the fact that dissolved mn values in subsurface pacific ocean waters closely approach the equilibrium solubility of this phase temporal and spatial gradients in the particulate mn distribution were used to calculate the in situ rate of mn precipitation and the results of these calculations then were fitted to theoretical rate equations which suggest that the precipitation of mn is controlled by 2 parallel processes bacterial oxidation and an inorganic autocatalytic oxidation reaction

deformation of till beneath ice stream b west antarctica the behaviour and possible instability of the west antarctic ice sheet depend fundamentally on the dynamics of the large ice streams which drain it model calculations show that most ice stream velocity arises at the bed1 2 and radar sounding has shown the bed to be wet3 but the basal boundary condition is not well understood seismic evidence from the upstream b camp upb on the siple coast of west antarctica4 shows that the ice stream there rests on a layer of unconsolidated sediment averaging 5 or 6 m thick in which the water pressure is only 50 kpa less than the overburden pressure because this thin layer occurs well inland beneath an active ice sheet and rests on a surface showing flutes4 characteristic of glacial erosion5 we presume that it is glacial till we propose here that deformation within the till is the primary mechanism by which the ice stream moves and we discuss implications of this hypothesis

fast flow signature in the stagnated kamb ice stream west antarctica among the major ice streams that drain west antarctica kamb ice stream formerly called ice stream c is unique in that it stagnated 150 yr ago but its former fast flow conditions are virtually unknown here we presentsurface based radar profiles of the ice stream s undulating internal stratigraphy which records these conditions our analysis of the profiles indicates that pre stagnation flow velocities averaged over a period 740 yr exceeded 350 m yr 1 in the trunk of the ice stream this velocity constraint would be lower if the ice had been thickening higher if thinning but suggests mass loss from the ice stream catchment that is of sufficient magnitude to reverse the gain estimated for today s siple coast region analysis of other ice streams would allow comparison of velocities over millennial time scales with observations of present day velocities useful for evaluating how west antarctic ice drainage has evolved

influence of subglacial geology on the position of a west antarctic ice stream from seismic observations ice streams drain much of the interior west antarctic ice sheet and buffer the main ice reservoir from oceanic influences1 2 the slow flowing interior feeds the floating ross ice shelf with ice via fast flowing ice streams3 that are believed to modulate sea level change through their control of inland ice storage understanding ice stream behaviour and predicting the response to climate change4 requires a better knowledge of the subglacial geology5 6 it is known that a thawed ice bed and high pressure basal water are necessary but not sufficient conditions to cause ice streaming7 8 moreover it has been hypothesized that a soft sedimentary bed is also required because of its intrinsic low frictional resistance to flow9 and owing to its high erodibility so as to generate till that can deform and lubricate ice motion10 11 or to bury rough features and smooth the bed for sliding here we use seismic observations to provide evidence that one margin of the upglacier part of an ice stream is directly above the boundary of a basin with such sedimentary fill the ice stream is within the basin and the ice outside the basin is slow flowing the basin fill presents an order of magnitude lower frictional resistance to ice flow than the subglacial material outside the basin we conclude that the ice stream position is dependent on subglacial geology

the internal layering of pine island glacier west antarctica from airborne radar sounding data this paper presents an overview of internal layering across pine island glacier west antarctica as measured from airborne radar data acquired during a survey conducted by the british antarctic survey and the university of texas in the 2004 05 season internal layering is classified according to type continuous discontinuous missing and the results compared with insar velocities several areas exhibit disruption of internal layers that is most likely caused by large basal shear stresses signs of changes in flow were identified in a few inter tributary areas but overall the layering classification and distribution of layers indicate that only minor changes in ice flow regime have taken place this is supported by bed topography data that show the main trunk of the glacier as well as some of the tributaries are topographically controlled and located in deep basins

ice sheet grounding zone stabilization due to till compaction 1 based on modeling motivated by new gps and radio echo sounding surveys a few kilometers long zone of whillans ice stream west antarctica just inland of the grounding line has higher basal shear stress than the ice farther upstream or the freely slipping ice shelf downstream data from this zone show a few meter high upwarp of the surface overlying a large fold extending through all internal radar layers observed flowband modeling shows that the fold can be generated by decreased basal lubrication beneath the upwarp basal topography alone cannot create this fold physical modeling and available data suggest that low amplitude tidal flexure of the ice shelf extends a few kilometers inland downward flexing of this grounded ice from the rising tide would compact subglacial till resulting in higher basal shear stress this result suggests that important processes influencing grounding line stability are not included in modern whole ice sheet models

longitudinal variations in glacial flow theory and test using data from the byrd station strain network antarctica application de la theorie de budd 1970 des effets du lit sur les variations d ecoulement du glacier aux observations de la calotte de glace a la station byrd on utilise une rheologie visqueuse lineaire et on resout une equation biharmonique des variations des efforts et des vitesses de deformation les conditions aux limites comportent une topographie du fond avec ondulations glissements et cisaillements

changes in the configuration of ice stream flow from the west antarctic ice sheet surface based ice penetrating radar profiles on the northeast flank of siple dome support the hypothesis that a curvilinear scar first observed in advanced very high resolution radiometer satellite imagery represents the margin of a formerly active ice stream the scar defines the southwestern boundary of an ice stream flowing from ice stream c to ice stream d close to where it enters the ross ice shelf our studies show that the scar coincides with a trough and upward step in surface topography approximately 5 km across underlain by a zone of disturbed internal stratigraphy revealed by the radar burial depth of the disturbed zone enables us to calculate the time of shutdown as occurring prior to approximately 1 3 ka the configuration of the ice streams draining the west antarctic ice sheet into the ross ice shelf evidently changes with time and attempts to predict the evolution of the ice sheet must incorporate this observation

discovery of till deposition at the grounding line of whillans ice stream we report on the discovery of a grounding line sedimentary wedge till delta deposited by whillans ice stream west antarctica our observation is that grounding line deposition serves to thicken the ice and stabilize the position of the grounding line the ice thickness at the grounding line is greater than that of floating ice in hydrostatic equilibrium thus the grounding line will tend to remain in the same location despite changes in sea level until sea level rises enough to overcome the excess thickness that is due to the wedge further our observation demonstrates the occurrence of rapid subglacial erosion sediment transport by distributed subglacial till deformation and grounding line sedimentation which have important implications for ice dynamics numerical modeling of ice flow and interpretation of the sedimentation record