glacial landscape evolution by subglacial quarrying a multiscale computational approach quarrying of bedrock is a primary agent of subglacial erosion although the mechanical theory behind the process has been studied for decades it has proven difficult to formulate the governing principles so that large scale landscape evolution models can be used to integrate erosion over time the existing mechanical theory thus stands largely untested in its ability to explain post glacial topography in this study we relate the physics of quarrying to long term landscape evolution with a multi scale approach that connects meter scale cavities to kilometer scale glacial landscapes by averaging the quarrying rate across many small scale bedrock steps we quantify how regional trends in basal sliding speed effective pressure and bed slope affect the rate of erosion a sensitivity test indicates that a power law formulated in terms of these three variables provides an acceptable basis for quantifying regional scale rates of quarrying our results highlight the strong influence of effective pressure which intensifies quarrying by increasing the volume of the bed that is stressed by the ice and thereby the probability of rock failure the resulting pressure dependency points to subglacial hydrology as a primary factor for influencing rates of quarrying and hence for shaping the bedrock topography under warm based glaciers when applied in a landscape evolution model the erosion law for quarrying produces recognizable large scale glacial landforms u shaped valleys hanging valleys and overdeepenings the landforms produced are very similar to those predicted by more standard sliding based erosion laws but overall quarrying is more focused in valleys and less effective at higher elevations

geomorphic relations among glacial lake algonquin and the munising and grand marais moraines in eastern upper michigan usa abstract data obtained from ground penetrating radar gpr optically stimulated luminescence osl dating and geostatistical reconstructions of lake algonquin water planes indicate that high standing outwash aprons flanking the munising moraine s southern margin in eastern upper michigan terminate as large coalescing gilbert type ice contact deltas graded to the main level of lake algonquin nearly 30 km of gpr imagery provides clear evidence of topset and foreset beds diagnostic of deltaic deposition landform assemblages suggest that the deltas likely evolved from subaqueous grounding line fans formed along a retreating ice margin characterized by widespread stagnation in time these deltas aggraded to the main lake algonquin level as the ice margin stabilized an osl date of 12 5 1 1 ka on a nearby beach ridge associated with the main algonquin shoreline is consistent with this interpretation these new data coupled with the presence of nested fans at the downstream end of meltwater channels incised into the delta indicate that lake algonquin was falling as delta deposition waned eventually reaching a level concordant with the lower orillia level before final abandonment large regionally extensive heads of outwash marking the crest of the munising moraine are graded to the upper margins of these deltas and by inference must also correlate with main lake algonquin and the associated two rivers deglaciation ca 13 12 5 ka the deltas in turn are conspicuously crosscut by outwash aprons that are graded to levels much lower than any recognized upper group lake algonquin shoreline because these aforementioned heads of outwash part of drexler and others grand marais moraine correlate with the marquette moraine farther west they likely date to the marquette advance ca 11 5 ka thus landforms related to two rivers and to marquette glaciations appear to comingle across the study area in the absence of extensive exposures and datable materials our work highlights the fact that crosscutting relationships and distinct differences in base level can provide an important first step for untangling the complicated landform relationships in this part of michigan

postglacial paleoecological history of a cedar swamp manitoulin island ontario canada abstract a cedar swamp on manitoulin island ontario canada was chosen for a paleoecological study of pollen macrofossils and cladocera a new elevation of 316 7 m a s l is given for the position of main lake algonquin on northeastern manitoulin island based on a wave cut feature 4 7 m above the swamp immediately adjacent to the site deposits inferred to predate 10 500 yr b p are dominated by picea artemisia cyperaceae and other herbs likely derived from spruce parkland climate on the small proto manitoulin island group was cool and possibly dry the cladoceran assemblage includes alona lapidicola acroperus harpae and chydorus brevilabris which resembles the modern fauna of wave swept rocky shores of georgian bay this suggests that the site was an embayment of main lake algonquin local lake waters were cold and shallow pinus banksiana resinosa populus cupressineae artemisia pteridium and other herbs dominate pollen assemblages from 10 500 to 10 000 yr b p an open pine dominated woodland prevailed under a warming and dry climate and marked progression towards the holocene climatic optimum on manitoulin island glacial lake algonquin levels fell and the embayment was transformed into a small alkaline lake potamogeton filiformis hippuris vugaris and scirpus plants provided habitat for a diverse littoral and planktonic cladoceran fauna which included chydorus brevilabris c cf gibbus and bosmina longirostris waters in the swamp basin were rich in nutrients warm and possibly transparent from 10 000 to 8000 years b p picea returned as the dominant pollen type and was slightly more abundant than pinus banksiana resinosa toward the end of this period abies larix and betula increased in frequency picea forest with p banksiana resinova grew on shallow well drained soils climate became more continental winters more severe and summers drier and hotter as the moderating effects of the great lakes ceased during the lake stanley lake hough stage at the site a shallow pond with abundant submersed and emergent aquatic plants and a diverse littoral cladoceran community existed at 8000 yr b p pinus strobus replaced picea and pinus banksiana resinosa shortly after tsuga canadensis and larix become important this conifer dominated pollen assemblage persists to the present and reflects modern forests the presence of nyssa pollen and decodon verticillatus seeds contemporaneous with their range extensions elsewhere in the great lakes region implies that the hypsithermal maximum occurred about 6000 yr b p on manitoulin island when climate remained warmer than present but became humid after about 8000 yr b p by 5000 yr b p conditions became cooler prairie and cordilleran floristic elements in the modern manitoulin flora are probably remnants predating 10 000 yr b p the southern floristic element may represent late hypsithermal relicts fluctuating water levels and influence of mineral rich groundwater probably were key factors controlling hydroseral succession in cedar swamps on manitoulin island

evidence for an eolian origin for the silt enriched soil mantles on the glaciated uplands of eastern upper michigan usa abstract we provide textural geochemical and mineralogical data on a thin silty deposit that unconformably mantles glaciated uplands in the eastern upper peninsula of michigan previous research on this deposit which we hypothesize to be loess is nonexistent the uplands were islands or narrow peninsulas within one or more glacial lakes we compare the distribution likely source and nature of the 20 60 cm thick silty mantle by using the loess formation model of mason et al mason j a nater e a zanner c w bell j c 1999 a new model of topographic effects on the distribution of loess geomorphology 28 223 236 which focuses on the generation of eolian silt by saltating sand across upwind barren surfaces parabolic dunes with arms open to the nw are common on former lake floors upwind of the silt mantled uplands attesting to the strength and direction of paleowinds the abrupt termination of the dunes at the footslopes of the uplands associated with silt deposition on upland soil surfaces in downwind locations are both consistent with the model of mason et al mason j a nater e a zanner c w bell j c 1999 a new model of topographic effects on the distribution of loess geomorphology 28 223 236 sediments on former lake floors contain abundant strata of fine medium sand and silt and thus are likely sources for the silt and dune sand the cap dune and lake sediments are similar along many different geochemical axes whereas the substrate sediment i e the drift below the cap is unique cap sediments normally containing roughly 30 silt are enriched in quartz and depleted in ti and zr relative to dune sediment the dune sediment a more residual eolian deposit is enriched in ti and zr relative to the cap probably due to its greater abundance of heavy minerals therefore we conclude that the silty cap is loess that was deflated from abandoned lake floors after nearby glacial lakes drained probably contemporaneously with dune migration across the former lake floors

the northern limits of glacial lake algonquin in upper michigan abstract a number of ancient shorelines formed by late pleistocene proglacial lakes have been found in eastern upper michigan these shorelines delimit several water planes the uppermost of which is correlated with the main lake algonquin stage this correlation is based on the continuity of the highest water plane with main algonquin shorelines in wisconsin and ontario the strength of the shoreline features its altitudinal relationship with lower water planes and a reinterpretation of radiocarbon dates from the sault ste maria area the isobases of this water plane have a bearing of s75 e at the time of the maximum extent of lake algonquin ca 10 600 yr b p its northern ice limited border lay along the munising moraine the northernmost of the two main morainic systems of eastern upper michigan this interpretation lends support to the idea of a period of slow deglaciation from ca 11 000 to 10 000 yr b p an ice lobe occupied the central lake superior basin until early holocene time radiocarbon dates on wood found beneath till or outwash at several sites indicate a minor ice readvance from the central lake superior basin ca 10 000 yr b p if true this would have prevented the development of the post duluth series of glacial lakes in the western lake superior basin until ca 9900 yr b p well after the end of the main lake algonquin stage

weak bed control of the eastern shear margin of thwaites glacier west antarctica recent acceleration and thinning of thwaites glacier west antarctica motivates investigation of the controls upon and stability of its present ice flow pattern its eastern shear margin separates thwaites glacier from slower flowing ice and the southern tributaries of pine island glacier troughs in thwaites glacier s bed topography bound nearly all of its tributaries except along this eastern shear margin which has no clear relationship with regional bed topography along most of its length here we use airborne ice penetrating radar data from the airborne geophysical survey of the amundsen sea embayment antarctica agasea to investigate the nature of the bed across this margin radar data reveal slightly higher and rougher bed topography on the slower flowing side of the margin along with lower bed reflectivity however the change in bed reflectivity across the margin is partially explained by a change in bed roughness from these observations we infer that the position of the eastern shear margin is not strongly controlled by local bed topography or other bed properties given the potential for future increases in ice flux farther downstream the eastern shear margin may be vulnerable to migration however there is no evidence that this margin is migrating presently despite ongoing changes farther downstream

groundwater recharge and evolution in the dunhuang basin northwestern china groundwater recharge and evolution in the quaternary aquifer beneath the dunhuang basin was investigated using chemical indicators stable isotopes and radiocarbon data to provide guidance for regional water management the quality of groundwater and surface water is generally good with low salinity and it is unpolluted the dissolution of halite and sylvite from fine grained sediments controls concentrations of na and k in the groundwater but na cl molar ratios 1 in all samples are also indicative of weathering of feldspar contributing to excess na the dissolution of carbonate minerals yields ca2 to the groundwater thereby exerting a strong influence on groundwater salinity the delta o 18 and delta h 2 values in unconfined groundwater are enriched along the groundwater flow path from sw to ne in contrast confined groundwater was depleted in heavy isotopes with mean values of 10 4 parts per thousand delta o 18 and 74 4 parts per thousand delta h 2 compared with the precipitation values all of the groundwater samples were strongly depleted in heavy isotopes indicating that modern direct recharge to the groundwater aquifers in the plains area is quite limited the unconfined water is generally young with radiocarbon values of 64 9 79 6 pmc in the northern basin radiocarbon content in the confined groundwater is less than 15 pmc and an uncorrected age of similar to 15 ka indicates that this groundwater was recharged during a humid climatic phases of the late pleistocence or early holocene the results have important implications for inter basin water allocation programmes and groundwater management in the dunhuang basin c 2012 elsevier ltd all rights reserved

carbonate diagenesis in ice the fine particles created by glacial comminution of carbonate minerals are susceptible to interaction with meltwater and the isotopic composition of fine carbonate in glacial deposits has the potential of recording this interaction here we focus on the carbonate fraction of glacial sediment and debris within basal ice at the tsanfleuron glacier switzerland size separates of basal ice debris and melt out tills show a collinear isotopic trend interpreted as a mixing line between detritus 18 o pdb 5 and 13 o pdb 0 6 and authigenic calcite which in one case had 18 o values as light as 18 7 and 13 c values as light as 5 7 in most cases the finer fractions with calcite crystals as small as 0 1 m are enriched in the isotopically light component which is interpreted to form largely by freezing in basal ice the isotopic compositions of ice and included gases could be influenced by this process melt out tills inherit the authigenic calcite thus carbonate bearing till should no longer be regarded simply as clastic sediment

direct observation of basal sliding and deformation of basal drift at sub freezing temperatures in a tunnel at the base of sub polar urumqi glacier no 1 china three new mechanisms of glacier flow at sub freezing temperatures have been observed taken individually or in combination these modes of flow can account for nearly all 60 80 of the overall glacier motion and yet they act only within the lowermost 1 2 of the effective glacier thickness these mechanisms are 1 enhanced deformation of the frozen and ice laden subglacial drift 2 motion across discrete shear planes or shear bands within the frozen drift or at the ice drift interface and 3 basal sliding at an ice rock interface at a temperature of nearly 5 c the ice laden drift has an effective viscosity of more than one hundred times less than that measured in the overlying ice thus allowing very rapid shear deformation the observed rate or basal sliding at the ice rock interface agrees favorably with that predicted by the recent work of shreve 1984 if proper account is taken of the measured surface roughness and reduced ice viscosity

glacier sliding at subfreezing temperatures theorie de nye modifiee par l incorporation du modele de gilpin d un film liquide le long des inclusions solides dans la glace effets des temperatures sur la regulation de vitesse applications aux glaciers que l on classe en glaciers a exces de fusion et ceux a deficit de fusion

reconstructing past glacier dynamics and erosion from glacial geomorphic evidence snowdon north wales bedrock surfaces exposed around llyn llydaw north wales demonstrate contrasting styles of erosion beneath a late devensian ice sheet and a loch lomond stadial lls valley glacier ice sheet erosion involved lee side fracturing surface fracture wear and abrasive wear while lls erosion was primarily by abrasive wear preservation of ice sheet erosional features indicates limited rates of erosion during the lls analysis of the geometry and distribution of erosional markings suggests that the low erosional capacity of the lls glacier was due to a low basal sliding velocity this prevented the formation of lee side cavities reduced the debris flux over the bed and minimised particle bed contact loads reconstructions of the mass balance and geometry of the lls glacier indicate that most of its balance velocity could be achieved by internal deformation alone a combination of low subglacial water pressures and an unusually rough substrate explain the low sliding velocities high bed roughness is due to the absence of leeside cavities and a change in flow orientation between ice sheet and lls times which meant that the lls glacier was in contact with roughness elements which were generated in cavities beneath the ice sheet

late holocene formation of lake michigan beach ridges correlated with a 70 yr oscillation in global climate abstract a radiocarbon dated series of 75 beach ridges formed at regular intervals averaging 72 yr over the past 5400 yr provides further support for the existence of a 70 yr oscillation in northern hemisphere climate postulated recently from instrument data representing less than two cycles of this climate oscillation results from this study lend support to the interpretation that internal variations in the ocean atmosphere system are an important factor in climate fluctuations on a decadal centennial time scale a temperature oscillation with a period of about 70 yr has been a previously unrecognized but fundamental part of the global climate system since at least the middle holocene

geophysical constraints on the dynamics and retreat of the barents sea ice sheet as a paleobenchmark for models of marine ice sheet deglaciation our understanding of processes relating to the retreat of marine based ice sheets such as the west antarctic ice sheet and tidewater terminating glaciers in greenland today is still limited in particular the role of ice stream instabilities and oceanographic dynamics in driving their collapse are poorly constrained beyond observational timescales over numerous glaciations during the quaternary a marine based ice sheet has waxed and waned over the barents sea continental shelf characterized by a number of ice streams that extended to the shelf edge and subsequently collapsed during periods of climate and ocean warming increasing availability of offshore and onshore geophysical data over the last decade has significantly enhanced our knowledge of the pattern and timing of retreat of this barents sea ice sheet bsis particularly so from its late weichselian maximum extent we present a review of existing geophysical constraints that detail the dynamic evolution of the bsis through the last glacial cycle providing numerical modelers and geophysical workers with a benchmark data set with which to tune ice sheet reconstructions and explore ice sheet sensitivities and drivers of dynamic behavior although constraining data are generally spatially sporadic across the barents and kara seas behaviors such as ice sheet thinning major ice divide migration asynchronous and rapid flow switching and ice stream collapses are all evident further investigation into the drivers and mechanisms of such dynamics within this unique paleo analogue is seen as a key priority for advancing our understanding of marine based ice sheet deglaciations both in the deep past and in the short term future

paleowind 11 000 bp directions derived from lake spits in northern michigan we report on the characteristics of several previously unstudied late pleistocene spits in northern lower michigan each spit developed as strong waves eroded a headland or island within the main and or later stages of glacial lake algonquin most have ese to wnw orientations with prominent recurved hooks at their ends some are as long as 20 km sedimentologically the spits contain thick several meters or more sequences of sand and well rounded gravel we suggest that summertime winds during the spits formation 11 800 to 10 500 bp were both very strong and dominantly from the e and se based on the following data 1 their ese source or head of the spit to wnw orientation 2 the presence of steep wave cut bluffs on the east sides of the islands and headlands and 3 spit locations on the northeastern shore of michigan s lower peninsula coupled with their absence on the northwestern shore just 100 km away wind direction data provided by these spits agree with paleoclimatic models that suggest that the laurentide ice sheet had developed a strong anticyclonic circulation the near lack of archeological sites from this time period in the northern lower peninsula which was surrounded by lake algonquin at that time supports the notion that the climate of northern lower michigan was inhospitably cold and very windy in the late pleistocene

stress gradient coupling in glacier flow i longitudinal averaging of the influence of ice thickness and surface slope for a glacier flowing over a bed of longitudinally varying slope the influence of longitudinal stress gradients on the flow is analyzed by means of a longitudinal flow coupling equation derived from the vertically cross sectionally integrated longitudinal stress equilibrium equation by an extension of an approach originally developed by budd 1968 linearization of the flow coupling equation by treating the flow velocity u vertically averaged ice thickness h and surface slope in terms of small deviations u h and a from overall average datum values u 0 h 0 and 0 results in a differential equation that can be solved by green s function methods giving u x as a function of h x and x x being the longitudinal coordinate the result has the form of a longitudinal averaging integral of the influence of local h x and x on the flow u x u x u0 2l l 0 ln n nh n l exp x x l dx where the integration is over the length l of the glacier the operator specified deviations from the datum state and the term on which it operates which is a function of the integration variable x represents the influence of local h x x and channel shape factor x at longitudinal coordinate x on the flow u at coordinate x the influence being weighted by the influence transfer function exp x x l in the integral the quantity l that appears as the scale length in the exponential weighting function is called the longitudinal coupling length it is determined by rheological parameters via the relationship l 2h n n 3n where n is the flowlaw exponent n the effective longitudinal viscosity and n the effective shear viscosity of the ice profile n is an average of the local effective viscosity n over the ice cross section and n 1 is an average of n 1 that gives strongly increased weight to values near the base theoretically the coupling length l is generally in the range one to three times the ice thickness for valley glaciers and four to ten times for ice sheets for a glacier in surge it is even longer l 12h it is distinctly longer for non linear n 3 than for linear rheology so that the flow coupling effects of longitudinal stress gradients are markedly greater for non linear flow the averaging integral indicates that the longitudinal variations in flow that occur under the influence of sinusoidal longitudinal variations in h or with wavelength are attenuated by the factor 1 1 2 l 2 relative to what they would be without longitudinal coupling the short intermediate and long scales of glacier motion raymond 1980 over which the longitudinal flow variations are strongly partially and little attenuated are for 2l 2l 20l and 20l for practical glacier flow calculations the exponential weighting function can be approximated by a symmetrical triangular averaging window of length 4l called the longitudinal averaging length the traditional rectangular window is a poor approximation because of the exponential weighting the local surface slope has an appreciable though muted effect on the local flow which is clearly seen in field examples contrary to what would result from a rectangular averaging window tested with field data for variegated glacier alaska and blue glacier washington the longitudinal averaging theory is able to account semi quantitatively for the observed longitudinal variations in flow of these glaciers and for the representation of flow in terms of effective surface slope values exceptions occur where the flow is augmented by large contributions from basal sliding in the ice fall and terminal zone of blue glacier and in the reach of surge initiation in variegated glacier the averaging length 4l that gives the best agreement between calculated and observed flow pattern is 2 5 km for variegated glacier and 1 8 km for blue glacier corresponding to l h 2 in both cases if l varies with x but not too rapidly the exponential weighting function remains a fairly good approximation to the exact green s function of the differential equation for longitudinal flow coupling in this approximation l in the averaging integral is l x but is not a function of x effects of longitudinal variation of l are probably important near the glacier terminus and head and near ice falls the longitudinal averaging formulation can also be used to express the local basal shear stress in terms of longitudinal variations in the local stope stress with the mediation of longitudinal stress gradients

buried soils in a perched dunefield as indicators of late holocene lake level change in the lake superior basin abstract a stratigraphic analysis of buried soils within the grand sable dunes a dune field perched 90 m above the southern shore of lake superior reveals a history of eolian activity apparently linked with lake level fluctuations over the last 5500 yr a relative rise in the water plane of the nipissing great lakes initially destabilized the lakeward bluff face of the grand sable plateau between 5400 and 4600 14 c yr b p this led to the burial of the sable creek soil by eolian sediments derived from the bluff face subsequent episodes of eolian activity appear to be tied to similar destabilizing events high lake levels may have initiated at least four and perhaps eleven episodes of dune building as expressed by soil burials within the dunes intervening low lake levels probably correlate with soil profile development which varies from the well developed sable creek spodosol catena to thin organic layers containing in place stumps and tree trunks paleoecological reconstructions available for the area do not imply enough climatic change to account for the episodic dune activity burial of soils by fine fraction sediments links dune building episodes with destabilization of the lower lake facing bluff which is rich in fines

a hydrologically coupled higher order flow band model of ice dynamics with a coulomb friction sliding law 1 the influence of hydrologic transience and heterogeneity on basal motion is an often neglected aspect of numerical ice flow models we present a flow band model of glacier dynamics with a coulomb friction sliding law that is coupled to a model of the basal drainage system by means of subglacial water pressure the ice flow model contains higher order stress gradients from the stokes flow approximation originally conceived by blatter 1995 the resulting system of nonlinear equations is solved using a modified picard iteration that is shown to improve the rate of convergence a parameterization of lateral shearing is included to account for the effects of three dimensional geometry we find that lateral drag has a discernible effect on glacier speed even when glacier width exceeds glacier length variations in flow band width are shown to have a greater influence on flow line speed than either different valley cross sectional shapes or the presence or absence of glacier sliding along valley walls modeled profiles of subglacial water pressure depart significantly from pressures prescribed as a uniform fraction of overburden thus producing profiles of glacier sliding that are distinctly different from those that would be described by a sliding law controlled by overburden pressures simulations of hydraulically driven glacier acceleration highlight the value of including a representation of basal hydrology in models aiming for improved predictive capability of glacier dynamics

direct measurement of basal motion at a hard bedded temperate glacier glacier de tsanfleuron switzerland hubbard b 2002 direct measurement of basal motion at a hard bedded temperate glacier glacier de tsanfleuron switzerland journal of glaciology 48 160 pp 1 8 rae2008

a 14 6 kyr record of nitrogen flux from desert soil profiles as inferred from vadose zone pore waters a 14 6 kyr chronology of infiltration developed from deep vadose unsaturated zone cores in southern nevada is presented to assess the chronology of nitrogen loss from the active rooting zone soil water chemistry in the deep vadose zone is first used to develop a chronology of paleohydrology and subsequently nitrogen fluxes while elevated nitrogen concentrations as no3 are commonly found in desert vadose zones no3 cl ratios indicate that nitrate behaved conservatively beneath the active rooting zone mean nitrogen fluxes from the active root zone range from 103 to 108 mg m yr and appear relatively constant over time in spite of dramatic climate and vegetation changes the long term loss of nitrogen from the active rooting zone implies that nitrogen cycling processes have been relatively constant since the pleistocene holocene transition that the biological community may not be primarily limited by the availability of nitrogen and that the loss of nitrogen into the vadose zone should be considered in desert ecosystem productivity studies

travel times in the vadose zone variability in space and time water travel times reflect hydrological processes yet we know little about how travel times in the unsaturated zone vary with time using the soil physical model hydrus 1d we derived time variable travel time distributions for 35 study sites within the attert catchment in luxembourg while all sites experience similar climatic forcing they differ with regard to soil types 16 cambisols 12 arenosols and 7 stagnosols and the vegetation cover 29 forest and 6 grassland we estimated site specific water flow and transport parameters by fitting the model simulations to observed soil moisture time series and depth profiles of pore water stable isotopes with the calibrated model we tracked the water parcels introduced with each rainfall event over a period of several years our results show that the median travel time of water from the soil surface to depths down to 200 cm is mainly driven by the subsequent rainfall amounts the median time until precipitation is taken up by roots is governed by the seasonality of evapotranspiration rates the ratio between the amount of water that leaves the soil profile by on the one hand and evaporation and transpiration on the other hand also shows an annual cycle this time variable response due to climatic forcing is furthermore visible in the multimodal nature of the site specific master transit time distribution representing the flow averaged probability density for rainwater to become recharge the spatial variability of travel times is mainly driven by soil texture and structure with significant longer travel times for the clayey stagnosols than for the loamy to sandy cambisols and arenosols

organized flow from the south pole to the filchner ronne ice shelf an assessment of balance velocities in interior east antarctica using radio echo sounding data 1 ice flow through central antarctica has the potential to transmit accumulation changes from deep interior east antarctica rapidly to the shelf but it is poorly constrained owing to a dearth of ice velocity observations we use parameters derived from airborne radio echo sounding res data to examine the onset areal extent and englacial conditions of an organized flow network tributaries feeding an ice stream draining from the south pole to the filchner ronne ice shelf we classified res flight tracks covering the region according to whether englacial stratigraphy was disrupted i e internal layers diverged significantly from the surface and bed echoes or undisrupted i e internal layers closely parallel surface and basal topography and we calculated subglacial roughness along basal reflectors where satellite measured surface ice flow speeds are available covering 39 of the study region regions of fast and tributary flow correspond with res flight tracks that exhibit more disrupted internal layers and smoother subglacial topography than their counterparts in regions of slow flow this suggests that disrupted internal layering and smooth subglacial topography identified from res profiles can be treated as indicators of past or present enhanced flow tributaries where neither satellite nor ground based ice flow measurements are available we therefore use these res derived parameters to assess the balance flux modeled steady state flow regime between the south pole and filchner ronne ice shelf the res analysis confirms that an organized flow network drains a wide region around the south pole into the filchner ronne ice shelf however the spatial extent of this network as delineated by the res data diverges from that predicted by currently available balance flux models

the basal roughness of pine island glacier west antarctica we assess basal roughness beneath pine island glacier pig west antarctica based on a recent airborne radio echo sounding dataset we identify a clear relationship between faster ice flow and decreased basal roughness in significant parts of pig the central portion and two of its tributaries are particularly smooth but the majority of the tributaries feeding the main trunk are rougher we interpret the presence of a smooth bed as being a consequence of the deposition of marine sediments following disappearance of the west antarctic ice sheet in the pliocene or pleistocene and conversely a lack of marine sedimentation where the bed is rough importantly we also identify a patchy distribution of marine sediments and thus a bed over which the controls on flow vary while there is a notable correspondence between ice velocity and bed roughness we do not assume a direct causal relationship but find that an indirect one is likely where low basal roughness results in low basal resistance to flow a lower driving stress is required to produce the flux required to achieve mass balance this in turn means that the surface in that area will be lower than surrounding areas with a rougher bed and this will tend to draw flow into the area with low bed roughness since our studies shows that bed roughness beneath the tributaries of the trunk varies substantially there is a strong likelihood that these tributaries will differ in the rate at which they transmit current velocity changes on the main trunk into the interior of the glacier basin

quantifying subglacial bed roughness in antarctica implications for ice sheet dynamics and history abstract glaciated landscapes consist of complex assemblages of landforms resulting from ice flow dynamic regimes and ice sheet history superimposed over and in turn modifying preglacial topography lithology and geological structure insights into the formation of glaciated landscapes can in principle be obtained by analysing modern ice sheet beds but terrain analyses beneath modern ice sheets are restricted by the inaccessibility of the bed it is however possible to quantify roughness the vertical variation of the subglacial interface with horizontal distance along two dimensional images of the bed obtained from radio echo sounding res here we collate several case studies from antarctica where roughness calculations have been used as a glaciological tool to infer basal processes and ice sheet history over large 500 km 2 areas we present two examples from west antarctica which demonstrate the utility of bed roughness in determining the presence and extent of subglacial sediments glacial dynamics and former ice sheet size we also present two examples from east antarctica which illustrate how roughness provides knowledge of ice sheet dynamics in the interior and pre quaternary ice sheet histories in modern ice sheet settings characterising bed roughness along res tracks has the twin advantages of being relatively simple to calculate while producing informative subsurface data and is especially powerful at furthering understanding when coupled with knowledge of ice flow from field satellite and modelling investigations the technique also offers significant potential for the comparison of modern and former ice sheet terrains contributing to an improved understanding of the formation and evolution of glaciated landscapes

inorganic carbon isotope systematics in soil profiles undergoing silicate and carbonate weathering southern michigan usa abstract the upper midwest usa features glacial derived till materials enriched in carbonate minerals but with the uppermost soil layer progressively leached of carbonates in the interval since glaciation groundwaters and groundwater fed surface waters are profoundly influenced by carbonate mineral dissolution stable carbon isotope compositions of soil waters and groundwaters in two southern michigan watersheds huron and kalamazoo were studied as a function of ph 13cco2 types of weathering reactions silicate vs carbonate and degree of isotope equilibration this comprehensive study of carbon isotope biogeochemistry in the vadose zone including soil gas soil water groundwater and soils organic matter carbonate phases elucidates relations between the chemical weathering rates and co2 fluxes in the soil zone such information is important to evaluate responses of terrestrial ecosystems to global climate change in shallow soil zones where only silicate weathering was occurring respiratory co2 was the major source of soil water dic with little addition from the atmospheric co2 isotopic equilibration between 13cdic and 13cco2 occurred in an open system with respect to soil co2 in the deeper soil horizons carbonate dissolution dominated soil water chemistry and saturation with respect to calcite and dolomite was attained rapidly mass balance calculation showed that large amounts of soil co2 were consumed by carbonate dissolution such that the deeper soil zone may not have been an open system with respect to co2 constant 13cdic values 11 were observed in these deep soil waters and also in shallow groundwaters of the huron watershed thus isotopic equilibrium might not be reached between dic and co2 possibly due to a rapid kinetics of carbonate dissolution and limited gas water exchange in the soils if so dic was equally contributed by carbonate minerals 13ccaco3 0 in reaction with soil co2 13cco2 22 soils beneath an agricultural site with a wheat corn soybean rotation the kalamazoo watershed displayed a wide range in 13cco2 values 22 to 12 and the 13cdic of deeper soil waters in contact with carbonate minerals was controlled by seasonal variations of 13cco2 as well as by strong acids produced by nitrification and to a lesser degree by pyrite oxidation both of which could react to dissolve carbonate minerals in addition to carbonic acid dissolution

bedrock surface roughness and the distribution of subglacially precipitated carbonate deposits implications for formation at glacier de tsanfleuron switzerland two carbonate deposits are identified on the exposed bedrock surface in the forefield of glacier de tsanfleuron switzerland macrocrystalline sparite and microcrystalline micrite comparison of the distributions of these forms with lee side slope facets identified by high pass filtering of a flow parallel bedrock profile at a range of frequencies reveals two significant results first while the distribution of sparite is consistent with formation in the lee side of subglacial bedrock hummocks that of micrite is not this contrasts with previous investigations in which both sparite and micrite have been considered to form by mineral concentration and precipitation during the refreezing of regelation related basal meltwaters in the lee side of bedrock hummocks alternative mechanisms of micrite formation involving carbonate deposition and or precipitation within subglacial bedrock hollows are proposed second the distribution of sparite is most strongly correlated with the distribution of lee side slope facets identified by filtering at a frequency equivalent to a hummock wavelength of c 0 1 m this correspondence indicates empirically that pressure related melting and refreezing regelation operates most effectively around bedrock hummocks that are shorter than c 0 1 m 1998 john wiley sons ltd

response of deep groundwater to land use change in desert basins of the trans pecos region texas usa effects on infiltration recharge and nitrogen fluxes quantifying the effects of anthropogenic processes on groundwater in arid regions can be complicated by thick unsaturated zones with long transit times human activities can alter water and nutrient fluxes but their impact on groundwater is not always clear this study of basins in the trans pecos region of texas links anthropogenic land use and vegetation change with alterations to unsaturated zone fluxes and regional increases in basin groundwater no3 concentrations median increases in groundwater no3 by 0 7 0 9 mg n l over periods ranging from 10 to 50 years occurred despite low precipitation 220 360 mm year high potential evapotranspiration 1570 mm year and thick unsaturated zones 10 150 m recent model simulations indicate net infiltration and groundwater recharge can occur beneath trans pecos basin floors and may have increased due to irrigation and vegetation change these processes were investigated further with chemical and isotopic data from groundwater and unsaturated zone cores some unsaturated zone solute profiles indicate flushing of natural salt accumulations has occurred results are consistent with human influenced flushing of naturally accumulated unsaturated zone nitrogen as an important source of no3 to the groundwater regional mass balance calculations indicate the mass of natural unsaturated zone no3 122 910 kg n ha was sufficient to cause the observed groundwater no3 increases especially if augmented locally with the addition of fertilizer n groundwater no3 trends can be explained by small volumes of high no3 modern recharge mixed with larger volumes of older groundwater in wells this study illustrates the importance of combining long term monitoring and targeted process studies to improve understanding of human impacts on recharge and nutrient cycling in arid regions which are vulnerable to the effects of climate change and increasing human reliance on dryland ecosystems

interfacial water in polar glaciers and glacier sliding at 17 c we have observed sliding at a cold 17 oc ice rock interface beneath meserve glacier antarctica and the segregation of ice into clean lenses amidst the dirty basal layers of this glacier we interpret these as manifestation s of thin water films at ice rock interfaces we use shreve s theory for sub freezing sliding to esti mate the nominal film thickness to be at least tens of nanometers such water films should exist around rocks in most polar ices and likely have high solute concen trations due to solute rejection during regelation and due to exchange with veins and grain boundaries where impurities reside

macro scale bed roughness of the siple coast ice streams in west antarctica subglacial bed conditions are key to understanding ice stream behaviour and evolution with bed roughness re ecting substrate composition and ow resistance here we present an analysis of bed roughness in the siple coast region of west antarctica from airborne radio echo sounding data the ice streams are associated generally with low bed roughness values which decrease downstream the bed of the slow owing ice stream c 10 000 km2 is also characterized by being smooth at all scales wavelengths ranging from 5 km to in excess of 40 km furthermore the bed is smooth either side of ice stream c this suggests the location of the ice stream is controlled by internal ice sheet dynamics rather than by bed morphology if the ice stream were encouraged to migrate laterally when active there would be little resistance offered by the subglacial morphology other inter ice stream regions are rough however indicating a subglacial topographic in uence on ice stream position bed roughness increases up ow of ice streams which unless the bed is modi ed may limit the inland migration of these systems copyright 2004 john wiley sons ltd

resolving the internal and basal geometry of ice masses using imaging phase sensitive radar the phase sensitive radio echo sounder pres is a powerful new instrument that can measure the depth of internal layers and the glacier bed to millimetre accuracy we use a stationary 16 antenna pres array on store glacier in west greenland to measure the three dimensional orientation of dipping internal reflectors extending the capabilities of pres beyond conventional depth sounding this novel technique portrays the effectiveness of pres in deriving the orientation of dipping internal layers that may complement profiles obtained through other geophysical surveying methods deriving ice vertical strain rates from changes in layer depth as measured by a sequence of pres observations assumes that the internal reflections come from vertically beneath the antenna by revealing the orientation of internal reflectors and the potential deviation from nadir of their associated reflections the use of an antenna array can correct this assumption while the array configuration was able to resolve the geometry of englacial layers the same configuration could not be used to accurately image the glacier bed here we use simulations of the performance of different array geometries to identify configurations that can be tailored to study different types of basal geometry for future deployments

basal roughness of the institute and moller ice streams west antarctica process determination and landscape interpretation we present a detailed analysis of bed roughness beneath institute and moller ice streams west antarctica using radio echo sounding data res acquired in the austral summer of 2010 11 we assess roughness using a two parameter approach and also assess the directionality of roughness relative to present day ice flow our work highlights the wealth of additional information that resides in analyses of bed roughness employing these multiple approaches we show that spatially variable roughness patterns are partly a consequence of the ability of flowing ice not only to smooth the bed but also to redistribute and remove sediments and to do this along flow accordingly we identify some fast flow tributaries underlain by topography that has been streamlined and other tributaries that are underlain by sediments we also identify locations that are currently protected from erosion but where more ancient erosion may once have occurred we conclude that detailed roughness analysis is a useful tool for landscape interpretation and we suggest that the roughness of an ice sheet s bed should be viewed not only as the consequence of ancient marine sedimentation but also as a product of more contemporary erosion and redistribution of sediments as well as bedrock smoothing that is ongoing because of continuing dynamic activity in this way basal roughness has the potential to evolve continually with ice sheet form and flow and should not be viewed simply as a snapshot of either present day or palaeo basal conditions

measuring glacier surface roughness using plot scale close range digital photogrammetry glacier roughness at sub metre scales is an important control on the ice surface energy balance and has implications for scattering energy measured by remote sensing instruments ice surface roughness is dynamic as a consequence of spatial and temporal variation in ablation to date studies relying on singular and or spatially discrete two dimensional profiles to describe ice surface roughness have failed to resolve common patterns or causes of variation in glacier surface morphology here we demonstrate the potential of close range digital photogrammetry as a rapid and cost effective method to retrieve three dimensional data detailing plot scale supraglacial topography the photogrammetric approach here employed a calibrated consumer grade 5 mpix digital camera repeatedly imaging a plot scale 25 m2 ice surface area on midtre lovenbreen svalbard from stereo pair images digital surface models dsms with sub centimetre horizontal resolution and 3 mm vertical precision were achieved at plot scales 4 m2 extraction of roughness metrics including estimates of aerodynamic roughness length z 0 was readily achievable and temporal variations in the glacier surface topography were captured close range photogrammetry with appropriate camera calibration and image acquisition geometry is shown to be a robust method to record sub centimetre variations in ablating ice topography while the dsm plot area may be limited through use of stereo pair images and issues of obliquity emerging photogrammetric packages are likely to overcome such limitations

stable isotope evidence for an atmospheric origin of desert nitrate deposits in northern chile and southern california u s a natural surficial accumulations of nitrate rich salts in the atacama desert northern chile and in the death valley region of the mojave desert southern california are well known but despite many geologic and geochemical studies the origins of the nitrates have remained controversial n and o isotopes in nitrate and s isotopes in coexisting soluble sulfate were measured to determine if some proposed n sources could be supported or rejected and to determine if the isotopic signature of these natural deposits could be used to distinguish them from various types of anthropogenic nitrate contamination that might be found in desert groundwaters high grade calich a type nitrate deposits from both localities have 15n values that range from 5 to 5 but are mostly near 0 values of 15n near 0 are consistent with either bulk atmospheric n deposition or microbial n fixation as major sources of the n in the deposits 18o values of those desert nitrates with 15n near 0 range from about 31 to 50 v smow significantly higher than that of atmospheric o2 23 5 such high values of 18o are considered unlikely to result entirely from nitrification of reduced n but rather resemble those of modern atmospheric nitrate in precipitation from some other localities assuming that limited modern atmospheric isotope data are applicable to the deposits and allowing for nitrification of co deposited ammonium it is estimated that the fraction of the nitrate in the deposits that could be accounted for isotopically by atmospheric n deposition may be at least 20 and possibly as much as 100 34s values are less diagnostic but could also be consistent with atmospheric components in some of the soluble sulfates associated with the deposits the stable isotope data support the hypothesis that some high grade caliche type nitrate rich salt deposits in some of the earth s hyperarid deserts represent long term accumulations of atmospheric deposition possibly in the order of 104 yr for the death valley region 107 yr for the atacama desert in the relative absence of soil leaching or biologic cycling the combined n and o isotope signature of the nitrate in these deposits is significantly different from those of many other natural and anthropogenic sources of nitrate

early holocene dune activity linked with final destruction of glacial lake minong eastern upper michigan usa abstract the early holocene final drainage of glacial lake minong is documented by 21 osl ages on quartz sand from parabolic dunes and littoral terraces and one radiocarbon age from a lake sediment core adjacent to mapped paleoshorelines in interior eastern upper michigan we employ a simple model wherein lake level decline exposes unvegetated littoral sediment to deflation resulting in dune building dunes formed subsequent to lake level decline prior to stabilization by vegetation and provide minimum ages for lake level decline optical ages range from 10 3 to 7 7 ka 15 ages on dunes adjacent to the lowest lake minong shoreline suggest final water level decline 9 1 ka the clustering of optical ages from vertically separated dunes on both sides of the nadoway gros cap barrier around 8 8 ka and a basal radiocarbon date behind the barrier 8120 40 14 c yr bp 9 1 cal ka bp support the hypothesis that the barrier was breached and the final lake level drop to the houghton low occurred coincident with 1 high meltwater flux into the superior basin and 2 an abrupt negative shift in oxygen isotope values in lake huron

finite element modeling of subglacial cavities and related friction law 1 sliding velocity and basal drag are strongly influenced by changes in subglacial water pressure or subglacial water storage associated with opening and closing of water cavities in the lee of bedrock obstacles to better understand this influence finite element simulations of ice flowing past bedrock obstacles with cavity formation are carried out for different synthetic periodic bedrock shapes in the numerical model the cavity roof is treated as an unknown free surface and is part of the solution as an improvement over earlier studies the cases of nonlinear ice rheology and infinite bedrock slopes are treated our results show that the relationship between basal drag and sliding velocity the friction law can be easily extended from linear to nonlinear ice rheology and is bounded even for bedrocks with locally infinite slopes combining our results with earlier works by others a phenomenological friction law is proposed that includes three independent parameters that depend only on the bedrock geometry this formulation yields an upper bound of the basal drag for finite sliding velocity and a decrease in the basal drag at low effective pressure or high velocity this law should dramatically alter results of models of temperate glaciers and should also have important repercussions on models of glacier surges and fast glacier flows

the carbonate system geochemistry of shallow groundwater surface water systems in temperate glaciated watersheds michigan usa significance of open system dolomite weathering we present here a field geochemical study of controls on carbonate weathering within rapidly circulating shallow groundwater surface water systems in the glaciated mid continent region groundwaters and surface waters in three watersheds spanning the upper to lower peninsulas of michigan consist of ca 2 mg 2 hco 3 solutions derived from the open system dissolution of calcite and dolomite in soils developed on mixed mineralogy glacial drift the thermodynamic stabilities of calcite and dolomite both decrease with decreasing temperature with dolomite more strongly affected thus the low mean annual temperature of these temperate weathering environments maximizes the absolute solubility of dolomite as well as its solubility relative to calcite many groundwaters in the study area approach equilibrium with respect to the more soluble dolomite and are moderately supersaturated with respect to calcite groundwaters in each watershed have distinct and relatively narrow ranges of carbon dioxide partial pressure p co 2 values which increase significantly from north to south log p co 2 of 3 0 to 2 2 atm suggesting that there are landscape level differences in carbon transformation rates in soil weathering zones increases in weathering zone p co 2 values produce hco 3 concentrations that vary by a factor of five but the mg 2 ca 2 and mg 2 hco 3 ratios of all groundwaters are similar suggesting relatively constant weathering input ratios of calcite and dolomite although surface waters commonly are between 2 and 10 times supersaturated with respect to calcite the mg 2 hco 3 ratios of surface waters are very close to initial groundwater values suggesting that back precipitation of calcite is not a significant process in these systems the enhanced solubility of dolomite at low temperatures coupled with the landscape level differences in carbon cycling suggest that temperate zone weathering reactions in glaciated terrains are significant contributors to continent scale fluxes of both mg 2 and hco 3

paleobotanical and environmental implications of a buried forest bed in northern lower michigan usa sediments and stratigraphy at the tower buried forest site provide a glimpse into the immediate post glacial environment of northern lower michigan usa at this site sandy glacial outwash is overlain by 1 37 cm of peat associated with a wetland above which are 2 flat lying spruce and larch logs and branches that date between 10 910 and 10 340 cal years bp above the woody materials are 55 75 cm of sand interbedded with organic muck laminae which we interpret as local alluvium this stratigraphic sequence is overlain by muck soil materials associated with the modern wetland pollen and plant macrofossil analysis of the lower peat indicate that a tundra boreal parkland had been established here shortly after final deglaciation later picea glauca white spruce picea mariana black spruce larix laricina larch and abies balsamea balsam fir became abundant in an open boreal forest spaghnum peatland subsequent increases in pinus pine and typha cattail indicate drying and possibly warming conditions at ca 10 340 cal years bp or a few centuries prior nearly two millennia after final deglaciation water flowed across the site possibly knocking over the trees interbedded sand and muck deposits above the flat lying logs are interpreted as alluvial deposits from this event after which the wetland became quiescent again

multiscale analysis of topographic surface roughness in the midland valley scotland surface roughness is an important geomorphological variable which has been used in the earth and planetary sciences to infer material properties current past processes and the time elapsed since formation no single definition exists however within the context of geomorphometry we use surface roughness as an expression of the variability of a topographic surface at a given scale where the scale of analysis is determined by the size of the landforms or geomorphic features of interest six techniques for the calculation of surface roughness were selected for an assessment of the parameter s behavior at different spatial scales and data set resolutions area ratio operated independently of scale providing consistent results across spatial resolutions vector dispersion produced results with increasing roughness and homogenization of terrain at coarser resolutions and larger window sizes standard deviation of residual topography highlighted local features and did not detect regional relief standard deviation of elevation correctly identified breaks of slope and was good at detecting regional relief standard deviation of slope sdslope also correctly identified smooth sloping areas and breaks of slope providing the best results for geomorphological analysis standard deviation of profile curvature identified the breaks of slope although not as strongly as sdslope and it is sensitive to noise and spurious data in general sdslope offered good performance at a variety of scales while the simplicity of calculation is perhaps its single greatest benefit

mapped plant macrofossil and pollen records of late quaternary vegetation change in eastern north america abstract macrofossil presence absence maps and isopoll maps in 3000 year intervals show how ranges and abundance maxima for 12 eastern north american tree and shrub taxa picea p glauca p mariana larix laricina abies balsamea tsuga canadensis pinus strobus p resinosa p banksiana betula papyrifera b alleghaniensis b series humiles have changed from the last glacial maximum to the present the macrofossil maps corroborate patterns shown by the isopoll maps and provide spatial detail and taxonomic resolution the macrofossils confirm the inference from pollen data that unglaciated southeastern north america was cooler during the last glacial maximum 18 and 15 ka than simulated by the cohmap experiments with the ncar ccm0 general circulation model the geographic distribution of macrofossil occurrences during the late glacial 12 and 9 ka indicate that migration lag of boreal species did not occur at regional to subcontinental scales and that pollen assemblages lacking modern analogs resulted from climate gradients lacking modern analogs early holocene 9 and 6 ka macrofossil maps show rapid northward expansion of tree species ranges into deglaciated regions the data also show modest contractions of northern range limits of temperate species and expansions of southern range limits of boreal species in response to cooling trends during the late holocene 3 and 0 ka comparison of modern macrofossil maps of nine of these taxa with corresponding range maps confirm that the macrofossils record the geographic ranges accurately comparison of the modern macrofossil maps with maps of tree growing stock volume shows that for some taxa abies tsuga macrofossil occurrences were most frequent in regions of maximum tree abundance comparison of modern isopoll maps with the modern range and growing stock volume maps indicate that in contrast to the macrofossil data the pollen data provide poorer resolution of range limits for most taxa but better indications of abundance maxima and minima within the ranges

linking bedrock discontinuities to glacial quarrying quarrying and abrasion are the two principal processes responsible for glacial erosion of bedrock the morphologies of glacier hard beds depend on the relative effectiveness of these two processes as abrasion tends to smooth bedrock surfaces and quarrying tends to roughen them here we analyze concentrations of bedrock discontinuities in the tsanfleuron forefield switzerland to help determine the geologic conditions that favor glacial quarrying over abrasion aerial discontinuity concentrations are measured from scaled drone based photos where fractures and bedding planes in the bedrock are manually mapped a tukey honest significant difference test indicates that aerial concentration of bed normal bedrock discontinuities is not significantly different between quarried and non quarried areas of the forefield thus an alternative explanation is needed to account for the spatial variability of quarried areas to investigate the role that bed parallel discontinuities might play in quarrying we use a finite element model to simulate bed normal fracture propagation within a stepped bed with different step heights results indicate that higher steps larger spacing of bed parallel discontinuities propagate bed normal fractures more readily than smaller steps thus the spacing of bed parallel discontinuities could exert strong control on quarrying by determining the rate that blocks can be loosened from the host rock

quantification of nitrate storage in the vadose unsaturated zone a missing component of terrestrial n budgets national terrestrial nitrogen budgets for many developed countries have been calculated as part of the management of impacts of n on the environment but these rarely represent the subsurface explicitly using estimates of vadose zone travel time and agricultural nitrate loading we quantify for the first time the total mass of nitrate contained in the vadose zone of aquifers in england and wales this mass peaked in 2008 at 1400 kt n 800 to 1700 kt n from sensitivity analyses which is approximately 2 5 to 6 times greater than saturated zone estimates for this period and indicates that the subsurface is an important store of reactive nitrogen about 70 of the nitrate mass is estimated to be in the chalk with the remainder split between the permo triassic sandstones the jurassic oolitic limestones and minor aquifers current controls on fertiliser application mean that the vadose zone is now a nitrate source and in 2015 we estimate the net flux from the unsaturated zone to groundwater to be 72 kt n annum the mass of nitrate in the vadose zone should be included in future terrestrial nitrogen budgets at national and global scales to improve ecosystem management this article is protected by copyright all rights reserved

impacts of glacial interglacial cycles on continental rock weathering inferred using sr ca and 87sr 86sr ratios in michigan watersheds abstract michigan soils have developed on thick glacial drift deposits that include different proportions of ground granite and gneiss from the canadian shield region with radiogenic sr and carbonate sedimentary rocks from within the michigan basin with non radiogenic sr this study of the cheboygan huron and kalamazoo watersheds shows how sr isotope and sr ca ratios in soil waters ground waters and soils reflect relative weathering intensities of the dominant minerals in michigan soils including carbonates from the michigan basin and amphibole plagioclase and k feldspar derived from the canadian shield soil water 87 sr 86 sr ratios evolve quickly to the carbonate weathering end member 0 709 0 711 once a calcite and dolomite layer is reached at depth 100 200 cm in the huron and the kalamazoo watersheds dissolution of plagioclase and amphibole controls shallow soil water 87 sr 86 sr ratios 0 711 0 713 with minor contributions from k feldspar weathering in contrast soils in the previously studied cheboygan watershed are completely depleted in carbonate minerals and contain little plagioclase and amphibole in the top 300 cm of the profile as a result soil waters in this watershed are ionically dilute with high 87 sr 86 sr ratios 0 72 and 0 74 dominantly contributed by k feldspar dissolution subsequent dissolution of plagioclase and amphibole at greater depths sharply increases soil water and ground water mg 2 ca 2 and sr 2 concentrations and lowers the sr isotopic ratios to 0 709 for the cheboygan watershed similarly along hydrologic flow paths soil water sr ca ratios move from the silicate end member defined by amphibole and plagioclase towards the carbonate end member the sr isotopic compositions and sr ca ratios of soil waters thus reveal the types directions and extent of chemical weathering processes in michigan soils augmenting information from previous soil water chemistry and soil mineralogy studies this work also highlights the two fold impacts of glacial interglacial cycles on the riverine and oceanic sr isotopes due to the great extent of continental glaciation paleozoic carbonate minerals from the michigan basin were redistributed widely within the interior of the north american continent leading to elevated sr fluxes with lower sr isotopic ratios in natural waters after glacial retreat the glacial ice also ground up the ancient precambrian canadian shield accelerating mineral weathering rates and releasing highly radiogenic sr from k feldspar

lakes of the huron basin their record of runoff from the laurentide ice sheet the 189 000 km2 hur n basin is central in the catchment area f the present q s r lanrentian great lakes that now drain via the st lawrence river to the north atlantic ocean during deglaciation from 21 7 5 ka bp and owing to the interactions of ice margin positions crustal rebound and regional topography this basin was much more widely connected hydrologi cally draining by various routes to the gulf of mexico and atlantic ocean and receiving over flows from lakes impounded north and west of the great lakes hudson bay drainage divide early ice marginal lakes formed by impoundment between the laurentide ice sheet and the southern margin of the basin during recessions to interstadial positions at 15 5 and 13 2 ka be in i each of these recessions lake drainage was initially southward to the mississippi river and gulf of mexico in the first recession drainage subsequently switched eastward along the ice margin to the north atlantic ocean in the second recession drainage continued southward through the michigan basin and later eastward via the ontario basin and mohawk river valley to the north atlantic ocean during the final retreat of ice in the huron basin from 13 to 10 ka be proglacial lake drainage switched twice from the michigan basin and the mississippi river system to the i north atlantic via the ontario basin and mohawk river valley finally diverting to the champlain sea in the st lawrence river valley at about 11 6 ka be new seismo and litbo stratigraphic information with ostracode data from the offshore lacustrine sediments were integrated with the traditional data of shorelines uplift histories of outlets and radio carbon dated shallow water evidence of transgressions and regressions to reconstruct the water level history and paleolimnological record for the northern huron basin for the 11 7 ka bp period negative excursions in the 8 80 isotopic composition of ostracodes and bivalves in southern lake michigan southwestern lake huron and eastern lake erie indicate an influx of water from ice marginal lake agassiz in central north america about 11 ka be a major decline in water levels of the huron basin after 10 5 ka bp followed the high level main lake algonquin phase as ice receded and drainage was established through the north bay area to ottawa river valley during the subsequent mattawa stanley phase the lake level history was dominated by fluctuations of tens of meters highstands of the earliest oscillations whose origin is not clear might be related to some of the well known post algonquin shorelines after 9 6 ka be it is suggested that large inflows from lake agassiz and hydraulic damming in downstream outlets were the likely cause of the lake mattawa highstands a lowstand at 9 3 9 1 ka bp occurred when these inflows were diverted or impeded by an ice advance in the nipigon basin area while undiluted meltwater continued to enter the huron basin assemblages and isotopic composition of the ostracode fauna indicate very dilute meltwater during the lowstands as late as 7 5 ka be and precipitation runoff with comparatively higher dissolved solids dur ing the highstands we speculate that the water composition of the lake mattawa highstands was dom inated by the agassiz inflows by that time much of lake agassiz was remote from ice marginal envi ronments and the inflows were drawn from surface water of the southern sector of the lake which was largely supplied by runoff and dissolved solids from the exposed land area of western canada major inflows apparently ended about 8 ka be but northern proglacial lakes apparently continued as melt water persisted in the huron basin until about 7 5 ka bp the cessation of major inflows initiated the final lowstand in the huron basin and the present hydrological regime of local runoff

spatial variability in the water content and rheology of temperate glaciers glacier de tsanfleuron switzerland the physical properties of eight ice coresrecovered from along a flowline at glacier detsanfleuron switzerland have led to the identification of three distinctive internal zones we use variations in the bulk ionic chemistry of these zonesto approximate their relative liquid water concentrations and ice viscosities results suggest that relative bulk water concentration and ice softness vary by over an order of magnitude between the zones implications of this variability for predictions of the glacier s response to climate change are evaluated by incorporating these relative softnesses into a multi layered two dimensional model of ice flow model output is compared with that from an identical model constrainedwith a spatially uniform ice viscosity under advance and retreatmodel ling scenarios the former scenario isusedto tuneviscosity by growinga glacier to itspres ent long section geometry resulting in best fit ice hardness values of 1 2a 1 bar 3 for the englacial ice in the multi layered model and 7 0a 1 bar 3 for all of the ice in the single layered model both result in close approximations to the current long profile yielding rmsdeviationsbetween measuredandmodelledicethicknessesthatare 55m in contrast a single layered model constrained with a hardness of 1 2a 1 bar 3 overestimates the current measured long section area by 31 having a rms ice thickness error of 15 0m under the retreat modelling scenario which gauges the response of the glacier to an imposed 75m rise in equilibrium line altitude ela the multi layered model predicts a long section area reduction of 78 this contrasts with a reduction of 64 for the single layered model hardness 7 0a 1 bar 3 and 85 forthe single layered model hardness 1 2a 1 bar 3

numerical simulation of three dimensional velocity fields in pressurized and non pressurized nye channels channels incised into bedrock or nye channels often form an important component of subglacial drainage at temperate glaciers and their structure exerts control over patterns and rates of a channel erosion b water flow velocity and c water pressure the latter in turn exerts a strong control over basal traction and thus ice dynamics in order to investigate these controls it is necessary to quantify detailed flow processes in subglacial nye channels however it is effectively impossible to acquire such measurements from fully pressurized subglacial channels to solve this problem we here apply a three dimensional finite volume solution of the reynolds averaged navier stokes rans equations with a one equation mixing length turbulence closure to simulate flow in a 3 m long section of an active nye channel located in the immediate foreground of glacier de tsanfleuron switzerland numerical model output permits high resolution visualization of water flow through the channel reach and enables evaluation of the experimental manipulation of the pressure field adopted across the overlying ice lid this yields an increased theoretical understanding of the hydraulic behaviour of nye channels and in the future of their effect on glacier drainage geomorphology and ice dynamics

a mechanism of basal ice layer formation involving major ice fabric changes an opportunity to analyse the mechanism for the formation of a basal ice layer was provided by glacier de tsanfleuron in the swiss alps this glacier has some lateral subglacial cavities in which a basal ice layer forms on the bedrock floor and is subsequently incorporated at the base of the glacier petrographic and crystallographic analyses of the different types of ice have provided a means of investigating the successive stages of the process these analyses show major structural changes which provide field confirmation of the deformation mechanisms studied by several authors in laboratory experiments

characterization of subglacial landscapes by a two parameter roughness index previous studies using fourier transformation ft methods to analyze subglacial roughness have shown promise for distinguishing between different types of subglacial landscape from raw subglacial elevation data we derive a two parameter ft roughness index whereis based on the ft of elevation as previously considered in isolation andis based on both the ft of elevation and the ft of bed slope profile in this way we take account of both vertical and horizontal irregularities in subglacial surfaces we demonstrate the statistical veracity of using to consider roughness in terms of obstacle amplitudes and spacing and consider the use of in studies of ice dynamics and subglacial geomorphological interpretation we show that can be linked to basal sliding rates on the metre scale and can be used to differentiate further than single parameter roughness indices between different classes of subglacial landscape in particular between erosional and depositional settings

no 3 sources and circulation in the shallow vadose zone in the edge of dunhuang mingsha sand dunes in an extremely arid area of northwestern china abstract the unsaturated zone is a significant feature of the nitrogen cycle in arid areas connecting atmospheric precipitation and surface water to groundwater to measure no3 cl and nh4 concentrations precipitation samples 39 9592 n 94 3302 e were collected at the western edge of the mingsha sand dunes soil profiles were taken along the northern edge of the dunes to determine no3 and cl concentrations and 18o no3 and 15n no3 levels in soil water the mno3 cl mnh4 cl and nh4 n no3 n values in precipitation showed seasonal variations reflecting the influence of distinct anthropogenic sources the 15n no3 and 18o no3 of the lt profile ranged from 2 38 to 7 84 and 14 72 to 57 5 respectively and that of gc profile ranged from 1 36 to 2 35 and 5 07 to 21 3 respectively these results suggest that the main sources of vadose zone nitrogen in the profiles are no3 fertilizer and nh4 in fertilizer and precipitation all of which are influenced by agricultural sources obvious nitrification and the mixing of different sources were noted but the profiles showed no evidence of denitrification the findings of this study show that migration of no3 and cl in the desert vadose zone is influenced by heavy rainfall events vegetation and evaporation heavy rainfall events promote leaching of no3 and cl into the deep vadose zone while evaporation at the surface prevents leaching and vegetation hinders the downward migration of no3 and cl migration of no3 n and cl in sand dunes is affected by the solute gradient concentration difference of the soil water moving from areas of higher concentrations to lower concentration the no3 n and cl accumulations were 1 02 kg n ha 1 and 3 45 kg ha 1 respectively throughout autumn these were larger than could be attributed to the input flux of atmospheric precipitation especially in the near surface soil layer likely illustrating the influence of atmospheric dry deposition

a 2000 year geochemical record of palaeoclimate and hydrology derived from dune sand moisture abstract chloride concentrations in the interstitial water of the unsaturated zone in dune sands of the badain jaran desert northwestern china have been used to examine the recharge history over the last 2000 years using a chloride mass balance approach the estimated 0 9 mm yr 1 recharge represents approximately 1 of annual precipitation in the western part of the desert and this low but finite infiltration allows preservation of this record the 30 m deep profile yields a total archive equivalent to 2050 years with well preserved climatic events of 30 50 years duration periods of relatively dry years occurred during ad 100 250 350 600 870 1220 1330 1450 1570 1720 1780s and 1900 1970 the unsaturated zone profile provides a robust climate record with a resolution of 20 yr comparable favourably to tree ring and ice core records in this region

holocene lake effect precipitation in northern michigan holocene sediments from nelson lake on michigan s eastern upper peninsula provide isotopic pollen and charcoal evidence for a two step sequence of changes in moisture source and increased lake effect precipitation during the late holocene between 8000 and 5300 cal yr b p a warm dry climate and zonal atmospheric circulation produced enriched stable oxygen and carbon isotopic values in combination with high percentages of pine pollen and sustained influx of charcoal particles after 5300 cal yr b p decreasing isotopic values in marl and increasing pollen percentages of mesic hardwoods and northern white cedar indicate increased meridional air flow and precipitation from cold winter storms generated in alberta canada after 3000 cal yr b p abrupt declines in values of 13c and 18o and increased pollen representation of hemlock american beech spruce and aquatic plants indicate paludification from increased lake effect snowfall the moisture was derived from the great lakes and transported by alberta cyclonic storms that were steered across lakes superior and michigan by a southward shift in the modal winter position of the polar jet stream

sub temperate basal sliding d apres des observations de glissement a des temperatures inferieures a la temperature de fusion on explique le mecanisme en incorporant un frottement solide a la loi de glissement

nitrogen isotope studies of nitrate contamination of the thick vadose zones in the wastewater irrigated area the objective of this study was to investigate natural abundance and the distribution of nitrogen isotopic compositions to assess denitrification in two 30 m thick vadose zones beneath the different land uses in the wastewater irrigated area located in southern shijiazhuang china sediment samples were collected from cores of boreholes drilled in the vegetable growth plot and the wastewater irrigated farmland for analyses of nitrogen isotopes physical and chemical properties respectively the profile of borehole a drilled in the vegetable growth plot only applied animal wastes had lower 15n values of mean 7 5 in the upper vadose zone but higher values of mean 10 9 in the lower vadose zone 15n values in each part varied little with depth indicating no or little denitrification occurred in the deep vadose zone below the soil zone the profile of borehole b drilled in the wastewater irrigated farmland had low 15n values of mean 5 7 below the soil zone and little variations of 15n values with depth indicating no or little denitrification occurred in the deep vadose zone below the soil zone this was also verified by consistent variations of no3 and so42 contents with cl contents our results suggested most of leachable nitrate from the soil zone was hardly subjected to biological attenuation into groundwater

spatial distribution of chloride and nitrate within an unsaturated dune sand of a cold arid desert implications for paleoenvironmental records abstract based on chloride mass balance approach we used two tracers cl and no 3 to study the interstitial water in four profiles of an unsaturated dune sand the aim was to reconstruct the recharge history and use this to infer the long term related climate changes and vegetation transitions in a cold arid desert region of northwestern china the estimated recharge rate of 0 21 to 0 59 mm year 1 represented approximately 0 2 to 0 7 of the annual precipitation in the western badain jaran desert the orientation of a megadune s slopes appeared to greatly affect recharge variability below the near surface peaks the total cumulative no 3 n inventories ranged from 61 to 121 kg ha 1 the near surface peaks in no 3 n with larger no 3 n cl molar ratios reflected active modern n fixation by cyanobacteria and the nitrate enrichment deeper in the unsaturated moisture zone indicated drier periods with less vegetation limited nitrate fixation or a combination of the two

the origin of high nitrate ground waters in the australian arid zone abstract nitrate concentrations beyond the drinking water limit of 10 mg1 1 no3 n are common in australian arid zone ground waters and are often associated with otherwise potable waters in some aquifers nitrate n concentrations of up to 80 mg1 1 have been found and this is a severe constraint on water supply development for small settlements water bore data indicate a correlation of high nitrate ground waters with shallow unconfined aquifers aguifer hydrochemistry indicats that these ground waters were emplaced by episodic holocene recharge events in an otherwise arid climate regime nitrate has been flushed through the unsaturated zone which apparently lacks denitrification activity the nitrate originates by near surface biological fixation and contributing organisms include cyanobacteria in soil crusts and bacteria in termite mounds with the highest soil nitrate concentrations found in the outer skin of termite mounds bacteria associated with the termites appear to fix nitrogen which eventually appears in an inorganic form principally as ammonia nitrate is produced by bacterial oxidation of the ammonia and is leached to the outside of the termite mound by capillary action diffuse recharge from extreme rainfall events then flushes this nitrate to the water table

subglacial roughness of the former barents sea ice sheet 1 the roughness of a glacier bed has high importance for the estimation of the sliding velocity and can also provide valuable insights into the dynamics and history of ice sheets depending on scale measurement of basal properties in present day ice sheets is restricted to ground penetrating radar and seismics with surveys retrieving relatively coarse data sets deglaciated areas like the barents sea can be surveyed by shipborne 2 d and 3 d seismics and multibeam sonar and provide the possibility of studying the basal roughness of former ice sheets and ice streams with high resolution here for the first time we quantify the subglacial roughness of the former barents sea ice sheet by estimating the spectral roughness of the basal topography we also make deductions about the past flow directions by investigating how the roughness varies along a 2 d line as the orientation of the line changes lastly we investigate how the estimated basal roughness is affected by the resolution of the basal topography data set by comparing the spectral roughness along a cross section using various sampling intervals we find that the roughness typically varies on a similar scale as for other previously marine inundated areas in west antarctica with subglacial troughs having very low roughness consistent with fast ice flow and high rates of basal erosion the resolution of the data set seems to be of minor importance when comparing roughness indices calculated with a fixed profile length a strong dependence on track orientation is shown for all wavelengths with profiles having higher roughness across former flow directions than along them

quantifying bed roughness beneath contemporary and palaeo ice streams bed roughness is an important control on ice stream location and dynamics the majority of previous bed roughness studies have been based on data derived from radio echo sounding res transects across antarctica and greenland however the wide spacing of res transects means that the links between roughness and flow are poorly constrained here we use digital terrain model dtm bathymetry data from a well preserved palaeo ice stream to investigate basal controls on the behaviour of contemporary ice streams artificial transects were set up across the minch palaeo ice stream nw scotland to mimic res flight lines over institute and moller ice streams antarctica we then explored how different data resolution transect orientation and spacing and different methods impact upon roughness measurements our results show that fast palaeo ice flow can occur over a rough hard bed not just a smooth soft bed which much previous work has suggested smooth areas of the bed occur over both bedrock and sediment covered regions similar trends in bed roughness values were found using fast fourier transform analysis and standard deviation methods smoothing of bed roughness results can hide important details we propose that the typical spacing of res transects is too wide to capture different landform assemblages and that transect orientation influences bed roughness measurements in both contemporary and palaeo ice stream setting

subglacial carbonate deposition an isotopic study of a present day case abstract different types of calcite deposits may be formed in the subglacial environment patchy coatings on polished and striated bedrock pavements occur on outcrops recently exposed by retreating temperature glaciers coated pebbles and thin limestone crusts in fissures are present in recent basal till exposures freezing of meltwater is the main process susceptible to explain most of these carbonate deposits partial freezing is accompanied by a rejection of ions from the growing ice and a concentration increase in the residual water eventually until saturation is reached glacier sliding over a protuberance by pressure melting on the stoss side and refreezing on the lee side is likely to be responsible for subglacial carbonate deposition a fixed bedrock protuberance will give rise to fluted and furrowed coatings on its lee side a mobile protuberance like a pebble at the ice bedrock interface because it is susceptible to rotate while in traction will have a coating on most of its surface a present day case in the swiss alps is studied by a comparison of the isotopic composition of calcite deposits ice and meltwater from the glacier this study indicates that melting of the basal ice layer not of glacier ice is at the origin of the initial water giving rise to the precipitate since the basal ice layer is formed in the marginal zone of the glacier subglacial carbonate deposition is a marginal feature in this case

drainage through subglacial water sheets 1 subglacial drainage plays an important role in controlling coupling between glacial ice and underlying bed here we study the flow of water in thin macroporous sheets between ice and bed previous work shows that small perturbations in depth of a nearly parallel sided water film grow unstably because these areas have enhanced viscous dissipation that leads to enhanced melting of an ice roof we argue that in the presence of bed protrusions bridging a water sheet downward motion of the ice roof can stabilize this sheet stability results when the rate of roof closure increases faster with water depth than the rate of viscous dissipation we therefore modify existing theory to include protrusions that partially support the overlying glacier differences in the pressure on protrusions relative to water pressure drive roof closure the mechanisms of both regelation and creep normal to the bed close the overlying ice roof and decrease the ice bed gap in order to account for multiple protrusion sizes along the bed for instance resulting from an assortment of various sized sediment grains we incorporate a method of partitioning overburden pressure among different protrusion size classes and the water sheet partitioning is dependent on the amount of ice protrusion contact and therefore water depth this method allows prediction of roof closure rates we then investigate stable steady sheet configurations for reasonable parameter choices and find that these steady states can occur for modest water depths at very low effective pressures as is appropriate for ice streams moreover we find that multiple steady sheet thicknesses exist raising the possibility of switches between low and high hydraulic conductivity regimes for the subglacial water system

spectral roughness of glaciated bedrock geomorphic surfaces implications for glacier sliding a microroughness meter mrm was used to measure the high frequency roughness of a number of geomorphic surfaces in the forefield of glacier de tsanfleuron switzerland resulting spectral power densities are added to low frequency spectra measured by electro optical distance meter edm to generate composite roughness spectra that include almost 5 orders of magnitude of roughness in the frequency domain these are used to define two roughness indices a general index of bed roughness is defined as the integral of the raw spectral power densities and a sliding related index of bed roughness is defined as the integral of the spectral power densities weighted to account for the optimum dependence of glacier sliding speed on hummock wavelength results indicate that mrm measured geomorphic components vary in roughness by 3 orders of magnitude principally depending on the surface microenvironment measured and profile orientation relative to the direction of former ice flow both mrm and edm measured roughnesses are lower parallel to the direction of former ice flow than perpendicular to it composite roughness spectra consequently indicate that the glacier bed is smoothed in the direction of former ice flow at all horizontal scales from 1 mm to 40 m typically resulting in an order of magnitude decrease in sliding related roughness relative to that measured perpendicular to ice flow comparison of data from two survey sites located adjacent to and 1 2 km from the current glacier margin indicates that postglacial subaerial weathering homogenizes bedrock roughness in particular reducing high frequency flow orthogonal roughness accounting for the effect of 28 ice bedrock separation over one of the profiles reduces net sliding dependent roughness by between 27 and 43 depending on the transition wave number used

quaternary evolution of glaciated gneiss terrains pre glacial weathering vs glacial erosion vast areas previously covered by pleistocene ice sheets consist of rugged bedrock dominated terrain of innumerable knolls and lake filled rock basins the cnoc and lochan landscape or landscape of areal scour these landscapes typically form on gneissose or granitic lithologies and are interpreted 1 either to be the result of strong and widespread glacial erosion over numerous glacial cycles or 2 formed by stripping of a saprolitic weathering mantle from an older deeply weathered landscape we analyse bedrock structure erosional landforms and weathering remnants and within the cnoc and lochan gneiss terrain of a rough peneplain in nw scotland and compare this with a geomorphologically similar gneiss terrain in a non glacial arid setting namaqualand south africa we find that the topography of the gneiss landscapes in nw scotland and namaqualand closely follows the old bedrock saprolite contact weathering front the roughness of the weathering front is caused by deep fracture zones providing a highly irregular surface area for weathering to proceed the weathering front represents a significant change in bedrock physical properties glacial erosion and aeolian erosion in namaqualand is an efficient way of stripping saprolite but is far less effective in eroding hard unweathered bedrock significant glacial erosion of hard gneiss probably only occurs beneath palaeo ice streams we conclude that the rough topography of glaciated cnoc and lochan gneiss terrains is formed by a multistage process 1 long term pre glacial chemical weathering forming deep saprolite with an irregular weathering front 2 stripping of weak saprolite by glacial erosion during the first glaciation s resulting in a rough land surface broadly conforming to the pre existing weathering front etch surface 3 further modification of exposed hard bedrock by glacial erosion in most areas glacial erosion is limited but can be significant beneath palaeo ice stream the roughness of glaciated gneiss terrains is crucial for modelling of the glacial dynamics of present day ice sheets this roughness is shown here to depend on the intensity of pre glacial weathering as well as glacial erosion during successive glaciations