reply to comments by s r dickman on fortnightly earth rotation ocean tides and mantle anelasticity dickman argues that our model of the mf ocean tide is unrealistic and that this invalidates conclusions regarding mantle anelasticity his evidence is based on comparison with his own ocean modelling experiments and on his physical intuition regarding near equilibrium tides that evidence is unconvincing simple physical arguments alone are enough to rebut his main points furthermore we test here his suggestion of increasing bottom friction dissipation by a factor of 100 over our preferred solution and we show that this results in unacceptable polar motion and poor agreement with independent tide gauge data in contrast tests against independent data lend support to the realism of our mf tide model and give confidence that our estimates of mantle anelasticity are reliable within stated error bounds

relict non glacial surfaces in formerly glaciated landscapes abstract relict non glacial surfaces occur within many formerly glaciated landscapes and contain important information on past surface processes and long term landscape evolution relict non glacial surfaces are distinguishable from glacial surfaces by large scale morphologies including rounded summits fluvial valleys and cryoplanation terraces and pediments and the presence of tors blockfields and or saprolites preservation during glaciation occurs either through coverage by non erosive cold based ice or as nunataks although surface morphologies and denudation rates indicate a continuous non glacial surface history since preglacial times relict non glacial surfaces are dynamic features that have evolved during the quaternary depending on spatial variables such as lithology slope regolith depth and the abundance of fine matrix and water some surfaces are denuding very slowly while others display more rapid denudation high spatial variability in denudation rates results in changing surface morphologies over time denudation rates also display high temporal variability with much surface evolution having perhaps occurred soon after the initial onset of glaciation or during paraglacial phases while some parts of non glacial landscapes are currently active others may be largely inactive relicts of past higher energy regimes although non glacial surfaces are dynamic much remains to be determined regarding surface denudation rates and the magnitude of morphological changes over time

residual circulations due to bottom roughness variability under tidal flows abstract tidal flows over irregular bathymetry are known to produce residual circulation flows due to nonlinear interaction with gradients of depth using the depth averaged vorticity equations the generation of residual vorticity and residual flows due to variation of the frictional coefficient are examined the authors find that the contribution due to bottom roughness variations can be as large as that arising from gradients of depth and velocity specific cases are considered on the northern california shelf georges bank and the u s south atlantic bight the generation of residual vorticity is a strong function of the length scales at which roughness or depth vary length scales of bottom roughness variation are commonly within the range of greatest effect e g sand patchiness cobbly outcrops etc the site specific cases show that the bottom roughness variability can generate as much residual circulation as that expected from depth variability the implication for numerical modeling studies

constraints on mantle anelasticity from geodetic observations and implications for the j2 anomaly summary we use geodetic observations of the earth to constrain anelasticity in the earth s mantle at periods between 12 hr and 18 6 yr the observations include satellite laser ranging slr measurements of 12 hr and 18 6 yr tides in the j 2 component of the gravity field spacebased observations of tidal variations in the earth s rotation rate and optical and space based measurements of the chandler wobble period and damping these geophysical signals are mostly sensitive to the lower mantle the results suggest the dissipative process could consist of a single absorption band that extends across seismic periods out at least as far as 20 yr the results also require values of the anelastic parameter q that are smaller than those required by seismic observations we interpret this as evidence that q in the lower mantle is frequency dependent the frequency dependence suggested by the geodetic observations is reasonably consistent with laboratory measurements though those measurements have only been done on rocks at upper mantle conditions after fitting and removing the 18 6 yr tide from the slr j 2 results we find that the 1998 2002 anomaly present in the original j 2 observations is no longer a singular anomaly in the j 2 residuals but becomes one of a series of maxima in a quasi decadal oscillation

identification of subannual patterns in microbial community signatures from individual sedimentary laminae using a freeze coring approach discrete biological community signatures were identified in individual sub annually deposited sedimentary laminae of anoxic lake sediments from two lakes in the minneapolis st paul minnesota u s a urban area recognizing variation in microbial communities associated with discrete millimeter scale sedimentary horizons was made possible using a freeze coring method to recover bacterial dna for amplicon itag sequencing and terminal restriction fragment length polymorphism analyses variation in 16s rrna gene composition between laminae suggests that seasonal changes in cell transport from the water column impart a residual molecular signature on subsurface communities direct comparison of frozen in situ core samples to ambient temperature sediment indicates that freeze coring methodology imposes no significant bias on dna based community fingerprints this work further supports previous observations demonstrating the efficacy of freeze coring for high resolution analysis of microbial communities but here it is applied to resolving molecular signatures derived from sedimentary laminae

the fortnightly and monthly tides resonant rossby waves or nearly equilibrium gravity waves abstract the fortnightly and monthly tides are discussed in the light of recent sea level observations and numerical modeling results within the tide gauge network of the low latitude pacific the fortnightly tide is shown to possess a large scale phase lag of roughly 10 40 degrees although the nonequilibrium part of the fortnightly tide is traditionally thought to be dominated by rossby wave dynamics it is shown via global shallow water modeling studies that this large scale phase lag is explicable in terms of remotely forced gravity waves whose origin is mainly in the arctic ocean although future observations outside the low latitude region of the pacific may eventually reveal rossby wave excitation the fortnightly tidal signal in the tide gauge network at hand appears to reveal at most only weak excitation of rossby waves compared to the phase lag due to remotely forced gravity waves the observed monthly tide appears to be only slightly closer to equilibrium than the fortnightly tide the reaso

teaching geomorphology through spreadsheet modelling abstract geomorphology like most scientific disciplines has evolved from a descriptive stage through quantification to modelling of processes and outcomes indeed high resolution modelling has been termed the third branch of science for its ability to generate high quality hypotheses testable in turn through field mapping and laboratory experimentation i teach the principles and basic applications of modelling using microcomputer spreadsheets these serve as transparent boxes in which graphical output is generated in response to numerical input and more importantly in which the modeler student can see the equations and order of steps unlike traditional black box models the technology is widely available and familiarity with it can be assumed required or taught at the undergraduate level modelling can be taught through a series of spreadsheet exercises in which students while learning topical material in a traditional sequence progress from a simple cookbook exercise through more realistic process based exercises to the level of addressing a previously unstudied research question at each step the model can be used to generate testable hypotheses i have worked with scarp evolution stream longitudinal profiles and glacier reconstructions and plan to include eolian soil development mass wasting and coastal processes in additional exercises the first year of use of this technique in a junior level geomorphology course clarified the strengths and weaknesses of the modelling approach the strengths involve students learning the capabilities and flaws of modelling a stronger understanding of causeeffect relationships and the effects of time on landforms the weaknesses involve time commitment supervision in model implementation and limitations to student ability to independently pursue openended research

a younger dryas plateau icefield in the monadhliath scotland and implications for regional palaeoclimate a record of younger dryas glaciation in scotland is well established however the role of the monadhliath a significant plateau area extending over 840 km2 in central scotland has never been investigated systematically we present the first systematic glacial geomorphological mapping across the whole region which has led to the identification of hitherto unrecorded glacial and associated landforms the spatial distribution of these landforms indicates that the last phase of glaciation in the area was that of a local plateau icefield in addition a clear morphostratigraphical signature provides a strong indication that the icefield dates to the younger dryas 12 9 11 7 ka which is supported by numerical ages in the southeast of the study area based on the geomorphological evidence and 2d glacier surface profile modelling a 280 km2 icefield is reconstructed a novel approach is introduced to quantify plateau icefield thickness for equilibrium line altitude ela and palaeoprecipitation calculations resulting in greater overall data confidence compared to traditional reconstruction methods the ela for the whole icefield is calculated to be 714 25 m whilst the elas of individual outlet glaciers range from 560 m in the west to 816 m in the east demonstrating a significant w e precipitation gradient across the region during the younger dryas these elas compare well with those calculated for younger dryas ice masses reconstructed in neighbouring regions and are in good agreement with overall precipitation patterns suggested for scotland during this time whilst the total amount of precipitation calculated from these elas is highly dependent on the method used irrespective of this the study suggests a more arid younger dryas climate in the region compared to the present day

digital surface models are not always representative of former glacier beds palaeoglaciological and geomorphological implications abstract quantitative palaeoglaciological studies that use digital surface models dsms may be subject to error because former glacier beds are not always accurately represented this is because the earth s surface may have changed significantly since deglaciation this paper evaluates some of the potential errors caused by postglacial sedimentation by comparing the results of physical palaeoglaciological reconstructions and bedform morphometric analyses in parts of scotland using both the modern land surface and interpolated former glacier beds derived from borehole data for a former terrestrial outlet glacier removal of postglacial sediments increases the modelled ice surface elevation and ice thickness by 0 7 and 5 respectively over a 27 km flow line for a former tidewater glacier the reconstructed steady state ice flux is increased by 250 when the modern land seabed surface is replaced with an interpolated former glacier bed in a classical drumlinised landscape removal of postglacial sediments affects bedform morphometrics with an increase in measured drumlin length width relief and volume the cases presented in this paper are from environments known to have experienced postglacial sedimentation they provide situational examples of the degree of error that can be introduced when the modern land surface is used to represent former glacier beds in these environments in some regions sufficient subsurface data exists over large areas to create improved topographic representations of former glacier beds these could form important inputs to the next generation of palaeo ice sheet and palaeo glacier simulations

deviation of long period tides from equilibrium kinematics and geostrophy new empirical estimates of the long period fortnightly mf tide obtained from topex poseidon t p altimeter data confirm significant basin scale deviations from equilibrium elevations in the low latitude pacific have reduced amplitude and lag those in the atlantic by 308 or more these interbasin amplitude and phase variations are robust features that are reproduced by numerical solutions of the shallow water equations even for a constant depth ocean with schematic interconnected rectangular basins a simplified analytical model for cooscillating connected basins also reproduces the principal features observed in the empirical solutions this simple model is largely kinematic zonally averaged elevations within a simple closed basin would be nearly in equilibrium with the gravitational potential except for a constant offset required to conserve mass with connected basins these offsets are mostly eliminated by interbasin mass flux because of rotation this flux occurs mostly in a narrow boundary layer across the mouth and at the western edge of each basin and geostrophic balance in this zone supports small residual offsets and phase shifts between basins the simple model predicts that this effect should decrease roughly linearly with frequency a result that is confirmed by numerical modeling and empirical t p estimates of the monthly mm tidal constituent this model also explains some aspects of the anomalous nonisostatic response of the ocean to atmospheric pressure forcing at periods of around 5 days

departures from the local inverse barometer model observed in altimeter and tide gauge data and in a global barotropic numerical model sea level data from the topex poseidon altimeter satellite and from subsets of the global tide gauge and bottom pressure recorder networks have been employed to study the worldwide distribution of departures from the simple local inverse barometer lib model from a combination of measurement techniques the lib model was found to provide a reasonable representation of the data within 5 10 outside of the tropics for timescales from several days to several weeks for most locations however several parts of the southern ocean and other higher latitude areas were seen from the altimetry to contain significant departures across the range of timescales accessible for study by the technique within the tropics the response of sea level to air pressure forcing was observed to be typically 50 of that of the lib model at timescales of several days with considerable spatial variation and to approximate the lib model more closely at timescales of several weeks a coarse grid global barotropic numerical model was found to reproduce qualitatively the global average response as a function of frequency to simulate many of the characteristics of the spatial variation of the response and to demonstrate the relative importance of air pressure and wind forcing at different timescales data sets from the permanent service for mean sea level and u k meteorological office were used to investigate lib departures at intraseasonal and longer timescales along continental coastlines and at ocean islands increasingly large departures were observed along many parts of the world coastline as timescales increased from months to seasons

late pleistocene stratigraphy and implications for deglaciation and subglacial processes of the flathead lobe of the cordilleran ice sheet flathead valley montana usa abstract the flathead lobe of the cordilleran ice sheet advanced and retreated across the flathead valley a 90 km long by 15 25 km wide basin the glacier terminated at the southern end of the flathead valley during its last glacial maximum i used geologic mapping sedimentologic study and mapping from 3300 descriptive water well logs to define the stratigraphy of glacial and post glacial deposits in the flathead valley and to infer subglacial processes and retreat rates units in the 30 200 m thick stratigraphic sequence include deep sand and gravel proglacial alluvium diamicton till locally gravelly silt and clay coarse grained subaqueous deposits at recessional moraines and glaciolacustrine deposits and surficial sand and gravel outwash and holocene stream deposits a nearly continuous till overlies alluvium and is in turn directly overlain by glaciolacustrine deposits glaciolacustrine shoreline indicators at altitudes of 940 958 m show that the flathead lobe receded as a proglacial lake expanded in that range of altitudes this lake the ancestral flathead lake was impounded behind bedrock that was downcut 60 78 m since the late pleistocene glaciolacustrine deposits are as much as 180 m thick in discontinuous troughs that locally cut through till to alluvium and bedrock the troughs are mostly 1 5 km in width 6 25 km in length sinuous in plan view and undulatory in longitudinal profile the troughs extend below the elevation of flathead lake and have been below local base level since glaciation these characteristics point to incision by meltwater hydrostatically pressurized beneath the flathead lobe in subglacial tunnel channels sand and gravel at the trough bases and part of the glaciolacustrine fill in the troughs are subglacial deposits tunnel channels that terminate at recessional moraines suggest excavation occurred sporadically during deglaciation the distribution of glaciolacustrine silts indicates that the flathead lobe retreated and the ancestral flathead lake expanded by 87 km before the lake outlet stream could downcut its dam by 500 m year 1

modelling of icecap glaciation of the northern rocky mountains of montana abstract the extent of the lastglacial icecap over the northern rocky mountains of montana has been inferred only from cursory correlation of its marginal deposits which leaves several significant unresolved controversies those controversies all involve the maximum altitude and shape of that interconnected ice mass and include 1 the source of the two medicine piedmont lobe local or cordilleran ice 2 correlation of terminal deposits of the flathead lobe late lastglacial early lastglacial or prelastglacial and 3 regional paleoclimate at last glacial maximum dominant westerlies or local easterlies theoretical reconstructions of the glacial surface along major flowlines constrained by ice marginal features nunataks and breached divides throughout the region tentatively resolve those issues the two medicine lobe was dominantly composed of northeast flowing local ice not ice of northwestern canadian cordillera origin flathead lobe deposits include lastglacial deposits both supported by and without a component from the swan valley there is evidence of only a regional westerly flow of moisture across the region in addition a proglacial lake 60 km long occupied the swan valley during the early stages of deglaciation although subject to revision from fieldwork glacial process modelling remains one of the few geological arenas in which rigorous process modelling can be used to predict the evolution of form

dynamics of the long period tides abstract the long period tides are a tool for understanding oceanic motions at low frequencies and large scales here we review observations and theory of the fortnightly monthly and pole tide constitutents observations have been plagued by low signal to noise ratios and theory by the complex lateral geometry and great sensitivity to bottom slopes a new spectral element model is used to compute the oceanic response to tidal forcing at 2 week and monthly periods the general response is that of a heavily damped q 5 system with both the energy input from the moon and the dissipation strongly localized in space the high dissipation result is probably generally applicable to all low frequency barotropic oceanic motions over much of the ocean the response has both the character of a large scale and a superposed rossby wave like character thus vindicating two apparently conflicting earlier interpretations to the extent that free waves are excited they are consistent with their being dominated by rossby and topographic rossby wave components although gravity modes are also necessarily excited to some degree in general a modal representation is not very helpful the most active regions are the southern ocean and the western and northern north atlantic these results are stable to changes in geometry topography and tide period on a global average basis the dynamical response of mm is closer to equilibrium than is mf

the last ice sheet in north west scotland reconstruction and implications recent models of the last scottish ice sheet suggest that nunataks remained above the ice surface in areas peripheral to the main centres of accumulation this proposition has been investigated on 140 mountains over an area of 10 000 km2 in nw scotland outside the limits of the later loch lomond readvance in this area there is evidence for a single high level weathering limit that separates glacially eroded terrain from higher areas of in situ frost debris this limit occurs at altitudes ranging from 425 to 450 m in the outer hebrides to 950 m on the mainland and is best developed on lithologies that resisted breakdown after ice sheet downwastage interpretation of this weathering limit as a periglacial trimline cut by the last ice sheet at its maximum thickness is supported by 1 joint depth and schmidt hammer measurements that indicate significantly more advanced rock breakdown above the weathering limit 2 a much greater representation of gibbsite a pre late devensian weathering product in the clay fraction of soils above the limit 3 cosmogenic isotope dating of the exposure ages of rock outcrops above and below the limit 4 the sharpness of the limit at some sites and its regular decline along former ice flowlines and 5 shear stress calculations based on the inferred altitude and gradient of the former ice surface reconstruction of the ice surface based on trimline evidence indicates that the mainland ice shed lay near or slightly east of the present watershed and descended northwards from 900 m to ca 550 m at the north coast independent dispersion centres fed broad ice streams that occupied major troughs on skye an ice dome 800 m deflected the northwestwards movement of mainland ice but the mountains of rum were over ridden by mainland ice up to an altitude of ca 700 m the outer hebrides supported an independent ice cap that was confluent with mainland ice in the minches extrapolation of the trimline evidence indicates that most reconstructions of ice extent are too conservative and suggests that low gradient ice streams extended across the hebridean shelf offshore wider implications of this research are 1 that blockfields and other periglacial weathering covers are not all of the same age or significance depending on the resistance of different lithologies to frost weathering 2 that the contrasting degree of glacial modification in the western and eastern highlands of scotland may reflect a former cover of predominantly warm based ice in the former and predominantly cold based ice in the latter and 3 that the approach and techniques developed in this study have potential application for constraining ice sheet models not only in areas peripheral to the main centres of ice accumulation in britain and ireland but also in other mountain areas where nunataks protruded through warm based late pleistocene ice masses

fortnightly earth rotation ocean tides and mantle anelasticity summary this study of the fortnightly mf tide comprises three main topics 1 a new determination of the fortnightly component of polar motion and length of day lod from a multidecade time series of observed space geodetic data 2 the use of the polar motion determination as one constraint in the development of a hydrodynamic ocean model of the mf tide and 3 the use of these results to place new constraints on mantle anelasticity at the mf tidal period our model of the mf ocean tide assimilates more than 14 years of altimeter data from the topex poseidon and jason 1 satellites because the mf altimetric signal to noise ratio is very small it is critical that altimeter data not be overweighted the polar motion data plus tidegauge data and independent altimeter data give useful additional information with only the polar motion putting constraints on tidal current velocities the resulting ocean tide model plus the dominant elastic body tide leaves a small residual in observed lod caused by mantle anelasticity the inferred effective tidal q of the anelastic body tide is 90 and is in line with a frequency dependence with in the range 0 2 0 3

former plateau ice fields in the godeanu mountains southern carpathians first evidence of glaciated peneplains in the carpathians abstract the existence of plateau ice fields in the southern carpathians has long been suggested due to the widespread presence of the bor scu surface in the region the bor scu surface is a peneplain consisting of flat plateaus in the elevation range of 1800 2200 m a s l it is present throughout the southern carpathians with the most typical appearance in the godeanu mountains these plateaus could have served as ice accumulation sites during the pleistocene glaciations as they were well above the steady state equilibrium line altitude ela 0 direct geomorphological evidence on the existence of plateau ice fields and thus well founded reconstructions are absent due to the lack of glacial landforms on the plateaus in order to test the existence of plateau ice fields a previous geomorphological survey and theoretical ice surface profiles based on a steady state perfectly plastic ice flow model were used based on these methods maps and three dimensional surface models of the former glaciers were created the ela 0 s of the paleoglaciers were estimated by the accumulation area ratio aar method according to our results three major ice fields on the central plateaus and several smaller ice fields on wide saddles were present in the godeanu mountains during the maximal glaciation the ice fields fed numerous surrounding valley glaciers several independent valley and cirque glaciers completely separated from the ice fields were also present further from the central mass of the mountain range the average ela 0 of the northern 1855 2 m a s l and the southern 1700 2 m a s l glaciers differed greatly we suggest that the surprisingly high average ela 0 of the northern glaciers was mostly caused by the missing lower sections of these paleoglaciers from our reconstructions due to the destroyed terminal glacial landforms however the terminal glacial landforms are quite well preserved in the southern valleys thus the average ela 0 of the southern paleoglaciers was suitable to correlate the maximal glaciation of the godeanu mountains with the maximal glaciation of the neighbouring retezat mountains

combined numerical and geomorphological reconstruction of the serra da estrela plateau icefield portugal abstract the paper focuses on reconstructing a plateau icefield surface from field geomorphological data and a physical based glacier model the results allow the analysis of the patterns of glacial erosion and the estimation of the palaeo equilibrium line altitudes ela the study area is the serra da estrela a plateau in central portugal rising to 2000 m asl the glaciated area during the last maximum of the serra da estrela glaciation lmgse was 66 km 2 the reconstruction of the topography of the icefield and valley glaciers in the lmgse is based on the schilling and hollin model it iterates along the valley longitudinal profile and is based on the gradient on valley shape indices and on yield basal shear stresses these variables influence ice thickness and therefore also the slope of the ice surface allowing for its reconstruction the key variable is basal yield shear stress and its value was included in the model manually starting from the points of maximum extent of the valley glaciers and following a range known to occur in contemporary conditions the input values are validated by matching the resulting ice surface to geomorphological features where these are absent a constant value of 100 kpa was used the icefield was reconstructed from a radiating set of long sections along which ice thicknesses were calculated a dem of the ice surface was constructed allowing the estimation of the hypsometric curves of the distinct glacier catchments and the calculation of the palaeo elas the results show a regional ela at 1650 m asl with spatial variations across the icefield reflecting mainly the effect of eastward snow drift the lmgse glaciers were very sensitive to minor climatic changes especially due to the large area of the plateau icefield and to the positioning of the elas close to or in the flat part of the hypsometric curve the model of the ice surface is of significant value for the analysis of the patterns of glacial erosion at the landscape level in the serra da estrela most of the glacial erosion occurred near the plateau margins and in valley heads where glacier surface slope was steeper allowing for a faster ice flow and where ice flow concentrated strong glacier erosion in the zezere valley is linked to the tectonic setting but also to the confluence of glaciers and to the overfeeding of snow from the plateau

glaciers and climate in pacific far ne russia during the last glacial maximum a combined geomorphological physical model approach is used to generate three dimensional reconstructions of glaciers in pacific far ne russia during the global last glacial maximum glgm the horizontal dimensions of these ice masses are delineated by moraines their surface elevations are estimated using an iterative flowline model and temporal constraints upon their margins are derived from published age estimates the equilibrium line altitudes elas of these ice masses are estimated and glgm climate is reconstructed using a simple degree day melt model the results indicate that during the glgm ice masses occupying the pekulney kankaren and sredinny mountains of pacific far ne russia were of valley glacier and ice field type these glaciers were between 7 and 80 km in length and were considerably less extensive than during pre lgm phases of advance glgm ice masses in these regions had elas of between 575 22 m and 1035 41 m above sea level corresponding to an ela depression of 350 740 m relative to present data indicate that in the pekulney mountains this ela depression occurred because of a 6 48c reduction in mean july temperature and 200 mm a 1 reduction in precipitation relative to present thus reconstructions support a restricted view of glgm glaciation in pacific far ne russia and indicate that the region s aridity precluded the development of large continental ice sheets copyright 2011 john wiley sons ltd

surface form of the southern laurentide ice sheet and its implications to ice sheet dynamics reconstructions of the ice surface morphology of several lobes of the southern laurentide ice sheet reinforce previous arguments that this sector of the ice sheet was thin and low sloping driving stresses estimated from the geometry of the reconstructed ice surfaces are 0 7 4 3 kpa for the 14 ka des moines lobe 0 9 1 2 kpa for the 14 ka james lobe 0 9 1 7 kpa for the 18 20 ka lake michigan lobe 1 8 2 9 kpa for the 15 18 ka chippewa sublobe and 17 22 kpa for the 15 18 ka green bay lobe previous estimates of rates of ice margin advance 450 2 000 m yr indicate moderate to fast ice velocities for the ice lobes reconstructed driving stresses and velocity estimates of the des moines james and lake michigan lobes are analogous to the distal ends ice plains of low sloping 0 4 x 10 3 but fast moving 500 m yr west antarctic ice streams whose dynamics have been attributed to sliding and or subglacial sediment deformation by pervasive shear these reconstructions support recent models of the laurentide ice sheet which include movement by sliding or by subglacial sediment deformation along its southern western and northwestern sectors evidence for either mechanism should be represented in the sedimentologic and geomorphic records thin ice in these regions indicates that the laurentide ice sheet contained less ice volume and represented less of an orographic obstacle to atmospheric circulation than has been considered in models of the ice sheet on a rigid bed with steep profiles

using the surface profiles of modern ice masses to inform palaeo glacier reconstructions abstract morphometric study of modern ice masses is useful because many reconstructions of glaciers traditionally draw on their shape for guidance here we analyse data derived from the surface profiles of 200 modern ice masses valley glaciers icefields ice caps and ice sheets with length scales from 100 to 103 km from different parts of the world four profile attributes are investigated relief span and two parameters c and c that result from using nye s 1952 theoretical parabola as a profile descriptor c and c respectively measure each profile s aspect ratio and steepness and are found to decrease in size and variability with span this dependence quantifies the competing influences of unconstrained spreading behaviour of ice flow and bed topography on the profile shape of ice masses which becomes more parabolic as span increases with c and c tending to low values of 2 5 3 3 m1 2 the same data reveal coherent minimum bounds in c and c for modern ice masses that we develop into two new methods of palaeo glacier reconstruction in the first method glacial limits are known from moraines and the bounds are used to constrain the lowest palaeo ice surface consistent with modern profiles we give an example of applying this method over a three dimensional glacial landscape in kamchatka in the second method we test the plausibility of existing reconstructions by comparing their c and c against the modern minimum bounds of the 86 published palaeo ice masses that we put to this test 88 are found to be plausible the search for other morphometric constraints will help us formalise glacier reconstructions and reduce their uncertainty and subjectiveness

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation

quantifying climate and glacier mass balance in north norway during the younger dryas abstract oksfjordjokelen is located at 70 n on the troms finnmark border in north norway during the younger dryas it was decoupled from and sat just beyond the margin of the scandinavian ice sheet at this time the major fjords in troms and finnmark were ice free with outlet glaciers from the icefield filling a number of smaller side valleys only one outlet from the icefield sorfjorddalen is temporally well constrained by 14 c dating and association with the main shoreline associated with a period of minimal crustal rebound dated to the younger dryas sorfjorddalen is reconstructed using a valley centre line iterative model and assuming a no slip basal boundary condition this assumption of cold based ice is supported by the geomorphological evidence of angular bouldery fronto lateral moraines formed during the younger dryas the equilibrium line altitude for the sorfjorddalen is calculated using both the balance ratio and accumulation area ratio methods and this is used to constrain the snout positions generally to mapped moraines of the other outlets this approach assumes similarity of mass balance gradients and geometries of the outlet glaciers which is supported by present day symmetry of the icefield this method is extremely useful in such environments where dateable material is often difficult if not impossible to find some margins terminated in deep water where bathymetry was lacking making calving quantification problematic with subsequent impacts on equilibrium line altitudes poorly constrained these deep water terminating snouts were discounted from subsequent palaeo climate reconstructions an empirical equilibrium line altitude temperature precipitation relationship was used to define limits of climate change required to sustain the reconstructed icefield palaeo precipitation estimates were refined using a palaeo temperature estimate for the younger dryas from andoya calculations of ice flux through the equilibrium line altitude were used to further constrain the mass balance characteristics of the reconstructed icefield and these suggest similarities with ice masses found in the northern nordaustlandet regions of svalbard