dynamics of a turbulent buoyant plume in a stratified fluid an idealized model of subglacial discharge in greenland fjords abstractthis study reports the results of large eddy simulations of an axisymmetric turbulent buoyant plume in a stratified fluid the configuration used is an idealised model of the plume generated by a subglacial discharge at the base of a tidewater glacier with an ambient stratification typical of greenland fjords the plume is discharged from a round source of various diameters and characteristic stratifications for summer and winter are considered the classical theory for the integral parameters of a turbulent plume in a homogeneous fluid gives accurate predictions in the weakly stratified lower layer up to the pycnocline and the plume dynamics are not sensitive to changes in the source diameter in winter when the stratification is similar to an idealised two layers case turbulent entrainment and generation of internal waves by the plume top are in agreement with the theoretical and numerical results obtained for turbulent jets in a two layer stratification in summer instead the stratification

subaqueous melting of store glacier west greenland from three dimensional high resolution numerical modeling and ocean observations we present three dimensional high resolution simulations of ice melting at the calving face of store glacier a tidewater glacier in west greenland using the massachusetts institute of technology general circulation model we compare the simulated ice melt with an estimate derived from oceanographic data the simulations show turbulent upwelling and spreading of the freshwater laden plume along the ice face and the vigorous melting of ice at rates of meters per day the simulated august 2010 melt rate of 2 0 0 3 m d is within uncertainties of the melt rate of 3 0 1 0 m d calculated from oceanographic data melting is greatest at depth above the subglacial channels causing glacier undercutting melt rates increase proportionally to thermal forcing raised to the power of 1 2 1 6 and to subglacial water flux raised to the power of 0 5 0 9 therefore in a warmer climate store glacier melting by ocean may increase from both increased ocean temperature and subglacial discharge key points simulated melt agrees with estimates from a hydrographic survey of the glacier with more runoff glaciers will melt faster at constant ocean temperature 2013 american geophysical union all rights reserved

spreading of greenland meltwaters in the ocean revealed by noble gases we present the first noble gas observations in a proglacial fjord in greenland providing an unprecedented view of surface and submarine melt pathways into the ocean using optimum multiparameter analysis noble gas concentrations remove large uncertainties inherent in previous studies of meltwater in greenland fjords we find glacially modified waters with submarine melt concentrations up to 0 66 0 09 and runoff 3 9 0 29 radiogenic enrichment of helium enables identification of ice sheet near bed melt 0 48 0 08 we identify distinct regions of meltwater export reflecting heterogeneous melt processes a surface layer of both runoff and submarine melt and an intermediate layer composed primarily of submarine melt intermediate ocean waters carry the majority of heat to the fjords glaciers and warmer deep waters are isolated from the ice edge the average entrainment ratio implies that ocean water masses are upwelled at a rate 30 times the combined glacial meltwater volume flux

submarine melting at the terminus of a temperate tidewater glacier leconte glacier alaska u s a heat fresh and sea water balances indicate that the late summer rate of submarine melting at the terminus of tidewater leconte glacier alaska u s a in 2000 was about 12md 1 w e averaged over the submerged face this is 57 of the estimated total ice loss at the terminus calving plus melting at this time submarine melting may thusprovidea significantcontributiontotheoverallablationofatidewaterglacier oceano graphic measurements conductivity temperature depth made 200 500m from the ter minus identified an isohaline 27ppt and isothermal 7 2 c layer extending from 130m depthto the fjord floor capping this is a 40mthick overflow plume distinguishedby high outflow rates low salinity 22 25ppt and lower temperatures 5 6 c mixing models indicate that fresh water comprised about11 of this plume it originates mostly as sub glacial discharge whose buoyancy drives convection at the terminus deep warm saline watersareincorporatedintotheplumeasitascends causingsubstantialmeltingoficealong the submarine face the calving terminus undergoes seasonal changes that coincide with changes in subglacial discharge and fjord water temperatures and we suggest that these fluctuations interminuspositionare directly relatedto changes in submarine melting

temporal variations in the trace element content of stream sediments an example from a tropical rain forest regime solomon islands abstract a stream sediment geochemical anomaly in a tropical rain forest environment on the island of guadalcanal was monitored at monthly intervals over a period of 15 months major changes in stream sediment chemistry took place after heavy rainfall associated with the passage of the tail of a cyclone through the region these changes were directly linked to changes in the mineralogical composition of the sediments significant chemical variations also occurred in the period before the cyclone but these appear to have been related to variations in hydromorphic dispersion processes the data suggest that common exploration practices such as the use of threshold values should be applied with caution in tropical rain forest terrain the use of element fe ratios in exploration work and smoothing techniques in regional geochemical mapping may help eliminate some of the more pronounced effects of temporal variations in the trace element contents of stream sediments

distributed subglacial discharge drives significant submarine melt at a greenland tidewater glacier this is the publisher s final pdf the article is copyrighted by american geophysical union and published by john wiley sons inc it can be found at http agupubs onlinelibrary wiley com agu journal 10 1002 28issn 291944 8007

rapid submarine melting of the calving faces of west greenland glaciers widespread glacier acceleration has been observed in greenland in the past few years oceanographic observations taken in summer 2008 show that ocean waters melted a substantial fraction of ice along the calving fronts of three west greenland glaciers indicating that submarine melting has a profound influence on grounding line stability widespread glacier acceleration has been observed in greenland in the past few years1 2 3 4 associated with the thinning of the lower reaches of the glaciers as they terminate in the ocean5 6 7 these glaciers thin both at the surface from warm air temperatures and along their submerged faces in contact with warm ocean waters8 little is known about the rates of submarine melting9 10 11 and how they may affect glacier dynamics here we present measurements of ocean currents temperature and salinity near the calving fronts of the eqip sermia kangilerngata sermia sermeq kujatdleq and sermeq avangnardleq glaciers in central west greenland as well as ice front bathymetry and geographical positions we calculate water mass and heat budgets that reveal summer submarine melt rates ranging from 0 7 0 2 to 3 9 0 8 m d 1 these rates of submarine melting are two orders of magnitude larger than surface melt rates but comparable to rates of iceberg discharge we conclude that ocean waters melt a considerable but highly variable fraction of the calving fronts of glaciers before they disintegrate into icebergs and suggest that submarine melting must have a profound influence on grounding line stability and ice flow dynamics

on meltwater under ice shelves the basic features of the flow of meltwater under ice shelves can be described by a set of simple relations and length scales the flow may be divided into two regions with different basic processes dominating in each in the first region melting of the underside of the ice shelf is important and the temperature and salinity of the current tend toward equilibrium values such that the changes due to melting of the ice shelf are balanced by changes due to entrainment of ambient seawater the equilibrium values change with depth owing to the effect of the change in pressure on the freezing point as the current increases in thickness it is no longer able to adjust sufficiently rapidly to the changing equilibrium values arid the flow moves into the second region the extent of the first region is governed by the location of the ambient freezing point in the second region melting is less important and the current behaves as an entraining drag limited gravity current in a stratified ambient fluid leaving the shelf once the current has the same density as the ambient seawater the heights of the two regions depend mainly on the ambient conditions and only indirectly on parameters such as slope angle entrainment constant drag coefficient and turbulent transfer coefficients

nonlinear response of iceberg side melting to ocean currents icebergs calving into greenlandic fjords frequently experience strongly sheared flows over their draft but the impact of this flow past the iceberg is not fully captured by existing parameterizations we present a series of novel laboratory experiments to determine the dependence of submarine melting along iceberg sides on a background flow we show for the first time that two distinct regimes of melting exist depending on the flow magnitude and consequent behaviour of melt plumes side attached or side detached with correspondingly different meltwater spreading characteristics when this velocity dependence is included in melt parameterizations melt rates estimated for observed icebergs in the attached regime increase consistent with observed iceberg submarine melt rates we show that both attached and detached plume regimes are relevant to icebergs observed in a greenland fjord further depending on the regime iceberg meltwater may either be confined to a surface layer or distributed over the iceberg draft

some geological implications of average quaternary glacial conditions analyses of quaternary landscape evolution tend to focus on events associated with culminations of glacial and interglacial ages but for most of quaternary time environments were intermediate in character average quaternary glacial conditions based on assessment of the marine isotope record approximated those near the stage 2 stage 1 transition and during substages 5b and 5d isotope stages 3 and 4 and substages 5a d lie within one standard deviation of the mean value under average glacial conditions ice sheets lying over northern north america and europe were much more contracted than their full glacial counterparts and the distribution of mountain glaciers reflected a snowline depression of some 500 m geomorphic processes operating under average quaternary conditions contributed importantly to landscape evolution examples of landscapes that may represent such average conditions include cirques and fluvial deposits of the pacific northwest the fjords and strandflat of western norway and atolls of the tropical oceans by examining the geologic record from the perspective of average conditions rather than those of climatic extremes added insight can be gained regarding the evolution of quaternary landscapes

impact of two plumes interaction on submarine melting of tidewater glaciers a laboratory study idealized laboratory experiments investigate the glacier ocean boundary dynamics near a vertical glacier in a two layer stratified fluid discharge of meltwater runoff at the base of the glacier subglacial discharge enhances submarine melting in the laboratory the effect of multiple sources of subglacial discharge is simulated by introducing freshwater at freezing temperature from two point sources at the base of an ice block representing the glacier the buoyant plumes of cold meltwater and subglacial discharge water entrain warm ambient water rise vertically and interact within a layer of depth h2 if the distance between the sources x0 is smaller than h2 0 35 where is the entrainment constant the plume water detaches from the glacier face at the interface between the two layers and or at the free surface as confirmed by previous numerical studies and field observations a plume model is used to explain the observed nonmonotonic dependence of submarine melting on the sources separation the distance between the two sources influences the entrainment of warm water in the plumes and consequently the amount of submarine melting and the final location of the meltwater within the water column two interacting plumes located very close together are observed to melt approximately half as much as two independent plumes the inclusion or parameterization of the dynamics regulating multiple plumes interaction is therefore necessary for a correct estimate of submarine melting hence the distribution and number of sources of subglacial discharge may play an important role in glacial melt rates and fjord stratification and circulation

convection driven melting near the grounding lines of ice shelves and tidewater glaciers subglacial meltwater draining along the bed of fast flowing marine terminating glaciers emerges at the groundingline wheretheiceeithergoesafloattoformaniceshelforterminates inacalvingface theinputof freshwater to the ocean provides a source of buoyancy and drives convective motion alongside the ice ocean interface this process is modeled using the theory of buoyant plumes that has previously been applied to the study of the larger scale circulation beneath ice shelves the plume grows through entrainment of ocean waters and the heat brought into the plume as a result drives melting at the ice ocean interface the equations are nondimensionalized by using scales appropriate for the region where the subglacial drainage rather than the subsequent addition of meltwater supplies the majority of the buoyancy forcing it is found that the melt rate within this region can be approximated reasonably well by a function that is linear in ocean temperature has a cube root dependence on the flux of subglacial meltwater and has a complex dependency on the slope of the ice ocean interface the model is used to investigate variability in melting induced by changes in both ocean temperature and subglacial discharge for a number of realistic examples of ice shelves and tidewater glaciers the results show how warming ocean waters and increasing subglacial drainage both generate increases in melting near the grounding line

modeling turbulent subglacial meltwater plumes implications for fjord scale buoyancy driven circulation abstractfjord scale circulation forced by rising turbulent plumes of subglacial meltwater has been identified as one possible mechanism of oceanic heat transfer to marine terminating outlet glaciers this study uses buoyant plume theory and a nonhydrostatic three dimensional ocean ice model of a typical outlet glacier fjord in west greenland to investigate the sensitivity of meltwater plume dynamics and fjord scale circulation to subglacial discharge rates ambient stratification turbulent diffusivity and subglacial conduit geometry the terminal level of a rising plume depends on the cumulative turbulent entrainment and ambient stratification plumes with large vertical velocities penetrate to the free surface near the ice face however midcolumn stratification maxima create a barrier that can trap plumes at depth as they flow downstream subglacial discharge is varied from 1 750 m3 s 1 large discharges result in plumes with positive temperature and salinity anomalies in the upper water column for

reconstruction of the little ice age glaciers and equilibrium line altitudes in the kodar range southeast siberia abstract little ice age lia a time of global cooling widely manifested in the 14th 19th centuries was characterized by worldwide expansion of mountain glaciers unfortunately little is known about the lia glacier changes in remote areas of continental siberia in this work we studied the evolution of the glaciers of the kodar range southeast siberia these glaciers are mainly of small size

increased flow speed on a large east antarctic outlet glacier caused by subglacial floods large ice streams and outlet glaciers drain greenland and antarctica an observed acceleration of ice velocity in one of these outlet glaciers byrd glacier east antarctica coincides with a large water discharge from two subglacial lakes allowing direct attribution of the change in glacier dynamics to the water drainage network beneath the ice

the north american lightning detection network naldn analysis of flash data 2001 09 abstractcloud to ground cg lightning data have been analyzed for the years 2001 09 for north america which includes alaska canada and the lower 48 u s states flashes recorded within the north american lightning detection network naldn are examined no corrections for detection efficiency variability are made over the 9 yr of the dataset or over the large geographical area comprising north america there were network changes in the naldn during the 9 yr but these changes have not been corrected for nor have the recorded data been altered in any way with the exception that all positive lightning reports with peak currents less than 15 ka have been deleted thus the reader should be aware that secular changes are not just climatological in nature all data were analyzed with a spatial resolution of 20 km the analyses presented in this work provide a synoptic view of the interannual variability of lightning observations in north america including the impacts of physical changes in the network dur

separating snow clean and debris covered ice in the upper indus basin hindukush karakoram himalayas using landsat images between 1998 and 2002 summary the hindukush karakoram himalayan mountains contain some of the largest glaciers of the world and supply melt water from perennial snow and glaciers to the upper indus basin uib upstream of tarbela dam which constitutes greater than 80 of the annual flows and caters to the needs of millions of people in the indus basin it is therefore important to study the response of perennial snow and glaciers in the uib under changing climatic conditions using improved hydrological modeling glacier mass balance and observations of glacier responses however the available glacier inventories and datasets only provide total perennial snow and glacier cover areas despite the fact that snow clean ice and debris covered ice have different melt rates and densities this distinction is vital for improved hydrological modeling and mass balance studies this study therefore presents a separated perennial snow and glacier inventory perennial snow cover on steep slopes perennial snow covered ice clean and debris covered ice based on a semi automated method that combines landsat images and surface slope information in a supervised maximum likelihood classification to map distinct glacier zones followed by manual post processing the accuracy of the presented inventory falls well within the accuracy limits of available snow and glacier inventory products for the entire uib estimates of perennial and or seasonal snow on steep slopes snow covered ice clean and debris covered ice zones are 7238 724 5226 522 4695 469 and 2126 212 km2 respectively thus total snow and glacier cover is 19 285 1928 km2 out of which 12 075 1207 km2 is glacier cover excluding steep slope snow cover equilibrium line altitude ela estimates based on the snow line elevation sle in various watersheds range between 4800 and 5500 m while the accumulation area ratio aar ranges between 7 and 80 0 c isotherms during peak ablation months july and august range between 5500 and 6200 m in various watersheds these outputs can be used as input to hydrological models to estimate spatially variable degree day factors for hydrological modeling to separate glacier and snow melt contributions in river flows and to study glacier mass balance and glacier responses to changing climate

the dynamics of a subglacial salt wedge marine terminating glaciers such as those along the coastline of greenland often release meltwater into the ocean in the form of subglacial discharge plumes though these plumes can dramatically alter the mass loss along the front of a glacier the conditions surrounding their genesis remain poorly constrained in particular little is known about the geometry of subglacial outlets and the extent to which seawater may intrude into them here the latter is addressed by exploring the dynamics of an arrested salt wedge a steady state two layer flow system where salty water partially intrudes a channel carrying fresh water building on existing theory we formulate a model that predicts the length of a non entraining salt wedge as a function of the froude number the slope of the channel and coefficients for interfacial and wall drag in conjunction a series of laboratory experiments were conducted to observe a salt wedge within a rectangular channel for experiments conducted with laminar flow reynolds number re 800 good agreement with theoretical predictions are obtained when the drag coefficients are modelled as being inversely proportional to re however for fully turbulent flows on geophysical scales these drag coefficients are expected to asymptote toward finite values adopting reasonable drag coefficient estimates for this flow regime our theoretical model suggests that typical subglacial channels may permit seawater intrusions of the order of several kilometres while crude these results indicate that the ocean has a strong tendency to penetrate subglacial channels and potentially undercut the face of marine terminating glaciers

timing and extent of late quaternary glaciation in the western himalaya constrained by 10be moraine dating in garhwal india glacial chronologies from the himalayan region indicate various degrees of asynchronous glacial behavior part of this has been related to different sensitivities of glaciers situated in contrasting climatic compartments of the orogen but so far field data in support for this hypothesis is lacking here we present a new 10 be derived glacial chronology for the upper tons valley in western garhwal india and initial results for the pin and thangi valleys in eastern himachal pradesh these areas cover a steep gradient in orographic precipitation and allow testing for different climatic sensitivities our data provide a record of five glacial episodes at w16 ka w11 12 ka w8 9 ka w5 ka and 1 ka in the thangi valley our results indicate a glacial episode at w19 ka but no data are available for younger glacial deposits in this valley at their largest mapped extent w16 ka the two main glaciers in the upper tons valley joined and descended down to w2500 m asl which represents a drop of w1400 m compared to the present day glacial extent during the holocene the two largest glaciers produced distinct glacial landforms that allowed us to reconstruct changes in the equilibrium line altitude ela over w20 km north south distance that is presently associated with a steep gradient in rainfall we observe that ela changes have been consistently w2 times higher for the glacier located in a presently wetter climate pointing at different climate sensitivities related to the amount of precipitation that they receive at regional scale our data is in reasonable agreement with other published glacial chronologies from the western himalaya and suggest that glacial advances during the holocene have been largely synchronous in this region comparison of glacial chronologies from the western himalaya with other palaeoclimatic proxy data suggests that long term changes in glacial extents are controlled by glacial interglacial temperature oscillations related to the waxing and waning of the large northern hemisphere ice sheets while the timing of millennial scale advance and retreat cycles are more directly related to monsoon strength

mass balance in the glacier bay area of alaska usa and british columbia canada 1995 2011 using airborne laser altimetry the glacier bay region of southeast alaska usa and british columbia canada has undergone major glacier retreat since the little ice age lia we used airborne laser altimetry elevation data acquired between 1995 and 2011 to estimate the mass loss of the glacier bay region over four time periods 1995 2000 2000 05 2005 09 2009 11 for each glacier we extrapolated from center line profiles to the entire glacier to estimate glacier wide mass balance and then averaged these results over the entire region using three difference methods normalized elevation area weighted method and simple average we found that there was large interannual variability of the mass loss since 1995 compared with the long term post lia average for the full period 1995 2011 the average mass loss was 3 93 0 89 gt a 1 0 6 0 1 m w e a 1 compared with 17 8 gt a 1 for the post lia 1770 1948 rate our mass loss rate is consistent with grace gravity signal changes for the 2003 10 period our results also show that there is a lower bias due to center line profiling than was previously found by a digital elevation model difference method

surface expression of a wall fountain application to subglacial discharge plumes abstractwe use laboratory experiments and theoretical modeling to investigate the surface expression of a subglacial discharge plume as occurs at many fjords around greenland the experiments cons

last glacial maximum equilibrium line altitude and paleo temperature reconstructions for the cordillera de merida venezuelan andes abstract the pattern and magnitude of glacier equilibrium line altitude ela lowerings in the tropics during the last glacial maximum lgm are topics of current debate in the northern tropics paleo ela data are particularly limited inhibiting the ability to make regional and large scale paleoclimatic inferences to improve these records nine paleo glaciers in the venezuelan andes were reconstructed based on field observations aerial photographs satellite imagery and high resolution digital topographic data paleo glacier equilibrium line altitudes elas were estimated using the accumulation area ratio aar and the area altitude balance ratio aabr methods during the local lgm in venezuela 22 750 to 19 960 cal yr bp elas were 850 to 1420 m lower than present local lgm temperatures were are at least 8 8 2 c cooler than today based on a combined energy and mass balance equation to account for an ela lowering this is greater than estimates using an atmospheric lapse rate calculation which yields a value of 6 4 1 c cooler the paleo glacial data from the venezuelan andes support other published records that indicate the northern tropics experienced a greater ela lowering and possibly a greater cooling than the southern hemisphere tropics during the lgm

modeling thermodynamic ice ocean interactions at the base of an ice shelf abstract models of ocean circulation beneath ice shelves are driven primarily by the heat and freshwater fluxes that are associated with phase changes at the ice ocean boundary their behavior is therefore closely linked to the mathematical description of the interaction between ice and ocean that is included in the code an hierarchy of formulations that could be used to describe this interaction is presented the main difference between them is the treatment of turbulent transfer within the oceanic boundary layer the computed response to various levels of thermal driving and turbulent agitation in the mixed layer is discussed as is the effect of various treatments of the conductive heat flux into the ice shelf the performance of the different formulations that have been used in models of sub ice shelf circulation is assessed in comparison with observations of the turbulent heat flux beneath sea ice formulations that include an explicit parameterization of the oceanic boundary layer give results that

geochemical changes recorded in lynch s crater northeastern australia over the past 50 ka there are many geochemical reconstructions of environmental change in the mid and high latitudes but relatively few in the tropical latitudes despite their considerable potential for reconstructing environmental processes that cannot be identified using more traditional proxies here we present one reconstruction of environmental change for the tropics this reconstruction covers the past 50 ka using a suite of geochemical data from the high resolution sequence of lynch s crater in northeast queensland australia a region highly sensitive to el nino southern oscillation enso activity the 23 major oxides and trace elements measured could be summarised by extracting three axes using principal components analysis accounting for 72 of the variability the data indicate that the greatest variability in the geochemical data accounted for erosional activity within the catchment that was associated with past changes in the frequency of enso activity though this was less sensitive during wetter periods probably as a result of buffering by high vegetation cover the remaining variability was largely explained by elements that form complexes with organic compounds e g humic acids and those that are important nutrients for specific vegetation types and therefore a measure of vegetation distribution for more detailed reconstructions further work is required to disentangle the complex controls of clements within sedimentary sequences c 2005 elsevier b v all rights reserved

modern glacier characteristics as a basis for inferring former climates with particular reference to the loch lomond stadial abstract studies of the mass balance of modern glaciers have indicated that the equilibrium line altitude ela is the most critical parameter in the link between glaciers and climate average accumulation on a glacier includes components derived from direct precipitation on the glacier surface as well as wind drifting and avalanching of snow and approximates closely to accumulation at the equilibrium line ablation is most usefully predicted by mean summer temperature and there is a close non linear relationship between accumulation and mean summer temperature at the equilibrium line following discussion of methods of reconstructing former glaciers and calculating their equilibrium line altitudes the application of the above relationships to the loch lomond readvance glaciers of highland britain is considered and an outline of the precipitation pattern and the mean summer temperature of the loch lomond stadial is given

a subsynoptic analysis of the denver tornadoes of 3 june 1981 abstract on the afternoon of 3 june 1981 a severe thunderstorm spawned two tornadoes which moved across a portion of metropolitan denver the tornadoes were classified as strong f2 intensity and caused damage totaling over 1 5 million the synoptic scale setting for this event was similar to that associated with many other occurrences of severe convection in eastern colorado with post frontal moist southeasterly upslope flow at low levels and southwesterly flow aloft in advance of an approaching trough we chose to study this event in part because of its occurrence within the profs program for regional observing and forecasting services surface mesonetwork emphasis is placed on mesoscale evolution culminating in the formation of the tornadic storm a zone of surface convergence and cyclonic vorticity developed during the early daylight hours over and north of denver between southeasterly flow over the plains and a region of lighter generally northerly flow just east of the foothills the tornadic s

late pleistocene glacial equilibrium line altitudes in the colorado front range a comparison of methods abstract six methods for approximating late pleistocene pinedale equilibrium line altitudes elas are compared for rapidity of data collection and error rmse from first order trend surfaces using the colorado front range trend surfaces computed from rapidly applied techniques such as glaciation threshold median altitude of small reconstructed glaciers and altitude of lowest cirque floors have relatively high rmses 97 186 m because they are subjectively derived and are based on small glaciers sensitive to microclimatic variability surfaces computed for accumulation area ratios aars and toe to headwall altitude ratios thars of large reconstructed glaciers show that an aar of 0 65 and a thar of 0 40 have the lowest rmses about 80 m and provide the same mean ela estimate about 3160 m as that of the more subjectively derived maximum altitudes of pinedale lateral moraines rmse 149 m second order trend surfaces demonstrate low elas in the latitudinal center of the front range perhaps due to higher winter accumulation there the mountains do not presently reach the ela for large glaciers and small front range cirque glaciers are not comparable to small glaciers existing during pinedale time therefore pleistocene ela depression and consequent temperature depression cannot reliably be ascertained from the calculated ela surfaces

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

a high resolution lightning map of the state of colorado abstractfor the state of colorado 10 years 2003 12 of 1 april 31 october cloud to ground cg lightning stroke data are mapped at 500 m spatial resolution over a 10 m spatial resolution u s geological survey usgs digital elevation model dem spatially the 12 5 million strokes that are analyzed represent ground contacts but translate to density values that are about twice the number of ground contacts visual interpretation of the mapped data reveals the general lightning climatology of the state while geospatial analyses that quantify lightning activity by elevation identify certain topographic influences of colorado s physical landscape elevations lower than 1829 m 6000 ft and above 3200 m 10 500 ft show a positive relationship between lightning activity and elevation while the variegated topography that lies between these two elevations is characterized by a fluctuating relationship though many topographic controls are elucidated through the mappings and analyses the major finding of

late quaternary glaciation of costa rica the highest peaks of costa rica 9 15 9 36 n were glaciated during the late quaternary attesting to a significantly cooler climate in central america than today during the last local glacial maximum llgm an ice cap 35 km2 in extent covered the highest peaks of the cordillera de talamanca around cerro chirripo and around cerros de la muerte and kamuk 5 and 2 km2 of ice existed respectively in chirripo national park three moraine groups define three glacial stages the talamanca stage extends to 3040 m and represents the last local glacial maximum chirripo stage moraines reach elevations of 3300 m and talari stage moraines formed at 3300 and 3420 m former equilibrium line altitudes elas were 3500 m 3600 m and 3620 m respectively cirque floor elevations of 3260 m at cerro kamuk suggest a lower pre llgm ela radiosonde data from san jose place the modern 0 c isotherm at 5000 m which suggests a late quaternary ela depression of 1500 m which is consistent with a temperature reduction at chirripo of 8 9 c during the llgm some of this cooling may be attributable to a steeper lapse rate associated with a drier atmosphere possibly due to a more restricted position of the intertropical convergence zone decreased yearly convection or more frequent incursion of polar air masses

comparing reconstructed pleistocene equilibrium line altitudes in the tropical andes of central peru glacier equilibrium line altitude ela and the difference between modern and palaeo ela can be interpreted as a proxy for climate change one issue in ela reconstruction is that different methods of ela reconstruction may produce a range of results for the same palaeoglacier when a range of methods is used to reconstruct elas across a region resulting variations may be related to the method rather than the past climate palaeoclimatic interpretation of elas that were reconstructed by different methods may prompt spurious inferences if the ela range is the result of methodological differences rather than climatic variation we address the relationship and degree of variation between methods by comparing terminus to headwall altitude ratio thar accumulation area ratio aar and accumulation area balance ratio aabr methods for palaeoglaciers in four valleys in the tropical andes valleys in the eastern cordillera of the peruvian andes bordering the junin plain 11 s 76 w ca 4100 m a s l are presently ice free but were glaciated repeatedly during the pleistocene we use a combination of 90 m shuttle radar topography mission srtm data 15 m advanced spaceborne thermal emission and reflection radiometer aster data and 1 25 000 topographic maps to reconstruct elas within each of three groups of moraines map based thar and aabr estimates of ela tend to be highest followed by dem derived thar elas with aar reconstructed elas somewhat lower in this region ela estimates for the local last glacial max imum llgm range from ca 4250 to 4570 m a s l with elas of ca 220 to 550 m depending on valley and method used within individual valleys elas for the same palaeoglaciers calculated by different methods vary by 100 m elas of the llgm glaciers and those of the largest glaciers to occupy the junin valleys 65 ka are not markedly different from each other regardless of the method used in their calculation which is largely a reflection of the valley hypsometry in the region our analysis suggests relatively low decreases in temperature during glacial periods in the region ca 2 5 1 c copyright 2005 john wiley sons ltd

holocene glacier fluctuations and migration of neolithic yak pastoralists into the high valleys of northwest bhutan abstract here we present geomorphologic palaeoenvironmental and archaeo botanical data which elucidate the late pleistocene and holocene glacial history of the high mountain locked himalayan valleys in northwest bhutan and provide one of the earliest proofs of human activity yet known for the high himalaya range in this area difficult to access close linkage between climatic change glacier fluctuations and human migration patterns has been discovered glacier systems in the studied area are characterized by avalanching and debris mantled glacier snouts with the significant local influence of the indian summer monsoon causing decoupling of glacier responses from temperature changes but supporting the idea of monsoonal forcing geomorphologic mapping together with optically stimulated luminescence osl and radiocarbon dating of ice proximal sediments has been used to construct a local glacial chronology local ice stream networks developed during the early holocene ca 10 000 9000 a ago and during the early part of the mid holocene 6710 90 4680 155 cal a bp at which times there were ice advances of about 5 km from the modern glacier termini at such times the intensity of pro and periglacial processes would have intensified and ice dammed lakes were probably common as well rendering human colonization of the high valleys in northwest bhutan impossible an abrupt shift to dry climatic conditions on the tibetan plateau between 5000 and 4500 a bp coincided with glacial decay and the onset of morphodynamically stable conditions on the broad valley floors of the high valleys in this part of the himalaya palynological data suggest that the sudden disappearance of juniper and rhododendron pollen the immediate onset of pollen input from cereals confirmed by detailed sem analysis and a clear pattern of over grazing trampling and peat deterioration can be linked to human arrival in the valleys at ca 4280 130 cal a bp extensive charcoal horizons dating to 4745 250 and 4680 155 cal a bp are interpreted as evidence for human use of fire and forest clearances and agree spatially and temporally with the pollen based picture charcoal occurrences as old as 6710 90 cal a bp might be linked to yet earlier exploration of these himalayan valleys during phases of low glacial activity we provide an account of the colonization of these high valleys in response to glacial and monsoonal change and argue that the most likely founder societies come from the tibetan plateau where yak and barley based pastoralism and neolithic settlements are known to have existed since the mid holocene

ice thickness and topographic relief in glaciated landscapes of the western usa abstract the development of relief in glaciated landscapes plays a crucial role in hypotheses relating climate change and tectonic processes in particular glaciers can only be responsible for peak uplift if they are capable of generating significant relief in formerly nonglaciated landscapes previous work has suggested that relief in glaciated landscapes should scale with the thickness of the ice here we summarise a field based test of this hypothesis in two mountain ranges in the western united states the sierra nevada california and the sangre de cristo range colorado these areas exhibit a range of degrees of glacial occupation during the quaternary including some drainage basins essentially unoccupied by ice allowing a detailed exploration of how relief in different parts of a drainage basin evolves in response to glacial modification we mapped last glacial maximum lgm trimlines to estimate the ice thickness at the equilibrium line altitude during the lgm and determined several metrics of relief for drainage basins across the full spectrum of lgm ice extents comparison between measures of relief and ice thickness estimates indicates that relief production in glaciated mountain belts scales with ice thickness and consequently also drainage area we extended our study to the bitterroot range in idaho montana and the teton range in wyoming for a more comprehensive understanding of sub ridgeline relief or missing mass this measure of mean relief is surprisingly little affected by either the degree of glacial modification or the total material removed by glaciers but appears to be influenced by the more active tectonics of the teton range while the effects of glacial modification on the landscape are clear valley widening hanging valley formation the overall change in the relief structure of the mountain ranges studied here is surprisingly modest

late pleistocene climate inferred from the reconstruction of the taylor river glacier complex southern sawatch range colorado abstract ice surface topography of a late pleistocene glacier complex herein named the taylor river glacier complex trgc was reconstructed on the basis of detailed mapping of glacial landforms combined with analyses of aerial photos and topographic maps during the last glacial maximum lgm the trgc covered an area of 215 km 2 and consisted of five valley or outlet glaciers that were nourished by accumulation in cirques basins and or upland ice fields equilibrium line altitudes elas for the glaciers of the trgc were estimated using the accumulation area ratio method assuming that ratio to be 0 65 0 05 elas thus derived ranged from about 3275 to 3400 m with a mean of 3340 60 m a degree day model ddm was used to infer the climatic significance of the lgm ela with no appreciable differences in precipitation with respect to modern climate the ela implies that mean summer temperatures during the lgm were 7 6 c cooler than today the ddm was also used to determine the temperatures required to maintain steady state mass balances for each of the reconstructed glaciers the required reductions in summer temperature vary little about a mean of 7 1 c the sensitivity of these results to slight 25 changes assumed for lgm precipitation are less than 0 5 c even under an lgm climate in which precipitation is assumed to be substantially different 50 than the present mean summer temperatures must be on the order of 7 0 to 8 5 c lower to depress equilibrium lines to lgm altitudes the greater sensitivity of the ela to changes in temperature suggests that glaciation in the region was driven more by decreases in summer temperature rather than increases in precipitation

regional geochemical mapping in developing countries and its application to environmental studies abstract the application of regional geochemical data for baseline environmental impact animal health and land use planning studies is illustrated using examples from bolivia kenya sumatra and swaziland pre mining baseline and post mining environmental impact assessements outline potential as hazards associated with au mineralization the relevance of regional drainage geochemistry maps to animal mineral deficiency studies is demonstrated by comparing the results of local soil plant animal studies with regional and national drainage geochemical maps the identification of broad areas with adequate or deficient nutrient levels including cu zn co and k on regional geochemical maps of northern sumatra has land use planning applications regional geochemical mapping is a relatively rapid cost effective and reliable method of providing a data base on the background levels of metals in the environment that would permit governments to monitor environmental degradation and pollution and to investigate trace element linked degenerative diseases in crops animals and humans

numerical experiments on subaqueous melting of greenland tidewater glaciers in response to ocean warming and enhanced subglacial discharge the largest dischargers of ice in greenland are glaciers that terminate in the ocean and melt in contact with sea water studies of ice sheet ocean interactions have mostly focused on melting beneath near horizontal floating ice shelves for tidewater glaciers melting instead takes place along the vertical face of the calving front here we modify the massachusetts institute of technology general circulation model mitgcm to include ice melting from a calving face with the freshwater outflow at the glacier grounding line we use the model to predict melt rates and their sensitivity to ocean thermal forcing and to subglacial discharge we find that melt rates increase with approximately the one third power of the subglacial water flux and increase linearly with ocean thermal forcing our simulations indicate that consistent with limited field data melting ceases when subglacial discharge is shut off and reaches several meters per day when subglacial discharge is high in the summer these results are a first step toward a more realistic representation of subglacial discharge and of ocean thermal forcing on the subaqueous melting of tidewater glaciers in a numerical ocean model our results illustrate that the ice front melting process is both complex and strongly time dependent

the effect of a salinity gradient on the dissolution of a vertical ice face we investigate experimentally the effect of stratification on a vertical ice face dissolving into cold salty water we measure the interface temperature ablation velocity and turbulent plume velocity over a range of salinity gradients and compare our measurements with results of similar experiments without a salinity gradient kerr mcconnochie j fluid mech vol 765 2015 pp 211 228 mcconnochie kerr j fluid mech vol 787 2016 pp 237 253 we observe that stratification acts to reduce the ablation velocity interface temperature plume velocity and plume acceleration we define a stratification parameter s n 2 q it phi o that describes where stratification will be important where n is the brunt vaisala frequency q is the height dependent plume volume flux and it phi o is the buoyancy flux per unit area without stratification the relevance of this stratification parameter is supported by our experiments which deviate from the homogeneous theory at approximately s 1 finally we calculate values for the stratification parameter at a number of ice shelves and conclude that ocean stratification will have a significant effect on the dissolution of both the antarctic and greenland ice sheets

seasonal variability of submarine melt rate and circulation in an east greenland fjord 1 the circulation in a glacial fjord driven by a large tidewater glacier is investigated using a nonhydrostatic ocean general circulation model with a melt rate parameterization at the vertical glacier front the model configuration and water properties are based on data collected in sermilik fjord near helheim glacier a major greenland outlet glacier the approximately two layer stratification of the fjord s ambient waters causes the meltwater plume at the glacier front to drive a double cell circulation with two distinct outflows one at the free surface and one at the layers interface in summer the discharge of surface runoff at the base of the glacier subglacial discharge causes the circulation to be much more vigorous and associated with a larger melt rate than in winter the simulated double cell circulation is consistent in both seasons with observations from sermilik fjord seasonal differences are also present in the vertical structure of the melt rate which is maximum at the base of the glacier in summer and at the layers interface in winter simulated submarine melt rates are strongly sensitive to the amount of subglacial discharge to changes in water temperature and to the height of the layers they are also consistent with those inferred from simplified one dimensional models based on the theory of buoyant plumes our results also indicate that to correctly represent the dynamics of the meltwater plume care must be taken in the choice of viscosity and diffusivity values in the model

distinguishing between natural and anthropogenic sources of metals entering the irish sea international agreements e g ospar on the release of hazardous substances into the marine environment and environmental assessments of shelf seas require that concentrations and bioavailability of metals from anthropogenic sources can be distinguished from those originating as a result of natural geological processes the development of a methodology for distinguishing between anthropogenic and natural sources of metals entering the irish sea through river inputs is described the geochemistry of stream river and estuarine sediments has been used to identify background geochemical signatures related to geology and modifications to these signatures by anthropogenic activities the british geological survey bgs geochemical database based on stream sediments from 1 to 2 km2 catchments was used to derive the background signatures where mining activity was present the impact on the signature was estimated by comparison with the geochemistry of sediments from a geologically similar but mining free area river sediment samples taken upstream and downstream of major towns were used respectively to test the validity of using stream sediments to estimate the chemistry of the major river sediment and to provide an indication of the anthropogenic impact related to urban and industrial development the geochemistry of estuarine sediments from surface samples and cores was then compared with river and offshore sediment chemistry to assess the importance of riverine inputs to the irish sea studies were undertaken in the solway ribble wyre and mersey estuaries the results verify that catchment averages of stream sediments and major river samples have comparable chemistry where anthropogenic influences are small major urban and industrial including mining development causes easily recognised departures from the natural multi element geochemical signature in river sediment samples downstream of the development and enhanced metal levels are observed in sediments from estuaries with industrial catchments stream sediment chemistry coupled with limited river and estuarine sampling provides a cost effective means of identifying anthropogenic metal inputs to the marine environment investigations of field and laboratory protocols to characterise biological impact bioaccumulation of metals in sediments of the irish sea and its estuaries show that useful assessments can be made by a combination of surveys with bioindicator species such as clams scrobicularia plana selective sediment measurements that mimic the biologically available fractions and laboratory mesocosm studies

reconstruction of little ice age glacier area and equilibrium line attitudes in the central and western himalaya abstract glacial changes during the little ice age lia in the himalayan mountains are important for understanding changes in the monsoonal and westerly climate of the so called the third pole however knowledge of these changes and their dynamics remains limited because of the region s geographical inaccessibility in addition to geopolitical reasons in this study we used high resolution three dimensional images from google earth to identify lateral and terminal moraines as delineators of paleoglacier boundaries and mapped the boundaries of both modern and lia glaciers arcgis 9 3 software was applied to map data and to calculate glacier lengths and areas modern glacier surface elevation data were derived from srtm shuttle radar topography mission records three methods the toe to headwall altitude ratio thar the toe to summit altitude method tsam and the toe to ridge altitude method tram were used to estimate equilibrium line altitude ela the transient snowlines tsl of ninety one modern glaciers were acquired using landsat 8 oli images in late summer to evaluate the reliability of the calculated elas our results showed that the total length and total area of two hundred and twenty glaciers in the central and western himalaya cwh had decreased respectively by 35 and 31 since the lia the tram method was the preferred method for the reconstruction of elas the mean depression of elas from the lia to the first decade of the 21st century as reconstructed using the tram method was 123 m the ela depression and rate of change of glacier length and glacier area displayed generally increasing trends from west to east along the central and western himalaya suggesting that the moisture was most likely transported from an easterly direction these changes were more intensive on southern than northern slopes suggesting that southerly and westerly precipitation likely increased over the same period we speculated that the cwh had been influenced by both the indian summer monsoon ism and westerlies since the lia ism moisture as in modern times was the main factor controlling the distribution of glaciers during the lia further precipitation carried by the westerlies likely intensified along southerly pathways along the cwh during the lia

a one dimensional model of ice shelf ocean interaction large scale oceanic circulation beneath antarctic ice shelves is driven by the thenmohaline differences which result from mass and energy exchange at the ice ocean interface dense saline waters are drawn underneath the ice shelves and emerge cooled and diluted as plumes of ice shelf water a simple one dimensional model of this process has been developed in which the ice shelf water plume is treated as a turbulent gravity current initiated at the inland margin by a flow of fresh meltwater emerging from beneath the grounded ice subsequent evolution of the plume as it ascends along an ice shelf base of specified geometry can be simulated the model has been applied to a flow line on ronne ice shelf antarctica to explain the observed distribution and rate of basal melting and freezing calculations indicate that the present mean melt rate of 0 6 m yr 1 would increase to 2 6 m yr 1 if the underlying water were to warm by 0 6 c this would not only lead to significant thinning of the ice shelf but could also cause a profound change in ocean circulation on the open continental shelf