productivity collapses in the arabian sea during glacial cold phases 1 productivity in the arabian sea is one of the highest in the world it is controlled by seasonally reversing monsoonal wind driven upwelling of nutrient rich deeper waters which fuel phytoplankton growth the detailed history of upwelling induced productivity in the eastern arabian sea is unknown here we present paleoproductivity records from a composite sediment core at the millennial scale during the last 80 kyr b p these records are based on relative abundance counts of planktonic foraminifera and organic carbon contents which are shown to mainly vary in concert the eastern arabian sea upwelling induced productivity was higher in the glacial period than in the holocene but it fell repeatedly on millennial timescales these productivity declines occurred during cold events in the north atlantic region with the most pronounced changes prevailing during the heinrich events hence seasonal monsoon winds that drive upwelling induced productivity in the east were weak when the north atlantic was cold these weak winds resulted in stratification of the water column comparable to today s arabian sea stratification in the intermonsoonal period combining the new eastern with published western arabian sea results shows that the entire biological factory was severely diminished during the north atlantic heinrich events and the seasonal productivity change in the arabian sea monsoon system was reduced with year round low productivity

regionally differentiated contribution of mountain glaciers and ice caps to future sea level rise the contribution to sea level rise from mountain glaciers and ice caps has grown over the past decades a projection of their melting during the twenty first century based on temperature and precipitation projections from ten climate models suggests that by 2100 these glaciers will lose about 21 of their total global volume

the climate memory of an arctic polythermal glacier knowledge of glacier equilibrium line altitude ela changes and trends in time is essentialfor future predictions of glacier volumes we present a novel method for determining trends in elachange at mccall glacier alaska usa over the last 50 years based on mapping of the cold temperatetransition surface cts marking the limit between cold and temperate ice of a polythermal glacier latent heat release from percolating meltwater and precipitation keeps the ice column temperate in theaccumulation area a change from accumulation to ablation zone reduces this heat release leadinglocally to glacier ice cooling by mapping the cts along the whole glacier length using radio echosounding and employing a thermodynamic model the timing of the cooling was determined fromwhich past elas were constructed these are in accord with mass balance measurements carried out onmccall glacier since the 1950s we show that with a warming climate mccall glacier tends to cool ina counter intuitive way

monsoonal variability in the northeastern arabian sea during the past 5000years geochemical evidence from laminated sediments abstract a high resolution laminated sediment record from the oxygen minimum zone in the northeastern arabian sea off pakistan was studied to reconstruct climatic variations to infer the monsoon driven moisture history in the northeastern arabian sea during the past 5000 years we have used three types of independant proxies 1 varve thickness 2 stable isotope ratios of planktic foraminifera and 3 inorganic geochemical composition on the basis of these proxies we have subdivided the sedimentary record into five intervals the first time interval from 5000 to 3900 yr bp period i is dominated by summer monsoon activity deduced from ti al zr al k al and sr ca ratios and oxygen isotope data of planktonic foraminifera slightly enhanced winter monsoon conditions can be inferred for the period from 3900 to about 3000 yr bp period ii maximum precipitation during enhanced winter monsoon activity at about 3100 yr bp was followed by an onset of aridification at 3000 yr bp which continued until about 2000 2200 yr bp period iii the textural mineralogical and geochemical data suggest that this aridification was a gradual century scale process rather than an abrupt event comparison to late holocene records in nw and sw india the near east and tropical africa supports our interpretation that period iii from 3000 to 2000 yr bp is characterized by a gradual change in the atmospherical moisture budget over much of this area reduced monsoonal rainfall may be linked to variations of eurasian snow cover as deduced from varve thickness and element to al ratios period iv from 2000 to about 1500 yr bp is characterized by a summer monsoon dominated sequence with higher precipitation than during period iii the 18o record shows an abrupt shift at 2000 yr bp coinciding with an increase of varve thickness which suggests a cooling of surface waters in the northern arabian sea present day conditions in the makran area were established at 1500 yr bp period v based on inorganic geochemical data and meteorological records at several stations in the makran we conclude that period v is dominated by precipitation during the winter season here declined rainfall associated with the summer monsoon may be related to a less northward position of the intertropical convergence zone itcz during summer and a stronger influence of winter monsoon linked phenomenona

evolution of productivity and monsoonal dynamics in the eastern arabian sea during the past 68ka using dinoflagellate cyst records for the first time here we report the dinoflagellate cyst assemblage response to the monsoon variability over the last 68 ka from the eastern arabian sea eas based on the cyst assemblage five dinoflagellate cyst zones were established corresponding to four marine isotopic stages mis 1 4 an increased abundance of autotrophic gonyaulacoid species especially spiniferites during glacials mis 2 and 4 and late mis 3 41 67 to 25 3 ka reflects high productivity driven by strong winter convection during the northeast monsoon in contrast their decreased abundance during mis 1 and early mis 3 58 6 to 42 87 ka reveals decrease in productivity due to strong stratification caused by intense monsoon precipitation induced runoff from the western ghats and reduced light penetration driven by cloud cover the variation in heterotrophic protoperidinium species abundance could be related to variation in the oxygen minimum zone omz intensity with better preservation during intense omz in mis 3 and the late holocene 3 ka onwards therefore it is proposed here that the abundance of protoperidinium can be used as an index of omz in the eas

late quaternary protoperidinium cysts as indicators of paleoproductivity in the northern arabian sea the reliability of organic walled cysts of the heterotrophic dinoflagellate protoperidinium as paleoproductivity indicators and the influence of bottom water oxygenation on cyst preservation is assessed by using arabian sea records of the past 125 kyr as a natural laboratory multidisciplinary geochemical micropaleontological and palynological datasets are integrated to analyze the relationship between protoperidinium cyst concentrations and other paleoproductivity proxies differential preservation potential is quantified in order to establish threshold oxidative degradation values for a possible application of quantitative protoperidinium cyst records in paleoenvironmental reconstructions results indicate that variations in protoperidinium cyst concentration closely correspond to other marine productivity and or upwelling proxies although oxygenation will lead to significant cyst degradation and thus decreased concentrations down core patterns in protoperidinium cyst concentration still primarily reflect changes in sea surface productivity in view of differential preservation among dinoflagellate cysts down core variations in relative abundance of protoperidinium should be treated with caution

the mass balance of circum arctic glaciers and recent climate change the sum of winter accumulation and summer losses of mass from glaciers and ice sheets net surface mass balance varies with changing climate in the arctic glaciers and ice caps excluding the greenland ice sheet cover about 275 000 km2of both the widely glacierized archipelagos of the canadian norwegian and russian high arctic and the area north of about 60 n in alaska iceland and scandinavia since the 1940s surface mass balance time series of varying length have been acquired from more than 40 arctic ice caps and glaciers most arctic glaciers have experienced predominantly negative net surface mass balance over the past few decades there is no uniform recent trend in mass balance for the entire arctic although some regional trends occur examples are the increasingly negative mass balances for northern alaska due to higher summer temperatures and increasingly positive mass balances for maritime scandinavia and iceland due to increased winter precipitation the negative mass balance of most arctic glaciers may be a response to a step like warming in the early twentieth century at the termination of the cold little ice age arctic ice masses outside greenland are at present contributing about 0 13 mm yr 1to global sea level rise

primary production in the arabian sea during the last 135 000 years abstract variations in primary productivity pp have been reconstructed in eutrophic mesotrophic and oligotrophic parts of the arabian sea over the past 135 000 years applying principal component analysis and transfer function to planktic foraminiferal assemblages temporal variation in paleoproductivity is most pronounced in the mesotrophic northern nast site and oligotrophic eastern east site arabian sea and comparatively weak in the western eutrophic geob 3011 1 site in the upwelling area off oman higher pp during interglacials 250 320 g c m 2 year 1 than during cold stages 210 270 g c m 2 year 1 at geob 3011 1 could have been caused by a strengthened upwelling during intensified summer monsoons and increased wind velocities at nast during interglacials pp is estimated to exceed 250 g c m 2 year 1 and during glacials to be as low as 140 180 g c m 2 year 1 these fluctuations may result from a 1 varying impact of filaments that are associated to the oman coastal upwelling and 2 from open ocean upwelling associated to the findlater jet at east highest productivity of about 380 g c m 2 year 1 is documented for the transition from isotope stage 5 to 4 we suggest that during isotope stages 2 4 5 2 the transition 5 4 and the end of stage 6 deep mixing of surface waters was caused by moderate to strong winter monsoons and induced an injection of nutrients into the euphotic layer leading to enhanced primary production the deepening of the mixed layer during these intervals is confirmed by an increased concentration of deep dwelling planktic foraminiferal species a high productivity event in stage 3 displayed by estimated pp values and by planktic foraminifera and radiolaria flux and accumulation rate likely resulted from a combination of intensified sw monsoons with moderate to strong ne monsoons differential response of globigerina bulloides globigerinita glutinata and mixed layer species to the availability of food is suited to subdivide productivity regimes on a temporal and spatial scale

high resolution hydrothermal structure of hansbreen spitsbergen mapped by ground penetrating radar detailed ground penetrating radar gpr surveys at 50 and 200 mhz on hansbreen a polythermal glacier in southern svalbard are presented and interpreted comparison of the variations in character of the radar reflections with borehole thermometry and water levels in moulins suggests that gpr can be used to study the hydrothermal properties of the glacier the high resolution of the gpr data shows that the hydrothermal structure of the glacier is highly variable both along the centre line and on transverse profiles water contents for many places and depths within the glacier were calculated by estimating radar wave velocities to point reflectors we find typical water contents of 1 2 for the temperate ice but wetter ice associated with surface crevassing and moulins typically 4 water content there is evidence that wet ice sometimes overlays drier ice the hydrothermal structure is thus shown to be very complex temperature gradients in the cold ice indicate freezing rates of temperate ice below cold ice of 0 1 0 5 m a while isolated point reflectors within the cold ice indicate large water filled bodies that are probably related to the regular drainage structure of the glacier

ice bed interface and englacial properties of svalbard ice masses deduced from airborne radio echo sounding data un ensemble de donnees de sondages par echo radio ont ete collectees sur 44 masses de glace au spitsberg et les calottes glaciaires de nordaustlandet svalbard ces donnees ont permis de produire les coefficients de reflexion en puissance pour l interface glace manteau sur une grande etendue de svalbard nord

tidewater glacier surges initiated at the terminus terrasar x data were provided by dlr project oce1503 and funded by the conoco phillips lundin northern area program through the crios project calving rates and impact on sea level c n acknowledges funding from european union erc grant 320816 and esa project glaciers cci 4000109873 14 i nb

spatial pattern and stability of the cold surface layer of storglaciaren sweden the mechanisms controlling the spatial distribution and temporal fluctuations of the thermal structure in polythermal glaciers have to date been poorly investigated and are not fully understood

cold surface layer thinning on storglaciaren sweden observed by repeated ground penetrating radar surveys 1 a characteristic feature of ground penetrating radar gpr surveys on polythermal glaciers is an internal reflection presumably caused by the cold temperate transition surface cts hence providing a possible tool for mapping thermal structure with high accuracy comparison of detailed temperature measurements in bore holes and gpr profiles at 345 mhz and 800 mhz center frequencies on storglaciaren sweden show that the cts can be detected and mapped with an accuracy of about 1 m at both frequencies a comparison between comprehensive gpr surveys of the cold surface layer separated by 12 years 1989 2001 shows a substantial and complex thinning of the cold layer an overall decrease of 8 3 m 22 of average thickness of the cts depth is much larger than uncertainties in cts depth determinations the stability of the cold surface layer depends on the net ice ablation at the surface and the downward migration of cts there is no evidence of substantial increased net ablation between the survey dates that could explain the observed thinning however small increase in average winter air temperature a limiting factor for the temperature gradient through the cold surface layer may provide a partial explanation the weaker temperature gradient reduces the transport of latent heat from the cts thus slowing down its downward migration

dinoflagellate cyst distribution in surface sediments from the arabian sea northwestern indian ocean in relation to temperature and salinity gradients in the upper water column abstract surface sediment samples from the arabian sea indian ocean have been investigated for their dinoftagellate cyst content to obtain information about the environmental affinity and potential palaeo environmental significance of the cyst species their distribution is compared with the environmental characteristics of the overlying water column using detrended correspondence analysis and canonical correspondence analysis the distribution patterns of individual species are compared with temperature and salinity gradients over four seasons the main variation in cyst association appears to be related to variation in those gradients affected by the sw and ne monsoons on the basis of this relationship four groups of species can be recognised 1 central arabian sea species 2 sw monsoon upwelling species 3 ne monsoon eutrophic species 4 species with no distinct relationship with monsoon related gradients the downcore occurrences of species from groups 1 2 and 3 have potential as indicators for palaeo sw and ne monsoon strength

force budget i theory and numerical methods a practical method is developed for calculating stresses and velocities at depth using field measurements of the geometry and surface velocity of glaciers to do this it is convenient to partition full stresses into lithostatic and resistive components the horizontal gradient in vertically integrated lithostatic stress is the driving stress and it describes the horizontal action of gravity the horizontal resistive stress gradients describe the reactions resistive stresses are simply related to deviatoric stresses and hence to strain rates through a constitutive relation a numerical scheme can be used to calculate stresses and velocities from surface velocities and slope and from ice thickness there is no mathematical requirement that the variations in these quantities be small

the influence of basal processes on the dynamic behaviour of cold based glaciers abstract there exists within glaciology a widely held assumption that basal sliding and bed deformation do not operate beneath cold based ice and that their basal velocity is therefore zero irrespective of bed conditions consequently their ability to erode entrain and transport sediment and thereby alter the landscape is assumed to be limited consequently very little research has been focused towards describing and understanding the motion of cold based ice masses and our knowledge of their behaviour remains poor and the assumption of zero basal velocity unchallenged in this review paper it is argued that this assumption is not universally applicable and that in certain circumstances basal processes not only remain active at sub freezing temperatures but can significantly influence glacier motion this is particularly the case in glaciers where sub freezing basal thermal conditions coincide with the presence of fine grained ice rich subglacial sediments due to the lack of work undertaken on contemporary cold based glaciers much of the information used to support this argument is derived from field research in permafrost areas and on quaternary glacial sediments and from the laboratory testing of ice sediment mixtures it is concluded that the assumption of zero basal velocity beneath cold based ice is overly simplistic and that in reality the situation is likely to be much more complex work is therefore urgently required firstly to investigate the circumstances in which basal motion remains active at sub freezing temperatures and to determine their influence on glacier motion and secondly to examine the likely extent of subglacial permafrost in both the contemporary and quaternary glacial environment

monsoonal dynamics and evolution of the primary productivity in the eastern arabian sea over the past 30 ka abstract this study presents a high resolution primary productivity record for the last 30 ka in the eastern arabian sea eas based on the coccolithophore assemblage at sk 17 core in the continental slope off goa india coccolithophores were proposed as indicators of primary productivity and nutricline position and the results were used to reconstruct the monsoonal dynamics which is a main factor controlling productivity changes in the eas both seasons in the indian monsoon winter and summer monsoon exert a strong control over the primary productivity in the arabian sea an increased productivity was recorded during the late glacial period in the eas contrasting with records obtained in the western and northern arabian sea this enhanced productivity was related to strengthened winter monsoon winds planktonic foraminifera data suggested a weakened winter mixing during the last deglaciation which would reduce productivity in the area however our coccolithophore data reveal a high primary productivity during the deglaciation provably maintained by the nutrient supply from the continental runoff due to the presence of enhanced summer monsoon regarding the holocene surface waters were highly stratified since 10 5 ka our data were compared with ice cores isotopic records from high latitudes of both hemispheres allowing us to observe a good correlation between the stratification of the eas and the climate variability over high latitude regions in the northern hemisphere however there has been some inconsistency between our coccolithophore data and planktonic foraminiferal records particularly during the short time intervals corresponding to the heinrich cold events described in the north atlanctic region

quaternary carbonate record from the equatorial indian ocean and its relationship with productivity changes abstract the caco3 content in quaternary deep sea sediments from pacific and atlantic oceans have been suggested to respond differently to glacial interglacial cycles caco3 contents are highest during glacials in the pacific but highest during interglacials in the atlantic ocean it is not yet clear as to whether a pacific or an atlantic pattern of caco3 fluctuations dominates the indian ocean we have analyzed the ocean drilling program odp site 709a from the western equatorial indian ocean for the last 1370 ka to determine the relationships between percentages and fluxes of caco3 and quaternary paleoclimatic changes we also analyzed the coarse 25 m and fine 18 o of the planktonic foraminifera globigerinoides ruber this indicates that caco3 fluctuations at this site do not show either a pacific or an atlantic pattern of caco3 fluctuations fluxes of caco3 0 38 to 2 46 g cm 2 ka 1 in total sediment and ba al ratios 0 58 to 3 93 g cm 2 ka 1 show six fold variability through the last 1370 ka which points out that productivity changes are significant at this site fluxes of the fine caco3 component demonstrate a 26 fold change 0 02 to 0 52 g cm 2 ka 1 whereas the coarse caco3 component exhibit eight fold change 0 13 to 1 07 g cm 2 ka 1 this suggests that productivity variations of calcareous nannofossils are greater in comparison with the foraminifera on the other hand mean values of coarse caco3 fluxes are higher compared to those of fine caco3 which reveals that the foraminifera contribute more to the bulk caco3 flux than the calcareous nannofossils in the equatorial indian ocean

glacier surge propagation by thermal evolution at the bed bakaninbreen southern svalbard began a prolonged surge during 1985 in 1986 an internal reflecting horizon on radio echo sounding data was interpreted to show that the position of the surge front coincided with a transition between areas of warm unfrozen and cold frozen bed ground penetrating radar lines run in 1996 and 1998 during early quiescence show that the basal region of the glacier is characterized by a strong reflection interpreted as the top of a thick layer of sediment rich basal ice down glacier of the present surge front features imaged beneath the basal reflection are interpreted as the bottom of the basal ice layer the base of a permafrost layer and local ice lenses this indicates that this region of the bed is cold up glacier of the surge front a scattering zone above the basal reflection is interpreted as warm ice there is no evidence for this warm zone down glacier of the surge front nor do we see basal permafrost up glacier of it thus as in early surge phase the location of the surge front is now at the transition between warm and cold ice at the glacier bed we suggest that the propagation of the front is associated with this basal thermal transition throughout the surge because propagation of the front occurs rapidly and generates only limited heat basal motion during fast flow must have been restricted to a thin layer at the bed and occurred by sliding or deformation localized at the ice bed interface

sea surface temperature and productivity records for the past 240 kyr in the arabian sea abstract deep sea sediments of two cores from the western ty93 929 p and the southeastern md900963 arabian sea were used to study the variations of the indian monsoon during previous climatic cycles core ty93 929 p was located between the sw monsoon driven upwelling centres off somalia and oman which are characterized by large seasonal sea surface temperature sst and particle flux changes by contrast core md900963 was situated near the maldives platform an equatorial ocean site with a rather small sst seasonality less than 2 c for both cores we have reconstructed sst variations by means of the unsaturation ratio of c37 alkenones which is compared with the 18o records established on planktonic foraminifera in general the sst records follow the 18o variations with an sst maximum during oxygen isotope stage 5 5 the last interglacial at about 120 130 kyr and a broad sst minimum during isotope stage 4 and 3 3 approximately 40 50 kyr the sst difference between the holocene and the last glacial maximum lgm is of the order of 2 c in both cores the ssts during isotope stage 6 are distinctly higher by 1 2 c than the cold sst minima during the last glacial cycle lgm and stage 3 to reconstruct qualitatively the past productivity variations for the two cores we used the concentrations and fluxes of alkenones and organic carbon together with a productivity index based on coccolith species florisphaera profunda relative abundance within each core there is a general agreement between the different palaeoproductivity proxies in the southeastern arabian sea core md900963 glacial stages correspond to relatively high productivity whereas warm interstadials coincide with low productivity all time series of productivity proxies are dominated by a cyclicity of about 21 23 kyr which corresponds to the insolation precessional cycle a hypothesis could be that the ne monsoon winds were stronger during the glacial stages which induced deepening of the surface mixed layer and injection of nutrients to the euphotic zone by contrast the records are more complicated in the upwelling region of the western arabian sea core ty93 929 p this is partly due to large changes in the sedimentation rates which were higher during specific periods isotope stages 6 5 4 5 2 3 and 2 unlike core md900963 no simple relationship emerges from the comparison between the 18o stratigraphy and productivity records the greater complexity observed for core ty93 929 p could be the result of the superimposition of different patterns of productivity fluctuations for the two monsoon seasons the sw monsoon being enhanced during interglacial periods whereas the ne monsoon was increased during glacial intervals a similar line of reasoning also could help explain the sst records by the superimposition of variations of three components global atmospheric temperature and sw and ne monsoon dynamics

micropaleontology and palynology of core par87a 10 a 23 000 year record of paleoenvironmental changes in the gulf of alaska northeast north pacific micropaleontological data of core par87a 10 reveal that the last glacial interval prior to 13 ka was marked by low biogenic fluxes and poor caco3 preservation quantitative estimates of sea surface conditions based on dinocyst assemblages suggest that cold temperatures and freezing winter conditions existed during this period the glacial to interglacial transition i e the 13 8 ka interval was characterized by an increase in fluxes of microfossils indicating enhanced productivity in surface waters a higher biogenic carbonate production probably resulted in better preservation of caco3 this interval was marked by relatively low salinity and by sea surface temperatures increasing toward modern values relatively high pollen flux during the transition suggests nutrient inputs through atmospheric and or fluvial transport from the adjacent north american continent after 8 ka diminished fluxes of plankton concomitant with a decline in pollen input are associated with decreasing nutrient supply as predominantly eastward winds became established over the north pacific

glacier bed characteristics of midtre lovenbreen svalbard from high resolution seismic and radar surveying we conducted a seismic and radar survey of the central part of midtre lovenbreen a small polythermal valley glacier in svalbard we determined the physical properties of the material beneath the glacier by measuring the reflection coefficient of the bed by comparing the energy of the primary and multiple reflections and deriving the acoustic impedance by making reasonable assumptions about the properties of the basal ice we determined the acoustic impedance of the bed material as 6 78 1 53 x 10 6 kg m 2 s 1 we interpret the material beneath the glacier to be permafrost with up to 50 ice and we speculate that the material may be frozen talus similar to a deposit observed directly by others beneath another svalbard glacier the implication for midtre lovenbreen is that the basal material beneath the present glacier is not able to support fast flow we conclude that midtre lovenbreen has most likely had limited capability for faster flow in the past with motion dominated by internal deformation midtre lovenbreen is used as a study glacier for the scientific community in svalbard and a large number of studies have been based there our results show that it cannot be used as an analogue for larger glaciers in svalbard having distinct basal boundary conditions

twenty years of cold surface layer thinning at storglaciaren sub arctic sweden 1989 2009 this paper presents the changes in the thermal structure of the polythermal glacier storglaciaren northern sweden over the 20 year period 1989 2009 derived by comparing maps of the depth of the englacial transition between cold ice permanently frozen and temperate ice which contains water inclusions the maps are based on interpreted ice penetrating radar surveys from 1989 2001 and 2009 complex thinning of the cold layer first identified between 1989 and 2001 is still ongoing a volume calculation shows that storglaciaren has lost one third of its cold surface layer volume in 20 years with a mean thinning rate of 0 80 0 24 m a 1 we suggest that the thinning of the cold layer at storglaciaren is connected to the climatic warming experienced by sub arctic scandinavia since the 1980s and we argue that repeated ice penetrating radar surveys over the ablation area of polythermal glaciers offer a useful proxy for evaluating glacier responses to changes in climate

temporal variability in the northern arabian sea oxygen minimum zone omz during the last 225 000 years the northern arabian sea is one of the few regions in the open ocean where thermocline water is severely depleted in oxygen the intensity of this oxygen minimum zone omz has been reconstructed over the past 225 000 years using proxies for surface water productivity water column denitrification winter mixing and the aragonite compensation depth acd changes in omz intensity occurred on orbital and suborbital timescales lowest o2 levels correlate with productivity maxima and shallow winter mixing precession related productivity maxima lag early summer insolation maxima by 6 kyr which we attribute to a prolonged summer monsoon season related to higher insolation at the end of the summer periods with a weakened or even non existent omz are characterized by low productivity conditions and deep winter mixing attributed to strong and cold winter monsoonal winds the timing of deep winter mixing events corresponds with that of periods of climatic cooling in the north atlantic region

vertical distribution of water within the polythermal storglaciaren sweden 1 knowledge of water content and its distribution in polythermal glaciers is required to model their flow and thermal state however observations of water content variations with depth in polythermal glaciers are scarce water content can be estimated from radio wave speed because they depend on one another we obtained continuous profiles of radio wave speed variations with depth from zero offset radar profiles collected in boreholes approximately 80 m deep in the upper ablation area of storglaciaren northern sweden these profiles show that the microcrystalline water system in the temperate ice is relatively homogeneous the overall hydrothermal structure at this location is composed of a 20 m thick upper layer of cold water free ice underlain by a temperate ice layer whose average water content is 0 6 0 3 these results are corroborated by surface radar and thermistor measurements which show that the depth of the cold temperate transition is 21 m and the calculated water content at that transition is 0 6 0 1 these findings imply that the whole temperate ice layer is from 3 to 4 times softer than the cold ice and consequently that realistic ice flow models of polythermal glaciers should include the effect of water content on viscosity

meltwater production due to strain heating in storglaciaren sweden 1 storglaciaren northern sweden is temperate in most parts except for a cold surface layer in the ablation zone one of four possible sources for liquid water in temperate ice is melting due to strain heating velocity fields are calculated with an ice flow model so that calculated and observed surface velocities agree meltwater accumulation is computed by integrating strain heating along trajectories starting at the surface in the accumulation area and ending at the cold temperate transition surface in the ablation zone the distribution of moisture content due to strain heating alone is mapped in a longitudinal section of storglaciaren values reach more than 10 g of water per kilogram ice water mixture in the lowest parts of the temperate domain for this moisture content the rate factor is more than 3 times higher than for water free ice and therefore water production by strain heating is important for the modeling of temperate and polythermal glaciers

low sea level rise projections from mountain glaciers and icecaps under global warming the mean sea level has been projected to rise in the 21st century as a result of global warming such projections of sea level change depend on estimated future greenhouse emissions and on differing models but model average results from a mid range scenario a1b suggests a 0 387 m rise by 2100 refs 1 2 the largest contributions to sea level rise are estimated to come from thermal expansion 0 288 m and the melting of mountain glaciers and icecaps 0 106 m with smaller inputs from greenland 0 024 m and antarctica 0 074 m here we apply a melt model and a geometric volume model to our lower estimate of ice volume and assess the contribution of glaciers to sea level rise excluding those in greenland and antarctica we provide the first separate assessment of melt contributions from mountain glaciers and icecaps as well as an improved treatment of volume shrinkage we find that icecaps melt more slowly than mountain glaciers whose area declines rapidly in the 21st century making glaciers a limiting source for ice melt using two climate models we project sea level rise due to melting of mountain glaciers and icecaps to be 0 046 and 0 051 m by 2100 about half that of previous projections

the influence of snow cover thickness on the thermal regime of tete rousse glacier mont blanc range 3200 m a s l consequences for outburst flood hazards and glacier response to climate change 1 tete rousse glacier french alps was responsible for an outburst flood in 1892 that devastated the village of st gervais le fayet close to chamonix causing 175 fatalities changes in the hydrothermal configuration of the glacier are suspected to be the cause of this catastrophic outburst flood in 2010 geophysical surveys of this glacier revealed a subglacial lake that was subsequently drained artificially the processes controlling the thermal regime of the glacier have been investigated on the basis of measurements and snow firn cover and heat flow models using meteorological data covering the last 200 years temperature measurements show a polythermal structure with subglacial water trapped by the cold lowest part of the glacier 2 c the modeling approach shows that the polythermal structure is due to temporal changes in the depth of the snow firn cover at the glacier surface paradoxically periods with negative mass balances associated with warmer air temperature tend to cool the glacier whereas years with colder temperatures associated with positive mass balances tend to increase the glacier temperature by increasing the firnpack depth and extent the thermal effect of the subglacial lake is evaluated and shows that the lake was formed around 1980 according to future climate scenarios modeling shows that the glacier may cool again in the future this study provides insights into the thermal processes responsible for water storage inside a small almost static glacier which can lead to catastrophic outburst floods such as the 1892 event or potentially dangerous situations as in 2010

landscape evolution and ice sheet behaviour in a semi arid polar environment james ross island ne antarctic peninsula this study of landscape evolution presents both new modern and palaeo process landform data and analyses the behaviour of the antarctic peninsula ice sheet through the last glacial maximum lgm the holocene and to the present day six sediment landform assemblages are described and interpreted for ulu peninsula james ross island ne antarctic peninsula 1 the glacier ice and snow assemblage 2 the glacigenic assemblage which relates to lgm sediments and comprises both erratic poor and erratic rich drift deposited by cold based and wet based ice and ice streams respectively 3 the boulder train assemblage deposited during a mid holocene glacier readvance 4 the ice cored moraine assemblage found in front of small cirque glaciers 5 the paraglacial assemblage including scree pebble boulder lags and littoral and fluvial processes and 6 the periglacial assemblage including rock glaciers protalus ramparts blockfields solifluction lobes and extensive patterned ground the interplay between glacial paraglacial and periglacial processes in this semi arid polar environment is important in understanding polygenetic landforms crucially cold based ice was capable of sediment and landform genesis and modification this landsystem model can aid the interpretation of past environments but also provides new data to aid the reconstruction of the last ice sheet to overrun james ross island

accelerated volume loss in glacier ablation zones of ne greenland little ice age to present mountain glaciers at the periphery of the greenland ice sheet are a crucial freshwater and sediment source to the north atlantic and strongly impact arctic terrestrial fjord and coastal biogeochemical cycles in this study we mapped the extent of 1 848 mountain glaciers in ne greenland at the little ice age we determined area and volume changes for the time periods little ice age to 1980s and 1980s to 2014 and equilibrium line altitudes there was at least 172 76 34 55 km3 volume lost between 1910 and 1980s that is a rate of 2 61 0 52 km3 year between 1980s and 2014 the volume lost was 90 55 18 11 km3 that is a rate of 3 22 0 64 km3 year implying an increase of 23 in the rate of ice volume loss overall at least 7 of mass loss from greenland mountain glaciers and ice caps has come from the ne sector

selective preservation of organic walled dinoflagellate cysts as a tool to quantify past net primary production and bottom water oxygen concentrations to understand the role of the ocean within the global carbon cycle detailed information is required on key processes within the marine carbon cycle bio production in the upper ocean export of the produced material to the deep ocean and the storage of carbon in oceanic sediments quantification of these processes requires the separation of signals of net primary production and the rate of organic matter decay as reflected in fossil sediments this study examines the large differences in degradation rates of organic walled dinoflagellate cyst species to separate these degradation and productivity signals for this accumulation rates of cyst species known to be resistant r cysts or sensitive s cysts to aerobic degradation of 62 sites are compared to mean annual chlorophyll a sea surface temperature sea surface salinity nitrate and phosphate concentrations of the upper waters and deepwater oxygen concentrations furthermore the degradation of sensitive cysts as expressed by the degradation constant k and reaction time t has been related to bottom water o2 the studied sediments were taken from the arabian sea north western african margin north atlantic western equatorial atlantic ocean caraibic south western african margin south atlantic and southern ocean atlantic sector significant relationships are observed between a accumulation rates of r cysts and upper water chlorophyll a concentrations b accumulation rates of s cysts and bottom water o2 and c degradation rates of s cysts kt and bottom water o2 relationships that are extremely weak or are clearly insignificant on all confidence intervals are between 1 s cyst accumulation rates and chlorophyll a concentrations sea surface temperature sst sea surface salinity sss phosphate concentrations p and nitrate concentrations n 2 between r cyst accumulation rates and bottom water o2 sst sss p and n and between 3 kt and water depth co variance is present between the parameters n and p n p and chlorophyll a oxygen and water depth correcting for this co variance does not influence the significance of the relationship given above the possible applicability of dinoflagellate cyst degradation to estimate past net primary production and deep ocean ventilation is discussed 2007 published by elsevier b v

late holocene changes in character and behaviour of land terminating glaciers on james ross island antarctica virtually no information is available on the response of land terminating antarctic peninsula glaciers to climate change on a centennial timescale this paper analyses the topography geomorphology and sedimentology of prominent moraines on james ross island antarctica to determine geometric changes and to interpret glacier behaviour the moraines are very likely due to a late holocene phase of advance and featured 1 shearing and thrusting within the snout 2 shearing and deformation of basal sediment 3 more supraglacial debris than at present and 4 short distances of sediment transport retreat of 100m and thinning of 15 20m has produced a loss of 0 1km3 of ice the pattern of surface lowering is asymmetric these geometrical changes are suggested most simply to be due to a net negative mass balance caused by a drier climate comparisons of the moraines with the current glaciological surface structure of the glaciers permits speculation of a transition from a polythermal to a cold based thermal regime small land terminating glaciers in the northern antarctic peninsula region could be cooling despite a warming climate

comparison of radio echo sounding 30 1000 mhz and high resolution borehole temperature measurements at finsterwalderbreen southern spitsbergen svalbard

a model computation of moisture content in polythermal glaciers measurements in boreholes and internal radar horizons confirm the existence of polythermal structures in polar and subpolar glaciers and ice sheets the occurrence of an intraglacial phase boundary makes it necessary to consider two layers and transition conditions between cold and temperate ice the governing field equations and constitutive relations for a two layer model are stated with emphasis on boundary and transition conditions a reduced plane flow model is introduced by using dimensionless variables and performing a scale analysis according to the stated aim of this paper a parallel sided slab model is suitable for rough analyses of borehole measurements its governing equations are deduced and their analytical and numerical treatment is discussed sensitivity tests reveal a strong dependence of moisture content profiles on the numerical value of the water diffusivity coefficient and especially on strain heating

evidence towards a thermal lag in the response of karsaglaciaren northern sweden to climate change recent topographical and ground penetrating radar gpr surveys of karsaglaciaren which is a small 1 km 2 and thin 56 m mountain glacier in arctic sweden show that there are small areas of temperate ice in the lowermost part of the glacier this is curious because we would expect such a small and thin glacier to have a fully cold ablation zone specifically with our analyses of present glacier geometry and thickness and of the prevailing climate we are unable to explain the presence of temperate ice within the snout of karsaglaciaren using prevailing models of glacier thermal structure this leads us to suggest that the presence of temperate ice within karsaglaciaren is a remnant of a previous polythermal state that existed when the glacier was larger and thicker karsaglaciaren is thus out of synch with current geometry and climate and is exhibiting a thermal lag we propose that with time karsaglaciaren s ablation zone and perhaps the entire glacier may well become fully cold as the temperate zone shrinks further we anticipate that such a thermal lag is likely to be present within other arctic glaciers a thermal lag and an evolution to a fully cold thermal state have significant implications for the dynamic behaviour of small arctic glaciers and for meltwater production from them

sub milankovitch cycles in periplatform carbonates from the early pliocene great bahama bank high resolution bulk sediment magnetic susceptibility and aragonite content and 18o records from two different planktonic foraminifera species were analyzed in an early pliocene core interval from the straits of florida ocean drilling program site 1006 the 18o record of the shallow dwelling foraminifera g sacculifer and the aragonite content are dominated by sub milankovitch variability in contrast magnetic susceptibility and the 18o record of the deeper dwelling foraminifera g menardii show precession cycles the relationship between the aragonite and the paleoproxy data suggests that the export of sediment from the adjacent great bahama bank was triggered directly by atmospheric processes rather than by sea level change we propose a climate mechanism that bears similarities with the semiannual cycle component of eastern equatorial pacific sea surface temperatures under present day conditions

variations in tropical convection as an amplifier of global climate change at the millennial scale the global expression of millennial scale climatic change during the glacial period and the persistence of this signal in holocene records point to atmospheric teleconnections as the mechanism propagating rapid climate variations we suggest rearrangements in the tropical convection system globally affected the concentration and location of atmospheric water vapour and modulated terrestrial and marine emissions of ch4 and n2o providing a tropical mechanism of amplifying and perpetuating millennial scale climate changes a multi proxy reconstruction reflecting various aspects of the intensity of the arabian sea summer monsoon shows strong millennial scale variability over the past 90 kyr in which low intensity is associated with a southern shift of the intertropical convergence zone itcz and an eastward shift in the equatorial convergence zone the monsoon reconstruction which is based on new data from a somali margin sediment core is supported by previously reported tropical paleoclimatic records and suggests that global scale millennial climatic variability is in part driven by modulations in the tropical hydrological cycle and tropical emissions of the greenhouse gases ch4 and n2o

quiescent phase dynamics and surge history of a polythermal glacier hessbreen svalbard hessbreen is a 5 km 2 polythermal glacier in southern spitsbergen it is believed to have surged at the end of the 19th century and another surge started in 1969 not in 1972 as earlier studies suggested the surge was probably triggered in the middle section of the glacier and affected the upper part approximately 4 years before including the whole glacier present velocities are low increasing from 0 3 m a 1 at the snout to 4 8 m a 1 above the equilibrium line a distinct velocity reduction occurs where the glacier narrows this suggests the velocities here are affected by the cold marginal and frontal ice large seasonal variations with summer velocities of more than twice the winter velocities in the middle part of the glacier indicate a seasonal change in the drainage system in this area in the lower part there is no apparent sliding the balance flux estimate indicates that the actual ice flux is only about 50 of that required for steady state so hessbreen appears to be building up in the accumulation area the surge duration is now estimated to be 8 years

high resolution mapping of supra glacial drainage pathways reveals link between micro channel drainage density surface roughness and surface reflectance this paper reports on the use of a small unmanned aerial vehicle suav carrying a standard compact camera to construct a high resolution orthomosaic om and digital elevation model dem over the lower reaches of the glacier midtre lovenbreen svalbard structure from motion sfm techniques were used to build the om and dem and together these reveal insights into the nature of supra glacial drainage major meandering supra glacial drainage pathways show clear dynamism via meander cutoffs and abandoned channels in addition the imagery reveals a very extensive network of smaller channels that may well carry substantial amounts of water this network of channels is in part controlled by the structure of the glacier but in turn these channels have a significant impact on the ice surface roughness of the ice surface is higher where channels are most extensive in addition we find a relationship between channel density and surface reflectance such that greater channel density is associated with lower reflectance values given the role of surface reflectance and roughness in the energy balance of glaciers it is therefore apparent that extensive networks of small supra glacial channels across such glaciers have the potential to have an important impact on energy exchanges between the atmosphere and the ice surface copyright 2015 john wiley sons ltd

palaeo ecological significance transport and preservation of organic walled dinoflagellate cysts in the somali basin nw arabian sea to date relatively little information is available about factors influencing organic walled cyst production of tropical dinoflagellates and processes influencing the final burial of cysts in bottom sediments such as transport and preservation to extend this information cyst fluxes were documented for three sediment traps from june 1992 to february 1993 at two sites in the somali basin northwestern arabian sea as well as the cyst association of underlying sediments by comparing cyst associations of contemporaneously collected trap samples at different depths at one site information about transport and processes of decay in the water column was obtained neither transport nor decay appears to have any detectable influence on cyst association during cyst settlement through the water column comparing the trap associations with the underlying sediments indicates that downslope transport appears to have influenced the cyst association on a local scale only species selective decay probably related to the presence of oxygen in bottom sediments has influenced the cyst association most pronouncedly at the most offshore site relating variations in the trap associations with environmental conditions of the overlying surface waters indicates that highest production of both filled and empty cysts occurs during the sw monsoon upwelling based on this correlation three groups of species can be distinguished species with highest fluxes during 1 the first half of the sw monsoon june august bitectatodinium spongium echinidinium granulatum echindinium transparantum echinidnium spp cysts of protoperidinium compressum and cysts of protoperidinium subinerme 2 the transition between the sw monsoon and inter monsoon spiniferites mirabilis and spiniferites spp 3 no particular season all other species cyst associations of all trap samples are dominated by cyst of protoperidinium species cysts with highest fluxes during the sw monsoon form about a third of the associations

coupled sea surface temperature seawater δ18o reconstructions in the arabian sea at the millennial scale for the last 35 ka two sediment cores from the western 905 10 46 9 n 51 56 4 e water depth 1586 m and eastern sk17 15 15 n 72 58 e water depth 840 m arabian sea were used to study past sea surface temperatures sst and seawater 18o 18ow variations for the past 35 ka we used coupled mg ca 18o calcite variability in two planktonic foraminiferal species globigerinoides ruber which thrives throughout the year and globigerina bulloides which occurs mainly when surface waters contain high nutrients during upwelling or convective mixing ssts in both areas based on mg ca in g ruber were 3 to 4 c lower during the last glacial maximum lgm 21 ka than today and the holocene period the sst records based on g bulloides also indicate general cooling down to 18 c in both areas ssts in the western arabian sea based on g bulloides were always lower than those based on g ruber indicating the presence of strong seasonal temperature contrast during the holocene and lgm we interpret the consistent presence of this seasonal temperature contrast to reflect a combination of seasonal summer upwelling sw monsoon and winter convective mixing ne monsoon in the western arabian sea in the eastern arabian sea g bulloides based ssts were slightly lower about 1 c than g ruber based ssts during the holocene indicating the almost absence of a seasonal temperature gradient similar to today however a large seasonal temperature contrast occurred during the lgm which favors the assumption that strong ne monsoon winds forced winter upwelling or convective mixing offshore goa sst and 18ow reconstructions reveal evidence of millennial scale cycles particularly in the eastern arabian sea here the stadial periods northern hemisphere cold periods such as younger dryas and heinrich events are marked by increasing ssts and salty sea surface conditions relative to those during the interstadial periods indeed the 18ow record shows evidence of low saline surface waters during interstadial periods indicating increased freshwater runoff from the western ghats as a consequence of enhanced sw monsoon intensity

the thermal regime of sub polar glaciers mapped by multi frequency radio echo sounding radio echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale radar signals of 320 370 mhz penetrate ice at sub freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water radar signals of 5 20 mhz on the other hand see through both the cold and the temperate ice down to the glacier bed radio echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in svalbard kongsvegen uversbreen midre lovenbreen and austre broggerbreen in the ablation area of kongsvegen a cold surface layer 50 160m thick was underlain by a warm basal layer which is advected from the temperate accumulation area the surface ablation of this cold layer may be compensated by freezing at its lower cold temperate interface this requires that the free water content in the ice at the freezing interface is about 1 of the volume the cold surface layer is thicker beneath medial moraines and where cold based hanging glaciers enter the main ice stream on uversbreen the thermal regime was similar to that of kongsvegen a temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between kongsvegen and uversbreen where meltwater accumulates during the summer near the subglacial lake setevatnet 250 m a s l lovenbreen was frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer up to 50m thick was fed by temperate ice from two cirques on austre broggerbreen a temperate basal layer was not detected by radio echo soundings but the basal ice was observed to be at the melting point in two boreholes

detection of buried ice and sediment layers in permafrost using multi frequency ground penetrating radar a case examination on svalbard abstract we use multi frequency ground penetrating radar gpr to detect and map buried relic glacier ice and sediments in permafrost old aerial photographs 1936 1990 are used to show the origin of a sediment covered ice body and illustrate how it has been buried together with a newly exposed ice sediment cliff this serves as excellent ground truthing for the gpr data empirical gpr frequency dependent relations are established to quantify the loss of the signal power through the layer of sediment the loss through ice is in comparison negligible these relations indicate that the maximum ice pocket detection depth for this sediment type with the different gpr systems used are 90 150 and 200 ns for the 800 500 and 200 mhz systems respectively the electromagnetic em wave velocities calculated from diffractions yield velocities ranging between 0 115 0 135 m ns for the sediment and 0 15 0 17 m ns for the ice with the derived em wave velocities these two way travel twt times correspond to a depth of 6 9 and 13 m respectively this loss cannot be tested for the 200 and 500 mhz systems due to lack of such a deep sediment layer on top of the ice but is consistent with the 800 mhz data

dinoflagellate cysts as environmental indicators in surface sediments from the congo deep sea fan and adjacent regions abstract forty nine surface sediment samples from the congo deep sea fan and adjacent hydrographic environments were prepared palynologically and analyzed for fossilizable dinoflagellate cysts the main objective was to investigate the extent to which cysts reflect present day hydrography and therefore may be used downcore as paleoceanographic indicators the region sampled covers a range of marine environments including the congo river plume the area of pronounced upwelling off west central africa and a nearshore offshore gradient from coastal to oceanic waters this is the first study of the effect of a major tropical river plume on associated cyst assemblages cyst counts were low particularly near the river mouth and furthest offshore a combination of statistical treatments was used to analyze the surface cyst assemblages including cluster analysis correspondence analysis and canonical correspondence analysis this helped to identify five distinctive sample groupings representing the main ecological signals in the cyst assemblage data group a dominated by spherical brown protoperidinioid cysts is an upwelling signal group b dominated by the cosmopolitan species o centrocarpum is the main signal for the river plume effect interpreted as reflecting the environmental instability this creates group c dominated by s delicatus with accessory o centrocarpum characterizes the outer plume somehow reflecting the mixing of progressively diluted river plume water and the surrounding oceanic waters group d with high proportions of impagidinium and nematosphaeropsis together with o centrocarpum and s delicatus characterizes the location of the angola benguela front group e with mainly impagidinium species is an oceanic signal the identification of nutrients and water stability as main determining factors influencing cyst signals has implications for cyst based paleoenvironmental interpretations using transfer functions which are developed almost exclusively from comparisons with more easily available data for sea surface temperature salinity and sea ice

improved method to determine radio echo sounding reflector depths from ice core profiles of permittivity and conductivity we present a technique that modifies and extends down hole target methods to provide absolute measures of uncertainty in radar reflector depth of origin we use ice core profiles to model wave propagation and reflection and then cross correlate the model results with radio echo sounding res data to identify the depth of reflector events stacked traces recorded with res near the epica drill site in dronning maud land antarctica provide reference radargrams and dielectric properties along the deep ice core form the input data to a forward model of wave propagation that produces synthetic radargrams cross correlations between synthetic and res radargrams identify differences in propagation wave speed they are attributed to uncertainties in pure ice permittivity and are used for calibration removing conductivity peaks results in the disappearance of related synthetic reflections and enables the unambiguous relation of electric signatures to res features we find that i density measurements with attenuation or dielectric profiling are too noisy below the firn ice transition to allow clear identification of reflections ii single conductivity peaks less than 0 5 m wide cause the majority of prominent reflections beyond a travel time of about 10 s 900 m depth and iii some closely spaced conductivity peaks within a range of 1 2m cannot be resolved within the res or synthetic data our results provide a depth accuracy to allow synchronization of age depth profiles of ice cores by res modeling of isochronous internal structures and determination of wave speed and of pure ice properties the technique successfully operates with dielectric profiling and electrical conductivity measurements suggesting that it can be applied at other ice cores and drill sites

a high resolution record of late quaternary upwelling along the oman margin arabian sea based on planktonic foraminifera planktonic foraminiferal abundances fluxes test sizes and coiling properties are influenced in various ways by the southwest monsoon winds and associated upwelling in the western arabian sea to determine the short term changes in the southwest monsoon we have carried out a high resolution time series analysis of three upwelling indices total flux of planktonic foraminiferal tests and flux and relative abundance of the planktonic foraminiferal species globigerina bulloides from ocean drilling program odp site 723a oman margin western arabian sea spanning the last 19 kyr in addition we have determined the relationships between upwelling intensity and the relative abundance fluxes and shell concentrations of various planktonic foraminiferal species upwelling indices suggest that from 19 to 16 ka 22 to 18 2 cal kyr b p the sw monsoon was relatively strong compared to the period 15 8 to 12 5 ka 17 8 to 13 8 cal kyr b p the intensification of the sw monsoon took place at 12 ka 13 1 cal kyr b p and reached a peak between 10 and 5 ka 10 6 and 4 8 cal kyr b p the high resolution data further demonstrate that the sw monsoon has started weakening from 5 ka 4 8 cal kyr b p and the weakest phase was in place at 3 5 ka 3 cal kyr b p which coincides with evidence of an arid climate in western tibet fluxes and shell concentrations of many of the planktonic foraminiferal species increased between 12 and 5 ka in response to the intensification of the sw monsoon winds after the last glacial period globigerina bulloides shows a fivefold to tenfold increase in flux during this period of intense upwelling the other species whose fluxes are influenced by this upwelling change are in order from strongest to weakest response globigerinita glutinata globigerinoides ruber neogloboquadrina dutertrei globigerinella aequilateralis globigerina falconensis and globigerinoides sacculifer the relative abundances of g bulloides and g ruber increased during intense upwelling whereas the relative abundances of g glutinata n dutertrei g falconensis and g sacculifer did not increase during this period which might be due to differences in the productivity of various species in relation to upwelling change therefore the fluxes and shell concentrations provide better and more reliable information about the changes in the monsoon system in the arabian sea than relative abundance data

high resolution holocene monsoon record from the eastern arabian sea through stable oxygen and carbon analyses of rapidly accumulating sediment cores from the eastern arabian sea we show that the excess of evaporation over precipitation e p steadily appears to have decreased during the last 10 000 to 2000 years most probably due to an increasing trend in the summer monsoon rainfall contrary to the land based paleoclimatic data from this region which indicate onset of aridity around 4000 years ago our results are consistent with the hypothesis that significant spatial variability in the monsoon rainfall observed today was persistent during most of the holocene alternatively the trend can be seen as an adjustment between two phases one between 10 000 and 6000 years ago of increasing precipitation and another between 3500 and 2000 years ago after the arid episode we also report a significant 700 year periodicity similar to that reported recently from the south china sea indicating that the centennial millennial scale response of the indian and chinese monsoons to high latitude forcing may be alike

comparison of thermal structure and evolution between neighboring subarctic glaciers 1 the distribution of cold and temperate ice within glaciers and ice sheets affects processes relevant to englacial and basal hydrology sliding and material rheology thermal regimes in turn are shaped by glacier and ice sheet dynamics as well as environmental setting we investigate the thermal structures of two small 7 km2 neighboring glaciers in the st elias mountains of southwestern yukon canada using ice penetrating radar and borehole temperature measurements our data reveal polythermal regimes in both glaciers that are strongly influenced by accumulation zone meltwater entrapment suggesting a climatic control on thermal structure differences in hypsometry and glacier dynamics nevertheless result in observed variations in the distribution of temperate ice between the two sites experiments with a thermomechanically coupled flow band model corroborate the strong control of meltwater entrapment on thermal structure and suggest a generally minimal role for strain heating an exception to this occurs where localized basal sliding produces lateral shearing and thus enhanced heat generation time dependent model simulations suggest that the future thermal evolution of the two glaciers may differ and therefore simple parameterizations of thermal response based on regional climate may not capture realistic variability between individual glaciers despite these differences both glaciers are ultimately expected to become fully cold prior to disappearing under negative mass balance conditions

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

hydrology and dynamics of a polythermal mostly cold high arctic glacier to improve our understanding of the interactions between hydrology and dynamics in mostly cold glaciers in which water flow is limited by thermal regime we analyse short term every two days variations in glacier flow in the ablation zone of polythermal john evans glacier high arctic canada we monitor the spatial and temporal propagation of high velocity events and examine their impacts upon supraglacial drainage processes and evolving subglacial drainage system structure each year in response to the rapid establishment of supraglacial subglacial drainage connections in the mid ablation zone a spring event of high horizontal surface velocities and high residual vertical motion propagates downglacier over two to four days from the mid ablation zone to the terminus subsequently horizontal velocities fall relative to the spring event but remain higher than over winter reflecting channelization of subglacial drainage but continued supraglacial meltwater forcing further transient high velocity events occur later in each melt season in response to melt induced rising supraglacial meltwater inputs to the glacier bed but the dynamic response of the glacier contrasts with that recorded during the spring event with the degree of spatial propagation a function of the degree to which the subglacial drainage system has become channelized copyright 2006 john wiley sons ltd

imaging the mountainless root of the 1 8 ga cheyenne belt suture and clues to its tectonic stability receiver function analysis across the cheyenne belt an archean proterozoic suture images a 100 km wide zone of 50 60 km thick crust this thick crust is thought to be a remnant from the original 1 8 ga suturing event the thick and presumably buoyant crust is remarkable in that it is not associated with a large topographic or gravitational anomaly suggesting isostatic balance and a high density mass at depth to compensate the crustal root these features could account for the lithosphere s long term stability the presence of eclogite below the crustal root is a likely source for the high density mass as it would not produce a seismically unusual moho yet it would provide the required excess mass

review of subglacial hydro mechanical coupling trapridge glacier yukon territory canada abstract the interaction of basal processes with the subglacial drainage system is a critical issue in understanding glacier dynamics since the recognition that many glaciers and ice masses overlie soft sediments rather than hard bedrock much research has been undertaken to investigate how mechanical and hydrological conditions of a deformable substrate control the coupling at the ice bed interface and thus affect fast ice flow and glacier surging in research undertaken on trapridge glacier a small surge type glacier in the st elias mountains yukon territory canada we have combined extensive field investigations using novel measurement techniques and theoretical modelling to study hydro mechanical coupling processes measurements of subglacial water pressure indicate that the basal water system can be dramatically inhomogeneous both spatially and temporally since ice bed coupling is strongly influenced by subglacial water pressure the stresses at the bed are also markedly heterogeneous and are expected to form a patchwork distribution which mimics the pressure distribution of the basal water system this heterogeneity in the stress field at the ice bed interface introduces a pronounced variability to the basal motion mechanics as such basal sliding and subglacial sediment deformation are not steady and continuous processes instead the variability of the subglacial water system leads to a spatial and temporal interplay of increased ice bed coupling at low water pressures at one site or time with ice bed decoupling during rising water pressures at other sites or times thus on the one hand there is downglacier shear deformation of the bed and accumulation of elastic strain in ice and sediment while on the other hand there is enhanced slip sliding of the glacier and upglacier shear motion of the bed due to an elastic relaxation of the sediment

ice thickness areal and volumetric changes of davies dome and whisky glacier james ross island antarctic peninsula in 1979 2006 this study calculates area volume and elevation changes of two glaciers on james ross island antarctica during the period 1979 2006 davies dome is a small ice cap whisky glacier is a valley glacier ground penetrating radar surveys indicate ice thickness which was used for calculations of the bed topography and volume of both glaciers maximum measured ice thicknesses of davies dome and whisky glacier are 83 2 and 157 2 m respectively between 1979 and 2006 the area of the ice cap decreased from 6 23 0 05 km2 to 4 94 0 01 km2 20 7 while the area of the valley glacier reduced from 2 69 0 02 km 2 to 2 40 0 01 km2 10 6 over the same period the volume of the ice cap and valley glacier reduced from 0 23 0 03 km3 to 0 16 0 02 km3 30 4 and from 0 27 0 02 km3 to 0 24 0 01 km3 10 6 respectively the mean surface elevation decreased by 8 5 2 8 and 10 1 2 8 m the average areal 0 048 0 011 km2 a 1 and volumetric 0 003 0 001 km3 a 1 changes are higher than the majority of other estimates from antarctic peninsula glaciers