spatial and seasonal effects of temperature variability in a positive degree day glacier surface mass balance model this doctoral dissertation presents a study of the glacial history of the north american cordillera using numerical ice sheet modelling calibrated against field evidence this area characterized by the steep topography of several mountain ranges separated by large inter montane depressions was once covered by a large scale ice mass the former cordilleran ice sheet because of the irregular topography on which the ice sheet formed geological studies have often had only local or regional relevance thus leaving the cordilleran ice sheet least understood among pleistocene ice sheets in terms of its extent volume and dynamics here i present numerical simulations that allow quantitative reconstructions of the former ice sheet evolution based on approximated physics of glacier flow these simulations show that the geometry of the last glacial maximum cordilleran ice sheet was largely controlled by sharp contrasts in regional temperature precipitation and daily temperature variability associated with the presence of mountain ranges however this maximum stage appears short lived and out of balance with contemporaneous climate during most of the simulated last glacial cycle the north american cordillera is characterized by an intermediate state of glaciation including isolated glaciers and ice caps covering major mountain ranges the largest of which is located over the skeena mountains the numerically modelled cordilleran ice sheet appears in constant imbalance with evolving climate conditions while the complexity of this transient response transcends that encapsulated in two dimensional conceptual models of ice sheet growth and decay this thesis demonstrates the potential of numerical ice sheet modelling to inform on ice sheet history and former climate conditions over a glacial cycle given that ice sheet models can be calibrated against field constraints

a rise in the carbonate compensation depth of western tethys in the carnian late triassic deep water evidence for the carnian pluvial event the upper triassic of the lagonegro basin southern apennines southern italy is represented by hemipelagic cherty limestones of the calcari con selce formation deposited in an oceanic setting two stratigraphic sections petina chiana and pignola 2 representative of the evolution of the lagonegro basin during the carnian have been studied in detail with a multidisciplinary approach in the pignola 2 section within the calcari con selce formation a unique interval composed of green shales and radiolarites has been identified the absence of carbonate deposition within this interval is interpreted as evidence of a contemporaneous shallowing of the carbonate compensation depth conodont and palynomorph biostratigraphy constrain the age of this interval to the julian tuvalian lower carnian upper carnian boundary the age and characteristics of this interval suggest correlation with a putative climatic event known as the carnian pluvial event which has also been recognized in continental and shallow marine successions from different european localities this event is thus now documented also in a deep marine setting like the continental and shallow water settings it is characterized by a sudden input of siliciclastics petina chiana and pignola 2 integrate current knowledge of the carnian distribution of conodonts paragondolella praelindae kozur to date known only from the lower tuvalian has now been documented from the uppermost julian moreover a drastic turnover was recorded between julian and tuvalian conodont assemblages which is clearly associated with the carnian pluvial event thus a biotic crisis oceanographic changes associated with the rise of the carbonate compensation depth increased rainfall and an anomalous siliciclastic input occur contemporaneously at the time of the carnian pluvial event a similar pattern is associated with perturbations of the carbon cycle that occur during the jurassic and cretaceous e g in the early aptian thus it is hypothesized that the carnian pluvial event may have analogous causes

linking fluvial bed sediment transport across scales 1 we present a new random walk model for bed load sediment transport that explains the scale dependency generally observed in transport rates and captures the transient anomalous dispersion often seen in rivers particles alternate between mobile and resting phases with a tempered stable probability distribution for both particle step length and resting time tempered fractional mobile immobile differential equations model the ensemble average of particle dynamics the model is tested against data from three sediment dispersion experiments using tempering in both space and time the new model is able to capture the full range of observed ensemble particle dynamics the random walk model illuminates the physical meaning of all transport parameters in the mobile immobile equations and explains transitions between observed super diffusive sub diffusive and regular diffusive ensemble particle dynamics by explicitly predicting the effects of spatial and temporal averaging on particle dynamics this method can be used to link observations of fluvial sediment dynamics across scales this approach is also generally applicable to a wide variety of geophysical and ecological dynamics such as ecological dispersal pathogen transmission in rivers nutrient export from watersheds and large scale geomorphodynamics associated with infrequent phenomena such as avalanches and turbidity currents

positive degree day factors for ablation on the greenland ice sheet studied by energy balance modelling ice ablation is related to air temperature by the positive degree day factor variations of the positive degree day factor in west greenland are studied using an energy balance model to simulate ablation under different conditions degree day factors for simulated and measured ice ablation at nordbogletscher and qaman rssup sermia agree well with values around 8 mm d 1 c 1 degree day factors for snow are less than half those for ice energy balance modelling shows that degree day factors vary with summer mean temperature surface albedo and turbulence but there is only evidence of large positive degree day factors at lower temperatures and with low albedo 0 3 the greatest effect of albedo variations 0 3 0 7 is at lower temperatures while variations in turbulence have greater effect at higher temperatures current models may underestimate runoff from the greenland ice sheet by several tenths because they use a degree day factor for melting ice that is too small for the colder parts of the ice sheet i e the upper ablation area and the northerly margin

melting at the base of the greenland ice sheet explained by iceland hotspot history basal melting is widespread in the north central greenland ice sheet geophysical data and numerical modelling suggest a geothermal anomaly in this region resulting from the earlier passage of greenland over the iceland mantle plume

recent cooling in coastal southern greenland and relation with the north atlantic oscillation 1 analysis of new data for eight stations in coastal southern greenland 1958 2001 shows a significant cooling trend line change 1 29 c for the 44 years as do sea surface temperatures in the adjacent part of the labrador sea in contrast to global warming 0 53 c over the same period the land and sea temperature series follow similar patterns and are strongly correlated but with no obvious lead lag either way this cooling is significantly inversely correlated with an increased phase of the north atlantic oscillation nao over the past few decades r 0 76 and will probably have significantly affected the mass balance of the greenland ice sheet

late triassic and early jurassic palaeogeography of the world abstract a new version of global and regional palaeogeographic maps is presented for two time intervals these maps depict the plate tectonic configuration palaeoenvironment and lithofacies during the late triassic carnian norian and early jurassic hettangian toarcian time the individual maps illustrate the general conditions present during the maximum marine transgressions of higher frequency cyclicity within the absaroka sequence of sloss during triassic time pangaea began to stretch initiating the rifting and future break up of the supercontinent the continued northward drift of the cimmerian continent corresponded with the progressive closure and consumption of palaeotethys oceanic crust and the opening of the neotethys ocean the most significant late triassic convergent event was the indosinian orogeny occurring as a result of the consolidation of south china and north china blocks also indochina and indonesia were sutured to south china at the same time the qiangtang block approached the eurasian margin the consolidation of the north chinese and amurian blocks left open a large embayment of panthalassa between amuria and laurasia the so called mongol okhotsk ocean active subduction existed along the margin of this ocean dipping cratonwards towards east siberia the last collisional events of the uralian orogeny took place during the triassic and early jurassic time the conclusion of the uralian orogeny was accompanied by uplift of the adjacent areas of eastern europe and western siberia during the early jurassic the palaeotethys ocean was finally closed and the cimmerian continent collided with asia causing the cimmerian orogeny the time around the triassic jurassic boundary marked an important biotic extinction event plate tectonic activity caused palaeogeographic and palaeoclimatic change which may have contributed to the mass extinction from the plate tectonic and palaeogeographic point of view the following events could have influenced the extinction 1 the closure of palaeotethys and assembly of the asian part of pangaea 2 the break up of pangaea in the future central atlantic area and transition from rifting to drifting and 3 the very extensive basaltic volcanism of the central atlantic magmatic province

triassic climates state of the art and perspectives abstract the climate of the triassic period was characterized by a non zonal pattern dictated by a strong global monsoon system with effects that are most evident in the tethys realm this strong monsoonal regime is related to the aggregation of the pangaean supercontinent which by triassic time was already completed climate oscillations existed within this framework the harsh hot house climatic conditions that characterized the late permian and perhaps precipitated the end permian mass extinction were probably maintained during the early triassic and may account for the impoverished but distinctive faunal and floral lower triassic associations although metazoan reef builders were probably the most affected group carbonate production remained high at least in the western tethys realm the middle triassic was characterized locally by humid episodes although their geographical distribution has yet to be clarified the carnian pluvial event marks an episode of increased rainfall documented worldwide was the most distinctive climate change within the triassic different hypotheses have been proposed for its causes changes of atmospheric or ocean circulation driven by plate tectonics a peak of the global monsoon due to maximum continent aggregation or triggering by the eruption of a large igneous province subsequently the late carnian and norian seem to have been climatically stable although minor climatic changes have recently been described even from this time period finally the end triassic extinction event is also associated with climate change specifically warming and increased rainfall but this evidence comes mostly from the northern parts of the central atlantic magmatic province and the global pattern of climate change at the triassic jurassic boundary has still to be resolved many facets of triassic climate are intriguing and deserve further research however palaeoclimate studies on the triassic have so far been carried out only locally with different proxies those proxies will require inter calibration in order to depict correctly the temporal and geographical patterns of triassic climate

climate variability during the carnian pluvial phase a quantitative palynological study of the carnian sedimentary succession at lunz am see northern calcareous alps austria abstract the middle and upper triassic prevailing dry climate was interrupted by a global phase of increased humidity during the early carnian the carnian pluvial phase cpp it started at the julian 1 2 boundary and lasted approximately until the latest julian or early tuvalian in the tethys this is reflected by a change from limestone deposits to first organic rich mudstones and then to siliciclastics the cpp occurred along the northern rim of the tethys and is reported from many locations within and surrounding europe in this study samples from lunz am see in austria were analyzed for palynology and for bulk carbon isotope values covering a 450 m thick succession a known 3 bulk organic carbon isotope excursion possibly as a result of the eruption of large amounts of volcanogenic material in the gostling member and the basal reingraben formation has been confirmed a total of five distinctive palynology assemblages were recognized and correlated regionally while the under and overlying formations yield terrestrial and subordinate also marine palynomorphs the palynoflora of the lunz formation is near wholly terrestrial in origin climate trends were inferred from multivariate statistical analysis pca of the palynofloral record palynomorphs show a general trend from a dry climate during the julian 1 to wetter conditions during the julian 2 the wetter conditions were periodically interrupted by shorter periods of dryer climate in terms of temperature trends the climate was warmer during the early julian 2 which corresponds with the deposition of the reingraben formation temperature decreased again and remained fairly stable during most of later part of the julian 2 which corresponds to the deposition of the lunz formation this study correlates with similar observations from other locations from the western tethys region that support the theory of a wide ranging to global carnian pluvial phase

surface energy balance in the ablation zone of langfjordjokelen an arctic maritime glacier in northern norway glaciers in northern and southern norway are subject to different daily and seasonal cycles of incoming solar radiation which is presumably reflected in the importance of net solar radiation in their surface energy balance we present a 3 year continuous record from an automatic weather station in the ablation zone of the ice cap langfjordjokelen one of the most northerly glaciers of mainland norway despite its location at 708 n langfjordjokelen was found to have a maritime climate with an annual mean air temperature of 1 08c frequent cloud cover and end of winter snow depths over 3m in all three years the main melt season was may october but occasional melt events occurred on warm cloudy winter days net solar and longwave radiation together accounted for 58 of the melt energy with a positive contribution by net longwave radiation 7 the sensible and latent heat fluxes supplied the remainder of the melt energy cloud optical thickness over langfjordjokelen was larger than on two glaciers in southern norway especially in the summer months this resulted in a smaller contribution of net solar radiation to surface melt on langfjordjokelen the effect of the higher latitude on net solar radiation was found to be small

recent ice dynamics and mass balance of jorge montt glacier southern patagonia icefield the southern patagonia icefield spi withdrawal in recent decades shows contrasting behaviours between adjacent basins one of the basins with highest volumetric losses is located at northernmost spi we refer to jorge montt tidewater glacier 48 30 s 73 30 w 445 km 2 in 2018 which retreated 2 7 km between 2011 and 2018 and thinned at rates of up to 21 m a 1 over this period based on the retreat record remote sensing imagery field data a mass balance model and a calving parameterisation we attempted to differentiate climatic induced changes i e surface mass balance and dynamic responses i e calving fluxes the surface mass balance reached 4 15 km 3 w e a 1 between 2012 and 2017 when frontal ablation is included the net mass balance is 17 79 km 3 w e a 1 this represents a change of trend compared with modelling estimations of positive surface mass balance prior to 2010 this shift is attributed to higher ablation rates given that accumulation is known to have increased between 1980 and 2015 the available evidence therefore indicates that frontal ablation is the main factor supported by observed rates at jorge montt as high as 3 81 km 3 w e a 1 in 2015 with ice velocities peaking at 11 km a 1

greenland ice sheet surface mass balance variability 1991 2003 the polar mm5 mesoscale atmospheric model was run for 13 years 1991 2003 over greenland at 24 km horizontal resolution box and others 2004 the model physics were driven by satellite station and weather balloon observational data assimilation i e european centre for medium range weather forecasts ecmwf operational analysis the analysis in this study focuses on the response of the surface mass balance to its primary controls temperature and precipitation the results indicate coherent spatial patterns of variability and statistically significant links with temperature and precipitation and the north atlantic oscillation precipitation trends have the same spatial pattern and sign as temperature suggesting an association of precipitation and temperature variability increasing temperatures contribute to an increasing ablation trend and expansion of the ablation zone despite increasing accumulation trends the pinatubo philippines volcanic cooling in the early 1990s enhances this apparent warming trend only in the northeast does precipitation appear to dominate the surface mass balance where both temperature and precipitation have decreased there is little evidence for a total ice sheet surface mass balance trend although the meltwater runoff has a positive trend and combined with iceberg discharge and basal melting estimates suggests the ice sheet as a whole is in a state of net mass loss over this period

climate variations in the boreal triassic inferred from palynological records from the barents sea this paper presents palynological evidence from the late early triassic late smithian to the late triassic rhaetian of the barents sea area a continuous palynological succession from an exploration well 7228 7 1a in the nordkapp basin sw barents sea and palynological data from a series of shallow cores drilled at the svalis dome central barents sea representing selected triassic intervals these fully marine sediments are independently dated by marine faunas both records show significant shifts in the distribution of the main floral elements changing ratios of spore pollen taxa grouped as hygrophytes versus xerophytes and spores versus pollen reveal major changes of the floras within the studied interval one distinct turnover coincides with the smithian spathian boundary where lycopsid and pteridophyte spores dominated assemblages change to pollen pteridosperms and conifers dominated assemblages lower middle triassic assemblages are again dominated by lycopsid spores while the assemblages from the upper part of the middle triassic and the lower part of the late triassic are characterised by dominance of coniferous pollen and show the decline of pteridosperms in the latest triassic fern spores are abundant and diverse in contrast to the middle triassic the pollen assemblages are characterized by cycadophytes and araucariacites these distribution patterns are interpreted to reflect climatic changes the presented results from norwegian boreal areas confirm the significant differences between quantitative distribution of specific taxa as well as diversity of major groups in plant assemblages from low and mid latitudes the present survey opens new perspectives for more detailed comparisons and climatic interpretations of floras from the triassic period a time during which mesozoic vegetation established the major changes in the dominance of specific floral elements especially the diversification and spreading of the conifers can probably be related to climatic changes

modelling of large scale melt parameters with a regional climate model in south greenland during the 1991 melt season large scale positive degree day based melt parameterizations for the greenland ice sheet are highly sensitive to their parameters standard temperature deviation snow and ice degree day factors in this paper these parameters are simulated with a coupled atmosphere snow regional climate model for southern greenland during summer 1991 forced at the lateral boundaries with european centre for medium range weather forecasts re analyses at a high horizontal resolution of 20 kin the calculated from net ablation i e melt minus refreezing snow and ice positive degree day factors vary considerably over the ice sheet at low elevations the modelled snow degree day factor closely approaches the generally accepted value of 3 mm w e d 1 degreesc 1 higher up the ice sheet large values up to 15 mm w e d 1 degreesc 1 are simulated for ice melt maximum values of 40 mm w e d 1 degreesc 1 are found the snow and ice positive degree day factor distributions peak respectively at 3 and 8 mm w e d 1 degreesc 1 refreezing is of small importance close to the ice sheet margin higher up the ice sheet refreezing considerably lowers the amount of net ablation the monthly simulated 2 in air temperature standard deviation exhibits a strong seasonal cycle with the highest 3 0 5 0degreesc values in may and june july shows the lowest temperature fluctuations due to the melting of the surface

a new classification of the turkish terranes and sutures and its implication for the paleotectonic history of the region abstract the turkish part of the tethyan realm is represented by a series of terranes juxtaposed through alpine convergent movements and separated by complex suture zones different terranes can be defined and characterized by their dominant geological background the pontides domain represents a segment of the former active margin of eurasia where back arc basins opened in the triassic and separated the sakarya terrane from neighbouring regions sakarya was re accreted to laurasia through the balkanic mid cretaceous orogenic event that also affected the rhodope and strandja zones the whole region from the balkans to the caucasus was then affected by a reversal of subduction and creation of a late cretaceous arc before collision with the anatolian domain in the eocene if the anatolian terrane underwent an evolution similar to sakarya during the late paleozoic and early triassic times both terranes had a diverging history during and after the eo cimmerian collision north of sakarya the kure back arc was closed during the jurassic whereas north of the anatolian domain the back arc type oceans did not close before the late cretaceous during the cretaceous both domains were affected by ophiolite obduction but in very different ways north directed diachronous middle to late cretaceous melange obduction on the jurassic sakarya passive margin senonian synchronous southward obduction on the triassic passive margin of anatolia from this it appears that the izmir ankara suture currently separating both terranes is composite and that the passive margin of sakarya is not the conjugate margin of anatolia to the south the cimmerian taurus domain together with the beydaglari domain part of the larger greater apulian terrane were detached from north gondwana in the permian during the opening of the neotethys east mediterranean basin the drifting cimmerian blocks entered into a soft collision with the anatolian and related terranes in the eo cimmerian orogenic phase late triassic thus suturing the paleotethys at that time the taurus plate developed foreland type basins filled with flysch molasse deposits that locally overstepped the lower plate taurus terrane and were deposited in the opening neotethys to the south these olistostromal deposits are characterized by pelagic carboniferous and permian material from the paleotethys suture zone found in the mersin melange the latter as well as the antalya and mamonia domains are represented by a series of exotic units now found south of the main taurus range part of the mersin exotic material was clearly derived from the former north anatolian passive margin huglu type series and re displaced during the paleogene this led us to propose a plate tectonic model where the anatolian ophiolitic front is linked up with the samail baer bassit obduction front found along the arabian margin the obduction front was indented by the anatolian promontory whose eastern end was partially subducted continued slab roll back of the neotethys allowed anatolian exotics to continue their course southwestward until their emplacement along the taurus southern margin mersin and up to the beydaglari promontory antaya mamonia in the latest cretaceous paleocene the supra subduction ocean opening at the back of the obduction front troodos type ocean was finally closed by eocene north south shortening between africa and eurasia this brought close to each other cretaceous ophiolites derived from the north of anatolia and those obducted on the arabian promontory the latter were sealed by a maastrichtian platform and locally never affected by alpine tectonism whereas those located on the eastern anatolian plate are strongly deformed and metamorphosed and affected by eocene arc magmatism these observations help to reconstruct the larger frame of the central tethyan realm geodynamic evolution

a new chronology for the end triassic mass extinction article i nfo the transition from the triassic to jurassic period initiating the age of the dinosaurs approximately 200 ma is marked by a profound mass extinction with more than 50 genus loss in both marine and continental realms this event closely coincides with a period of extensive volcanism in the central atlantic magmatic province camp associated with the initial break up of pangaea but a causal relationship is still debated the triassic jurassic t j boundary is recently proposed in the marine record at the first occurrence datum of jurassic ammonites post dating the extinction interval that concurs with two distinct perturbations in the carbon isotope record the continental record shows a major palynological turnover together with a prominent change in tetrapod taxa but a direct link to the marine events is still equivocal here we develop an accurate chronostratigraphic framework for the t j boundary interval and establish detailed trans atlantic and marine continental correlations by integrating astrochronology paleomagnetism basalt geochemistry and geobiology we show that the oldest camp basalts are diachronous by 20 kyr across the atlantic ocean and that these two volcanic pulses coincide with the end triassic extinction interval in the marine realm our results support the hypotheses of phanerozoic mass extinctions resulting from emplacement of large igneous provinces lips and provide crucial time constraints for numerical modelling of triassic jurassic climate change and global carbon cycle perturbations

the treatment of meltwater retention in mass balance parameterisations of the greenland ice sheet retention of melt water runoff by percolation and or refreezing in the snowpack cannot be neglected when studying the surface mass balance of the greenlandice sheet in this paper we make a detailed comparison of several treatments proposed in the literature to account for this process in large scale mass balanceparameterizations the melt on the greenland ice sheet is calculated with a revised degree day model using updated datasets of surface elevation and precipitationrate on a 5 km grid crucial model parameters are recalibrated by comparing mass balance characteristics with available observations on a regional basis wediscuss the role of meltwater retention in the light of the overall mass balance of the greenland ice sheet and its sensitivity to climatic change and displaypatterns of effective retention fractions for the various methods as a main conclusion it appears that overall results are quite similar for the various models butthat meltwater retention has a large spatial variation not described by the simple treatments using the most comprehensive retention model the sensitivity of therunoff is found to be 0 35 mm deg c of sea level change per year we also present a new map of the different zones facies that characterize the accumulationarea of the greenland ice sheet that is useful for interpreting field data and calibrating satellite observations

a simple physics based improvement to the positive degree day model meltwater is important to understanding glacier health and dynamics since melt measurements are uncommon ice ablation estimates are often based on models including the positive degree day pdd model the pdd estimate is popular since it only requires air temperature as input but suffers from the lack of physical motivation of an energy balance model we present a physics based alternative to the pdd model that still only takes air surface temperature as input the model resembles the pdd model except accounting for time lags in ablation when cold ice needs to be warmed the model is expressed as a differential equation with a single extra parameter related to the efficiency of heating a near surface layer of ice with zero thickness the model reduces to the pdd model providing a physical basis for the pdd model applying the model to data from greenland it improves modestly upon the pdd model with the main improvement being better prediction of early season melting this new model is a useful compromise with some of the physics of more realistic models and the simplicity of a pdd model the model should improve estimates of meltwater production and help constrain pdd parameters when empirical calibration is challenging

degree day glacier mass balance modelling with applications to glaciers in iceland norway and greenland a degree day glacier mass balance model is applied to three glaciers in iceland norway and greenland for which detailed mass balance measurements are available over a period of several years model results are in good agreement with measured variations in the mass balance with elevation over the time periods considered for each glacier in addition the model explains 60 80 of the year to year variance in the elevation averaged summer season mass balance measurements on the glaciers using a single parameter set for each glacier the increase in ablation on the glaciers due to a warming of 2 c is predicted to range from about 1 m w e year 1 at the highest elevations to about 2 5 m w e year 1 at the lowest elevations predicted changes in the winter balance measured between fixed date are relatively small except at the lowest elevations on the icelandic and norwegian glaciers where the winter balance is significantly reduced equilibrium line altitudes are raised by 200 300 m on the icelandic and norwegian glaciers except at the highest elevations the winter balance of the icelandic and norwegian glaciers is predicted to decrease even if the warming is accompanied by a 10 increase in the precipitation no firm evidence of a climate related variation in the degree day factors or in the temperature lapse rate on the same glacier could be found the model furthermore reproduces large variations in the mass balance with elevation and from year to year on each glacier using the same parameter set we assume therefore that these parameters will not change significantly for the climate scenarios considered here

the changing climate framework and depositional dynamics of triassic carbonate platforms from the dolomites abstract the triassic of the dolomites offers a valuable opportunity to investigate the relationships between climate fluctuations and the changing depositional dynamics of carbonate platforms the reconstruction of the large palaeoclimatic modification is based on the synthesis of multiple sedimentological palaeobotanical pedological and geochemical proxies the triassic climate fluctuations were generally fast in nature and were probably associated with a latitudinal shift of the monsoon belts during the triassic the dolomites were placed at an intertropical northern latitude of about 16 18 and were generally dominated by dry climate and elevated temperature at least five pulses toward moister climate are however documented dated to early olenekian middle anisian late ladinian middle carnian and late norian times within this variable climatic scenario the carbonate systems record a global evolutionary trend from late permian early triassic regional shelves rich in loose micrites and bio calcarenites to anisian ladinian synsedimentary cemented steep sided 35 40 high relief platforms and back to carnian low angle ramps moist transgressive episodes were surprisingly prone to the spreading of corals and other colonial reef organisms probably because of the reduced space competition by syndepositional cementation structures the permo triassic boundary extinction dramatically impacted on the calcified organism communities but the carbonate depositional architecture nevertheless stayed almost unaffected through the boundary the early triassic and earliest anisian were commonly associated with hyperhaline sometimes evaporitic conditions intervals of moister climate and efficient river discharge are however documented by earliest induan and early olenekian sediments the latter terrigenous deposits matched a crisis in the carbonate production after a return to arid conditions during the anisian a fluctuation toward moister climate developed associated to a massive continental vegetation cover the anisian tectonic activation of the region fragmented the previous carbonate shelf triggering the development of three generations of fast prograding but globally backstepping isolated platforms recording an increasing role of the synsedimentary cementation a dry climate dominated the late anisian and early ladinian interval at the time a fast subsidence pulse was associated with platform drowning and basinal anoxia only a few aggrading pinnacles were able to survive providing the nuclei for larger prograding platforms during a dry climate interval massive syndepositional cementation generated a major source of carbonate carbonate production stayed active through the ladinian magmatic phase but the onset of volcanism was associated with a large modification in the platform carbonate facies which became dominated by automicrites moist climate phases are well documented again during the late ladinian followed by a return to dry conditions the late ladinian early carnian platforms prograded toward the eastern dolomites depocentre eventually infilling almost the whole of the accommodation space the middle portion of the carnian recorded renewed sharply moist phases associated with the demise of the rimmed platforms and with the return to loose sediment ramps at least four separated humid fluctuations can be identified in this carnian interval alone climate then returned to persistent aridity until the late norian moist phase

a carbon isotope perturbation at the pliensbachian toarcian boundary evidence from the lias group ne england a perturbation in the carbon isotope record at the time of the pliensbachian toarcian boundary 184 ma in the early jurassic is reported based on new data from yorkshire england two sharp 13 c org negative excursions each with a magnitude of 2 5 and reaching minimum values of 28 5 are recorded in the bulk organic matter record in sediments of latest pliensbachian to earliest toarcian age a similar pattern of negative carbon isotope excursions has been observed at the stage boundary in the sw european section at peniche portugal in 13 c carbonate 13 c wood and 13 c brachiopod records the isotopic excursion is of interest when considering the genesis and development of the later toarcian oceanic anoxic event oae as well as the second order global extinction event that spans the stage boundary furthermore the isotope excursion potentially provides a chemostratigraphic marker for recognition of the stage boundary which is currently achieved on the basis of different ammonite faunas in the nw european and tethyan realms

surface mass balance changes of the greenland ice sheet since 1866 mass loss from the greenland ice sheet over the past decade has caused the impression that the ice sheet has been behaving anomalously to the warming of the 1990s we have reconstructed the recent 1866 2005 surface mass balance smb history of the greenland ice sheet on a 5 5 km grid using a runoff retention model based on the positive degree day method the model is forced with new datasets of temperature and precipitation patterns dating back to 1866 we use an innovative method to account for the influence of year on year surface elevation changes on smb estimates and have found this effect to be minor all smb estimates are made relative to the 1961 90 average smb and we compare annual smb estimates from the period 1995 2005 to a similar period in the past 1923 33 where smb was comparable and conclude that the present day changes are not exceptional within the last 140 years peripheral thinning has dominated the smb response during the past decade as in 1923 33 but we also show that thinning was not restricted to the margins during this earlier period

estimating greenland surface melt is hampered by melt induced dampening of temperature variability he positive degree day pdd model provides a particularly simple approach to estimate surface melt from land ice based solely on air temperature here we use a climate and snow pack simulation of the greenland ice sheet modele atmospherique regional mar as a reference to analyze this scheme in three realizations that incorporate the sub monthly temperature variability differently i by local values ii by local values that systematically overestimate the dampened variability associated with intense melting or iii by one constant value local calibrations reveal that incorporating local temperature variability particularly resolving the dampened variability of melt areas renders model parameters more temperature dependent this indicates that the negative feedback between surface melt and temperature variability introduces a non linearity into the temperature melt relation to assess the skill of the individual realizations we hindcast melt rates from mar temperatures for each realization for this purpose we globally calibrate greenland wide constant parameters realization i exhibits shortcomings in the spatial representation of surface melt unless temperature dependent instead of constant parameters are calibrated the other realizations perform comparatively well with constant parametrizations the skill of the pdd model primarily depends however on the consistent calibration rather than on the specific representation of variability

calibrating a glaciological model of the greenland ice sheet from the last glacial maximum to present day using field observations of relative sea level and ice extent we constrain a three dimensional thermomechanical model of greenland ice sheet gris evolution from the last glacial maximum lgm 21 ka bp to the present day using primarily observations of relative sea level rsl as well as field data on past ice extent our new model huy2 fits a majority of the observations and is characterised by a number of key features i the ice sheet had an excess volume relative to present of 4 1 m ice equivalent sea level at the lgm which increased to reach a maximum value of 4 6 m at 16 5 ka bp ii retreat from the continental shelf was not continuous around the entire margin as there was a younger dryas readvance in some areas the final episode of marine retreat was rapid and relatively late c 12 ka bp leaving the ice sheet land based by 10 ka bp iii in response to the holocene thermal maximum htm the ice margin retreated behind its present day position by up to 80 km in the southwest 20 km in the south and 80 km in a small area of the northeast as a result of this retreat the modelled ice sheet reaches a minimum extent between 5 and 4 ka bp which corresponds to a deficit volume relative to present of 0 17 m ice equivalent sea level our results suggest that remaining discrepancies between the model and the observations are likely associated with non greenland ice load differences between modelled and observed present day ice elevation around the margin lateral variations in earth structure and or the pattern of ice margin retreat

a tethys wide mid carnian upper triassic carbonate productivity crisis evidence for the alpine reingraben event from spiti indian himalaya abstract a significant mid carnian lithological change from carbonatic to siliciclastic sedimentation is described from the spiti himalaya n india the recorded sudden increase of terrigenous influx occurs at the boundary from the chomule to the rama formation it is dated within the late lower carnian uppermost aonoides zone and isochronous all over the tethys himalaya bio and chemostratigraphic data point to a synchrony with changes in carbonate productivity known from on area of wide extent along the nw tethys the reingraben event of the northern calcareous alps austria defines a regional decline in carbonate productivity related to both a platform demise and enhanced siliciclastic input laminated shales found in a distal part of the spiti basin document the onset of anoxic conditions within the deeper shelf synchronous to the reingraben event in austria high resolution biostratigraphy and identical 13ccarb curves are therefore in support of a direct link between the change in spiti and the reingraben event our data combined with a comprehensive review of previously postulated scenarios regarding the reingraben event suggest linking of climatic change with siliciclastic input and a carbonate productivity crisis initiated by onset of a relatively humid megamonsoonal late lower carnian atmospheric system that affected both the southern and northwestern tethys and point to a supra regional trigger of the alpine reingraben event

carbon isotope stratigraphy and palynostratigraphy of the triassic jurassic transition in the tiefengraben section northern calcareous alps austria abstract the end triassic is characterized by enhanced rates of biotic turnover in both the marine and terrestrial realms carbon isotope anomalies have been reported worldwide that may indicate coeval global disturbances in the biogeochemical cycles here we present the results of an integrated study of the palynomorph assemblages and the carbon isotope composition of organic matter in the tiefengraben section near st wolfgang austria carbon isotope values from bulk organic matter show significant fluctuations through the triassic jurassic t j boundary interval with two prominent negative 13 c org excursions an initial negative carbon isotope excursion occurs at the base of the kendlbach formation tiefengraben member pre planorbis beds although triassic ammonoids and conodonts have their highest occurrence at the top of the underlying kossen formation the palynomorph and calcareous microfossil assemblages indicate still a rhaetian age for the lower part of the tiefengraben member high abundance of prasinophytes during the interval of the initial carbon isotope excursion may represent a bloom of green algae that flourished as a result of the disturbance of the marine ecosystems increased spore abundance together with the disappearance of distinctive late triassic pollen types e g ovalipollis rhaetipollis indicate vegetation changes on land that are contemporaneous with the marine biotic crisis a second negative carbon isotope excursion occurs in the middle part of the tiefengraben member based on palynological evidence the t j boundary may be drawn at about this level by the lowest occurrence of cerebropollenites thiergartii the established carbon isotope curve as well as palynostratigraphic and other biostratigraphic events can be correlated with st audrie s bay england

a 5 year record of surface energy and mass balance from the ablation zone of storbreen norway a 5 year record of data from an automatic weather station aws operating in the ablation zone of storbreen norway has been used to calculate the local surface energy and mass balance the aws observations cover five mass balance years with an unusually strong mass deficit on storbreen the average energy flux q contributing to melt for the period 2001 06 is 113wm 2 of this the net shortwave radiation flux is the dominant contributor 92wm 2 followed by the sensible heat flux 20 wm 2 and the latent heat flux 9 w m 2 the net longwave radiation 6w m 2 and the subsurface heat flux 2 w m 2 contribute negatively to the budget net radiation thus produces 76 of the melt while the turbulent fluxes and the subsurface heat flux produce 24 of the total melt the seasonal mean incoming shortwave radiation is remarkably constant between the years whereas variations in temperature and reflected shortwave radiation albedo explain most of the interannual variation in melt the modelled ablation compares well with the measured ablation from stake readings the sensitivity of the energy balance model was examined by varying the surface roughness length of momentum and the sensitivity of the calculated melt by perturbations of temperature wind speed and relative humidity

a benchmark dataset of in situ antarctic surface melt rates and energy balance abstract surface melt on the coastal antarctic ice sheet ais determines the viability of its ice shelves and the stability of the grounded ice sheet but very few in situ melt rate estimates exist to date here we present a benchmark dataset of in situ surface melt rates and energy balance from nine sites in the eastern antarctic peninsula ap and coastal dronning maud land dml east antarctica seven of which are located on ais ice shelves meteorological time series from eight automatic and one staffed weather station neumayer ranging in length from 15 months to almost 24 years serve as input for an energy balance model to obtain consistent surface melt rates and energy balance results we find that surface melt rates exhibit large temporal spatial and process variability intermittent summer melt in coastal dml is primarily driven by absorption of shortwave radiation while non summer melt events in the eastern ap occur during fohn events that force a large downward directed turbulent flux of sensible heat we use the in situ surface melt rate dataset to evaluate melt rates from the regional atmospheric climate model racmo2 and validate a melt product from the quikscat satellite

assessment of current methods of positive degree day calculation using in situ observations from glaciated regions the continued use of the positive degree day pdd method to predict ice sheet melt is generally favoured over surface energy balance methods partly due to the computational efficiency of the algorithm and the requirement of only one input variable temperature in this paper we revisit some of the assumptions governing the application of the pdd method using hourly temperature data from the gc net network we test the assumption that monthly pdd total pddm can be represented by a gaussian distribution with fixed standard deviation of monthly temperature m the results presented here show that the common assumption of fixed m does not hold and that m may be represented more accurately as a quadratic function of average monthly temperature for greenland the mean absolute error in predicting pddm using our methodology is 3 9 c day representing a significant improvement on current methods 7 8 c day when m 4 5 c over a range of glaciated settings our method reproduces pddm on average to within 1 5 8 5 c day compared to 4 4 15 7 c day when m 4 5 the improvement arises because we capture the systematic reduction in temperature variance that is observed over melting snow and ice when surface temperatures cannot warm above o c