distribution of calcareous dinoflagellates from the maastrichtian to early miocene of dsdp site 357 rio grande rise western south atlantic ocean the evolution of calcareous dinoflagellate communities has been investigated for the latest cretaceous to earliest neogene interval of the mid latitude south atlantic in doing so the response of calcareous dinoflagellates to cenozoic climatic change has been addressed for the first time trends in species composition and distribution patterns of wall types indicate significant changes which correlate with major palaeoenvironmental modifications a first major shift concerning the relative abundance of species and wall types occurred across the cretaceous tertiary boundary the associations remained stable during the entire paleocene and eocene only in the late eocene did a dramatic decrease in temperature cause a slight diversification a second major shift in the abundance patterns occurred across the eocene oligocene boundary the early miocene warming is possibly reflected in the distinct increase in relative abundance of one species the assemblages of calcareous dinoflagellates evidently react to major climatic changes during the cenozoic these poorly investigated organisms may thus provide an important contribution to the understanding of earth s palaeoclimatic evolution

sensitivity of a heavy rain producing western mediterranean cyclone to embedded potential vorticity anomalies the development and track of a surface cyclone that produced heavy precipitation in the western mediterranean region on 28 29 september 1994 is numerically simulated using a mesoscale model diagnostic calculations reveal that surface pressure falls and upward motion occur in response to a well defined pattern of upward quasi geostrophic forcing at all tropospheric levels in addition convective instability and low tropospheric water vapour flux convergence are significant over the western mediterranean and therefore the environment is highly supportive for convection development the appreciable dynamical forcing at upper levels appears to be associated with two positive potential vorticity pv anomalies that are embedded within the large scale trough and rotate about each other motivated by the fact that the small scale features of the pv field are more prone to analysis or forecast error than the large scale components a sensitivity study is conducted in order to analyse the dependence of the mesoscale forecast on the initial intensity and position of the two embedded pv centres this is accomplished by first applying a piecewise pv inversion technique which allows the balanced flow associated with each pv centre to be calculated and then the inverted mass and wind fields are used to modify the model initial conditions eight simulations are run after doubling or removing one or both anomalies sensitivity to intensity and eight other simulations after displacing the anomalies towards or away from the iberian peninsula sensitivity to position the results exhibit a clear dependence of the track and shape of the surface cyclone and its associated pattern of low tropospheric warm air advection on the characteristics of the pv anomalies therefore spatial details of the mesoscale forecast are shown to be highly sensitive to the precise structure of the upper level dynamic forcing nevertheless for the full set of arbitrarily defined initial conditions one or several low pressure systems develop in the western mediterranean area and heavy precipitation always occurs on the other hand there is an overall tendency of the simulations to favour cyclone development leeward of the atlas mountain range and local rainfall enhancements over the exposed mountains of eastern spain the relative roles of the orography and sea surface latent heat flux versus the action of the upper level pv centres are examined by means of additional simulations

the poleward motion of extratropical cyclones from a potential vorticity tendency analysis abstractthe poleward propagation of midlatitude storms is studied using a potential vorticity pv tendency analysis of cyclone tracking composites in an idealized zonally symmetric moist gcm a detailed pv budget reveals the important role of the upper level pv and diabatic heating associated with latent heat release during the growth stage the classic picture of baroclinic instability emerges with an upper level pv to the west of a low level pv associated with the cyclone this configuration not only promotes intensification but also a poleward tendency that results from the nonlinear advection of the low level anomaly by the upper level pv the separate contributions of the upper and lower level pv as well as the surface temperature anomaly are analyzed using a piecewise pv inversion which shows the importance of the upper level pv anomaly in advecting the cyclone poleward the pv analysis also emphasizes the crucial role played by latent heat release in the poleward motion of the cyclone the l

global dinoflagellate event associated with the late paleocene thermal maximum the late paleocene thermal maximum or lptm ca 55 ma represents a geologically brief time interval 220 k y characterized by profound global warming and associated environmental change the lptm is marked by a prominent negative carbon isotope excursion cie interpreted to reflect a massive and abrupt input of 12 c enriched carbon to the ocean atmosphere reservoir possibly as a result of catastrophic gas hydrate release on time scales equivalent to present day rates of anthropogenic carbon input the lptm corresponds to important changes in the global distribution of biota including mass extinction of marine benthic organisms the dinoflagellate cyst record indicates that surface dwelling marine plankton in marginal seas also underwent significant perturbations during the lptm we report on the dramatic response of representatives of the genus apectodinium from two upper paleocene lower eocene sections in the southern new zealand and northern austria hemispheres where the dinoflagellate records are directly correlated with the cie benthic foraminifera extinction event and calcareous nannofossil zonation the results indicate that the inception of apectodinium dominated assemblages appears to be synchronous on a global scale and that the event is precisely coincident with the beginning of the lptm apectodinium markedly declined in abundance near the end of the lptm this apectodinium event may be associated with 1 exceptionally high global sea surface temperatures and or 2 a significant increase in marginal marine surface water productivity such a globally synchronous acme of dinoflagellate cysts is unprecedented within the dinoflagellate cyst fossil record

dinoflagellate cysts sea level changes and planktonic foraminifers across the cretaceous tertiary boundary at el haria northwest tunisia abstract dinoflagellate cysts and planktonic foraminifers have been studied from the cretaceous tertiary k t boundary interval at el haria northwest tunisia a high resolution integrated biostratigraphy is presented the k t boundary is drawn at the level of extinction of cretaceous planktonic foraminifers and is coincident with the first occurrence of the dinoflagellate cyst species danea californica the final extinction of planktonic foraminifers is foreshadowed by a reduction in their total abundance some 5 kyr earlier at the base of the boundary clay this reduction is coeval with reported anomalies in siderophyle elements and 13 c values in the same area dinoflagellate cysts do not show accelerated rates of extinction at k t time associations of dinoflagellate cysts however change drastically and parallel changes in relative numbers of sporomorphs spores and pollen and in the quantity of land derived organic matter jointly these changes reflect a rapidly falling sea level during the final 17 kyr of the mesozoic which culminates at the level of the k t boundary this steep sea level fall at k t time represents a peak regressive pulse at the end of the well documented latest cretaceous regressive trend this short term sea level fall might show to be a wide spread phenomenon which could have caused an excess shrinking of the already reduced areal extent of marginal seas since deep waters in cretaceous oceans were primarily produced in shallow marginal seas the rate of formation of deep water might have been minimized at k t time minimum rates of formation of deep water might have curtailed the slow upward mixing of relatively cool and nutrient rich deeper water through which the thermocline weakened and surficial waters became depleted in nutrients consequently phytoplankton productivity rapidly diminished which in combination with a weakened thermal gradient pushed the highly depth stratified cretaceous planktonic foraminiferal fauna to extinction over a period of time of some 5 kyr guembelitria cretacea was the sole planktonic foraminifer which could accommodate to the low productivity conditions the oscillating rise in sea level at the beginning of the cenozoic reinforced the upward mixing of relatively cool and nutrient rich deeper water steepened the thermocline and replenished the photic layer with nutrients concomitant niche differentiation in the photic layer progressively stimulated morphological innovation amongst early cenozoic planktonic foraminifers the final return of normally sized planktonic foraminifers and of stable and well balanced dinoflagellate cyst associations at about 125 kyr after the k t boundary seems to indicate that primary productivity and niche differentiation in the photic layer begin to revert to optimum levels the earliest cenozoic planktonic foraminiferal species globoconusa minutula and parvularugoglobigerina fringa are thought to have developed from a benthic foraminiferal species rather than having a planktonic ancestry

jokulhlaups a reassessment of floodwater flow through glaciers 1 in glaciated catchments glacier generated floods jokulhlaups put human activity at risk with large sporadic jokulhlaups accounting for most flood related fatalities and damage to infrastructure in studies of jokulhlaup hydrodynamics the view predominates that floodwater travels within a distinct conduit eroded into the underside of a glacier however some jokulhlaups produce subglacial responses wholly inconsistent with the conventional theory of drainage by focusing on icelandic jokulhlaups this article reassesses how floodwater flows through glaciers it is argued that two physically separable classes of jokulhlaup exist and that not all jokulhlaups are an upward extrapolation of processes inherent in events of lesser magnitude and smaller scale the hydraulic coupling of multiple nonlinear components to the flood circuit of a glacier can induce extreme responses including pressure impulses in subglacial drainage representing such complexity in mathematical form should be the basis for upcoming research as future modeling results may help to determine the glaciological processes behind heinrich events moreover such an approach would lead to more accurate predictive models of jokulhlaup timing and intensity

global cooling accelerated by early late eocene impacts at ocean drilling program site 689 maud rise southern ocean 18o records of fine fraction bulk carbonate and benthic foraminifers indicate that accelerated climate cooling took place following at least two closely spaced early late eocene extraterrestrial impact events a simultaneous surface water productivity increase as interpreted from 13c data is explained by enhanced water column mixing due to increased latitudinal temperature gradients these isotope data appear to be in concert with organic walled dinoflagellate cyst records across the same microkrystite bearing impact ejecta layer in the mid latitude massignano section central italy in particular the strong abundance increase of thalassiphora pelagica is interpreted to indicate cooling or increased productivity at massignano because impact induced cooling processes are active on time scales of a few years at most the estimated 100 k y duration of the cooling event appears to be too long to be explained by impact scenarios alone this implies that a feedback mechanism such as a global albedo increase due to extended snow and ice cover may have sustained impact induced cooling for a longer time after the impacts

the cretaceous tertiary boundary stratotype section at el kef tunisia how catastrophic was the mass extinction abstract the cretaceous tertiary k t boundary stratotype section at el kef tunisia represents the most complete and expanded sedimentary record across this important mass extinction horizon presently known high resolution analysis of planktic foraminifera in two outcrops el kef i stratotype and el kef ii along with comparisons between planktic and benthic foraminifera calcareous nannofossils ostracods pollen and spores and dinoflagellates indicate that major changes across the k t boundary are registered only in benthic and planktic foraminifera and calcareous nannofossils biotic changes in benthic foraminifera are unique to el kef and similarly shallow continental shelf sections and appear to be the result of a sea level regression in the latest maastrichtian followed by a sea level rise across the k t boundary that was accompanied by expansion of the local oxygen minimum zone omz biotic changes in planktic foraminifera appear partly related to these conditions also but in general reflect more global oceanographic changes for instance species extinctions are gradual and selective as observed in k t sections worldwide rather than random and abrupt although there is a 69 decline in species richness between 25 cm below and 10 cm above the k t boundary only rare species disappeared their combined relative abundance constitute less than 20 of the total population about 52 of these extinct taxa 8 of the population are large ornate morphologically complex tropical subtropical forms that lived at or below the thermocline no planktic foraminifera from this depth range survived the k t boundary event all survivor taxa were surface dwellers living within the photic zone their relative abundance 80 dominates both cretaceous and early tertiary populations these data indicate that the k t biotic record in the shallow continental shelf section at el kef was significantly influenced by local conditions which combined with the latest maastrichtian sea level regression and subsequent sea level rise resulted in shallowing of the local omz relative to the sea surface shallowing of the local omz lead to the selective disappearance of benthic faunas and may have adversely affected the surviving photic zone dwellers the selective nature of species extinctions however appear to be related partly to long term global oceanographic changes which were accelerated at the k t boundary possibly by a bolide impact

end cretaceous marine mass extinction not caused by productivity collapse an asteroid impact at the end of the cretaceous caused mass extinction but extinction mechanisms are not well understood the collapse of sea surface to sea floor carbon isotope gradients has been interpreted as reflecting a global collapse of primary productivity strangelove ocean or export productivity living ocean which caused mass extinction higher in the marine food chain phytoplankton dependent benthic foraminifera on the deep sea floor however did not suffer significant extinction suggesting that export productivity persisted at a level sufficient to support their populations we compare benthic foraminiferal records with benthic and bulk stable carbon isotope records from the pacific southeast atlantic and southern oceans we conclude that end cretaceous decrease in export productivity was moderate regional and insufficient to explain marine mass extinction a transient episode of surface ocean acidification may have been the main cause of extinction of calcifying plankton and ammonites and recovery of productivity may have been as fast in the oceans as on land

a history of jokulhlaups from strandline lake alaska u s a les vidanges brutales du strandline lake se produisent tous les 1 a 5 ans la vidange est precedee par le developpement d un golfe de velage dans le lobe du triumvirate glacier qui barre le lac et par le remplissage de petits lacs sur le glacier on analyse le mecanisme a partir de cartes photogrammetriques dressees avant et apres la vidange

spatial distribution of the calcareous dinoflagellate thoracosphaera heimii in the upper water column of the tropical and equatorial atlantic the horizontal and vertical distribution of the phototrophic calcareous dinoflagellate thoracosphaera heimii in the upper part of the water column 10 200 m of the equatorial and tropical atlantic ocean has been studied this first survey has been made to determine which part of the water column is inhabited by t heimii and is subsequently represented as a signal in the sediment record by this species the study concentrates on the fossilisable vegetative coccoid life stage of the species and differentiates between t heimii shells with cell content and empty ones the highest quantities of t heimii shells with cell content have been observed in water depths between 50 and 100 m and coincide with relatively lower temperatures and relatively higher salinities than respective surface conditions we propose that in the tropical equatorial atlantic the major part of the environmental signal given by t heimii can be assumed to represent the deeper levels of the upper water column

latest eocene early oligocene climate change and southern ocean fertility inferences from sediment accumulation and stable isotope data abstract the earliest oligocene 33 5 ma is marked by a major step in the long term transition from an ice free to glaciated world the transition characterized by both cooling and ice sheet growth triggered a transient but extreme glacial period designated oi 1 high resolution isotope records suggest that oi 1 lasted for roughly 400 000 yr the duration of magnetochron 13n before partially abating and that it was accompanied by an ocean wide carbon isotope anomaly of 0 75 one hypothesis relates the carbon isotope anomaly to enhanced export production brought about by climate induced intensification of wind stress and upwelling particularly in the southern ocean to understand how this climatic event affected export production in the southern ocean biogenic silica opal and carbonate accumulation rates were computed for the sub polar indian ocean using deep sea cores from odp site 744 kerguelen plateau our findings suggest that net productivity in this region increased by several fold in response to the oi 1 glaciation in addition calcareous primary producers dominant in the late eocene were partially replaced by opaline organisms suggesting a trend toward seasonally greater surface divergence and upwelling in this sector of the southern ocean we attribute these changes to intensification of atmospheric oceanic circulation brought about by high latitude cooling and the appearance of a full scale continental ice sheet on east antarctica higher terrigenous sediment accumulation rates support the idea that wind induced changes in regional productivity were augmented by an increased supply of glacial dust and debris that provided limiting micro nutrients e g iron rich dust particles we speculate that the rapid changes in biogenic sediment accumulation in the southern ocean and other upwelling dominated regions contributed to the ocean wide positive carbon isotope anomaly by temporarily increasing the burial rate of organic carbon relative to carbonate carbon the changes in burial rates in turn may have produced a positive feedback on climate by briefly drawing down atmospheric pco2

potential vorticity diagnosis of the severe convective regime part i methodology observational and modeling studies have shown that shear and instability are powerful predictors of the likelihood of severe weather and tornadoes to the extent that upper tropospheric forecast errors can be described as potential vorticity pv anomalies on the forecasted pv field knowing and being able to quantify the effects of such errors on shear and instability would allow forecasters to anticipate the effects of those errors on the likely mode of severe weather to test the sensitivity of the severe convective environment to pv fluctuations a pv inversion framework is adopted that utilizes nonlinear balance the observed pv field is modified in a way that mimics realistic perturbations of trough intensity location or shape soundings including moisture profiles are reconstructed from the balanced geopotential height field assuming that air parcels conserve mixing ratio while their isentropic surfaces are displaced upward or downward by the addition of anomalous pv unperturbed balanced soundings agree reasonably well with full unbalanced soundings and differences are attributable to departures from nonlinear balance in areas of strong vorticity or acceleration balanced vertical wind profiles do not include the effects of friction so the vertical shear of the balanced wind departs unacceptably from total shear within the lowest 1 km of the troposphere the balanced wind perturbations are added to the total analyzed shear profile to estimate the effect of pv perturbations on shear and storm relative helicity by this process the importance of typical or hypothesized upper tropospheric forecast errors may be addressed in an idealized case study or operational context

the cretaceous paleogene transition at galanderud northern alborz iran a multidisciplinary approach abstract we investigated the cretaceous paleogene k pg transition at the galanderud section northern alborz iran to identify the pattern of mass extinction of planktic foraminifera and to unravel the associated paleoenvironmental changes in a little studied area of the eastern tethys we applied a high resolution quantitative and multidisciplinary study based upon benthic and planktic foraminiferal assemblages clay mineralogy rock magnetic properties stable isotopes and geochemistry in this section the k pg boundary is marked by an abrupt change in lithology from marl to a clay boundary layer a marked decrease in magnetic susceptibility a negative 2 2 13c excursion and a peak in iridium in the uppermost maastrichtian foraminifera are well preserved and diversified suggesting a stable mesotrophic environment by contrast the k pg boundary and basal danian is marked by high values of epifaunal benthic morphogroups low planktic diversity and high percentages of opportunistic species guembelitria cretacea and cervisiella operculata suggesting highly stressed and variable conditions partly due to the dramatic collapse of calcareous primary producers benthic foraminiferal assemblages indicate outer neritic uppermost bathyal depths with slight bathymetric variations the most peculiar and unique aspect of the galanderud section is the occurrence of the three thin chalk layers interbedded within clays above the k pg boundary each marked by positive shifts in 13c and 18o values and consisting of 80 carbonate we propose that the chalk clay deposits in the basal danian reflect changes in seawater chemistry and dynamic changes in circulation upwelling alternating with episodes of enhanced weathering and runoff this section on the northern margin of eastern tethys provides new clues about the pattern of the k pg mass extinction and the paleoenvironmental changes occurring during the biotic recovery phase

middle eocene to early oligocene paleoceanography of the antarctic ocean maud rise odp leg 113 site 689 change from a low to a high productivity ocean the sediment record from the middle eocene about 45 ma to the early oligocene about 33 ma on maud rise site 689 weddell sea paleodepth 1400 1650 m has been studied by means of a coarse fraction analysis in order to reconstruct variations in surface water productivity and bottom water masses productivity has been estimated using carbonate dissolution and accumulation rates of radiolaria diatoms benthonic and planktonic foraminifers sponge debris ostracods and echinoids accumulation rates of bolboforma spp vary parallel to these proxies productivity increased with time three episodes were found in which productivity increased sharply and productivity varied cyclically with a period of 430 ky the middle eocene ca 45 44 37 26 ma was a period of generally low productivity no opal was deposited and carbonate preservation was excellent during periods of a slight increase in productivity accumulation rates of benthonic and planktonic foraminifers ostracods and echinoids increased in spite of an increase in carbonate dissolution in the period ca 41 62 43 07 ma productivity rose in three distinct pulses clinoptilolite formed from biogenous opal is a common mineral in these sediments these three productivity maxima coincide with a mica rich unit mica probably originated from erosion on antarctica and was transported by an intermediate water depth current in the late eocene ca 36 9 34 95 ma productivity increased considerably and opal skeletons were deposited carbonate dissolution increased but planktonic foraminifer accumulation rates were not markedly decreased in periods of higher productivity because productivity increase exceeded or equalled rises in dissolution rates increasing opal accumulation rates coincided with increases in the rates for benthonic foraminifers sponge debris ostracods and echinoids in the late eocene early oligocene period 34 95 33 05 ma a further increase in productivity led to a strong dissolution of planktonic foraminifers in high productivity periods the productivity increase is probably due to the increasing pole equator temperature gradient which led to stronger atmospheric and oceanic turnover and mixing in the oceans in the uppermost late eocene two unusual layers suggest changes in bottom water masses affecting the seafloor at site 689 a sediment interval with especially well preserved carbonate microfossils underlies an interval that has poor carbonate preservation despite evidence of low productivity these intervals suggest a change in bottom water conditions from warm saline deep water wsdw which favors carbonate preservation to antarctic bottom water aabw which promotes carbonate dissolution cooling of surface waters over a period of 300 ky led to a thickening of the deep aabw layer and an upward shift of the overlying wsdw until the aabw finally reached the top of the maud rise in the area of site 689 this period of aabw influence on top of the maud rise lasted 200 ky

on the response of calcareous dinoflagellates to oligotrophy and stratification of the upper water column in the equatorial atlantic ocean abstract large numbers of calcareous dinoflagellate cysts and the vegetative calcareous coccoid species thoracosphaera heimii are generally found in sediments underlying oligotrophic and or stratified sub surface water environments it is difficult to distinguish between the relative importance of these two environmental parameters on calcareous cyst and t heimii distribution as they usually covary but this information is essential if we want to apply cysts properly in the reconstruction of palaeoenvironments and past surface water hydrography in the multi proxy core geob 1523 1 from the ceara rise region in the western equatorial atlantic ocean covering the past 155 ka periods of greatest oligotrophy are not synchronous with periods of greatest stratification ruhlemann et al mar geol 135 1996 127 152 mulitza et al geology 25 1997 335 338 mulitza et al earth planet sci lett 155 1998 237 249 giving us the unique opportunity to differentiate between the effects of both parameters on cyst accumulation the calcareous cyst record of the core reflects prominent increases in accumulation rate of nearly all observed species only during the nutrient enriched but more stratified isotopic sub stages 5 5 5 3 5 1 and 1 in this respect the distribution trends in the core are more similar to those of the eastern equatorial upwelling region geob 1105 4 than they are to those of the oligotrophic north eastern brazilian continental slope geob 2204 2 even though temporal changes in bioproductivity are principally in antiphase between the eastern and western equatorial regions we conclude that stratification of the upper water column and the presence of a well developed thermocline are probably the more important factors controlling cyst distribution in the equatorial atlantic whereas the state of oligotrophy secondarily influences cyst production within a well stratified environment

suitability of stable oxygen and carbon isotopes of calcareous dinoflagellate cysts for paleoclimatic studies evidence from the campanian maastrichtian cooling phase abstract in order to determine the possible usefulness of stable isotope measurements on calcareous dinoflagellate cysts for paleoceanographic and paleoclimatic studies we have produced oxygen and carbon isotope records of the species pirumella krasheninnikovii bolli h m 1974 jurassic and cretaceous calcisphaerulidae from dsdp leg 27 eastern indian ocean initial reports of the deep sea drilling project 27 843 907 for the latest campanian to earliest maastrichtian 73 68 ma of high latitude ocean drilling program hole 690c in the southern south atlantic eastern weddell sea foraminiferal stable isotope values characterize this time interval as a phase of continuous cooling superimposed by a short term strong cooling event between 71 and 70 ma that was detected at various sites in the mid to high latitudes this event is interpreted to reflect short term surface water cooling leading to changes in the mode and direction of deep water formation and possibly the growth of continental ice sheets our 18o values of calcareous cysts verify this event as well as the general cooling of surface waters during the latest campanian and early maastrichtian prior to this cooling event between 72 and 71 ma a negative excursion in accompanying 13c records of planktic and benthic foraminifera was observed this negative excursion and the subsequent positive one were proposed to reflect sea level fluctuations changes in productivity and or changes in the ratio of organic to inorganic carbon input to the ocean the 13c values of calcareous cysts show the positive excursion between 71 and 70 ma but don t show the expected negative excursion before in addition they yield extremely light carbon isotope values that probably resulted from photosynthetic processes as the stable oxygen isotope data of the calcareous dinoflagellate species p krasheninnikovii show isotopic shifts comparable to planktic foraminifera from the same locality and from various other sites in the pacific and south atlantic oceans we suggest that calcareous cyst oxygen isotopes can provide information for paleoceanographic reconstructions of sea surface water temperatures and paleoceanographic changes however the application of carbon isotope data from cysts of p krasheninnikovii appears to be questionable and investigations of different species are needed to further evaluate the reconstruction potential based on stable isotopes and to assess species specific vital effects

the ohio valley wave merger cyclogenesis event of 25 26 january 1978 part ii diagnosis using quasigeostrophic potential vorticity inversion abstract the dynamical interactions between precursor disturbances during the wave merger cyclogenesis event of 25 26 january 1978 over eastern north america are diagnosed using quasigeostrophic potential vorticity qgpv inversion this case is characterized by two prominent preexisting upper level disturbances that induce rapid surface cyclogenesis as they come into close proximity static qgpv inversion is used to attribute a particular geopotential height field to the qgpv associated with each precursor disturbance the full flow is partitioned into the following components the northern upper precursor the southern upper precursor and the background flow prognostic qgpv inversion is used to quantify the instantaneous geopotential height tendencies attributable to each of these flow components the static inversion results for the upper precursors exhibit the structure of baroclinic vortices with maximum amplitude near the tropopause during the 48 h period spanning the period of study of this even

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

palaeoenvironmental changes of the early pliocene zanclean in the eastern mediterranean pissouri basin cyprus evidenced from calcareous dinoflagellate cyst assemblages abstract the first 100 ka of the earliest pliocene zanclean sediments of the eastern mediterranean pissouri basin on cyprus have been investigated on calcareous dinoflagellate cyst assemblages these assemblages reflect the return in three phases to the open oceanic conditions following the messinian salinity crisis msc 5 33 ma ago the lowermost phase dominated by leonella granifera cysts indicates substantial land derived nutrient supply and low salinities this confirms earlier observations of enhanced continental water runoff during the earliest pliocene in the eastern mediterranean basin the second phase dominated by caracomia stella and calciodinellum albatrosianum cysts indicates a change to warmer meso to oligotrophic waters the third phase marks the first appearance and still continuing dominance of thoracosphaera heimii in the region in addition the endemic eastern mediterranean species lebessphaera urania peaks within this upper interval it probably survived the salinity crisis in the mediterranean the assemblage reflects the establishment of typical open marine well stratified and oligotrophic surface conditions similar but not yet identical to the situation in the mediterranean sea today this study points out a discrepancy between the fast refilling scenario 1 2 ka in the pissouri basin and a long time 100 ka environmental reorganisation in the surface waters as indicated by the calcareous dinoflagellate cysts the onset of the pliocene is also marked by the first appearance of calciodinellum elongatum and calciodinellum levantinum which must have migrated from the atlantic ocean

interaction of potential vorticity anomalies in extratropical cyclogenesis part ii sensitivity to initial perturbations in part i of this series of papers the static potential vorticity pv inversion diagnostics are performed to examine the lateral and vertical interactions between two upper level northern and southern troughs and their possible influences on the development of the march 1993 superstorm this study continues the investigation of the relative importance of two pv anomalies associated with the short wave troughs and their interaction in the surface cyclogenesis by considering their individual roles as an initial value problem the piecewise pv inversion technique is first used to isolate the upper level disturbances with a balanced vortex for each the vortex is then either removed or its intensity doubled by subtracting the balanced vortex from or adding to the control initial conditions with the modified initial conditions a mesoscale model is integrated for 36 h to examine how each of the upper level disturbances contributes to the surface development it is found that the northern and southern troughs play different roles in the surface cyclogenesis without the northern trough the eastward propagation of the southern trough slows down and the surface development is severely impeded more rapid cyclogenesis occurs when the northern trough s intensity is doubled on the other hand the deepening rate increases considerably when the southern trough is removed doubling the southern trough intensity slows the eastward progression of the northern trough and leads to a reduced deepening rate in conclusion the northern trough is crucial for the rapid development of the superstorm whereas the southern trough is important only during the incipient stage of the cyclone in particular a much stronger surface cyclone could be spawned in the absence of the southern trough this finding appears to contradict the previous work on the roles of trough mergers in extratropical cyclogenesis

a method for quantifying the impacts and interactions of potential vorticity anomalies in extratropical cyclones the theory of potential vorticity pv allows us to describe the life cycle of mid latitude baroclinic systems in terms of the individual impacts and interactions of distinct pv anomalies embedded in the background flow pv anomalies associated with the undulating tropopause the low level thermal field and key diabatic processes such as the latent heat release within the cloudy systems of the cyclone are often considered as evolving features regulated by their lateral and vertical mutual interactions and their interaction with the stratospheric high latitude pv reservoir under some balance flow assumptions pv inversion can be used to quantify the contribution of the pv anomalies to the cyclone depth or other attributes at various stages of its life cycle a static approach but it is less clear how to diagnose with similar quantitative detail the various types of time dependent interactions among the anomalies and mean flow that govern the processes of cyclogenesis and cyclolysis a dynamic approach this paper presents a method that implements the concepts of pv thinking quantitatively the method first applies a piecewise pv inversion scheme formulated according to the charney nonlinear mass wind balance approximation then it combines a prognostic system of balance equations that are consistent with the applied inversion scheme with a factor separation technique by switching on and off the pv anomalies of interest various flow configurations are generated and the corresponding solutions to the prognostic equations can be algebraically combined to isolate the magnitude of both the individual and the synergistic effects of the pv anomalies on the spatial pattern of geopotential height tendency and vertical motion around the cyclone with low computational cost the potential of the method to elucidate the relative importance of physically meaningful pv anomalies for the growth or decay of baroclinic systems is illustrated for the intense mediterranean cyclone of 10 12 november 2001 using the ncep meteorological grid analyses at 12 h intervals the upper level pv anomalies contributed very significantly during the whole life cycle of this mediterranean cyclone surface thermal anomalies were fundamental during the development period and induced the general northeastward movement of the system during the later stages during the mature stage of the cyclone the interaction between the two types of anomalies became the dominant effect all other contributions including the individual and synergistic effects of diabatically generated pv were generally most relevant during this mature stage copyright 2008 royal meteorological society

large scale antecedent conditions associated with the 12 14 march 1993 cyclone superstorm 93 over eastern north america abstract the results of a multiscale analysis of the 12 14 march 1993 superstonn ss93 over eastern north america are presented a time sequence of overlapping 10 day time mean 5oo hpa geopotential height and anomaly composites shows that the northern hemisphere nh flow pattern from 18 february to 15 march 1993 is characterized by 1 three persistent troughs situated over eastern asia and the northwestern pacific over eastern north america and over northwestern africa and southwestern europe eastward to central russia and 2 a massive blocking anticyclone located over the central and eastern atlantic beginning 8 9 march 1993 the planetary scale flow amplifies substantially the explosive ss93 cyclogenesis and the transport of cold air to very low latitudes occurs a few days later as the nh available potential energy content after peaking on 9 march 1993 decreases by about 6 7 a dynamical tropopause analysis is used to track coherent transient potential vorticity pv anomalies and show their q

a diagnostic analysis of the superstorm of march 1993 abstract in this study the synoptic evolution of the march 1993 superstorm is documented using conventional observations and the predictability and deepening mechanisms of the storm are investigated using a newly implemented mesoscale version of the canadian regional finite element rfe mode it is found that although the rfe model can predict well the large scale background flow associated with the storm it fails to predict various important mesoscale elements when it is initialized with fields that contain weak signals of the low level circulations however when the storm is located close to the data rich region the model has considerable skill in predicting those mesoscale elements such as a prefrontal squall line upper and low level jets as well as the quantitative aspects of their associated precipitation observational analysis reveals that the storm developed in a convectively unstable prestorm environment with ample moisture content it first experienced an antecedent surface vorticity g

new chronology for the late paleocene thermal maximum and its environmental implications the late paleocene thermal maximum lptm is associated with a brief but intense interval of global warming and a massive perturbation of the global carbon cycle we have developed a new orbital chronology for ocean drilling program odp site 690 weddell sea southern ocean by using spectral analysis of high resolution geochemical records the lptm interval spans 11 precessional cycles yielding a duration of 210 to 220 k y the 13 c anomaly associated with the lptm has a magnitude of about 2 5 to 3 we show that about 2 of the excursion occurs within two steps that each were less than 1000 yr in duration the remainder developed through a series of steps over 52 k y the timing of these steps is consistent with a series of nearly catastrophic releases of methane from gas hydrates punctuated by intervals of relative equilibria between hydrate dissociation and carbon burial further we are able to correlate the records between odp sites 690 and 1051 western north atlantic on the scale of 21 k y cycles which demonstrates that the details of the 13 c excursion are recognizable between distant sites comparison of cycle records at sites 690 and 1051 suggests that sediment representing the interval 30 k y just prior to and at the onset of the lptm are missing in the latter location this unconformity probably resulted from slope failure accompanying methane hydrate dissociation within 10 k y of the start of the lptm

prevention of outburst floods from periglacial lakes at grubengletscher valais swiss alps flood and debris flow hazards at grubengletscher near saas balen in the saas valley valais swiss alps result from the formation and growth of several lakes at the glacier margin and within the surrounding permafrost in order to prevent damage related to such hazards systematic investigations were carried out and practical measures taken the evolution of the polythermal glacier the creeping permafrost within the large adjacent rock glacier and the development of the various periglacial lakes were monitored and documented for the last 25 years by photogrammetric analysis of annually flown high resolution aerial photographs seismic refraction d c resistivity and gravimetry soundings were performed together with hydrological tracer experiments to determine the structure and stability of a moraine dam at a proglacial lake the results indicate a maximum moraine thickness of 100 m extremely high porosity and even ground caverns near the surface may have resulted from degradation of sub and periglacial permafrost following 19th 20th century retreat of the partially cold glacier tongue the safety and retention capacity of the proglacial lake were enhanced by deepening and reinforcing the outlet structure on top of the moraine complex the water level of an ice dammed lake was lowered and a thermokarst lake artficially drained

assessing risks from glacier hazards in high mountain regions some experiences in the swiss alps assessing risks from potential glacier hazards in relation to safety considerations for settlements and other fixed installations in high mountain areas requires the application of experience gained from previous events combined with simple rules derived from basic glaciological theory the general characteristics of steep and usually un measured glaciers can be estimated on the basis of a rough parameterization scheme variations in glacier length ice avalanches and glacier floods then have to be considered for time periods ranging from a few years up to a few decades as a result of such systematic assessments maps of potentially dangerous zones can be prepared although the inhabitants of many alpine villages have always lived with the risk of glacier hazards it now appears that modern construction work especially that connected with the development of tourism has started to infiltrate previously avoided high risk zones more and more in order to plan reasonable safety measures risks from glacier hazards have to be compared with those from other natural hazards in mountain areas such as snow avalanches landslides rock falls or storm induced floods decisions about the acceptable level of risk are difficult and subjective they are also often influenced by political and economical considerations rather than by scientific reasoning

global environmental changes preceding the cretaceous tertiary boundary early late maastrichtian transition stable carbon oxygen and strontium isotope data from maastrichtian planktic and benthic foraminifera from southern high latitude ocean drilling program sites 690 750 and 761 reveal major changes in climate and ocean chemistry during the early to late maastrichtian transition some 4 to 6 m y prior to the cretaceous tertiary k t boundary the 18o results suggest accelerated cooling resulting in the lowest marine temperatures of the late cretaceous the late maastrichtian rise in the seawater 87sr 86sr ratio begins at the time of this change and suggests increased rates of continental weathering and or runoff the 13c values show a negative shift of 0 5 followed by a positive shift of 1 these 13c fluctuations may reflect change in deep water chemistry with cooling variation in reduced carbon storage in coastal areas caused by eustatic sea level fluctuation and increased surface water productivity these findings contradict the common representation of stable and climatically equable environmental conditions in the latest cretaceous before the k t boundary event

eocene paleoceanographic evolution at 20 30 s in the atlantic ocean abstract oceanographic changes in eocene bottom water have been traced with oxygen and carbon isotope values and gradients and benthic foraminiferal assemblages the south atlantic sections chosen for this study are located on an east west traverse depositional depths range from middle bathyal through abyssal the dsdp sites are located on the walvis ridge site 363 in the angola basin sites 522 523 the brazil basin site 19 hole 20c and on the rio grande rise site 357 in abyssal sites of the south atlantic the eocene bottom water environment can be divided into two distinct regimes the early eocene and the late eocene the middle eocene is transitional faunal distribution pattern indicate that source areas where bottom water formed were probably different between the two regimes during the early eocene warm saline water formed possibly in the tethyan ocean east of gibraltar there is good evidence that the late eocene bottom water of the south atlantic recorded at lower bathyal down to middle abyssal environments was formed in southern high latitude regions first invasion of cooler bottom water is recorded at upper abyssal depths around 46 ma earliest zone p12 site 19 from 40 ma late zone p15 onwards this signal is recorded at all sites except middle bathyal depth site 357 selected faunal parameters allow reconstruction of bottom water oxygenation episodically increased abundance of epifaunal species indicate a renewal of the bottom water accompanying these faunal changes 13 c values of benthic foraminefera increase whereas vertical 13 c benthic planktonic foraminifera gradients decrease

maastrichtian climate productivity and faunal turnovers in planktic foraminifera in south atlantic dsdp sites 525a and 21 abstract stratigraphic faunal and isotopic analyses of the maastrichtian at dsdp sites 525a and 21 in the south atlantic reveal a planktic foraminiferal fauna characterized by two major events an early late maastrichtian diversification and end maastrichtian mass extinction both events are accompanied by major changes in climate and productivity the diversification event which occurred in two steps between 70 5 and 69 1 ma increased species richness by a total of 43 and coincided with the onset of major cooling in surface and bottom waters and increased surface productivity the onset of the terminal decline in maastrichtian species richness began at 67 5 ma and the first significant decline in surface productivity occurred at 66 2 ma coincident maximum cooling to 13 c in surface waters and the reduction of the surface to deep temperature gradient to less than 5 c major climatic and moderate productivity changes mark the mass extinction and the last 500 kyr of the maastrichtian between 200 and 400 kyr before the k t boundary surface and deep waters warmed rapidly by 3 4 c and cooled again during the last 100 kyr of the maastrichtian surface productivity decreased only moderately across the k t boundary species richness began to decline during the late maastrichtian cooling and by k t boundary time the mass extinction had claimed 66 of the species viewed within the context of maastrichtian climate and productivity changes the k t mass extinction could have resulted from extreme environmental stress even without the addition of an extraterrestrial impact

abrupt climate change and transient climates during the paleogene a marine perspective detailed investigations of high latitude sequences recently collected by the ocean drilling program odp indicate that periods of rapid climate change often culminated in brief transient climates with more extreme conditions than subsequent long term climates two examples of such events have been identified in the paleogene the first in latest paleocene time in the middle of a warming trend that began several million years earlier the second in earliest oligocene time near the end of a middle eocene to late oligocene global cooling trend superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice sheet on antarctica in both cases the climate extremes were not stable lasting for less than a few hundred thousand years indicating a temporary or transient climate state geochemical and sedimentolog

detection of a subglacial lake in glacier de tete rousse mont blanc area france the processes that form intraglacial lakes are poorly understood because of the difficulty in detecting and assessing such hidden lakes extensive geophysical surveys were performed between 2007 and 2010 in order to reassess the risk of an outburst flood from glacier de tete rousse where outburst flooding from an intraglacial lake caused 175 fatalities in 1892 our geophysical survey combined ground penetrating radar measurements and nuclear magnetic resonance imaging we found a subglacial water filled reservoir with a volume of 55 000 m 3 artesian outpourings occurred when the subglacial cavity was reached by two borehole drillings indicating that the hydrostatic water pressure exceeded the ice pressure at the bottom of the cavity on the basis of these geophysical and glaciological findings we warned the public authorities in july 2010 of the risk facing the 3000 inhabitants downstream of the glacier the subglacial reservoir was drained artificially this example demonstrates how geophysical surveys can be used to detect this type of hazard when it is suspected in particular when no hydraulic outlet from the snout exists numerous ice temperature measurements have shown that the tongue of this glacier is cold based this thermal regime could explain the accumulation of water in this glacier

a case study of cyclogenesis using a model hierarchy abstract it is universally agreed that cyclogenesis in midlatitudes occurs through baroclinic conversion of the potential energy available from an initial state the mechanical process by which that conversion takes place is a perennial subject of discussion at least as far back as the 1950s it was recognized that in any practical forecast problem the initial condition is influential observational research continues to confirm the prevalence of tropopause level perturbations preceding surface cyclogenesis the observations also suggest that the growing disturbances have time varying vertical structures relating these observations to the classical linear theory of baroclinic instability is not immediately obvious since in the latter the precise form of the initial condition is not important and the theory predicts cyclogenesis with a fixed in time vertical structure these differences between theory and observations are but a few of the many that have been recognized and treated in modified theorie

central arctic ocean paleoceanographic interpretations based on late cenozoic calcareous dinoflagellates abstract four calcareous dinoflagellate morphotypes interpreted to represent a single species thoracosphaera arctica n sp occur in upper miocene to holocene sediments of the central arctic ocean the calcareous fossils generally are rare except during one interval that of the latest pliocene to late pleistocene during this interval the fossil dinoflagellates were alternately abundant and rare in approximate coordination with greater and lesser times of foraminifera productivity dinoflagellates and foraminifera generally are rare during times of accumulation of abundant coarse textured ice rafted sediment during this interval the life cycle of the dinoflagellate that produces the arctic ocean calcareous fossil is unknown but the fossils probably are either resting cysts motile vegetative cells or hypnozygotes a vegetative cell origin better explains the co occurrence of foraminifera as well as the negative correlation with ice rafting this tentative interpretation leads to the conclusion that during the interval 2 0 to 0 7 m y b p the arctic ocean had relatively productive surface waters with very thin or even periodic absence of pack ice alternating with conditions more like that of the present during periods before 2 0 m y and since 0 7 m y the arctic ocean probably was ice covered with oceanographic conditions similar to that of the modern ocean these conclusions differ from previous interpretations that the arctic was continually ice covered had no surface productivity or was covered by a giant antarctic like ice cap

a case study of downstream baroclinic development over the north pacific ocean part i dynamical impacts abstract the impact of eddy energy growth and radiation from a western north pacific cyclone on the intensity of an eastern north pacific cyclone a few days later is examined associated with the western cyclone is an upstream ridge and trough couplet initially over siberia on 8 march 1977 the amplitude of this couplet is perturbed in 5 day numerical simulations of the two marine cyclones balanced initial conditions are created by potential vorticity inversion the magnitude of the upper level couplet governs much of the subsequent growth of eddy energy in the western cyclone as well as the propagation of eddy energy between the two cyclones this culminates in measurable changes in the maximum intensity of the eastern surface cyclone the broader question of the sensitivity of this cyclone to upstream perturbations is also briefly addressed

frequency and characteristics of glacier floods in the swiss alps damage due to glacier floods in the swiss alps occurs about once every two years at present despite the pronounced retreat of glaciers during the twentieth century and the installation of many water reservoirs which act as flood retention basins over half 60 to 70 of the observed floods are caused by outbursts of marginal glacier lakes or sudden breaks of ice dams and 30 to 40 by ruptures of water pockets in a glacierized mountain region as densely populated as the swiss alps even debris flows triggered by outbursts of very small water masses may be dangerous historical information about glacier floods in the swiss alps although incomplete and heterogeneous is used as an empirical basis for an attempt to recognize potential hazards at an early stage by considering outburst processes volumes of water involved potential peak discharge values lithology and inclination within the reach of glacier streams

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

geochemical evidence for suppression of pelagic marine productivity at the cretaceous tertiary boundary the normal biologically productive ocean is characterized by a gradient of the 13c 12c ratio from surface to deep waters here we present stable isotope data from planktonic and benthic micro fossils across the cretaceous tertiary boundary in the north pacific which reveal a rapid and complete breakdown in this biologically mediated gradient the fluxes of barium a proxy for organic carbon and caco3 also decrease significantly at the time of the major marine plankton extinctions the implied substantial reduction in oceanic primary productivity persisted for 0 5 myr before the carbon isotope gradient was gradually re established in addition the stable isotope and preservational data indicate that environmental change including cooling began at least 200 kyr before the cretaceous tertiary boundary and a peak warming of 3 c occurred 600 kyr after the boundary event

paleoceanographic and paleoclimatic evolution in the weddell sea antarctica during the middle eocene late oligocene from a coarse sediment fraction and clay mineral data odp site 689 abstract paleoceanographic and paleoclimatic variations from the middle eocene to the late oligocene in the antarctic area atlantic sector have been deduced from a coarse fraction and clay mineral analysis of odp site 689 leg 113 sediments in the middle eocene smectite rich sediments were a consequence of warm climate with alternating wet and dry seasons on the antarctic margins productivity in the maud rise area of the southern ocean was low no opal was deposited preservation of carbonate is very good carbonate preservation shows cyclic changes clinoptilolite is a common mineral at the middle late eocene boundary 40 8 ma productivity suddenly increased enough to allow preservation of opal skeletons clinoptilolite disappeared where opal appeared illite appearance points to cooling of antarctic climates the presence of detrital kaolinite indicates a change in oceanic circulation in the late eocene cyclic changes in productivity cycle length 0 42 ma were associated with clay mineral compositional variations sediments from colder highly productive periods generally contain more illite and less smectite than warmer ones the early oligocene was a period of very high productivity highest opal accumulation rates correspond to strongest carbonate dissolution cyclic changes in productivity with a mean cycle duration of 0 4 0 5 myr were associated with cyclic changes in clay mineral composition highest productivity intervals are generally those with highest smectite content because of strong erosion of sediments of the antarctic margins sediments from less productive warmer periods most of the time contain more illite in the late oligocene the intensity of physical weathering on antarctica was stronger as documented by increasing fluxes of illite muscovite amphiboles and talc ice expanded on the east antarctic continent lower productivity than in the early oligocene is indicated by lower accumulation rates of opal and weaker carbonate dissolution cyclic variations in productivity correlate to cyclic variations in illite and smectite contents as in the early oligocene

calcareous dinoflagellate associations and maastrichtian tertiary climatic change in a high latitude core odp hole 689b maud rise weddell sea abstract the distribution of calcareous dinoflagellates has been analysed for the maastrichtian miocene interval of ocean drilling project hole 689b maud rise weddell sea the investigation thus represents a primary evaluation of the long term evolution in high latitude calcareous dinoflagellate assemblages during the transition from a relatively warm late cretaceous to a cold neogene climate major assemblage changes during this interval occurred in characteristic steps 1 an increase in relative abundance of tangentially structured species particularly operculodinella operculata at the cretaceous tertiary boundary 2 a diversity decrease and several first and last appearances across the middle late eocene boundary possibly attributed to increased climate cooling 3 a diversity decrease associated with the dominance of calciodinellum levantinum in the late early oligocene 4 the reappearance and dominance of pirumella edgarii in the early miocene probably reflecting a warming trend 5 monogeneric assemblages dominated by caracomia spp denoting strong middle miocene cooling the results not only extend the biogeographic ranges of many taxa into the antarctic region but also indicate that the evolution of high latitude calcareous dinoflagellate assemblages parallels the changing environmental conditions in the course of the cenozoic climate transition therefore calcareous dinoflagellates contribute to our understanding of the biotic effects associated with palaeoenvironmental changes and might possess the potential for reconstructing past conditions the flora in the core includes one new taxon caracomia arctica forma spinosa hildebrand habel and streng forma nov additionally two new combinations are proposed fuettererella deflandrei kamptner 1956 hildebrand habel and streng comb nov and fuettererella flora futterer 1990 hildebrand habel and streng comb nov

the impact of various potential vorticity anomalies on multiple frontal cyclogenesis events summary it is shown that most of the frontal cyclones can still develop in the absence of diabatic heating indicating the important role of dry dynamics in controlling the multiple frontal cyclogenesis events however the dry mfc fails to form a closed isobar when the trough related pv anomaly is removed the associated pv inversion and sensitivity simulation results suggest that even though the low level thermal advection plays an important role in deepening the frontal cyclones it is the upper level pv anomalies that provide the necessary forcing for its amplie cation and the frontal cyclogenesis it is concluded that the upper level propagating multiple pv anomalies play a major role in triggering but a secondary role in determining the e nal depth of the multiple frontal cyclones it is the subsequent growth of the bottom thermal anomaly that accounts for most of the enal depth of the frontal cyclones

carbon isotope evidence for unusual plankton blooms and fluctuations of surface water co2 in strangelove ocean after terminal cretaceous event abstract a decrease in 13c kerogen by 3 and increase in 13c carbonate kerogen by 1 2 has been observed in sediments at the k t boundary substantiating the occurrence of a strangelove ocean wherein dissolved co2 was enriched in 12c because of mass mortality or reduced plankton production a subsequent increase in 13c kerogen by 7 and decrease in 13c carbonate kerogen by 5 4 indicate a dramatic reduction in pco2 this decrease could be the consequence of depletion of co2 in surface waters because of unusual plankton blooms these environmental changes which characterize the strangelove ocean occurred after the terminal cretaceous event during this time rapid fluctuations in dissolved co2 of ocean surface waters may have caused significant perturbations in atmospheric pco2 levels and consequently major instability of the global climate

explosive cyclogenesis in the west central north atlantic ocean 1981 84 part i composite structure and mean behavior abstract tracks and central values of surface low pressure centre and 500 mb absolute vorticity maxima were gathered from operational analysis for 48 casts of expressive cyclogenesis in the west central north atlantic the cases were stratified into relatively strong moderate and weak categories tracking was done from 36 h before to 24 h after the time of most rapid surface deepening the surface center often first appeared only 12 to 24 h before maximum deepening but the upper vorticity maximum was present 36 h or more in advance often many days mean motion of the surface low was rapidly northeastward from the southeastern states or just offshore to newfoundland intense deepening occurred in a period of no more than 24 36 h strong cyclones moved most rapidly and most meridionally traveled farther over warm water and deepened dramatically in a single 12 h period while crossing the closely spaced isotherms of sea surface temperature north of the gulf stream the upper vorticity center moved rapid

delineation of a complexly dipping temperate glacier bed using short pulse radar arrays we have defined the complex bed topography for a section of a small temperate glacier using 50 mhz monostatic short pulse radar data and a synthetic aperture array processing method the data were collected on a 100 m by 340 m array grid in the upper stem of gulkana glacier central alaska u s a the array processing was based on a modified three dimensional 3 d kirchhoff migration integral and implemented with a synthetic aperture approach that uses sequences of overlapping sub arrays to generate depth images in vertical planes typical sub array beam patterns are generally 5 at the 6 db level giving a flashlight like searching capability without distorting the wavelet shape the bed topography was constructed using normal reflections picked from 3 d array depth images in some instances reflections were imaged outside the data coverage area the bed surface dips steeply both parallel and transverse to the direction of ice flow the maximum observed depth is roughly 140 m the 3 d method resolved bed dips up to 45 in regions of steepest dip it improved depth accuracy by 36 compared with raw data and by 15 compared with standard two dimensional 2 d migration over 12 db of signal to noise improvement and improved spatial resolution was achieved compared to raw data and 2 d migration false bottom layering seen in the raw data and in 2 d migrations is not observed in the 3 d array results furthermore loss of bottom reflections is shown by the 3 d migration to be attributable to the dip and curvature of the reflector and not scattering losses or signal clutter from englacial inclusions

environmental controls on marine ecosystem recovery following mass extinctions with an example from the early triassic abstract the recovery of marine ecosystems following a mass extinction event involves an extended interval of increasing biotic diversity and ecosystem complexity the pace of recovery may be controlled by intrinsic ecosystem or extrinsic environmental factors here we present an analysis of changes in marine conditions following the end permian mass extinction with the objective of evaluating the role of environmental factors in the protracted 5 myr long recovery of marine ecosystems during the early triassic specifically our study examines changes in weathering productivity and redox proxies in three sections in south china chaohu daxiakou and zuodeng and one in northern india mud our results reveal 1 recurrent environmental perturbations during the early triassic 2 a general pattern of high terrestrial weathering rates and more intensely reducing marine redox conditions during the early griesbachian late griesbachian mid smithian and more weakly the mid spathian 3 increases in marine productivity during the aforementioned intervals except for the early griesbachian and 4 stronger and more temporally discrete intervals of environmental change in deepwater sections chaohu and daxiakou relative to shallow and intermediate sections zuodeng and mud our analysis reveals a close relationship between episodes of marine environmental deterioration and a slowing or reversal of ecosystem recovery based on metrics of biodiversity within community alpha diversity infaunal burrowing and ecosystem tiering we infer that the pattern and pace of marine ecosystem recovery was strongly modulated by recurrent environmental perturbations during the early triassic these perturbations were associated with elevated weathering and productivity fluxes implying that nutrient and energy flows were key influences on recovery more regular secular variation in deepwater relative to shallow water environmental conditions implies that perturbations originated at depth i e within the oceanic thermocline and influenced the ocean surface layer irregularly finally we compared patterns of environmental disturbance and ecosystem recovery following the other four big five phanerozoic mass extinctions to evaluate whether commonalities exist in general the pace of ecosystem recovery depends on the degree of stability of the post crisis marine environment

seasonal changes in ground penetrating radar signature observed at a polythermal glacier bylot island canada in recent years ground penetrating radar gpr has been increasingly used for characterization of subglacial and englacial environments at polythermal glaciers the geophysical method is able to exploit the dielectric difference between water air sediment and ice allowing delineation of subsurface hydrological thermal and structural conditions more recent gpr research has endeavoured to examine temporal change in glaciers in particular the distribution of the cold ice zone at polythermal glaciers however the exact nature of temporal change that can be identified using gpr has not been fully examined this research presents the results of three gpr surveys conducted over the course of a summer ablation season at a polythermal glacier in the canadian arctic a total of approximately 30 km of gpr profiles were collected in 2002 repeatedly covering the lower 2 km of stagnation glacier bylot island 72 58 n 78 22 w comparison between profiles indicated changes in the radar signature including increased noise appearance and disappearance of englacial reflections and signal attenuation in the latter survey further an area of chaotic returns in up glacier locations which was interpreted to be a wet temperate ice zone showed marked recession over the course of the ablation season combining all the temporal changes that were detected by gpr results indicate that a polythermal glacier may exhibit strongly seasonal changes in hydrological and thermal characteristics throughout the ice body including the drainage of 17 000 m 3 of temporarily stored intra glacial meltwater it is also proposed that the liquid water content in the temperate ice zone of polythermal glaciers can be described as a fraction of a specific retention capacity copyright 2006 john wiley sons ltd

the cretaceous tertiary biotic transition mass extinctions are recognized through the study of fossil groups across event horizons and from analyses of long term trends in taxonomic richness and diversity both approaches have inherent flaws and data that once seemed reliable can be readily superseded by the discovery of new fossils and or the application of new analytical techniques herein the current state of the cretaceous tertiary k t biostratigraphical record is reviewed for most major fossil clades including calcareous nannoplankton dinoflagellates diatoms radiolaria foraminifera ostracodes scleractinian corals bryozoans brachio pods molluscs echinoderms fish amphibians reptiles and terrestrial plants macrofossils and palynomorphs these reviews take account of possible biasing factors in the fossil record in order to extract the most comprehensive picture of the k t biotic crisis available results suggest that many faunal and floral groups ostracodes bryozoa ammonite cephalopods bivalves archosaurs were in decline throughout the latest maastrichtian while others diatoms radiolaria benthic foraminifera brachiopods gastropods fish amphibians lepidosaurs terrestrial plants passed through the k t event horizon with only minor taxonomic richness and or diversity changes a few microfossil groups calcareous nannoplankton dinoflagellates planktonic foraminifera did experience a turnover of varying magnitudes in the latest maastrichtian earliest danian however many of these turnovers along with changes in ecological dominance patterns among benthic foraminifera began in the latest maastrichtian improved taxonomic estimates of the overall pattern and magnitude of the k t extinction event must await the development of more reliable systematic and phylogenetic data for all upper cretaceous clades

interaction of potential vorticity anomalies in extratropical cyclogenesis part i static piecewise inversion the relative importance of various potential vorticity pv perturbations and their mutual interactions associated with the superstorm of 12 14 march 1993 are investigated by applying a piecewise pv inversion diagnostic system to a 36 h simulation of the storm it is shown that the contributions from all pv anomalies to the surface development increase with time although their relative significance varies during the rapid deepening stage in general the upper level dry pv anomalies contribute the most to the rapid deepening of the storm followed in order by the lower level thermal anomaly and latent heat release comparing the pv anomalies and their inverted circulations reveals that there exists a favorable phase tilt between the upper and lower level anomalies that allows lower and upper level mutual interactions in which the circulations associated with the upper level pv anomalies enhance the lower level anomalies and vice versa in addition to the vertical interactions lateral interactions are also present among the upper level pv anomalies and the background flow it is also found that the background flow advection dominates the vortex vortex and vortex background flow interactions in the deepening of the storm the vortex vortex interactions of the two upper level positive pv anomalies cause the negative tilt of the main upper level trough during the rapid deepening period

palaeoenvironmental information gained from calcareous dinoflagellates the late quaternary eastern and western tropical atlantic ocean in comparison abstract the environmental preferences of calcareous dinoflagellates have been investigated over the last 140 ka by comparing material from two sediment cores one from the highly productive equatorial divergence of the eastern atlantic ocean and the other from the low productivity western tropical atlantic ocean pronounced differences in palaeoproductivity between the two sediment cores are indicated by high and variable organic carbon accumulation rates in the east in contrast to relatively constant and low values in the west calcareous dinoflagellates show just the opposite pattern high accumulation rates in the west and lower in the east at the equatorial divergence temporal variations of calcareous dinoflagellate and organic carbon accumulation rates show for the most part an inverse relationship high calcareous dinoflagellate content coincides with low organic carbon accumulation rates and vice versa in the investigated region and time interval enhanced production of calcareous dinoflagellates can be correlated to periods of reduced palaeoproductivity probably related to relatively stratified conditions of the upper water column

the miocene palaeoenvironmental and palaeoceanographic evolution of the gippsland basin southeast australia a record of southern ocean change abstract the gippsland basin in southeastern australia preserves up to 2 5 km thick tertiary to recent marine carbonate sediments included in the seaspray group during the neogene the seaspray group carbonates of the mackerel and flounder petroleum fields lay at the shelfal to bathyal palaeoenvironmental transition an ideal palaeoceanographic setting to study the neogene history of events in the evolving southern ocean seismic foraminiferal and facies analyses of the miocene seaspray group sediments at the mackerel 1 and flounder 1 wells have revealed the following palaeoenvironmental history of the area relatively cool to temperate upwelling conditions prevailed in the area during the earliest miocene during this time low energy upper slope globigerina ooze calcareous mudstone was deposited in the oxygen minimum zone during the early to lower middle miocene upper slope marl was deposited in oligotrophic conditions the presence of neritic subtropical foraminifera and abundant shallow and deep dwelling warm to cool temperate plankton in the upper slope suggests that warm poorly stratified oceanic conditions prevailed in the region this upper early miocene warm phase and mid miocene climatic optimum in gippsland corresponds to a time when global ocean conditions were much warmer and less vertically and latitudinally stratified than at present these oceanic conditions were associated with a reduced east antarctic ice sheet a higher sea level a relatively weak antarctic circumpolar current and weak atmospheric and wind driven circulation during the upper middle miocene to late miocene cool phase after c 14 5 ma strong upwelling and cooler oceanic conditions prevailed in the outer shelf to upper slope canyon facies in gippsland the occurrence of common deep dwelling plankton taxa in this interval suggests that regional oceanic conditions became more vertically stratified during this time from 14 5 and 5 million years ago the middle to late miocene palaeoenvironmental change recorded in seaspray group sediments corresponds to global cooling and major antarctic ice sheet expansion when the world s oceans became more vertically and latitudinally stratified from around 14 5 million years the transition from a warm miocene optimum to cooler oceanic conditions was associated with a strengthened antarctic circumpolar current and more intense wind driven atmospheric circulation in the southern ocean

type b cyclogenesis in a zonally varying flow abstract it is hypothesized that surface cyclogenesis in the northern hemisphere storm track regions can be described by the structural modification of baroclinic wave packets traversing a zonally varying flow field we test this hypothesis using a linear quasigeostrophic model with a zonally varying basic state and zonally varying ekman layer eddy viscosity at midchannel the basic state consists of a region of strong low level baroclinicity and weak ekman dissipation surrounded by regions of weak low level baroclinicity strong ekman dissipation and enhanced low level static stability eigenanalyses and initial value integrations support this model of type b cyclogenesis the results can be summarized as follows 1 a disturbance initiated upstream of the midchannel baroclinic zone rapidly evolves into a wave packet with maximum amplitude near the tropopause the wave packet undergoes a structural modification upon entering the low level baroclinic zone developing maximum amplitude at the surface t

using 2d inversion of magnetic resonance soundings to locate a water filled karst conduit a new methodology for magnetic resonance sounding mrs data acquisition and interpretation was developed for locating water filled karst cavities this methodology was used to investigate the ouysse karst system in the poumeyssens shaft in the causse de gramat france a new 2d numerical mrs response model was designed for improved accuracy over the previous 1d mrs approach a special survey performed by cave divers confirmed the accuracy of the mrs results field results demonstrated that in favourable conditions a low em noise environment and a relatively shallow large target the mrs method used with a coincident transmitter receiver loop can be an effective tool for locating a water filled karst conduit it was shown numerically that because an a priori orientation of the mrs profile with the karst conduit is used in the inversion scheme perpendicular for instance any error in this assumption introduces an additional error in locating the karst however the resulting error is within acceptable limits when the deviation is less than 30 the mrs results were compared with an electrical resistivity tomography ert survey it was found that in poumeyssens ert is not able to locate the water filled karst on the other hand ert provides additional information about heterogeneities in the limestone

numerical simulations of the genesis of hurricane diana 1984 part i control simulation abstract the complete transformation of a weak baroclinic disturbance into hurricane diana is reproduced by numerical simulations using the fifth generation pennsylvania state university national center for atmospheric research mesoscale model three distinct phases of the evolution are evident first baroclinic and barotropic development strongly modified by the effects of latent heating occurs during the latter part of this phase the low level circulation is strengthened through the axisymmetrization of remote potential vorticity anomalies that are generated by condensational heating and then advected toward the incipient storm the axisymmetrization process evinces properties of both nonlinear discrete vortex merger and vortex rossby wave dynamics the transformation from cold core to warm core vortex occurs in this development stage in the second phase lasting 10 12 h little deepening occurs spiral bands of convection begin to form and the core of the storm moistens eventually reaching 95

the source and fate of massive carbon input during the latest paleocene thermal maximum lithologic faunal seismic and isotopic evidence from the blake nose subtropical western north atlantic links a massive release of biogenic methane 55 5 million years ago to a warming of deep ocean and high latitude surface waters a large perturbation in the combined ocean atmosphere carbon cycle the largest of the past 90 million years a mass extinction event in benthic faunas and a radiation of mammalian orders the deposition of a mud clast interval and seismic evidence for slope disturbance are associated with intermediate water warming massive carbon input to the global exogenic carbon cycle pelagic carbonate dissolution a decrease in dissolved oxygen and a benthic foraminiferal extinction event these events provide evidence to confirm the gas hydrate dissociation hypothesis and identify the blake nose as a site of methane release

distribution and character of water in a surge type glacier revealed by multifrequency and multipolarization ground penetrating radar 1 we have investigated the distribution and character of radar scatterers in the glacier bakaninbreen svalbard using ground penetrating radar gpr the gpr profiles showed scattering regions with an undulating upper boundary in both along and across glacier orientations the simplest interpretation of such scattering regions would be a layer of randomly distributed scatterers with an undulating upper boundary underlying a layer without scatterers we propose an alternative model of scatterer distribution in which the scatterers are confined to obliquely dipping planes this model is shown to be able to reproduce the shape of the scattering regions observed in the field data and is consistent with previous observations of dipping thrust features in bakaninbreen from radar data and in outcrop multifrequency profiles 50 100 and 200 mhz contained scatterers with similar measured power indicating that the scatterers have decimeter scale dimensions multipolarized antenna configurations were used to detect a preferred polarization direction for scattered radiation which was approximately across glacier suggesting that the scatterers are nonspherical and aligned across glacier the scatterers are thought to be large water bodies confined to dipping planar features and elongated in the strike orientation of the planes

rapid diversification of planktonic foraminifera in the tropical pacific odp site 865 during the late paleocene thermal maximum the planktonic foraminiferal generamorozovellaandacarininarapidly in 10 k y diversified during the late paleocene thermal maximum lptm giving rise to such morphotypes asm allisonensis new species m africana anda sibaiyaensis single specimen isotopicanalysisconfirmsthatm allisonensisanda sibaiyaensisarerestrictedtothelptm carbon isotope excursion recorded at ocean drilling program site 865 equatorial pacific ocean the short lived 50 to several 100 k y excursion taxa attest to the ephemeral effectsofthelptmonthecalcareousplankton single specimenoxygenisotopedatashow that evolution of m allisonensis and a sibaiyaensis was accompanied by migration to deeper water depths ancestralm velascoensisanda soldadoensiswere extremely rare or absent during the early stages of the lptm but immigrated back into the study area to coexist with their descendants in later lptm horizons photosymbiosis may have facilitatedthemorozovellidandacarininiddiversificationsduringtheoligotrophicconditionsof the lptm

frequent outburst floods from south tahoma glacier mount rainier u s a relation to debris flows meteorological origin and implications for subglacial hydrology destructive debris flows occur frequently at glacierized mount rainier volcano washington u s a twenty three such lows have occurred in the tahoma creek valley since 1967 hydrologic and geomorphic evidence indicate that all or nearly all of these lows began as outburst loods from south tahoma glacier flood waters are stored subglacially the volume of stored water discharged during a typical outburst flood would form a layer several centimeters thick over the bed of the entire glacier although it is more likely that large linked cavities account for most of the storage statistical analysis shows that outburst floods usually occur during periods of atypically hot or rainy weather in summer or early autumn and that the probability of an outburst increases with temperature a proxy measure of ablation rate or rainfall rate we suggest that outburst floods are triggered by rapid water input to the glacier bed causing water pressure transients that destabilize the linked cavity system the correlation between outburst floods and meteorological factors casts doubt on an earlier hypothesis that melting around geothermal vents triggers outburst floods from south tahoma glacier

calcareous nannofossil and dinoflagellate stratigraphy across the cretaceous tertiary boundary at hor hahar israel in israel the cretaceous tertiary k t boundary at hor hahar occurs within the interval from the top of the ghareb formation maastrichtian to just below the horizon of dark marl and clay within the overlying taqiye formation paleocene the studied interval contains all the calcareous nannofossil zones micula prinsii latest maastrichtian markalius inversus np1 earliest paleocene andcruciplacolithus tenuis np2 early paleocene they correlate in sequence with theabathomphalus mayaroensis p0 p1a p1b and p1c planktic foraminiferal zones the palynological assemblages consist mainly of dinocysts with only few pollen grains and spores these assemblages are used to interpret five stratigraphic phases of environmental change across the k t boundary in the hor hahar section in the latest maastrichtian there is an overwhelming dominance of the nannofossilmicula decussata which probably reflects environmental stress preceding the terminal cretaceous mass extinction a nearshore marine environment at the boundary is suggested by the increase in number of specimens of the dinocystcyclonephelium and by the predominance of terrigenous organic matter sediment there followed two episodes of transgression and regression the calcareous cyst producing dinoflagellatethoracosphaera futterer 1976 becomes dominant in two episodes at the boundary and approximately one meter above it it alternates in abundance with the organic walled dinoflagellates which suggests that different environmental parameters were operating for each group maastrichtian dinocysts decline in abundance toward the k t boundary they reach greatest abundance and species diversity at the same strata where foraminiferids recover after their mass extinction at the boundary calcareous nannofossils recover only later in the early paleocene changes in 13c and total organic carbon as as well as dinocyst and nannofossil composition indicate an episode of strong ecological stress about one meter above the boundary

cloud resolving simulations of mesoscale vortex intensification and its effect on a serial mesoscale convective system abstract the authors performed numerical simulations of the 27 28 may 1998 mesoscale convective vortex mcv and mesoscale convective system mcs to understand how the mcv modulated the convection and how the convection intensified the vortex the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 was used initialized with the analysis from the rapid update cycle version 2 ruc 2 and nested to achieve 1 5 km grid spacing covering the mcs the model successfully simulated a north south convective band that formed near the center of the mcv in the early evening the simulation then correctly reoriented the convection along a roughly east west line in response to northward transport of warm conditionally unstable air within the nocturnal low level jet balanced vertical motion was found to contribute substantially to mesoscale lifting and thermodynamic destabilization which localized the convection horizontal transport of moist uns

short pulse radar wavelet recovery and resolution of dielectric contrasts within englacial and basal ice of matanuska glacier alaska u s a wavelets transmitted by short pulse radar are recovered from continuous profiles and used to determine interfacial dielectric contrasts within the englacial and basal ice at the terminus area of matanuska glacier alaska u s a the field studies were in the ablation region where radar horizons could at some point be identified with interfaces between clear ice and air water or basal ice and were performed in early spring before drainage fully developed the profiles usedclosely spaced antennas with bandwidths centered near 50 and 400 mhz transmitted wavelets reflected from interfaces of known dielectric contrasts are used to establish a phase reference for other events from interfaces between unknown contrasts migration and fourier transform filtering are then applied to the profiles and shown to recover these wavelets from diffractions and reflections interfacial dielectric contrasts are determined from the relative phase of the wavelets near the terminus lake some basal ice events above 8 m depth are interpreted as voids further up glacier most englacial events are interpreted as voids but deeper localized reflectors and horizons to 90 m depth and within the basal zone are interpreted as voids water or debris phase cannot be determined for the basal substrate transition reflections recommendations are made for improving the wavelet recovery process and the quality of gpr migration

the role of hydrologically driven ice fracture in drainage system evolution on an arctic glacier 1 observations from ellesmere island suggest that the connection between surface and subglacial drainage on a predominantly cold glacier is made abruptly by hydrologically driven propagation of fractures from the surface to the bed where ice is 150 m thick water ponded to a depth of 6 9 m within a supraglacial stream system before establishing a permanent bed connection multiple premonitory drainage events preceded the final drainage of ponded water implying that fracturing is necessary but insufficient to establish a permanent link between surface and subglacial drainage refreezing of water that penetrates the first fractures to form may reseal the connection while flow resistance within the subglacial system may delay the onset of continuous through flow a large volume of ponded water is required to enlarge fractures sufficiently by melting to maintain continuous drainage while feedbacks between subglacial hydrology and ice dynamics may assist in maintaining the connection and initiating subglacial outflow

modelling heat flow in a cold high altitude glacier interpretation of measurements from colle gnifetti swiss alps modelling the heat flow in small cold high altitude glaciers is important for the interpretation of paleoclimatic data from ice cores coupled glacier flow and heat flow models are presented that incorporate the densification heat advection and possible phase transitions at the permafrost boundaries within the bedrock marked bends observed in the temperature profiles from two recent boreholes on colle gnifetti swiss alps are interpreted with the help of a transient heat flow model driven with a temperature history the conclusion is that substantial warming of the mean firn temperature at shallow depths has taken place over the last few decades this has not been observed before in cold firn regions of the alps modelled heat fluxes in the monte rosa massif are strongly influenced by the mountain topography this leads to a spatial variability of the temperature gradient near the glacier base which has been observed in boreholes to the bedrock in order to match the measured temperature profiles in the glacier the vertical heat flux at great depth must be set to an extremely low value it is shown with the help of the transient heat flow model that this is a paleoclimatic effect possibly enhanced by a degrading permafrost base

englacial water distribution in a temperate glacier from surface and borehole radar velocity analysis we have obtained common offset common midpoint cmp and borehole vertical vrp ground penetrating radar profiles close to the margin of falljokull a small steep temperate valley glacier situated in southeast iceland velocity analysis of cmp and vrp surveys provided a four layered velocity model this model was verified by comparison between the depths of englacial reflectors and water channels seen in borehole video and from the depths of boreholes drilled to the bed in the absence of sediment within the glacier ice radar velocity is inversely proportional to water content using mixture models developed by paren and looyenga the variation of water content with depth was determined from the radar velocity profile at the glacier surface the calculated water content is 0 23 0 34 velocity 0 166 m ns 1 which rises sharply to 3 0 4 1 velocity 0 149 m ns 1 at 28 m depth interpreted to be the level of the piezometric surface below the piezometric surface the water content drops slowly to 2 4 3 3 velocity 0 152 m ns 1 until 102 m depth where it falls to 0 09 0 14 velocity 0 167 m ns 1 the water content of the ice then remains low to the glacier bed at about 112 m these results suggest storage of a substantial volume of water within the glacier ice which has significant implications for glacier hydrology ice rheology and interpretations of both radar and seismic surveys