seasonal variation in boreal early cretaceous calcareous nannofossils the laminated munk marl bed of barremian early cretaceous age in the central trough of the north sea consists of alternating laminae of calcareous nannofossils 15 70 m thick and clay laminae 3 15 m thick comparison with laminated marls from the deeper parts of the modern black sea suggests that the nannoplankton laminae in the munk marl record annual variations in the nannofossils production the production rate of calcareous nannoplankton in the munk marl sea was comparable to that of modern seas the species composition was determined on 64 bedding planes distributed on three samples on the basis of sem photographs of bedding planes forty bedding planes comprising a total of 48 species were examined in the lowermost sample the species composition fluctuated strongly and 19 bedding planes were almost monopolized by a single species at least nine different species occasionally attained complete dominance succession of different floras within a single lamina was demonstrated in the uppermost sample watznaueria barnesae andmicrantholithus obtusus characteristically dominated in the lower and upper part of the laminae while the middle part was occupied by other species for exampleaxopodorhabdus dietzmannii andrhagodiscus asper a nannofossil lamina represents the annual nannoplankton production succession within a lamina is therefore the result of seasonal variation in the species composition the same succession could be repeated in several consecutive years but often a certain pattern was suddenly interrupted giving way to a complete different one

large values of hydraulic roughness in subglacial conduits during conduit enlargement implications for modeling conduit evolution hydraulic roughness accounts for energy dissipated as heat and should exert an important control on rates of subglacial conduit enlargement by melting few studies however have quantified how subglacial conduit roughness evolves over time or how that evolution affects models of conduit enlargement to address this knowledge gap we calculated values for two roughness parameters the darcy weisbach friction factor f and the manning roughness coefficient n using dye tracing data from a mapped subglacial conduit at rieperbreen svalbard values of f and n calculated from dye traces were compared with values of f and n calculated from commonly used relationships between surface roughness heights and conduit hydraulic diameters roughness values calculated from dye tracing ranged from 75 0 97 for f and from 0 68 0 09 s m 1 3 for n equations that calculate roughness parameters from surface roughness heights underpredicted values of f by as much as a factor of 326 and values of n by a factor of 17 relative to values obtained from the dye tracing study we argue these large underpredictions occur because relative roughness in subglacial conduits during the early stages of conduit enlargement exceeds the 5 range of relative roughness that can be used to directly relate values of f and n to flow depth and surface roughness heights simple conduit hydrological models presented here show how parameterization of roughness impacts models of conduit discharge and enlargement rate we used relationships between conduit relative roughness and values of f and n calculated from our dye tracing study to parameterize a model of conduit enlargement assuming a fixed hydraulic gradient of 0 01 and ignoring creep closure it took conduits 9 25 days to enlarge from a diameter of 0 44 m to 3 m which was 6 7 fold longer than using common roughness parameterizations copyright 2013 john wiley sons ltd

evidence for annual records of phytoplankton productivity in the kimmeridge clay formation coccolith stone bands upper jurassic dorset uk the upper jurassic kimmeridge clay formation is a c org rich sequence of mudrocks that was deposited in a dysoxic basin which served unusually to preserve primary coccolithophorid proportions strikingly contrasting within this dark coloured formation are the white coccolith stone bands which contain pristinely preserved coccolithophorid assemblages preserving potentially primary coccolithophorid abundances with minimal diagenetic alteration using methodology described herein scanning electron microscopy sem observation of mum scale laminae within selected stone bands has revealed five distinctive types of microlamina type 1 being barren clay type 2 comprising coccoliths associated with varying amounts of clay or amorphous organic matter type 3 being purely coccolithic type 4 being of putative microbial origin and type 5 containing frequent calcispheres these are all described and illustrated here illustrated sequences of these are discussed with reference to an hypothetical model sequence based on modem records representing a kimmeridgian year of coccolithophorid productivity annual signals are thus interpreted based on the observations presented here and including summaries of the palynomorph records from the stone bands we comment on watznaueriacean palaeoecology and particularly the interpretation of watznaueria fossacincta barnesiae as an opportunistic growth maximising taxon c 2004 elsevier b v all rights reserved

the carbonate signal and calcareous nannofossil distribution in an upper jurassic section balingen tieringen late oxfordian southern germany total abundance assemblage composition and the stratigraphic distribution of the six most abundant species of calcareous nannofossil were analysed in the upper oxfordian succession of balingen tieringen western swabian alb south germany this locality represents a deep shelf less than 200 m environment that is strongly influenced by its proximity to the jura shallow platform nannofossil abundance negatively correlates with carbonate content as well as with accumulation rate calcareous nannofossils thus did not produce the bulk of carbonates and their abundance was essentially controlled by the import of allochthonous carbonate mud gradual increase in carbonate content in the balingen tieringen succession can be related to an intensified carbonate mud export from the jura shallow platform to the swabian alb deep shelf during the late oxfordian changes in the nannofossil assemblage composition along the profile are interpreted as primary although a partial control by diagenesis on the assemblage can not be completely excluded the coccoliths lotharingius hauffii watznaueria britannica cyclagelosphaera margereli watznaueria barnesae watznaueria manivitae and the incertae sedis schizosphaerella spp display their highest relative abundance one after the other in a stratigraphic order this nannofossil succession parallels the gradual increase in allochthonous carbonate mud accumulation on the deep shelf as well as the gradual decrease in the intensity of siliciclastic input recorded on the jura shallow platform this suggests a climatic control by humidity on shallow platform carbonate production and export basinwards and on nutrient availability in deep shelf surface waters that itself controlled the nannofossil assemblage composition therefore the succession of highest relative abundance of l hauffii w britannica c margereli w barnesae w manivitae and schizosphaerella spp can represent a trophic preference continuum from more eutrophic to oligotrophic conditions

melting of the glacier base during a small volume subglacial rhyolite eruption evidence from blahnukur iceland abstract although observations of recent volcanic eruptions beneath vatnajokull iceland have improved the understanding of ice deformation and meltwater drainage little is known about the processes that occur at the glacier base we present observations of the products of a small volume effusive subglacial rhyolite eruption at blahnukur torfajokull iceland lava bodies typically 7 m long have unusual conical morphologies and columnar joint orientations that suggest emplacement within cavities melted into the base of a glacier cavities appear to have been steep walled and randomly distributed these features can be explained by a simple model of conductive heat loss during the ascent of a lava body to the glacier base the released heat melts a cavity in the overlying ice the development of vapour escape pipes in the waterlogged permeable breccias surrounding the lava allows rapid heat transfer between lava and ice the formed meltwater percolates into the breccias recharging the cooling system and leaving a steam filled cavity the slow ascent rates of intrusive rhyolitic magma bodies provide ample time for a cavity to be melted in the ice above even during the final 10 m of ascent to the glacier base an equilibrium cavity size is calculated at which melting is balanced by creep closure this is dependent upon the heat input and the difference between glaciostatic and cavity pressure the cavity sizes inferred from blahnukur are consistent with a pressure differential of 2 4 mpa suggesting that the ice was at least 200 m thick this is consistent with the volcanic stratigraphy which indicates that the ice exceeded 350 m in thickness although this is the first time that a subglacial cavity system of this type has been reconstructed from an ancient volcanic sequence it shares many characteristics with the modern firn cave system formed by fumarolic melting within the summit crater of mount rainier washington at both localities it appears that localised heating at the glacier base has resulted in heterogeneous melting patterns despite the different rheological properties of ice and firn similar patterns of cavity roof deformation are inferred the development of low pressure subglacial cavities in regions of high heat flux may influence the trajectory of rising magma with manifold implications for eruptive mechanisms and resultant subglacial volcanic landforms

middle cretaceous calcareous nannofossil biogeography and preservation in the atlantic and indian oceans implications for paleoceanography abstract the quantitative study of calcareous nannofossil preservation and biogeographic distribution puts constraints on paleoceanographic models for the atlantic and indian oceans during the middle cretaceous we establish a dissolution ranking of middle cretaceous calcareous nannofossils based on susceptibility to dissolution a positive correlation of organic carbon content of the sediments and the relative abundance of watznaueria indicates that much of the carbonate dissolution was caused by the release of carbon dioxide during oxidation of organic matter the depth distribution of the most dissolution resistant species watznaueria barnesae shows relative abundance maxima at the deepest sites and a maximum where intermediate waters impinge on slopes this reflects stagnant oxygen poor bottom waters and possibly a mid water oxygen minimum zone with increased deposition and catabolic breakdown of organic matter factor analyses are performed on various data sets for three different time slices ranging in age from late aptian to early albian middle albian and late albian to cenomanian the resulting factors can be related to paleoceanographic conditions such as colder water at high latitudes high fertility upwelling conditions and neritic conditions for all three time intervals a wide tropical to subtropical zone was flanked by boreal and austral zones upwelling conditions probably existed along the north african margin and over the falkland plateau zonal upwelling is tentatively postulated for the northwestern and northeastern margin of the north atlantic in the middle albian and for the eastern margin of the north atlantic off western europe for the late albian to cenomanian we speculate on surface water current patterns location of upwelling regions and haline driven deep circulation for the middle cretaceous

modeling the diurnal variation of tracer transit velocity through a subglacial channel 1 tracer injections into a moulin connecting to a subglacial channel at unteraargletscher were repeated at intervals of about two hours over two diurnal discharge cycles in august and september 2000 the pronounced hysteresis in the relationships between tracer transit velocity and proglacial discharge may be explained by adjustments of the channel cross section in response to discharge variations or alternatively by modulation of inflow from the tributary moulin into a main subglacial channel to test these hypotheses we employ a physically based time dependent model of channelized subglacial drainage in a series of numerical experiments we explore the general characteristics of each mechanism before the model is applied to diurnal discharge variations measured during the tracer tests at unteraargletscher we found that the ability of a rothlisberger channel to adjust its size to the prevailing hydraulic conditions can contribute to the hysteresis in the velocity discharge relationships however using plausible parameter values r channel hydraulics alone is not satisfactory in reproducing the magnitude of observed transit velocities the model further confirms that retardation of the tracer in the tributary moulin due to inflow modulation has major effects on transit velocities both in magnitude and timing with appropriate assumptions on channel sinuosity and moulin size a combination of both mechanisms can be found that is capable of reproducing the observed transit velocities

assessing the catastrophic break up of briksdalsbreen norway associated with rapid climate change abstract recent research has raised concerns about the potential influence of rapid climate change on the stability of major ice sheets the behaviour of glaciers is determined largely by the processes and conditions operating at their base technological advances have allowed these factors to be examined and their contribution to ice flow constrained this study investigated the rapid disintegration of an aquatic based norwegian glacier through the study of boreholes video ground penetrating radar differential global positioning system bathymetry and glacsweb wireless probes briksdalsbreen retreated dramatically between 2000 and 2007 with c 56 10 5 m 3 of ice lost from the glacier tongue equivalent to a rate of 70 m a 1 this was due to the combined effect of higher summer temperatures decreased precipitation resulting from a negative phase of the north atlantic oscillation and increased fracturing of the glacier tongue the enlargement of a proglacial lake played a key role in brikdalsbreen9s rapid retreat allowing calving events and promoting crevassing and fluctuating water contents at the glacier margin we suggest that hydro fracturing was the dominant mechanism responsible for generating more crevasses each year which facilitated the development of an efficient englacial drainage system this fed increasing quantities of water to the bed where it was stored in subglacial cavities and transferred through a distributed slow9 drainage system however despite this increase in subglacial water content ice velocities remained constant during the break up comparisons are made between the processes observed at briksdalsbreen and those associated with the acceleration and rapid retreat of greenland9s tidewater glaciers

sedimentologic evidence for outburst floods from the laurentide ice sheet margin in wisconsin usa implications for tunnel channel formation abstract clast supported boulder gravel in outwash fans along the glacial maximum margin of the laurentide ice sheet in wisconsin indicates the occurrence of outburst floods these sediments with clast intermediate axes of up to 2 m are located downstream of tunnel channels and were deposited shortly before cessation of glaciofluvial activity on each fan since tunnel channels with fans are widespread along the ice sheet margin in the western great lakes region these outburst floods were probably common paleodischarge estimates derived from the boulder deposits are poorly constrained but values of at least several hundred m3 s 1 are likely four potential water sources for the floods exist an extreme surface melt event an extreme precipitation event drainage of supraglacial lakes or drainage of stored subglacial meltwater we focus on the storage of subglacial meltwater behind the ice sheet margin as proglacial permafrost was present as ice advanced to its maximum extent and a frozen bed zone upstream from the margin probably impeded drainage through groundwater aquifers decay of this permafrost seal would have eventually allowed trapped water to drain through the tunnel channels we suggest that the 2 m boulders were entrained in an outburst of subglacial water that enlarged a pre existing channel cut by ablation derived flows

effects of ice deformation on rothlisberger channels and implications for transitions in subglacial hydrology along the base of glaciers and ice sheets the sliding of ice over till depends critically on water drainage in locations where drainage occurs through rothlisberger channels the effective pres sure along the base of the ice increases and can lead to a strengthening of the bed which reduces glacier sliding the formation of rothlisberger channels depends on two competing effects 1 melting from tur bulent dissipation opens the channel walls and 2 creep flow driven by the weight of the overlying ice closes the channels radially inward variation in downstream ice velocity along the channel axis re ferred to as an antiplane shear strain rate decreases the effective viscosity the softening of the ice increases creep closure velocities in this way even a modest addition of antiplane shear can double the size of the rothlisberger channels for a fixed water pressure or allow channels of a fixed radius to operate at lower effective pressure potentially decreasing the strength of the surrounding bed furthermore we show that rothlisberger channels can be deformed away from a circular cross section under applied antiplane shear these results can have broad impacts on sliding velocities and po tentially affect the total ice flux out of glaciers and ice streams

palaeoenvironmental control on sponge microbialite reefs and contemporaneous deep shelf marl limestone deposition late oxfordian southern germany abstract the late oxfordian bimammatum zone deep shelf deposits of southern germany are characterised by abundant reefs that laterally pass into marl limestone alternations the bioconstructions are made from three main components sponges microbialites and allochthonous sediment a detailed morphological analysis of sponge microbialite reefs in the plettenberg section swabian alb southern germany is combined with investigation of calcareous nannofossil assemblages in laterally correspondent marl limestone alternations in order to trace the evolution of palaeoenvironmental conditions during reef development fluctuations of caco3 content in deep shelf deposits provides evidence of a succession of small scale lithological units generally formed by five to six marl limestone couplets within a small scale lithological unit a close link is observed between growth patterns of sponge microbialite reefs and the changes in the nannofossil assemblage composition phases of expansion of the build ups correspond to carbonate deposits characterised by a relative dominance of large oligotrophic nannoplankton species large watznaueria britannica watznaueria manivitiae and schizosphaerella spp marly intervals reveal a high relative abundance of small sized taxa mainly lotharingius hauffii small w britannica and subordinated biscutum dorsetensis and bioconstructions show a net reduction in size or a total demise this suggests that the same palaeoenvironmental parameters controlled at the same time marl versus limestone deposition reef growth phases and calcareous nannofossil assemblage composition successive reef growth phases recognized within a bioherm are correlated to the limestone hemi couplets each reef growth phase is composed of several stacked elementary sequences comprising the following succession i sponge ii microbialites and iii carbonate mud in turn the microbialitic crust is formed of three successive microbial layers 1 a fine crust of dense to clotted micrite 2 a centimetre scale to multicentimetric columnar layer of clotted to peloidal micrite 3 a centimetre scale stromatolitic crust the passage from an initial dense microbial layer with numerous microencrusters to a final stromatolitic crust is interpreted as resulting from an increase of the microbial growth rate mainly driven by changes in the accumulation rate deep shelf deposits resulted from changes in platform carbonate production and export basinwards controlled both by sea level and climate changes climate controlled the intensity of carbonate production in shallow platform environments and export towards the deep shelf as well as the trophic conditions of the deep shelf marine waters low trophic conditions favoured platform carbonate production and export basinwards and a large development of the sponge microbialite reefs in the deep shelf however a high carbonate accumulation rate in the deep shelf was also commonly responsible for the demise of sponge microbialite reefs during unfavourable and higher trophic conditions during marl deposition reduced development and frequent demise of the sponge microbialite reefs is observed

water pressure and basal sliding on storglaciaren northern sweden the subglacial hydrology of the ablation area of storglaciaren a small valley glacier in northern sweden is dramatically affected by a subglacial ridge or riegel water pressures above this riegel are relatively constant while down glacier from it they vary significantly the lower part of the glacier accelerates in response to peaks in basal water pressure the upper part may be weakly coupled to the lower part during these peaks a power law fit of observed basal water pressures and measured surface velocities yields where u s is the surface velocity and p e is the effective water pressure ice overburden pressure minus subglacial water pressure data from findelengletscher reported by iken and bindschadler 1986 yield an identical exponent and a coefficient one order of magnitude larger the similar exponent implies that the process producing the velocity variations on both glaciers is similar the variations in velocity are inferred to be due to hydraulic jacking on both glaciers

calcium isotope evidence for suppression of carbonate dissolution in carbonate bearing organic rich sediments pore fluid calcium isotope calcium concentration and strontium concentration data are used to measure the rates of diagenetic dissolution and precipitation of calcite in deep sea sediments containing abundant clay and organic material this type of study of deep sea sediment diagenesis provides unique information about the ultra slow chemical reactions that occur in natural marine sediments that affect global geochemical cycles and the preservation of paleo environmental information in carbonate fossils for this study calcium isotope ratios 44 40ca of pore fluid calcium from ocean drilling program odp sites 984 north atlantic and 1082 off the coast of west africa were measured to augment available pore fluid measurements of calcium and strontium concentration both study sites have high sedimentation rates and support quantitative sulfate reduction methanogenesis and anaerobic methane oxidation the pattern of change of 44 40ca of pore fluid calcium versus depth at sites 984 and 1082 differs markedly from that of previously studied deep sea sites like 590b and 807 which are composed of nearly pure carbonate sediment in the 984 and 1082 pore fluids 44 40ca remains elevated near seawater values deep in the sediments rather than shifting rapidly toward the 44 40ca of carbonate solids this observation indicates that the rate of calcite dissolution is far lower than at previously studied carbonate rich sites the data are fit using a numerical model as well as more approximate analytical models to estimate the rates of carbonate dissolution and precipitation and the relationship of these rates to the abundance of clay and organic material our models give mutually consistent results and indicate that calcite dissolution rates at sites 984 and 1082 are roughly two orders of magnitude lower than at previously studied carbonate rich sites and the rate correlates with the abundance of clay our calculated rates are conservative for these sites the actual rates could be significantly slower because other processes that impact the calcium isotope composition of sedimentary pore fluid have not been included the results provide direct geochemical evidence for the anecdotal observation that the best preserved carbonate fossils are often found in clay or organic rich sedimentary horizons the results also suggest that the presence of clay minerals has a strong passivating effect on the surfaces of biogenic carbonate minerals slowing dissolution dramatically even in relation to the already slow rates typical of carbonate rich sediments

impact of the circulation on sapropel formation in the eastern mediterranean the role of the thermohaline circulation in controlling export production oxygenation of deep waters and hence possible sapropel formation in the eastern mediterranean is examined using a simple nutrient cycling model the model is driven by velocity fields from a general circulation model and receives fluxes of nutrient from river run off and atmospheric deposition the model is used to study three scenarios a strong anti estuarine circulation a weakened anti estuarine circulation and a weak estuarine circulation nutrient transports ventilation of oxygen and deposition of organic matter are investigated in each case with a present day circulation the model provides reasonable agreement with observed phosphate and oxygen profiles and for export production with the weakened anti estuarine circulation consistent with surface salinity reconstructions for the most recent sapropel s1 there is a modest increase in export production and reduced ventilation leading to anoxia in intermediate and deep waters sapropel formation is possible near the coastal margins particularly if there is enhanced river run off with an estuarine circulation there is significant increase in export production in addition to anoxia below a shallow winter mixed layer while both the latter circulations allow sapropel formation in the model the estuarine case is distinguished by higher organic carbon deposition and anoxia in the near surface waters

modifications to the theory of intraglacial waterways for the case of subglacial ones on defend l idee que dans les glaciers de montagne temperes les voies d eau sont sous glaciaires pour un conduit noye sous glaciaire il faut introduire deux processus importants l accroissement de la deformation plastique sur les cotes amont des bosses et la chaleur apportee par l eau des sources qui en hiver rend compte de la plus grande partie du debit la theorie explique pourquoi rothlisberger 1972 dut adopter une valeur non realiste pour le parametre rheologique de la glace elle conduit a la conclusion que dans les zones non surcreusees la plus grande partie de l annee les conduits sous glaciaires doivent rester non noyes et a la pression atmospherique cas des surcreusements l incidence de ce nouveau modele sur la theorie du glissement des glaciers

physical volcanology of a subglacial to emergent rhyolitic tuya at rauðufossafjoll torfajokull iceland we present the first modern volcanological study of a subglacial to emergent rhyolite tuya at se rau ufossafjoll torfajokull iceland a flat topped edifice with a volume of 1 km3 was emplaced in upper pleistocene time beneath a glacier 350 m thick although it shares morphological characteristics with basaltic tuyas the lithofacies indicate a very different eruption mechanism field observations suggest that the eruption began with vigorous phreatomagmatic explosions within a well drained ice vault building a pile of unbedded ash up to 300 m thick this was followed by a subaerial effusive phase in which compound lava flows were emplaced within ice cauldrons small volume effusive eruptions on the volcano flanks created several lava bodies with a variety of features columnar jointed sides subaerial tops peperitic bases that are used to reconstruct spatially heterogeneous patterns of volcano ice interaction volcaniclastic sediments exposed in a stream section provide evidence for channelised meltwater drainage and fluctuating depositional processes during the eruption we develop models for the evolution of se rau ufossafjoll and discuss the differences between subglacial rhyolitic and basaltic eruption mechanisms which are principally caused by contrasting hydrological patterns

geometry and flow conditions of subglacial water at south cascade glacier washington state u s a an analysis of tracer injections tracers were injected into south cascade glacier to determine the flow condition and geometry of the subglacial water system results indicate that two distincts drainage basins on the glacier feed the two main streams flowing from the glacier in the largest basin two parallel drainage networks exist one englacial and the other subglacial

velocity discharge relationships derived from dye tracer experiments in glacial meltwaters implications for subglacial flow conditions repeated dye tracer tests were undertaken from individual moulins at haut glacier d arolla switzerland over a number of diurnal discharge cycles during the summers of 1989 1991 it was hoped to use the concepts of at a station hydraulic geometry to infer flow conditions in subglacial channels from the form of the velocity discharge relationships derived from these tests the results however displayed both clockwise and anticlockwise velocity discharge hysteresis in addition to the simple power function relationship assumed in the hydraulic geometry approach clockwise hysteresis seems to indicate that a moulin drains into a small tributary channel rather than directly into an arterial channel and that discharges in the two channels vary out of phase with each other anticlockwise hysteresis is accompanied by strong diurnal variations in the value of dispersivity derived from the dye breakthrough curve and is best explained by hydraulic damming of moulins or sub englacial passageways despite the complex velocity discharge relationships observed some indication of subglacial flow conditions may be obtained if tributary channels comprise only a small fraction of the drainage path and power function velocity discharge relationships are derived from dye injections conducted during periods when the supraglacial discharge entering the moulin and the bulk discharge vary in phase analyses based on this premise suggest that both open and closed channel flow occur beneath haut glacier d arolla and that flow conditions are highly variable at and between sites

a paleoceanographic model for the late campanian early maastrichtian sedimentation in the polish carpathian flysch basin based on nannofossils abstract the study is a qualitative and semi quantitative analysis of calcareous nannofossils in marlstone and calcareous mudstone beds in a 4 6 m thick section of the kropivnik fucoid marls late campanian early maastrichtian in the skole nappe of the polish outer carpathians this turbiditic succession is conspicuous by its short term alternation of marlstone rich and siliciclastic rich packages ca 1 m thick a model for paleoceanographic control on sedimentation is proposed on the basis of nannofossil assemblages in the studied section the nannofossils form assemblages of mixed synsedimentary taxa derived from diverse marine environments differing in trophy water temperature and distance from land the mixing occurred due to submarine resedimentation processes the nannofossils indicate that the siliciclastic rich packages were deposited during periods of lowered water temperature decreased calcareous nannoplankton production and oligotrophic to mesotrophic water conditions which corresponded to the sea level fall and lowstand anti estuarine circulation and downwelling due to arising shelf break front are inferred as the factors responsible for oligotrophy in contrast in the marlstone rich packages the calcareous nannofossils indicate sedimentation during periods of significantly increased calcareous nannoplankton production which corresponded to the sea level rise and highstand the increased nannoplankton production is attributed to estuarine circulation and upwelling the changes in sea level and water circulation conform to the climate changes postulated independently for the late campanian early maastrichtian

palaeobiogeography of early cretaceous berriasian barremian calcareous nannoplankton in order to assess early cretaceous nannoplankton biogeography we studied a series of sites which provide a north south transect across the atlantic ocean supplemented by sections from the north sea basin barents sea falkland plateau weddell sea antarctica argo abyssal plain nw of australia and neuquen basin argentina quantitative assemblage data were gathered from each site for seven time slices within the berriasian to barremian interval each horizon being determined by a nannofossil datum trends in species relative abundance and measures of diversity evenness and richness provide revealing biogeographic information a broad low to mid palaeolatitude zone 50 degrees n 50 degrees s is flanked in both northern and southern hemispheres by distinct high palaeolatitude zones major changes in assemblage abundance and composition occur across a sharp biogeographic front at around 50 degrees n and s palaeolatitude high palaeolatitude assemblages are lower in species richness and diversity and characterised by the presence of abundant typically bipolar taxa e g crucibiscutum salebrosum a less distinct biogeographic boundary at similar to 40 degrees n is distinguished by the presence absence of rarer but biogeographically significant taxa many of which have previously been assigned to boreal or tethyan provinces continental shelf sites are characterised by lower diversity assemblages with common to dominant diagnostic taxa which vary with palaeolatitude nannoconus and micrantholithus at low palaeolatitudes and biscutum constans and zeugrhabdotus spp at higher palaeolatitudes the latter two taxa are considered to be indicative of elevated surface water fertility and the former two may have been similarly adapted the genus watznoueria is ubiquitously dominant giving the populations an unevenness which appears to be a common feature throughout coccolithophore history c 2000 published by elsevier science b v all rights reserved

hydraulics of subglacial cavities modele theorique du comportement a l etat stationnaire des cavites remplies d eau et interconnectees sur le lit du glacier

lowstand carbonates highstand sandstones the sedimentary facies sediment dynamics and sequence architecture of modern high energy shelves in the mid and high latitudes are largely governed by wave abrasion processes cool water carbonates may form there if the influx and or net accretion of siliciclastics is kept at a minimum little dilution of the carbonate produced in situ is generally promoted by a wide epicontinental shelf subdued topography of the adjacent mainland the predominance of limestone outcrops and an arid climate the aforementioned requirements are rarely met and thus will automatically lead to the formation of mixed siliciclastic cool water carbonates such an example is found in the early to mid miocene lagos portimao formation algarve s portugal which formed on a narrow high energy shelf of the atlantic ocean that was bounded by a mountain range the sediments of the formation consist of fossiliferous sandstone fs shell beds and rhodolith blankets along strike the stratification of the formation is monotonous for tens of kilometres and well exposed in coastal cliffs whereas no outcrops of dip sections exist the bulk skeletal composition of the sediments is typical for the warm temperate climatic zone various endo and epibenthic bivalves bryozoans coralline algae echinoderms gastropods and large foraminifers heterostegina in some very rare beds a few isolated not framework forming specimens of zooxanthellate corals porites tarbellastrea indicate temporally elevated surface water temperatures close to the lower threshold of the coral reef ecosystem in sandstones the fauna is well preserved and burrowing bivalves are commonly found in life position in limestone beds the state of preservation of the grains ranges from intact to disintegrated and abraded specimens we infer an accumulation of the shell beds through winnowing of fine materials siliciclastic sand and carbonate mud at wave abrasion depth and concentration of calcareous skeletons associated with the subsequent attraction of new epibiota in a complex shell bed the vertical alternation of fossiliferous sandstone and shell beds and in phase variations of the photo index photic biota vs bryozoans and bryozoan index bivalves vs bryozoans is envisaged to document variations of water depth and sea level sandstone units built up when wave abrasion depth wad rose above the sea floor during tst and early hst whereas the shell beds formed during lst when the wad for sand intersected with the sea floor clastic sediments were probably brought on the outer shelf during early transgression and by longshore currents sea level signatures inferred in the mixed siliciclastic cool water carbonate shelf setting of s portugal therefore significantly deviate from conventional concepts of carbonate sequence stratigraphy which were developed for flat topped platforms successful interpretations of ancient mixed sequences must therefore take into consideration the processes of production concentration and accretion of the carbonate sediments

evidence of increasing surface water oligotrophy during the campanian maastrichtian boundary interval calcareous nannofossils from dsdp hole 390a blake nose abstract the latest cretaceous campanian maastrichtian is characterized by several global cooling and intermittent warming events these climatic changes influenced the palaeoceanography substantially including changes of the deep water sources and surface water currents one of the most prominent episodes of climatic cooling occurred during the campanian maastrichtian transition this study focuses on the palaeoclimate and palaeoceanography of the campanian maastrichtian transition by analysing the calcareous nannofossils of dsdp hole 390a 139 92 126 15 mbsf blake nose for the examination of calcareous nannofossils sixty samples were processed using the settling technique biostratigraphical index taxa broinsonia parca constricta uniplanarius trifidus and tranolithus orionatus suggest a late campanian age for the major part of the studied section the calcareous nannofossils are well preserved highly abundant 6 80 billion specimens gram sediment and diverse 80 species sample the assemblages are dominated by prediscosphaera spp 20 5 watznaueria spp 20 3 and retecapsa spp 9 8 cool water taxa ahmuellerella octoradiata gartnerago segmentatum and kamptnerius magnificus however appear less frequently and do not exceed more than 1 due to their rarity these cool water taxa do not support the existence of an intense cooling phase during the campanian maastrichtian transition at dsdp hole 390a around 133 mbsf several nannofossil taxa however show a distinctive turnover mesotrophic species like discorhabdus ignotus zeugrhabdotus bicrescenticus and zygodiscus exmouthiensis are abundant below 133 mbsf whereas oligotrophic taxa like watznaueria spp eiffellithus spp and staurolithites flavus become common above this level these changes imply a decrease in the input of nutrients perhaps caused by a reorganization of ocean currents palaeo gulf stream and reduced upwelling

thermal response of a small ice cap to climatic forcing two dimensional finite element calculations of velocity and temperature fields have been applied to the energy balance of a cross section of barnes ice cap baffin island canada the flow plane currently is cooling near the ice divide and warming near the margin long term simula tions show a net warming trend followed by a cooling trend with a steady state average temperature similar to the present sensitivity studies on an idealized version of the flow plane show that the overall temperature responds less than surface temperature forcing because a negative feed back in temperature advection is substantially larger than a positive feed back in strain heating the response times of the flow plane by itself are somewhat faster but of the same magnitude as response times that would be estimated from one dimensional modeling when bedrock temperature calculations are included response times increase an order of magnitude but these do not substantially affect the short term response

on the role of mechanical energy in maintaining subglacial water conduits at atmospheric pressure recent theo retical studies of glacier hydrology have assumed that subglacial conduits are completely filled with water under steady state conditions this however is not necessarily the case where discharges are larger than a few tens of liters per second and the down glacier slope of the bed is more than a few degrees the potential energy released by water descending this slope may be capable of melting the walls of a subglacial conduit many times faster than the conduit can close by plastic flow of the ice as a result the pressure in such tunnels may normally be atmospheric or possibly even at the triple point pressure if there is no open connection to the glacier surface simple calcu lations suggest that such pressures in subglacial conduits may be more common than herclofore anticipated the positions of such open conduits may be unstable to small per turbations in discharge or ice veloci ty this is because the mechanical energy available in excess of that needed to balance closure can instead offset the gene ral flow of the ice cond ui ts can thus trend diago nally across the direction of ice aow if an increase in the angle which such a conduit makes with the ice flow direction also results in an increase in slope of he conduit more mechanical energy will become available resulting in a positive feedback process subglacial channels at atmospheric pressure may inauence the origin and morphology of certain glacial landforms such as eskers and plastically molded features resume sur le role de l inergie newtonnienne dam le maintien du riseau aquiflrl sous glaciaire cl la pression almosph irique de recentes etudes theoriques d hydrologie glaciaire ont suppose que le reseau sous glaci aire clait corn pletement rempli d eau en condition d cquil ibre stable ceci neanmoins n est pas necess airement le cas lorsque les debits sonl superieurs a quelques dizaines de litres par seconde et que la pente du lit du glacier est superieure a quelques degres i energie potentielle mise en oeuvre par i eau descendant celle pente peut ire capable de fondre les parois d un chenal sous glaciaire beaucoup plus vite que le chenal ne peut se refermer par le auage plastique de la glace il en resuhe que la pression dans de tels chenaux peut nor rnalement etre atrnospherique

calcareous nannofossils and milankovitch cycles the example of the albian gault clay formation southern england a quantitative study of calcareous nannofossil assemblages was carried out on the albian gault clay formation england this unit consists of grey marly claystones and marlstones with phosphatic nodules and glauconitic layers as minor lithologies two cores were analyzed in detail to focus on changes in nannofloral assemblages and consider their significance preservation of calcareous nannofossils is excellent and therefore diagenesis cannot be invoked to explain not even partially the changes registered in assemblages fast fourier spectral analysis was performed on percentages of selected nannofossil species fluctuations in abundance of both biscutum constans and watznaueria barnesae regarded as fertility and non fertility indices respectively appear to be orbitally driven because spectral analysis showed periodicities of approximately 41 kyr obliquity cycle and 100 kyr short eccentricity cycle in all the spectra the axial obliquityc cycle is a strong signal as expected at these high latitude sites from the boreal realm the same pattern was observed in another fertility controlled taxon zygodiscus cf erectus but cross correlation shows that its abundance plot is displaced with respect to that of b constans orbital perturbations induce variations in climate and ocean circulation because they influence the earth s insolation and seasonality during times of high seasonality strong gradients cause vigorous oceanic circulation a better cycling of nutrients and higher fertility whereas during times of low seasonality low gradients induce more sluggish circulation and lower fertility the carbonate content of the gault clay cores is not correlatable to the higher fertility indices as the abundance curves of b constans w barnesae and z cf erectus are displaced with respect to caco3 content variations this also means that cyclicity in nannofossil assemblages is not a result of diagenesis but an original signal abundance fluctuations of repagulum parvidentatum and combined parhabdolithus asper p splendens colder and warmer water indicators respectively provide evidence for orbital periodicities suggesting that also cyclic variations of surface water temperature might have influenced the nannofossil assemblage patterns within the gault clay

sulfur iron and calcium cycling associated with natural electric currents running through marine sediment natural electric currents running through marine sediments have recently been found to couple oxygen reduction at the surface to sulfide oxidation in deeper anoxic layers here we show that such spatial separation of oxidation and reduction processes causes non conventional sulfur iron and calcium mobilization and reallocation reduced marine sediment was incubated with overlying oxic water and the vertical distribution of solutes and solids was analyzed after 45 150 days as much as 44 of sediment oxygen consumption was driven by electric currents and electrogenic oxidation of sulfide to sulfate with concurrent proton generation resulted in significant dissolution of iron sulfides and calcium carbonates in the anoxic layers of the sediment most of the mobilized iron diffused to the oxic zone where it formed oxidized iron minerals calcium precipitated in the oxic zone as magnesium calcite the electric coupling of biogeochemical processes in distant regions thus generates unique chemical conditions in marine sediments whereby key elements are mobilized and relocated probably along with trace elements and nutrients we suggest that such electrically coupled biogeochemistry flourishes in marine sediments after transient oxygen depletion leaving distinct signatures of such events in the geological record

controls on the basal water pressure in subglacial channels near the margin of the greenland ice sheet assuming a channelized drainage system in steady state we investigate the influence of enhanced surface melting on the water pressure in subglacial channels compared to that of changes in conduit geometry ice rheology and catchment variations the analysis is carried out for a specific part of the western greenland ice sheet margin between 668 n and 66830 0 n using new high resolution digital elevation models of the subglacial topography and the ice sheet surface based on an airborne ice penetrating radar survey in 2003 and satellite repeat track interferometric synthetic aperture radar analysis of european remote sensing satellite 1 and 2 ers 1 2 imagery respectively the water pressure is calculated up glacier along a likely subglacial channel at distances of 1 5 and 9 km from the outlet at the ice margin using a modified version of rothlisberger s equation our results show that for the margin of the western greenland ice sheet the water pressure in subglacial channels is not sensitive to realistic variations in catchment size and mean surface water input compared to small changes in conduit geometry and ice rheology

ground water intrusions in a mine beneath hoganesbreen svalbard assessing the possibility of evacuating water subglacially evacuation of the ground water intruding into a coal mine beneath ho ganesbreen svalbard is difficult and expensive to solve this problem it was proposed thatthe minebeconnectedtotheice bedrock interface pumpinghot waterfromthe mine should establish a flow path along the glacier bed where the ground water would drain gravitationally in this paper we assess the requirements for maintaining such a drainage system in open channel conditions to obtain the bedrock topography we determined the ice thickness by ground penetrating radar and subtracted it from the surface elevation measured by global positioning system a measured temperature profile at the site where themineshouldconnecttotheglacierbed 140mdepth revealedthatthebasal iceisbelow thepressure melting point thelocations of majorsubglacialconduitswereestimatedusing ahydraulic potentialapproach weadoptedamodeloftime dependentdischargethrougha ro thlisberger channel to calculate a set of scenarios using different flow law parameters resultsofthesimulationssuggestthatforthegivenconditions waterflow wouldbepressur ized thereby inhibiting the gravitational drainage of the mine

sedimentary record of a scandinavian ice sheet drainage system and till deposition over subglacial obstacles promoting basal sliding an example from southern poland abstract subglacial obstacles occurring in the path of advancing ice sheets generally generate higher longitudinal compression and higher frictional drag than a flat substrate however in the case of a soft sediment substratum they can have a very different effect on ice sheet behaviour this study concerns a substrate composed of very fine grained sediments with low permeability the relationship between subglacial obstacles and the overriding scandinavian ice sheet was studied in an area of southern poland where a small intervalley neogene clay ridge 40 m high was present based on sedimentological and structural analysis of subglacial till and gravelly sandy sediments the basal depositional processes and subglacial conditions and their influence on ice sheet behaviour were analysed the till and related deposits within the ridge reflecting high water pressure conditions and lack of glacitectonic deformations indicate that the clay ridge did not generate much resistance against the advancing ice sheet but instead favoured basal slip the impermeable substratum weakened the ice bed coupling and promoted ice detachment from the substratum gravelly sandy inclusions at the till clay contact indicate that during the first stage of ice sheet overriding a canal drainage system developed at the ice substrate interface varied geometry size and location of inclusions of sorted sediments suggest periodic instability of the canal system which could lead to its transformation from initially uniform to being composed of conduits of different sizes during later stages of ice sheet overriding a traction till was deposited and occasional drainage through a water film was sufficient to evacuate basal meltwater the resulting change in the character of subglacial drainage was probably related to variations in water pressure gradient during progressive ice sheet advance

deciphering the paleoceanographic significance of early oligocene braarudosphaera chalks in the south atlantic abstract the recurrence of braarudosphaera chalks in the lower oligocene sequences of the subtropical south atlantic has been a long standing conundrum with many hypotheses having been advanced to explain the genesis of these exotic nannofossil assemblages here we evaluate different paleoceanographic models within the context of stable isotope 18o 13c data measured from bulk sediment samples and well preserved foraminifera two closely spaced braarudosphaera layers from a lower oligocene foram subzone p21a 29 4 28 5 ma section drilled in the southeastern atlantic dsdp site 363 are investigated maximum durations for the blooms that deposited the lower and upper braarudosphaera layers are estimated to be 1 1 and 2 2 k y respectively bulk sediment samples enriched in braarudosphaerid carbonate exhibit pronounced 18o increases on the order of 0 6 1 0 which we attribute to isotopic disequilibria driven by braarudosphaerid vital effects the two braarudosphaera layers straddle a single peak in benthic foraminiferal 18o values suggesting that these blooms may recur on glacial interglacial timescales this same pair of braarudosphaerid layers also occurs as a couplet bundled with prolonged 6 7 k y thermocline cooling evidence that these stratigraphically distinct deposits may represent a split signal for a single paleoceanographic paleoclimatic event subsumed within this episode of subsurface cooling are two short lived negative excursions 0 5 in the 13c record of a thermocline dwelling planktonic foraminifer that coincide with the braarudosphaerid layers thus benthic to thermocline 18o and 13c gradients were reduced during the braarudosphaerid blooms a hallmark signature for strengthened upwelling both braarudosphaerid layers are marked by transient divergences in the stable isotopic signals of two shallow dwelling species of planktonic foraminifera these transient 18o offsets may reflect subtle differences in the depth ecologies of these two mixed layer species if so then braarudosphaerid depositional events may represent subsurface blooms that took place within the lower parts of the euphotic zone alternatively these transient 18o offsets may reflect periods of pronounced seasonality with braarudosphaerid blooms occurring during spring upwelling the recurrence of braarudosphaera blooms on both sides of the south atlantic is believed to reflect rhythmic changes in the vigor and configuration of gyre circulation we speculate that the termination of braarudosphaera blooms in the south atlantic near the end of the early oligocene may be related to paleoceanographic change caused by the crossing of a critical threshold in the tectonic opening of the drake passage and the development of the antarctic circum polar current

variability of the large scale general circulation of the mediterranean sea from observations and modelling a review abstract in this paper we present an overview of the most recent findings about the mediterranean sea present day circulation structure both historical observations and numerical model simulations are presented outlining the differences and agreement the model simulations are presented for both an eddy resolving and a coarse resolution numerical model and the results are intercompared the importance of the mesoscales in modifying the large scale flow field is elucidated the critical point is the discovery of the large amplitude interannual variability of the circulation and water mass structure associated with the anomalies of atmospheric forcing over the basin the seasonal variability can be strictly related to changes in heat and momentum fluxes while the interannual variability has a component which is related to the mesoscale field the latter is very intense in the algerian current region and levantine basin but different in structure in the two regions results are shown which confirm the importance of wind driving in establishing the kinetic energy of the flow field by comparing the current transport at the strait of corsica with observations in conclusion the essential characteristics of the present day circulation are associated with the atmospheric forcing and the basin topographic structure results from palaeoceanographic simulations for the last 20 000 years show that changing the atmospheric forcing can cause large changes in the circulation structure which may have affected sapropel formation

pleistocene fluctuations in the northern benguela current system as revealed by coccolith assemblages late pleistocene coccolith data of odp site 1082 from the eastern south atlantic off namibia were analysed to document spatial and temporal changes in surface ocean circulation upwelling intensity and associated productivity the studied site is located on the continental slope close to prominent oceanographic features such as the coastal upwelling mixing area the openoceanic realm and the warm water regime of the angola current highest numbers of total coccoliths up to 30 10 9 coccoliths g 1 sediment were observed during relatively warm periods characterised bydecreased upwellingintensity these elevatednumbers ofcoccoliths are due to highersurface water temperatures anddocumentadomainprobablyinfluencedbylowernutrientconcentrationsinanareawhereoceanicandfilamentouswatermix in contrast low numbers of coccoliths during glacial periods probably characterise time intervals of enhanced upwelling accompanied byabroad filamentous mixing area coccoliths of the genusgephyrocapsaarethe most abundant taxain samples of site 1082 their occurrences are characterised by abrupt changes in the investigated time interval in addition calcidiscus leptoporus pseudoemilinia lacunosa and reticulofenestra asanoi contribute a common part of the assemblage coccoliths accountformorethanhalfofthecarbonate withpeakcontributionofupto 80 intheinterval560to280kawhengephyrocapsa caribbeanica is the major caco3 producer increased carbonate accumulation during this time interval point to an overall weakening of the coastal upwelling intensity accompanied by a reduction of the mixing zone influencing the site location during this event d 2004 elsevier b v all rights reserved

spatial distribution patterns of calcareous nannofossils across the callovian oxfordian transition in the french subalpine basin abstract callovian oxfordian calcareous nannofossils are documented from four sections distributed along a proximal distal slope to central basin transect in the french subalpine basin south eastern france the sections were dated and correlated using integrated ammonite dinoflagellate and nannofossil biostratigraphies the nannofossil assemblages are constantly dominated by watznaueria britannica however significant spatial changes in nannofossil assemblage composition are recorded nannofossil assemblages recovered in slope and slope to basin transition sections are characterized by high abundances lowest diversities highest percentages of smallest sized morphotypes of w britannica subordinated w britannica manivitiae a morphotype described in this study and are indicative of turbulent unstable and or eutrophic conditions towards the central part of the basin as the nutrient content and turbulence declined and paleoenvironmental stability increased the nannofossil assemblages become more diverse and characterized by lower relative abundances of w britannica but higher contribution of larger morphotypes and higher relative abundances of w barnesiae fossacincta biscutum dubium and zeugrhabdotus erectus these latter small coccoliths markers of high surface waters fertility for the cretaceous were probably not competitive with respect to smaller sized w britannica in unstable and eutrophic surface waters for the jurassic an increase in the surface water productivity is recorded both in proximal and distal sections at the callovian oxfordian transition and is demonstrated both by an increase in nannofossil total abundances and in the relative abundances of taxa adapted to high trophic levels thermal minimum in surface waters as indicated by an increase in the percentages of the cool water nannofossil taxa is associated to increased productivity further studies will be necessary to demonstrate whether surface water productivity changes already recorded in the eastern paris basin were global

icelandic jokulhlaup impacts implications for ice sheet hydrology sediment transfer and geomorphology abstract glaciers and ice sheets erode entrain and deposit massive quantities of debris fluxes of subglacial meltwater exert a fundamental control on ice dynamics and sediment transport budgets within many glacial systems outburst floods jokulhlaups constitute high magnitude high frequency fluxes of meltwater relative to normal ablation controlled discharge this paper presents a synthesis of research on recent icelandic jokulhlaups and their geomorphological and sedimentary impact we identify jokulhlaup impacts within subglacial englacial and proglacial settings and discuss their wider significance for ice sheet hydrology sediment transfer and geomorphology because jokulhlaups erode deposit and re work sediment simultaneously they usually cause significant glaciological and sedimentological impacts jokulhlaups that propagate as subglacial flood waves often produce widespread hydromechanical disruption at the glacier base recent icelandic jokulhlaups have been recognised as highly efficient agents of reworking subglacial sediment and glacial sediment entrainment models of jokulhlaup impact therefore need to encompass the sub and englacial environment in addition to the proglacial zone where research has traditionally been focussed most jokulhlaups transport sediment to proglacial sandar and often directly to oceans where preservation potential of the impact is greater proglacial jokulhlaup deposits form distinctive sedimentary assemblages coupled with suites of high energy erosional landforms this study of modern jokulhlaup processes and sedimentary products may be useful for the interpretation of meltwater processes associated with quaternary ice sheets

facies analysis and sequence stratigraphy of a miocene warm temperate carbonate ramp montagna della maiella italy abstract the uppermost oligocene lower miocene to upper miocene ramp carbonates from montagna della maiella italy form a supersequence bounded by deeply incised truncation surfaces this supersequence is subdivided into four sequences each sequence is composed of skeletal limestones in its lower part and marly limestones in its upper part the lower parts of the sequences are foramol limestones which suggest deposition in the warm temperate climate zone changes in climate oceanography and relative sea level combined to control sedimentation in the four sequences in the lower parts of the two older sequences the skeletal sands built dunes suggesting high energy conditions the dominant skeletal grains in the oldest sequence are larger foraminifers and in the next sequence they are bryozoans this change reflects cooling around the time of the aquitanian burdigalian boundary in the lower parts of the two younger sequences of middle and late miocene age sediment sheets with red algal bryozoan oncoids suggest deposition under calmer conditions transgressive and highstand systems tracts are recognized in all sequences a shelf margin systems tract may be exposed in the second oldest sequence in contrast to the situation that exists when warm water carbonates are deposited sedimentation of the foramol limestones on this isolated ramp was unable to balance accommodation during sea level rise this led to hemipelagic sedimentation during sea level highstands conglomerates resulted from reworking along flooding surfaces

ice fracturing during jokulhlaups implications for englacial floodwater routing and outlet development theoretical studies of glacial outburst floods jokulhlaups assume that i intraglacial floodwater is transported efficiently in isolated conduits ii intraglacial conduit enlargement operates proportionally to increasing discharge iii floodwater exits glaciers through pre existing ice marginal outlets and iv the morphology and positioning of outlets remains fixed during flooding direct field observations together with historical jokulhlaup accounts confirm that these theoretical assumptions are not always correct this paper presents new evidence for spatial and temporal changes in intraglacial floodwater routing during jokulhlaups secondly it identifies and explains the mechanisms controlling the position and morphology of supraglacial jokulhlaup outlets and finally it presents a conceptual model of the controls on supraglacial outbursts field observations are presented from two icelandic glaciers skei ararjokull and solheimajokull video footage and aerial photographs taken before during and after the skei ararjokull jokulhlaup and immediately after the solheimajokull jokulhlaup reveal changes in floodwater routing and the positioning and morphology of outlets field observations confirm that glaciers cannot transmit floodwater as efficiently as previously assumed rapid increases in jokulhlaup discharge generate basal hydraulic pressures in excess of ice overburden under these circumstances floodwater can be forced through the surface of glaciers leading to the development of a range of supraglacial outlets the rate of increase in hydraulic pressure strongly influences the type of supraglacial outlet that can develop steady increases in basal hydraulic pressure can retro feed pre existing englacial drainage whereas transient increases in pressure can generate hydraulic fracturing the position and morphology of supraglacial outlets provide important controls on the spatial and temporal impact of flooding the development of supraglacial jokulhlaup outlets provides a new mechanism for rapid englacial debris entrainment

character of the englacial and subglacial drainage system in the lower part of the ablation area of storglaciaren sweden as revealed by dye trace studies

rothlisberger channel theory its origins and consequences the theory of channelized water flow through glaciers most commonly associated with the names of hans rothlisberger and ron shreve and their 1972 papers in the journal of glaciology was developed at a time when interest in glacier bed processes was expanding and the possible relationship between glacier sliding and water at the bed was becoming of keen interest the r channel theory provided for the first time a physically based conceptual model of water flow through glaciers the theory also marks the emergence of glacier hydrology as a glaciological discipline with goals and methods distinct from those of surface water hydrology

the climate of the late cretaceous new insights from the application of the carbonate clumped isotope thermometer to western interior seaway macrofossil abstract we apply the carbonate clumped isotope thermometer 47 to macrofossils from the baculites compressus 73 5 ma and the hoploscaphites nebrascensis 67 ma ammonite zones of the western interior seaway wis of north america and nearby coeval terrestrial and open marine environments the carbonate clumped isotope thermometer is based on a single phase isotope exchange equilibrium that promotes the clumping of two heavy isotopes together within a single carbonate molecule as temperature decreases due to the thermometer s isotopic independence from water coupled measurements of 47 and the bulk oxygen isotopic composition of a carbonate 18 o c enable the reconstruction of both paleotemperature and the isotopic composition of the water in which the organisms grew before applying the technique to the aragonite shells of fossil marine organisms mostly ammonites but also some gastropods bivalves and one belemnite we measure the clumped isotopic composition of modern nautilus and cuttlefish two of the nearest living relatives to the cretaceous ammonites modern cephalopods exhibit disequilibrium isotope effects with respect to 47 but not 18 o c therefore a simple correctional scheme is applied to the late cretaceous macrofossil data before reconstructing paleotemperatures diagenesis is also assessed by visual preservation and previously measured sr concentrations cochran et al 2003 temperatures reconstructed for the late cretaceous western interior seaway range from 16 4 3 5 c for an offshore interior seaway environment from the h nebrascensis zone to 24 2 0 4 c for the b compressus ammonite zone the seaway itself has an isotopic composition of approximately 1 relative to vsmow the expectation for an ice free global ocean average while a nearby freshwater environment has an isotopic composition approaching 20 we compare the attributes of the reconstructed climate to predictions based on late cretaceous climate models and previous reconstructions of the seaway and also assess the sensitivity of our results to the modern cephalopods correction by comparisons to suitable modern analogs finally our clumped isotope data are consistent with cooling between the late campanian and maastrichtian as also seen in benthic foraminfera 18 o

photic zone palaeoenvironments of the kimmeridge clay formation upper jurassic uk suggested by calcareous nannoplankton palaeoecology nannoplankton abundance data has revealed significant and systematic population fluxes through all representative lithologies and cycle types of the kimmeridge clay formation kcf and also through intervals in which lithology is visually homogeneous the majority of kcf samples yielded nannofossil assemblages of low species richness 1 to 10 and marked unevenness independent of preservational state all samples were dominated by coccoliths of one family the watznaueriaceae while assemblage unevenness is characteristic of nannofossil populations such low species richness is atypical particularly when compared with coeval assemblages of similar latitude such anomalously low nannofossil diversity may be explained as a response to nutrient rich euphotic environments we postulate that consistently high trophic conditions supported the eurytopic watznaueriaceans but excluded most normal open ocean taxa the switching of dominance within this group most likely reflects different adaptations within an r selected ecological strategy related to nutrient concentration lowest diversities were recorded in mudstone oil shale lithologies where watznaueria britannica is the dominant species suggesting adaptation to the highest nutrient concentrations watznaueria barnesiae fossacincta is particularly dominant in coccolith stone bands where diversity is slightly higher suggesting adaptation to lower high nutrient levels cyclagelosphaera margerelii appears to be the most extremely r selected species exploiting unusual very high trophic lowered sea level conditions that excluded even w britannica d 2005 elsevier b v all rights reserved

visions of ice sheets in a greenhouse world abstract backstripped eustatic estimates from new jersey and the russian platform show large 25 m and rapid 18 o record highlights the enigma this was the warmest interval of the past 200 my yet it was bracketed by two inferred eustatic falls of 25 m that were associated with two large 0 75 deep sea 18 o increases 92 93 ma mid turonian and 96 ma mid cenomanian we reconcile records of warm high latitudes with glacioeustasy by proposing that late cretaceous early eocene ice sheets generally reached maximum volumes of 8 12 10 6 km 3 20 30 m glacioeustatic equivalent but did not reach the antarctic coast hence coastal antarctica hence deep water remained relatively warm even though there were significant changes in sea level as the result of glaciation unlike the oligocene and younger icehouse world these ice sheets only existed during short intervals of peak milankovitch insolation leaving antarctica ice free during much of the greenhouse late cretaceous to middle eocene these results highlight the need to re evaluate the paradigm that polar ice sheets did not exist during times of warm high latitude climates

short term variability in greenland ice sheet motion forced by time varying meltwater drainage implications for the relationship between subglacial drainage system behavior and ice velocity 1 high resolution measurements of ice motion along a 120 km transect in a land terminating section of the gris reveal short term velocity variations 1 day which are forced by rapid variations in meltwater input to the subglacial drainage system from the ice sheet surface the seasonal changes in ice velocity at low elevations 1000 m are dominated by events lasting from 1 day to 1 week although daily cycles are largely absent at higher elevations reflecting different patterns of meltwater input using a simple model of subglacial conduit behavior we show that the seasonal record of ice velocity can be understood in terms of a time varying water input to a channelized subglacial drainage system our investigation substantiates arguments that variability in theduration and rate rather than absolute volume of meltwater delivery to the subglacial drainage system are important controls on seasonal patterns of subglacial water pressure and therefore ice velocity we suggest that interpretations of hydro dynamic behavior in land terminating sections of the gris margin which rely on steady state drainage theories are unsuitable for making predictions about the effect of increased summer ablation on future rates of ice motion

models of ice melting and edifice growth at the onset of subglacial basaltic eruptions 1 models of the early stages of basaltic eruptions beneath temperate glaciers are presented that consider the evolving sizes of volcanic edifices emplaced within subglacial cavities the cavity size reflects the competing effects of enlargement by melting and closure by downward ductile deformation of the ice roof which occurs when the cavity pressure is less than glaciostatic due to meltwater drainage eruptions of basaltic magma from fissures and point sources are considered which form either hemicylindrical or hemispherical cavities the rate of roof closure can therefore be estimated using nye s law the cavity size edifice size and depth of meltwater above the edifice are predicted by the model and are used to identify two potential eruption mechanisms explosive and intrusive when the cavity is considerably larger than the edifice hydroclastic fragmentation is possible via explosive eruptions with deposition of tephra by eruptionfed aqueous density currents when the edifice completely fills the cavity rising magma is likely to quench within waterlogged tephra in a predominantly intrusive manner the models were run for a range of magma discharge rates ice thicknesses and cavity pressures relevant to subglacial volcanism in iceland explosive eruptions occur at high magma discharge rates when there is insufficient time for significant roof closure the models correctly predict the style of historic and pleistocene subglacial fissure eruptions in iceland and are used to explain the contrasting sedimentology of basaltic and rhyolitic tuyas the models also point to new ways of unraveling the complex coupling between eruption mechanisms and glacier response during subglacial eruptions

middle to late miocene fluctuations in the incipient benguela upwelling system revealed by calcareous nannofossil assemblages odp site 1085a middle to late miocene calcareous nannofossil data of odp site 1085 from the eastern south atlantic off namibia were analysed to document spatial and temporal changes in surface ocean circulation upwelling initiation and associated productivity our data show that calcareous nannofossils constitute a significant part of the carbonate fraction throughout the investigated interval from 12 5 to 7 7 million years ma highest numbers of calcareous nannofossils up to 38 000 10 6 nannofossils g 1 sediment were observed during the intervals 9 9 to 9 7 and 8 7 to 8 0 ma these elevated numbers of calcareous nannofossils may generally be linked to the initiation of upwelling at about 10 ma in the studied region in contrast diminished numbers of calcareous nannoplankton as in the interval 9 6 to 9 0 ma probably characterise time intervals of weaker productivity resulting in a decrease of nannofossil carbonate contents in the sediments of site 1085 this decrease in nannofossil production could be one possible explanation for the major caco3 depression in between 9 6 and 9 0 ma coccoliths of the genus reticulofenestra are the most abundant taxa their occurrences are characterised by changes in the investigated time interval in addition coccolithus pelagicus calcidiscus leptoporus and umbilicosphaera spp contribute a common part of the assemblage calcareous nannofossils account for more than half of the carbonate with peak contribution up to 80 at 8 8 ma d 2005 elsevier b v all rights reserved

oxygen isotopes in glacier river water austre okstindbreen okstindan norway there is no discernible river discharge from austre okstindbreen norway in winter any water formed by basal melting is likely to be stored in isolated cavities or sediments at the bed in summer a baseflow component of discharge relatively depleted of 18 o is diluted by water more enriched in 18 o glacier ice meltwater with a high 18 o value passes rapidly through channelized systems and emerges in the glacier river within a few hours headward extension of the systems in late summer may tap water stored within the glacier since the previous summer s close down stored water also is released during early melt season events when the low capacity drainage systems cannot accommodate inputs the high 18 o value indicates that the probable source of the released water is glacier ice or low altitude snowfall stratigraphic variations of 18 o values resulting from changing weather conditions characterize the accumulating winter snowpack during the melt season the mean 18 o value of the residual pack rises the water leaving it depleted of 18 o passes slowly through the glacier smoothing out variations of supply 18 o values of rain vary between and within events and their effect on glacier river 18 o values is unpredictable

ultra depleted peridotite xenoliths in the northern taihang mountains implications for the nature of the lithospheric mantle beneath the north china craton abstract we report the finding of peridotite xenoliths in the early cretaceous longmengou olivine bearing diabase 138 ma in the northern taihang mountains in the central north china craton based on the modal proportions of olivine clinopyroxene amphibole and anorthite these peridotite xenoliths can be divided into three zones clinopyroxene bearing olivine zone coz olivine clinopyroxene zone ocz and amphibole bearing anorthite clinopyroxene zone aacz the core of olivine grains in clinopyroxene bearing olivine zone have higher mg 95 sio2 41 80 42 53 wt and lower cao 95 and lower nio content

a fully three dimensional finite element model applied to velocities on storglaciaren sweden a finite element model that solves the stress balance equations for glacier dynamics in three dimensions has been developed by extending previous flow plane models this model retains all terms of the stress tensor and uses a glen type power law for viscosity calculations in the paper the model is applied to storglaciaren sweden to explore both the glacier s dynamics and the model s characteristics values of the stiffness parameter b of 0 20 0 22 mpa year 1 n were required to match observed strain rates on storglaciaren overall velocities required imposition of a problematically small sliding speed stress fields implied by the model simulation showed that the glacier receives its largest driving force from a high slope zone near the equilibrium line and that a large proportion of the resistive stress comes from lateral drag lateral drag is enhanced on this glacier by being frozen to ts sidewalls and by a turning of the main flow as it comes out of the main or northern cirque

coccolithophores in the equatorial atlantic ocean response to seasonal and late quaternary surface water variability abstract the present study was initiated to ascertain the significance of coccolithophores as a proxy for paleoceanographic and paleoproductivity studies in the equatorial atlantic data from a range of different samples from the plankton surface sediments as well as sediment cores are shown and compared with each other in general the living coccolithophores in the surface and subsurface waters show considerable variation in cell numbers and distribution patterns cell densities reached a maximum of up to 300 103 coccospheres l in the upwelling area of the equatorial atlantic here emiliania huxleyi is the dominant species with relatively high cell numbers whereas umbellosphaera irregularis and umbellosphaera tenuis are characteristic for oligotrophic surface waters although they are observed in high relative abundances these species only occur in low absolute numbers the lower photic zone is dominated by high abundances and considerable cell numbers of florisphaera profunda the geographical distribution pattern of coccoliths in surface sediments reflects the conditions of the overlying surface water masses however abundances of the oligotrophic species umbellosphaera irregularis and umbellosphaera tenuis are strongly diminished causing an increase in relative abundance of the lower photic zone taxa florisphaera profunda and gladiolithus flabellatus during the past 140 000 years the surface water circulation of the equatorial atlantic has changed drastically as can be seen from changes in the coccolithophore species composition absolute coccolith numbers as well as coccolith accumulation rates significant increases in coccolith numbers and accumulation rates is observed in the southern equatorial atlantic during the last glacial interval oxygen isotope stages 2 4 which we attribute to enhanced upwelling intensities and advection of cool nutrient rich waters at this site in the western equatorial atlantic we observe an opposite trend with decreasing numbers of coccoliths during glacial periods which probably is caused by a deepening of the thermocline

polythermal glacier hydrology a review 1 the manner by which meltwater drains through a glacier is critical to ice dynamics runoff characteristics and water quality however much of the contemporary knowledge relating to glacier hydrology has been based upon and conditioned by understanding gleaned from temperate valley glaciers globally a significant proportion of glaciers and ice sheets exhibit nontemperate thermal regimes the recent growing concern over the future response of polar glaciers and ice sheets to forecasts of a warming climate and lengthening summer melt season necessitates recognition of the hydrological processes in these nontemperate ice masses it is therefore timely to present an accessible review of the scientific progress in glacial hydrology where nontemperate conditions are dominant this review provides an appraisal of the glaciological literature from nontemperate glaciers examining supraglacial englacial and subglacial environments in sequence and their role in hydrological processes within glacierized catchments in particular the variability and complexity in glacier thermal regimes are discussed illustrating how a unified model of drainage architecture is likely to remain elusive due to structural controls on the presence of water cold ice near glacier surfaces may reduce meltwater flux into the glacier interior but observations suggest that the transient thermal layer of near surface ice holds a hydrological role as a depth limited aquifer englacial flowpaths may arise from the deep incision of supraglacial streams or the propagation of hydrofractures forms which are readily able to handle varied meltwater discharge or act as locations for water storage and result in spatially discrete delivery of water to the subglacial environment the influence of such drainage routes on seasonal meltwater release is explored with reference to summer season upwellings and winter icing formation moreover clear analogies emerge between nontemperate valley glacier and ice sheet hydrology the discussion of which indicates how persistent reassessment of our conceptualization of glacier drainage systems is required there is a clear emphasis that continued integrated endeavors focused on process glaciology at nontemperate glaciers are a scientific imperative to augmenting the existing body of research centered on ice mass hydrology

internal geometry and evolution of moulins storglaciaren sweden depart ment of physical geog raphy university of stoc kholm s 106 91 stockholm sweden abstract the initial conditions needed for formation of moulins are crevasses and a supply of melt water water pouring into a crevasse may fill it until it ove rflows at the lowest point which is normally near the margin however as the crev asse deepens it intersects englacial chann els through which the water can drain these chann els may be finger tip tributaries in a dendritic system such as that described by shreve 1972 and observ ed by raymond and harrison 1975 when the cre vasse closes heat in the melt water keeps the conne ction open and a moulin is formed the englacial channel enlarges rapidly by melt ing utilizing mechanical energy released by the descending water descents into moulins and mapping of stru ctures exposed at the surface after many years of melting demonstrate that the drainage channels leading down from the bottoms of the moulins have incli nations of 0 450 from the vertical these channels trend in the dire ction of the original crevasse but appear to be deeper than the expected depth of the crevasse they have not

water flow through temperate glaciers understanding water movement through a glacier is fundamental to several critical issues in glaci ology including glacier dynamics glacier induced floods and the prediction of runoff from glacierized drainage basins to this end we have synthesized a conceptual model of water movement through a temper ate glacier from the surface to the outlet stream pro cesses that regulate the rate and distribution of water input at the glacier surface and that regulate water movement from the surface to the bed play important but commonly neglected roles in glacier hydrology where a glacier is covered by a layer of porous perme able firn the accumulation zone the flux of water to the glacier interior varies slowly because the firn tempo rarily stores water and thereby smooths out variations in the supply rate in the firn free ablation zone in con trast the flux of water into the glacier depends directly on the rate of surface melt or rainfall and therefore varies greatly in time water moves from the surface to the bed through an upward branching arborescent net work consisting of both steeply inclined conduits formed by the enlargement of intergranular veins and gently inclined conduits spawned by water flow along the bottoms of near surface fractures crevasses engla cial drainage conduits deliver water to the glacier bed at a limited number of points probably a long distance downglacier of where water enters the glacier englacial conduits supplied from the accumulation zone are quasi steady state features that convey the slowly varying water flux delivered via the firn their size adjusts so that they are usually full of water and flow is pressurized in contrast water flow in englacial conduits supplied from the ablation area is pressurized only near times of peak daily flow or during rainstorms flow is otherwise in an open channel configuration the subglacial drainage system typically consists of several elements that are distinct both morphologically and hydrologically an up glacier branching arborescent network of channels in cised into the basal ice conveys water rapidly much of the water flux to the bed probably enters directly into the arborescent channel network which covers only a small fraction of the glacier bed more extensive spatially is a nonarborescent network which commonly includes cav ities gaps between the glacier sole and bed channels incised into the bed and a layer of permeable sediment the nonarborescent network conveys water slowly and is usually poorly connected to the arborescent system the arborescent channel network largely collapses during winter but reforms in the spring as the first flush of meltwater to the bed destabilizes the cavities within the nonarborescent network the volume of water stored by a glacier varies diurnally and seasonally small temper ate alpine glaciers seem to attain a maximum seasonal water storage of 200 mm of water averaged over the area of the glacier bed with daily fluctuations of as much as 20 30 mm the likely storage capacity of subglacial cavities is insufficient to account for estimated stored water volumes so most water storage may actually occur englacially stored water may also be released abruptly and catastrophically in the form of outburst floods

modeling of subglacial hydrological development following rapid supraglacial lake drainage the rapid drainage of supraglacial lakes injects substantial volumes of water to the bed of the greenland ice sheet over short timescales the effect of these water pulses on the development of basal hydrological systems is largely unknown to address this we develop a lake drainage model incorporating both 1 a subglacial radial flux element driven by elastic hydraulic jacking and 2 downstream drainage through a linked channelized and distributed system here we present the model and examine whether substantial efficient subglacial channels can form during or following lake drainage events and their effect on the water pressure in the surrounding distributed system we force the model with field data from a lake drainage site 70 km from the terminus of russell glacier in west greenland the model outputs suggest that efficient subglacial channels do not readily form in the vicinity of the lake during rapid drainage and instead water is evacuated primarily by a transient turbulent sheet and the distributed system following lake drainage channels grow but are not large enough to reduce the water pressure in the surrounding distributed system unless preexisting channels are present throughout the domain our results have implications for the analysis of subglacial hydrological systems in regions where rapid lake drainage provides the primary mechanism for surface to bed connections

an unusual jokulhlaup resulting from subglacial volcanism solheimajokull iceland jokulhlaups glacial outburst floods are frequent in glaciated terrain jokulhlaups exhibiting a sudden rise to peak discharge have not been subject to detailed investigation a volcanically generated flood burst from solheimajokull iceland in july 1999 this paper accounts for the causes characteristics and impacts of this flood pre and post flood fieldwork was carried out at solheimajokull allowing the reconstruction of mean flow velocities and peak discharge flood onset was rapid rising to a peak discharge of 4 4 x 103 m3s 1 1 2 x 103 m3s 1 within one hour high basal water pressures resulted in floodwater bursting through the glacier surface ice rip up clasts containing glacial diamict provided evidence of floodwater contact with the glacier bed within the glacier jokulhlaup sedimentation occurred within hydrofractures and conduits generating complex hydrofracture fills and esker ridges in the proglacial zone regions of flow expansion associated with rapid reductions in sediment transport capacity controlled the locations of major jokulhlaup sedimentation a large fan composed of material of up to boulder size was deposited at the glacier snout two ice marginal basins filled and drained during the jokulhlaup one of the basins jokulsargil emptied rapidly during the flood via ice dam flotation accentuating peak jokulhlaup discharge high rates of downstream peak discharge attenuation during the july 1999 jokulhlaup provides an analogy with flash flood hydrographs in semi arid regions and the catastrophic failure of man made dams the july 1999 jokulhlaup was initially triggered by the subglacial volcanic eruption but the characteristics of the flood were accentuated by within event meltwater storage and release this unusual jokulhlaup provides an important addition to our understanding of the spectrum of distinctive jokulhlaup characteristics

short term velocity variations and basal coupling near a bergschrund storglaciaren sweden distance measurements using an automated electronic distance measurement system in the north cirque of storglaciaren sweden during the summer of 1989 revealed a diurnal variation in glacier speed amplitude and timing of the diurnal cycle correlate well with the timing and intensity of the diurnal temperature cycle indicating that speed responds to variations in daily melt with a lag of approximately 4 h one 2 d period of non diurnal velocity variations corresponded with a large rainfall event finite element modeling suggests that these velocity variations must be closely related to water inputs in the cirque rather than to longitudinal coupling with lower parts of the glacier

toward better paleocarbonate ion reconstructions new insights regarding the caco3 size index 1 the reconstruction of paleocarbonate ion concentrations provides an important constraint on the contribution of the caco3 cycle to the decrease in atmospheric co2 content during glacial time such reconstructions have been challenging because each of the existing paleo co32 indices has serious limitations in this study we reexamine the broecker clark caco3 size index by analyzing the 20 m 20 to 38 m and 38 to 63 m fractions in sediments from the ontong java plateau and the ceara rise scanning electron microscope analyses demonstrate that the less than 20 m caco3 is dominated by coccoliths and the greater than 20 m caco3 is dominated by foraminifera our results clearly indicate that the coccoliths are far more resistant to dissolution than the foraminifera referenced to a core top sample from 2 31 km depth in a core top sample from 4 04 km depth on the ontong java plateau 70 of the foraminifera caco3 was dissolved as opposed to only 7 of the coccolith caco3 we found that the dissolution of foraminifera shells did not produce a significant amount of fragments smaller than 63 m in size and thus the broecker clark size index is not a measure of the extent of fragmentation rather it is a measure of the extent of differential dissolution of foraminifera relative to coccoliths on the basis of these results we propose a new dissolution index which involves the ratio of dissolution susceptible foraminifera caco3 to total caco3

investigations of glacier hydrological systems using dye tracer techniques observations at pasterzengletscher austria a l aide de traceurs colores on a mis en evidence une division laterale du drainage dans le bas de la langue qui n est pas determinee par la direction des crevasses obliques la reapparition de l eau dans les differents moulins est complexe bien qu elle reste constante dans le temps

reconstructing nutricline dynamics of mid cretaceous oceans evidence from calcareous nannofossils from the niveau paquier black shale se france abstract a high resolution calcareous nannofossil record is presented from the lower albian niveau paquier black shale from the vocontian basin se france the niveau paquier black shale represents the regional equivalent of the supraregionally distributed oceanic anoxic event 1b oae 1b to reconstruct surface water fertility a nutrient index based on zeugrhabdotus erectus discorhabdus rotatorius high fertility indicators and watznaueria barnesae low fertility indicator was established using principal component analysis in addition the distribution of nannoconus spp and absolute abundances of coccoliths coccoliths per gram were used for reconstructing nutricline dynamics of the surface waters high surface water fertility coincides with low percentages of nannoconids and vice versa moreover high percentages of nannoconids correlate with low absolute abundances of all other coccoliths based on the observed nannoplankton distribution pattern and a suggested similarity in ecological requirements between nannoconids and the modern taxon florisphaera profunda a model is proposed that couples nannoconid abundances with dynamics of the nutricline time series analyses of the nutrient index show fluctuations within the precessional band the precession controlled fluctuations of the surface water fertility may represent a monsoonal signal with the nutrient supply in the surface waters depending on the strength of monsoonal activity during periods of enhanced monsoonal activity which were characterized by humid conditions and stronger winds mixing of the upper water column was enhanced during that time the abundance of nannoconids decreased as a consequence of enhanced wind stress that improved vertical mixing and led to an entrainment of nutrients into the surface waters this resulted in an increase of primary production during periods of reduced monsoonal activity marked by drier conditions and reduced wind stress the surface waters were depleted in nutrients as a result of a deep nutricline and a reduced nutrient supply to the upper photic zone in a stratified water column percentages of nannoconids increased according to the mechanisms outlined above fluctuations of the nutrient index and nannoconid percentages have been used as a proxy for reconstructing the physical structure of mid cretaceous oceans steered by precession forced monsoonal activity the results of the study show that the formation of the lower albian oae 1b from the vocontian basin occurred under strongly fluctuating surface waters fertility

modelling the evolution of subglacial tunnels due to varying water input the time evolution ofa subglacial tunnel cross section is examined using a two dimensional finite element ice flow model coupled to an idealized drainage system simulations are driven by physically based calculations of surface water input variations at storglaciaren sweden highlights of the model are its ability to handle unsteady conditions and irregular tunnel shapes agreement between modelled water pressure and borehole water levels is good the following conclusions are reached i tunnels adapt to fluctuating inflow on time scales of days storms during which effective pressure ranges from 0 to 0 9 mpa cause significant adjustments but daily fluctuations due solely to meltwater inflow are minor ii open channel flow may become commonplace late in the ablation season iii initial tunnel shape influences subsequent tunnel evolution and seasonal water pressure variation over the course of a summer tunnels retain some of their initial shape though in all experiments the width to height ratio increased with time iv tunnel contraction forms broad low tunnels however v given two tunnels of equal initial area the higher narrower one expands more rapidly thus more semi circular tunnels may capture flow from broader neighbours early in the summer

sinking of coccolith carbonate and potential contribution to organic carbon ballasting in the deep ocean abstract there exists a great need to better understand the controls on organic carbon sequestration to the deep sea by virtue of its role in modulating atmospheric co 2 concentrations recent studies suggest that organic fluxes to the oceanic interior are higher in regions dominated by carbonate sedimentation thus also concluding that relatively heavy carbonate particles are an effective mineral ballast for organic carbon caco 3 production in the pelagic ocean is mainly mediated by foraminifera and coccolithophores but the precise role of these carbonate producers as mineral ballast for organic carbon in the ocean has not yet been tested here we evaluate sediment trap flux data from an array of 13 moorings 15 traps situated in diverse conditions and with global coverage all for organic carbon flux calculated coccolith carbonate flux and fine fraction flux when available discrepancies are recorded between the amount of carbonate fine fraction and calculated coccolith carbonate and there is the need to determine the origin of the unknown caco 3 in the fine fraction the coccolith carbonate flux magnitude is determined not only by the coccolith flux number but also by the carbonate mass of the key species for example very abundant coccolithophore species such as emiliania huxleyi have a very low species specific carbonate mass and are therefore of lower carbonate flux significance than expected intuitively among the main coccolith carbonate species contributors in our sediment trap sites are calcidiscus leptoporus and helicosphaera carteri in that these are all relatively massive compared to their numerical abundances we observed generally positive correlations between calculated coccolith carbonate and organic carbon daily fluxes suggesting that on a global basis there is a ballasting mechanism at work seemingly most efficiently with c leptoporus in the carbonate dominated north atlantic a fairly constant global relationship between annual fluxes of calculated coccolith carbonate and organic carbon implies some uniformity in the pic poc rain ratio however improvements in coccolith carbonate estimation are needed to not only understand this ratio currently but also to help understand future sequestration of organic carbon to the oceanic interior

combined measurements of subglacial water pressure and surface velocity of findelengletscher switzerland conclusions about drainage system and sliding mechanism interpretation des mesures de pression dans les forages et des vitesses superficielles la comparaison avec les modeles suggere que l on a neglige le frottement du aux debris dans les modeles et qu il n existe jamais de chenaux cylindriques rectilignes