devonian tetrapod trackways and trackmakers a review of the fossils and footprints abstract the earliest tetrapods are known from the upper devonian their remains are becoming better known from increasing numbers of specimens localities environments and ichnofossils each of the eight or possibly nine genera now represented by skeletal fossils is reviewed in its sedimentological faunal and stratigraphic context with an assessment of what might be inferred about the habitus and locomotory capabilities of each fossil trackways and their interpretations are then re examined in the context of the known body forms and consideration given to the degree of fit between the skeletal fossils the trackways and their interpretations the currently known devonian tetrapods are unlikely to have made any of the known tracks unless they were produced under water neither the skeletal fossils nor the trackways show good evidence of terrestrial locomotion among devonian tetrapods when the fossil material and recent phylogenetic analyses are taken in combination it appears that neither tetrapods nor limbs with digits are likely to have arisen before the frasnian this should be borne in mind in palaeoecological studies of these animals

origin of the northern atlantic s heinrich events as first noted by heinrich 1988 glacial age sediments in the eastern part of the northern atlantic contain layers with unusually high ratios of ice rafted lithic fragments to foraminifera shells he estimated that these layers are spaced at intervals of roughly 10 000 years in this paper we present detailed information documenting the existence of the upper five of these layers in odp core 609 from 50 n and 24 w their ages are respectively 15 000 radiocarbon years 20 000 radiocarbon years 27 000 radiocarbon years about 40 000 years and about 50 000 years we also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers although we are not of one mind regarding the origin of these layers we lean toward an explanation that the heinrich layers are debris released during the melting of massive influxes of icebergs into the northern atlantic these sudden inputs may be the result of surges along the eastern margin of the laurentide ice sheet

establishment of modern circulation pattern at c 6000 cal a bp in disko bugt central west greenland opening of the vaigat strait variations in the holocene circulation of the west greenland current wgc in the disko bugt region have been reconstructed from a suite of sediment cores palaeoceanographic proxies include magnetic susceptibility ms and x ray fluorescence titanium counts which document a major shift in circulation at c 6000 cal a bp before this date sediments in southern disko bugt were characterized by high terrigeneous and basaltic input suggesting widespread influence of meltwater plumes our data show that the wgc re circulated in the southern disko bugt area because a potential northern pathway the narrow vaigat strait was blocked by icebergs that calved from marine outlet glaciers in eastern disko bugt sediments in southern disko bugt deposited after c 6000 cal a bp have significantly lower terrestrial and basaltic sediment input which coincides with minimum holocene ice sheet extent the reduced meltwater and iceberg discharge to the embayment caused the vaigat strait to become free of blocking icebergs and terrigenous input was partly diverted to the outer shelf thus the modern circulation pattern of the wgc was established in the disko bugt region through the opening of the vaigat strait c 6000 cal a bp

apatite for destruction isotopic and geochemical analyses of bioapatites and sediments from the upper devonian escuminac formation miguasha quebec abstract the paleoenvironmental context and diagenetic history of the middle frasnian escuminac formation were investigated through geochemical rare earth elements and isotopic rb sr nd sm analyses of fossil fish material and sediments samples of sediments and bioapatite were collected from the base to the top of the escuminac formation strontium isotope ratios 87 sr 86 sr for bioapatites vary from 0 70804 to 0 70845 and overlap with frasnian seawater sr isotope compositions though most of the biogenic apatites analyzed show a variable drift from marine values toward a more radiogenic continental signature this trend is possibly the result of post mortem sr exchange between fossils and a fluid isotopically distinct from the waters in which they developed all bioapatites are heavily enriched in rare earth elements ree and display a shale normalized pattern that shows heavy ree hree depletion and a slight middle ree mree enrichment the e nd t values of the sediments range from 4 8 to 6 4 and are consistent with a sedimentary provenance derived from an appalachian source for the escuminac formation in contrast more radiogenic e nd t values ranging from 2 6 to 4 6 were obtained for the bioapatites the discrepancy between sediments and fossil material e nd t implies the presence of a second diagenetic nd reservoir for the escuminac bioapatites we propose that this reservoir reflects in part seawater the similarity between the nd isotope compositions of the escuminac fossils and late devonian conodonts from poland argues for a close connection between waters of the devonian rheic ocean and the escuminac formation collector basin

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

spatial and temporal patterns of iceberg rafting ird along the east greenland margin ca 68 n over the last 14 cal ka twelve 1 2 m 10 cm diameter gravity cores collected in 1988 and 1991 from the continental shelf and fjords of east greenland near kangerlussuaq fjord trough ca 68 n 32 w have distinct changes in lithofacies and in the quantity of iceberg rafted ird sediments these changes are readily observed in x radiographs of the split cores we quantify the ird contribution through grain size analyses and counting the number of clasts 2 mm from the x radiographs chronological control is provided by acclerated mass spectroscopy 14c dates on foraminifera during deglaciation after 14 cal ka there was one interval of ird accumulation ca 12 13 cal ka followed by a brief return to ird conditions centred at 9 cal ka thereafter a prominent feature of most cores on the shelf is an increase in ird accumulation that started ca 5 6 cal ka and which has increased toward the present indicators of iceberg rafting such as the net sand flux and numbers of clasts 2 mm ka 1 follow a power law distribution when graphed against distance from the present east greenland coast a measure of the position of the glacier margins the form of the relationship indicates that there is a dramatic decrease in the supply of sediment from the fjords to the shelf these relationships are used to estimate changes in the location of the ice margin during the late quaternary based on a site on the east greenland slope denmark strait and to discuss factors that can negate such a simple transfer function 1997 by john wiley sons ltd

global energy conversion rate from geostrophic flows into internal lee waves in the deep ocean a global estimate of the energy conversion rate from geostrophic flows into internal lee waves in the ocean is presented the estimate is based on a linear theory applied to bottom topography at o 1 10 km scales obtained from single beam echo soundings to bottom stratification estimated from climatology and to bottom velocity obtained from a global ocean model the total energy flux into internal lee waves is estimated to be 0 2 tw which is 20 of the global wind power input into the ocean the geographical distribution of the energy flux is largest in the southern ocean which accounts for half of the total energy flux the results suggest that the generation of internal lee waves at rough topography is a significant energy sink for the geostrophic flows as well as an important energy source for internal waves and the associated turbulent mixing in the deep ocean

foraminiferal reconstruction of mid to late holocene ocean circulation and climate variability in disko bugt west greenland benthic foraminifera from two cores collected from disko bugt a large marine embayment in west greenland are used to investigate hydrographic changes during the mid to late holocene the records document fluctuations in the west greenland current wgc linked to large scale changes in north atlantic circulation and for one core impacts of local climate changes in particular changes in the cold east greenland current egc and the warm more saline irminger current ic influence the wgc and propagate into disko bugt the cores record subsurface warming associated with the holocene thermal maximum htm from c 6 to 5 ka cal bp gradual cooling of wgc from 5 ka cal bp was interrupted by an abrupt warm interval from 3 9 to 3 5 ka cal bp before cooling became more prominent from 3 5 to 2 ka cal bp this cold period corresponds to the well documented northern hemisphere cooling of the neoglacial and we interpret it as reflecting enhanced flux from the egc and reduced ic flux to the wgc in disko b

north atlantic warming and the retreat of greenland s outlet glaciers mass loss from the greenland ice sheet quadrupled over the past two decades contributing a quarter of the observed global sea level rise increased submarine melting is thought to have triggered the retreat of greenland s outlet glaciers which is partly responsible for the ice loss however the chain of events and physical processes remain elusive recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes multidecadal natural ocean variability and a long term increase in the north atlantic s upper ocean heat content since the 1950s all contributed to a warming of the subpolar north atlantic this led in conjunction with increased runoff to enhanced submarine glacier melting future climate projections raise the potential for continued increases in warming and ice mass loss with implications for sea level and climate

glacier and ocean variability in ata sund west greenland since 1400 ce to improve knowledge of marine terminating glaciers in western greenland marine sediment cores from the ata sund fjord system hosting two outlet glaciers eqip sermia and kangilerngata sermia were investigated the main objective was to reconstruct glacial activity and paleoceanographic conditions during the past 600 years ice rafted debris ird was quantified by wet sieving sediment samples and by using a computed tomography scan variability in relative bottom water temperatures in the fjord was reconstructed using foraminiferal analysis on the basis of this three periods of distinct glacial regimes were identified period 1 1380 1810 ce which covers the culmination of the little ice age lia and is interpreted as having advanced glaciers with high ird content period 2 1810 1920 ce the end of the lia which was characterised by a lowering of the glaciers calving flux in response to climate cooling during period 3 1920 2014 ce both glaciers retreated substantially to their present day extent the bottom water temperature started to decrease just before period 2 and remained relatively low until just before the end of period 3 this is interpreted as a local response to increased glacial meltwater input our study was compared with a study in disko bay nearby jakobshavn glacier and the result shows that both of these greenlandic marine terminating glaciers are responding to large scale climate change however the specific imprint on the glaciers and the different fjord waters in front of them result in contrasting glacial responses and sediment archives in their respective fjords

holocene glacimarine sedimentary environments in fiords of disko bugt west greenland abstract acoustic and sedimentary properties of three fiord systems were examined in the region of disko bugt west greenland to understand variability in the processes rates and sources of sediment delivery during the late glacial and holocene kangerluk and kangersooq of western disko are dominated by meltwater inputs of sediment from local ice fields of the island interior modern sediments are delivered primarily via overflow currents rainout occasional bottom currents and small amounts of iceberg rafting where exposure to baffin bay allows penetration of the west greenland current 14 c and acoustic derived accumulation rates for the last 1 2 ka vary from about 1 mm a 1 in distal fiord settings to more than 5 mm a 1 in proximal sites adjacent to actively building deltas these rates are generally larger than has been observed in other greenland and baffin bay fiords the tidewater terminus of inland ice at ikerasak is also meltwater dominated but produces lower than expected sediment accumulation due to low gradients of the outlet ice and resistant substrates these high latitude west greenland fiords are subarctic in character and contrast significantly with colder polar type fiords at similar latitudes in east greenland sediment deposition which was focused in the outer disko fiords during the late glacial and early holocene is due to one of two possible mechanisms standstill of local ice or enhanced rafting of sediment from disko bugt icebergs this study contributes to the debate on the extent of glaciation and holocene spatial variability in fiord processes of west greenland

the biostratigraphical and palaeogeographical framework of the earliest diversification of tetrapods late devonian the biostratigraphical and palaeogeographical framework of the earliest diversification of tetrapods late devonian

ice flow in greenland for the international polar year 2008 2009 a digital representation of ice surface velocity is essential for a variety of glaciological geologic and geophysical analyses and modeling here we present a new reference comprehensive high resolution digital mosaic of ice motion in greenland assembled from satellite radar interferometry data acquired during the international polar year 2008 to 2009 by the envisat advanced synthetic aperture radar asar the advanced land observation system alos s phase array l band sar palsar and the radarsat 1 sar that covers 99 of the ice sheet in area the best mapping performance is obtained using alos palsar data due to higher levels of temporal coherence at the l band frequency but c band frequency sar data are less affected by the ionosphere the ice motion map reveals various flow regimes ranging from patterned enhanced flow into a few large glaciers in the cold low precipitation areas of north greenland to diffuse enhanced flow into numerous narrow fast moving glaciers in the warmer high precipitation sectors of northwest and southeast greenland we find that the 100 fastest glaciers v 800m yr drain 66 of the ice sheet in area marine terminating glaciers drain 88 of greenland and basal sliding motion dominates internal deformation over more than 50 of the ice sheet this view of ice sheet motion provides significant new constraints on ice flow modeling copyright 2012 by the american geophysical union

the sedimentary environment of the late devonian east greenland tetrapods the late devonian early tetrapods in east greenland occur in the celsius bjerg group key occurrences are located in a detailed stratigraphic section used here to interpret the sedimentary palaeoenvironments the palaeoenvironment for the britta dal formation which contains both ichthyostega and acanthostega is reinterpreted the britta dal formation channels have flat bases are poorly channelized are of low sinuosity and are part of a very major distributory system that periodically experienced extreme flooding the tetrapod fossils were recovered from an ephemeral system that was not permanently habitable in the immediate area plant megafossils are poorly preserved casts and impressions dominated by lycopsids and fern like plants the overbank siltstones are dominated by arid soil forming processes and comprise a spectacular sequence of vertisols the 1174 m in situ ichthyostega locality in paralleldal was relocated and occurs just below the midpoint of the second megacycle in the britta dal formation

sediment characteristics in iceberg dominated fjords kangerlussuaq region east greenland abstract sediment cores from three east greenland fjords contain sediment lithofacies and depositional processes in an iceberg dominated glacial marine setting three major lithofacies diamicton fine grained mud and sand are deposited by two processes sediment rain out and sediment gravity flows the sediments in kangerlussuaq fjord are predominately fine grained muds deposited by rain out from icebergs and glacier meltwater with sediment gravity flows acting as secondary agents of deposition miki fjord records rain out of fine grained muds from a river plume emanating from a proglacial delta at the fjord head alternating units of diamicton and fine grained mud in nansen fjord are deposited by sediment rain out from icebergs particle size is governed by the oceanographic conditions in the fjord at the time of deposition despite their proximity to each other each fjord is distinguished by a distinct sedimentological signature kangerlussuaq fjord has low total organic carbon contact miki fjord has high mass magnetic susceptibility and nansen fjord has high amounts of ice rafted debris comparison of the east greenland iceberg dominated and alaska glacial meltwater dominated environments indicates few major differences between sediments deposited in these two settings this similarity raises doubt as to how well glacial marine sedimentary sequences can be used to interpret and reconstruct differences between glacial marine environments in the past without knowledge of sediment accumulation rates environmental conditions at the time of sediment deposition and comparable sedimentological data between studies

flow dynamics of tidewater glaciers a numerical modelling approach the dynamics of grounded tidewater glaciers is investigated with a time dependent numerical flow model which solves the full equations for the stress and velocity fields and includes a water pressure dependent sliding law the calving criterion implemented in the model shifts the calving front at each time step to the position where the frontal ice thickness exceeds flotation height by a prescribed value with this model the linear relation between calving rate and water depth proposed on empirical grounds is qualitatively reproduced for the situation of a slowly retreating or advancing terminus but not for situations of rapid changes length changes of tidewater glaciers i e especially rapid changes are dominantly controlled by the bed topography and are to a minor degree a direct reaction to a mass balance change thus accurate information on the near terminus bed topography is required for reliable prediction of the terminus changes due to climate changes the results also confirm the suggested cycles of slow advance and rapid retreat through a basal depression rapid changes in terminus positions preferably occur in places where the bed slopes upwards in the ice flow direction

undercutting of marine terminating glaciers in west greenland marine terminating glaciers control most of greenland s ice discharge into the ocean but little is known about the geometry of their frontal regions here we use side looking multibeam echo sounding observations to reveal that their frontal ice cliffs are grounded deeper below sea level than previously measured and their ice faces are neither vertical nor smooth but often undercut by the ocean and rough deep glacier grounding enables contact with subsurface warm salty atlantic waters aw which melts ice at rates of meters per day we detect cavities undercutting the base of the calving faces at the sites of subglacial water sgw discharge predicted by a hydrological model the observed pattern of undercutting is consistent with numerical simulations of ice melt in which buoyant plumes of sgw transport warm aw to the ice faces glacier undercutting likely enhances iceberg calving impacting ice front stability and in turn the glacier mass balance

variable north atlantic climate seesaw patterns documented by a late holocene marine record from disko bugt west greenland abstract the reconstruction of past sea surface conditions in the labrador sea is essential for understanding climate fluctuations in the north atlantic region we here study late holocene sea surface conditions off west greenland in order to elucidate the possible relationship between a north atlantic seesaw and centennial to millennial scale climate fluctuations in the labrador sea region for that purpose we have studied the particulate organic matter especially dinoflagellate cysts and acritarchs from two marine sediment cores from disko bugt central west greenland our data show significant variations in sea surface temperature and sea ice cover during the last ca 3200 years after a cooling at ca 2 9 ka cal bp presumably related to the neoglacial cooling seen in large parts of the northern hemisphere the area was subjected to significant variability both in the entrainment of atlantic water west greenland current water and in atmospheric temperatures from 2 0 1 5 ka cal bp corresponding to the later part of the roman warm period the area experienced a return to a stronger influx of atlantic water and an increased fresh water influx from land probably related to increased precipitation or to melt water outflow from the nearby inland ice the dark ages 1 5 1 3 ka cal bp were characterised by an only minor cooling of the surface waters however as seen in other records from the labrador sea region the beginning of the medieval warm period 1 3 0 9 ka cal bp signified a severe cooling presumably due to a significant reduction in atlantic water entrainment the cold conditions continued through the little ice age after 0 9 ka cal bp although the area seems to have experienced a minor decrease in sea ice cover until 0 5 ka cal b p after which sea ice cover may again have increased the period of modern warming is not represented in our data our study shows that a north atlantic oscillation type pattern played a significant role in the late holocene centennial to millennial scale climate fluctuations in the labrador sea region however this cannot explain the full complexity of the climate signal the fact that a simple pattern of cold versus warm climate scenario does not exist demonstrates that it will hardly be feasible to select the correct baseline data set when modelling future climate development

upper devonian tetrapod palaeoecology in the light of new discoveries in east greenland for the first time new material of one of the world s oldest known tetrapods acanthostega has been studied in its sedimentological context the reported evidence suggests that acanthostega was primarily aquatic and inhabited active fluvial channels in fluvial dominated environments

tetrapod or near tetrapod fossils from the upper devonian of scotland since 1932 the earliest known undisputed tetrapods have been of uppermost famennian late upper devonian age1 3 although a probable tetrapod jaw has been described from the lower famennian4 and tetrapod tracks of supposedly frasnian5 and possibly earlier6 age are known no fossil limb material older than the latest famennian has been discovered the panderichthyids panderichthys7 and elpistostege8 from the lower frasnian early upper devonian are regarded by some8 10 as the closest known sister group of tetrapods but panderichthyshas paired fins rather than limbs11 here i describe a hitherto unrecognized tibia from the upper frasnian middle upper devonian site of scat craig near elgin scotland12 14 collected during the nineteenth century which extends the fossil record of the tetrapod type hind limb by roughly seven million years15 other isolated bones from the same locality also show tetrapod characteristics the tibia a humerus and some incomplete jaws are discussed below but a complete description of the material is in preparation

a devonian tetrapod from north america an early tetrapod fossil from the upper devonian of pennsylvania catskill formation extends the temporal range of tetrapods in north america and suggests that they attained a virtually global equatorial distribution by the end of the devonian derived features of the shoulder girdle indicate that appendicular mechanisms of support and propulsion were well developed even in the earliest phases of tetrapod history the specialized morphology of the pectoral skeleton implies that the diversity of early tetrapods was great and is suggestive of innovative locomotor patterns in the first tetrapods

east greenland tetrapods are devonian in age palynological dates unambiguously resolve the stratigraphic age of the east greenland sedimentary rocks containing the earliest well preserved tetrapod remains this is the first time that spore samples have been discovered in the sedimentary succession that has yielded acanthostega and ichthyostega two tetrapods that are regarded as critically important taxa for our understanding of the origin and early evolution of the tetrapods these palynological assemblages conclusively show that the rocks are devonian in age the evidence resolves a 60 year old dispute regarding the age of these rocks and contradicts a recent controversial study suggesting a much younger carboniferous visean age for these tetrapods spore samples bracketing the in situ occurrences of both tetrapod genera place them securely within the famennian age of the devonian period and at least as old as famennian 2b the ages of all known devonian tetrapods are reviewed and related to a common palynological standard this review places ichthyostega and acanthostega as the earliest of the famennian tetrapods

dissolved particulate and acid leachable trace metal concentrations in north atlantic precipitation collected on the global change expedition rainwater samples from six precipitation events were collected on board ship during legs 3 and 4 of the global change expedition over the north atlantic ocean and analyzed for dissolved particulate al and pb and acid leachable trace metals al fe mn cd cu pb zn acid leachable concentrations of the elements in 0 4 v v hno3 were similar to reported values from the north atlantic and pacific oceans which were measured using comparable acidification procedures concentrations of dissolved and particulate al and pb were determined in rain events concurrently sampled comparisons between acid leachable and total dissolved plus particulate trace metal concentrations suggest that the acid leachable fraction of metals can significantly underestimate total concentrations of crustal elements e g al in rain the solubilities of al and pb in precipitation were variable and mean solubilities of the elements were 13 and 45 respectively recycled sea salt components were less than 14 for al fe mn pb cd cu and zn indicating that the net trace metal flux is from the atmosphere to the oceans deep sea particle fluxes for these metals through the western tropical north atlantic exceed atmospheric deposition fluxes by a factor of 18 41