late quaternary spatial and temporal variability in arctic deep sea bioturbation and its relation to mn cycles changes in intensity and composition of bioturbation and trace fossils in deep sea settings are directly related to changes in environmental parameters such as food availability bottom water oxygenation or substrate consistency because trace fossils are practically always preserved in situ and are often present in environments where other environmental indicators are scarce or may have been compromised or removed by diagenetic processes the trace fossils provide an important source of paleoenvironmental information in regions such as the deep arctic ocean detailed analysis of x ray radiographs from 12 piston and gravity cores from a transect spanning from the makarov basin to the yermak plateau via the lomonosov ridge the morris jesup rise and the gakkel ridge reveal both spatial and temporal variations in an ichnofauna consisting of chondrites nereites phycosiphon planolites scolicia trichichnus zoophycos as well as deformational biogenic structures the spatial variability in abundance and diversity is in close correspondence to observed patterns in the distribution of modern benthos suggesting that food availability and food flux to the sea floor are the most important parameters controlling variations in bioturbation in the arctic ocean the most diverse ichnofaunas were observed at sites on the central lomonosov ridge that today have partially ice free conditions and relatively high summer productivity in contrast the most sparse ichnofauna was observed in the ice infested region on the lomonosov ridge north of greenland since primary productivity and therefore also the food flux at a certain location is ultimately controlled by the geographical position in relation to ice margin and the continental shelves temporal variations in abundance and diversity of trace fossils have the potential to reveal changes in food flux and consequently sea ice conditions on glacial interglacial time scales down core analysis reveal clearly increased abundance and diversity during interglacial interstadial intervals that were identified through strongly enhanced mn levels and the presence of micro and nannofossils warm stages are characterized by larger trace fossils such as scolicia planolites or nereites while cold stages typically display an ichnofauna dominated by small deep penetrating trace fossils such as chondrites or trichichnus the presence of biogenic structures in glacial intervals clearly show that the arctic deep waters must have remained fairly well ventilated also during glacials thereby lending support to the hypothesis that the conspicuous brown layers rich in mn which are found ubiquitously over the arctic basins are related to input from rivers and coastal erosion during sea level high stands rather than redox processes in the water column and on the sea floor however the x ray radiograph study also revealed the presence of apparently post sedimentary diagenetically formed mn layers which are not directly related to mn input from rivers and shelves these observations thus bolster the hypothesis that the bioturbated brownish mn rich layers can be used for stratigraphic correlation over large distances in the arctic ocean but only if post sedimentary diagenetic layers can be identified and accounted for in the mn cycle stratigraphy

geological evaluation of multiple general circulation model simulations of late jurassic palaeoclimate abstract general circulation models gcms are currently used to predict future global change however the robustness of gcms should be evaluated by their ability to simulate past climate regimes their success in retrodiction can then be assessed by reference to the geological record geological evidence provides a database that can be used in the estimation of sea surface temperatures orography and other proxy data useful in palaeoclimatic studies these data can then be used to refine the prescribed boundary conditions for running gcms themselves results from a series of modelling experiments run with late jurassic kimmeridgian boundary conditions and using the uk university global atmospheric modelling programme ugamp gcm and the uk meteorological office gcm are presented simulations from these two quite independently generated models although subtly different confirm a generally warmer jurassic earth with arid zones over the tethys and sw usa parts of gondwana dominated by monsoonal systems and convective rainfall generally higher over the oceans than at present circum polar wetlands are also indicated these results generally conform well to the distributions of known facies in these regions modelled cloudiness is also higher in the jurassic and although unconfirmed geologically such conditions would have contributed to greenhouse conditions at high latitudes and could have influenced both terrestrial biomes and marine ecosystems using one of the gcms ugamp we have also investigated the role of orbital parameters for high latitude climate at times of minimum seasonal forcing comparable with an orbital geometry affecting the earth at 115 ka bp parts of antarctica could have sustained a modest ice sheet over areas exceeding 1 km elevation but such modelled sheets would have been ephemeral features and very dynamic in character

arctic ocean mn stratigraphy genesis synthesis and inter basin correlation abstract across the arctic ocean late quaternary deep marine sediments are characterized by the occurrence of brownish layers intercalated with yellowish to olive gray sediments these layers show enhanced levels of bioturbation peaks in mn content and typically contain elevated abundances of planktonic and benthic micro and nannofossils it was early surmised that these layers were deposited under interglacial conditions and that their cyclical downcore occurrence could be correlated to the global benthic oxygen isotope curve however the synchronicity of mn layers with interglacial conditions and the underlying mechanisms responsible for their formation remain controversial here we compile and synthesize findings of the last decades with several recent studies that shed light on issues such as the sources of mn to the arctic ocean the processes and pathways for mn to the deep sea the chemical processes active in the sediment and the spatial and temporal distribution of mn rich layers in arctic deep marine sediments budget calculations show that about 90 of mn input to the arctic ocean originates from arctic rivers or coastal erosion two sources effectively shut down during mid to late quaternary glacial intervals by continental ice sheets blocking or re directing the rivers and vast subaerial exposure of the shelf areas thus the strong late quaternary interglacial glacial cyclicity in mn content is clearly an input related signal and only secondarily influenced by chemical processes in the water column and in the sediment on the shelves the mn undergoes repeated geochemical recycling caused by the high organic carbon content in the sediments before it is ultimately exported to the deep basins where scavenging processes in the water column effectively bring the mn to the sea floor in the form of mn oxyhydr oxides the close synchronicity with enhanced bioturbation and elevated micro and nannofossil abundances shows that the mn peaks are preserved at a stratigraphic level closely corresponding to the interglacial intervals however under certain biogeochemical conditions mn oxyhydr oxides may diagenetically become both dissolved and re precipitated deep in the sediments as shown by pore water analyses and x ray radiograph studies dissolution is particularly conspicuous in late quaternary sediments from the lomonosov ridge where in rapidly deposited coarse grained intervals diamictons with elevated total organic carbon toc contents mn appears almost completely removed from within the glacial sediments and also the surrounding interglacial sediments correspondingly bundles of closely spaced mm thick mn rich horizontal bands are observed in sediment otherwise devoid of indicators for interglacial conditions suggesting that these bands were purely formed by diagenetic processes redistributing the mn from deeper sediment layers this type of diagenetic mn redistribution within the sediment can be recognized in xrf core scanner data combined with sedimentological information from x ray radiographs while pore water data are highly promising if clear diagenetic features in the sediment are missing with this increasing ability to recognize intervals where a diagenetic overprint exists in the mn record the recently improved understanding of the mn cycle in the arctic ocean provides a conceptual paleoenvironmental framework in which carefully applied mn stratigraphy can provide a powerful correlation tool when combined with other paleoceanographic proxies and sedimentological data

is the central arctic ocean a sediment starved basin abstract numerous short sediment cores have been retrieved from the central arctic ocean many of which have been assigned sedimentation rates on the order of mm ka implying that the arctic basin was starved of sediments during plio pleistocene times a review of both shorter term sedimentation rates through analysis of available sediment core data and longer term sedimentation rates through estimates of total sediment thickness and bedrock age suggests that cm ka scale rates are pervasive in the central arctic ocean this is not surprising considering the physiographic setting of the arctic ocean being a small land locked basin since its initial opening during early cretaceous times we thus conclude that the central arctic ocean has not been a sediment starved basin either during plio pleistocene times or during pre pliocene times rigorous chronstratigraphic analysis permits correlation of sediment cores over a distance of 2600 km from the northwestern amerasia basin to the northwestern eurasia basin via the lomonosov ridge using paleomagnetic biostratigraphic and cyclostratigraphic data

paleo sea levels reconsidered from direct observation of paleoshoreline position during glacial maxima for the last 500 000 yr the drastic climatic changes which characterise the cooling trend of the last few million years of earth history led to variations in eustatic sea level that had tremendous impact on the geology and ecology of continental margins reconstructing a sea level curve back in time is not an easy task observations of shoreline positions are always a local measurement of relative sea level that needs to be corrected from the effect of tectonic and thermal subsidence sediment loading compaction and glacio hydro isostasy extensive studies have been done for the last deglaciation and for the last 100 000 yr cycle but very few studies deal with position of sea level during earlier cycles simply because conditions are very rarely favourable for the preservation of such witnesses the shelf of the golfe du lion western mediterranean reveals a unique record of shoreline paleopositions during glacial maxima of at least the last five circa 100 kyr glacial interglacial cycles in fact it is the entire glacial deltaic lobe of up to 50 m thick from delta front or shoreface to prodelta that has been preserved in place and which provides direct and independent constraints for relative sea level minima we measure a relative sea level of 112m 128 134 246 and 262 m for mis 2 6 8 10 and 12 respectively after corrections taking into account postdepositional movement of strata subsidence we find that sea level dropped to a depth of 102 6 m during the last three glaciations mis2 mis6 mis8 but reached exceptionally low values of more than 150 10 m during the preceding glaciations mis10 and mis 12 at about 340 and 434 kyr bp this general time framework and sedimentological interpretation has been confirmed by preliminary results from two deep drillings during the promess cruise july 2004 which validate our methodology however no detailed and absolute datings of such witnesses are available so far so that we cannot prove that these levels are the lowest ever reached during each glacials but they correspond undoubtedly to the last preserved shoreface before rapid sea level rise we also suggest that the abrupt change in sea level maxima might be the overprint of 400 kyr orbital periodicity cycles last but not least these results prove that the golfe du lion is indeed a unique laboratory to study paleoclimates and sea level variations on a larger time scale further work is needed for a complete glacio hydro sedimento isostatic modelling of each sequence and each glacial to further constraint local sea level versus global sea level and quantify in particular the relative effect of glacio hydro isostatic effect which differ according to ice sheet extend but also of erosion sedimentation isostatic effect erosion on land and deposition on the outer shelf and slope

eustatic sea level changes interpreted from seismic stratigraphy a critique of the methodology with particular reference to the north sea jurassic record seismic stratigraphic methods for interpreting eustatic sea level change are based on generalized stratigraphic models and chronostratigraphic interpretations that have not been substantiated by publication of the necessary basic supportive data chronostratigraphic correlations of sea level change curves between basins are based partly on circular reasoning onlap and offlap seismic models may not indicate sea level change but flexural subsidence facies shifts or changes in sea level in the opposite direction to that proposed resolution of some of these problems may be achieved by publication of basic data now in confidential industry files the widely acclaimed vail curves should not be used as templates for basin correlation until such data have been provided and such use should be supported by appropriate conventional lithostratigraphic and biostratigraphic documentation from each new basin where such data have been made available as with the north sea jurassic serious questions of interpretation are raised

regional variations in provenance and abundance of ice rafted clasts in arctic ocean sediments implications for the configuration of late quaternary oceanic and atmospheric circulation in the arctic abstract the composition and distribution of ice rafted glacial erratics in late quaternary sediments define the major current systems of the arctic ocean and identify two distinct continental sources for the erratics in the southern amerasia basin up to 70 of the erratics are dolostones and limestones the amerasia suite that originated in the carbonate rich paleozoic terranes of the canadian arctic islands these clasts reached the arctic ocean in glaciers and were ice rafted to the core sites in the clockwise beaufort gyre the concentration of erratics decreases northward by 98 along the trend of the gyre from southeastern canada basin to makarov basin the concentration of erratics then triples across the makarov basin flank of lomonosov ridge and siltstone sandstone and siliceous clasts become dominant in cores from the ridge and the eurasia basin the eurasia suite the bedrock source for the siltstone and sandstone clasts is uncertain but bedrock distribution and the distribution of glaciation in northern eurasia suggest the taymyr peninsula kara sea regions the pattern of clast distribution in the arctic ocean sediments and the sharp northward decrease in concentration of clasts of canadian arctic island provenance in the amerasia basin support the conclusion that the modern circulation pattern of the arctic ocean with the beaufort gyre dominant in the amerasia basin and the transpolar drift dominant in the eurasia basin has controlled both sea ice and glacial iceberg drift in the arctic ocean during interglacial intervals since at least the late pleistocene the abruptness of the change in both clast composition and concentration on the makarov basin flank of lomonosov ridge also suggests that the boundary between the beaufort gyre and the transpolar drift has been relatively stable during interglacials since that time because the beaufort gyre is wind driven our data in conjunction with the westerly directed orientation of sand dunes that formed during the last glacial maximum on the north slope of alaska suggests that atmospheric circulation in the western arctic during late quaternary was similar to that of the present

calibration of marine sediment core loggers for quantitative acoustic impedance studies abstract accurate density and p wave velocity measurements on marine sediment cores are needed for quantitative acoustic impedance studies an increasing number of international marine laboratories routinely measure p wave velocity and bulk density the product of which gives the acoustic impedance on marine sediment cores using automated core loggers mscls despite the progressive standardisation of mscls in recent years no standard calibration technique has been decided that will enable datasets from different marine laboratories to be validated and compared with confidence this problem is particularly acute for bulk density measurements because systematic mscl errors are typically much greater than 10 one solution is to use a calibration tube comprising a stepped aluminium insert inside a water filled core liner that mimics marine sediment porosities and velocities and that can be used during normal core logging the calibration tube enables a reliable gamma ray reference intensity to be measured and an apparent compton mass attenuation coefficient to be derived that is suitable for most marine sediments and that simplifies data processing the calibration tube results show that the mscl belonging to southampton oceanography centre soc used as part of the standard analysis procedure of the british ocean sediment core repository boscor gives measurement accuracies of better than 0 07 g cm 3 for bulk density and 0 3 for p wave velocity

the plio pleistocene glaciation of the barents sea svalbard region a new model based on revised chronostratigraphy based on a revised chronostratigraphy and compilation of borehole data from the barents sea continental margin a coherent glaciation model is proposed for the barents sea ice sheet over the past 3 5 million years ma three phases of ice growth are suggested 1 the initial build up phase covering mountainous regions and reaching the coastline shelf edge in the northern barents sea during short term glacial intensification is concomitant with the onset of the northern hemisphere glaciation 3 6 2 4 ma 2 a transitional growth phase 2 4 1 0 ma during which the ice sheet expanded towards the southern barents sea and reached the northwestern kara sea this is inferred from step wise decrease of siberian river supplied smectite rich sediments likely caused by ice sheet blockade and possibly reduced sea ice formation in the kara sea as well as glacigenic wedge growth along the northwestern barents sea margin hampering entrainment and transport of sea ice sediments to the arctic atlantic gateway 3 finally large scale glaciation in the barents sea occurred after 1 ma with repeated advances to the shelf edge the timing is inferred from ice grounding on the yermak plateau at about 0 95 ma and higher frequencies of gravity driven mass movements along the western barents sea margin associated with expansive glacial growth

10be records from sediments of the arctic ocean covering the past 350 ka records of be 10 be 9 mineralogy and grain size were obtained from two cores collected by the polarstern expedition 1991 in the southern nansen basin core 2213 6 and the yermak plateau core 22

constraints on the pleistocene chronology of sediments from the lomonosov ridge 1 despite its importance in the global climate system age calibrated marine geologic records reflecting the evolution of glacial cycles through the pleistocene are largely absent from the central arctic ocean this is especially true for sediments older than 200 ka three sites cored during the integrated ocean drilling program s expedition 302 the arctic coring expedition acex provide a 27 m continuous sedimentary section from the lomonosov ridge in the central arctic ocean two key biostratigraphic datums and constraints from the magnetic inclination data are used to anchor the chronology of these sediments back to the base of the cobb mountain subchron 1215 ka beyond 1215 ka two best fitting geomagnetic models are used to investigate the nature of cyclostratigraphic change within this chronology we show that bulk and mineral magnetic properties of the sediments vary on predicted milankovitch frequencies these cyclic variations record glacial and interglacial modes of sediment deposition on the lomonosov ridge as evident in studies of ice rafted debris and stable isotopic and faunal assemblages for the last two glacial cycles and were used to tune the age model potential errors which largely arise from uncertainties in the nature of downhole paleomagnetic variability and the choice of a tuning target are handled by defining an error envelope that is based on the best fitting cyclostratigraphic and geomagnetic solutions

calibration and application of marine sedimentary physical properties using a multi sensor core logger abstract we examined geophysical data from a multi sensor core logger mscl a logging device providing continuous measurements of gamma ray attenuation p wave travel time and magnetic susceptibility on marine sediment cores in the first part we focused on the gamma ray system and compared two different calibration methods from the gamma ray attenuation we calculated densities and porosities by incorporating mass weighted attenuation coefficients the application of an iteration method reduces the error of the density and porosity estimates compared to grape data in addition we derived equations to calculate water content and dry bulk density from gamma ray attenuation measurements comparison with physical properties determined on discrete samples revealed a very good correlation of both data sets r 0 99 this correlation is valid for sediments from substantially different geological settings e g turbidites hemipelagic muds and opal rich sediments in the second part we applied our data to marine geological questions for sediments from the antarctic polar frontal zone there is indication that the content of biogenic opal can be assessed using a correlation of density and p wave velocity for sediments from the bengal fan the relationship between the mscl acoustic impedance the product of density and p wave velocity and the grain size distribution in discrete samples can be used to predict clay and sand silt ratios for sediment cores from the shelf and upper continental slope

sources of sediment found in sea ice from the western arctic ocean new insights into processes of entrainment and drift patterns 1 the geochemical fingerprint of entrained fe oxide mineral grains in arctic ocean sea ice is used to determine precise sources of this sediment this approach substantiates the importance of the laptev sea as a source of sea ice and even the presence of russian ice in the beaufort sea off alaska fe oxide grains from the laptev sea were found in floes in the beaufort sea chukchi borderland and central arctic ocean demonstrating the importance of sea ice in distributing itself throughout the arctic ocean and the potential of transporting sediment from russian rivers to north american shelves banks island shelf is the most important source of sediment sampled from ice floes in the beaufort sea northern chukchi sea and chukchi borderland area although most of the entrained sediment fits the criteria for suspension freezing in shallow water the presence of winter polynyas with offshore winds and not the size of shallow areas appears to be the critical factor for sea ice entrainment seven of the 18 ice floes sampled contained fe oxide grains from more than one source area the two most common sources that are found in the same ice floes are banks island and the laptev sea multiple sources in ice floes suggest that either mingling of fragmented ice floes occurs or that a source area containing grains from both these sources has yet to be located the addition of fine sand sized windblown sediment is not thought to be significant

stratigraphic constraints on late pleistocene glacial erosion and deglaciation of the chukchi margin arctic ocean at least two episodes of glacial erosion of the chukchi margin at water depths to 450 m and 750 m have been indicated by geophysical seafloor data we examine sediment stratigraphy in these areas to verify the inferred erosion and to understand its nature and timing our data within the eroded areas show the presence of glaciogenic diamictons composed mostly of reworked local bedrock the diamictons are estimated to form during the last glacial maximum lgm and an earlier glacial event possibly between ois 4 to 5d both erosional events were presumably caused by the grounding of ice shelves originating from the laurentide ice sheet broader glaciological settings differed between these events as indicated by different orientations of flutes on eroded seafloor postglacial sedimentation evolved from iceberg dominated environments to those controlled by sea ice rafting and marine processes in the holocene a prominent minimum in planktonic foraminiferal 18 o is identified in deglacial sediments at an estimated age near 13 000 cal yr bp this 18 o minimum also reported elsewhere in the amerasia basin is probably related to a major laurentide meltwater pulse at the younger dryas onset the bering strait opening is also marked in the composition of late deglacial chukchi sediments

influence of brine formation on arctic ocean circulation over the past 15 million years the early oceanographic history of the arctic ocean is important in regulating and responding to climatic changes however constraints on its oceanographic history preceding the quaternary the past 1 8 myr have become available only recently because of the difficulties associated with obtaining continuous sediment records in such a hostile setting here we use the neodymium isotope compositions of two sediment cores recovered near the north pole to reconstruct over the past approx15 myr the sources contributing to arctic intermediate water a water mass found today at depths of 200 to 1 500 m we interpret high neodymium ratios for the period between 15 and 2 myr ago and for the glacial periods thereafter as indicative of weathering input from the siberian putoranan basalts into the arctic ocean arctic intermediate water was then derived from brine formation in the eurasian shelf regions with only a limited contribution of intermediate water from the north atlantic in contrast the modern circulation pattern with relatively high contributions of north atlantic intermediate water and negligible input from brine formation exhibits low neodymium isotope ratios and is typical for the interglacial periods of the past 2 myr we suggest that changes in climatic conditions and the tectonic setting were responsible for switches between these two modes

mid to late pleistocene ice drift in the western arctic ocean evidence for a different circulation in the past the provenance of ice rafted debris ird in four arctic sediment cores implies that icebergs from the northwestern laurentide ice sheets drifted across the western arctic ocean along the 180 0 meridian toward fram strait during mid to late pleistocene deglaciations within the last 700 000 years this iceberg drift was different from the present day beaufort gyre circulation and resembled a dislocated transpolar drift tpd sea ice mainly followed the iceberg trajectories but also frequently drifted from the russian shelves eastward into the amerasian basin

an arctic ocean ice shelf during mis 6 constrained by new geophysical and geological data the hypothesis of floating ice shelves covering the arctic ocean during glacial periods was developed in the 1970s in its most extreme form this theory involved a 1000 m thick continuous ice shelf covering the arctic ocean during quaternary glacial maxima including the last glacial maximum lgm while recent observations clearly demonstrate deep ice grounding events in the central arctic ocean the ice shelf hypothesis has been difficult to evaluate due to a lack of information from key areas with severe sea ice conditions here we present new data from previously inaccessible unmapped areas that constrain the spatial extent and timing of marine ice sheets during past glacials these data include multibeam swath bathymetry and subbottom profiles portraying glaciogenic features on the chukchi borderland southern lomonosov ridge north of greenland morris jesup rise and yermak plateau sediment cores from the mapped areas provide age constraints on the glaciogenic features combining these new geophysical and geological data with earlier results suggests that an especially extensive marine ice sheet complex including an ice shelf existed in the amerasian arctic ocean during marine isotope stage mis 6 from a conceptual oceanographic model we speculate that the cold halocline of the polar surface water may have extended to deeper water depths during mis 6 inhibiting the warm atlantic water from reaching the amerasian arctic ocean and thus creating favorable conditions for ice shelf development the hypothesis of a continuous 1000 m thick ice shelf is rejected because our mapping results show that several areas in the central arctic ocean substantially shallower than 1000 m water depth are free from glacial influence on the seafloor

glacial geomorphology of the central arctic ocean the chukchi borderland and the lomonosov ridge the last decade of geophysical seafloor mapping in the arctic ocean from nuclear submarines and icebreakers reveals a wide variety of glaciogenic geomorphic features at water depths reaching 1000 in these findings provide new and intriguing insights into the quaternary glacial history of the northern hemisphere here we integrate multi and single beam bathymetric data chirp sonar profiles and sidescan images from the chukchi borderland and lomonosov ridge to perform a comparative morphological seafloor study this investigation aims to elucidate the nature and provenance of ice masses that impacted the arctic ocean sea floor during the quaternary mapped glaciogenic bedforms include iceberg keel scours most abundant at water depths shallower than similar to 350 400 m flutes and megascale glacial lineations extending as deep as similar to 1000 m below the present sea level small drumlin like features and morainic ridges and grounding zone wedges the combination of these features indicates that very large glacial ice masses extended into the central arctic ocean from surrounding north american and eurasian ice sheets several times during the quaternary ice shelves occupied large parts of the arctic ocean during glacial maxima and ice rises were formed over the chukchi borderland and portions of the lomonosov ridge more geophysical and sediment core data combined with modeling experiments are needed to reconstruct the timing and patterns of these events

an arctic perspective on dating mid late pleistocene environmental history to better understand pleistocene climatic changes in the arctic integrated palaeoenvironmental and palaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologic age control are required not least for correlation to extra arctic records in this paper we discuss from an arctic perspective methods and correlation tools that are commonly used to date arctic pleistocene marine and terrestrial events we review the state of the art of arctic geochronology with focus on factors that affect the possibility and quality of dating and support this overview by examples of application of modern dating methods to arctic terrestrial and marine sequences event stratigraphy and numerical ages are important tools used in the arctic to correlate fragmented terrestrial records and to establish regional stratigraphic schemes age control is commonly provided by radiocarbon luminescence or cosmogenic exposure ages arctic ocean deep sea sediment successions can be correlated over large distances based on geochemical and physical property proxies for sediment composition patterns in palaeomagnetic records and increasingly biostratigraphic data many of these proxies reveal cyclical patterns that provide a basis for astronomical tuning recent advances in dating technology calibration and age modelling allow for measuring smaller quantities of material and to more precisely date previously undatable material i e foraminifera for c 14 and single grain luminescence however for much of the pleistocene there are still limits to the resolution of most dating methods consequently improving the accuracy and precision analytical and geological uncertainty of dating methods through technological advances and better understanding of processes are important tasks for the future another challenge is to better integrate marine and terrestrial records which could be aided by targeting continental shelf and lake records exploring proxies that occur in both settings and by creating joint research networks that promote collaboration between marine and terrestrial geologists and modellers

north american origin of pink white layers at the mendeleev ridge arctic ocean new insights from lead and neodymium isotope composition of detrital sediment component abstract dolomite rich layers of distinct pinkish colour are used as lithostratigraphic markers in the amerasian basin of the arctic ocean however origin of dolomite in these sediment units has not been studied in detail in this study lead pb and neodymium nd isotope composition of detrital clay size fraction from different lithofacies were investigated in core ps72 340 5 recovered at the eastern flank of the mendeleev ridge prior to the geochemical analyses grain size distribution was analyzed in order to minimize the grain size effect on the provenance signature for provenance discrimination results of isotope measurements were compared with marine surface sediment data and values for the circum arctic subaerial provinces late quaternary sediment supply variability was analyzed using the mixing model constrained by two tracers 207pb 206pb and end variations of sediment isotopic composition are inferred to result from mixing of volcanic and plutonic components usage of pb isotopic ratios alone does not allow distinction between these two types of sources results confirm that over the last estimated ca 200 ka dolomite rich pink layers at the mendeleev ridge were deposited during events probably associated with intensified iceberg transport from north america in general however sedimentation was mostly controlled by terrigenous input from the chukchi and east siberian seas whereas sediment supply from the laptev sea area remained less important and relatively constant at the studied location

source of the climate signal recorded by magnetic susceptibility variations in indian ocean sediments the origins of magnetic susceptibility variations in deep sea sediments from the indian ocean ocean drilling program odp leg 117 have been examined to identify the specific connections between climate shifts and sediment magnetic properties in a previous study the magnetic susceptibility variations in odp hole 722b were identified as an outstanding proxy paleoceanographic record despite evidence of postdepositional loss of magnetic minerals through reductive diagenesis this paradox is addressed by assessing the contributions of ferrimagnetic detrital iron oxides bacterial magnetosomes and paramagnetic detrital fe silicate minerals to the magnetic susceptibility signal in addition to detailed magnetic analyses mineralogical morphological and grain size data have been obtained from representative magnetic extracts for hole 722b we find that magnetic responses to climate change result from 1 fluctuations in the volume magnetic susceptibility which is primarily controlled by carbonate dilution 2 a ferrimagnetic signal which is restricted to the upper 7 meters below sea floor mbsf and which largely reflects source area aridity and 3 a paramagnetic susceptibility record below 7 mbsf which is coincident in frequency with variations in lithogenic grain size

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

paleomagnetic constraints on sedimentation ratesin the eastern arctic ocean abstract deep sea sediments recovered from six sites visited during the international arctic ocean expedition of 1991 were examined to determine sedimentation rates in the eastern arctic ocean basin the dearth of age diagnostic biogenic material in these sediments precludes the application of biostratigraphic methods but ages can be deduced using paleomagnetism in conjunction with measurements of radiocarbon and carbonate concentration although no one of these techniques gives an unambiguous determination of age the interpretation most consistent with these diverse data implies that sedimentation rates in the eastern arctic are in general a few centimeters per thousand years such estimates of sedimentation rate are an order of magnitude greater than those previously determined from many sediment cores taken from the canada basin however one site examined on the morris jesup rise shows a relatively low rate of sediment accumulation less than 0 6 cm 103yr suggesting that although higher than in the canada basin sedimentation rates in the eastern arctic can be highly variable

a shift in heavy and clay mineral provenance indicates a middle miocene onset of a perennial sea ice cover in the arctic ocean during the arctic coring expedition acex a 428 m thick sequence of upper cretaceous to quaternary sediments was penetrated the mineralogical composition of the upper 300 m of this sequence is presented here for the first time heavy and clay mineral associations indicate a major and consistent shift in provenance from the barents kara western laptev sea region characterized by presence of common clinopyroxene to the eastern laptev east siberian seas in the upper part of the section characterized by common hornblende amphibole sea ice originating from the latter source region must have survived at least one summer melt cycle in order to reach the acex drill site if considering modern sea ice trajectories and velocities this shift in mineral assemblages probably represents the onset of a perennial sea ice cover in the arctic ocean which occurred at about 13 ma thus suggesting a coeval freeze in the arctic and antarctic regions

quaternary dinoflagellate cysts in the arctic ocean potential and limitations for stratigraphy and paleoenvironmental reconstructions abstract the arctic ocean is a siliciclastic depositional environment which lacks any rock forming biogenic calcareous and siliceous components during large parts of its quaternary history these hemipelagic sediments are nevertheless suitable for the study of organic walled microfossils of which the fossil remains of dinoflagellates dinoflagellate cysts are the most important group dinoflagellate cysts have become an important tool in paleoceanography of the high northern latitudes but their potential for quaternary biostratigraphy has remained largely unexplored dinoflagellate cysts are the dominant marine palynomorph group which is more continuously present in the marginal seas e g barents sea bering sea than in the arctic ocean itself throughout the quaternary most species have long stratigraphic ranges are temporary absent and show abundance variations on glacial interglacial timescales of the more than 30 taxa recorded only habibacysta tectata and filisphaera filifera became extinct in the pleistocene the highest persistent occurrence of h tectata at ca 2 0 ma and the top of f filifera acme at ca 1 8 ma can be used for supra regional stratigraphic correlation between the arctic ocean and adjacent basins these events corroborate a slow sedimentation rate model for the quaternary section on the central lomonosov ridge but a combination of different methods will have to be applied to provide a detailed chronostratigraphy the occurrence of cysts of phototrophic dinoflagellates in certain stratigraphic intervals on lomonosov ridge supports published evidence of episodic opening of the multiyear arctic sea ice cover during the quaternary probably related to a stronger inflow of atlantic water this contradicts the hypothesis of a permanently ice covered central arctic ocean in the quaternary

the thermohaline circulation of the arctic ocean and the greenland sea the thermohaline circulation of the arctic ocean and the greenland sea is conditioned by the harsh high latitude climate and by bathymetry warm atlantic water loses its heat and also becomes less saline by added river run off in the arctic ocean this leads to rapid cooling of the surface water and to ice formation brine released by freezing increases the density of the surface layer but the ice cover also insulates the ocean and reduces heat loss this limits density increase and in the central arctic ocean a low salinity surface layer and a permanent ice cover are maintained only over the shallow shelves where the entire water column is cooled to freezing can dense water form and accumulate to eventually sink down the continental slope into the deep ocean the part of the atlantic water which enters the arctic ocean is thus separated into a low density surface layer and a denser deep circulation these two loops exit through fram strait the waters are partly rehomogenized in the greenland sea the main current is confined to the greenland continental slope but polar surface water and ice are injected into the central gyre and create a low density lid allowing for ice formation in winter this leads to a density increase sufficient to trigger convection upwelling and subsequent ice melt the convection maintains the weak stratification of the gyre and also reinforces the deep circulation loop as the transformed waters return to the north atlantic the low salinity upper water of the east greenland current enters the labrador sea and influences the formation of labrador sea deep water the dense loop passes through denmark strait and the faroe shetland channel and sinks to contribute to the north atlantic deep water changes in the forcing conditions might alter the relative strength of the two loops this could affect the oceanic thermohaline circulation on a global scale

optically stimulated luminescence dating supports central arctic ocean cm scale sedimentation rates 1 this paper presents new results from optically stimulated luminescence osl dating on a sediment core raised from the crest of the lomonosov ridge in the central arctic ocean there has been much debate about dating sediment cores from the central arctic ocean and by using an independent absolute dating technique we aim to test whether or not relatively fast cm scale ka sedimentation rates were typical of arctic s pleistocene depositional mode on the basis of mainly paleomagnetic reversal stratigraphy many previous studies suggest mm scale ka sedimentation rates a common feature in these studies is that the first down core paleomagnetic negative inclination is consistently interpreted as the brunhes matuyama boundary at about 780 ka our osl dating results indicate that this assumption is not generally valid and that the first encountered negative inclination represents younger age excursions within the brunhes chron implying reinterpretation of many published core studies where paleoenvironmental reconstructions have been made for the central arctic ocean our dating results furthermore corroborates a correlation of the uppermost 2 3 m of the lomonosov ridge cores to a well dated core located off the barents kara sea margin that in turn is correlated to cores in the fram strait valuable information on the paleoceanographical evolution in the arctic ocean from mis 6 to the holocene is given through this correlation of records from the central arctic ocean to records off the eurasian continental margin

spatial and temporal arctic ocean depositional regimes a key to the evolution of ice drift and current patterns sediment physical properties measured in cores from all the major ridges and plateaus in the central arctic ocean were studied in order to analyze the spatial and temporal consistency of sediment d

seabed erosion on the lomonosov ridge central arctic ocean a tale of deep draft icebergs in the eurasia basin and the influence of atlantic water inflow on iceberg motion 1 the submarine lomonosov ridge which bisects the arctic ocean is covered by 450 m of hemipelagic sediments high resolution chirp sonar and side scan data have documented erosion of a section of the ridge here we present multichannel seismic and chirp sonar data which show removal of unconsolidated sediments along the eurasia basin side of the lomonosov ridge where the central ridge is shallower than 1000 m the incomplete erosion of the hemipelagic drape and probable topographic control of ice motion suggest that the deepest draft glacier ice which reached the central arctic ocean from the eurasia basin was in the form of armadas of large icebergs embedded in sea ice rather than a single continuous floating ice shelf massive rapid discharge of glacier ice was probably required to produce the deepest draft 800 m icebergs eastward and northward drift trajectories from a likely iceberg source area on the kara barents sea margin would reflect the relative strength of atlantic inflow through the fram strait however only icebergs with drafts exceeding bathymetric thresholds on the lomonosov ridge would leave an erosive imprint on the seabed advection of atlantic water may have been relatively strong at times of discharge from the saalian ice sheet icebergs exiting the arctic ocean caused massive erosion and redeposition of the hemipelagic sediments on top of yermak plateau

arctic perennial ice cover over the last 14 million years knowledge of the long term history of the perennial ice is an important issue that has eluded study because the cenozoic core material needed has been unavailable until the recent arctic coring expedition acex detrital fe oxide mineral grains analyzed by microprobe from the last 14 ma 164 m of the acex composite core on the lomonosov ridge were matched to circum arctic sources with the same mineral and 12 element composition these precise source determinations and estimates of drift rates were used to determine that these sand grains could not be rafted to the acex core site in less than a year thus the perennial ice cover has existed since 14 ma except for the unlikely rapid return to seasonal ice between the average sampling interval of about 0 17 ma both north america and russia contributed significant fe grains to the acex core during the last 14 ma

glacial history and paleoceanography of the southern yermak plateau since 132 ka bp abstract the southern yermak plateau yp is situated at the entrance to the arctic ocean in the narrow marginal ice zone miz between the polar and arctic fronts north west of svalbard a gravity core jm10 02gc has been analysed in order to reconstruct paleoceanographic conditions and the movement of the sea ice margin as well as the glacier ice conditions of the svalbard barents sea ice sheet sbis during the last interglacial glacial cycle the distribution of planktic and benthic foraminifera planktic and benthic oxygen and carbon isotopes and variations in ice rafted debris ird has been investigated the sediment core covers the time interval from the marine isotope stage mis 6 5e transition termination ii c 132 ka bp to the early holocene during termination ii tii the sbis retreated and the sea ice margin was in distal position whereas during mis 5 to mis 4 the sea ice margin was close to the core site several core intervals interpreted as representing mis 5e mis 5c mis 5a mis 3 and mis 1 were barren of calcareous microfossils whereas the intervals representing mis 4 and mis 2 were characterised by high productivity hp of planktic and benthic foraminifera these glacial hp zones were associated with the open water conditions resulting from the advection of atlantic water aw and retreat of the sea ice margin the barren zones during mis 5 mis 3 and mis 1 resulted from the proximity of the sea ice margin whereas during mis 2 the likely cause was an advance of the sbis

quaternary paleoceanography of the central arctic based on integrated ocean drilling program arctic coring expedition 302 foraminiferal assemblages the integrated ocean drilling program iodp arctic coring expedition acex hole 4c from the lomonosov ridge in the central arctic ocean recovered a continuous 18 m record of quaternary foraminifera yielding evidence for seasonally ice free interglacials during the matuyama progressive development of large glacials during the mid pleistocene transition mpt 1 2 0 9 ma and the onset of high amplitude 100 ka orbital cycles 500 ka foraminiferal preservation in sediments from the arctic is influenced by primary sea ice organic input and other environmental conditions and secondary factors syndepositional long term pore water dissolution taking these into account the acex 4c record shows distinct maxima in agglutinated foraminiferal abundance corresponding to several interglacials and deglacials between marine isotope stages mis 13 37 and although less precise dating is available for older sediments these trends appear to continue through the matuyama the mpt is characterized by nearly barren intervals during major glacials mis 12 16 and 22 24 and faunal turnover mis 12 24 abundant calcareous planktonic mainly neogloboquadrina pachyderma sin and benthic foraminifers occur mainly in interglacial intervals during the brunhes and very rarely in the matuyama a distinct faunal transition from calcareous to agglutinated foraminifers 200 300 ka in acex 4c is comparable to that found in arctic sediments from the lomonosov alpha and northwind ridges and the morris jesup rise down core disappearance of calcareous taxa is probably related to either reduced sea ice cover prior to the last few 100 ka cycles pore water dissolution or both

high temperatures in the late cretaceous arctic ocean to understand the climate dynamics of the warm equable greenhouse world of the late cretaceous period it is important to determine polar palaeotemperatures the early palaeoceanographic history of the arctic ocean has however remained largely unknown because the sea floor and underlying deposits are usually inaccessible beneath a cover of floating ice a shallow piston core taken from a drifting ice island in 1970 fortuitously retrieved unconsolidated upper cretaceous organic rich sediment from alpha ridge a submarine elevated feature of probable oceanic origin a lack of carbonate in the sediments from this core has prevented the use of traditional oxygen isotope palaeothermometry here we determine arctic palaeotemperatures from these upper cretaceous deposits using tex86 a new palaeothermometer that is based on the composition of membrane lipids derived from a ubiquitous component of marine plankton crenarchaeota from these analyses we infer an average sea surface temperature of approximately 15 degrees c for the arctic ocean about 70 million years ago this calibration point implies an equator to pole gradient in sea surface temperatures of approximately 15 degrees c during this interval and by extrapolation we suggest that polar waters were generally warmer than 20 degrees c during the middle cretaceous approximately 90 million years ago

plio pleistocene trends in ice rafted debris on the lomonosov ridge although more than 700 sediment cores exist from the arctic ocean the plio pleistocene evolution of the basin and its marginal seas remains virtually unknown this is largely due the shallow penetration of most of these records and difficulties associated with deriving chronologies for the recovered material the integrated ocean drilling program s iodp expedition 302 arctic coring expedition acex recovered 197 m of neogene quaternary sediment from the circumpolar regions of the lomonosov ridge as detailed analyses of this material emerge research is beginning to formulate a long term picture of paleoceanographic changes in the central arctic ocean this paper reviews the acex plio pleistocene age model identifies uncertainties and addresses ways in which these may be eliminated within the established stratigraphic framework a notable reduction in the abundance of ice rafted debris ird occurs in the early part of the pleistocene and persists until marine isotope stage 6 mis 6 therefore while global oceanographic proxies indicate the gradual growth of terrestrial ice sheets during this time ird delivery to the central arctic ocean remained comparatively low and stable within the resolution of existing data the pleistocene reduction in ird is synchronous with predicted changes in both the inflow of north atlantic and pacific waters which in modern times are known to exert a strong influence on sea ice stability

test of the concepts of sequence stratigraphy in the kimmeridgian late jurassic of england and northern france abstract three distinct models are available for the prediction of sediment accumulation patterns the sequence stratigraphic models of both galloway 1989 and exxon are derived from passive margins whereas the model of einsele 1985 is based on marginal sedimentation in epicontinental seas the models are tested on the marine mudrocks and minor sandstones of the kimmeridgian epicontinental seas of england and northern france a total of ten hiatus bounded sedimentary packages sequences can be delimited and aspects of both the exxon and galloway models are applicable however only a few of the sequence boundaries correspond to the eustatic sea level chart of haq et al 1989 the sequence boundaries appear to be caused by falls in a base level controlled by a storm wave base and the transgressive regressive cycles appear symmetrical as predicted by the einsele model in both the exxon and galloway models condensed sections are predicted to form in distal basin settings beyond the reach of terrigenous sediments but they are not developed in the relatively small kimmeridgian half grabens which were infilled with non progradational packages of sediment thus the basin centres such as the kimmeridge bay type locality contain the thickest and most complete sequences

corrigendum to paleo sea levels reconsidered from direct observation of paleoshoreline position during glacial maxima for the last 500 000 years earth planet sci lett 252 2006 119 137

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

pleistocene benthic foraminifers in the arctic ocean implications for sea ice and circulation history abstract three sediment cores from the northwind mendeleev and lomonosov ridges distributed across the western arctic ocean were investigated for foraminiferal composition with a focus on benthic assemblages this investigation provides insights into middle to late pleistocene history of paleoceanographic and sea ice conditions on multi millennial time scales calcareous foraminiferal abundances and assemblage composition show stratigraphically consistent development including glacial interglacial variability and long term evolution of foraminiferal assemblages major long term changes occurred at the end of the mid pleistocene transition estimated ca 0 7 0 8 ma and later near the bottom of marine isotope stage 7 ca 0 25 ma and near the top of mis 5 ca 0 1 ma these changes include notably a diminishing role of phytodetritus related species such as epistominella exigua at the expense of oligotrophic species adapted to live under persistent sea ice presumably indicating an overall expansion of year round ice cover in the arctic during the pleistocene the pronounced mpt shift from mostly seasonal to perennial sea ice was coeval and possibly related to a growth of north american ice sheets and the beginning of glacially controlled sedimentation in the western arctic ocean the ca 0 25 ma transition interpreted as another step in sea ice expansion also co occurs with signs of ice sheet expansion in both north america and especially eurasia the apparent synchronicity of major steps in sea ice and glaciation histories necessitates a more in depth investigation of feedbacks involved and broader linkages beyond the arctic region the ca 0 1 ma change in foraminiferal assemblages marks a consistent stratigraphic event expressed notably in a proliferation of the cosmopolitan species oridorsalis tener although its paleoenvironmental significance is not yet fully understood

multibeam bathymetric and sediment profiler evidence for ice grounding on the chukchi borderland arctic ocean multibeam bathymetry and 3 5 khz sub bottom profiler data collected from the us icebreaker healy in 2003 provide convincing evidence for grounded ice on the chukchi borderland off the northern alaskan margin arctic ocean the data show parallel glacially induced seafloor scours or grooves and intervening ridges that reach widths of 1000 m rim to rim and as much as 40 m relief following previous authors we refer to these features as bmegascale glacial lineations msgls q additional support for ice grounding is apparent from stratigraphic unconformities interpreted to have been caused by ice induced erosion most likely the observed sea floor features represent evidence for massive ice shelf grounding the general ese wnw direction of the msgls together with sediment evidently bulldozed off the chukchi plateau that is mapped on the western siberian side of the plateau suggests ice flow from the canada basin side of chukchi borderland two separate generations of glacially derived msgls are identified on the chukchi borderland from the healy geophysical data the deepest and oldest extensive msgls appear to be draped by sediments less than 5 m thick whereas no sediment drape can be distinguished within the resolution of the sub bottom profiles on the younger generation d 2005 university of washington all rights reserved

estimation of elastic moduli of mixed porous clay composites we have developed a procedure for estimating the effective elastic properties of various mixtures of smectite and kaolinite over a range of confining pressures based on the individual effective elastic properties of pure porous smectite and kaolinite experimental data for the pure samples are used as input to various rock physics models and the predictions are compared with experimental data for the mixed samples we have evaluated three strategies for choosing the initial properties in various rock physics models 1 input values have the same porosity 2 input values have the same pressure and 3 an average of 1 and 2 the best results are obtained when the elastic moduli of the two porous constituents are defined at the same pressure and when their volumetric fractions are adjusted based on different compaction rates with pressure furthermore our strategy makes the modeling results less sensitive to the actual rock physics model the method can help obtain the elastic properties of mixed unconsolidated clays as a function of mechanical compaction the more common procedure for estimating effective elastic properties requires knowledge about volume fractions elastic properties of individual constituents and geometric details of the composition however these data are often uncertain e g large variations in the mineral elastic properties of clays have been reported in the literature which makes our procedure a viable alternative

on sediment deposition and nature of the plate boundary at the junction between the submarine lomonosov ridge arctic ocean and the continental margin of arctic canada north greenland abstract the first seismic reflection data from the shallowest part of the submarine lomonosov ridge north of arctic canada and north greenland comprise two parallel single channel lines 62 and 25 km long offset 580 m acquired from a 10 day camp on drifting sea ice the top of southern lomonosov ridge is bevelled 550 m water depth and only thin sediments

high resolution geophysical observations of the yermak plateau and northern svalbard margin implications for ice sheet grounding and deep keeled icebergs high resolution geophysical evidence on the seafloor morphology and acoustic stratigraphy of the yermak plateau and northern svalbard margin between 79 20 and 81 30 n and 5 and 22 e is presented

reconstructing the origin and trajectory of drifting arctic sea ice recent studies have indicated that drifting arctic sea ice plays an important role in the redistribution of sediments and contaminants here we present a method to reconstruct the back ward trajectory of sea ice from its sampling location in the eurasian arctic to its possible site of ori gin on the shelf based on historical drift data from the international arctic buoy program this method is verified by showing that origins derived from the backward trajectories are generally con sistent with other indicators such as comparison of the predicted backward trajectories with known buoy drifts and matching the clay mineralogy of sediments sampled from the sea ice with that of the seafloor in the predicted shelf source regions the trajectories are then used to identify regions where sediment laden ice is exported to the transpolar drift stream from the new siberian islands and the central kara plateau calculation of forward trajectories shows that the kara sea is a major contributor of ice to the barents sea and the southern limb of the transpolar drift stream

arctic ocean deep sea record of northern eurasian ice sheet history the sediment composition of deep sea cores from the central arctic ocean the fram strait and the yermak plateau was analyzed for several parameters to reconstruct the history of marine paleoenvironment and terrestrial glaciation in the last 200 000 years layers with high amounts of coarse terrigenous ice rafted debris ird and often high contents of smectite were deposited during extensive glaciations in northern eurasia when ice sheets reached the northern continental margins of the barents and kara seas and discharged icebergs into the arctic ocean intercalated layers with relatively low ird and smectite contents but abundant planktic foraminifers in the coarse fraction were deposited during periods of atlantic water inflow to the arctic ocean and seasonally open waters leads in a sea ice cover with only few icebergs in the arctic ocean high ird contents in the sediments reflect the presence of ice sheets on the kara and barents seas shelves and the hinterland during the entire oxygen isotope stage 6 ca 190 130 ka in substage 5b ca 90 80 ka at the stage boundary 5 4 around 75 ka and in late stage 4 early stage 3 ca 65 50 ka these results are in excellent correlation with those from recent field work in northern scandinavia european russia siberia and on the shelves relatively low amounts of ird in central arctic ocean sediments from the late weichselian glacial maximum ca 24 18 ka correlate well with the recent reconstruction of a very limited eastern ice sheet extension during this time oxygen and carbon isotope records of planktic foraminifers from the analyzed sediment cores show a number of prominent excursions which can be interpreted as evidence for freshwater events in the arctic ocean the synchroneity of freshwater events and ird input suggests a common source strongest events were associated with deglaciations of the barents and kara seas after the ice sheets had blocked the outflow of large rivers for several millennia the outflow of freshwater from large ice dammed lakes occurred at ca 130 80 75 and 52 ka freshwater events in the central arctic ocean during the last deglaciation ca 18 ka were relatively small compared to the previous events this indicates that during most of the late weichselian glacial maximum a river outflow from northern siberia to the arctic ocean was possible atlantic water inflow to the arctic ocean and seasonally open waters in the ice leads occurred during the interglacials ofoxygen isotope stage 1 and substage 5e during several interstadials stage 3 substages 5a and 5c and to a lesser degree within stadials and glacials stages 2 4 and 6 with the exception ofthe interglacials these periods were times ofstrong ice growth on the continents as revealed by terrestrial data the coincidence suggests that open waters in the arctic ocean and the nordic seas were an important moisture source in addition to more southerly sources which fostered the growth of ice sheets on northern eurasia

dating late quaternary planktonic foraminifer neogloboquadrina pachyderma from the arctic ocean using amino acid racemization the long term rate of racemization for amino acids preserved in planktonic foraminifera was determined by using independently dated sediment cores from the arctic ocean the racemization rates for aspartic acid asp and glutamic acid glu in the common taxon neogloboquadrina pachyderma were calibrated for the last 150 ka using 14c ages and the emerging quaternary chronostratigraphy of arctic ocean sediments an analysis of errors indicates realistic age uncertainties of about 12 for asp and 17 for glu fifty individual tests are sufficient to analyze multiple subsamples identify outliers and derive robust sample mean values the new age equation can be applied to verify and refine age models for sediment cores elsewhere in the arctic ocean a critical region for understanding the dynamics of global climate change

environmental magnetism past present and future environmental magnetism involves the application of rock and mineral magnetic techniques to situations in which the transport deposition or transformation of magnetic grains is influenced by environmental processes in the atmosphere hydrosphere and lithosphere the first explicit description of environmental magnetism as a distinct field was in 1980 since that time environmental magnetism has become a broad field that is finding application in an ever increasing array of scientific disciplines in this review of the present state of environmental magnetic studies we divide the field into three broad but arbitrary categories the first involves the use of mineral magnetic assemblages in the geological record to study physical processes in depositional environments this category includes the correlation of sediment cores using magnetic susceptibility measurements studies of geomagnetic field behavior the analysis of depositional and postdepositional mechanical processes that affect sediments and the examination of magnetic parameters that might represent proxies for paleoclimatic variation the second category encompasses studies of the processes responsible for variations in the magnetic minerals brought into a sedimentary environment these provenance investigations include studies of changes in catchment derived sediment in lakes fluctuations in contributions from terrigenous aeolian and glaciogenic components in deep sea sediments and the origin of atmospheric particulates the final category addresses in situ changes and transformations of magnetic minerals in sedimentary environments including pedogenesis authigenetic diagenetic formation of ferrimagnetic phases dissolution of magnetic minerals due to reductive diagenesis and contributions of biomagnetism to sedimentary magnetism because environmental magnetism can address problems in so many disciplines and because many of these problems may be inaccessible to other techniques it is likely that the scope of environmental magnetism will continue to expand rapidly environmental magnetism is capable of providing important data for studies of global environmental change climatic processes and the impact of humans on the environment all of which are major research initiatives in the international scientific community these factors suggest that environmental magnetism has a bright and diverse future

manganese and color cycles in arctic ocean sediments constrain pleistocene chronology sequential variations in manganese mn content and color of deepsea sediments retrieved from the lomonosov ridge 87 n in the central arctic ocean apparently mimic low latitude 18 o glacial interglacial cyclicity thereby providing stratigraphic information that together with biostratigraphic data permit the construction of a detailed chronological model correlation of this mn and color chronology to established apparent brunhes age estimates of geomagnetic excursions reveals a remarkable fit between these two independently derived time scales the mn and color cycles probably provide paleoenvironmental information about material fluxes in the arctic ocean over the past 1 m y we suggest that the primary source for the observed manganese variations in our sediment core is northern siberia which has extensive peat bogs and boreal forests these siberian source areas could operate in an off and on mode tuned to pleistocene glacial and interglacial periods contrasts in ventilation of arctic ocean waters during interglacial glacial cycles probably could also enhance the observed mn and color variability

contrasting glacial interglacial regimes in the western arctic ocean as exemplified by a sedimentary record from the mendeleev ridge distinct cyclicity in lithology and microfaunal distribution in sediment cores from the mendeleev ridge in the western arctic ocean water depths ca 1 5 km reflects contrasting glacial interglacial sedimentary patterns we conclude that during major glaciations extremely thick pack ice or ice shelves covered the western arctic ocean and its circulation was restricted in comparison with interglacial modern type conditions glacier collapse events are marked in sediment cores by increased contents of ice rafted debris notably by spikes of detrital carbonates and iron oxide grains from the canadian arctic archipelago composition of foraminiferal calcite n 18 o and n 13 c also shows strong cyclicity indicating changes in freshwater balance and or ventilation rates of the arctic ocean light stable isotopic spikes characterize deglacial events such as the last deglaciation at ca 12 14 c kyr bp the prolonged period with low n 18 o and n 13 c values and elevated contents of iron oxide grains from the canadian archipelago in the lower part of the mendeleev ridge record is interpreted to signify the pooling of freshwater in the amerasia basin possibly in relation to an extended glaciation in arctic north america unique benthic foraminiferal events provide a means for an independent stratigraphic correlation of sedimentary records from the mendeleev ridge and other mid depth locations throughout the arctic ocean such as the northwind and lomonosov ridges this correlation demonstrates the disparity of existing age models and underscores the need to establish a definitive chronostratigraphy for arctic ocean sediments 2003 elsevier b v all rights reserved

new insights on arctic quaternary climate variability from palaeo records and numerical modelling terrestrial and marine geological archives in the arctic contain information on environmental change through quaternary interglacial glacial cycles the arctic palaeoclimate and its extremes apex scientific network aims to better understand the magnitude and frequency of past arctic climate variability with focus on the extreme versus the normal conditions of the climate system one important motivation for studying the amplitude of past natural environmental changes in the arctic is to better understand the role of this region in a global perspective and provide base line conditions against which to explore potential future changes in arctic climate under scenarios of global warming in this review we identify several areas that are distinct to the present programme and highlight some recent advances presented in this special issue concerning arctic palaeo records and natural variability including spatial and temporal variability of the greenland ice sheet arctic ocean sediment stratigraphy past ice shelves and marginal marine ice sheets and the cenozoic history of arctic ocean sea ice in general and holocene oscillations in sea ice concentrations in particular the combined sea ice data suggest that the seasonal arctic sea ice cover was strongly reduced during most of the early holocene and there appear to have been periods of ice free summers in the central arctic ocean this has important consequences for our understanding of the recent trend of declining sea ice and calls for further research on causal links between arctic climate and sea ice

the context of lowstand events in the kimmeridgian late jurassic sequence stratigraphic evolution of the wessex weald basin southern england abstract a depositional sequence stratigraphic framework for the kimmeridgian stage of the wessex weald basin southern england is applied in the investigation of the sedimentary and erosional response to proposed lowstand events this framework recognises 13 sequence boundaries km1 km13 and is based on the integrated assessment of geophysical sedimentological palaeontological and geochemical data changes in the nature and continuity of kimmeridgian unconformity surfaces record the effect of the reorganisation of the onshore basins in response to eustasy and tectonic movements during the earliest kimmeridgian the basin geometry was such that falls in relative sea level generated widespread unconformities associated lowstand events are recorded in marginal areas by a number of sand units derived from a variety of local sources a tectonically enhanced deepening event during the late early kimmeridgian eudoxus zone led to unconformities being confined in their distribution to the basin margins as sea level fell during the latest kimmeridgian a progressive reduction in the depositional area led to an amplification of the effects of lowstand processes at the basin margins where unconformity surfaces are amalgamated on the most positive areas these surfaces are overprinted by a major interregional hiatus the late cimmerian unconformity the timing and effects of kimmeridgian lowstand events were intimately linked to the tectonic evolution of the wessex weald basin thus at times when rates and amounts of eustatic change are small i e during greenhouse times the tectonic signature of a basin will be the primary signal recorded in sedimentary successions

deep pleistocene iceberg plowmarks on the yermak plateau sidescan and 3 5 khz evidence for thick calving ice fronts and a possible marine ice sheet in the arctic ocean the southern yermak plateau northwest of spitsbergen was investigated with 11 12 khz sidescan sonar and 3 5 khz profiler to test whether thick pleistocene ice streams ever calved into the arctic ocean and or whether a continuous arctic ice sheet existed in either case the ice would have grounded on the plateau crest on its way out of the arctic several distinct sets of relict iceberg plowmarks were discovered at present water depths from less than 450 m to at least 850 m perhaps recording the deepest iceberg keels known the plateau crest 510 530 m is nearly bare of plowmarks perhaps because of beveling by an ice rise formed of grounding shelf ice this implies continuous 400 600 m thick grounded ice consistent with but not proving the postulated existence of an arctic ice sheet most plowmarks are probably late pleistocene products of the calving of barents kara ice sheets into the arctic ocean plowmarks in 450 850 m deep water require unusually deep ice sheet grounding lines e g svyataya anna trough and or drat increasing capsizing events even if sea levels were 100 50 m lower than today at water depths of 800 to 1800 m the sidescan texture and topography suggest bottom currents descending the northeast slope of the plateau

paleomagnetism of quaternary sediments from lomonosov ridge and yermak plateau implications for age models in the arctic ocean abstract inclination patterns of natural remanent magnetization nrm in quaternary sediment cores from the arctic ocean have been widely used for stratigraphic correlation and the construction of age models however shallow and negative nrm inclinations in sediments deposited during the brunhes chron in the arctic ocean appear to have a partly diagenetic origin rock magnetic and mineralogical studies demonstrate the presence of titanomagnetite and titanomaghemite thermal demagnetization of the nrm indicates that shallow and negative inclination components are largely unblocked below 300 c consistent with a titanomaghemite remanence carrier following earlier studies on the mendeleev alpha ridge shallow and negative nrm inclination intervals in cores from the lomonosov ridge and yermak plateau are attributed to partial self reversed chemical remanent magnetization crm carried by titanomaghemite formed during seafloor oxidation of host detrital titanomagnetite grains distortion of paleomagnetic records due to seafloor maghemitization appears to be especially important in the perennially ice covered western mendeleev alpha ridge and central arctic ocean lomonosov ridge and to a lesser extent near the ice edge yermak plateau on the yermak plateau magnetic grain size parameters mimic the global benthic oxygen isotope record back to at least marine isotope stage 6 implying that magnetic grain size is sensitive to glacial interglacial changes in bottom current velocity and or detrital provenance

arctic ocean glacial history while there are numerous hypotheses concerning glacial interglacial environmental and climatic regime shifts in the arctic ocean a holistic view on the northern hemisphere s late quaternary ice sh

late neogene climate evolution of the central arctic ocean abstract because no sediment of post eocene to late miocene or pliocene age has been recovered from the central arctic ocean oceanographic conditions during the middle cenozoic are unknown the oldest late cenozoic sediment is glacial marine and contains agglutinated foraminifera a few calcareous organisms are present in the oldest late cenozoic sediment with an age of 2 4 ma but at approximately the time as deposition of lithostratigraphic unit f sometime between 2 0 and 1 5 ma there was an abrupt and dramatic increase in calcareous species diversity and abundance in the central arctic ocean many of the newly introduced species are atlantic in origin preliminary evidence suggests that the introduction of a moderately large and diverse calcareous fauna at this time corresponds to the lowering of the arctic ocean ccd level and this may be explained by increased circulation with the northern greenland sea details of the change in threshold values in the fram strait required for the introduction of relatively warmer and carbonate rich water into the central arctic ocean are unknown there is evidence that spreading rates along the north atlantic nansen ridge system increased during the pleistocene and this may have permitted increased circulation between the north atlantic and the central arctic ocean this important change in arctic ocean circulation corresponds to increased pleistocene seasonality in the northern hemisphere

arctic ocean record of last two glacial interglacial cycles off north greenland ellesmere island implications for glacial history a sediment record from the practically unknown southernmost part of the lomonosov ridge off north greenland ellesmere island has been studied greenice core 10 encompasses marine isotope stages mis 7 1 and reveals changing paleoceanographic conditions and land ocean connections during the last two glacial interglacial cycles the isotope record of planktic foraminifera neogloboquadrina pachyderma s show large similarities to other arctic ocean key records supporting that the pattern reflect over regional changes of the halocline structure the relatively low 18 o values of subpolar foraminifera turborotalita quinqueloba in the last interglacial unit support that the specimens represent local production related to warm interglacial conditions and a reduced sea ice cover in the interior arctic ocean enhanced deposition of coarse ice rafted debris took place during the mis 8 7 transition periods of mis 6 mis 6 5 transition mis 5d mis 4 and late mis 3 30 40 14 c kyr bp in mis 2 ird flux was low in the area the ird contains detrital carbonate similar to other amerasia basin records the occurrence of finegrained calcite rich detrital carbonate layers at glacial interglacial transitions seems unique to this area we suggest that detrital carbonate was transported and deposited from nepheloid flows during deglaciations of ellesmere island when the atlantic water boundary current along the continental margin was gaining strength 2007 elsevier b v all rights reserved

self reversal and apparent magnetic excursions in arctic sediments the arctic oceans have been fertile ground for the recording of apparent excursions of the geomagnetic field implying that the high latitude field had unusual characteristics at least over the last 1 2 myrs alternating field demagnetization of the natural remanent magnetization nrm of core hly0503 6jpc from the mendeleev ridge arctic ocean implies the presence of primary magnetizations with negative inclination apparently recording excursions in sediments deposited during the brunhes chron thermal demagnetization on the other hand indicates the presence of multiple often anti parallel magnetization components with negative inclination components having blocking temperatures predominantly but not entirely below 350 c thermo magnetic tests x ray diffraction xrd and scanning electron microscopy sem indicate that the negative inclination components are carried by titanomaghemite presumably formed by seafloor oxidation of titanomagnetite the titanomaghemite apparently carries a chemical remanent magnetization crm that is partially self reversed relative to the detrital remanent magnetization drm carried by the host titanomagnetite the partial self reversal could have been accomplished by ionic ordering during oxidation thereby changing the balance of the magnetic moments in the ferrimagnetic sublattices

new constraints on arctic ocean mn stratigraphy from radiocarbon dating on planktonic foraminifera abstract variations in the abundance of manganese mn in arctic ocean sediments are used as a tool to identify glacial and interglacial periods this study aims to provide new insight into the applicability of mn as a stratigraphic tool in the topmost sediment and to investigate the occurrence of mn peaks in sediments within the range of radiocarbon dating in combination with variations in ice rafted debris ird radiocarbon dating is used to better constrain the stratigraphic occurrence of mn peaks and the synchroneity between multiple records especially during the late glacial and the holocene we find that a hiatus spanning mis 2 is widely observed in most of our cores resulting in a merging of mn peaks of holocene age and the later part of mis 3 the holocene mn peak is usually high amplitude but short while the mis 3 mn peak has a lower amplitude and is protracted where preserved mis 2 sediments form a 2 3 cm thick layer characterized by a light color low mn content sparse ird and low foraminiferal abundance ird variations provide a powerful tool to identify the boundary of the holocene and late mis 3 in cores with a mis 2 hiatus because the ird content displays a general increment from the start of mis 3 and both the holocene and mis 2 show small ird variations the end of mis 3 can be pinpointed to the point of decrease in ird the hiatus of mis 2 is widely observed in our cores suggesting extensive persistent sea ice coverage during the peak of the last glacial cycle with sharply reduced sedimentation throughout the arctic ocean identifying similar events during previous glacial periods may be an important step towards constructing longer and more accurate chronologies for arctic ocean sediments

estimating the dispersion of biostratigraphic events in the subsurface by graphic correlation an example from the late jurassic of the wessex basin uk abstract the strikingly cyclic character of digitally filtered gamma ray logs from the oxfordian to portlandian interval of the wessex basin onshore united kingdom facilitates high resolution log correlation over considerable distances allowing the systematic calibration of biostratigraphic with lithostratigraphic data through graphic correlation this involves the systematic cross plotting of biostratigraphic events based on samples taken from cuttings and sidewall cores from a set of wells to produce a composite standard initially the standard is a single well chosen for maximum thickness and completeness biostratigraphic events are added to by drawing lines of correlation and projecting the data points onto the composite standard the scatter of biostratigraphic events is generally such that a line of correlation cannot be drawn with confidence from the biostratigraphic data alone independent lines of correlation are established between wells by first matching cycles parasequences on digitally filtered gamma ray traces and using these as a framework for adding biostratigraphic events to the composite standard this has advantages over the conventional approach in that the effects of outliers in the data are minimized and hiatuses and subtle changes in rock accumulation rates become apparent by adding all the biostratigraphic events from all wells to the composite standard a range chart is produced depicting the scatter or dispersion of all biostratigraphic events relative to the log based cycles the end result is an integrated stratigraphy in which biostratigraphic events are calibrated against rock events giving a measure of dispersion and hence confidence for each biostratigraphic event

severnaya zemlya arctic russia a nucleation area for kara sea ice sheets during the middle to late quaternary quaternary glacial stratigraphy and relative sea level changes reveal at least four expansions of the kara sea ice sheet over the severnaya zemlya archipelago at 79 degrees n in the russian arctic as indicated from tills interbedded with marine sediments exposed in stratigraphic superposition and from raised beach sequences that occur at altitudes up to 140 m a s l chronologic control is provided by ams c 14 electron spin resonance green stimulated luminescence and aspartic acid geochronology major glaciations followed by deglaciation and marine inundation occurred during mis 10 9 mis 8 7 mis 6 5e and mis 5d 3 the mis 6 5e event associated with the high marine limit implies ice sheet thickness of 2000m only 200km from the deep arctic ocean consistent with published evidence of ice grounding at similar to 1000m water depth in the central arctic ocean till fabrics and glacial tectonics record repeated expansions of local ice caps exclusively suggesting wet based ice cap advance followed by cold based regional ice sheet expansion local ice caps over highland sites along the perimeter of the shallow kara sea including the byrranga mountains appear to have repeatedly fostered initiation of a large kara sea ice sheet with exception of the last glacial maximum mis 2 when kara sea ice did not impact severnaya zemlya and barely graced northernmost taymyr peninsula

biochronology and paleoceanography of late pleistocene and holocene calcareous nannofossil abundances across the arctic basin biochronology and paleoceanography of late pleistocene and holocene calcareous nannofossils across the arctic basin