past glacial and interglacial conditions in the arctic ocean and marginal seas a review past changes in the arctic ocean and its marginal seas have been profound even during the last 10 000 years understanding these changes such as those occurring during the transition from glacial to interglacial climates are important for research on modern processes because this knowledge provides a framework and unique perspective in which to view the modern physical and biological processes this paper discusses our current understanding of past environmental change and processes relative to those currently in progress special emphasis is placed on the most recent transition from a glacial state to the modern interglacial conditions

1 500 year cycle in the arctic oscillation identified in holocene arctic sea ice drift decadal to centennial scale variability has been identified in the arctic oscillation but less is known about variations on the millennial scale a record of sea ice drift from off the alaskan coast shows a 1 500 year cycle in the phase of the arctic oscillation

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

quaternary ice transport in the canadian arctic and extent of late wisconsinan glaciation in the queen elizabeth islands most of the ice rafted debris in channels off the queen elizabeth islands nunavut is of local origin particularly in the inner part of the archipelago but samples from the arctic shelf contain as much as 40 grains from sources as far away as 2000 km including the siberian shelves particle transport by drifting sea ice from distant shelves is an important process on the arctic continental shelf of the queen elizabeth islands in the interior of the queen elizabeth islands and in the viscount melville and lancaster sounds particle transport is limited to distances of approximately 200 km mixing is more common among grains of coarse silt to fine sand than in the 250 m fraction but even the latter contains debris from sources far apart during the late wisconsinan the northern southern and eastern queen elizabeth islands were covered by glaciers flowing radially from ice centers on the islands into the inter island channels queens channel was completely filled by ice and a glacier lobe moved

astrochronology and radio isotopic dating of the alano di piave section ne italy candidate gssp for the priabonian stage late eocene abstract we have carried out an integrated chronostratigraphic analysis of the alano di piave section proposed gssp for the bartonian priabonian boundary late eocene age constraints were derived independently from a floating cyclochronology based on carbon isotope and wt caco3 records and 206pb 238u dating of zircons from four volcanic tuffs orbital and radio isotopic estimates of the duration of intervals bracketed by consecutive crystal rich volcanic tuff layers are in good overall agreement but discrepancies of 40 160 kyr are present between nominal volcanic tuff dates derived from astrochronology and 206pb 238u the degree to which these discrepancies are statistically significant at the 2 level depends on the interpretation of the u pb zircon data and the uncertainties assigned to the astronomical age model the possible source and significance of these discrepancies are explored in detail the resulting age model combined with published bio and magnetostratigraphic data is used to establish the duration of individual magnetochrons in the interval spanning the bartonian priabonian transition and the timing of late bartonian early priabonian biostratigraphic and magnetostratigraphic events relative to the proposed gssp the regionally traceable crystal rich tuff layer tiziano bed the chronostratigraphic framework developed at alano di piave will facilitate the global correlation of the priabonian gssp based on both bio and magnetostratigraphic criteria the obtained astrochronology allows a precise correlation of the alano di piave 13c record with oceanic successions confirming a strong dependency of the marine carbon cycle on astronomical forcing although with inter site differences which could be related to water mass organization

ephemeral formation of perennial sea ice in the arctic ocean during the middle eocene arctic sea ice is a key component of the modern climate system marine sediment analyses suggest that perennial sea ice in the arctic ocean first formed transiently about 44 million years ago

thresholds for cenozoic bipolar glaciation the long standing view of earth s cenozoic glacial history calls for the first continental scale glaciation of antarctica in the earliest oligocene epoch 33 6 million years ago1 followed by the onset of northern hemispheric glacial cycles in the late pliocene epoch about 31 million years later2 the pivotal early oligocene event is characterized by a rapid shift of 1 5 parts per thousand in deep sea benthic oxygen isotope values3 oi 1 within a few hundred thousand years4 reflecting a combination of terrestrial ice growth and deep sea cooling the apparent absence of contemporaneous cooling in deep sea mg ca records4 5 6 however has been argued to reflect the growth of more ice than can be accommodated on antarctica this combined with new evidence of continental cooling7 and ice rafted debris8 9 in the northern hemisphere during this period raises the possibility that oi 1 represents a precursory bipolar glaciation here we test this hypothesis using an isotope capable global climate ice sheet model that accommodates both the long term decline of cenozoic atmospheric co2 levels10 11 and the effects of orbital forcing12 we show that the co2 threshold below which glaciation occurs in the northern hemisphere 280 p p m v is much lower than that for antarctica 750 p p m v therefore the growth of ice sheets in the northern hemisphere immediately following antarctic glaciation would have required rapid co2 drawdown within the oi 1 timeframe to levels lower than those estimated by geochemical proxies10 11 and carbon cycle models13 14 instead of bipolar glaciation we find that oi 1 is best explained by antarctic glaciation alone combined with deep sea cooling of up to 4 c and antarctic ice that is less isotopically depleted 30 to 35 than previously suggested15 16 proxy co2 estimates remain above our model s northern hemispheric glaciation threshold of 280 p p m v until 25 myr ago but have been near or below that level ever since10 11 this implies that episodic northern hemispheric ice sheets have been possible some 20 million years earlier than currently assumed although still much later than oi 1 and could explain some of the variability in miocene sea level records

variability in arctic sea ice drift 1 analysis of arctic sea ice drift from 1979 1997 using a lagrangian perspective shows the complexities of ice drift response to variations in atmospheric conditions changes in ice dynamics influence the redistribution of ice and any transported material from different source areas sources of ice exported to fram strait shifted in about 1986 87 from dominance of the kara sea and severnaya zemlya to the new siberian islands east siberian sea and chukchi sea average travel time of multiyear ice within the perennial pack of the central arctic basin reached a maximum in 1987 88 and decreased by at least 1 year between 1984 1989 and 1990 1997 consistent with the observations of other investigators this decrease in ice travel time occurred following a major export or surge of old ice to fram strait from the beaufort gyre in 1988 through 1990 which decreased the fraction of thick ridged ice within the central basin

sediments in arctic sea ice implications for entrainment transport and release despite the arctic sea ice cover s recognized sensitivity to environmental change the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood sea ice sediment inclusions were studied in the central arctic ocean during the arctic 91 expedition and in the laptev sea east siberian arctic region expedition 1992 results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central arctic ocean this study documents the regional distribution and composition of particle laden ice investigates and evaluates processes by which sediment is incorporated into the ice cover and identifies transport paths and probable depositional centers for the released sediment in april 1992 sea ice in the laptev sea was relatively clean the sediment occasionally observed was distributed diffusely over the entire ice column forming turbid ice observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment in the central arctic ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes the surface sediment accumulation in central arctic multi year sea ice exceeds by far the amounts observed in first year ice from the laptev sea in april 1992 sea ice sediments are generally fine grained although coarse sediments and stones up to 5 cm in diameter are observed component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles the biogenous components namely shells of pelecypods and benthic foraminiferal tests point to a shallow benthic marine source area apparently sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing clay mineralogy of ice rafted sediments provides information on potential source areas a smectite maximum in sea ice sediment samples repeatedly occurred between 81 n and 83 n along the arctic 91 transect indicating a rather stable and narrow smectite rich ice drift stream of the transpolar drift the smectite concentrations are comparable to those found in both laptev sea shelf sediments and anchor ice sediments pointing to this sea as a potential source area for sea ice sediments in the central arctic ocean sea ice clay mineralogy is significantly different from deep sea clay mineral distribution patterns the contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms

pollen analysis of coprolites from a late pleistocene holocene cave deposit wezmeh cave west iran insights into the late pleistocene and late holocene vegetation and flora of the central zagros mountains abstract coprolite pollen analysis is increasingly used by palynologists to reconstruct the palaeovegetation especially in the arid to semi arid regions where lakes and peat bogs are scarce this study is the first palynological analysis of coprolites in iran to examine their potential in palaeoenvironmental reconstructions four pollen rich coprolite samples were studied from the wezmeh cave in western iran with a recently discovered late quaternary 70 ka to sub recent faunal assemblage dominated by carnivore remains pollen analysis of coprolites shows that a mountain steppe dominated the glacial landscapes of the area only one sub recent sample indicates the presence of dispersed tree stands one sample was rich in tulipa pollen suggesting that tulips were relatively abundant during the glacial periods cousinia asteraceae pollen was found in all samples with considerable values in one sample indicating its importance in the glacial landscapes of the zagros mountains this study revealed that coprolite pollen analysis can provide an invaluable source of information to understand the floristic composition of palaeolandscapes of the irano turanian region

not only hyenids a multi scale analysis of upper pleistocene carnivore coprolites in cova del coll verdaguer ne iberian peninsula three morphotypes of fossil fecal material coprolites have been identified from the upper pleistocene site of cova del coll verdaguer ne iberian peninsula coprolites are commonly found in pleistocene records and also in places in which human and carnivore activities co occurred however coprolite identification is typically limited to hyenids the most readily recognizable fossilized feces owing to their distinctive shape and good preservation although non hyena carnivore coprolites are also likely to be present in these assemblages several criteria for a multi scale integrative analysis are proposed here for discriminating different morphotypes hence this analysis provides an opportunity to assess the involvement of several carnivores in bone accumulations to identify carnivores not specifically represented by skeletal remains and to evaluate interactions between humans and the carnivore guild especially medium and small carnivores

the airfall pollen budget of archaeologically important caves creswell crags england this paper investigates fundamental taphonomic issues for palynologists working on archaeologically important cave deposits the extent to which the pollen and spores reaching the accumulating sediment surfaces reflect the vegetation in cave entrances or reflect the more regional environments beyond the caves the study sites were four adjacent caves at creswell crags near sheffield england church hole dog hole c7 and robin hood s cave the compositions of the pollen and spore assemblages caught in the caves over a one year period were shown to reflect the vegetation in the cave mouths and the wider area beyond the ap nap ratio in the assemblages trapped in the caves corresponded with the proportions of woodland and open ground within a 5 km radius of the site comparatively high representations of fern spores in caves were a persistent feature and were attributed to the interactions of habitat distribution and taphonomic processes i the abundance of ferns in cave mouths and ii the effects produced by a combination of diurnal micro climatological process interacting with diurnal variations in spore production in the cave entrance in two caves church hole cave and dog hole cave the numbers of grains caught appeared to decline with increasing distance into the cave in cave c7 the numbers of grains caught increased towards the back of the cave the number of grains caught appears to be a principal determinant of the number of plant taxa identified there were no clear relationships between the presence of a flue effect in the cave and the presence of an increase or a decrease in the number of grains caught with changing distance into the caves it is concluded that as long as account is taken of the particular topographic microclimatic and taphonomic conditions in these caves it is possible to infer the character of the vegetation beyond their confines from the airfall pollen and spores trapped with them at the cave sediment surface

characterizing the 2d shape complexity dynamics of the islands of sundarbans bangladesh a fractal dimension approach fractal dimension index fdi and shape index si of the islands of bangladesh sundarbans situated at the estuarine part of the ganges brahmaputra meghna gbm delta were estimated with the aid of remote sensing techniques between the years 1989 and 2010 the main objective was to correlate the temporal change in these two indices within two decades with the possible geomorphic processes regulating these patterns the sundarban region is composed of almost 200 islands having self similar coastlines with fdi and si ranged from 1 002 to 1 202 and 1 016 to 7 546 respectively both fdi and si values along with their temporal change showed that the complexity and irregularity in the island shape increased in the northern and north eastern parts of the sundarbans while in the southern end it exhibited an opposite trend apart from a few exceptions the longer serrated coastlines of the north fdi 1 18 became more serrated and rough due to the predominant tidal effect particularly ebb tidal flow within the two decades the comparatively smoother coastlines of the southern islands fdi 1 18 became more compact and circular due to strong sea wave action during the same course of time the spatial variation in fdi was explained in terms of the relative elevation of the islands which was found to be lower in the northern part their differential response to rising sea level and the amplified tidal action in this funnel shaped estuary apart from changes in fractal dimension a net land loss of 60 km2 was observed within this island system during the study period these observations imply that with an increasing sea level rise the northern and southern parts of sundarbans island system will respond differentially resulting in inundation in northern area water encroachment in the low lying islands and land loss in the southern part erosion in the coastal boundary causing a severe loss of ecosystem services provided by the mangrove forest

vegetation reconstruction on the basis of pollen in late pleistocene hyena coprolites from san teodoro cave sicily italy vegetation reconstruction based on pollen from coprolites of extinct spotted hyena crocuta crocuta spelaea goldfuss 1832 recovered from excavations carried out in 1998 at san teodoro cave sicily italy supports previous indications of pre late glacial conditions eight of the twelve coprolites analysed contained well preserved pollen grains there is a general similarity between the pollen contents from the coprolites but they show variability they suggest a main vegetation type dominated by steppic taxa poaceae artemisia ephedra chenopodiaceae and asteraceae but also including arboreal taxa pinus and cupressaceae low percentages of pollen of mesophilous woody taxa quercus betula abies alnus pistacia among others are noticeable suggesting the existence of nearby refugia for temperate and mediterranean vegetation a reconstruction of the landscape using the coprolite pollen record and other pollen records from sicily and south italy shows the predominance during the pre late glacial of a wooded steppe biome with elements representing a variety of local environmental conditions

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

fractal geometry in the san andreas fault system it has been noted that the spatial distribution of earthquakes and the mode of strain release in the san andreas fault system is related to the complexity of fault geometry because of their rough appearance over many length scales faults can be regarded as fractal surfaces direct estimates of fractal dimension d of portions of the san andreas fault system between the northern gabilan range and the salton sea including the postulated extent of the great 1857 fort tejon earthquake are obtained from measured fault lengths analogous to the lengths of coastlines as discussed by mandelbrot regions characterized by complicated fault geometry are associated with larger values of d based on fault traces mapped at a scale of 1 750 000 d is 1 3 for this reach of the fault defined as a 30 km wide band about a main fault trace for that part near parkfield which could be associated with the nucleation of the 1857 earthquake d is 1 1 at this same scale d is 1 4 for the san andreas and related faults near san bernardino where the 1857 rupture stopped compared to 1 2 for the san andreas san juan fault segments near the point of arrest of the 1966 parkfield earthquake at finer map scales 1 24 000 and 1 62 500 critical lengths of 500 m and 1 km are identified which might relate to the extent of off san andreas fault offsets the critical lengths also suggest that fault geometry is not self similar if this fractal geometry persists through the seismic cycle it may be possible to use a quantitative measure of complexity to explain the occurrence of great and characteristic earthquakes along a given reach of fault

pliocene warmth polar amplification and stepped pleistocene cooling recorded in ne arctic russia understanding the evolution of arctic polar climate from the protracted warmth of the middle pliocene into the earliest glacial cycles in the northern hemisphere has been hindered by the lack of co

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures

continental ice in greenland during the eocene and oligocene the eocene and oligocene epochs approximately 55 to 23 million years ago comprise a critical phase in earth history an array of geological records supported by climate modelling indicates a profound shift in global climate during this interval from a state that was largely free of polar ice caps to one in which ice sheets on antarctica approached their modern size however the early glaciation history of the northern hemisphere is a subject of controversy here we report stratigraphically extensive ice rafted debris including macroscopic dropstones in late eocene to early oligocene sediments from the norwegian greenland sea that were deposited between about 38 and 30 million years ago our data indicate sediment rafting by glacial ice rather than sea ice and point to east greenland as the likely source records of this type from one site alone cannot be used to determine the extent of ice involved however our data suggest the existence of at least isolated glaciers on greenland about 20 million years earlier than previously documented at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher

central arctic surface ocean environment during the past 80 000 years stable oxygen and carbon isotope and sedimentological paleontological investigations supported by accelerator mass spectrometry 14 c datings were carried out on cores from north of 85 degrees n in the eastern central arctic ocean significant changes in accumulation rates provenance of ice rafted debris ird and planktic productivity over the past 80 000 years are documented during peak glacials i e oxygen isotope stages 4 and 2 the arctic ocean was covered by sea ice with decreased seasonal variation limiting planktic productivity and bulk sedimentation rates in early stage 3 and during termination i major deglaciations of the circum arctic regions caused lowered salinities and poor oxygenation of central arctic surface waters a meltwater spike and an associated ird peak dated to similar to 14 12 14 c ka can be traced over the southern eurasian basin of the arctic ocean this event was associated with the early and rapid deglaciation of the marine based barents sea ice sheet a separate termination ib meltwater event is most conspicuous in the central arctic and is associated with characteristic dolomitic carbonate ird this lithology suggests an origin of glacial ice from northern canada and northern greenland where lower paleozoic platform carbonates crop extensively out

origin and development of artemisia asteraceae in asia and its implications for the uplift history of the tibetan plateau a review abstract the spatial and temporal evolution of artemisia and its relationship with the tibetan plateau tp uplift are examined by summarizing pollen data from 122 sites across china the pollen morphological data reveal that artemisia may have originated from the arid semiarid middle latitudes of asia in the late eocene and spread west and east in the oligocene as the result of early uplift of the tibetan plateau and the global cooling during the miocene artemisia reached the southeastern part of the tp and became common in the western tp due to the high elevation in these regions at the same time the asian monsoon prevented the spread of artemisia to the southern part of the tp since the pliocene especially in the pleistocene artemisia distribution was very similar to its current distribution which indicates that the topography of the tp and the paleoenvironmental conditions in the east asia became more like today thus the cenozoic origin and evolution of artemisia in the asia was strongly influenced by the uplift of the tp global cooling as well as monsoon development

eocene north south trending dikes in central tibet new constraints on the timing of east west extension with implications for early plateau uplift east west extension has been a prominent feature of cenozoic tectonics in central southern tibet and the onset of this extension has been interpreted as indicating the surface uplift of the tibetan plateau to a critical level previous studies suggested that extension started in the neogene between 18 13 ma and 8 ma based on dating results from north south trending normal faults grabens or rifts and dikes we report here the discovery of widespread north south trending diabase and andesitic porphyry dikes in and around the shuang hu graben central tibet where crustal extension has previously been argued to start from 13 5 ma based on mineral ages from graben bounding faults our results show that dikes in this area were mainly formed in the eocene 47 38 ma geochemical and nd sr isotopic data suggest that the diabase dikes originated from partial melting of an enriched lithospheric mantle source metasomatized by melts from subducted continental crust and the andesitic porphyry dikes were probably derived from interactions between the subducted continental crust derived melts and the mantle given that north south trending eocene dikes are found widely dispersed in central tibet we argue that the onset of east west extension and likely regional uplift of the tibetan plateau began much earlier than previously thought our study implies that a large part of the tibetan plateau had already attained near maximum elevation in the eocene and is consistent with recent investigations regarding the middle late eocene 47 34 ma initiation of aridification in asia evidence from contemporary global oceanic o sr isotope curves and temperatures and the carbon cycle 2010 elsevier b v

variable eocene miocene sedimentation processes and bottom water redox conditions in the central arctic ocean iodp expedition 302 abstract in 2004 integrated ocean drilling program expedition 302 arctic coring expedition acex to the lomonosov ridge drilled the first central arctic ocean sediment record reaching the uppermost cretaceous 430 m composite depth while the neogene part of the record is characterized by grayish yellowish siliciclastic material the paleogene part is dominated by biosiliceous black shale type sediments the lithological transition between paleogene and neogene deposits was initially interpreted as a single sedimentological unconformity hiatus of 26 ma duration separating eocene from miocene strata more recently however continuous sedimentation on lomonosov ridge throughout the cenozoic was proclaimed questioning the existence of a hiatus in this context we studied the elemental and mineralogical sediment composition around the paleogene neogene transition at high resolution to reconstruct variations in the depositional regime e g wave current activity detrital provenance and bottom water redox conditions already below the hiatus mineralogical and geochemical proxies imply drastic changes in sediment provenance and or weathering intensity in the hinterland and point to the existence of another earlier gap in the sediment record the sediments directly overlying the hiatus the zebra interval are characterized by pronounced and abrupt compositional changes that suggest repeated erosion and re deposition of material regarding redox conditions euxinic bottom waters prevailed at the eocene lomonosov ridge and became even more severe directly before the hiatus with detrital sedimentation rates decreasing authigenic trace metals were highly enriched in the sediment this continuous authigenic trace metal enrichment under persistent euxinia implies that the arctic trace metal pool was renewed continuously by water mass exchange with the world ocean so the eocene arctic ocean was not fully restricted above the hiatus extreme positive ce anomalies are clear signs of a periodically well oxygenated water column but redox conditions were highly variable during deposition of the zebra interval significant mn enrichments only occur above the zebra interval documenting the miocene establishment of stable oxic conditions in the arctic ocean in summary extreme and abrupt changes in geochemistry and mineralogy across the studied sediment section do not suggest continuous sedimentation at the lomonosov ridge around the eocene miocene transition but imply repeated periods of very low sedimentation rates and or erosion

a global synthesis of the marine and terrestrial evidence for glaciation during the pliocene epoch abstract the pliocene climate is globally warm and characterised by high atmospheric carbon dioxide concentrations yet the terrestrial and marine scientific communities have gathered considerable evidence for substantial glaciation events in both the northern and southern hemisphere prior to the quaternary evidence on land is fragmentary but marine records of glaciation present a more complete history of pliocene glaciation here we present a global compilation of the terrestrial and marine glacial evidence for the pliocene and demonstrate four glaciation events that can be identified in the southern and or northern hemisphere prior to the latest pliocene intensification of northern hemisphere glaciation there are two globally recognisable glacial events in the early pliocene c 4 9 4 8 ma and c 4 0 ma one event around the early late pliocene transition c 3 6 ma and one event during marine isotope stage m2 c 3 3 ma long term climate cooling decreasing carbon dioxide concentrations in the atmosphere and high climate sensitivity in the pliocene probably facilitated each glaciation event however the mechanisms behind the early pliocene glacial events are unclear the global glaciation at c 3 3 ma may be caused by changes in ocean gateways whereas the decline in carbon dioxide concentrations is important for the latest pliocene intensification of northern hemisphere glaciation

lonestones as indicators of tsunami deposits in deep sea sedimentary rocks of the miocene morozaki group central japan abstract lonestones are isolated larger clasts enclosed in muddy fine grained deposits and are usually interpreted as iceberg rafted dropstones this interpretation implies the existence of glaciers continental ice sheets and consequently a cool climate however alternative interpretations are possible as lonestones may also be deposited by non glacial processes therefore clarification of the depositional processes associated with lonestones is fundamental for studies based on lonestone bearing deposits a field survey of lonestone bearing deposits from early miocene deep sea sedimentary rocks found around the chita peninsula of central japan suggests that tsunami induced flows on the sea bottom may also form lonestones these lonestones are associated with sandy to gravelly deposits and were deposited by high energy episodic currents the main features of these deposits are the multiple stacking of normally graded units and the laterally discontinuous distribution of coarse grained clastic material sands and gravels such features are consistent with deposition by tsunamis and suggest that lonestone bearing depositional successions must be carefully interpreted especially where lonestones are used as glacial indicators as some lonestones were probably put in place by ancient tsunami events

the heartbeat of the oligocene climate system a 13 million year continuous record of oligocene climate from the equatorial pacific reveals a pronounced heartbeat in the global carbon cycle and periodicity of glaciations this heartbeat consists of 405 000 127 000 and 96 000 year eccentricity cycles and 1 2 million year obliquity cycles in periodically recurring glacial and carbon cycle events that climate system response to intricate orbital variations suggests a fundamental interaction of the carbon cycle solar forcing and glacial events box modeling shows that the interaction of the carbon cycle and solar forcing modulates deep ocean acidity as well as the production and burial of global biomass the pronounced 405 000 year eccentricity cycle is amplified by the long residence time of carbon in the oceans

a statistical approach to source determination of lithic and fe oxide grains an example from the alpha ridge arctic ocean abstract discriminant function analysis dfa of microprobe data on 12 elements in nine fe oxide mineral types was used to match each fe oxide grain from an arctic ocean core to similarly analyzed grains in probable source areas for ice rafted detritus this approach to provenance allows us to determine the proportion of multiple sources with a high degree of statistical probability counts of microscopically identified dropstones 250 m from centimeter thick samples of the core and from source area samples provide a direct link to the sediment source multiple types of dfa e g direct vs stepwise on the dropstone data provide slightly different sources for many samples from the core this is due to multiple sources for each core sample and provides a more accurate picture of ources than one dfa procedure alone most of the lithic grains were derived from the northwestern queen elizabeth islands centered around ellef ringnes island and from the vicinity of victoria and banks islands whereas the microprobe data from individual fe oxide grains led to these same source areas they always showed that several sources contributed to each centimeter thick core sample significant input from both the dominant source areas to the same intervals in the core indicates that the ice sheets or ice caps covering these different areas coexisted during several pre wisconsin glaciations

cooling mediterranean sea surface temperatures during the late miocene provide a climate context for evolutionary transitions in africa and eurasia abstract in the late miocene grasslands proliferated succulent plants diversified in the mid latitudes and the desert like conditions appeared in the sahara despite this major environmental change on land the coeval deep sea oxygen isotope record does not provide evidence for significant high latitude cooling or continental ice growth making it difficult to relate widespread terrestrial environmental change to global climatic changes a u 37 k derived sea surface temperature sst reconstruction spanning 13 to 6 ma from uplifted hemipelagic sediments in northern italy provides the first continuous mid latitude temperature record with which to compare the evolution of aridity and biotic events at similar latitudes in northern africa and pakistan between 13 and 8 8 ma mediterranean sst lay near the upper limit of the alkenone temperature proxy 28 c exceeding modern sst at the site by as much as 10 c throughout the record sapropel layers correspond to local sst maxima suggesting that late miocene hydrological conditions in the mediterranean responded to insolation forcing via mechanisms similar to those documented for the plio pleistocene mediterranean sst cooled rapidly beginning at 8 ma with an episode of intense cooling to 19 c between 7 2 ma and 6 6 ma followed by a rebound to 25 c preceding the messinian salinity crisis at 5 9 ma these observations establish for the first time a direct relationship between increasing aridity in the northern hemisphere mid latitudes and significant cooling evidently this cooling was not accompanied by significant growth in continental ice volume the extreme warmth and subsequent cooling of the mediterranean sea are not well represented in current late miocene climate models which our results suggest underestimate regional warmth prior to the late miocene cooling evidence of secular cooling during the late miocene gives new support to the much debated link between a possible decline in atmospheric co2 levels and late miocene changes in vegetation on land

production of giant marine diatoms and their export at oceanic frontal zones implications for si and c flux from stratified oceans from a synthesis of recent oceanic observations and paleo data it is evident that certain species of giant diatoms including rhizosolenia spp thalassiothrix spp and ethmodiscus rex may become concentrated at oceanic frontal zones and subsequently form episodes of mass flux to the sediment within the nutrient bearing waters advecting towards frontal boundaries these species are generally not dominant but they appear selectively segregated at fronts and thus may dominate the export flux ancient thalassiothrix diatom mat deposits in the eastern equatorial pacific and beneath the polar front in the southern ocean record the highest open ocean sedimentation rates ever documented and represent vast sinks of silica and carbon several of the species involved are adapted to a stratified water column and may thrive in deep chlorophyll maxima thus in oceanic regions and or at times prone to enhanced surface water stratification e g during meltwater pulses they provide a mechanism for generating substantial biomass at depth and its subsequent export with concomitant implications for si export and c drawdown this ecology has important implications for ocean biogeochemical models suggesting that more than one diatom functional type should be used in spite of the importance of these giant diatoms for biogeochemical cycling their large size coupled with the constraints of conventional oceanographic survey schemes and techniques means that they are undersampled an improved insight into these key species will be an important prerequisite for enhancing our understanding of marine biogeochemical cycling and for assessing the impacts of climate change on ocean export production

an exclusively hyena collected bone assemblage in the late pleistocene of sicily taphonomy and stratigraphic context of the large mammal remains from san teodoro cave north eastern sicily italy a detailed taphonomic analysis of the large mammal assemblage from 1998 to 2006 excavations at san teodoro cave is presented taking into account the stratigraphic context of the deposits three not strictly contemporary fossiliferous levels having different lithological features have been detected here named b i b ii and b iii fossil remains are prevalently accumulated in b i and b ii the three levels are characterized by evidence of crocuta crocuta spelaea occupation represented by their skeletal remains coprolites and distinctive damages on the bones similar to fossil and modern spotted hyena dens from europe and africa a differential distribution of coprolites and small digested bones probably due to different humidity conditions has been recognized in b i and b ii and can be related to different topographic locations within the cave or to different climate conditions during the sedimentation phases the very low density of fossil remains in b iii which is the oldest level could indicate an area that was less inhabited by hyenas probably due to geomorphological conditions taphonomic comparison of the three fossiliferous levels of the san teodoro cave deposits points to a long term perhaps cyclic occupation of the cave by hyenas and confirms the cave as one of the most important pleistocene hyena dens in europe

early and middle miocene stable isotopes implications for deepwater circulation and climate the middle miocene 18o increase represents a fundamental change in the ocean atmosphere system which like late pleistocene climates may be related to deepwater circulation patterns there has been some debate concerning the early to early middle miocene deepwater circulation patterns specifically recent discussions have focused on the relative roles of northern component water ncw production and warm saline deep water originating in the eastern tethys our time series and time slice reconstructions indicate that ncw and tethyan outflow water two relatively warm deepwater masses were produced from 20 to 16 ma ncw was produced again from 12 5 to 10 5 ma another feature of the early and middle miocene oceans was the presence of a high 13c intermediate water mass in the southern hemisphere which apparently originated in the southern ocean miocene climates appear to be related directly to deepwater circulation changes deep waters warmed in the early miocene by 3 c 20 to 16 ma and cooled by a similar amount during the middle miocene 18o increase 14 8 to 12 6 ma corresponding to the increase 20 ma and subsequent decrease 16 ma in the production of ncw and tethyan outflow water large 0 6 relatively rapid 0 5 m y 18o increases in both benthic and planktonic foraminifera i e the mi zones of miller et al 1991a and wright and miller 1992a were superimposed in the long term deepwater temperature changes they are interpreted as reflecting continental ice growth events seven of these m y glacial interglacial cycles have been recognized in the early to middle miocene two of these glacial interglacial cycles mi3 and mi4 combined with a 2 to 3 c decrease in deepwater temperatures to produce the middle miocene 18o shift

cenozoic global sea level sequences and the new jersey transect results from coastal plain and continental slope drilling the new jersey sea level transect was designed to evaluate the relationships among global sea level eustatic change unconformity bounded sequences and variations in subsidence sediment supply and climate on a passive continental margin by sampling and dating cenozoic strata from coastal plain and continental slope locations we show that sequence boundaries correlate within 0 5 myr regionally onshore offshore and interregionally new jersey alabama bahamas implicating a global cause sequence boundaries correlate with 18o increases for at least the past 42 myr consistent with an ice volume glacioeustatic control although a causal relationship is not required because of uncertainties in ages and correlations evidence for a causal connection is provided by preliminary miocene data from slope site 904 that directly link 18o increases with sequence boundaries we conclude that variation in the size of ice sheets has been a primary control on the formation of sequence boundaries since 42 ma we speculate that prior to this the growth and decay of small ice sheets caused small amplitude sea level changes 20 m in this supposedly ice free world because eocene sequence boundaries also appear to correlate with minor 18o increases subsidence estimates backstripping indicate amplitudes of short term million year scale lowerings that are consistent with estimates derived from 18o studies 25 50 m in the oligocene middle miocene and 10 20 m in the eocene and a long term lowering of 150 200 m over the past 65 myr consistent with estimates derived from volume changes on mid ocean ridges although our results are consistent with the general number and timing of paleocene to middle miocene sequences published by workers at exxon production research company our estimates of sea level amplitudes are substantially lower than theirs lithofacies patterns within sequences follow repetitive predictable patterns 1 coastal plain sequences consist of basal transgressive sands overlain by regressive highstand silts and quartz sands and 2 although slope lithofacies variations are subdued reworked sediments constitute lowstand deposits causing the strongest most extensive seismic reflections despite a primary eustatic control on sequence boundaries new jersey sequences were also influenced by changes in tectonics sediment supply and climate during the early to middle eocene low siliciclastic and high pelagic input associated with warm climates resulted in widespread carbonate deposition and thin sequences late middle eocene and earliest oligocene cooling events curtailed carbonate deposition in the coastal plain and slope respectively resulting in a switch to siliciclastic sedimentation in onshore areas oligocene sequences are thin owing to low siliciclastic and pelagic input and their distribution is patchy reflecting migration or progradation of depocenters in contrast miocene onshore sequences are thicker reflecting increased sediment supply and they are more complete downdip owing to simple tectonics we conclude that the new jersey margin provides a natural laboratory for unraveling complex interactions of eustasy tectonics changes in sediment supply and climate change

response of sea ice to the arctic oscillation abstract data collected by the international arctic buoy programme from 1979 to 1998 are analyzed to obtain statistics of sea level pressure slp and sea ice motion sim the annual and seasonal mean fields agree with those obtained in previous studies of arctic climatology the data show a 3 hpa decrease in decadal mean slp over the central arctic ocean between 1979 88 and 1989 98 this decrease in slp drives a cyclonic trend in sim which resembles the structure of the arctic oscillation ao regression maps of sim during the wintertime january march ao index show 1 an increase in ice advection away from the coast of the east siberian and laptev seas which should have the effect of producing more new thin ice in the coastal flaw leads 2 a decrease in ice advection from the western arctic into the eastern arctic and 3 a slight increase in ice advection out of the arctic through fram strait taken together these changes suggest that at least part of the thinning of sea ice recently observed ov

cyclicity in the middle eocene central arctic ocean sediment record orbital forcing and environmental response 1 continuous x ray fluorescence scanning of middle eocene 46 ma core m0002a 55x 236 241 m composite depth recovered during integrated ocean drilling program expedition 302 revealed a strong cyclical signal in some major and trace geochemical elements we performed a multiproxy study of the same core which included organic geochemical sedimentological and biological parameters and integrated our results with available geochemical and physical properties data the target was to look for cyclicity in the several proxies investigate their frequency and understand the environmental response to the potential forcing results indicate that a higher terrigenous component corresponds to lower organic carbon concentration smaller contributions by angiosperm pollen and spores organic walled dinoflagellate cysts and chrysophyte cysts lower productivity shorter growing season for flowering plants and lower stratification but higher contributions by bisaccate pollen and diatoms drier conditions on land more marine conditions and higher terrigenous sand ice rafted debris ird our investigation shows that physical proxy parameters hold cyclicity with periods of about 50 and 100 cm and that these frequency components are compatible with a milankovitchtype orbital forcing representing precession and obliquity respectively the longer 100 cm cyclicity is also present in the biological pollen dinoflagellate cysts and siliceous microfossils and in the sedimentological ird proxies the environmental signal derived from the integrated multiproxy analysis suggests that in an enclosed arctic ocean at time of ice sea ice and glacial ice initiation the biological proxies responded more strongly to growing season length darkness whereas the terrigenous components directly driven by sea ice and or glacial ice formation and extent responded more directly to seasonal insolation

orphan arctic ocean metasediment clasts local derivation from alpha ridge or pre 2 6 ma ice rafting phyllonite and metaquartzite clasts occur in early pliocene or possibly miocene sediment at the base of the university of wisconsin arctic ocean core fl 380 single crystal 40 ar 39 ar laserprobe ages derived from feldspars in sediment enclosing the clasts range from middle and late proterozoic to paleozoic the clasts occur in sediment deposited 1 2 m y earlier than any previously reported central arctic ocean ice rafted debris and although an ice rafted origin may be possible a local source such as adjacent alpha ridge bedrock should also be considered

history of the greenland ice sheet paleoclimatic insights abstract paleoclimatic records show that the greenland ice sheet consistently has lost mass in response to warming and grown in response to cooling such changes have occurred even at times of slow or zero sea level change so changing sea level cannot have been the cause of at least some of the ice sheet changes in contrast there are no documented major ice sheet changes that occurred independent of temperature changes moreover snowfall has increased when the climate warmed but the ice sheet lost mass nonetheless increased accumulation in the ice sheet s center has not been sufficient to counteract increased melting and flow near the edges most documented forcings and ice sheet responses spanned periods of several thousand years but limited data also show rapid response to rapid forcings in particular regions near the ice margin have responded within decades however major changes of central regions of the ice sheet are thought to require centuries to millennia the paleoclimatic record does not yet strongly constrain how rapidly a major shrinkage or nearly complete loss of the ice sheet could occur the evidence suggests nearly total ice sheet loss may result from warming of more than a few degrees above mean 20th century values but this threshold is poorly defined perhaps as little as 2 c or more than 7 c paleoclimatic records are sufficiently sketchy that the ice sheet may have grown temporarily in response to warming or changes may have been induced by factors other than temperature without having been recorded

environmental change in the subtropics during the late middle eocene greenhouse and global implications 1 oxygen isotope records from odp site 1052 blake nose subtropical north atlantic ocean indicate significant short term high amplitude variability up to 1 4 in about 2500 to 4000 years during the late middle eocene 37 9 37 5 ma these variations reflect a combination of changes in sea surface temperature and the oxygen isotope composition of the regional seawater in order to independently evaluate the magnitude of sst changes at blake nose and better understand the nature of environmental change during the late middle eocene we present planktonic foraminiferal mg ca data combined with 18o data from the same samples the calculated mg ca paleotemperatures indicate a decrease in ssts over the study interval from 33 to 28 c at the same time that previously published foraminiferal 18ocalcite values from the same samples also decrease thus the 18ocalcite values must reflect a significant component of seawater 18o change in order to reconcile the opposite paleotemperature trends reflected by both proxies calculated 18oseawater values decreased from 3 at 37 83 ma to 2 at 37 6 ma the combined trends of the sst and 18oseawater cannot be explained by an increase of continental ice over this time interval instead the data favor an overall weakening of the hydrological cycle as global climate transitioned from the greenhouse to icehouse

arctic ocean chronology confirmed by accelerator 14c dating the role of the arctic ocean in earth s climatic and oceanographic development is significant but has become controversial because of disagreements concerning a reliable arctic chronology the first arctic ocean chronology based on u th and 14c data was in agreement with magnetostratigraphy developed later but these data have been challenged by recent amino acid diagenesis dates new accelerator 14c data support the earlier u th magnetostratigraphic dates and confirm the reliability of the established arctic ocean chronology

cenozoic ice rafting history of the central arctic ocean terrigenous sands on the lomonosov ridge the cenozoic ice rafted debris ird history of the central arctic is reconstructed utilizing the terrigenous coarse sand fraction in iodp 302 cores from 0 to 273 meters composite depth this holocene middle eocene quantitative record of terrigenous sand accumulation on the lomonosov ridge along with qualitative information on grain texture and composition confirms the interpretation that ice initiation sea ice and glacial ice occurred 46 ma in the arctic and provides a long term pattern of arctic ice expansion and decay since the middle eocene ird mass accumulation rates range from 0 to 0 13 g cm2 ka in the middle eocene and from 0 to 0 36 g cm2 ka in the neogene ird mass accumulation rate mar maxima in the miocene and pliocene cooccur with either glacial initiation or intensification in the sub arctic the 46 25 ma ird onset in the central arctic slightly precedes the earliest evidence of ice in the antarctic and compares in timing with a 1000 ppm decrease in atmospheric concentrations of co2 the decline of pco2 in the middle eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface arctic ocean especially during times of low insolation

southward shift of the intertropical convergence zone due to northern hemisphere cooling at the oligocene miocene boundary the mi 1 glaciation ca 23 ma which marks the oligocene miocene boundary was an aberrant cooling event that led to a build up of the antarctic ice sheet which reached the near modern volume or greater from its ephemeral or partial existence an increase of 1 in the 18o of benthic foraminifera during this interval has been attributed to the development of antarctic ice sheets and deep water cooling without definitive evidence northern hemisphere nh glaciation has not been a material consideration for the 18o increase here we investigate the interhemispheric temperature contrast during mi 1 with the movement of the intertropical convergence zone itcz at a site 10 31 n in the east pacific integrated ocean drilling program site u1333 to understand nh cooling and the possibility of nh glaciation the measured 143nd 144nd 87sr 86sr and clay mineral compositions of eolian dust fractions indicate unequivocally the deposition of asian dust during mi 1 and of central american and south american dust before and after mi 1 this is attributed to the southward displacement of the itcz over site u1333 during mi 1 the itcz shifts toward the warmer hemisphere thus our results suggest that the cooling during mi 1 was more significant in the nh than in the southern hemisphere which underwent a sudden expansion of continental ice sheets our data call for a forcing mechanism to drive significant nh cooling during this episode based on the available data we propose that the widespread growth of nh ice sheets and or changes in the production of north atlantic origin deep water could be possible causes of the nh cooling at that time

characterization and depositional evolution of hyaena crocuta crocuta coprolites from la valina cave northwest spain archaeological excavation of la valina site a karstic cave located in northwest spain documented a level of human occupation and a later one of carnivores that can be attributed to upper plesitocene 35 000 bp by the 14 c dating obtained from bone samples among carnivore remains many coprolites were recovered which based on morphological and biometrical characteristics correspond to crocuta crocuta micromorphological analysis of thin sections mineralogical and palynological analysis let us deduce the deposition period of scats during the year and also the postdepositional changes undergone by coprolites to reach their present state

the transitional climate of the late miocene arctic winter dominated precipitation with high seasonal variability the late miocene 11 6 5 3 ma was an important transitional period following the greenhouse conditions of the eocene in order to gain insight into the arctic paleoclimate of the time we performed high resolution intraring 13 c analyses on fossil wood collected from the late miocene khapchansky sediments of northeastern siberia 69 n from these data we quantified the ratio of summer to winter precipitation ps pw and compared it to current values for the region determined from modern wood samples and instrumental records we observed much greater frequency of winter dominated precipitation ps pw 1 and much greater variability in ps pw during the miocene than today specifically years with ps pw 1 occurred three times more often and years with at least three times as much precipitation in summer or winter 0 33 ps pw 3 0 occurred approximately twice as often during the miocene than today we attribute the high interannual variability in precipitation to an inconsistent moisture source associated with the relatively unstable and incomplete ice cover in the arctic ocean during the late miocene our result highlights the potential for enhanced variability in arctic precipitation in response to arctic sea ice decline caused by anthropogenic co 2 induced warming

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

variability in the length of the sea ice season in the middle eocene arctic finely laminated middle eocene sediments from the central arctic contain high abundances of the delicate sea ice dwelling fossil diatoms synedropsis spp and sea ice rafted debris sea ice ird establishing an offshore seasonal sea ice regime ca 47 ma synedropsis spp co occur with other diatom taxa and microfossils requiring open water this strongly indicates seasonality nonetheless seasonal reconstruction of the flux cycle cannot be resolved by standard bulk sediment analysis which destroys sedimentary fabrics and averages data within samples here we resolve and reconstruct seasonal scale flux events from these sediments using backscattered electron imagery bsei of resin embedded sediment a nondestructive technique that preserves the integrity of sedimentary microfabrics thus revealing discrete productivity flux events at ultrahigh e g 30 m resolution seasonality is expressed at the submillimeter scale by successions of discrete mono specific laminae and micro lenses of synedropsis spp terrigenous material sea ice ird and open water taxa indicating that first year ice existed in the central arctic further bsei reveals millimeter scale alternation of bundles of laminae and microlenses of two distinct types one characterized by synedropsis spp and terrigenous material the other by mainly open water taxa and little terrigenous material the sedimentation rate and preliminary assessment of annual cycles indicate suborbital variability on the order of multi decadal to centennial duration we argue that this reflects variations in the sea ice season length

middle miocene deepwater paleoceanography in the southwest pacific relations with east antarctic ice sheet development a suite of middle miocene deep sea drilling project sites in the southwest pacific reveals large scale changes in deepwater circulation associated with east antarctic ice sheet eais variations from 16 5 to 13 8 ma oxygen and carbon isotopic records based on cibicidoides benthic foraminifera from a depth transect sites 590b 588a 591b and 206 from 1200 to 3150 m paleodepth at 35 s paleolatitude and from a meridional transect sites 588a 590b 593 and 594 from 30 to 48 s paleolatitude at intermediate water depth allow detailed examination of southwest pacific deepwater circulation from 17 5 to 12 ma significantly intervals of low 18o from 16 5 to 16 3 ma and perhaps at 15 7 ma were marked by similar 18o values at upper bathyal 1200 1500 m sites 588a and 590b and midbathyal 2100 m site 591b water depths small vertical 18o gradients during 18o minima may indicate warm saline deep water wsdw at midbathyal depths in the southwest pacific during intervals of inferred global warmth and low global ice volume increased vertical 18o gradients after 15 6 ma and especially after 13 8 ma indicate increased production of southern component water scw in association with eais growth these data are consistent with the hypothesis woodruff and savin 1989 that major eais growth was fostered by diminished meridional heat transport to the high southern latitudes related to the termination of tethyan indian saline water tisw and an increase in scw production during the early middle miocene after 15 6 ma further a maximum vertical carbon isotopic gradient of 0 8 at 13 6 ma suggests that southern component intermediate water sciw production and pacific deep water pdw strength were each at a maximum at this time and were critical to major eais growth the establishment of near modern 13c and 18o gradients following major eais growth from 14 0 to 13 8 ma marks a major step in the development of the neogene ocean cryosphere system

fractal analysis of shoreline patterns for crenulate bay beaches southern china shoreline patterns of 34 crenulate bay beaches in southern china were investigated the differentiated criteria for log spiral shoreline curves offered by silvester am soc civ eng proc 96 1970 275 coastal engineering elsevier amsterdam 1974 338 and hsu et al j waterw port coast eng 115 1989 285 were used to determine the equilibrium morphology of each beach results show that the discriminated principles of the equilibrium log spiral curve were not suitable for all the beaches based on the theory of the log spiral stable curve and beach morphology and the dynamic action setting in southern china fractal analysis was adopted to classify the patterns in the shorelines it shows that shorelines include three modes dynamic balance of accretion static equilibrium and the dynamic balance of erosion

suspension freezing of bottom sediment and biota in the northwest passage and implications for arctic ocean sedimentation ice observations and sediment collected in a summer transit through the northwest passage provide insights on suspension freezing the most important sediment entrainment mechanism for the arctic ocean no evidence was seen for entrainment by bottom adfreezing bluff slumping river flooding dragging ice keels or significant eolian transport from land to sea lack of eolian sediment loading in the northwest passage together with that already reported for northern alaska eliminates wind as an important source for fine sediment in the pack of the beaufort gyre and related parts of the transpolar drift muddy sediment with pebbles and cobbles algae with holdfasts ostracodes with appendages and well preserved mollusks and sea urchins were collected from two sites in a 50 km long stretch of turbid ice these materials indicate that suspension freezing reaching to a water depth of 25 30 m during the previous fall was responsible for entrainment this mechanism requires rapid ice formation in open shallo

history of terrigenous sedimentation during the past 10 m y in the north atlantic odp legs 104 and 105 and dsdp leg 81 bulk sediment measurements and analyses of the input of 63 m terrigenous particles have enabled us to reconstruct the variability of sediment flux in the norwegian and the labrador seas as a function of paleoceanographic and paleoclimatic changes in both areas minor amounts of coarse terrigenous particles occur in sediments that were deposited between 9 5 and 7 0 ma the higher amounts are only documented in the norwegian sea around 5 7 5 4 ma variations in bulk sediment accumulation are related to a strengthening of denmark strait overflow which is closely connected with the production of norwegian sea deep water between 8 3 and 7 8 ma 6 9 and 6 1 ma and 5 3 and 4 2 ma in the labrador sea reduced bottom water activity coincided with the highest levels of organic carbon accumulation and an increase in bulk sediment accumulation and may correlate with the latest miocene messinian event in both the labrador sea and the norwegian sea a drastic increase in the amount of coarse terrigenous particles rock fragments and quartz started at around 4 0 ma recording a nearly simultaneous onset of large scale ice rafting this was ultimately caused by a deterioration in the northern hemisphere climate possibly related to the final closure of the isthmus of panama

sea ice feedback and cenozoic evolution of antarctic climate and ice sheets 1 the extent and thickness of antarctic sea ice have important climatic effects on radiation balance energy transfer between the atmosphere and ocean and moisture availability this paper explores the role of sea ice and related feedbacks in the cenozoic evolution of antarctic climate and ice sheets using a numerical climate model with explicit dynamical representations of sea ice and continental ice sheets in a scenario of decreasing cenozoic greenhouse gas concentrations our model initiates continental glaciation before any significant sea ice forms around the continent once variable ice sheets are established seasonal sea ice distribution is highly sensitive to orbital forcing and ice sheet geometry via the ice sheet s control on regional temperature and low level winds although the expansion of sea ice has significant climatic effects near the coast it has only minimal effects in the continental interior and on the size of the ice sheet therefore the cenozoic appearance of antarctic sea ice was primarily a response to the growth of grounded ice sheets and was not a critical factor in episodes of paleogene and neogene glaciation the influence of the east antarctic ice sheet on sea ice southern ocean surface temperatures and winds has important implications for ocean circulation the marine carbon cycle and the development of the west antarctic ice sheet the sensitivity of sea ice to grounded ice sheets implies reconstructions of sea ice based on marine diatoms are good indicators of glacial conditions in the continental interior and may provide insight into the long term stability of antarctic ice sheets

paleoceanographic and paleoclimatic constraints on the global eocene diatom and silicoflagellate record abstract eocene diatom and silicoflagellate biostratigraphy are summarized and correlated with the most recent geologic time scale as well as with the global oxygen isotope and eustatic sea level curves the global distribution of eocene diatom silicoflagellate bearing sediments varies considerably reflecting changing oceanic gateways and paleoceanography with changing patterns that are punctuated by four major depositional events event 1 49 million years ago ma at the end of the early eocene climatic optimum eeco saw the cessation of diatom silicoflagellate deposition in epicontinental regions of the north sea region and in the northern russia and the onset of biosilica deposition in the arctic event 2 46 ma which coincided with intensification of the middle eocene cooling trend marked the widespread expansion of diatom silicoflagellate deposition in both the north and south atlantic a shift of diatom silicoflagellate deposition from the atlantic to the pacific began at event 3 at the end of the middle eocene climatic optimum meco 40 ma that was likely tied to the initial opening of the drake passage between antarctica and south america event 4 39 ma coincided with a major sea level fall and a widespread deep sea hiatus in the latest middle eocene late eocene diatom silicoflagellate deposition became more concentrated in middle to high latitude regions and coastal upwelling regions particularly in the pacific ocean tabulation of the first and last occurrences of 132 biostratigraphically important diatoms suggests increased species turnover during the latest paleocene to earliest eocene that may be in part due to a monographic effect an increasing rate of evolution of new diatom species between 46 and 43 ma and after 40 ma coincides respectively with the widespread expansion of diatom deposition in the atlantic and with an increased pole to equator thermal gradient that witnessed the expansion of diatoms in high latitude oceans and coastal upwelling settings

imprint of late pleistocene continental processes visible in ice rafted grains from the central arctic ocean abstract ice rafted quartz sand grains of sediment samples representing marine isotope stages mis 3 and 4 from the lomonosov ridge arctic ocean are here analysed with a scanning electron microscope sem to characterise processes in the sediment source area the microtextural characteristics of the grains were observed and their microtexture frequencies calculated specific sets of microtextures were identified and classified group i iii using principal component analysis pca and cluster analysis the statistically analysed microtextural data were used to identify signals of continental processes that operated during the late pleistocene mis 4 to mis 3 in the eurasian arctic the microtextures of group i generally formed as a result of prolonged fluvial alluvial or aeolian transport the glacial microtextures of groups ii and iii indicate subglacial conditions and transport based on the data two principal components seem to characterise late pleistocene continental environmental conditions glacial and non glacial there is a signal of non glacial continental processes in the ice rafted grains at around 62 64 and 67 ka ago a signal of subglacial processes was observed in the grains at around 26 34 42 and 45 ka and concurrent with non glacial at around 62 and 64 ka ago we suggest that these signals in mis 4 sediments are related to deglaciation with an increased supply of glacial sediment to the arctic ocean whereas during mis 3 they were probably related more to iceberg calving from the oscillating barents kara ice sheet

sources and cycling of mercury in the paleo arctic ocean from hg stable isotope variations in eocene and quaternary sediments abstract mercury stable isotopic compositions were determined for marine sediments from eight locations in the arctic ocean basin mass dependent fractionation mdf and mass independent fractionation mif of hg stable isotopes were recorded across a variety of depositional environments water depths and stratigraphic ages 202hg mdf ranges from 2 34 to 0 78 199hg mif from 0 18 to 0 12 and 201hg mif from 0 29 to 0 05 for the complete data set n 33 holocene sediments from the chukchi sea and morris jesup rise record the most negative 199hg values while pleistocene sediments from the central arctic ocean record the most positive 199hg values the most negative 202hg values are recorded in pleistocene sediments eocene sediments lomonosov ridge show some overlap in their hg isotopic compositions with quaternary sediments with a sample of the arctic ocean petm 56 ma most closely matching the average hg isotopic composition of holocene arctic marine sediments collectively these data support a terrestrially dominated hg source input for arctic ocean sediment through time although other sources as well as influences of sea ice atmospheric mercury depletion events amdes and anthropogenic hg in core top samples on hg isotopic signatures must also be considered

late miocene biogeography and paleoclimatology of the central north atlantic abstract quantitative analyses of planktonic foraminiferal assemblages from deep sea drilling project dsdp holes 334 and 410 demonstrate that subpolar and subtropical faunal provinces existed in the north atlantic during the late miocene climatic oscillations are clearly recorded in hole 410 by variations in abundance of the neogloboquadrina subpolar assemblage these climatic oscillations have a period of about 1 m y higher frequency oscillations with a periodicity of one to several hundred thousand years are evident from about 6 5 to 7 5 m y and are probably present throughout the entire late miocene a revised age of 7 0 m y is proposed for the first occurrence of the calcareous nannofossil amaurolithus primus the amaurolithus datum

the evolution of climatically driven weathering inputs into the western arctic ocean since the late miocene radiogenic isotope evidence highlights seawater hf nd pb isotopic evolution in the deep arctic ocean of the past 7 myr climatically driven changes in weathering inputs since 4 ma north american laurentide ice sheet runoff controlled the isotopic budget in the canada basin more congruent hf release due to glacial weathering conditions past arctic ocean water masses show larger isotopic differences than today abstract we present the first continuous records of dissolved radiogenic neodymium hafnium and lead isotope compositions of deep waters in the western arctic ocean spanning the time from the late miocene to the present the data were obtained from three hydrogenetic ferromanganese fe mn crusts recovered from seamounts along the northernmost edge of the northwind ridge in the canada basin from water depths of 2200 2400 and 3600 m dating the crusts using cosmogenic 10be documents undisturbed present day growth surfaces and yields growth rates between 27 and 2 2 mm myr the nd hf isotope time series of the three crusts show similar evolutions from endend ehf ehf of 8 5 4 in the oldest parts to 11 5 4 at the surfaces and a pronounced trend to less radiogenic values starting at 4 ma this coincided with a trend of the pb isotope evolution towards more radiogenic 206pb 204pb 207pb 204pb and 208pb 204pb it is inferred that climatically controlled changes in weathering regime and sediment transport along the north american continent were responsible for the major change of the radiogenic isotope composition of the arctic deep water adw in the canada basin based on these records we conclude that weathering inputs from the north american continent linked to enhanced glacial conditions started to increase and to influence the radiogenic isotope composition of adw 4 million years ago and were further intensified at 1 ma these new time series differ markedly from the radiogenic isotope evolution of arctic intermediate water recorded on the lomonosov ridge and suggest that much larger isotopic differences between the water masses of the arctic ocean than today prevailed in the past

beryllium isotopes in central arctic ocean sediments over the past 12 3 million years stratigraphic and paleoclimatic implications the upper 200 m of the sediments recovered during iodp leg 302 the arctic coring expedition acex to the lomonosov ridge in the central arctic ocean consist almost exclusively of detrital material the scarcity of biostratigraphic markers severely complicates the establishment of a reliable chronostratigraphic framework for these sediments which contain the first continuous record of the neogene environmental and climatic evolution of the arctic region here we present profiles of cosmogenic 10be together with the seawater derived fraction of stable 9be obtained from the acex cores the down core decrease of 10be 9be provides an average sedimentation rate of 14 5 1 m ma for the uppermost 151 m of the acex record and allows the establishment of a chronostratigraphy for the past 12 3 ma the age corrected 10be concentrations and 10be 9be ratios suggest the existence of an essentially continuous sea ice cover over the past 12 3 ma

surface microtextures of ice rafted quartz grains revealing glacial ice in the cenozoic arctic abstract ice rafted grains of the central arctic ocean sediments provide a reliable proxy for arctic palaeoenvironments and climatic conditions that prevailed at the time of their deposition to understand ice involvement and implications for environmental advancement it has proven necessary to ascertain whether these detrital grains were rafted on glacial ice or sea ice surface microtexture identification allows grain differentiation based on the processes and conditions in its environmental provenance here quartz sand grain surface microtextures are used to detect glacially crushed and reworked grains from the lomonosov ridge sediments obtained by the integrated ocean drilling program expedition 302 arctic coring expedition the data show that the most frequent distributions of glacial grains were deposited at the middle late miocene and during the pliocene and early pleistocene especially the middle miocene climatic cooling and the presence of glacial ice are well indicated at 13 5 ma sediment grains earliest finding of the high frequency occurrence of glacigenic microtextures represents the age of 56 ma this first sedimentological evidence for the late palaeocene glacial ice supports the existing hypothesis of ephemeral polar glaciations during times of marked global warmth however due to lack of uninterrupted sediment recovery and non continuous nature of sampling the glacially influenced samples recovered here should be treated as an estimate of the minimum frequency of glacier appearance in the arctic

estimating short term changes in eustatic sea level the history of short term eustatic sea level change proposed by p r vail and his coworkers was originally based on shifts through time in the landward pinchout of seismic sequences in order to quantify the magnitude of these proposed sea level changes histories of subsidence sediment loading sediment compaction and paleowater depth are required of these accurate estimates of paleowater depth and subsidence are the most difficult to derive this approach is applied to two example data sets for one study the midway atoll we use the theoretical subsidence model of detrick et al 1981 the possible error in this model is approximately the same as the extreme differences in sea level highstands 50 100 m proposed by previous investigators the second example is from the baltimore canyon area here we estimate subsidence by an average angular tilt rate resulting estimates of sea level highstands for the past 30 ma are similar to the long term sea level estimates of kominz 1984 however the overall variation in the highstands parallels that of haq et al 1987 short term sea level falls are estimated to be similar in magnitude to those of haq et al 1987 most of these short term fluctuations are within the range of reasonable glacioeustatic fluctuations 30 100 m a correlation is found between the estimated short term changes in sea level and the miocene oxygen isotope record this correlation exists both prior to and after 14 ma however there is a 1 08 isotopic shift in the data in the middle miocene because estimated highstands are within 10 15 m of being the same magnitude before and after this shift we suggest that this shift is caused mainly by a cooling of deep waters

global cooling during the eocene oligocene climate transition about 34 million years ago earth s climate shifted from a relatively ice free world to one with glacial conditions on antarctica characterized by substantial ice sheets how earth s temperature changed during this climate transition remains poorly understood and evidence for northern hemisphere polar ice is controversial here we report proxy records of sea surface temperatures from multiple ocean localities and show that the high latitude temperature decrease was substantial and heterogeneous high latitude 45 degrees to 70 degrees in both hemispheres temperatures before the climate transition were 20 c and cooled an average of 5 c our results combined with ocean and ice sheet model simulations and benthic oxygen isotope records indicate that northern hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time

chemical fingerprinting a precise and efficient method to determine sediment sources abstract an accurate method of determining source locations for detrital sediment is presented using the chemical composition of fe oxide minerals like a fingerprint this method is an improvement in the use of fe oxide minerals for provenance determinations because it requires less time and fewer source samples a rigorous test of the method uses a database of more than 38 000 grains from known locations the average error of matching grains back to 45 source locations designated for this database is less than 2 the method allows for proportional matching of a grain to multiple sources if other grains in the source database meet the compositional match criteria which helps reduce the error of incorrect matches most provenance studies do not involve source basins as large as the entire arctic ocean where sediment can be ice rafted several thousand kilometers for most studies only a few samples 100 grain analyses sample would be required to characterize a source if strategically placed such as near a river mouth deposits more than 40 million years old can be traced to specific sources using this method because fe oxide grains are relatively stable in most deposits

leopards as taphonomic agents in the iberian pleistocene the case of raco del duc valencia spain bone accumulations created by carnivores during the pleistocene have been largely associated with the action of cave hyenas crocuta spelaea golfuss 1823 identified all over europe yet in recent years it has been shown that leopards panthera pardus linnaeus 1758 played a role in the creation of sites in the iberian peninsula in this study we present the taphonomic study of the bone accumulation of the pre solutrean level at the raco del duc cave south of the province of valencia where the dominant species capra pyrenaica schinz 1838 has been accumulated by leopards together with new data and other references taken from the bibliography we have summarised the main taphonomic characteristics of the sites accumulated by leopards the predator prey relationship has also been analysed and it has shown that during the pleistocene leopards in the iberian peninsula were specialised in catching goats showing similar behaviour to that of snow leopards said specialisation may have been due to the occupation of caves in steep areas where rupicolous fauna predominated

pollen analysis of hyena coprolites and sediments from equus cave taung southern kalahari south africa equus cave in quaternary tufa near taung in the semiarid woodland of the southern kalahari yielded 2 5 m of sediment in which a rich assemblage of bones and coprolites was preserved the fossils were accumulated mainly by hyenas during the late pleistocene and holocene pollen from coprolites reflects diet as well as vegetation over relatively large areas visited by hyenas while pollen from sediments represents more local sources the pollen sequence derived from coprolites and sediments demonstrates how the vegetation evolved from open grassland with small shrubs and occasional trees during the late pleistocene to open savanna with more small shurbs then during the last 7500 yr to modern savanna temperatures were not more than 4 c cooler and it was slightly moister than today during the late pleistocene phase it became gradually warmer but relatively dry before optimal temperature and moisture conditions developed around 7500 yr b p climatic conditions slightly less favorable for woodland occurred during part of the late holocene

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

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

anchor ice seabed freezing and sediment dynamics in shallow arctic seas diving investigations confirm previous circumstantial evidence of seafloor freezing and anchor ice accretion during freeze up storms in the alaskan beaufort sea these related bottom types were found to be continuous from shore to 2 m depth and spotty to 4 5 m depth spotty anchor ice occurred as pillow shaped crystal aggregates on buried slabs of frozen sand surrounded by unfrozen sand considerations of required conditions for ice bonding and anchor ice growth allows regional extrapolation and suggests the possibility of anchor ice growth out to 20 m depth the estimated maximum depth of supercooling during fall storms anchor ice and seabed freezing apparently do not develop during a calm freeze up because of the abrupt growth of anchor ice during a freezing storm and its release soon after formation of a surface ice cover this ice type has not been documented before the concretelike nature of frozen bottom where present should prohibit sediment transport by any conceivable wave or current regime during the freezing storm but elsewhere particularly where the bonded crust is broken by grounded ice anchor ice lifts coarse material off the bottom and incorporates it into the ice canopy thereby leading to significant ice rafting of shallow shelf sediment and likely sediment loss to the deep sea

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

a siliceous microfossil view of middle eocene arctic paleoenvironments a window of biosilica production and preservation integrated ocean drilling program iodp expedition 302 the arctic coring expedition acex unearthed the most significant find of paleogene siliceous microfossils in nearly 2 decades 100 m of early middle eocene organic rich finely laminated sediments contain abundant marine and freshwater siliceous microfossils allowing intriguing insights into central arctic paleoenvironments during the start of cenozoic cooling largely endemic assemblages of marine diatoms and ebridians are preserved along with very high abundances of chrysophyte cysts the endogenously formed resting stage of freshwater algae an overall brackish environment is invoked but variations in group dominance suggest episodic changes in salinity stratification and trophic status with the backing of inorganic geochemistry we synthesize the sediment characteristics by hypothesizing an environmental model for the cooccurrence of these diverse siliceous microfossil groups we also report on initial insights into the composition of some of the laminations which may help explain the formation of this rich sediment archive

surface textural analysis of quartz sand grains from odp site 918 off the southeast coast of greenland suggests glaciation of southern greenland at 11 ma shipboard analysis of the 1 183 m sedimentary section recovered at site 918 in the irminger basin during ocean drilling program leg 152 revealed material of glacial origin diamictons ice rafted debris ird and dropstones as deep as 543 m below sea floor bsf the sediment containing the deepest dropstone was biostratigraphically dated shipboard as approximately 7 ma pushing back the date for the onset of glaciation on southern greenland by 5 ma thin layers of fine sand were found as much as 60 m deeper in the core raising the possibility of an even earlier date for glaciation to determine the sedimentary history of these deeper sand layers the surface textures on quartz grains from eleven cores bracketing the interval of interest were analyzed by scanning electron microscope the results suggest that the grains in the 60 m interval below the deepest dropstone have a glacial history at that level an 11 ma sr isotope date was obtained from planktonic foraminifers this late miocene timing is supported biostratigraphically by both nanofossil and foraminifer assemblages indicating a new minimum age for the onset of glaciation on southern greenland and in the north atlantic

improved os isotope stratigraphy of the arctic ocean 1 the history of the arctic ocean remained poorly known until the 2004 iodp coring of lomonosov ridge sediments early studies of the recovered sequence demonstrated the existence of an eocene lake stage prior to the transition to marine conditions the marine stage onset was inferred to be 17 5 million years ma ago thus implying a nearly 26 ma gap between the lacustrine and marine episodes and an unusual tectonic history for lomonosov ridge in order to explain this gap more recently rhenium osmium re os isotope measurements of the transition from the lacustrine to marine sediments suggested a much earlier inception of marine conditions and the absence of any significant gap between both episodes here an improved osmium isotope stratigraphy and re os data concur to assign a late eocene age 36 ma to the marine invasion consistent with a relative change in sea level on top of lomonosov ridge either from tectonic origin or from another cause

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

palaeoclimate the sea ice thickens little is known about the presence of high latitude sea ice before 2 6 million years ago a reanalysis of marine sediments from the arctic ocean indicates an intermittent presence of perennial sea ice as early as 44 million years ago

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

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

microfeatures of modern sea ice rafted sediment and implications for paleo sea ice reconstructions distinguishing sea ice rafted debris sird from iceberg rafted debris is crucial to an interpretation of ice rafting history however there are few paleo sea ice proxies this study characterizes quartz grain microfeatures of modern sird from the arctic ocean and compares these results with microfeatures from representative glacial deposits to potentially differentiate sird from ice rafted sediments which have been recently subjected to glacial processes this allows us to evaluate the use of grain microfeatures as a paleo sea ice proxy sird grains were largely subrounded with medium relief pervasive silica dissolution and a high abundance of breakage blocks and microlayering the glacial grains were more angular with lower relief and higher abundances of fractures and striations gouges discriminate analysis shows a distinct difference between sird and glacial grains with 7 of the sird grains containing typical glacial microtextures suggesting this method is a useful means of inferring paleo sea ice presence in the marine record we propose that differences in microfeatures of sird and glacial ice rafted debris reflect differences in sediment transport and weathering histories sediment transported to a coastal setting and later rafted by sea ice would be subject to increased chemical weathering whereas glaciers that calve icebergs would bypass the coastal marine environment thus preserving their glacial signature

a study of pleistocene and holocene hyaena coprolites abstract hyaena coprolites from a diachronic series of archaeological sites in israel were examined and compared with recent faecal material from striped hyaena dens and zoos three methods were applied in the analysis of all samples gross morphometrical attributes x ray diffraction and petrological thin sections this last method is an innovation in the field of coprolite studies and facilitates the long term preservation of the original textural characteristics and fabric of sections of the coprolite the combination of these three approaches facilitated among other things the assessment of hyaena diet in the past as well as in the present and determination of local environmental factors affecting the composition of the coprolite we also obtained some indication of changes related to ageing of the material

the arctic forest of the middle eocene abstractlush forests dominated by deciduous conifers existed well north of the arctic circle during the middle eocene 45 ma the fossil forest site located on axel heiberg island canada has yielded a particularly rich assemblage of plant macro and microfossils as well as paleosols all exquisitely preserved methods ranging from classical paleobotany to stable isotope geochemistry have been applied to materials excavated from the fossil forest and have revealed layers of diverse conifer forests with a rich angiosperm understory that successfully endured three months of continuous light and three months of continuous darkness paleoenvironmental reconstructions suggest a warm ice free environment with high growing season relative humidity and high rates of soil methanogenesis methods to evaluate intraseasonal variability highlight the switchover from stored to actively fixed carbon during the short annual growing season

a holocene record of changing arctic ocean ice drift analogous to the effects of the arctic oscillation 1 the arctic oscillation ao controls the configuration of the transpolar drift tpd if thicker ice from the beaufort gyre were exported the volume of fresh water sea ice in the nordic seas would significantly increase decreasing the formation of north atlantic deep water this would cool large parts of the northern hemisphere and affect global climate therefore in order to understand how the global climate system functions it is imperative to know how the tpd changed over the last millennium or more the provenance of grains in a sediment core located near the confluence of the tpd and the beaufort gyre provides a direct proxy for changes in seaice drift owing to these circulation systems the core has more than 200 cm of holocene sediment with intervals dominated by grains from the russian shelves alternating with intervals of abundant grains from north american sources grains matched to russian shelves indicate that the tpd was shifted toward north america similar to what occurs during a more positive phase of the ao this condition alternated with intervals where few grains matched to russian sources presumably because the tpd was restricted to the russian half of the arctic far from the core site during the last 1300 years increased influx of russian grains occurred approximately every 50 150 years this fluctuation might represent the long term oscillation of the ao which modulates the same tpd shift today