impact processes permafrost dynamics and climate and environmental variability in the terrestrial arctic as inferred from the unique 3 6 myr record of lake el gygytgyn far east russia a review lake el gygytgyn in far east russia is a 3 6 myr old impact crater lake located in an area that has never been affected by cenozoic glaciations nor desiccation the unique sediment record of the l

comparison study of the modern ostracod associations in the kara and laptev seas ecological aspects recent ostracod assemblages were investigated from coretop sediment samples collected in the eastern kara sea from water depths down to 300 m a total of 45 species were identified 27 of them were reported for the kara sea for the first time the kara sea data were compared with our results on the distribution of ostracods in the eastern laptev sea the spatial distribution of recent taxa and the ecological groupings demonstrate a clear relation to dominant environmental factors which range from estuarine to full marine conditions four assemblages related to average summer bottom water salinities were established 1 a freshwater assemblage from the inner estuaries of the ob and yenisei rivers with salinities less than 2 and from thermokarst lagoons of the southern laptev sea coast with strong salinization in winter 2 a brackishwater assemblage of the outer estuaries of the ob and yenisei rivers with salinities up to 26 3 a mixed euryhaline marine assemblage dominated by euryhaline species paracyprideis pseudopunctillata and heterocyprideis sorbyana from the inner shelf river affected zone of the kara and laptev seas where salinities range between 26 and 32 4 a taxonomically diverse marine assemblage dominated by shallow water marine taxa from the northern parts of the kara and laptev shelves and upper continental slope with stable bottom environments and a salinity higher than 32 abundant euryhaline species found at greater water depths are identified as part of an ice rafted assemblage they are possibly entrained into the newly formed fast ice during autumn storms and freeze up period and then transported to the distal open sea areas during summer

a linear stratified ocean model of the coastal undercurrent the linear stratified ocean model of mccreary 1981 is used to study the wind driven response of the ocean near an eastern coast the model can be regarded as an extension of the inviscid models of lighthill 1969 and of gill clarke 1974 that allows the vertical diffusion of heat and momentum into the deep ocean solutions are still found as expansions of vertical normal modes vertical mixing affects each mode as a linear drag with a drag coefficient that increases rapidly with mode number n a zonally uniform band of steady equatorward winds forces the ocean and the resulting flow field has many features in common with observations at eastern boundaries there is a surface equatorward jet and a poleward coastal undercurrent confined within 10 20 km of the coast both currents extend well poleward of the wind band upwelling does not reach great depths but occurs only above the core of the undercurrent weak downwelling occurs at greater depths there is offshore ekman drift in the surface mixed layer and return flow at a depth slightly above the core of the undercurrent the baroclinic alongshore pressure gradient field and the vertical mixing of heat and momentum are essential elements of the model dynamics but the beta and horizontal mixing are not low order vertical modes n 6 tend toward a two dimensional balance they generate the transverse circulation pattern associated with coastal ekman pumping

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

a high resolution seismic reflection refraction study of the chugach peninsular terrane boundary southern alaska we present results from a high resolution seismic refraction analysis of the shallow approximately 2 km crustal structure along the 107 km long trans alaska crustal transect chugach reflection line in southern alaska and a comparison with laboratory measurements of field samples the refraction analysis includes the two dimensional interpretation of several thousand first and secondary arrival travel times digitized from 1024 channel split spread common shot gathers the velocity model derived from this analysis better defines the location and geometry of terrane boundaries than does the normal incidence reflection section and agrees well with surface mapping of lithologies furthermore the model predicts travel times within 100 ms of the reflection times recorded from the base of the quaternary on the chugach reflection section thicknesses of quaternary deposits with velocities between 1 1 and 2 0 km s correlate inversely with the quantity of observed lower crustal reflections on the chugach section suggesting that the presence or absence of these sediments in sufficient thickness exerted primary control on the quality of the deeper portion of the section there is a significant velocity contrast between crystalline rocks across the border ranges fault 5 0 versus 5 6 km s the major contact between the chugach and peninsular terranes in agreement with laboratory measurements of field specimens in the peninsular terrane the modeling indicates that an unnamed fault delimiting the southern flank of the copper river basin dips steeply northward at 50 and has about 1300 m of vertical offset laboratory measurements document a maximum velocity anisotropy of 20 for phyllitic schists of the valdez group in the chugach terrane in agreement with the observed e w strike and near vertical dip of the valdez group we determined a significant 14 velocity anisotropy for ray paths oriented n s versus ne sw

an early to mid pleistocene deep arctic ocean ostracode fauna with north atlantic affinities abstract an early to middle pleistocene ostracode fauna was discovered in sediment core p1 93 ar 23 p23 76 95 n 155 07 w from 951 meter water depth from the northwind ridge western arctic ocean piston core p23 yielded more than 30 000 specimens and a total of about 30 species several early to mid pleistocene species in the genera krithe echinocythereis pterygocythereis and arcacythere are now extinct in the arctic and show taxonomic affinities to north atlantic ocean species our results suggest that there was a major ostracode faunal turnover during the global climate transitions known as the mid pleistocene transition mpt 1 2 to 0 7 ma and the mid brunhes event mbe 400 ka reflecting the development of perennial sea ice during interglacial periods and large ice shelves during glacial periods over the last 400 000 years

development of near surface flow pattern and water mass distribution in the somali basin in response to the southwest monsoon of 1979 abstract near surface observations of temperature salinity and current are used to describe the seasonal reversal of the somali current during 1979 in response to the onset of the southwest monsoon winds during april prior to the reversal of the winds north of the equator the northward flowing east african coastal current eacc and the southward flowing somali current sc converged near the equator the eacc was characterized by surface waters with salinities less than 35 1 and the sc by salinities greater than 35 3 the winds reversed north of the equator during the first week of may and the boundary current intruded in the form of an anticyclonic gyre to 2 5 n most of the low salinity water was recirculated back south of the equator by the offshore limb of the gyre it did not flow continuously at the surface into the eastward equatorial jet which was present farther offshore during may and june that current was fed by high salinity water from the region to the north of the low latitude gy

late middle quaternary lithostratigraphy and sedimentation patterns on the alpha ridge central arctic ocean implications for arctic climate variability on orbital time scales abstract we use sediment cores collected by the chinese national arctic research expeditions from the alpha ridge to advance quaternary stratigraphy and paleoceanographic reconstructions for the arctic ocean our cores show a good litho biostratigraphic correlation to sedimentary records developed earlier for the central arctic ocean suggesting a recovered stratigraphic range of ca 0 6 ma suitable for paleoclimatic studies on orbital time scales this stratigraphy was tested by correlating the stacked alpha ridge record of bulk xrf manganese calcium and zirconium mn ca zr to global stable isotope lr04 18o and sea level stacks and tuning to orbital parameters correlation results corroborate the applicability of presumed climate sea level controlled mn variations in the arctic ocean for orbital tuning this approach enables better understanding of the global and orbital controls on the arctic climate orbital tuning experiments for our records indicate strong eccentricity 100 kyr and precession 20 kyr controls on the arctic ocean probably implemented via glaciations and sea ice provenance proxies like ca and zr are shown to be unsuitable as orbital tuning tools but useful as indicators of glacial deglacial processes and circulation patterns in the arctic ocean their variations suggest an overall long term persistence of the beaufort gyre circulation in the alpha ridge region some glacial intervals e g mis 6 and 4 3 are predominated by material presumably transported by the transpolar drift these circulation shifts likely indicate major changes in the arctic climatic regime which yet need to be investigated overall our results demonstrate applicability of xrf data to paleoclimatic studies of the arctic ocean

paleoclimate record for northwind ridge western arctic ocean core nwr 5 from northwind ridge in the western arctic ocean contains a climatic record that extends back for over 1 million years dark brown beds with abundant planktonic foraminifers represent interglacial conditions whereas glacial and transitional conditions are represented by lithologies barren or nearly barren of planktonic foraminifers we conclude that seven and possibly all nine interglacials of the brunhes magnetic chronozone the last 780 000 years are represented in nwr 5 for about the last 800 000 years the western arctic ocean apparently had a permanent thick ice cover and was unable to support significant populations of planktonic foraminifers except during major interglacials when seasonally open and high productivity surface waters occurred at least along the basin margins our results support previous interpretations that climate variations in the arctic are in phase with glacial interglacial cycles observed in other proxy records of the brunhes

microfaunal evidence for elevated pliocene temperatures in the arctic ocean the migration of thermophilic marine ostracoda into the arctic ocean during the pliocene indicates that winter and summer ocean temperatures around arctic margins were 0 c and 3 c respectively and that ice free conditions existed for most or all of the arctic by at least 3 5 3 0 ma probably earlier the opening of the bering strait allowed marine organisms to migrate through the arctic ocean mostly from the pacific ocean migrant taxa such as cythere hemicythere and neomonoceratina are known from pliocene deposits of alaska and canada as well as neogene deposits of the north pacific and atlantic oceans on the basis of ecological and zoogeographic information on ostracode species from more than 800 modern core top samples for the north atlantic north pacific and arctic oceans we determined winter and summer temperature tolerances for migrant taxa to be at or above about 0 c and 3 c this suggests ice free summers and probably a perennially ice free arctic ocean in some regions elevated water temperatures in the arctic ocean between 3 5 and 2 0 ma is supported by evidence for late pliocene increased meridional heat transport in the north atlantic ocean

recent ostracoda from the laptev sea arctic siberia species assemblages and some environmental relationships ostracod assemblages from coretop sediments collected at 26 localities at different depths of the laptev sea shelf and upper continental slope were investigated for assemblage studies a total of 41 species belonging to 19 genera and 12 families have been identified three assemblages have been established that could be linked to environmental factors such as water depth bottom salinities water mass circulation and sea ice transportation the species rich and abundant assemblages of the western and central laptev sea were related to the atlantic waters occupying the upper continental slope these include relatively deep water forms that show clear affinities to north atlantic and arctic ocean assemblages cytheropteron biconvexa c testudo c simplex c nodosoalatum c inflatum c porterae krithe glacialis k minima pseudocythere caudata polycope punctata p orbicularis in the eastern middle shelf region the assemblage is comprised of acanthocythereis dunelmensis together with other normal marine species semicytherura complanata elofsonella concinna cluthia cluthae this assemblage seems connected to the winter flaw polynya which is believed to be the main area of sediment entrainment into sea ice the inner shelf assemblage of the southern laptev sea is dominated by shallow water euryhaline species paracyprideis pseudopunctillata and heterocyprideis sorbyana with admixture of the brackish water species roundstonia macchesneyi the unusual occurrence of a number of shallow water ostracod species on the upper continental slope may be explained by ice rafting which these ostracods are probably able to survive

interglacial responses of the southern greenland ice sheet over the last 430 000 years determined using particle size specific magnetic and isotopic tracers abstract the past behavior of the greenland ice sheet can provide important insight into climatic thresholds that may initiate and drive major ice sheet retreat particle size specific magnetic and sr nd pb isotope records from eirik ridge sediments south of greenland track southern greenland ice sheet sgis erosional signatures over the past 430 ka by discriminating changes in sediment source and transport over the eirik ridge ground truthed magnetic and isotopic compositions of subglacial silt from south greenland s precambrian bedrock terranes constrain independent magnetic and isotopic estimates of eirik ridge silt provenance which in turn indicate that the southern greenland ice sheet sgis retreated within its present margin during three of the four previous interglaciations over the past 430 ka retreat of the sgis was extensive during the marine isotope stage mis 5e 9 and 11 interglaciations continuing unabated despite declining insolation during mis 5e and 9 with near complete deglaciation in mis 11 retreat of the sgis during mis 7 was minimal notwithstanding strong insolation forcing while holocene retreat slowed shortly after peak insolation the reconstruction of sgis retreat during the last five deglacial and interglacial periods suggests that a threshold for extensive sgis retreat exists between the insolation and co 2 states of the holocene and the mis 5e and 9 interglaciations with co 2 exerting a stronger control on sgis retreat than insolation our results also suggest that the extent and stability of the sgis in the holocene is anomalous in the context of late quaternary interglaciations

is ice rafted sediment in a north pole marine record evidence for perennial sea ice cover ice rafted sediments of eurasian and north american origin are found consistently in the upper part 13ma bp to present of the arctic coring expedition acex ocean core from the lomonosov ridge

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

kinematic inversion for the 2 d horizontal and vertical qp wave velocities and depths to interfaces applied to the tact seismic profile southern alaska summary we propose a quasi compressional wave qp wave traveltime inversion technique for determination of the 2 d horizontal and vertical qp wave velocities and depths to interfaces from seismic reflectiodrefraction data sets synthetic test model studies demonstrate that the method is effective if ray path coverage within the model is adequate and indicate that horizontal qp wave velocities and depths to interfaces are better resolved than vertical qp wave velocities we applied our inversion technique to the trans alaska crustal transect tact profile southern alaska between sp19 and sp11 the results of the inversion suggest that the upper 5 km of the crust is anisotropic the range of anisotropy for the derived model is between 10 and 25 per cent consistent with the range determined in previous studies and from laboratory measurements the cause of anisotropy is thought to be preferred mineral orientations in the foliation planes of the metasedimentary rocks based on the test model studies and the applications to actual seismic data sets it is suggested that future traveltime inversion studies will require particularly high quality data with dense ray path coverage in which multiple sources and receivers and both reflection and refraction data are utilized

accretion and subduction tectonics in the chugach mountains and copper river basin alaska initial results of the trans alaska crustal transect geologic seismic gravity and magnetic data from the northern chugach mountains and southern copper river basin alaska indicate that the chugach terrane cgt and the composite peninsular wrangellia terrane pet wrt are thin 10 km rootless sheets bounded on the south by north dipping thrust faults that sole into a shallow horizontal low velocity zone the cgt has been thrust at least 40 km beneath the pet wrt along the border ranges fault system brfs adjacent to the brfs uplift and erosion of 30 40 km since jurassic time have exposed blueschist facies rocks in the cgt and mafic and ultramafic cumulate rocks in the pet wrt four paired north dipping layers of low and high seismic velocities extend beneath the northern cgt and southern pet wrt and may be slices of subducted oceanic crust and upper mantle the upper two pairs may now be joined to the continental plate 15 references 5 figures

crustal structure of the active margin south central alaska an interpretation of seismic refraction data from the trans alaska crustal transect seismic refraction and wide angle reflection data from the u s geological survey s trans alaska crustal transect are used to investigate the upper crustal structure of southcentral alaska and to develop a model using two dimensional asymptotic ray theory the data considered here are from the n s 126 km cordova peak refraction profile which was positioned to cross the chugach and prince william terranes these two tectonostratigraphic terranes form part of a large accretionary complex related to the alaska subduction zone interpretation of data from the cordova peak profile indicates systematically higher velocities in chugach terrane rocks as compared with prince william terrane rocks at comparable depths unconsolidated sediment and glacial ice overlie chugach terrane rocks of unusually high compressional velocities 4 7 7 0 km s in the upper 10 km of crust a northward thickening metasedimentary and metavolcanic flysch sequence having an average velocity of 6 0 km s is underlain by metavolcanic mafic basement rocks having an average velocity of 6 6 km s the upper 10 km of the prince william terrane have compressional velocities ranging from 3 7 to 6 2 km s and are correlated with clastic sedimentary and volcanic rocks which are overlain by younger terrigenous sedimentary rocks and underlain by mafic to ultramafic prince william terrane basement rocks the upper crustal velocity structures of the chugach and prince william terranes are distinct to at least 10 km depth which suggests that the contact fault zone is a boundary which extends to at least 10 km midcrustal layers beneath the chugach terrane contain two velocity reversals which may indicate the presence of off scraped oceanic sediment overpressurized zones shear zones or some combination of these possibilities data from energy sampling midcrustal layers beneath the prince william terrane do not provide similar evidence for low high velocity zones in that area

reconstruction of sea surface conditions at middle to high latitudes of the northern hemisphere during the last glacial maximum lgm based on dinoflagellate cyst assemblages abstract a new calibration database of census counts of organic walled dinoflagellate cyst dinocyst assemblages has been developed from the analyses of surface sediment samples collected at middle to high latitudes of the northern hemisphere after standardisation of taxonomy and laboratory procedures the database comprises 940 reference data points from the north atlantic arctic and north pacific oceans and their adjacent seas including the mediterranean sea as well as epicontinental environments such as the estuary and gulf of st lawrence the bering sea and the hudson bay the relative abundance of taxa was analysed to describe the distribution of assemblages the best analogue technique was used for the reconstruction of last glacial maximum lgm sea surface temperature and salinity during summer and winter in addition to sea ice cover extent at sites from the north atlantic n 63 mediterranean sea n 1 and eastern north pacific n 1 three of the north atlantic cores from the continental margin of eastern canada revealed a barren lgm interval probably because of quasi permanent sea ice six other cores from the greenland and norwegian seas were excluded from the compilation because of too sparse assemblages and poor analogue situation at the remaining sites n 54 relatively close modern analogues were found for most lgm samples which allowed reconstructions the new lgm results are consistent with previous reconstructions based on dinocyst data which show much cooler conditions than at present along the continental margins of canada and europe but sharp gradients of increasing temperature offshore the results also suggest low salinity and larger than present contrasts in seasonal temperatures with colder winters and more extensive sea ice cover whereas relatively warm conditions may have prevailed offshore in summer from these data we hypothesise low thermal inertia in a shallow and low density surface water layer

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

out of the woods driftwood insights into holocene pan arctic sea ice dynamics the collation of 913 driftwood samples from across the western arctic with spatiotemporal distribution and available provenance data enabled the production of a high resolution proxy based reconstruction of holocene arctic ocean surface current and sea ice dynamics regionally bounded driftwood based sea ice reconstructions studies suggest spatiotemporally complex past arctic sea ice extent and movement however a large scale compilation of holocene arctic driftwood has not previously been developed sparse driftwood in the early holocene 8 2 cal ka b p deglacial period was followed by increased driftwood deposition in the warmer mid holocene 8 2 4 2 cal ka b p characterized by an enhanced transpolar drift tpd 7 cal ka b p leading to sea ice loss through the fram strait driftwood incursion peaks show spatial e w progression from the eurasian archipelagos to greenland and the canadian arctic archipelago suggesting a progressive shift in the orientation of the tpd on centennial millennial time scales and intermediate phases in the arctic oscillation late holocene cooling 4 2 cal ka b p is indicated by increased influx of probably north american picea via a strengthened beaufort gyre bg which enhanced sea ice recirculation starting in the western arctic and progressing eastward in recent millennia 2 cal ka b p a more variable driftwood record alternates between bg and tpd dominance on centennial time scales to further constrain a spatiotemporal reconstruction of variations in holocene ocean current and sea ice dynamics a more definitive determination of driftwood provenance is recommended to build upon the current framework such as through radiogenic isotope tracing and adna analysis

late twentieth century simulation of arctic sea ice and ocean properties in the ccsm4 abstractto establish how well the new community climate system model version 4 ccsm4 simulates the properties of the arctic sea ice and ocean results from six ccsm4 twentieth century ensemble simulations are compared here with the available data it is found that the ccsm4 simulations capture most of the important climatological features of the arctic sea ice and ocean state well among them the sea ice thickness distribution fraction of multiyear sea ice and sea ice edge the strongest bias exists in the simulated spring to fall sea ice motion field the location of the beaufort gyre and the temperature of the deep arctic ocean below 250 m which are caused by deficiencies in the simulation of the arctic sea level pressure field and the lack of deep water formation on the arctic shelves the observed decrease in the sea ice extent and the multiyear ice cover is well captured by the ccsm4 it is important to note however that the temporal evolution of the simulated arctic sea ice cover over the

tracing pacific water in the north atlantic ocean 1 in the arctic ocean pacific source water can be distinguished from atlantic source water by nitrate phosphate concentration relationships with pacific water having higher phosphate concentrations relative to those of nitrate furthermore pacific water originally from the inflow through bering strait is clearly recognizable in the outflows of low salinity waters from the arctic ocean to the northern north atlantic ocean through the canadian arctic archipelago and through fram strait in the canadian arctic archipelago we observe that almost all of the waters flowing through lancaster and jones sounds most of the water in the top 100 m in smith sound containing the flow through nares strait and possibly all waters in hudson bay contain no water of atlantic origin significant amounts of pacific water are also observed along the western coast of baffin bay along the coast of labrador and above the 200 m isobath of the grand banks there is a clear signal of pacific water flowing south through fram strait and along the east coast of greenland extending at least as far south as denmark strait pacific water signature can be seen near the east coast of greenland at 66 n but not in data at 60 n temporal variability in the concentrations of pacific water has been observed at several locations where multiple year observations are available

variability in drift ice export from the arctic ocean to the north icelandic shelf over the last 8000 years a multi proxy evaluation abstract north iceland represents a climatically sensitive region in part due to its location at the confluence of southward flowing and drift ice laden polar waters from the arctic ocean delivered by the east greenland current and the relatively warm and saline irminger current a northerly flowing branch of the north atlantic current despite its pivotal location there is a paucity of high resolution and long term sea ice records for the region with some disparities in certain previous investigations here the identification of the biomarker ip 25 as a reliable proxy for drift ice for north iceland has been confirmed by measuring its abundance in surface sediments from the region and comparison of outcomes with documentary records of sea ice and other proxy data by analysing ip 25 in a well dated marine sediment core from the north icelandic shelf nis md99 2269 we also provide a high resolution ca 25 yr record of drift sea ice for the region and complement this with a lower resolution record ca 100 yr obtained from a second core site located further east jr51 gc35 statistical treatment of equi spaced time series reveals strong linear correlations between ip 25 and a further drift ice proxy quartz in each core thus linear regression analysis between both proxies gave correlation coefficients r 2 of 0 74 and 0 66 for md99 2269 25 yr and jr51 gc35 100 yr respectively further the individual proxies were well correlated between the two cores with r 0 91 and 0 77 for ip 25 and quartz respectively the ip 25 based sea ice record for md99 2269 combined with other new biomarker and foraminifera data and previously published proxy data for primary productivity and sea surface temperature suggest that the paleoceanographic evolution for the nis over the last 8 ka can be classified into three main intervals the early mid holocene ca 8 6 2 cal ka bp was characterized by relatively low or absent drift ice low primary productivity and relatively high ssts during the mid holocene ca 6 2 3 3 cal ka bp drift ice increased concomitant with decreasing ssts although primary productivity was somewhat enhanced during this interval ip 25 first reached its mean value for the entire record at ca 5 cal ka bp before increasing continuously ca 4 3 cal ka bp broadly in line with the onset of neoglaciation as seen in some other proxy records further increases in drift ice were evident during the late holocene ca 3 3 cal ka bp to present culminating in maximum sea ice during the little ice age in addition the ip 25 record from md99 2269 shows some positive regime shifts from the general trend especially at ca 3 8 2 7 1 5 0 7 and 0 4 cal ka bp that have analogs in some other paleoceanographic reconstructions influenced by the east greenland current the abrupt increases in ip 25 at ca 1 5 and 0 7 cal ka bp are coincident with rapid cooling identified previously in an icelandic lacustrine temperature record suggesting significant coupling between the marine and terrestrial systems the contribution of sea ice to the broader climate system is further evidenced through the identification of statistically significant periodicities ca 1000 yr and ca 200 230 yr in the drift ice proxy data that have counterparts in previous studies concerning atmospheric and oceanic variability and solar forcing mechanisms

origin of apparent magnetic excursions in deep sea sediments from mendeleev alpha ridge arctic ocean 1 arctic deep sea sediments often record intervals of negative inclination of natural remanence that are tens of centimeters thick implying magnetic excursions with durations of tens of thousand years that far exceed excursion durations estimated elsewhere and the lack of tight age control usually provides excessive freedom in the labeling of arctic excursions fortuitous variations in sedimentation rate have been invoked to explain the amplified excursions alternating field demagnetization of natural remanent magnetization nrm of sediment cores 08jpc 10jpc 11jpc and 13jpc recovered by the healy oden trans arctic expedition in august 2005 hotrax05 to the mendeleev alpha ridge yields apparent magnetic excursions in sediments deposited in the brunhes chron thermal demagnetization of the nrm however implies multiple magnetization components with negative inclination components usually unblocked below 350 c analysis of isothermal remanent magnetization acquisition curves from magnetic extracts indicates two magnetic coercivity components superimposed on one another magnetic experiments conducted under high and low temperatures show features that are characteristic for titano magnetite and titanomaghemite presence of the two magnetic phases is further confirmed by elemental mapping on a scanning electron microscope equipped for x ray energy dispersive spectroscopy eds and by high resolution x ray diffraction xrd it is unlikely that anomalously thick intervals of negative inclination in these brunhes aged sediments are caused by unusual behavior of the magnetic field in the arctic area we therefore attribute low and negative nrm inclinations in these cores to partially self reversed chemical remanent magnetizations apparently carried by titanomaghemite and acquired during the oxidation of detrital titano magnetite grains the high ti contents and high oxidation states indicated by eds and xrd data provide the conditions required for partial self reversal by ionic reordering during diagenetic maghemitization and this process appears to have affected all hotrax05 cores collected from the mendeleev alpha ridge

seismic anisotropy due to preferred mineral orientation observed in shallow crustal rocks in southern alaska laboratory velocity measurements and structural field relations explain the observation of a significant seismic anisotropy within highly foliated rocks in southern alaska the orientation of the principal compressive stress indicates that this anisotropy is not related to extensive dilatancy but can be satisfactorily explained by the foliation of the metasedimentary rocks laboratory measurements indicate a significant anisotropy within these rocks even at pressures well above those thought to close microcracks these observations document that anisotropy related to preferred mineral orientation may be widespread in continental rocks thus pervasive foliation can play a more important role in causing anisotropy than dilatancy and inferences of principal stress orientations solely from anisotropy may be erroneous

central arctic paleoceanography for the last 50 kyr based on ostracode faunal assemblages abstract the paleoceanography of the central arctic ocean was reconstructed for the last 50 kyr marine isotope stages mis 1 3 based on ostracode assemblages from 21 14c dated sediment cores from the mendeleev lomonosov and gakkel ridges arctic sediments deposited during the holocene interglacial period mis 1 the bolling allerod and larger interstadial dansgaard oeschger do events 3 4 8 and 12 contain abundant cytheropteron spp henryhowella asperrima and krithe spp at intermediate deep depths 1000 to 3000 m these assemblages suggest a ventilated deep arctic ocean water mass similar to the modern arctic ocean deep water aodw during these time periods in contrast sediment deposited during stadial events corresponding to heinrich events 1 2 3 and 4 also possibly the younger dryas yd contain abundant polycope spp 60 80 suggesting a greater influence of the atlantic layer al on the arctic intermediate water aiw and aodw reduced sea ice during the early holocene the last deglacial and mis 3 interstadials is indicated by the reoccurrence of acetabulastoma arcticum an epipelagic species that is parasitic on sea ice dwelling amphipods one hypothesis to explain these oceanographic changes during longer stadial events particularly within the last glacial period mis 2 involves sluggish ocean circulation thicker sea ice cover and a deeper halocline with ocean exchange between greenland sea and arctic ocean deep water through the fram strait

variability of the somali current system during the onset of the southwest monsoon 1979 abstract an array of six current meter moorings and several coastal temperature recorders was deployed on the shelf and continental slope off northern somalia from march to july 1979 a seventh mooring was placed near 2 s in addition four deep sea moorings were deployed for a period of one month in may june farther offshore already during the late northeast monsoon in march the somali current north of 5 n was flowing northeastward in the top 150 m underneath in the depth range 150 400 m a narrow southward undercurrent was observed from march to june after the first onset of the southwest monsoon which occurred around 5 may when winds shifted from easterly to southwesterly parallel to the coast the near surface temperatures on the shelf decreased immediately with no detectable phase difference between 6 and 10 n but no change was observed in the offshore circulation pattern the final monsoon onset around 10 june was characterized by a drastic increase in wind speeds and the establishment of a st

sea ice in the paleoclimate system the challenge of reconstructing sea ice from proxies an introduction sea ice is an important component of the earth system with complex dynamics imperfectly documented from direct observations which are primarily limited to the last 40 years whereas large amplitude variations of sea ice have been recorded especially in the arctic with a strikingly fast decrease in recent years partly attributed to the impact of anthropogenic climate changes little is known about the natural variability of the sea ice cover at multi decadal to multi millennial time scales hence there is a need to establish longer sea ice time series to document the full range of sea ice variations under natural forcings to do this several approaches based on biogenic or geochemical proxies have been developed from marine ice core and coastal records the status of the sea ice proxies has been discussed by the sea ice proxy sip working group endorsed by pages during a first workshop held at geotop in montreal the present volume contains a set of papers addressing various sea ice proxies and their application to large scale sea ice reconstruction here we summarize the contents of the volume including a table of various proxies available in marine sediments and ice cores with their possibilities and limitations

stable isotope stratigraphy sedimentation rates and salinity changes in the latest pleistocene to holocene eastern central arctic ocean a high resolution study including oxygen and carbon stable isotopes as well as carbonate and total organic carbon contents has been performed on undisturbed near surface 0 40 cm sediment sequences taken in the eastern arctic ocean during the international arctic 91 expedition based on the oxygen stable isotope records measured on neogloboquadrina pachyderma sin and ams 14c dating the upper 10 to 20 cm of the sediment sequences represent isotope stage 1 and the base of termination i 15 7 ka can be identified very well stage 1 sedimentation rates vary between 0 4 and 2 0 cm kyr in general glacial stage 2 sedimentation rates are probably lower and vary between 0 4 and 0 7 cm kyr the glacial interglacial shifts in 18o values of n pachyderma sin may reach values of 1 3 to 2 5 indicating 1 that in addition to the glacial interglacial global ice volume signal changes in surface water salinity have effected the isotope records and 2 that these salinity changes have varied laterally glacial interglacial differences in salinity were small in the lomonosov ridge area 0 0 4 and relatively high in the morris jesup rise area up to 1 4 this implies that the supply of low saline waters onto the eurasian shelves and its further transport into the central arctic ocean via the transpolar drift should have continued during the last glacial and should have significantly influenced the surface water characteristics in parts of the central arctic on the morris jesup rise on the other hand the glacial low saline water signal at that time was strongly reduced in comparison to the modern situation at the glacial interglacial stage 12 boundary a strong meltwater signal is recorded in a sharp depletion in 18o as well as 13c this central arctic ocean meltwater event can be correlated from the makarov basin through the lomonosov ridge and amundsen basin to the eastern gakkel ridge the beginning of this event is ams 14c dated at 15 7 ka i e significantly older than the major decrease in the global ice volume signal which occurs between 9 and 13 5 ka large amounts of freshwater meltwater were probably supplied from the eurasian continent due to the decay of the barents sea ice sheet causing this distinct early meltwater anomaly in the central arctic ocean the extension of a well oxygenated surface near water mass in the arctic ocean and at least seasonal open ice conditions and some increased bioproductivity were probably established at the end of termination i as indicated by the increase in 13c to modern values as well as increased carbonate i e foraminifers coccoliths ostracodes and total organic carbon contents

quaternary sea ice history in the arctic ocean based on a new ostracode sea ice proxy paleo sea ice history in the arctic ocean was reconstructed using the sea ice dwelling ostracode acetabulastoma arcticum from late quaternary sediments from the mendeleyev lomonosov and gakkel ridges the morris jesup rise and the yermak plateau results suggest intermittently high levels of perennial sea ice in the central arctic ocean during marine isotope stage mis 3 25 45 ka minimal sea ice during the last deglacial 16 11 ka and early holocene thermal maximum 11 5 ka and increasing sea ice during the mid to late holocene 5 0 ka sediment core records from the iceland and rockall plateaus show that perennial sea ice existed in these regions only during glacial intervals mis 2 4 and 6 these results show that sea ice exhibits complex temporal and spatial variability during different climatic regimes and that the development of modern perennial sea ice may be a relatively recent phenomenon

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

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

ice events along the east siberian continental margin during the last two glaciations evidence from clay minerals abstract a large ice sheet or ice shelf may have developed repeatedly along the east siberian continental margin since the middle pleistocene in combination with ice rafted debris major elements and foraminifera clay mineral records from four gravity sediment cores are used to trace ice events along the east siberian continental margin during the last two glaciations the clay mineral assemblages show a strong link to the extent of the east siberian ice sheet esis rather than the ice shelf or icebergs sourced from the canadian arctic during the last two glaciations illite rich sediment from east siberia was transported mainly toward the deep basin whereas kaolinite rich sediment from the canadian arctic was mostly blocked from the east siberian continental margin we speculate that during marine isotope stage 2 mis2 the southern mendeleev ridge chukchi basin and chukchi rise may have been covered by an esis extended ice shelf however the chukchi plateau and northwind ridge were dominated by a laurentide sourced ice shelf during mis4 the esis may have undergone a marked expansion with an extended ice shelf occupying all of the chukchi plateau and northwind ridge thereby restricting iceberg discharge from other ice sheets

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

tomographic determination of velocity and depth in laterally varying media estimation of reflector depth and seismic velocity from seismic reflection data can be formulated as a general inverse problem the method used to solve this problem is similar to tomographic techniques in medical diagnosis and we refer to it as seismic reflection tomography seismic tomography is formulated as an iterative gauss newton algorithm that produces a velocity depth model which minimizes the difference between traveltimes generated by tracing rays through the model and traveltimes measured from the data the input to the process consists of traveltimes measured from selected events on unstacked seismic data and a first guess velocity depth model usually this first guess model has velocities which are laterally constant and is usually based on nearby well information and or an analysis of the stacked section the final model generated by the tomographic method yields traveltimes from ray tracing which differ from the measured values in recorded data by approximately 5 ms root mean square the i

development of the flow field during the onset of the somali current 1979 abstract during the spring and summer of 1979 a multi ship survey studied the changes in currents along the east african coast in response to the transition from the northeast to the southwest monsoon the somali current in late april and early may flowed southwestward along the coast from northern somalia to about the equator surface currents were 50 100 cm s 1 and the transport was 3 106 m3 s 1 south of the equator the east african coast current eacc flowed northward the two currents met in the vicinity of the equator and turned offshore to the southeast surface velocities in the eacc were about 200 cm s 1 and its transport in the top 100 m was 15 106 m3 s 1 with the initial onset of southerly winds in early may the somali current reversed by mid may at 3 n surface speeds of 200 cm s 1 were observed the flow did not continue up the coast but turned offshore by 4 n the second onset of the monsoon took place in mid june shortly after this surface currents 350 cm s 1 were observed at the tur

collapse of polar ice sheets during the stage 11 interglacial the magnitude of sea level rise during marine isotope stage 11 about 400 000 years ago is shown to have been probably only 6 to 13 metres in contrast to some earlier estimates of up to 20 metres the ice sheets in greenland and west antarctica are known to be susceptible to climate warming and both are losing mass how the east antarctic ice sheet will respond to warming is less clear recent evidence from shoreline features in bermuda and the bahamas suggested that during marine isotope stage 11 a period of warming that occurred about 400 000 years ago the sea level was 20 metres higher than it is today which pointed to significant melting of the east antarctic ice sheet now an estimate that takes into account post glacial crustal subsidence of the shoreline sites during an anomalously long interglacial period puts the sea level during stage 11 at 6 13 metres higher than today that can be explained by the collapse of the greenland and west antarctic ice sheets with only a small contribution from the east antarctic ice sheet contentious observations of pleistocene shoreline features on the tectonically stable islands of bermuda and the bahamas have suggested that sea level about 400 000 years ago was more than 20 metres higher than it is today1 2 3 4 geochronologic and geomorphic evidence indicates that these features formed during interglacial marine isotope stage mis 11 an unusually long interval of warmth during the ice age1 2 3 4 previous work has advanced two divergent hypotheses for these shoreline features first significant melting of the east antarctic ice sheet in addition to the collapse of the west antarctic ice sheet and the greenland ice sheet1 2 3 or second emplacement by a mega tsunami during mis 11 ref 4 5 here we show that the elevations of these features are corrected downwards by 10 metres when we account for post glacial crustal subsidence of these sites over the course of the anomalously long interglacial on the basis of this correction we estimate that eustatic sea level rose to 6 13 m above the present day value in the second half of mis 11 this suggests that both the greenland ice sheet and the west antarctic ice sheet collapsed during the protracted warm period while changes in the volume of the east antarctic ice sheet were relatively minor thereby resolving the long standing controversy over the stability of the east antarctic ice sheet during mis 11

quaternary ostracode and foraminiferal biostratigraphy and paleoceanography in the western arctic ocean abstract the stratigraphic distributions of ostracodes and selected calcareous benthic and planktic foraminiferal species were studied in sediment cores from 700 to 2700 m water depth on the northwind mendeleev and lomonosov ridges in the western arctic ocean microfaunal records in most cores cover mid to late quaternary sediments deposited in the last 600 ka with one record covering the last 1 5 ma results show a progressive faunal turnover during the mid pleistocene transition mpt 1 2 to 0 7 ma and around the mid brunhes event mbe 0 4 ma reflecting major changes in arctic ocean temperature circulation and sea ice cover the observed mpt shift is characterized by the extinction of species that today inhabit the sea ice free subpolar north atlantic and or seasonally sea ice free nordic seas echinocythereis sp rockallia cf enigmatica krithe cf aquilonia pterygocythereis vannieuwenhuisei after a very warm interglacial during marine isotope stage mis 11 dominated by the temperate planktic foraminifer turborotalita egelida the mbe experienced a shift to polar assemblages characteristic of predominantly perennial arctic sea ice cover during the interglacial and interstadial periods of the last 300 ka these include the planktic foraminifera neogloboquadrina pachyderma the sea ice dwelling ostracode acetabulastoma arcticum and associated benthic taxa pseudocythere caudata pedicythere neofluitans and polycope spp several species can be used as biostratigraphic markers of specific intervals such as ostracodes rabilimis mirabilis mis 5 and p vannieuwenhuisei extinction after mis 11 and foraminiferal abundance zones bulimina aculeata late mis 5 and bolivina arctica mis 5 11

low pressure facies series metamorphism in an accretionary sedimentary prism southern alaska the low pressure high temperature metamorphism of the chugach metamorphic complex alaska occurred in an ocean continent convergence zone to achieve the high temperatures at a relatively shallow depth in an accretionary prism we propose the large scale transport of heat by fluids which preheated the metamorphic belt by tectonic focusing of fluids followed by injection of melts both of which were generated downdip in a shallow subduction zone

paleogene metamorphism of an accretionary flysch terrane eastern gulf of alaska reconnaissance field studies have identified a regional metamorphic complex at least 200 km long and 25 to 50 km wide in the eastern chugach mountains southern alaska the metamorphic complex was developed within the cretaceous valdez group a flysch sequence that was accreted to the continental margin during the late cretaceous or early tertiary the metamorphic complex shows the progressive development from subgreenschist and green schist facies slate phyllite and semischist that is regionally characteristic of the valdez group to biotite plagioclase quartz schist muscovite cordierite andalusite staurolite garnet and sillimanite in an intermediate zone and amphibolite facies muscovite biotite plagioclase quartz schist and gneiss sillimanite and garnet in a higher grade central zone k feldspar is characteristically absent in the amphibolite facies schists but it is present in migmatitic rocks that are common to the central zone the mineral assemblages and petrographic relations indicate that metamorphism took place under low pressure intermediate facies series conditions partial melting took place at the highest grade of metamorphism melting produced granodioritic magmas in migma titic rocks of the central zone that were emplaced as discrete plutons in both the intermediate zone and peripheral rocks of the complex the timing of metamorphism as indicated by field relations and k ar data is about 50 to 65 m y ago and overlaps or is coeval with the emplacement throughout the gulf of alaska region of early tertiary plutons that are thought to be anatectic in origin the distribution of these plutons suggests that a high temperature low pressure metamorphic belt about 1 800 km long developed along the leading edge of the continental margin in late paleocene to early eocene time

seismic reflection imaging of the subducting juan de fuca plate mckenzie and parker s early suggestion1 that the juan de fuca plate is underthrusting north america has since been confirmed by numerous studies evidence for plate convergence along this junction includes a sediment filled trench2 7 intense compressional deformation of the continental slope and shelf sediments2 7 seafloor magnetic anomalies that extend beneath the continental slope2 4 inland andesitic volcanoes8 paired low high heat flow and gravity anomalies9 10 active onshore deformation11 12 onshore crustal earthquakes with compressional axes parallel to the direction of plate convergence13 sinistral strike slip earthquakes along the nootka fault fig 1 14 and a well defined benioff wadati zone6 15 16 here we report the results of a seismic reflection survey that has delineated two slabs of oceanic lithosphere underlying vancouver island one that is currently being subducted and one that is underplated these findings lead us to speculate that successive underplating of oceanic lithosphere may be an important process in the evolution and growth of continents

arctic planktic foraminiferal assemblages implications for subsurface temperature reconstructions abstract earlier reconstructions of the inflow of atlantic water to arctic and subarctic oceans based on foraminiferal proxy data have been obstructed by uncertain quantitative reconstructions of sea surface and subsurface temperatures in this study surface sediment samples with undisturbed sediment water interface from polar north atlantic and barents sea were retrieved and prepared at the size fractions from 100 m to 1000 m the foraminiferal analyses show that neogloboquadrina pachyderma constitutes 96 99 of the fauna in arctic and polar surface water masses the same result is obtained when investigating the 150 m size fraction however in arctic areas influenced by atlantic water additional faunal information is obtained when using the smaller 100 m size fraction in these areas n pachyderma is reduced to about 50 and the relatively small species turborotalita quinqueloba becomes very frequent this also applies to the coastal water masses which are dominated by neogloboquadrina incompta and globigerinita uvula transfer functions using the current dataset based on the 100 m size fraction were developed and assessed different statistical models were tested using both seasonal and annual temperature data from 0 m 10 m 50 m and 100 m water depth the most precise reconstructions of subsurface temperatures were found when using summer temperatures from the 100 m depth level the transfer function was tested on holocene foraminiferal records and compared to previous reconstructions the results show that our new transfer function based on the 100 m fraction generally yields lower temperatures at both 10 and 100 m water depth than earlier reconstructions e g hald et al 2007 this could be due to the increased number of samples containing both small species and or the presence of more small specimens representing cold conditions

quaternary history of sea ice in the western arctic ocean based on foraminifera sediment cores from the northwind ridge western arctic ocean including uniquely preserved calcareous microfossils provide the first continuous proxy record of sea ice in the arctic ocean encompassing more than half of the quaternary the cores were investigated for foraminiferal assemblages along with coarse grain size and bulk chemical composition by combination of glacial cycles and unique events reflected in the stratigraphy the age of the foraminiferal record was estimated as ca 1 5 ma foraminiferal abundances diversity and composition of benthic assemblages especially phytodetritus and polar species were used as proxies for sea ice conditions foraminiferal assemblage zone 2 in the lower pleistocene indicates diminished mostly seasonal sea ice probably facilitated by enhanced inflow of pacific waters a gradual decrease in ice free season with episodes of abrupt ice expansion is interpreted for the mid pleistocene transition consistent with climatic cooling and ice sheet growth in the northern hemisphere a principal faunal and sedimentary turnover occurred near the earlyemiddle pleistocene boundary ca 0 75 ma with mostly perennial sea ice indicated by the overlying assemblage zone 1 two steps of further increase in sea ice coverage are inferred from foraminiferal assemblage changes in the glacial pleistocene by ca 0 4 and 0 24 ma possibly related to hemispheric mid brunhes event and laurentide ice sheet growth respectively these results suggest that year round ice in the western arctic was a norm for the last several 100 ka in contrast to rapidly disappearing summer ice today

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

late quaternary paleoceanography of the eurasian basin arctic ocean we reconstructed late quaternary deep 3000 4100 m and intermediate depth 1000 2500 m paleoceanographic history of the eurasian basin arctic ocean from ostracode assemblages in cores from the lomonosov ridge gakkel ridge yermak plateau morris jesup rise and amundsen and makarov basins obtained during the 1991 polarstern cruise modern assemblages on ridges and plateaus between 1000 and 1500 m are characterized by abundant relatively species rich benthic ostracode assemblages in part reflecting the influence of high organic productivity and inflowing atlantic water in contrast deep arctic eurasian basin assemblages have low abundance and low diversity and are dominated by krithe and cytheropteron reflecting faunal exchange with the greenland sea via the fram strait major faunal changes occurred in the arctic during the last glacial interglacial transition and the holocene low abundance low diversity assemblages from the lomonosov and gakkel ridges in the eurasian basin from the last glacial period have modern analogs in cold low salinity low nutrient greenland sea deep water glacial assemblages from the deep nansen and amundsen basins have modern analogs in the deep canada basin during termination 1 at intermediate depths diversity and abundance increased coincident with increased biogenic sediment reflecting increased organic productivity reduced sea ice and enhanced inflowing north atlantic water during deglaciation deep nansen basin assemblages were similar to those living today in the deep greenland sea perhaps reflecting deepwater exchange via the fram strait in the central arctic early holocene faunas indicate weaker north atlantic water inflow at middepths immediately following termination 1 about 8500 7000 year b p followed by a period of strong canada basin water overflow across the lomonosov ridge into the morris jesup rise area and central arctic ocean modern perennial sea ice cover evolved over the last 4000 5000 years late quaternary faunal changes reflect benthic habitat changes most likely caused by changes in the import of cold deepwater of greenland sea origin and warmer and middepth atlantic water to the eurasian basin through the fram strait and export of arctic ocean deepwater

calcareous microfossil based orbital cyclostratigraphy in the arctic ocean abstract microfaunal and geochemical proxies from marine sediment records from central arctic ocean cao submarine ridges suggest a close relationship over the last 550 thousand years kyr between orbital scale climatic oscillations sea ice cover marine biological productivity and other parameters multiple paleoclimate proxies record glacial to interglacial cycles to understand the climate cryosphere productivity relationship we examined the cyclostratigraphy of calcareous microfossils and constructed a composite arctic paleoclimate index api stack from benthic foraminiferal and ostracode density from 14 sediment cores following the hypothesis that api is driven mainly by changes in sea ice related productivity the api stack shows the arctic experienced a series of highly productive interglacials and interstadials every 20 kyr these periods signify minimal ice shelf and sea ice cover and maximum marine productivity rapid transitions in productivity are seen during shifts from interglacial to glacial climate states discrepancies between the arctic api curves and various global climatic sea level and ice volume curves suggest abrupt growth and decay of arctic ice shelves related to climatic and sea level oscillations

sandstone petrographic evidence and the chugach prince william terrane boundary in southern alaska the contact between the upper cretaceous valdez group and the paleocene and eocene orca group has been inferred to be the boundary between the chugach and the prince william tectonostratigraphic terranes sandstone petrographic data from the prince william sound area show no compositional discontinuity across this contact these data are best explained by considering the valdez and orca groups to be part of a single terrane a thick flysch sequence derived primarily from a progressively unroofing magmatic arc with increasing input from subduction complex sources through time

variability of sea ice conditions in the fram strait over the past 30 000 years sea ice is a critical component of the climate and oceanographic system in the north atlantic ocean a biomarker record reveals millennial scale and glacial interglacial fluctuations in sea ice coverage in the northernmost atlantic ocean over the past 30 000 years

southward subsurface flow below the somali current the existence of a southward flowing current beneath the northern part of the seasonally reversing somali current is documented in a 2 year long time series of currents obtained at moored stations near 5 n about 30 km off the somali coast its mean annual transport in the layer 150 600 m amounts to about 5 106 m3 s the undercurrent has a pronounced seasonal cycle in phase with the near surface flow suggesting a close coupling to the monsoonal wind forcing with the spin up of the deepreaching northern somali gyre after the onset of the southwest monsoon the undercurrent is temporarily destroyed in the northern somali basin during june july but is re established in august the undercurrent does not reach 3 n but turns offshore north of that latitude

the northern cascadia subduction zone at vancouver island seismic structure and tectonic history the structure and tertiary tectonic history of the northern cascadia subduction zone have been delineated by a series of new multichannel seismic lines acquired across the continental shelf to the

deep arctic ocean warming during the last glacial cycle in the arctic ocean the cold and relatively fresh water beneath the sea ice is separated from the underlying warmer and saltier atlantic layer by a halocline ongoing sea ice loss and warming in t

late pleistocene and holocene meltwater events in the western arctic ocean accelerator mass spectrometer 14 c dated stable isotope data from neogloboquadrina pachyerma in cores raised from the mendeleyev ridge and slope provide evidence for significant influx of meltwater to the western arctic ocean during the early part of marine oxygen isotope stage 1 ois 1 and during several intervals within ois 3 the strongest ois 3 meltwater event occurred before ca 45 ka conventional radiocarbon age and was probably related to the deglaciation at the beginning of ois 3 major meltwater input to the western arctic ocean during the last deglaciation coincides closely with the maximum rate of global sea level rise as determined from the barbados sea level record demonstrating a strong link between the global record and changes in the central arctic ocean ois 2 which includes the last glacial maximum is very condensed or absent in the cores abundance and 13 c values for n pachyderma in the middle part of ois 3 are similar to modern values indicating high productivity and seasonal ice free areas along the arctic margin at that time these records indicate that the arctic ocean was a source of heat and moisture to the northern polar atmosphere during parts of ois 3

reconstruction of sea surface temperatures from assemblages of planktonic foraminifera multi technique approach based on geographically constrained calibration data sets and its application to glacial atlantic and pacific oceans abstract we present a conceptual framework for a new approach to environmental calibration of planktonic foraminifer census counts this approach is based on simultaneous application of a variety of transfer function techniques which are trained on geographically constrained calibration data sets it serves to minimise bias associated with the presence of cryptic species of planktonic foraminifera and provides an objective tool for assessing reliability of environmental estimates in fossil samples allowing identification of adverse effects of no analog faunas and technique specific bias we have compiled new calibration data sets for the north n 862 and south n 321 atlantic and the pacific ocean n 1111 we show evidence that these data sets offer adequate coverage of the sea surface temperature sst and faunal variation range and that they are not affected by the presence of pre holocene samples and or calcite dissolution we have applied four transfer function techniques including artificial neural networks revised analog method and simmax with and without distance weighting on faunal counts in a last glacial maximum lgm data set for the atlantic ocean 748 samples in 167 cores based on the glamap 2000 compilation and a new data set for the pacific ocean 265 samples in 82 cores and show that three of these techniques provide adequate degree of independence for the advantage of a multi technique approach to be realised the application of our new approach to the glacial pacific lends support to the contraction and perhaps even a cooling of the western pacific warm pool and a substantial 3 c cooling of the eastern equatorial pacific and the eastern boundary currents our results do not provide conclusive evidence for lgm warming anywhere in the pacific the atlantic reconstruction shows a number of robust patterns including substantial cooling of eastern boundary currents with considerable advection of subpolar waters into the benguela current a cooling of the equatorial atlantic by 5 c and steep sst gradients in the mid latitude north atlantic the transfer function techniques generally agree that subtropical gyre areas in both hemispheres did not change significantly since the lgm although the ann technique produced glacial sst in the southern gyre 1 2 c warmer than today we have revisited the issue of sea ice occurrence in the nordic seas and using the distribution of subpolar species of planktonic foraminifera in glacial samples we conclude that the norwegian sea must have been ice free during the summer

a 600 ka arctic sea ice record from mendeleev ridge based on ostracodes arctic paleoceanography and sea ice history were reconstructed from epipelagic and benthic ostracodes from a sediment core hly0503 06jpc 800 m water depth located on the mendeleev ridge western arctic ocean the calcareous microfaunal record ostracodes and foraminifers covers several glacial interglacial cycles back to estimated marine isotope stage 13 mis 13 500 ka with an average sedimentation rate of 0 5 cm ka for most of the stratigraphy mis 5 13 results based on ostracode assemblages and an unusual planktic foraminiferal assemblage in mis 11 dominated by a temperate water species turborotalita egelida show that extreme interglacial warmth high surface ocean productivity and possibly open ocean convection characterized mis 11 and mis 13 400 and 500 ka respectively a major shift in western arctic ocean environments toward perennial sea ice occurred after mis 11 based on the distribution of an ice dwelling ostracode acetabulastoma arcticum spectral analyses of the ostracode assemblages indicate sea ice and mid depth ocean circulation in western arctic ocean varied primarily at precessional 22 ka and obliquity 40 ka frequencies

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

holocene climatic records from agassiz ice cap ellesmere island nwt canada four ice cores from the top of the agassiz ice cap and down a flow line have been variously analysed for 8 18o ecm solid conductivity and ice melt layer stratigraphy stratigraphic correlation

dipping seismic reflectors electrically conductive zones and trapped water in the crust over a subducting plate the lithoprobe program across the northern cascadia subduction zone at vancouver island has obtained geophysical data that suggest a dipping zone of trapped free pore water in the overlying continental crust land and marine multichannel seismic reflection profiles show several bands of reflectors the primary one at a depth of about 30 km is about 5 km thick dips inland and appears to coincide with an electrically conductive layer defined by magnetotelluric data the downgoing oceanic crust is imaged as a thin reflector dipping at about 15 and 10 km deeper than the primary reflector a location that is consistent with seismicity and seismic refraction data both the reflectors and the conductor have been modeled by near horizontal lamellae with 1 4 saline water porosity detailed geothermal measurements defining heat flow that decreases inland indicate that the dipping bands are nearly isothermal at a temperature of 400 500 c it is suggested that free water generated by dehydration of the downgoing oceanic plate migrates upward until reduced temperature results in hydration reactions and mineral precipitation that forms an impermeable barrier low vertical permeability is required to keep the water from separating to the top of the layer this can be reconciled with the low electrical resistivity if pore interconnection is through thin grain boundary tubes as predicted by theoretical equilibrium pore geometry although very small effective grain size is necessary an abrupt transition from high permeability to very low permeability is predicted at a several percent porosity in agreement with the modeled porosity such pore geometry with low permeability may be restricted to temperatures above about 400 c i e in greenschist to amphibolite facies conditions where grains will deform to equilibrium geometry and cracks are annealed the region above the reflective and conductive band is estimated to be within blueschist conditions consistent with the inferred high seismic velocity from refraction data and high density from gravity data

crustal structure of accreted terranes in southern alaska chugach mountains and copper river basin from seismic refraction results seismic refraction data were collected along a 320 km long transect line in southern alaska crossing the prince william chugach peninsular and wrangellia terranes and along several shorter lines within individual terranes velocity structure in the upper crust less than 9 km depth differs among the four terranes in contrast layers in the middle crust 9 to 25 km depth in some cases extend across projected terrane boundaries the following observations can be made 1 an intermediate velocity layer 6 4 km s at 9 km depth extends across the deep projection of the suture between the chugach and peninsular terranes suggesting that the northern chugach and southern peninsular terranes are detached and rest on a deeper terrane of unknown origin 2 the top of a gently north dipping sequence of low and high velocity layers 5 7 7 8 km s more than 10 km thick extends from near the surface in the southern chugach terrane to more than 20 km depth beneath the southern peninsular terrane this sequence truncated by the suture between the prince william and chugach terranes is interpreted to be an underplated terrane made up of fragments of the kula plate and its sedimentary overburden that were accreted during subduction in the late mesozoic and or early tertiary during or between times of accretion of the prince william and chugach terranes 3 a thick crustal root with a laminated sequence at its top extends from a depth of 19 km to as much as 57 km beneath the northern peninsular and wrangellia terranes this root extends across the deep projection of the suture between the peninsular and wrangellia terranes although resolution of this apparent crosscutting relationship is relatively poor this root may represent tectonically or possibly magmatically emplaced rocks the lower crust beneath the prince william chugach and southern peninsular terranes includes a north dipping 3 to 8 km thick section of subducting oceanic crust

middle to late pleistocene arctic paleoceanographic changes based on sedimentary records from mendeleev ridge and makarov basin abstract three sediment cores from the makarov basin and mendeleev ridge off the siberian margin were analyzed for a number of litho bio and magnetostratigraphic proxies correlation to previously studied arctic records from mendeleev to lomonosov ridges enables paleoceanographic reconstructions for the middle to late pleistocene estimated 0 8 ma on orbital time scales cyclic changes in lithology corroborated by multiple stratigraphic constraints were tuned to global climate variations based on the manganese content that increases during interglacials while calcium and zircon were used as proxies for the laurentide and eurasian ice sheet inputs the combined evaluation of glacial and interglacial proxy variabilities provides a coherent picture of the western arctic ocean development in the pleistocene we suggest that major cyclic changes were driven by summer processes such as sea ice retreat and enhanced biological production vs suppressed ice melt in warmer and colder summers respectively a potential link to low latitudes via atmospheric moisture and heat transport is indicated by similarities in the western arctic ocean and east asian monsoon records long term cooling is signified by biogenic proxies related to sea ice expansion over the western arctic ocean with step changes at mis 11 and 7 0 4 and 0 2 0 3 ma this transition also features better fossil preservation indicating less corrosive oxidative bottom waters probably resulting from a decrease in organic export production and or weakening of bottom water ventilation under perennial sea ice the latter was possibly enhanced by atmospheric cooling and increased meltwater fluxes with the growth of circum arctic ice sheets

model for the origin of the yakutat block an accreting terrane in the northern gulf of alaska a composite oceanic and continental terrane the yakutat block is currently colliding with and accreting to north america in the northern gulf of alaska marine geophysical data indicate that the block has moved with the pacific plate during pliocene and quaternary time but are indeterminant about its previous movement history a model that explains some observed geologic and structural features of the block is that it originated as a result of subduction of the kula farallon spreading center beneath north america in this model the spreading center that formed the basaltic basement of the yakutat block was offset from a spreading center to the south by a left lateral transform fault 400 500 km long subduction of the northern spreading center about 45 m y ago sliced off part of the north america continental margin attached it to the kula plate and initiated northward movement of the composite terrane as the yakutat block during eocene and oligocene time migration of the southern spreading center toward north america truncated the yakutat block on the south and left a fossil fracture zone that is now seen as the transition fault the southern spreading center subducted about 25 m y ago and the yakutat block has since traveled with the pacific plate to southern alaska

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

seismic reflection images of the crust of the northern part of the chugach terrane alaska results of a survey for the trans alaska crustal transect tact deep crustal seismic reflection data show strong reflections from the middle and lower crust of the convergent continental margin near the eastern end of the aleutian trench these data were collected across the border ranges fault system a major suture zone that separates the peninsular and chugach tectonostratigraphic terranes the chugach terrane consists of metamorphosed strongly deformed flysch subduction melange as well as blueschist and greenschist facies rocks even so highly reflective rocks lie at great depth within or beneath this terrane the shallow part of the seismic section 0 5 s reveals only a few reflections which undulate and interweave indicating that some of them originate outside of the plane of the seismic section other undulating events could reveal early cenozoic granitic plutons or antiformal stacks of rock imbricated along thrust faults in contrast to this shallow reflection pattern three reflection bands contain most of the events on the middle part of the seismic section 5 12 s or 12 34 km we interpret divergent reflections within the uppermost band 5 5 5 s as gently north dipping thrust faults and subparallel reflections truncated at the boundaries of the upper and middle bands may image a metamorphic foliation or thrust faults if the truncated reflections represent thrust faults then the reflection geometry suggests that subparallel roof and floor thrust faults bound imbricated rocks forming duplex structures the upper and middle bands are separated by an area on the seismic section that reveals few reflections this area correlates approximately in depth with a high velocity 7 5 km s layer evident in refraction models the poorly reflective high velocity unit might be volcanic rocks like those exposed in the structurally lowest part of the chugach terrane if so then the bottom of the poorly reflective rocks indicates the base of the chugach terrane rocks that cause the upper and middle reflection bands and the intervening poorly reflective volcanic rocks may form a midcrustal shear zone that is about 10 km thick the deepest band of subparallel reflections 30 35 km correlates closely in depth with the top of the wadati benioff zone associated with the underthrusting pacific plate the reflections probably stem from the decollement that separates lithospheric plates within the subduction zone this reflection band increases abruptly in thickness possibly indicating local underplating of subducted sediment no events from the oceanic moho have been recognized neither the border ranges fault system the suture between the chugach and peninsular terranes nor deep crustal layers of the peninsular terrane are evident in these seismic reflection data

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

sea level rise due to polar ice sheet mass loss during past warm periods background although thermal expansion of seawater and melting of mountain glaciers have dominated global mean sea level gmsl rise over the last century mass loss from the greenland and antarctic ice sheets is expected to exceed other contributions to gmsl rise under future warming to better constrain polarice sheetresponse to warmer temperatures we draw on evidence from in terglacial periods in the geologic record that ex perienced warmer polar temperatures and higher gmsls than present coastal records of sea level from these previous warm periods dem onstrate geographic variability because of the influence of several geophysical processes that operate across a range of magnitudes and time scales inferring gmsl and ice volume changes from these reconstructions is nontrivial and generally requires the use of geophysical models advances interdisciplinary studies of geo logic archives have ushered in a new era of deciphering magnitudes rates and sources of sea level rise advances in our understanding of polar ice sheet response to warmer climates have been made through an increase in the number and geographic distribution of sea level reconstructions better ice sheet constraints and the recognition that several geophysical processes cause spatially complex patterns in sea level in particular accounting for glacial isostatic processes helps to decipher spatial variability in coastal sea level records and has reconciled a number of site specific sea level reconstructions for warm periods that have oc curred within the past several hundred thou sand years this enables us to infer that during recent interglacial periods small increases in

expanded record of quaternary oceanographic change amerasian arctic ocean four sediment cores collected from the northwind and mendeleyev ridges arctic ocean from 1089 m to 1909 m water depth provide an oceanographic record extending back into the matuyama reversed polarity chron benthic foraminiferal analyses show four prominent assemblage zones bolivina arctica cassidulina teretis bulimina aculeata and oridorsalis tener from the upper matuyama reversed polarity chronozone through the brunhes normal polarity chronozone these assemblage zones represent depth dependent benthic foraminiferal biofacies changes associated with oceanographic events that occurred in the amerasian basin at 780 and 300 ka and indicate oceanographic influence from the north atlantic recognition of these benthic assemblage zones in arctic cores from the alpha ridge indicates that the benthic foraminiferal zonations in intermediate to deep water 1000 m arctic cores may be more useful than preexisting lithostratigraphic zonations and should provide important information pertaining to the quaternary paleoceanographic evolution of the arctic ocean

reconstructing late quaternary deep water masses in the eastern arctic ocean using benthonic ostracoda abstract the distribution of ostracoda in three long cores from the deep eastern arctic ocean was studied to determine the palaeoceanographical history of the eurasian basin during the late quaternary the samples for this study were obtained from the lomonosov ridge morris jesup rise and yermak plateau during the arctic 91 expedition ostracoda previously studied in coretops at the same sites as the present study have shown that individual species have a strong association with different water masses and bathymetry throughout the late quaternary cores exhibit ostracod rich layers separated by barren intervals on the basis of biostratigraphical isotopic and palaeomagnetic data the fossiliferous levels are interpreted as representing interglacial stages the twenty most significant species were selected for subsequent quantitative investigation using cluster and factor analyses in order to determine similarity and variance between the assemblages an additional statistical method employing modern analogues and the squared chord distance dissimilarity coefficient was utilised to compare the present late quaternary fossil samples with a modern arctic database the results reveal a major faunal division within the arctic ocean deep water aodw highly abundant and diverse assemblages within the cores were found to group and have good analogues with the recent bathyal depth 1000 2500 m upper aodw assemblages conversely assemblages with low abundance and diversity correlate well with abyssal depth 3000 m lower aodw assemblages the palaeoceanographical history is complicated by the influence of adjacent water masses such as canada basin deep water cbdw greenland sea deep water gsdw and most importantly arctic intermediate water aiw which all had an influence on the ostracod assemblages during the late quaternary an enhanced flow of warm saline aiw into the eurasian basin results in species rich upper aodw assemblages having good analogues down to 2750 m in the water column in contrast lower aodw assemblages influenced by cold well oxygenated gsdw give analogues at depths as shallow as 1000 m the faunal changes are the consequence of rapid climatic fluctuations in the eastern arctic ocean during the late quaternary that are intrinsically linked to palaeoceanographical alternations in warm and cold current inflow from adjacent basins

a cold and fresh ocean surface in the nordic seas during mis 11 significance for the future ocean paleoceanographical studies of marine isotope stage mis 11 have revealed higher than present sea surface temperatures ssts in the north atlantic and in parts of the arctic but lower than present ssts in the nordic seas the main throughflow area of warm water into the arctic ocean we resolve this contradiction by complementing sst data based on planktic foraminiferal abundances with surface salinity changes using hydrogen isotopic compositions of alkenones in a core from the central nordic seas the data indicate the prevalence of a relatively cold low salinity surface water layer in the nordic seas during most of mis 11 in spite of the low density surface layer which was kept buoyant by continuous melting of surrounding glaciers warmer atlantic water was still propagating northward at the subsurface thus maintaining meridional overturning circulation this study can help to better constrain the impact of continuous melting of greenland and arctic ice on high latitude ocean circulation and climate

early middle pleistocene transitions linking terrestrial and marine realms abstract marked by a progressive increase in the amplitude of climate oscillations an evolving waveform and a shift towards a quasi 100 ky frequency the early middle pleistocene transition empt previously known as the mid pleistocene transition or mid pleistocene revolution 1 4 0 4 ma represents a fundamental transformation in the earth s climate state the empt began with a substantial change in climate dynamics and ended with the mid brunhes event signaling the establishment of a new steady state the reasons for the empt while uncertain appear to involve a non linear response of the earth climate system the physical and biotic responses to this transition amplified by the growth of northern hemisphere ice sheets have been profound two important chronostratigraphic markers characterize the empt the jaramillo subchron 1 070 0 988 ma and the matuyama brunhes chron boundary 773 ka the latter has been chosen as the primary guide for the lower middle pleistocene subseries boundary as it lies at the approximate midpoint of the empt and aids in global recognition both in marine and terrestrial deposits the jaramillo subchron has received less attention but the late early pleistocene is important in europe because it saw the progressive transition from the villafranchian to galerian mammal faunas and expansion of hominins into western and northern europe the jaramillo subchron is represented by marine isotope stages mis 31 to 28 with mis 30 already showing the asymmetrical sawtooth pattern characteristic of the middle pleistocene indeed while variation in the 40 ky band obliquity remains strong throughout the empt low frequency variability begins at around 1250 1200 ky which coincides with a progressive increase in global ice volume against a backdrop of increasingly severe glacial cycles notably during mis 36 34 24 22 the so called 0 9 ma event 16 and 12 pronounced phases of warming are also documented globally including the super interglacial mis 31 the early phase of the empt is characterized by important glaciations beginning with mis 36 and continuing to mis 24 22 a major intensification of the east asian monsoon system intensification of loess deposition in northern europe development of open landscapes in western siberia increased fluvial incision higher amplitude sea level change and spread of large mammals across northern eurasia and a strong reduction in the north atlantic thermohaline circulation in europe the loss of thermophilous plant taxa during the empt and indeed throughout the quaternary is a reminder of the progressive cooling that took place here and elsewhere

glacial north atlantic sea surface conditions reconstructed by glamap 2000 the response of the tropical ocean to global climate change and the extent of sea ice in the glacial nordic seas belong to the great controversies in paleoclimatology our new reconstruction of peak glacial sea surface temperatures ssts in the atlantic is based on census counts of planktic foraminifera using the maximum similarity technique version 28 simmax 28 modern analog technique with 947 modern analog samples and 119 well dated sediment cores our study compares two slightly different scenarios of the last glacial maximum lgm the environmental processes of the ice age land oceans glaciers epilog and glacial atlantic ocean mapping glamap 2000 time slices the comparison shows that the maximum lgm cooling in the southern hemisphere slightly preceeded that in the north in both time slices sea ice was restricted to the north western margin of the nordic seas during glacial northern summer while the central and eastern parts were ice free during northern glacial winter sea ice advanced to the south of iceland and faeroe in the central northern north atlantic an anticyclonic gyre formed between 45degrees and 60degreesn with a cool water mass centered west of ireland where glacial cooling reached a maximum of 12degreesc in the subtropical ocean gyres the new reconstruction supports the glacial to interglacial stability of sst as shown by climap project members climap 1981 the zonal belt of minimum sst seasonality between 2degrees and 6degreesn suggests that the lgm caloric equator occupied the same latitude as today in contrast to the climap reconstruction the glacial cooling of the tropical east atlantic upwelling belt reached up to 6degrees 8degreesc during northern hemisphere summer differences between these simmax based and published u37 k and mg ca based equatorial sst records are ascribed to strong sst seasonalities and sst signals that were produced by different planktic species groups during different seasons

wrangell benioff zone southern alaska the first unequivocal evidence for the existence of a benioff zone that may be related to the quaternary wrangell volcanoes comes from a set of 86 well located hypocenters for earthquakes smaller than about magnitude 4 in the region between lat 61 and 62 5 n and between long 142 and 145 5 w about half of the earthquakes occur at depths of 25 km or less below 40 km a clearly defined north northeast dipping zone of seismicity here termed the wrangell benioff zone extends to a depth of about 85 km and continues for about 115 km along strike subparallel to the volcanic trend the western end of the zone may be offset from the northern end of the much more active aleutian benioff zone where the benioff zone shoals to 30 to 40 km it becomes nearly horizontal and cannot be clearly distinguished from upper plate seismicity it is uncertain whether the subducted plate segment that contains the wrangell benioff zone is structurally part of the pacific plate or the yakutat block

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

a 10 000 year record of arctic ocean sea ice variability view from the beach we present a sea ice record from northern greenland covering the past 10 000 years multiyear sea ice reached a minimum between 8500 and 6000 years ago when the limit of year round sea ice at the coast of greenland was located 1000 kilometers to the north of its present position the subsequent increase in multiyear sea ice culminated during the past 2500 years and is linked to an increase in ice export from the western arctic and higher variability of ice drift routes when the ice was at its minimum in northern greenland it greatly increased at ellesmere island to the west the lack of uniformity in past sea ice changes which is probably related to large scale atmospheric anomalies such as the arctic oscillation is not well reproduced in models this needs to be further explored as it is likely to have an impact on predictions of future sea ice distribution

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

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

a novel chemical fossil of palaeo sea ice ip25 a unique and novel organic compound has been detected in sea ice samples from three locations in the canadian arctic thousands of kilometers apart it is likely that this biomarker is produced by diatoms living in the sea ice and we provide evidence which suggests that the compound a c25 monounsaturated hydrocarbon ip25 may be a specific sensitive and stable proxy for sea ice in sediments over at least the holocene since it has not been reported before we confirmed its identity by synthesis and used the synthesized compound as a reference for quantifying ip25 in a range of sediments from an east west transect in the canadian arctic the recent sediments are either seasonally covered with ice or have permanent ice cover older sediments containing ip25 have been dated using radiocarbon methods to at least 9000 yr if the concept proves generally applicable monitoring ip25 in further sediment cores along with other accepted proxies should allow movements in the position of the ice edge throughout the holocene at least to be better determined which is essential for accurate calibration of climate prediction models a similar approach for antarctic samples of ice and sediments would also seem worthwhile

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

south greenland ice sheet collapse during marine isotope stage 11 varying levels of boreal summer insolation and associated earth system feedbacks led to differing climate and ice sheet states during late quaternary interglaciations in particular marine isotope stage mis 11 was an exceptionally long interglaciation and potentially had a global mean sea level 6 to 13 metres above the present level around 410 000 to 400 000 years ago implying substantial mass loss from the greenland ice sheet gis there are however no model simulations and only limited proxy data to constrain the magnitude of the gis response to climate change during this super interglacial thus confounding efforts to assess climate ice sheet threshold behaviour and associated sea level rise here we show that the south gis was drastically smaller during mis 11 than it is now with only a small residual ice dome over southernmost greenland we use the strontium neodymium lead isotopic composition of proglacial sediment discharged from south greenland to constrain the provenance of terrigenous silt deposited on the eirik drift a sedimentary deposit off the south greenland margin we identify a major reduction in sediment input derived from south greenland s precambrian bedrock terranes probably reflecting the cessation of subglacial erosion and sediment transport as a result of near complete deglaciation of south greenland comparison with ice sheet configurations from numerical models suggests that the gis lost about 4 5 to 6 metres of sea level equivalent volume during mis 11 this is evidence for late quaternary gis collapse after it crossed a climate ice sheet stability threshold that may have been no more than several degrees above pre industrial temperatures

quaternary history of sea ice and paleoclimate in the amerasia basin arctic ocean as recorded in the cyclical strata of northwind ridge the 19 middle early pleistocene to holocene bipartite lithostratigraphic cycles observed in high resolution piston cores from northwind ridge in the amerasia basin of the arctic ocean provide a detailed record of alternating glacial and interglacial climatic and oceanographic conditions and of correlative changes in the character and thickness of the sea ice cover in the amerasia basin glacial conditions in each cycle are represented by gray pelagic muds that are suboxic laminated and essentially lacking in microfossils macrofossils trace fossils and generally in glacial erratics interglacial conditions are represented by ochre pelagic muds that are oxic and bioturbated and contain rare to abundant microfossils and abundant glacial erratics the synglacial laminated gray muds were deposited when the central amerasia basin was covered by a floating sheet of sea ice of sufficient thickness and continuity to reduce downwelling solar irradiance and oxygen to levels that precluded photosynthesis maintenance of a biota and strong oxidation of the pelagic sediment except during the early part of 3 of the 19 synglacial episodes when it was periodically breached by erratic bearing glacial icebergs the floating arctic ocean sea ice sheet was sufficiently thick to block the circulation of icebergs over northwind ridge and presumably other areas of the central arctic ocean interglacial conditions were initiated by abrupt thinning and breakup of the floating sea ice sheet at the close of glacial time which permitted surges of glacial erratic laden icebergs to reach northwind ridge and the central arctic ocean where they circulated freely and deposited numerous and relatively thick erratic clast rich beds breakup of the successive synglacial sea ice sheets initiated deposition of the interglacial ochre mud units under conditions that allowed sunlight and increased amounts of oxygen to enter the water column resulting in photosynthesis and biologic productivity and strong oxidization of the pelagic sediment the lithostratigraphy of northwind ridge suggests that during at least late pleistocene time glacial conditions in the arctic ocean were initiated abruptly and continued unabated until terminated also abruptly by onset of the succeeding interglacial warming variations in abundance of glacial erratics within the interglacial units of the late pleistocene indicate that during at least most interglacial episodes northern north america was glaciated but with generally diminishing severity until onset of the succeeding continental glaciation magnetostratigraphy suggests that the glacial interglacial cycles on northwind ridge had an average periodicity of approximately 93 5 k y during the brunhes normal and approximately 105 k y during the latter part of the matuyama reverse polarity zone these average periodicities are close to the 100 k y temperature cycles found in north atlantic deep water sediments of the brunhes normal polarity chron which have been ascribed to forcing by a milankovitch eccentricity cycle they are also close however to the average interval 101 k y between the aperiodic glacial terminations in the 500 k y pleistocene continental climate record from devil s hole nevada which have been ascribed to nonlinear feedbacks within the earth s atmosphere ice sheet ocean system

pleistocene deep sea ostracods from the bering sea iodp expedition 323 abstract the study presents the first pleistocene 0 1 9 ma record of deep sea ostracods from the bering sea derived primarily from integrated ocean drilling program expedition 323 site u1344 59 3 0 n 179 12 2 w 3171 m of water depth deep sea ostracod abundances in the bering sea sediments are some of the lowest that have been recorded in bathyal and abyssal marine environments

quaternary paleoceanography of the deep arctic ocean based on quantitative analysis of ostracoda abstract ostracodes were studied from deep arctic ocean cores obtained during the arctic 91 expedition of the polarstern to the nansen amundsen and makarov basins the lomonosov ridge morris jesup rise and yermak plateau in order to investigate their distribution in arctic ocean deep water aodw and apply these data to paleoceanographic reconstruction of bottom water masses during the quaternary analyses of coretop assemblages from arctic 91 boxcores indicate the following ostracodes are common at all depths between 1000 and 4500 m and species distribution is strongly influenced by water mass characteristics and bathymetry quantitative analyses comparing eurasian and canada basin assemblages indicate that distinct assemblages inhabit regions east and west of the lomonosov ridge a barrier especially important to species living in lower aodw deep eurasian basin assemblages are more similar to those living in greenland sea deep water gsdw than those in canada basin deep water two upper aodw assemblages were recognized throughout the arctic ocean one living between 1000 and 1500 m and the other having high species diversity at 1500 3000 m downcore quantitative analyses of species abundances and the squared chord distance coefficient of similarity reveals a distinct series of abundance peaks in key indicator taxa interpreted to signify the following late quaternary deep water history of the eurasian basin during the last glacial maximum lgm a gsdw aodw assemblage characteristic of cold well oxygenated deep water 3000 m today inhabited the lomonosov ridge to depths as shallow as 1000 m perhaps indicating the influence of gsdw at mid depths in the central arctic ocean during termination 1 a period of high organic productivity associated with a strong inflowing warm north atlantic layer occurred during the mid holocene several key faunal events indicate a period of warming and or enhanced flow between the canada and eurasian basins a long term record of ostracode assemblages from kastenlot core ps2200 5 1073 m water depth from the morris jesup rise indicates a quasi cyclic pattern of water mass changes during the last 300 kyr interglacial ostracode assemblages corresponding to oxygen isotope stages 1 5 and 7 indicate rapid changes in dissolved oxygen and productivity during glacial interglacial transitions