dinoflagellate cyst assemblages as tracers of sea surface conditions in the northern north atlantic arctic and sub arctic seas the new n 677 data base and its application for quantitative palaeoceanographic reconstruction the distribution of dinoflagellate cyst dinocyst assemblages in surface sediment samples from 677 sites of the northern north atlantic arctic and sub arctic seas is discussed with emphasis on the relationships with sea surface parameters including sea ice cover salinity and temperature of the coldest and warmest months difficulties in developing a circum arctic data base include the morphological variation within taxa e g operculodinium centrocarpum islandinium cezare and polykrikos sp which probably relate to phenotypic adaptations to cold and or low salinity environments sparse hydrographical data together with large interannual variations of temperature and salinity in surface waters of arctic seas constitute additional limitations nevertheless the use of the best analogue technique with this new dinocyst data base including 677 samples permits quantitative reconstruction of sea surface conditions at the scale of the northern north atlantic and the arctic domain the error of prediction calculated from modern assemblages is 1 3 ca nd 1 8 c for the temperature of february and august respectively 1 8 for the salinity and 1 5 months yr 1 for the sea ice cover application to late quaternary sequences from the western and eastern subpolar north atlantic labrador sea and barents sea provide reconstructions compatible with those obtained using the previous dinocyst data base n 371 which mainly included modern data from the northern north atlantic copyright 2001 john wiley sons ltd journal of quaternary science

impact of eastern arctic shelf waters on the nansen basin intermediate layers the eurasian shelves supply water to the nansen basin intermediate layers in two ways as buoyancy driven plumes of dense winter water and as permanent inflow of the barents sea branch of atlantic water while the plumes are local and seasonal phenomena the barents sea flow is part of the large scale circulation both interact with atlantic water which enters the arctic ocean through fram strait and moves as a subsurface boundary current eastward along the continental slope during the polarstern cruise ark ix 4 in summer 1993 the fram strait branch was observed as a narrow core within tens of kilometers of the barents sea shelf edge here several patches of cold low salinity water spread across the slope down to about 500 m depth their origin is assumed to be the northern barents sea they mix with the warm saline fram strait branch water fsbw so that the core properties of the latter become modified downstream in the eastern nansen basin the fram strait branch is displaced toward the inner basin by inflow of the barents sea branch of atlantic water bsbw this inflow appears as a broad 200 km wedge extending from 200 to 1300 m depth bsbw is colder and less saline than water of the fram strait branch and it is less dense and less stratified than the ambient water both branches appear to undergo vigorous mixing while spreading eastward so that any eastward continuation of the boundary flow transports about 50 bsbw and 50 fsbw above 600 m and about 80 bsbw and 20 fsbw below that level toward the canadian basin according to available observations the barents and kara seas are the only source areas for shelf waters ventilating the nansen basin below the halocline and these waters constitute a freshwater input rather than a salt input winter shelf water from the laptev sea cannot contribute to layers deeper than the upper halocline

relationships between dinoflagellate cyst assemblages in surface sediment and hydrographic conditions in the bering and chukchi seas palynological analyses were performed on 52 surface sediment samples from the eastern part of the bering sea and chukchi sea in order to document the regional distribution of dinoflagellate cyst assemblages and their relationship with sea surface conditions the assemblages present a relatively high species diversity 20 taxa are recovered routinely especially in the bering sea where they are dominated by operculodinium centrocarpum and the cyst of pentapharsodinium dalei accompanied mainly by spiniferites elongatus s l spiniferites ramosus impagidinium pallidum brigantedinium spp islandinium minutum selenopemphix quanta selenopemphix nephroides quinquecuspis concreta and the cyst of polykrikos kofoidii the percentages of the main taxa vary with latitude and principal component analysis shows that the distribution of assemblages is closely related to hydrographic conditions notably the seasonal duration of sea ice cover and the sea surface temperature in february the dinoflagellate cyst assemblages from the bering sea differ significantly from those of subarctic seas of the north atlantic with respect to their species composition and relationships with sea surface conditions in particular the occurrence of the cyst of polykrikos kofoidii and quinquecuspis concreta and the positive correlation between the percentages of operculodinium centrocarpum and the extent of sea ice constitute peculiar features in the bering sea assemblages copyright 2001 john wiley sons ltd journal of quaternary science

holocene paleoceanography of the northwest passage canadian arctic archipelago abstract a series of cores box and piston were collected at 2 key locations in lancaster sound cores 2004 804 009 bc and pc and barrow strait cores 2005 804 004 bc and pc in the canadian arctic archipelago to document the evolution of sea surface conditions in the main axis of the northwest passage during the holocene time period reconstruction of sea surface parameters summer temperature and salinity duration of sea ice cover were estimated based on transfer functions using dinoflagellate cyst assemblages as proxy indicators the chronology of these cores is based on calibrated ams 14c dates 210pb analyses and correlations between paleomagnetic secular variations of the geomagnetic field and a predicted spherical harmonic model of the geomagnetic field cals7 k 2 our age models for both cores indicate that 009 pc spans the last 11 100 cal bp while 004 pc encompasses the last 10 800 cal bp calculated sedimentation rates are in the range of 43 140 cm kyr for core 009 pc and 15 118 cm kyr for core 004 pc allowing for a millennial time scale resolution in each core our results indicate relatively harsh conditions in lancaster sound between 10 800 and 9000 cal bp summer temperatures 2 c cooler than at present which we associate with the presence of active ice streams in northernmost baffin bay and a weak west greenland current this is followed by a warming trend up to 3 c higher than present that took place between 8500 and 5500 cal bp which we associate with the holocene thermal maximum and to a large scale atmospheric pattern such as the arctic oscillation operating at the millennial time scale this is concomitant with an increase in the relative abundance of phototrophic dinoflagellate cyst taxa a gradual cooling of sea surface temperature and increased sea ice follow this from 5500 cal bp until the modern period in barrow strait harsh sea surface conditions prevailed from 11 100 to 5500 cal bp with summer temperatures as low as 4 c cooler than at present the warming trend occurred later in this region between 5500 and 1000 cal bp after which a gradual cooling is observed until the modern period the apparent shift or opposite warming trends between lancaster sound and barrow strait after 5500 cal bp could be the result of a change in atmospheric circulation patterns related to a possible shift in the ao mode from ao to ao comparison of ice core 18o record from devon island ice cap and the reconstructed sea surface temperature from core 009 pc suggests a strong atmospheric oceanic coupling throughout the holocene in this area

provenance of pliocene sediments and paleoenvironmental changes in the southern north sea region using samarium neodymium sm nd provenance ages and clay mineralogy abstract an 800 m thick sedimentary succession from the late pliocene north sea has been investigated on the provenance of the sediments and on changes of the source regions related to transport processes and climate changes the lower zanclean to piacenzian part of the succession from 1250 to 1050 m depth and the middle early gelasian part from 1100 to 700 m depth belong to one distributory system with at least two contributing source areas provenance ages calculated on basis of sm nd content indicate one old archean and one young

seven glacial cycles in the middle late pleistocene of northwest europe geomorphic evidence from buried tunnel valleys the deep ocean marine isotope record and the antarctic and greenland ice caps record numerous glacial and interglacial cycles since the middle pleistocene and yet evidence for similar numbers of ice sheet advances over the continent and shallow shelves of northwest europe is absent here we document seven generations of regionally correlatable subglacial tunnel valleys that record the geomorphic imprint of ice sheets traversing the north sea basin between ca 500 and 40 ka consistent with that predicted by proxy records of glacial and interglacial climate change over 180 subglacial tunnel valleys that incise into pleistocene sediments in the north sea basin were mapped over 60 000 km 2 of three dimensional seismic reflection data using a subset of these data we identified seven separate episodes of subglacial erosion that can be correlated regionally in the uk sector of the central north sea the characteristics of the valley morphologies orientations and infill stratigraphy indicate that each set of tunnel valleys formed during a separate ice sheet advance and retreat cycle stratigraphic data suggest that the tunnel valleys formed significantly later than the brunhes matuyama reversal event at 780 ka and before the last glacial maximum marine isotope stage mis 2 21 ka these results imply a more complicated glacial history for northwest europe and more glaciations than the three glaciation model traditionally interpreted from the terrestrial record for the past 500 k y our data provide the most complete documentary evidence for repeated advance and retreat of the northwest european ice sheets since the middle pleistocene and for the first time indicate that terrestrial ice sheet advances in the north sea can be matched in number with the cold events recorded in oceanic and or ice core proxies of climate change over the past 500 k y

application of artificial neural networks ann to high latitude dinocyst assemblages for the reconstruction of past sea surface conditions in arctic and sub arctic seas the artificial neural network ann method was applied to dinoflagellate cyst dinocyst assemblages to estimate palaeoceanographical conditions the ann method was adapted to three distinct data bases covering the northern north atlantic n 371 plus the arctic seas n 540 and the bering sea n 646 the relative abundance of 23 dinocyst taxa was calibrated against hydrographic variables sea surface temperature salinity and density in february and august and seasonal extent of sea ice cover using anns the estimation of hydrographical parameters based on an ann yields high coefficients of correlation between observations and reconstructions for each variable selected the validation tests performed on the different data bases suggest more accurate calibration at the scale of the north atlantic and arctic n 540 than on a multibasin scale i e when including the subpolar north pacific n 646 the ann calibrations and the modern analogue technique mat have been applied to two sequences from the northwest north atlantic spanning the past 25 000 yr for the purpose of comparison both approaches yielded similar results generally within the range of their respective uncertainties demonstrating their suitability the main discrepancies generally correspond to assemblages with poor modern analogues for which we have to admit a higher degree of uncertainties in the reconstruction whatever the approach used copyright 2001 john wiley sons ltd

variability of sea ice cover in the chukchi sea western arctic ocean during the holocene 1 dinocysts from cores collected in the chukchi sea from the shelf edge to the lower slope were used to reconstruct changes in sea surface conditions and sea ice cover using modern analogue techniques holocene sequences have been recovered in a down slope core b15 2135 m 75 44 n sedimentation rate of 1 cm kyr 1 and in a shelf core p1 201 m 73 41 n sedimentation rate of 22 cm kyr 1 the shelf record spanning about 8000 years suggests high frequency centennial oscillations of sea surface conditions and a significant reduction of the sea ice at circa 6000 and 2500 calendar cal years b p the condensed offshore record b15 reveals an early postglacial optimum with minimum sea ice cover prior to 12 000 cal years b p which corresponds to a terrestrial climate optimum in bering sea area dinocyst data indicate extensive sea ice cover 10 months yr 1 from 12 000 to 6000 cal years b p followed by a general trend of decreasing sea ice and increasing sea surface salinity conditions superimposed on large amplitude millennial scale oscillations in contrast 18o data in mesopelagic foraminifers neogloboquadrina pachyderma and benthic foraminifers cibicides wuellerstorfi reveal maximum subsurface temperature and thus maximum inflow of the north atlantic water around 8000 cal years b p followed by a trend toward cooling of the subsurface to bottom water masses sea surface to subsurface conditions estimated from dinocysts and 18o data in foraminifers thus suggest a decoupling between the surface water layer and the intermediate north atlantic water mass with the existence of a sharp halocline and a reverse thermocline especially before 6000 years b p the overall data and sea ice reconstructions from core b15 are consistent with strong sea ice convergence in the western arctic during the early holocene as suggested on the basis of climate model experiments including sea ice dynamics matching a higher inflow rate of north atlantic water

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

the low frequency gas shadow on seismic sections about six years ago greg partyka and his colleagues at amoco research showed how an old technique the fourier transform could be used effectively for seismic interpretation and visualization this idea has come to be known as spectral decomposition in recent years many spectral decomposition techniques have been developed and utilized for stratigraphic analysis and direct hydrocarbon detection with the refined spectral decomposition techniques now available the low frequency shadow beneath gas reservoirs is another old idea that has renewed importance and interest in the exploration community almost a decade ago dan ebrom studied a variety of possible mechanisms for the low frequency shadow and why it might be associated with hydrocarbons he presented his analysis at the 1996 seg summer research workshop

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

shallow gas accumulations in the german north sea abstract shallow gas here defined as free gas that is trapped in unconsolidated deltaic and shallow marine siliciclastic sediments of plio pleistocene age is found within the topmost 1000 m of sediment in the southern north sea shallow amplitude anomalies in seismic reflection data are likely due to the presence of gas the most prominent and easy to recognize indicators are high amplitude anomalies or bright spots that are widespread within the southern north sea gas from shallow reservoirs is currently produced offshore the netherlands in this study we determine whether there are analogous shallow gas accumulations within the german north sea therefore we screened 2d and 3d multichannel seismic data for shallow amplitude anomalies several clusters of bright spots are identified above salt domes that closely resemble the economic deposits known in the dutch sector in both size and their characteristic multilayered shape three of these potential gas accumulations occurring in combination with additional hydrocarbon indicators such as seismic attenuation and velocity push downs are investigated in detail and compared to shallow gas fields from offshore the netherlands amplitude anomalies indicate gas seepage on the seafloor that may contribute to the atmospheric methane budget and may have an impact on offshore infrastructure

a holocene palynological record from the northeastern laptev sea and its implications for palaeoenvironmental research a 844 cm long core ps51 118 3 77 53 54 n 132 11 92 e recovered from the upper slope 122 m water depth of the laptev sea russian arctic has been studied for pollen spores and aquatic palynomorphs including freshwater green algae and cysts of marine dinoflagellates the age model was established on the basis of radiocarbon dates obtained on marine bivalve mollusk shells the available dates suggest that the analyzed sediment was accumulated during the last ca 10 8 cal ka and reveal two intervals with markedly different sedimentation rates reflecting the sedimentary regime changes of the laptev sea shelf during postglacial sea level rise very high sedimentation rates ca 4 7 mm per year in the lower part of the core 120 866 cm between ca 9 2 and 10 8 cal ka bp reflect lower than present sea levels high erosion activity and much closer position of the palaeo shoreline with the lena and yana river mouths to the core site dramatic decrease in sedimentation rates ca 0 1 mm per year during the middle and late holocene interval reflects high sea level and decreased amount of suspended material transported to the outer shelf by rivers despite the location of the core site at the continental slope and far away from the modern coastline pollen spores and fresh water algae constitute a major part of the microfossils throughout the whole record indicating great impact of the lena and yana rivers and possibly prevalent wind regime on the pollen and non pollen palynomorph npp assemblages although a number of short term decadal to multi century oscillations deviate from the mean holocene values pollen taxa percentages and pollen based numerical biome reconstructions do not show very clear trends the latter is likely a result of the mixed environmental signal and complex pollen contribution of several large environmental regions and vegetation zones of siberia drained by the lena and yana rivers the greater pollen contribution of the forested regions to the ps51 118 3 record reflects higher pollen production of the boreal trees and shrubs over the low productive arctic vegetation the intervals of the relative increase in the tundra biome scores in the ps51 118 3 record reflect decreased arboreal pollen production or and increased landscape openness within the pollen source area and can be correlated within the uncertainty of the age models with the cold episodes observed in the greenland ice and north atlantic sediment records

distribution of dinoflagellate cysts in surface sediments of the northern north atlantic in relation to nutrient content and productivity in surface waters abstract analyses of dinoflagellate cyst assemblages from the surface sediments of 371 sites from the north atlantic ocean were performed in order to define relationships with nitrate phosphate silica and productivity in the upper water layer statistical analyses reveal close links between dinocyst assemblages and nitrate content in february that provide a measurement of nitrate availability amongst the taxa in the assemblages nematosphaeropsis labyrinthus which positively correlates with nutrients shows an eutrophic relationship whereas impagidinium aculeatum impagidinium patulum spiniferites ramosus spiniferites mirabilis and lingulodinium machaerophorum have a rather oligotrophic relationship on these grounds transfer functions were tested using multiple regressions and the best analogue technique to reconstruct nitrate content both methods yielded reasonable estimates and allow the reconstruction of the nitrate concentrations in february with an accuracy better than 1 45 mol m 3 at the scale of the study area there are also tenuous links between the dinocyst assemblages and productivity transfer functions were tentatively tested for the reconstruction of annual productivity and yield estimates with an accuracy of about 26 5 gc m 2 year 1 these results demonstrate that dinocyst assemblages can be used for the reconstruction of productivity and nitrates

reconstructing past sea ice cover of the northern hemisphere from dinocyst assemblages status of the approach abstract dinocysts occur in a wide range of environmental conditions including polar areas we review here their use for the reconstruction of paleo sea ice cover in such environments in the arctic ocean and subarctic seas characterized by dense sea ice cover islandinium minutum islandinium cezare echinidinium karaense polykrikos sp var arctic spiniferites elongatus frigidus and impagidinium pallidum are common and often occur with more cosmopolitan taxa such as operculodinium centrocarpum sensu wall dale cyst of pentapharsodinium dalei and brigantedinium spp canonical correspondence analyses conducted on dinocyst assemblages illustrate relationships with sea surface parameters such as salinity temperature and sea ice cover the application of the modern analogue technique permits quantitative reconstruction of past sea ice cover which is expressed in terms of seasonal extent of sea ice cover months per year with more than 50 of sea ice concentration or mean annual sea ice concentration in tenths the accuracy of reconstructions or root mean square error of prediction rmsep is 1 1 over 10 which corresponds to perennial sea ice such an error is close to the interannual variability standard deviation of observed sea ice cover mismatch between the time interval of instrumental data used as reference 1953 2000 and the time interval represented by dinocyst populations in surface sediment samples which may cover decades if not centuries is another source of error despite uncertainties dinocyst assemblages are useful for making quantitative reconstruction of seasonal sea ice cover

an overview and brief description of common marine organic walled dinoflagellate cyst taxa occurring in surface sediments of the northern hemisphere abstract organic walled resting cysts of planktonic dinoflagellates occur commonly in modern marine sediment where they represent with rare exceptions the only geologically preservable part of the life cycle although many species do not produce fossilizable resting cysts upper quaternary sediments contain a diverse cyst record that is used frequently for paleoenvironmental reconstruction and stratigraphic analysis reconstructions of past sea surface conditions rely on an understanding of the distributions of dinoflagellate cysts in modern sediments linked to their respective environmental parameters underpinned by sound taxonomy and standardized nomenclature stratigraphic studies additionally require knowledge of morphological details to distinguish extant from similar extinct taxa here 51 dinoflagellate cyst species and two informal cyst morphotypes that are commonly encountered during routine palynological analysis of upper quaternary marine sediments from the northern hemisphere are briefly described taxonomically and illustrated in addition their lowest stratigraphic occurrences are provided

distribution patterns of dinoflagellate cysts and other organic walled microfossils in recent norwegian greenland sea sediments dinoflagellate cysts and other organic walled microfossils have been studied in recent surface sediments from the entire norwegian greenland sea more than 30 taxa have been recognized of which only few show a distinct distribution pattern and allow description of four assemblages the occurrence of most taxa is related to the relatively warmer waters of the norwegian sea algidaspaeridium minutum s 1 brigantedinium simplex and impagidinium pallidum are the only species showing a preference for colder water masses two species i pallidum and nematosphaeropsis labyrinthus are mainly restricted to the oceanic environment whereas the other species have also been reported from neritic environments in previous studies due to the limited knowledge of the ecological and sedimentological factors influencing the occurrence of dinoflagellate cysts in oceanic environments their distribution in recent sediments can be only related to surface water masses in a broad sense although the distribution of assemblages correlates with specific surface water masses comparison with assemblages recovered from sediment traps deployed basinwide in the norwegian greenland sea dale and dale 1992 revealed some major discrepancies in species composition and percentage abundances the differences cannot be explained with certainty at the moment although there is some evidence that transport of dinoflagellate cysts and other fossilizable microplankton in water masses by currents in sea ice and sediments may modify the assemblages found in recent oceanic surface sediments from the norwegian greenland sea

holocene fluctuations in arctic sea ice cover dinocyst based reconstructions for the eastern chukchi sea cores from site hly0501 05 on the alaskan margin in the eastern chukchi sea were analyzed for their geochemical organic carbon 13corg corg n and caco3 and palynological dinocyst pollen and spores content to document oceanographic changes during the holocene the chronology of the cores was established from 210pb dating of near surface sediments and 14c dating of bivalve shells the sediments span the last 9000 years possibly more but with a gap between the base of the trigger core and top of the piston core sedimentation rates are very high 156 cm ka allowing analyses with a decadal to centennial resolution the data suggest a shift from a dominantly terrigenous to marine input from the early to late holocene dinocyst assemblages are characterized by relatively high concentrations 600 7200 cysts cm3 and high species diversity allowing the use of the modern analogue technique for the reconstruction of sea ice cover summer temperature and salinity results indicate a decrease in sea i

freshwater chlorophycean algae in recent marine sediments of the beaufort laptev and kara seas arctic ocean as indicators of river runoff freshwater chlorophycean algae are characteristic organic walled microfossils in recent coastal and shelf sediments from the beaufort laptev and kara seas arctic ocean the persistent occurrence of the chlorophycean algae pediastrum spp and botryococcus cf braunii in marine palynomorph assemblages is related to the discharge of freshwater and suspended matter from the large siberian and north american rivers into the arctic shelf seas the distribution patterns of these algae in the marine environments reflect the predominant deposition of riverine sediments and organic matter along the salinity gradient from the outer estuaries and prodeltas to the shelf break sedimentary processes overprint the primary distribution of these algae resuspension of sediments by waves and bottom currents may transport sediments in the bottom nepheloid layer along the submarine channels to the shelf break bottom sediments and microfossils may be incorporated into sea ice during freeze up in autumn and winter leading to an export from the shelves into the deep sea the presence of these freshwater algae in sea ice and bottom sediments in the central arctic ocean confirm that transport in sea ice is an important process which leads to a redistribution of shallow water microfossils

modern distribution of dinocysts from the north pacific ocean 37 64 n 144 e 148 w in relation to hydrographic conditions sea ice and productivity abstract palynological analyses were performed on 53 surface sediment samples from the north pacific ocean including the bering and okhotsk seas 37 64 n 144 e 148 w in order to document the relationships between the dinocyst distribution and sea surface conditions temperatures salinities primary productivity and sea ice cover samples are characterized by concentrations ranging from 18 to 143 816 cysts cm3 and the occurrence of 32 species a canonical correspondence analysis cca was carried out to determine the relationship between environmental variables and the distribution of dinocyst taxa the first and second axes represent respectively 47 and 17 8 of the canonical variance axis 1 is positively correlated with all parameters except to the sea ice and primary productivity in august which are on the negative side results indicate that the composition of dinocyst assemblages is mostly controlled by temperature and that all environmental variables are correlated together the cca distinguishes 3 groups of dinocysts the heterotrophic taxa the genera impagidinium and spiniferites as well as the cyst of pentapharsodinium dalei and operculodinium centrocarpum five assemblage zones can be distinguished 1 the okhotsk sea zone which is associated to temperate and eutrophic conditions seasonal upwellings and amur river discharges it is characterized by the dominance of o centrocarpum brigantedinium spp and islandinium minutum 2 the western subarctic gyre zone with subpolar and mesotrophic conditions due to the kamchatka current and alaska stream inflows assemblages are dominated by nematosphaeropsis labyrinthus pyxidinopsis reticulata and brigantedinium spp 3 the bering sea zone depicting a subpolar environment influenced by seasonal upwellings and inputs from the anadyr and yukon rivers it is characterized by the dominance of i minutum and brigantedinium spp 4 the alaska gyre zone with temperate conditions and nutrient enriched surface waters which is dominated by n labyrinthus and brigantedinium spp and 5 the kuroshio extension north pacific subarctic current zone characterized by a subtropical and oligotrophic environment which is dominated by o centrocarpum n labyrinthus and warm taxa of the genus impagidinium transfer functions were tested using the modern analog technique mat on the north pacific ocean 359 sites and the entire northern hemisphere databases 1419 sites results confirm that the updated northern hemisphere database is suitable for further paleoenvironmental reconstructions and the best results are obtained for temperatures with an accuracy of 1 7 c

surface and subsurface expressions of gas seepage to the seabed examples from the southern north sea expressions of gas seepage observable within north sea seismic and acoustic data include seabed pockmarks seepage plumes in the water column acoustic blanking shallow enhanced reflectors and shallow seismic chimneys three areas were selected for a marine survey in

a conceptual model for soils containing large gas bubbles offshore site investigations have indicated the presence of undissolved gas bubbles in the soils forming the sea bed at various locations throughout the world the gas bubbles are typically much larger than the normal void spaces so they cannot be considered as occluded bubbles within the pore water which simply change the compressibility of the pore fluid the effect of these large bubbles on the engineering properties of the soil must be understood if offshore construction is to take place in areas of gas bearing sediments this paper describes a conceptual model for soils containing large gas bubbles the model consists of a matrix of saturated soil surrounding isolated gas filled cavities the cavities forming the bubble sites are fixed within the soil so that gas drainage occurs only by the movement of dissolved gas the behaviour of the model is complicated by the processes of localized consolidation and bubble flooding des recherches conduites en mer ont indique qu il y a partout dans le monde d

surface sediment dinoflagellate cysts from the hudson bay system and their relation to freshwater and nutrient cycling abstract surface sediment samples from the hudson bay system were analysed in order to examine the role of key regulators of arctic marine productivity light and nutrients as affected by freshwater stratification and sea ice cover on the spatial distribution and production of dinoflagellate cysts total cyst fluxes vary from 0 2 10 6 to 30 6 10 6 cysts m 2 a 1 with the highest values observed in eastern hudson bay a total of 24 cyst taxa representing 11 genera of five orders were identified and distribution maps of the most common taxa have been produced this is the first record of echinidinium aculeatum echinidinium karaense cf echinidinium delicatum islandinium brevispinosum selenopemphix quanta cysts of protoperidinium americanum cysts of cf biecheleria sp and polarella glacialis in the hudson bay system dinoflagellate cyst assemblages show distinct spatial patterns revealing three compositional domains eastern hudson bay western central hudson bay and hudson strait the eastern domain is characterised by a dominance of autotrophic cysts of pentapharsodinium dalei whereas the western central domain is characterised by autotrophic operculodinium centrocarpum with some contribution by heterotrophic polykrikos sp var arctic morphotype and polykrikos spp sites from hudson strait are distinguished by an overwhelming prevalence of heterotrophic protoperidiniaceae cysts mainly islandinium minutum and have the highest values of sedimentary biogenic silica used as a proxy for diatom productivity sediment geochemical tracers are used as proxies for freshwater inputs lignin and its biomarkers and nitrate availability nitrogen isotopes and sea ice concentrations derived from passive microwave data as a proxy for light availability sea ice regulated length of the dark season has a negligible influence on the proportion and production of heterotrophic dark adapted versus autotrophic light dependent dinoflagellate cysts perhaps due to the location of our study area on the southern fringe of the arctic instead cyst populations in hudson bay are primarily regulated by vertical stratification and nitrate availability while in hudson strait the pivotal mechanism constitutes food availability

fluid flow during early compartmentalisation of rafts a north sea analogue for divergent continental margins high quality 3d seismic data tied to eighteen 18 boreholes are used to investigate the styles of faulting and associated fluid flow features in triassic early jurassic rafts of the broad fourteens basin southern north sea the study area is presented as an analogue for continental margins experiencing early stage gravitational gliding i e prior to complete separation and downslope translation of individual rafts in such a setting and for present day stress conditions fault slip data indicate that chasms and faults separating rafts in the broad fourteens basin comprise structures subject to dip slip and strike slip reactivation chasms and faults sub parallel to these latter chasms comprise the most significant bypass areas for fluid sourced from pre salt strata faults sub parallel to the main chasms show limited propagation into early cretaceous and cenozoic strata draping the rafts a character further stressed by the depth of occurrence of fluid pipes and dim spots this is an important observation and leads us to postulate that faults formed during early stage rafting control fluid flow in regions where gravitational gliding is limited such as west and equatorial africa southeast brazil and parts of the gulf of mexico

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

shallow water areas in space and time application of modern hypsometric relationships to former continental blocks allows calculation of the shallow sea area around each block for any given sea level using hallam9s 1984 sea level curve for the post triassic shallow sea area curves have been drawn for each continental block and a global curve of shallow sea area with time produced as the response of a block to sea level change depends upon the size of the block the cumulative curve does not vary in a straightforward manner with respect to sea level predictions of organic diversity change with sea level change must take account of this non linear relationship

3d seismic geomorphology of a large plio pleistocene delta bright spots and contourites in the southern north sea abstract regional 2d seismic interpretation has been integrated with high resolution 3d interpretation in dutch offshore blocks a f in the southern north sea 17 horizons mmu s1 s4 s4 1 s4 2 s5 s5 1 s6 s13 and 14 seismic units were interpreted expanding upon studies by kuhlmann and wong 2008 the study presents detailed and extensive twt structure and thickness maps of key depositional units allowing paleogeographic reconstructions detailed analysis of incisional scour marks and hypothesised iceberg scours and constructional features contourites identified initially by bright spots on seismic data linked to bottom currents was undertaken paleo paleographic reconstructions of water depth emphasise the role of hypothesised tidally generated contour currents in the late stage deltaic infill of an epicontinental basin north sea

sea surface hydrographical conditions off south faeroes and within the north eastern north atlantic through mis 2 the response of dinocysts the last glacial period showing the progressive development of large boreal ice sheets was punctuated by large climatic excursions these excursions were triggered mainly by atmosphereoceanice coupled dynamics and are thus exemplary case studies of natural climate variability to characterize the sea surface palaeohydrographical changes accompanying these oscillations along the european margin we have integrated new palynological data dinocysts acquired on core md99 2281 60 degrees n faeroe margin during marine isotope stage 2 in a latitudinal transect including published cores md95 2002 47 degrees n celtic margin and md95 2010 66 degrees n voring plateau this transect is superimposed on the modern north atlantic drift pathway but also at the outskirts of glacial european ice sheets thus ideally located to track sea ice extent and ice sheet instabilities through time the results show a coherent and sensitive response of sea surface environments to the complex chain of abrupt events that punctuated the end of the last glacial period the last glacial maximum was marked by large seasonal contrasts of temperatures whereas heinrich events he were characterized by a sharp cooling and sea ice development a tripartite structure is identified within he1 with indices of melting at 19k cal a bp followed by a temperate phase synchronous of a relative stability of ice sheets and a terminal phase 17 515k cal a bp characteristic of the conventional laurentian he1 copyright c 2013 john wiley sons ltd

dinoflagellate cyst assemblages in surface sediments of the laptev sea region arctic ocean and their relationship to hydrographic conditions the occurrence and distribution of dinoflagellate cysts in surface sediments from the laptev sea shelf and the adjacent continental margin has been studied in relation to surface water conditions assemblages were interpreted by visual inspection and q mode factor analysis the inner laptev shelf is a type area for polar environments because of near absence of relatively warm waters from the pacific or atlantic oceans and an extensive seasonal sea ice cover assemblages are of low diversity and are dominated by the cold water taxon islandinium minutum and related morphotypes the common occurrence of distinctive polykrikoid cyst morphotypes is an indicator of polar environments furthermore strong supply of freshwater in summer influences the surface water conditions and is a major factor controlling the occurrence and distribution of dinoflagellate cysts the dinoflagellate cysts nematosphaeropsis labyrinthus and operculodinium centrocarpum are restricted to the continental margin suggesting a relation to the inflow of relatively warm atlantic waters along the eurasian continental margin an abundance maximum of brigantedinium spp at the shelf break is related to the mean position of the marginal ice zone

pliocene paleoenvironment evolution as interpreted from 3d seismic data in the southern north sea dutch offshore sector a high resolution 3d seismic survey from the dutch offshore sector has been interpreted and subsequently correlated with existing regional seismo stratigraphic concepts derived from conventional 2d seismic data sets the interpreted 13 seismic units have been related to a newly established chrono stratigraphic framework kuhlmann et al 2006a b chronostratigraphy of late neogene sediments in the southern north sea basin and paleoenvironmental interpretations palaeogeography palaeoclimatology palaeoecology 239 426 455 integrated chronostratigraphy of the pliocene pleistocene interval and its relation to the regional stratigraphical stages in the southern north sea region netherlands journal of geosciences geologie en mijnbouw 85 1 19 35 resulting in up dated age control for the seismic units the generation of amplitude maps time slices and isopach maps from the 3d seismic data enabled detailed spatial and temporal reconstruction regarding the paleoenvironmental and climatological development as depicted by kuhlmann et al 2006a chronostratigraphy of late neogene sediments in the southern north sea basin and paleoenvironmental interpretations palaeogeography palaeoclimatology palaeoecology 239 426 455 the lowermost seismic units s1 s4 comprise condensed middle miocene to piacencian sediments deposited under warm open marine conditions these sediments show a uniform seismic facies of low amplitude reflectors the boundary of seismic unit s4 s5 around 2 6 ma delineates a shift towards generally colder climate conditions that are connected to the onset of northern hemisphere glaciation seismic unit s5 includes alternations of warmer and colder periods during warmer periods bottom currents generated elongated structures 2 5 4 km long 300 500 m wide on the horizon display these layers show as well shallow gas accumulations with a more regional extent and are related to coarser grained sediments sealed by clayey sediments of the cold phases a homogenous seismic facies is characteristic for the colder periods within seismic units s6 and s7 internal fore set structures display the regressional trend related to the cooling of this interval seismic units s8 s11 display a pattern of unoriented lineaments which was probably caused by icebergs drifting into the north sea and souring the sea floor this finding is in accordance with the shallow marine arctic conditions of this interval within these units a bright spot of 3 by 7 km in size is interpreted to result from shallow gas accumulation related to a grounded iceberg this feature represents another more local area of gas accumulation that is closely related to iceberg activity within the study area the uppermost seismic units s12 and s13 belong to a fluvial paralic paleo environment that is characterised by aggradational seismic reflectors pleistocene glacial valleys were recognised in the upper 200 m below sea floor 2007 elsevier ltd all rights reserved

seismic characteristics of fluid escape pipes in sedimentary basins implications for pipe genesis abstract fluid escape pipes were first documented from 3d seismic data over a decade ago and have subsequently been identified in many petroliferous basins worldwide they are characterized on seismic data by vertical to sub vertical zones of reduced reflection continuity that have a columnar geometry in three dimensions the upper terminations of these pipes commonly coincide with pockmarks or palaeo pockmarks signifying a close connection of pipe formation with a high flux fluid expulsion process dimensions range from tens to hundreds of metres in diameter and hundreds to over a thousand metres in height and the slenderness ratio defined as height diameter ranges from 0 8 to over 20 pipes are frequently associated with sub vertical clustering of amplitude anomalies on seismic data related either to the presence of free gas or to cementation linked to the passage of hydrocarbons three mechanisms have been suggested to explain pipe genesis 1 hydraulic fracturing 2 erosional fluidisation and 3 capillary invasion we suggest a further two possible mechanisms in the form of localised collapse by volume loss and synsedimentary flow localisation we review all five mechanisms and conclude that it is unlikely that a single mechanism applies but that combinations of these processes may all occur in particular contexts fluid escape pipes may be far more widespread that currently appreciated and they may play a critical role in secondary hydrocarbon migration and in providing leakage pathways for trapped hydrocarbons through overlying seals

middle late holocene palynology and marine mollusks from archipielago cormoranes area beagle channel southern tierra del fuego argentina abstract the palynology and marine mollusks of a marine sequence from rio ovando 54 51 s 68 35 w archipielago cormoranes beagle channel has been studied in order to reconstruct paleoenvironmental conditions during the middle late holocene the dinoflagellate cyst assemblages from rio ovando sequence reflect fjord estuarine environments close to terrestrial ice field affected by glacier meltwater discharge and characterized by short term oscillations of sea surface water parameters the base of the section which is dated at about ca 4160 14 c yr b p 4736 cal yr b p palynological subzone ro 2c is characterized by a high species diversity of dinocyst and mollusks and it is immediately followed by an interval palynological subzone ro 2b characterized by the presence of the echinidinium islandinium complex and the monospecific mytilus mollusk assemblage this subzone registers an inverse correlation between nothofagus dombeyi type and echinidinium islandinium complex concentration values during ca 4160 14 c yr b p 4736 cal yr b p 4064 14 c yr b p 4540 cal yr b p suggesting a variable climatic condition probably related to neoglacial episodes occurred in the southern patagonia andes during this interval the pollen assemblages permit direct correlations with the onshore palynostratigraphy from southern of tierra del fuego the high percentages of nothofagus dombeyi type recorded throughout most of the profile strongly suggest the presence of a closed forest confirming the existence of a variable cool and wet climate for the archipielago cormoranes area during the middle late holocene

distribution of dinoflagellate cysts in the canadian arctic marine region the canadian arctic is a major gateway for transport of freshwater from the arctic ocean to the north atlantic this region comprises the beaufort sea the canadian arctic archipelago caa and northern sections of baffin and hudson bays subregional differences include major freshwater runoff to the beaufort sea and hudson bay presence of pacific and atlantic intermediate water in the west and atlantic water in baffin and hudson bays principal component analysis of 50 core top samples shows four subregional dinoflagellate cyst assemblages outer beaufort shelf assemblage i is co dominated by operculodinium centrocarpum s l and brigantedinium spp with minor cysts of pentapharsodinium dalei algidasphaeridium minutum s l and cysts of polykrikos spp assemblage ii in the canadian arctic archipelago is co dominated by brigantedinium spp a minutum s l and cysts of polykrikos spp including two arctic morphotypes assemblage iii in the north water polynya exclusively comprises a minutum s l and brigantedinium spp assemblage iv in baffin bay is dominated by o centrocarpum s l and spiniferites spp with brigantedinium spp on the shelves the ratio of gonyaulacoid to protoperidinioid cysts g p generally decreases with increased sea ice cover but it may also decrease in river plumes and in polynyas copyright 2001 john wiley sons ltd journal of quaternary science

statistically assessing the correlation between salinity and morphology in cysts produced by the dinoflagellate protoceratium reticulatum from surface sediments of the north atlantic ocean mediterranean marmara black sea region and baltic kattegat skagerrak estuarine system abstract recent studies have correlated dinoflagellate resting cyst morphology to salinity and density variations in the water column suggesting that morphology can be used for paleoceanographic reconstructions however the univariate statistics used by these studies are appropriate only where morphology is related to a single variable density is a function of salinity and temperature so more advanced statistical methods are needed to understand which parameters affect morphology in this study based on surface coretop sediments a set of environmental variables sea surface salinity temperature nitrate and phosphate was simultaneously correlated to morphological variations seen in resting cysts produced by the dinoflagellate protoceratium reticulatum operculodinium centrocarpum sensu wall and dale approximately 3200 measurements were obtained from the north atlantic ocean and used to generate a working model based on the akaike information criterion hierarchical partitioning was then applied to establish the independent and joint effects for each predictor variable results from these analyses showed that while salinity constitutes the dominant variable affecting process length in the cysts of p reticulatum in the north atlantic it is not the sole explanatory variable and that multicollinearity exists temperature and nutrients also showed a significant relationship to the morphology requiring multiple regression to construct a representative model the applicability of the north atlantic working model was finally evaluated by comparing the results to data from the mediterranean marmara and black seas and baltic kattegat skagerrak estuarine system this comparison showed regional differences in morphological environmental correlation while salinity constitutes the most important explanatory factor in both the north atlantic and baltic skagerrak system this is not so for the mediterranean black sea region where temperature is the dominant variable it is concluded that a predictive salinity model based on p reticulatum cyst morphology has at best a regional application

contribution palynostratigraphique dinokystes pollen et spores a la connaissance de la mer de champlain coupe de saint cesaire quebec high resolution continental pollen and spores and marine dinoflagellate cysts microfloral records were obtained from a section consisting of about 0 5 m of glaciolacustrine and 2 5 m of champlain sea deposits at the saint cesaire site the pollen and spore assemblages indicate the existence of a regional open vegetation of shrub tundra to forest tundra fluctuations in the percentages of picea and shrub and herb taxa are related to regional afforestation and paleogeographical evolution of the basin the champlain sea sediments contain an abundant dinocyst flora dominated by operculodinium centrocarpum brigantedinium spp and algidasphaeridium minutum which indicate cold arctic conditions in surface waters fluctuations in concentration 102 104 cm 3 and relative abundance of dinocyst species are attributed to changes in dinoflagellate productivity and paleoceanographic conditions notably paleosalinity morphological variations of operculodinium centrocarpum and algidasphaeridium minutum led to

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

late holocene dinoflagellate cysts as indicators for short term climate variability in the eastern laptev sea arctic ocean a sediment sequence from the eastern laptev sea shelf siberian arctic russia has been studied for dinoflagellate cysts in order to reconstruct sea surface conditions during the late holocene variability of assemblage composition and derived sea surface temperature estimates indicate that the neoglacial cooling was not a gradual climate change from 2510 to 900 cal yr bp relatively stable conditions with temperatures that were warmer than today were punctuated by a few cooling events in summer on centennial time scales during these events temperatures reached modern values this suggests that modern conditions may have been established abruptly within a short period in the past 1000 yr which is not documented in our record copyright 2001 john wiley sons ltd

distribution patterns of diatom surface sediment assemblages in the laptev sea arctic ocean abstract the modern diatom distribution in the laptev sea arctic ocean was investigated in 89 surface sediment samples diatom concentrations are relatively low showing values between 0 01 10 6 and 6 7 10 6 valves per gram dry sediment based on a factor analysis using seventeen taxa or taxa groups five diatom surface sediment assemblages can be defined the ice diatom assemblage of the central region of the laptev sea the chaetoceros assemblage of the eastern and southeastern shelf the thalassiosira antarctica assemblage of the continental slope and deep sea the freshwater diatom assemblage in the vicinity of river mouths and deltas and the thalassiosira nordenskioeldii assemblage which shows a patchy occurrence on the central laptev sea shelf the distribution pattern of diatom assemblages in surface sediment is significantly related to oceanographic conditions of surface water masses the main factors controlling the distribution of diatoms in the laptev sea are the riverine freshwater input during the summer which strongly affects the salinity conditions and the sea ice extent furthermore the composition of the thalassiosira antarctica assemblage of the continental slope is largely influenced by dissolution and lateral transport processes

modern dinoflagellate cyst assemblages in surface sediments of nunatsiavut fjords labrador canada abstract in order to document long term climate cycles and predict future climate trends for the arctic geological records archived in ocean sediments can help establish the link between historical and pre historical sea surface parameters dinoflagellate cysts dinocysts are used as proxy indicators of sea surface parameters temperature salinity sea ice cover primary productivity jointly with transfer functions and a modern dinocyst reference database to reconstruct the evolution of sea surface conditions at decadal and millennial timescales here we present the surface distribution of recent dinocyst assemblages in 13 surface samples collected in four nunatsiavut fjords northern labrador canada along a latitudinal gradient and their relationship with various environmental and biological parameters dinocyst concentrations in surface sediments increased from the inner to the outer part of each fjord and also from the northernmost to the southernmost fjords there was also a southward increase in the species diversity with an occurrence and a dominance of cysts from autotrophic dinoflagellates the presence of cysts of the calcareous dinoflagellate species scrippsiella cf s crystallina in anaktalak fjord where mining activities are underway appears to be an indicator of human related pollution within the fjord

paleoceanographic changes in the disko bugt area west greenland during the holocene micropaleontological analyses of a sediment core raised in disko bugt west of greenland were undertaken in order to document paleoceanographical changes in the eastern baffin bay during the holoc

palynological evidence of holocene climate change in the eastern arctic a possible shift in the arctic oscillation at the millennial time scalethis article is one of a series of papers published in this special issue on the theme polar climate stability network dinocyst assemblages and the physical properties of two sediment cores collected in the easternmost part of the main axis of the northwest passage canadian arctic ocean cores 2004 804 009 bc and 2004 804 009 pc 74 11 2 n 81 11 7 w were used to reconstruct changes in sea surface conditions and to characterize changes in the depositional environment core 2004 804 009 pc spans the last 12 180 calibrated cal years bp with sedimentation rates ranging from 45 to 122 cm ka quantitative estimates of sea surface parameters reveal relatively large hydrographic variability at millennial time scale before 11 000 cal years bp our records suggest terrigenous inputs related to the last deglaciation between 11 000 and 9600 cal years bp harsh conditions prevailed with august sea surface temperatures 2 c and the dominance of heterotrophic taxa this episode was followed by a gradual increase in the relative abundance of phototrophic taxa and the establishment of milder condition with sea surface temperature

episodic basin wide hydrofracturing of overpressured early cenozoic mudrock sequences in the north sea basin a deformational fabric associated with the early cenozoic mudrock dominated sequences of the north sea is described seismic data show that the mudrock sequences are pervasively faulted over a large area of the basin axis in the central and northern north sea mapping the faults using regional two and three dimensional data shows that the faults are minor extensional structures arranged in stratigraphically bound tiers in the deep water sequences and bounded by regional condensed sequences seals the geometry of the faulting is complex faults are organized into cellular networks comprising polygonal prismatic and pyramidal forms a gravitational mechanism of downslope collapse faulting is rejected on the grounds that the distribution of the deformed sequences extends over large areas of formerly horizontal basin plain a mechanism involving the repeated development of basin wide overpressured compartments is proposed in which the cellular structure is related to deformation patterns associated with a density inversion between the overpressured units and the overlying seal hydrofracturing is invoked to account for the almost random strike distribution of the faulting the region affected by the pervasive fluid expulsion faulting encompasses almost half of the north sea basin basin wide collapse of the overpressured compartments could have resulted in a geologically rapid flux of enormous volumes of pore fluids this mechanism has implications for concepts of steady state compaction heat flow in basins hydrocarbon transport and the genesis of lead zinc ore deposits

interaction between subsurface ocean waters and calving of the jakobshavn isbrae during the late holocene a marine sediment core from vaigat in disko bugt west greenland has been analysed in terms of lithology dinoflagellate cysts and foraminifera in order to evaluate the influence of oceanographic variability on west greenland glacier stability the data show that during the past 5200 years the atlantic foraminiferal abundance in the subsurface waters of the west greenland current wgc episodically increased indicating periods of increases in the inflow of subsurface warm atlantic water at 2000 1500 cal yr bp and 1300 cal yr bp as well as periods of less pronounced increased bottom water temperatures around 4700 4000 cal yr bp 3100 2800 2600 1000 800 500 400 and at 200 cal yr the sedimentological and dinoflagellate cyst data indicate that these episodes with enhanced advection of irminger sea derived waters are accompanied by increased iceberg rafting which we link to increased iceberg calving in relation to destabilization of the jakobshavn isbrae the long term trend in the data documents the end of a late holocene thermal maximum between 5200 and 4300 cal yr bp and a final onset of the neoglaciation at 3500 cal yr bp increased responses of the iceberg rafting after 3500 cal yr bp reflects a westward seaward advance of the glacier margin in relation to onset of neoglaciation and a development of the glacier into a floating tongue after 2000 cal yr bp a comparison of our record with a record from the eastern north atlantic indicates that a nao like anomaly pattern between subsurface waters in west greenland and atmospheric temperature in the eastern north atlantic may have been operating during most of the late holocene however during the past 1000 years the nao signal may have weakened as some other mode of climate variability overprints the anti phase climate signal in this region