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

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

toxic dinoflagellate blooms in the kattegat north sea during the holocene data are presented on the temporal distribution of the toxic dinoflagellate gymnodinium catenatum in the kattegat region of the north sea based on dinoflagellate cyst and pollen analyses and a high resolution chronology a relationship between climatic and oceanographic variations and the blooming of g catenatum and other dinoflagellates is demonstrated gymnodinium catenatum first migrated into the kattegat about 6200 yr b p and had its first occurrence of high numbers at about 4300 4500 yr b p at about 4000 yr b p in connection with an oceanographic change and climatic deterioration the species decreased abruptly and subsequently disappeared it became re established again at about 2000 yr b p and occurred in massive blooms during the so called mediaeval warm epoch round about 700 800 yr b p 1200 1400 a d at the time of the so called little ice age approximately 300 yr b p 1500 1600 a d g catenatum again became extinct in the kattegat area this study clearly demonstrates that massive blooms of toxic dinoflagellates occur in the historical record before any anthropogenic impact on the environment

the effect of bottom friction on shallow water flow past an isolated obstacle abstract the effect of bottom friction on fluid flow past an isolated obstacle is investigated in the shallow water framework the controlling parameter for this effect is the nondimensional bottom friction number defined as a ratio of friction to inertia with the bottom stress related to the horizontal wind via standard bulk aerodynamic formula the friction number is proportional to the surface roughness the horizontal scale of the obstacle and the inverse of the upstream fluid depth thus under otherwise identical conditions the flow past larger obstacles will be more viscous bottom friction modifies the vorticity generation in several ways but under normal conditions the wake formation remains dominated by a pseudoinviscid process related to the presence of hydraulic jumps however friction strongly controls the velocity deficit region of the wake and thus influences the stability of the steady state wakes predictions of the linear stability analysis are compared with numerical simulation

palynomorph distribution in recent sediments from the labrador sea surface sediments from the labrador sea and baffin bay have been examined for their palynomorph content pollen and spore assemblages reflect the vegetation zones of eastern canada although long distance atmospheric transport results in over representation of pinus and spores a linear decrease of pollen input is observed with distance from the source vegetation the abyssal domain receives less than 2 of the initial input the abundance of dinoflagellate cysts reflects a relatively high primary productivity in surface water masses which seems proportional to the benthic productivity as shown by the concentrations of organic linings of foraminifers the relative abundance of dinoflagellate cyst taxa and principal component analysis led to the definition of three assemblages that can be related to sea surface conditions and current pattern the modern distribution of dinoflagellate cysts was used to interpret assemblages recovered in five box cores from the deep labrador sea results reveal important ch

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

organic walled microfossils and geochemical tracers sedimentary indicators of productivity changes in the north water and northern baffin bay during the last centuries analyses performed on 26 surface sediment samples collected with a box corer at 17 stations throughout the north water and northern baffin bay 75 791n 68 801w revealed abundantorganic walled microfossils most ly dinoflagellate cysts 10 3 10 4 cysts g 1 and organic linings of benthic foraminifers 10 2 10 3 ol g 1 as well as high organic carbon concentrations 0 87 2 81 dry weight these data indicate high productivity in both the pelagic and benthic environments of the north water and slightly lower productivity in northern baffin bay the data also showed calcium carbonate and biogenic silica dissolution throughout the study area the dinocyst assemblages were relatively uniform in the north water and dominated by heterotrophic taxa algidasphaeridium minutum and brigantedinium spp whereas northern baffin bay assemblages were dominated by autotrophic taxa notably operculodinium centrocarpum and spiniferites elongatus the difference between these two assemblages may be related to higher diatomaceous primary production in the north water than in northern baffin bay since diatoms constitute the principal food source of heterotrophic dinoflagellates the biogeographical boundary between the north water and northern baffin bay has been maintained for at least the last few centuries as shown by analyses of microfossils and geochemical tracers in two sediment cores one taken in the southeastern part of the north water 76117 0 n 72102 0 w and the other in northeastern baffin bay 75135 0 n 70148 0 w the analyses of the north water core revealed relatively uniform microfossil assemblages and organic carbon fluxes ranging from 1 1 to 1 5 mg corg cm 2 yr 1 for the last few centuries which corresponded to 4 6 of the present annual primary production in the euphotic zone these data suggest high productivity and relatively stable conditions in the polynya on a decadal time scale in the northeastern baffin bay core the analyses indicated generally lower organic carbon fluxes ranging from 0 3 to 0 6 mg corg cm 2 yr 1 and from the microfossil data significant variations in sea surface conditions at this lower latitude over the last centuries r 2002 elsevier science ltd all rights reserved

early diagenetic processes in deep labrador sea sediments reactive and nonreactive iron and phosphorus a sequential extraction procedure was applied to separate the oxides and lithogenous phases of iron and manganese and the organic and inorganic phosphorus phases in four box cores and one piston core from the slopes and rises of the labrador sea sedimentation rate rather than the location in the basin appears as a master variable of the diagenetic transformations of fe mn and p high sedimentation rate characteristic of two of the box cores led to the creation of zones near the redox boundary of partial reprecipitation of dissolved fe mn and p released in the deeper reducing portions of the sediments in contrast surficial sediments from box cores with 10 times lower sedimentation rate only have sufficient reductive capacity to remobilize mn hydroxides while leaving the fe oxyhydroxides intact under these conditions there is evidence for a redistribution of reactive inorganic p leading to the crystallization of carbonate fluorapatite in the top 30 cm of the cores gradual transformation of bur

the effect of rotation on the pressure drag force produced by flow around long mountain ridges the impact of rotation on the orographic drag experienced by air flowing around a wide mountain is investigated the work builds on numerical modelling studies performed by olafsson and bougeault who investigated the effect of rotation and surface friction on the drag experienced by flow around a single elongated mountain perpendicular to the direction of the flow the region of parameter space they explored is extended by performing a series of idealized model experiments with a larger range of ridge lengths the drag force in these simulations is compared with the predictions of a heuristic flow blocking model devised by shutts the results show that shutts s model overestimates the effect of rotation upon the drag force however we find that shutts s model predicts both the drag force exerted on the upstream side of the ridge and the upstream features reasonably well finally the implications of the results for nwp parametrizations of subgrid scale orographic drag are discussed copyright 2005 royal meteorological society

clay mineral signature of the nw atlantic boundary undercurrent abstract surface sediments were sampled along 2 transects across the iceland and irminger basins and in the labrador sea clay mineral assemblages deduced from x ray analyses of the carbonate free

sea surface conditions in northernmost baffin bay during the holocene palynological evidence the analysis of cores collected in northernmost baffin bay from within the area of the north water polynya permits definition of a composite sedimentary sequence ca 12 m thick spanning the last 10 000 14 c yr with only a few discontinuities palynological analyses were performed in order to reconstruct changes in surface water conditions and biogenic production transfer functions using dinocyst assemblages were applied to estimate sea surface temperature sst and salinity as well as the seasonal duration of sea ice cover at the base of the record prior to 9300 14 c yr bp dinocysts and organic linings of benthic foraminifers are sparse indicating harsh conditions and low productivity after ca 9300 14 c yr bp the increased concentration of benthic foraminifers up to 10 3 linings cm 3 and dinocyst fluxes 10 2 10 3 cysts cm 2 yr 1 reveals high biological productivity related to open water conditions the early to middle holocene from ca 9000 to ca 3600 14 c yr bp is marked by relatively high species diversity in dinocyst assemblages and the significant occurrence of autotrophic taxa such as spiniferites elongatus pentapharsodinium dalei and impagidinium pallidum this assemblage suggests conditions at least as warm as at present from ca 6400 to ca 3600 14 c yr bp transfer functions indicate warmer conditions than at present with sst in august fluctuating up to 5 5 c after 3600 14 c yr bp the dinocyst record suggests a trend of decreasing temperature toward modern values marked by recurrent cooling events copyright 2001 john wiley sons ltd

the wake of st vincent abstract the island of st vincent and the other windward islands in the southeastern caribbean were chosen as a field site for the study of weak mountain wakes by the authors definition a weak wake forms when the potential vorticity generated by a mountain is not strong enough to advect itself into eddies rather it is simply advected downstream by the ambient flow goes 8 and landsat sunglint images unambiguously revealed that the mountainous windward islands have remarkably long straight wakes the length of st vincent s wake exceeds 300 km although its width is only 20 km near the islands the wake structures reflect the details of the island topography these wakes do not exhibit any obvious diurnal effect boat surveys in the lee of st vincent confirmed the existence of features seen in the images the sharp wake boundary the small valley induced jet embedded in the near wake and the absence of any reverse flow aircraft surveys gave evidence of descent over the island and showed that the

dinoflagellate cysts from sediment traps deployed in the bellingshausen weddell and scotia seas antarctica dinoflagellate cysts have been recovered from six long term 1 2 yr sediment trap moorings deployed in the bellingshausen weddell and scotia seas antarctica these traps mostly moored near the sea bed to sample the nepheloid layer were located both within and to the north of the maximum sea ice limit the numbers of cysts together with the composition of the assemblages reinforce the importance of the maximum sea ice limit as a modern biogeographic boundary for the distribution of dinoflagellate cysts cysts derived from heterotrophic dinoflagellates make up the highest proportions within the assemblages recovered from the traps one trap sampled the export production revealing little difference in cyst flux over those sampling the nepheloid layer cyst flux appears to be highest in areas closest to the antarctic convergence north of the maximum sea ice limit and to high nutrient availability there are however differences between the sediment trap assemblages and those recovered from core top samples at the same or nearby sites these differences in the greater number of cysts and in the higher numbers of round brown protoperidinium cysts in the traps may reflect annual differences in the primary productivity and or cyst production in the area in some areas the sediment record may preserve little information about local surface water productivity because of the activity of bottom water currents for example those arising from the antarctic circumpolar current

gravity wave drag on two mountains the generation of linear internal gravity waves by the flow over two idealized mountains whose summits are aligned in the same direction as the mean wind is studied in particular the sensitivity of the wave drag to the downwind distance between the mountains is examined by using a three dimensional numerical model based on the linearized steady state boussinesq equations of motion both two and three dimensional orography is considered when the upstream conditions are such that the wind and buoyancy frequency do not vary with height and the mountains are wide enough for non hydrostatic effects to be unimportant the model predicts the same drag dependence on two dimensional ridge spacing as was derived analytically by grisogono et al the corresponding three dimensional numerical result predicted by the model is qualitatively very similar to the two dimensional result when the mountains are narrow and the waves are non hydrostatic the drag dependence on mountain spacing is more complicated maxima and minima in the drag can occur when the distance between the two mountains is such that waves generated by the mountain furthest upstream are in phase maxima in the drag or out of phase minima in the drag with the waves generated by the downstream mountain it is shown that this is an important effect when the waves are trapped by upstream profiles whose wind speed varies with height

the impact of mountain wakes on the drag exerted on downstream mountains the pressure drag exerted on two identical high idealised mountain ridges aligned perpendicular to the mean flow with the second mountain lying directly downstream of the first is investigated using a numerical model the drag is measured for a variety of different distances between the two peaks mountain heights and lengths and incident flows each two mountain simulation has a companion single mountain simulation with an identical mountain and identical upstream flow with which to compare the drag the maximum modelled drag in the two mountain simulations is close to two times the drag in the single mountain case while the minimum two mountain drag is similar to that exerted on the single mountain this change in drag is a result of the wake behind the first mountain reducing the speed of the flow impacting on the second mountain a parametrization of this effect is suggested which combines the distance between the two mountain peaks a measure of the velocity deficit in the wake of the first mountain and the wake decay scale a measure of the length scale over which the flow perturbation generated by the first mountain decays downwind copyright 2008 royal meteorological society and crown copyright 2008 published by john wiley sons ltd

palynological evidence of climatic and oceanographic changes in the north sea during the last deglaciation abstract palynological analyses performed on cores from the norwegian channel troll 8903 led to reconstruction of the late glacial variations in sea surface conditions using dinoflagellate cyst data and permitted direct correlation with the vegetation history of northwestern europe derived from pollen assemblages by 15 000 yr b p ice rapidly receded from the norwegian shelf and relatively warm summer conditions prevailed in surface waters a first late glacial cooling marked by extensive seasonal sea ice cover is dated at ca 13 600 13 00014c yr b p which coincides with the oldest dryas interval during the bolling allerod interval a rise in sea surface temperature both in february up to 3 c and august up to 15 c led to the establishment of ice free conditions in the northern north sea while pollen data reveal a densification of the vegetation cover the beginning of the younger dryas interval is marked by an increase in nonarboreal pollen input indicative of the opening of the forest vegetation cover concomitant with a cooling of surface waters during winter and development of sea ice cover however sea surface conditions remained relatively warm in summer until about 10 300 yr b p when extremely cold conditions and extensive sea ice cover developed up to 7 months yr improving conditions are recorded in surface waters by 10 100 yr b p a few hundred years before the development of forest cover onshore as shown by the pollen record such a discrepancy between marine and terrestrial indicators at the end of younger dryas time suggests a delayed response of the vegetation to regional climate warming

sea ice cover sea surface salinity and halo thermocline structure of the northwest north atlantic modern versus full glacial conditions abstract seasonal sea ice develops along the eastern continental margins in the northern north atlantic where freshwater and or meltwater outflow are responsible for relatively low salinity in surface waters and very pronounced water mass stratification sea ice constitutes a major parameter in the marine ecosystem since the duration and extent of its seasonal spreading constrain the plankton distribution and the related microfossil assemblages on the sea floor organic walled dinoflagellate cysts that are highly resistant to dissolution were recovered from surface sediments of the northern north atlantic and used to develop transfer functions best analogue method for the reconstruction of the seasonal spreading and duration of sea ice cover in addition to salinity and temperature of the warmest month of the year application of the best analogue approach to cores from the labrador sea reveals large variations in sea ice cover and sea surface conditions throughout the last glacial stage and during the early holocene isotopic analyses in epipelagic and mesopelagic planktonic foraminifers also suggest important changes in salinity and temperature gradients between the surface and sub surface water masses specific study of the last glacial maximum lgm time slice 16 20 ka on a 14 c time scale in the northwestern north atlantic shows much more extensive sea ice than at present with perennial sea ice lying along the continental margins of eastern canada seasonal spreading of the cover of sea ice offshore was accompanied by large seasonal contrasts in temperature with very cold winters but relatively warm summers a pattern linked to strong stratification between a buoyant low saline surface layer having a low thermal inertia and the underlying intermediate oceanic waters

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

dinoflagellate cyst distribution in high latitude marine environments and quantitative reconstruction of sea surface salinity temperature and seasonality a data base of 179 reference sites documents the relations between the assemblages of organic walled dinoflagellate cysts and sea surface temperature salinity and seasonality throughout the north atlantic adjacent subpolar basins labrador sea baffin bay irminger and iceland basins and epicontinental environments off eastern canada estuary and gulf of st lawrence hudson bay principal component analyses show close relationships between dinoflagellate cyst data and sea surface conditions the first component 71 1 of the variance correlates with the winter temperature salinity and seasonal duration of sea ice cover whereas the second component 11 3 of the variance appears mainly related to summer temperature transfer functions using the best analogue method were tested by reconstructing modern sea surface conditions on the basis of the reference dinoflagellate cyst assemblages the correlation coefficient between instrumental averages and reconstructed values ranges from 0 87 august tem

identifying the signature of sea surface properties in dinocyst assemblages implications for quantitative palaeoceanographical reconstructions by transfer functions and analogue techniques abstract dinoflagellate cyst dinocyst assemblages are widely used for the reconstruction of multiple oceanographic variables through the application of transfer functions there is evidence that the number and kind of variables driving compositional changes in dinocyst assemblages vary regionally and that the selection of driving factors and the evaluation of transfer function performances are method specific and complicated by spatial autocorrelation here we used two new modern datasets from the northern hemisphere atlantic arctic and the northern hemisphere pacific oceans to re evaluate the impact of sea surface properties in dinocyst assemblages we determined the dimensionality of the dinocyst ecological response and identified the main drivers for both regions we calibrated and evaluated transfer function methods for the prediction of these variables and estimated their performances considering spatial autocorrelation in both datasets multiple environmental variables mutually and independently affect assemblage compositions but the number and kind of these variables differ between datasets we detected spatial autocorrelation which was often due to environmental similarity but some variables appeared to reflect geographical closeness implying that spatial independence between sample sites depends upon the variables we identified different primary drivers in both areas highlighting the merit of regional calibrations and the necessity to carry out variable selection for each region separately the multiple gradients identified imply that potentially multiple parameters could be reconstructed from the same fossil dinocyst assemblages however as the multiple gradients reflect geographical structuring we propose that regional calibrations even at the expense of generalisation could improve the reliability and interpretation of transfer function reconstructions

micropaleontology and palynology of core par87a 10 a 23 000 year record of paleoenvironmental changes in the gulf of alaska northeast north pacific micropaleontological data of core par87a 10 reveal that the last glacial interval prior to 13 ka was marked by low biogenic fluxes and poor caco3 preservation quantitative estimates of sea surface conditions based on dinocyst assemblages suggest that cold temperatures and freezing winter conditions existed during this period the glacial to interglacial transition i e the 13 8 ka interval was characterized by an increase in fluxes of microfossils indicating enhanced productivity in surface waters a higher biogenic carbonate production probably resulted in better preservation of caco3 this interval was marked by relatively low salinity and by sea surface temperatures increasing toward modern values relatively high pollen flux during the transition suggests nutrient inputs through atmospheric and or fluvial transport from the adjacent north american continent after 8 ka diminished fluxes of plankton concomitant with a decline in pollen input are associated with decreasing nutrient supply as predominantly eastward winds became established over the north pacific

middle pleistocene to holocene palynostratigraphy of ocean drilling program site 887 in the gulf of alaska northeastern north pacific a palynological investigation was undertaken on the upper 29 m of sediment at ocean drilling program odp site 887 spanning the last 430 000 years i e isotopic stages 12 to 1 pollen and dinocyst assemblages reveal a major ecostratigraphical boundary at the middle late pleistocene transition the middle pleistocene pollen data doc ument the occurrence of a spruce forest vegetation in the source area likely located on the adjacent alaskan coast whereas the late pleistocene is marked by higher inputs of pine shrub and herb taxa suggesting predominant inputs from a more open landscape the middle pleistocene is characterized by a low diversity in dinocyst assemblages which are dominated by operculodinium centrocarpum whereas the late pleistocene is marked by the significant oc currence of pentapharsodinium dalei pyxidinopsis reticulata and by high percentages of brigantedinium spp such as semblages suggest open oceanic and cool temperate conditions during the middle pleistocene changing toward generally colder and less saline conditions during the late pleistocene in addition large fluctuations in the dinocyst assemblages during the late pleistocene are recorded in phase with the main shifts in the isotopic stratigraphy a new dinocyst taxon spiniferites alaskensis sp nov exclusively recorded in sediments of the isotopic substage 5e is de scribed herein resume une analyse palynologique a ete realisee sur une sequence sedimentaire de 29 metres prelevee au site odp 887 et couvrant les derniers 430 000 ans soit les stades isotopiques 12 a 1 les assemblages de pollen et de dinokystes revelent une transition ecostratigraphique majeure entre le pleistocene moyen et le pleistocene superieur les assembla ges polliniques du pleistocene moyen indiquent la presence d une vegetation dominee par l epinette et l aulne dans la region source qui etait sans doute localisee le long des cotes de l alaska de forts pourcentages de pin et des taxons arbustifs et herbaces au pleistocene superieur indiquent des apports issus d un paysage plus ouvert le pleistocene moyen est caracterise par une faible diversite dans les assemblages de dinokystes et par la dominance de operculodi nium centrocarpum tandis que le pleistocene superieur est marque par pentapharsodinium dalei pyxidinopsis reticulata et des pourcentages eleves de brigantedinium spp les assemblages suggerent des conditions oceaniques temperees fraiches pendant le pleistocene moyen et des eaux de surface plus froides et moins salines au cours du pleistocene su perieur par ailleurs de larges fluctuations sont enregistrees dans les assemblages de dinokystes au pleistocene supe rieur en phase avec la stratigraphie isotopique parmi les dinokystes une nouvelle espece spiniferites alaskensis sp nov observee exclusivement pendant le sous stade isotopique 5e est decrite ici marret et al 386

the climate of north america and adjacent ocean waters ca 6 ka the climate of north america and the adjacent ocean at 6000 bp was estimated using five independent approaches using pollen data the terrestrial climate was estimated by the movement of ecozone boundaries and by the method of modern analogues both analyses indicate warmer temperatures in the western great lakes area and the northern great plains a model of sphagnum dominated peatland initiation when forced by canadian climate model 6 ka output projected a cooler and or wetter climate for continental western north america contrary to this a reconstruction of the distribution of sphagnum dominated peatlands in western canada indicates that they were located north of their modern distribution suggesting warmer and or drier conditions at 6000 bp this interpretation is strengthened by observations of lower lake levels at 6000 bp in western canada this drier climate may have been associated with warmer conditions as indicated by the quantitative climate reconstructions in general eastern north a

exotic pollen as an indicator of variable atmospheric circulation over the labrador sea region during the mid to late holocene variability in the abundance of exotic non native pollen in sediment cores has long been considered as a potential proxy for changing atmospheric circulation but the difficulty of gaining sufficient total exotic pollen and the incomplete under standing of atmospheric pollen transport patterns has hindered its application in light of recent advances in the study of pollen transport we present an exotic pollen record from two fjord sediment cores taken from the west placentia bay newfoundland and east narsaq sund greenland labrador sea as a basis for studying variations in regional atmospheric circulation the two cores cover the last ca 5500 years and indicate a shift in dominant spring summer air masses at ca 2000 southern greenland and 3000 cal a bp newfoundland transporting reduced concentrations of pollen from southerly and south westerly vegetation zones this may suggest a shift away from more dominantly zonal atmospheric circulation a feature of positive north atlantic oscillation years to more frequent meridional circulation these results support sea ice sea surface temperature proxy reconstructions from newfoundland investigated as part of the same project which also suggest increased winter atmospheric circulation during the early part of the time period studied in this region more positive north atlantic oscillation years and therefore more zonal atmospheric circulation are associated with increased atmospheric circulation in both the winter and the summer seasons copyright 2011 john wiley sons ltd

oceanographic regimes in the northwest labrador sea since marine isotope stage 3 based on dinocyst and stable isotope proxy records abstract sea surface temperature sst salinity and density gradients in the upper water column of the northwest labrador sea have been reconstructed based on high resolution analysis of a core hu2008 029 004pc spanning the last 36 ka raised off hudson strait the modern analogue technique was applied to dinocyst assemblages and combined with stable isotope data from neogloboquadrina pachyderma left coiled npl for this purpose three oceanographic regimes were identified broadly corresponding to the glacial deglacial and postglacial intervals the site remained under the direct influence of the laurentide ice sheet lis margin until the postglacial and did not record the bolling allerod warming and weakly recorded the younger dryas event the glacial regime lasted until 12 2 cal ka bp it was characterized by generally low concentrations of dinocysts within an assemblage indicative of quasi perennial sea ice the deglacial regime ca 12 2 8 3 cal ka bp was marked by increased biogenic fluxes and more diversified dinocyst assemblages and possibly an enhanced subsurface inflow of north east atlantic deep water warm summer 11 c but low winter 0 c sea surface temperatures sea ice cover during about 3 months per year and low summer salinity 28 suggest strong stratification in the upper water layer in relation to meltwater supply from the lis following the final drainage of glacial lake agassiz through hudson strait which is dated here at 8 3 cal ka bp and the subsequent lis collapse increased summer salinity up to 35 was accompanied by a reduced seasonal gradient of sea surface temperature from winter 3 8 c to summer 8 6 c suggesting enhanced penetration of north atlantic water weakened stratification of the surface water layer then allowed for winter convection and labrador sea water formation which is consistent with increased npl 13c values in response to higher ventilation of the subsurface water layer

pollen distribution in recent marine sediments eastern canada analysis of 90 samples from coastal and continental shelf areas off eastern canada between 42 and 69 n shows that quaternary pollen and spores are present in recent marine muds throughout this region pollen and spore concentrations range from 50 000 to 100 grains per cm3 and they decrease both offshore as a function of distance from vegetation sources and northwards as a function of lower vegetation density north of the summer arctic frontal zone isopercentage contours show that maximum relative abundances of most palynomorphs occur in marine sediments adjacent to their regions of highest vegetation representation onshore however pinus and picea pollen tend to increase in percentage abundance with distance offshore presence of these tree pollen in marine sediments off baffin island implies that wind transport is an important pathway by which bisaccate pollen types enter the ocean in addition to fluvial transport q mode factor analysis shows that four major factors account for 89 of the variance amo

surface sediment diatom distribution and holocene paleotemperature variations in the greenland iceland and norwegian sea one hundred and four surface sediment samples and two piston cores from the greenland iceland and the norwegian gin sea hopkins 1988 were analyzed diatoms were common to abundant in most surface sediment samples and throughout the holocene q mode factor analysis allowed the definition of six significantly different floral assemblages which explained 91 7 of the total variance mapping of the six factors showed their close affinity to hydrographic regimes these are the norwegian atlantic current assemblage thalassionema nitzschioides paralia sulcata proboscia alata arctic water assemblage thalassiosira gravidaspores sea ice assemblage nitzschia grunowii nitzschia cylindra thalassiosira hyalina arctic norwegian waters mixing assemblage rhizosolenia hebetata f semispina rhizosolenia borealis atlantic assemblage thalassiosira oestrupii and norwegian arctic waters mixing assemblage thalassiosira gravida vegetative cells transfer functions gint2 relating factor distributions to winter february and summer august surface water temperatures were generated the transfer functions have a standard error of estimate of 1 5 c august and 1 0 c february downcore studies of core 52 43 from the norwegian basin and core 57 5 from the iceland plateau revealed diatom abundance and sea surface paleotemperature trends in the area during the holocene the first appearance of diatoms in cores 52 43 and 57 5 occurs within the vedde ash layer 10 600 years b p and the saksunarvatn ash layer 9100 years b p respectively diatom abundances increase steadily throughout the pre boreal atlantic time to 25 and 35 million valves per gram dry sediment in the norwegian basin and iceland plateau cores respectively application of the temperature transfer functions gint2 to the two holocene records revealed higher than present sea surface temperatures during the boreal atlantic chronozones for the iceland plateau and during the middle younger dryas sub boreal chronozones for the norwegian basin core temperatures decreased steadily since then with a slight increase to the present values both the iceland and the norwegian seas experienced a strong influx of temperate atlantic surface waters in the beginning of the holocene sea surface temperatures dropped steadily in the latter part of the holocene as the influx of the atlantic surface waters diminished

reconstruction of sea surface temperature salinity and sea ice cover in the northern north atlantic during the last glacial maximum based on dinocyst assemblages past sea surface conditions over the northern north atlantic during the last glacial maximum were examined from the study of 61 deep sea cores the last glacial maximum time slice studied here corresponds to an interval between heinrich layers h2 and h1 and spanningabout 20 16 ka on a 14c time scale transfer functions based on dinocyst assemblages were used to reconstruct sea surface temperature salinity and sea ice cover the results illustrate extensive sea ice cover along the eastern canadian margins and sea ice spreading only during winter over most of the northern north atlantic on the whole much colder winter prevailed despite relatively mild conditions in august 10 15 c at most offshore sites thus suggesting a larger seasonal contrast of temperatures than today lower salinity than at present is reconstructed especially along the eastern canadian and scandinavian margins likely because of meltwater supply from the surrounding ice sheets these reconstructions contrast with those established by climap on the basis of planktonic foraminifera these differences are discussed with reference to the stratigraphical frame of the last glacial maximum which was not the coldest phase of the last glacial stage the respective significance of dinocyst and foraminifer records is also examined in terms of the thermohaline characteristics of surface waters and the vertical structure of upper water masses which was apparently much more stratified than at present in the northern north atlantic thus preventing deep water formation

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

palynological implication of holocene vegetation and environment in pyeongtaek wetland korea abstract vegetational and depositional environmental changes were interpreted from a trench in ca 10 000 cal bp sediments in the pyeongtaek wetland korea based on palynomorph and grain size analysis from ca 10 400 8000 cal bp cool dry temperate conditions encouraged quercus dominated deciduous broadleaved forest with conifers and cool tolerant birch prevailing on hills and in mountainous areas as postglacial warming began halophytic chenopodiaceae pollen and marine dinoflagellates indicate the depositional environment was an intertidal flat conditions became warm and wet between ca 8000 and ca 6000 cal bp areas still contained quercus dominated deciduous broadleaved forest but with decreased conifers and cool tolerant birch the absence of marine dinoflagellates and abundant meso to hypersaline salt marshes of gramineae with a later increase of mesosaline cyperaceae marshes indicate a transition from intertidal flat to freshwater swamp from ca 6000 to ca 4500 cal bp quercus dominated forests were replaced by mixed conifer deciduous broadleaved forests under climatic deterioration aquatic genera and freshwater algae indicate that the study area completely changed to freshwater swamp the directional sequence in relative abundance of taxa maximum percentage of pollen of chenopodiaceae followed by gramineae cyperaceae and aquatics suggests a gradational pattern indicative of marked environmental clines typical of intertidal habitats

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

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

palaeoenvironmental reconstructions during the meso to neolithic transition 9 2 5 3 cal ka bp in northwestern france palynological evidences sedimentological palynological and micropalaeontological studies carried out throughout the first half of the holocene during the mesolithic neolithic transition in the bay of brest i e 9200 9

oceanic pollen transport and pollen dinocyst ratios as markers of late cenozoic sea level change and sediment transport abstract palynological studies of late cenozoic cores from nine sites show large peaks in the ratio of pollen and spores to dinocysts p d which reflect major increases in terrigenous sediment influx to the north atlantic ocean under normal pelagic conditions in the north atlantic i e in the absence of ice rafting or mass wasting p d in oceanic sediments is low usually

distribution of dinocyst assemblages in surface sediment samples from the west greenland margin abstract palynological analyses of 60 surface sediment samples from west greenland margin revealed high concentrations of dinoflagellate cysts dinocysts particularly in the disko bugt area where they reach 104 cysts g 1 dinocyst assemblages are characterized by a relatively high species diversity and are dominated by operculodinium centrocarpum cysts of pentapharsodinium dalei islandinium minutum islandinium cezare and brigantedinium spp on a regional scale the overall assemblages show statistical relationships with sea ice cover duration primary productivity salinity and summer fall temperature the cysts of pentapharsodinium dalei operculodinium centrocarpum and spiniferites elongatus appear linked to high productivity and to characterize the late summer fall bloom although islandinium minutum and islandinium cezare are generally associated with a seasonally sea ice covered environment there is no linear relationship between their relative abundance and sea ice concentration or duration on a regional scale along the west greenland margin the abundance of these taxa primarily reflects cold and low salinity water in the study area radionuclide measurements 210pb and 137cs allow the distinction between two categories of samples the modern ones likely encompassing the interval younger than 1950 ce and the others that may be considered sub modern statistical analyses indicate that dinocyst assemblages belonging to modern and sub modern categories are not significantly different hence the dinocyst assemblages of surface sediment samples both modern and sub modern represent fluxes homogenized over a relatively long time interval which illustrates a spatial distribution corresponding to the main gradient in oceanographic conditions consequently dinocyst assemblages in surface sediments can be assumed to represent the average modern conditions with a sufficiently high degree of confidence for their use in environmental studies and paleoclimate reconstructions

accelerator mass spectrometry radiocarbon stratigraphies in deep labrador sea cores paleoceanographic implications foraminiferal accelerator mass spectrometry ams 14c ages and benthic planktonic age differences in surface layer sediments of labrador sea are influenced by bioturbation and by changes in the relative abundance of foraminiferal species carrying the 14c signal using benthic mixing models we demonstrate that inverse benthic planktonic age differences can be generated when the effect of benthic mixing and abundance change exceeds apparent age differences between surface water and deep water ams 14c ages obtained put constraints on the timing of major paleoceanographic changes in the basin notably on the history of the western boundary undercurrent which was clearly reinitiated during the mid deglaciation and intensified during the last 2 3 ka

holocene sea surface conditions in the north atlantic contrasted trends and regimes in the western and eastern sectors labrador sea vs iceland basin abstract two sediment cores from the labrador sea and one from the iceland basin were analysed in order to compare holocene sea surface conditions across the northern north atlantic 18o measurements on meso and epi planktonic foraminifera neogloboquadrina pachyderma left coiling and globigerina bulloides along with sea surface condition reconstructions using transfer functions based on dinoflagellate cyst assemblages were used to document thermohaline properties of the upper water column at the labrador sea sites a decreasing trend in sea surface temperature following an early holocene maximum is observed at the iceland basin site a hiatus between 13 and 8 ka bp prevents us from documenting the entire holocene but a stable to slightly decreasing trend is observed from 8 ka bp onwards sea surface salinity and potential density show little variation at the orphan knoll site in the labrador sea since 7 ka bp whereas they depict a decreasing trend at the two other sites since ca 8 ka bp this shift in values suggests a progressive enhancement of labrador sea water formation and a relative decrease in the nordic seas components of the north atlantic deep water i e denmark strait overflow water and norwegian sea overflow water discrepancies are also observed with regard to millennial frequency oscillations in sea surface conditions at the easternmost site they likely match previously documented cold water pulses in the north eastern atlantic whereas they do not show any clear pattern at the westernmost sites hence the western and eastern areas show different behaviours with respect to both long term and high frequency fluctuations

recent anthropogenic and climatic history of nunatsiavut fjords labrador canada this study aimed at reconstructing past climatic and environmental conditions of a poorly known and documented subarctic region the nunatsiavut northern labrador a multiproxy approach was chosen using fossil dinoflagellate cysts diatoms and pollen from sediment cores taken into three fjords nachvak 59 n saglek 58 5 n and anaktalak 56 5 n it allowed estimating terrestrial and marine influences in each fjord and documenting the recent history of human activities of the southern fjords saglek and anaktalak fossil pollen and dinoflagellate cyst assemblages allowed depicting the climate history of the region over the last 200 300 years in contrast to the general warming trend observed in the arctic and subarctic canada since the beginning of the industrial era the nunatsiavut has experienced relative climate stability over this period fossil pollen data show a shift of the tree limit to the south illustrating the cooling of terrestrial conditions our reconstructions suggest that the labrador region has remained climatically stable over the last 150 300 years with just a slight cooling trend of the reconstructed sea surface temperatures only perceptible in saglek and anaktalak fjords

dating and palaeoenvironmental reconstruction of the sediments around the miocene pliocene boundary in yermak plateau odp hole 911a using marine palynology abstract the late neogene evolution of the arctic to subarctic region is poorly understood due to few available records and poor age control at the margin of the arctic ocean yermak plateau ocean drilling program odp hole 911a is strategically located for establishing a stratigraphic framework for the arctic here we present dinoflagellate cyst and acritarch data from 24 stratigraphic levels in the lower part 474 26 505 64 metres below the seafloor of odp hole 911a the marine palynomorphs indicate a latest miocene to earliest pliocene age between 5 8 and 5 0 ma for the base of the hole based on the co occurrence of the dinoflagellate cyst barssidinium evangelineae and acritarch lavradosphaera crista our age estimate can possibly be further refined to 5 0 5 33 ma based on the presence of achomosphaera andalousiensis suttonensis which apparently has a range restricted to the pliocene an age close to the miocene pliocene boundary agrees with the planktonic foraminifer data together with recently available magnetostratigraphic data the base of the hole is likely to be placed at 5 2 ma this new chronostratigraphy is a first step towards a better understanding of the late neogene palaeoenvironment for the yermak plateau and also for the wider arctic to the subarctic region the terrestrial and fresh water palynomorphs were most likely redistributed and or displaced from the shelf towards deeper parts of the basin during contourite deposition under the influence of the west spitsbergen current the in situ marine dinoflagellate cyst assemblage contains a mixture of cool water and thermophilic taxa indicating sea ice free cool temperate and warmer than present conditions at the yermak plateau rivers were likely the source for the freshwater influence warmer than present conditions may have occurred due to northward warm water transport via the west spitsbergen current but also the absence of sea ice and consequent lower albedo could have played a role

late quaternary sea surface conditions at dsdp hole 594 in the southwest pacific ocean based on dinoflagellate cyst assemblages investigation of organic walled dinoflagellate cyst distribution in 118 surface sediments from the southern ocean documents the relatively high diversity of cyst taxa 46 species and distinct cyst assemblages in relation to surface water masses and temperature gradient the antarctic water is characterised by the dominance of selenopemphix antarctica accompanied by brigantedinium spp and impagidinium pallidum the subantarctic water association consists mainly of nematosphaeropsis labyrinthus impagidinium paradoxum and impagidinium sphaericum whereas the subtropical water association is dominated by operculodinium centrocarpum and spiniferites membranaceus multivariate analyses non metric multidimensional scaling demonstrate the relationships with sea surface conditions and enable the application of the best analogue method on the southern ocean dinoflagellate cyst data base for reconstructing past sea surface conditions the dinoflagellate cyst record from dsdp 594 45 31 41 s 174 56 88 e 1204 m southern margin of the chatham rise shows important fluctuations in species composition from glacial to interglacial over the last 140 000 yr reconstruction of winter and summer ssts reveals much lower temperature than present by 6 to 10 c during marine oxygen isotope stages 6 4 and 2 and higher temperature by 2 3 c during substage 5e copyright 2001 john wiley sons ltd journal of quaternary science

the dynamics of orographic wake formation in flows with upstream blocking the development of orographic wakes and vortices is revisited from the dynamical perspective of a three dimensional 3d vorticity vector potential formulation particular emphasis is given to the role of upstream blocking in the formation of the wake scaling arguments are first presented to explore the limiting form of the 3d vorticity inversion for the case of flow at small dynamical aspect ratio it is shown that in the limit of small the inversion is determined completely by the two horizontal vorticity components that is the part of the velocity induced by the vertical component of vorticity vanishes in the small limit this result leads to an approximate formulation of small fluid mechanics in which the three governing prognostic variables are the two horizontal vorticity components and the potential temperature the remainder of the study then revisits the problem of orographic wake formation from the perspective of this small vorticity dynamics framework previous studies have suggested that one of the potential routes to stratified wake formation is through the blocking of flow on the upstream side of the barrier this apparent link between blocking and wake formation is shown to be relatively straightforward in the small vorticity context in particular it is shown that blocking of the flow inevitably leads to a horizontal vorticity distribution that favors deceleration of the leeside flow at the ground this process of leeside flow deceleration as well as the subsequent time evolution of the wake is illustrated through a series of numerical initial value problems involving flows past 2d and 3d barriers it is proposed that the initiation of the wake flow in these stratified problems resembles the flow produced by a retracting piston in shallow water theory

quantitative assessment of carbonate dissolution in marine sediments from foraminifer linings vs shell ratios davis strait northwest north atlantic a new method to evaluate quantitatively the degree of calcium carbonate preservation and dissolution in high latitude marine sediments is proposed on the basis of relative abundance of caco 3 shells and organic linings of benthic foraminifers this method was applied to a late quaternary sequence from davis strait in the northwest north atlantic and shows that caco 3 dissolution in sediments has increased since the last glacial maximum ca 18 000 b p and peaked when subpolar interglacial conditions were established in surface waters the dissolution in davis strait sediments appears to be closely related to organic biogenic production in surface waters with a regional pattern of bottom water formation and circulation

holocene variations of sea surface conditions in the southeastern barents sea reconstructed from dinoflagellate cyst assemblages palynomorphs were analysed in two sediment cores from the southeastern barents sea representing the past 8 3 and 4 4 kyr high dinocyst contents and species diversity enabled the application of the best analogue method to quantitatively reconstruct sea surface salinities temperatures and ice cover using 677 modern reference sites from the north atlantic and arctic seas including new data from the barents sea reported here at the southern core site where waters are affected by the atlantic inflow sea surface conditions were relatively warm and stable between ca 8000 and 5000 calendar yr bp in contrast the past 5 kyr had periods with cooler temperatures and extended ice cover fluctuating mostly at 1 1 5 kyr frequencies at both sites most pronounced coolings occurred around 8 1 5 3 5 3 2 and 2 5 ka the northern site additionally shows younger cooling events tentatively dated to 1 4 0 3 and 0 1 ka identified variations in sea surface conditions indicate changes in atlantic water inputs to the barents sea our results generally correlate to palaeoclimatic reconstructions from northwestern eurasia exemplified by palynological records from karelia this correlation suggests that sea surface variations in the barents sea reflect large scale changes in atmospheric and oceanic interactions between the north atlantic and the arctic copyright 2001 john wiley sons ltd

pollen stratigraphy of late quaternary cores from marmara sea land sea correlation and paleoclimatic history marine pollen analysis is an important tool for paleoclimatic reconstruction of regions like the eastern mediterranean and near east where few onshore sites provide long pollen records first a compilation was made of core top data from the eastern mediterranean to blackseas to map regional variations in modern marine pollenspore concentrations these data show a strong linkbetween pollen spore concentrations and sea surface salinity with minima of 5 grains g in the southern mediterranean and maxima of 160 000 grains g in the blacksea despite under representation of some forest and herbaceous vegetation indicators e g fagus and pistacia variations in species composition of the marine assemblages correspond closely with the distribution of regional vegetation zones and can be used as proxies for spatial differences in seasonal and total temperature and rainfall pollen spore assemblages in five cores from the marmara sea with multiple ages ranging from 33 550 to 1990 yr bp and one holocene core from southeastern blacksea were used to compile a late quaternary marine pollen stratigraphy these data were then compared with eastern mediterranean onshore reference sites in order to reconstruct a vegetation and paleoclimate history for the blacksea aegean corridor from the pleniglacial interval to present five marine pollen zones are recognized pz 5 v33 6 24 ka corresponds to the late wu rm pleniglacial pz 4 v24 13 ka spans the late glacial maximum lgm pz 3 v13 10 2 ka includes the allero d younger dryas glacial interglacial transition pz 2 10 2 4 ka marks the early holocene interglacial warm wet interval and pz 1 covers the latest holocene colonization phase which may also have been cooler and drier using the steppe forest index of traverse 1975 it is shown that the only intervals of severely dry conditions occurred briefly during the lgm and its transition during most of the pleniglacial and all of the postglacial time precipitation versus evaporation rates were sufficiently high to permit persistence of oro mediterranean forest vegetation furthermore there is no evidence for environmental conditions in the blacksea marmara region that would have encouraged pastoral or agricultural settlement in the littoral region prior to the bronze age commencing 4600 years ago crown copyright a 2002 elsevier science b v all rights reserved

holocene climate history of the nunatsiavut northern labrador canada established from pollen and dinoflagellate cyst assemblages covering the past 7000 years this study documents the past 7000 years of holocene climatic history for labrador and nunatsiavut using a sedimentary sequence of more than 8 m retrieved in nachvak fjord one of the northernmost fjords of nunatsiavut using a multi proxy approach combining a solid accelerator mass spectrometry ams 14c chronology and the fossil assemblages of pollen grains and dinoflagellate cysts dinocysts we were able to compare terrestrial and marine records in an effort to obtain a better understanding of the mid to late holocene climate history of the nunatsiavut records begin at the end of the deglaciation and showed a general delay in the sequence of climate events which followed both in terrestrial and marine realms the presence of pentapharsodinium dalei in great abundance in nachvak fjord revealed a strong influence of the north atlantic ocean and the labrador sea until 3000 yr bp afterward its rather fast disappearance marked the increased influence of arctic waters the last 1000 years show clim

time transgressive holocene maximum of temperate and mediterranean forest development across the iberian peninsula reflects orbital forcing abstract we describe a new pollen and sea surface temperature sst record with sub centennial to centennial resolution from a well dated sediment core d13882 obtained from the atlantic margin of the southwest iberian peninsula the core provides new insights into the dynamics of five ecological pollen based groups temperate forests mediterranean forests pinewoods heathlands and steppe since the late pleistocene last 13 260 cal yr bp the record shows that the early holocene was marked by an increase of temperate and mediterranean taxa accompanied by a reduction of steppic plants reflecting warm and relatively moist conditions when compared with the previous younger dryas episode the timing of this temperate and mediterranean forest tmf maximum which reflects optimum conditions of temperature and precipitation is regionally specific as detected through a comparison of three marine cores across the iberian peninsula maximum tmf development occurs between 9760 and 7360 cal yr bp in d13882 whereas at a site to the northwest md03 2697 the maximum occurs some centuries earlier and at a southeast site md95 2043 the maximum is evident later the duration of the forest maximum is also progressively longer from northwest to southwest to southeast a transition from forested ecosystems to heathland over western iberia characterises the middle holocene starting from around 7360 cal yr bp in d13882 suggesting reduced seasonality and a more atlantic climate character with more moisture evenly available through the year this contrasts with the aridity recorded in southeast iberian sites and reflects a stable precipitation gradient between the wetter west and drier east of the iberian peninsula against this backdrop pinewoods had a continuous presence albeit with a trend of steady decline through the holocene the time transgressive pattern in the tmf maximum is best explained by a less favourable moisture balance in the drier southeast sector which was particularly important during the early holocene despite the relatively short duration of the holocene interglacial one half precession cycle our observations support a key role for orbital forcing in the temporal expression of major vegetation groups specifically the decline in summer insolation and the precession related passage of perihelion season from summer to winter

the parametrization of drag induced by stratified flow over anisotropic orography a new parametrization of drag arising from the flow over unresolved topography ut in a general circulation model gcm is presented it is comprised of three principle components a parametrization of the source spectrum and drag associated with freely propagating hydrostatic gravity waves in the absence of rotation a parametrization of the drag associated with low level wave breaking and a parametrization of low level drag associated with upstream blocking and lee vortex dynamics novel features of the scheme include a new procedure for defining the ut in each gcm grid cell which takes account of the gcm resolution and includes only the scales represented by the parametrization scheme a new method of representing the azimuthal distribution of vertical momentum flux by two waves whose direction and magnitude systematically vary with the flow direction and with the anisotropy of the ut in each gcm grid cell and a new application of form drag in the lowest levels which can change the direction of the low level flow so that it is more parallel to unresolved two dimensional topographic ridges the new scheme is tested in the canadian centre for climate modelling and analysis third generation atmospheric gcm at horizontal resolutions of t47 and t63 five year seasonal means of present day climate show that the new scheme improves mean sea level pressures or mass distribution and improves the tropospheric circulation when compared with the gravity wave drag scheme used currently in the gcm the benefits are most pronounced during northern hemisphere winter it is also found that representing the azimuthal distribution of the momentum flux of the freely propagating gravity wave field with two waves rather than just one allows 30 50 more gravity wave momentum flux up into the middle atmosphere depending on the season the additional momentum flux into the middle atmosphere is expected to have a beneficial impact on gcms that employ a more realistic representation of the stratosphere

postglacial changes of terrestrial and marine environments along the labrador coast palynological evidence from cores 91 045 005 and 91 045 006 cartwright saddle the palynology of cores from cartwright saddle led to reconstruction of sea surface conditions on the basis of transfer functions using dinoflagellate cyst assemblages and to correlations with vegetational history on adjacent land as derived from pollen assemblages from deglaciation to about 8000 bp dinoflagellate cyst assemblages dominated by algidasphaeridium minutum indicate arctic type sea surface conditions and pollen assemblages reveal tundra vegetation in southeastern labrador codominance of a minutum and brigantedinium spp indicate persistence of cold sea surface conditions august temperature 3 c and extensive sea ice cover up to 11 months year until ca 6000 bp however the occurrence of abies which reached a maximum abundance at ca 7000 6000 bp and increasing percentages of alnus indicate northward tree migration and development of shrub tundra as a result of warmer terrestrial conditions around 6000 bp the significant occurrence of peridinium faeroense and nematosphaeropsi

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

a new subgrid scale orographic drag parametrization its formulation and testing a scheme for the representation of subgrid scale orography sso in numerical weather prediction and climate models is presented the new scheme arose in part from a desire to represent nonlinear low level mountain drag effects not currently parametrized an important feature of the scheme is that it deals explicitly with a low level flow which is blocked when the effective height of the subgrid scale orography is sufficiently high in this new scheme it is assumed that for this blocked flow separation occurs at the mountain flanks resulting in a form drag this drag is parametrized on model levels which are intersected by the sso and provides a dynamically based replacement for envelope orography the upper part of the low level flow goes over the orography and generates gravity waves at the model resolutions considered t106 and t213 it is assumed that the length scales characteristic of the sso are sufficiently small for the coriolis force to be neglected the various parameters of the scheme are adjusted using an off line procedure in which the scheme is used to estimate the mountain drag and the momentum profiles above the pyrenees and these estimates are validated with the pyrex data forecasts using t106 and t213 resolutions with this new scheme and with mean orography show that the forecast mountain drag consistently reproduces the drag measured during pyrex whenever the flow component normal to the ridge is large isentropic flow diagnostics further show that the new scheme has a realistic impact on the flow dynamics reinforcing the low level wake observed in mesoscale analyses of the flow with this new scheme and a mean orography the ecmwf model outperformed in forecast skill a version of the model which had an envelope orography and the old gravity wave drag scheme while no longer suffering any disadvantages of envelope orography the proposed low level drag parametrization should also be relevant at model horizontal resolutions much higher than t213

dinoflagellate cyst evidence of heinrich like events off portugal during the marine isotopic stage 5 abstract dinoflagellate cysts were analysed from images core md952042 37 48 n 10 01 w retrieved from the tagus abyssal plain previous results of stable isotope and magnetic susceptibility measurements as well as of planktonic foraminiferal temperature reconstruction from this core suggest the occurrence of heinrich like events i e large ice sheet decay during marine isotopic stage 5 mis 5 dinoflagellate assemblages of this time period have revealed six dinocyst events that are characterised by peaks in bitectatodinium tepikiense percentages these events occur synchronously with heinrich like events previously identified they are coeval with major retreats of the forest on land indicating therefore drastic changes in the regional climate however results from the ice rafted detritus ird analysis of the 150 m lithic fraction shows that mis 5 of md952042 has only recorded one significant input of iceberg discharge located at the mis 6 mis 5 transition it seems therefore that it is the only event that could be called a true heinrich event

a new 6 myr stratigraphic framework for the atlantic arctic gateway abstract a comprehensive stratigraphic framework for the atlantic arctic gateway has been established for the last 6 myr on the yermak plateau nw svalbard based on new paleomagnetic and biostratigraphic sampling and correlation of high resolution seismic data between ocean drilling program odp holes 911a 910c and 912a the new results indicate a late miocene age for the base of both holes 911a and 910c providing the first complete late neogene record for the marginal arctic ocean and extending the previously published age model by several million years during the late miocene pleistocene the southern yermak plateau was dominated by contourite deposition from the intensification of the northern hemisphere glaciation at 2 7 ma glacial fans from nw svalbard prograded onto the southernmost yermak plateau this indicates that the ice sheet on nw svalbard reached the shelf break at 2 7 ma much earlier than on the western barents sea svalbard margin 1 5 ma simultaneous with the first shelf break glaciation on the western barents sea svalbard margin at 1 5 ma we observe the first signs of extensive glacial erosion on the yermak plateau indicating a regional glacial intensification at this time for the whole barents sea svalbard region our results agree well with the widening deepening of the fram strait and the opening of the atlantic arctic gateway during the middle miocene

postglacial paleoceanography of hudson bay stratigraphic microfaunal and palynological evidence cores containing representative sequences of postglacial sediments in northern and southern hudson bay were analyzed for their microfaunal foraminifers and ostracods and palynological dinocysts

changes in miocene through pleistocene dinoflagellates from the eastern equatorial pacific odp site 1039 in relation to primary productivity abstract palynological data from offshore costa rica allow us to investigate the relationship between dinoflagellate cyst assemblages and changes in regional oceanic primary productivity from miocene to pleistocene productivity at odp site 1039 was influenced by tectonic drift as site 1039 approached the continent from the equator to its current position at 10 n in addition dinoflagellate abundance is modulated by regional productivity events which modified primary productivity as also indicated by available data on calcareous nannofossils diatoms toc and caco 3 content five palynomorph intervals are defined the early late miocene one dominated by batiacasphaera represents relatively stable productive oceanic conditions before the closure of the indonesian and panama seaways the late miocene decrease in palynomorph recovery is related to the carbonate crash event the high abundance and diversity of the assemblages at the end of the late miocene to early pliocene indicate increased productivity related to the global biogenic bloom and a change in dominance from batiacasphaera to impagidinium to nematosphaeropsis the low abundance of the late pliocene interval is related to el nino like conditions and there is another change related to the disappearance of batiacasphaera and dominance of impagidinium nematosphaeropsis and operculodinium the abundant pleistocene assemblages represent increased marine productivity and a high influx of continental palynomorphs and bissacate pollen associated with the proximity of the costa rica dome pleistocene dinoflagellates are characterized by spiniferites and selenopemphix together with rare impagidinium and nematosphaeropsis