secondary circulation in a region of flow curvature relationship with tidal forcing and river discharge 1 on the basis of a 301 day acoustic doppler current profiler mooring in an estuarine tidal strait the strength and structure of secondary circulation in a region of flow curvature is related to variations in tidal forcing and river discharge during low flow conditions the structure of secondary flow is consistent with a centrifugally forced helical flow with bottom flow toward the inside of the bend and surface flow toward the outside of the bend the strength of secondary flow increases linearly with tidal range and is consistent with a vertical eddy viscosity that is linearly dependent on tidal current speed during times of high river discharge the strength of secondary flow is significantly reduced and its vertical structure undergoes a fundamental change over the spring neap cycle during spring tides the classic helical flow pattern is evident albeit weaker than during low flow conditions however during neap tides a more complex two cell structure is evident the change between these two states occurs with a spring neap transition in the subtidal flow indicating that it is also accompanied by changing stratification simple scaling analysis suggests that during weakly stratified conditions secondary circulation will influence stream wise dynamics and dispersion for channels with widths on order or less than 0 1 h cd where h is the water column depth and cd is a quadratic bottom drag coefficient in contrast during highly stratified conditions lateral excursions due to secondary flows are limited to approximately one tenth of the channel s width and are an ineffective lateral mixing agent

mis 3 to mis 1 temporal and lgm spatial variability in arctic ocean sea ice cover reconstruction from biomarkers using the sea ice proxy ip25 and phytoplankton derived biomarkers brassicasterol and dinosterol arctic sea ice conditions were reconstructed for marine isotope stage mis 3 to 1 with special emphasis on the last glacial maximum lgm in sediment cores from the northern barents sea continental margin across the central arctic ocean to the southern mendeleev ridge our results suggest more extensive sea ice cover than present day during latter part of mis 3 increasing sea ice growth during mis 2 and decreased sea ice cover during the last deglacial the summer ice edge remained north of the barents sea even during extremely cold i e last glacial maximum lgm as well as warm periods i e bolling allerod during the lgm the western svalbard margin and the northern barents sea margin areas were characterized by high concentrations of both ip25 and phytoplankton biomarkers interpreted as a productive ice edge situation caused by the inflow of warm atlantic water in contrast the lgm central arctic ocean north of 84 n was covered by thick permanent sea ice throughout the year with rare break up indicated by zero or near zero biomarker concentrations the spring summer sea ice margin significantly extended southwards to the laptev sea shelf southern lomonosov ridge and southern mendeleev ridge during the lgm our proxy reconstructions are very consistent with published model results based on the north atlantic arctic ocean sea ice model naosim

interaction of lateral baroclinic forcing and turbulence in an estuary 1 observations of density and velocity in a channel in northern san francisco bay show that the onset of vertical density stratification during flood tides is controlled by the balance between the cross channel baroclinic pressure gradient and vertical mixing due to turbulence profiles of velocity salinity temperature and suspended sediment concentration were measured in transects across suisun cutoff in northern san francisco bay on two days over the 12 5 hour tidal cycle during flood tides an axial density front developed between fresher water flowing from the shallows of grizzly bay into the northern side of suisun cutoff and saltier water flowing up the channel north of the front transverse currents were driven by the lateral salinity gradient with a top to bottom velocity difference greater than 30 cm s south of the front the secondary circulation was weak and along channel velocities were greater than to the north the gradient richardson number shows that stratification was stable north of the front while the water column was turbulently mixed south of the front time series measurements of velocity and salinity demonstrate that the front develops during each tidal cycle in estuaries longitudinal dynamics predict less stratification during flood than ebb tides these data show that stratification can develop during flood tides due to a lateral baroclinic pressure gradient in estuaries with complex bathymetry

the tidally averaged momentum balance in a partially and periodically stratified estuary abstract observations of turbulent stresses and mean velocities over an entire spring neap cycle are used to evaluate the dynamics of tidally averaged flows in a partially stratified estuarine channel in a depth averaged sense the net flow in this channel is up estuary due to interaction of tidal forcing with the geometry of the larger basin the depth variable tidally averaged flow has the form of an estuarine exchange flow downstream at the surface upstream at depth and varies in response to the neap spring transition the weakening of the tidally averaged exchange during the spring tides appears to be a result of decreased stratification on the tidal time scale rather than changes in bed stress the dynamics of the estuarine exchange flow are defined by a balance between the vertical divergence of the tidally averaged turbulent stress and the tidally averaged pressure gradient in the lower water column in the upper water column tidal stresses are important contributors particularly during the n

modern seasonal variability and deglacial holocene change of central arctic ocean sea ice cover new insights from biomarker proxy records for the reconstruction of sea ice variability a biomarker approach which is based on 1 the determination of sea ice diatom specific highly branched isoprenoid ip25 and 2 the coupling of phytoplankton biomarkers and ip25 has been used for the first time such a data set was obtained from an array of two sediment traps deployed at the southern lomonosov ridge in the central arctic ocean at water depth of 150 m and 1550 m and recording the seasonal variability of sea ice cover in 1995 1996 these data indicate a predominantly permanent sea ice cover at the trap location between november 1995 and june 1996 an ice edge situation with increased phytoplankton productivity and sea ice algae input in july august 1996 and the start of new ice formation in late september the record of modern sea ice variability is then used to better interpret data from sediment core ps2458 4 recovered at the laptev sea continental slope close to the interception with lomonosov ridge and recording the post glacial to holocene change in sea ice cover based on ip25 and phytoplankton biomarker data from core ps2458 4 minimum sea ice cover was reconstructed for the bolling allerod warm interval between about 14 5 and 13 calendar kyr bp followed by a rapid and distinct increase in sea ice cover at about 12 8 calendar kyr bp this sea ice event was directly preceded by a dramatic freshwater event and a collapse of phytoplankton productivity having started about 100 years earlier these data are the first direct evidence that enhanced freshwater flux caused enhanced sea ice formation in the arctic at the beginning of the younger dryas in combination with a contemporaneous abrupt and very prominent freshwater meltwater pulse in the yermak plateau fram strait area these data may furthermore support the hypothesis that strongly enhanced freshwater and ice export from the arctic into the north atlantic could have played an important trigger role for the onset of the younger dryas cold reversal during the early holocene sea ice cover steadily increased again ice edge situation reaching modern sea ice conditions more or less permanent sea ice cover probably

the effects of channels and shoals on exchange between the chesapeake bay and the adjacent ocean the role of bathymetric changes in determining the transport of water and salt in the lower chesapeake bay lcb was investigated using high resolution acoustic doppler current profiler adcp and conductivity temperature depth profiles a cross channel transect was repeated eight times during neap tides on october 6 7 1993 which illustrated the lateral structure of the longitudinal and transverse flow fields and the intratidal variations in the flow structure across the lcb amplitude and phase of the m2 tidal component as well as the mean flow velocity were calculated using least squares fitting at every point of a uniform grid obtained from the adcp data the results differ from the classical two layer pattern of estuarine circulation modified by coriolis effects but are consistent with recent hydrographic observations semidiurnal flow was highest over the navigational channels and lateral gradients were strongest in regions of sharp bathymetric changes the phase lag of the semidiurnal flow also showed lateral and vertical gradients that represented advances at the bottom with respect to the surface and over the shoals in relation to the channels the section of the water column measured indicated a mean outflow of 0 7 104 m3 s and a mean inflow of 1 3 104 m3 s the apparent gain of water by the estuary during the period of observation can be explained by meteorologically forced net barotropic inflow the depth averaged mean longitudinal flow consisted of inflow in the navigational channels and outflow over the shoals the mean transverse flow showed near surface convergence over the channels we propose a possible explanation for the observed flow and density structure as follows the barotropic and baroclinic forcing interact with the bathymetry to extend the inflow from the bottom to the surface thereby inducing a transverse circulation that yields near surface convergence over the channels

particle trapping in estuarine tidal flows particle trapping in estuarine turbidity maxima etm is caused primarily by convergent mean and or tidal fluxes of sediment the result is an approximately bell shaped along channel distribution of vertically integrated tidal cycle mean suspended sediment concentration observations from the columbia river estuary suggest that 1 strong two layer or internal along channel residual and overtide flows are generated by time varying stratification and 2 correlations between the near bed velocity and the suspended sediment fields at these frequencies are important in landward transport of sediment a new spatially and temporally integrated form of the sediment conservation equation has been derived to analyze this trapping process time changes in tidally averaged sediment concentration between two estuarine cross sections can be shown to be related to the divergence of the seaward river flow transport the divergence of velocity shear sediment stratification correlations for the mean flow and each tidal constituent and net erosion or deposition at the bed vertically integrated variables other than seaward river transport are absent from this integrated balance analysis of sediment fluxes using this balance supports the idea that internal residual and overtide circulations are primarily responsible for the landward sediment transport on the seaward side of etm found near the upstream limits of salinity intrusion the balance also shows that attempts to represent fluxes causing trapping of sediment in an etm as a product of a time mean vertically integrated along channel gradient and a diffusivity inevitably lead to the appearance of countergradient transport and thus a negative diffusivity on the seaward side of the etm this result occurs because the trapping process is inherently nonlinear and at least two dimensional and because a one dimensional representation is physically unrealistic

insights into circum arctic sea ice variability from molecular geochemistry abstract geological records of past sea ice such as those contained in arctic marine sediments offer an opportunity to strengthen our understanding of long term sea ice variability provided unambiguous paleo sea ice proxies can be developed one such recently proposed proxy is ip25 a highly branched isoprenoid alkene biosynthesized exclusively by sea ice dwelling diatoms haslea spp which is well preserved in marine sediments and could be used to reconstruct past changes in spring sea ice extent however little is known about regional scale controls on ip25 production in sea ice limiting its wider applicability as a paleo sea ice proxy to address this issue we examined the distributions of ip25 and the marine productivity biomarkers dinosterol and brassicasterol in a suite of surface sediment samples distributed across the arctic we find a statistically significant logarithmic relationship between ip25 and spring sea ice cover in sediment samples from arctic and subarctic sites in the pacific n 96 r2 0 67 p

impact of the depth to width ratio of periodically stratified tidal channels on the estuarine circulation the dependency of the estuarine circulation on the depth to width ratio of a periodically weakly stratified tidal estuary is systematically investigated here for the first time currents salinity and other properties are simulated by means of the general estuarine transport model getm in cross sectional slice mode applying a symmetric gaussian shaped depth profile the width is varied over four orders of magnitude the individual along channel circulation contributions from tidal straining gravitation advection etc are calculated and the impact of the depth to width ratio on their intensity is presented and elucidated it is found that the estuarine circulation exhibits a distinct maximum in medium wide channels intermediate depth towidth ratio depending on various parameters which is caused by a maximum of the tidal straining contribution this maximum is related to a strong tidal asymmetry of eddy viscosity and shear created by secondary strain induced periodic stratification 2sips in medium channels transverse circulation generated by lateral density gradients due to laterally differential longitudinal advection induces stable stratification at the end of the flood phase which is further increased during ebb by longitudinal straining sips thus eddy viscosity is low and shear is strong in the entire ebb phase during flood sips decreases the stratification so that eddy viscosity is high and shear is weak the circulation resulting from this viscosity shear correlation the tidal straining circulation is oriented like the classical gravitational circulation with riverine outflow at the surface and oceanic inflow close to the bottom in medium channels it is about 5 times as strong as in wide quasi onedimensional channels in which 2sips is negligible

variability of sea surface temperature and sea ice cover in the fram strait over the last two millennia abstract a sediment core located on the west spitzbergen margin in the fram strait 78 54 931 n 6 46 005 e water depth 1497 m was analyzed for its dinocyst content in order to reconstruct hydroclimatic variations of the last 2500 years the relative abundance of dinocyst taxa and principal component analysis show a major transition at about 300 cal years bp it is characterized by the disappearance of thermophilic taxa spiniferites mirabilis hyperacanthus and impagidinium sphaericum and the increase of polar subpolar taxa impagidinium pallidum and pentapharsodinium dalei sea surface temperature sst estimates suggest warmer conditions than present anomaly 2 c averaging at 7 c in summer until 300 cal years bp although cooling pulses are recorded around 1700 1500 1200 and 800 cal years bp the last 300 years were marked by a cooling from 7 6 to 3 5 c and sea ice cover increasing up to 7 months yr the results demonstrate that the fram strait area is sensitive to hydroclimatic variations notably with respect to sea ice and ssts which are linked to the relative strength of northward flow of north atlantic waters to the east and southward outflow of cold and fresh waters from the arctic ocean based on our data the warmest part of our record around 1320 cal years bp is the only interval of the last 2500 years that provides a possible analogue for the modern post ad 2000 interval which is characterized by sea ice free conditions

improving the paleoceanographic proxy tool kit on the biogeography and ecology of the sea ice associated species fragilariopsis oceanica fragilariopsis reginae jahniae and fossula arctica in the northern north atlantic abstract a long term perspective is essential for understanding environmental change to be able to access the past environmental archives such as marine and lake sediments that store information in the form of diverse proxy records are used whilst many analytical techniques exist to extract the information stored in these proxy records the critical assessment and refinement of current methods in addition to developing new methods is crucial to improving our understanding this study aims to improve our knowledge on diatom species used for reconstructing ocean surface conditions especially temperature and sea ice variability over time we define the distribution and the relationship to sea surface temperature sst and sea ice concentrations sic of the species fragilariopsis oceanica fragilariopsis reginae jahniae and fossula arctica using diatom training sets from the northern north atlantic we further assess the effect of separating these species compared to grouping them under f oceanica as has been done in the past our results suggest that while these three species share similarities such as the preference for stratified waters induced by sea ice or glacier meltwater they also exhibit heterogeneous distributions across the northern north atlantic with individual optima for sst and sic this also affects quantitative reconstructions based on our data resulting in lower sst and higher sic estimates when the species are separated in the surface sediment and down core diatom assemblages

distributions of the arctic sea ice biomarker proxy ip25 and two phytoplanktonic biomarkers in surface sediments from west svalbard abstract the concentrations of the sea ice biomarker proxy ip25 ice proxy with 25 carbon atoms and two phytoplankton biomarkers a tri unsaturated highly branched isoprenoid hbi lipid hbi iii and epi brassicasterol have been measured in surface sediments from west svalbard ip25 concentration exhibited a positive relationship with that of hbi iii and epi brassicasterol suggesting that the rapidly fluctuating sea ice dynamics characteristic of west svalbard have a similar impact on these sea ice and phytoplankton lipids as hypothesised in earlier studies alternatively the multi year sedimentary signal may simply represent an integration of more subtle variations in biomarker distributions that reflect variability in sea ice conditions on a seasonal or annual timeframe our findings contrast with those reported previously for the barents sea possibly due to the latter experiencing a more prominent and consistent sea ice advance retreat cycle

semi quantitative estimates of paleo arctic sea ice concentration based on source specific highly branched isoprenoid alkenes a further development of the pip25 index abstract previously reported concentration data for highly branched isoprenoid hbi alkenes and the sterol 24 methylcholesta 5 22e dien 3 ol brassicasterol or epi brassicasterol obtained from 45 barents sea surface sediments reflecting contrasting sea ice conditions have been combined together in the form of the pip 25 index with outcomes compared with recent mean decadal satellite derived spring and summer sea ice concentrations reasonably good positive linear relationships were found between pip 25 indices and spring sea ice concentration with the strongest correlation found when using a tri unsaturated hbi hbi iii as the open water counterpart to the sea ice biomarker ip 25 likely as a result of the greater sensitivity and selectivity of hbi iii to the neighbouring sea ice conditions compared to epi brassicasterol the quality of the linear fits between p iii ip 25 i e pip 25 based on hbi iii and spring sea ice concentration together with their respective spatial distributions were also far less dependent on the balance factor c than for p b ip 25 i e pip 25 based on epi brassicasterol which may have important positive consequences for down core semi quantitative sea ice reconstruction and when making comparisons between outcomes from different arctic regions or climatic epochs in contrast consistently weak linear relationships were observed between individual biomarkers and spring or summer sea ice concentration and between pip 25 values and summer sea ice concentration however we provide evidence that a lower limit threshold for p iii ip 25 might represent a useful qualitative proxy for the past occurrence of summer sea ice surface sediment biomarker data from other regions will be needed before the significance of our findings can be fully evaluated

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

identification of contrasting seasonal sea ice conditions during the younger dryas abstract a palaeo sea ice reconstruction for northern norway for the interval ca 13 8 7 2 cal ka bp has been performed using a combined organic geochemical proxy based study of a marine sediment core jm99 1200 obtained from andfjorden 69 15 95 n 16 25 09 e and the outcomes compared with a series of other palaeoclimate studies carried out previously within this study particular emphasis has been placed on the identification of the sea ice conditions during the younger dryas and the application of different biomarker based proxies to both identify and quantify seasonal sea ice conditions firstly the appearance of the specific sea ice diatom proxy ip 25 at ca 12 9 cal ka bp in the sedimentary record has provided an unambiguous but qualitative measure of seasonal sea ice and thus the onset of the younger dryas stadial the near continuous occurrence of ip 25 for the next ca 1400 yr demonstrates seasonal sea ice during this interval although variable abundances suggest that the recurrent conditions in the early mid younger dryas ca 12 9 11 9 cal ka bp changed significantly from stable to highly variable sea ice conditions at ca 11 9 cal ka bp and this instability in sea ice prevailed for the subsequent ca 400 yr during which an extremely short interval of permanent or near permanent sea ice was observed at ca 11 75 cal ka bp at ca 11 5 cal ka bp ip 25 disappeared from the record indicating ice free conditions that signified the beginning of the holocene the ip 25 concentrations were also combined with those of the open water phytoplankton biomarker brassicasterol to generate p b ip 25 data from which more quantitative measurements of sea ice were determined p b ip 25 data were consistent with consecutively seasonal then infrequent sea ice cover for the early mid and late younger dryas while further comparisons of the p b ip 25 data with the outcomes of previous correlations with modelled sea ice concentrations suggested that these intervals were characterised by ca 60 90 and ca 0 60 sea ice cover respectively both qualitative and quantitative sea ice records were also consistent with sea surface temperature and other palaeoclimate estimates derived previously from various other proxy studies the contrasting seasonal sea ice conditions during the younger dryas were further verified through a comparison of the concentrations of ip 25 with those of another highly branched isoprenoid hbi alkene that is di unsaturated and believed to also be produced by sea ice diatoms the ratio of the hbi diene to ip 25 termed dip 25 is believed to provide a useful indicator of stability or variability in sea ice conditions and complements the outcomes from the ip 25 and p b ip 25 index data the identification of contrasting seasonal sea ice conditions during the younger dryas will likely contribute to the debate regarding the climatic impacts that took place during this intriguing interval

organic carbon carbonate and clay mineral distributions in eastern central arctic ocean surface sediments abstract results from a detailed sedimentological investigation of surface sediments from the eastern arctic ocean indicate that the distribution of different types of sediment facies is controlled by different environmental processes such as sea ice distribution terrigenous sediment supply oceanic currents and surface water productivity in comparison to other open ocean environments total organic carbon contents are high with maximum values in some deep basin areas as well as west and north of svalbard in general the organic carbon fraction is dominated by terrigenous material as indicated by low hydrogen index values and high c n ratios probably transported by currents and or sea ice from the eurasian shelf areas the amount of marine organic carbon is of secondary importance reflecting the low productivity environment described for the modern ice covered arctic ocean in the area north of svalbard some higher amounts of marine organic matter may indicate increased surface water productivity controlled by the inflow of the warm westspitsbergen current wsc into the arctic ocean and reduced sea ice cover this influence of the wsc is also supported by the high content of biogenic carbonate recorded in the yermak plateau area the clay mineral distribution gives information about different source areas and transport mechanisms illite the dominant clay mineral in the eastern central arctic ocean sediments reaches maximum values in the morris jesup rise area and around svalbard indicating north greenland and svalbard to be most probable source areas kaolinite reaches maximum values in the nansen basin east of svalbard and in the barents sea possible source areas are mesozoic sediments in the barents sea and franz josef land in contrast to the high smectite values determined in sea ice samples smectite contents are generally very low in the underlying surface sediments suggesting that the supply by sea ice is not the dominant mechanism for clay accumulation in the studied area of the modern central arctic ocean

quantitative measurement of the sea ice diatom biomarker ip25 and sterols in arctic sea ice and underlying sediments further considerations for palaeo sea ice reconstruction abstract the lipid content of sea ice samples collected in 2011 and 2012 from resolute passage in the canadian arctic archipelago was measured and compared with related samples obtained from the amundsen gulf in 2008 the highly branched isoprenoid hbi sea ice biomarker ip 25 was found in sea ice samples from each study consistent with its formation by diatoms during the spring bloom our analysis also revealed the occurrence of a number of sterols in arctic sea ice and these were rigorously identified and quantified for the first time concentrations of ip 25 and sterols exhibited some variability between sampling studies with somewhat higher values in samples from resolute in 2012 than for the other two datasets consistent with a general increase in biomass however major differences in biomarker concentration between sampling studies were not observed an estimate of the proportion of arctic sea ice diatoms that produce ip 25 ca 1 5 was obtained by comparison of the concentration of ip 25 in the samples with those in laboratory cultures of known hbi producing diatoms and cell enumeration in selected sea ice samples the estimate is similar to the proportion of haslea spp in the same samples providing further support to the suggestion that at least some species of the haslea genus may be responsible for the biosynthesis of ip 25 and related hbi diatom lipids in arctic sea ice and that ip 25 is made by a relatively small proportion of sea ice diatoms in contrast median sterol ip 25 values were all substantially higher than those in cultures of hbi producing diatoms suggesting that sterols are made by the majority of sea ice diatoms the sterol ip 25 ratio was quite variable between locations and samples likely as a result of differences in diatom assemblage however a comparison of individual and median sterol ip 25 values in sea ice with those from surface sediments from different arctic regions demonstrated that sterols from sea ice diatoms may in some cases have a significant impact on the sedimentary budget this should be considered carefully for quantitative estimates of palaeo sea ice reconstruction using methods such as the pip 25 index which are based on the relative concentrations of ip 25 and sterols in arctic marine sediment cores

sea ice variations in the central canadian arctic archipelago during the holocene abstract a sea ice record for barrow strait in the canadian arctic archipelago caa is presented for the interval 10 0 0 4 cal kyr bp this holocene record is based primarily on the occurrence of a sea ice biomarker chemical ip25 isolated from a marine sediment core obtained from barrow strait in 2005 a core chronology is based on 14c ams dating of mollusc shells obtained from ten horizons within the core the primary ip25 data are compared with complementary proxy data obtained from analysis of other organic biomarkers stable isotope composition of bulk organic matter benthic foraminifera particle size distributions and ratios of inorganic elements the combined proxy data show that the palaeo sea ice record can be grouped according to four intervals and these can be contextualised further with respect to the holocene thermal maximum htm spring sea ice occurrence was lowest during the early mid holocene 10 0 6 0 cal kyr bp and this was followed by a second phase 6 0 4 0 cal kyr bp where spring sea ice occurrence showed a small increase between 4 0 and 3 0 cal kyr bp spring sea ice occurrence increased abruptly to above the median and we associate this interval with the termination of the htm elevated spring sea ice occurrences continued from 3 0 to 0 4 cal kyr bp although they were more variable on shorter timescales within this fourth interval we also provide evidence for slightly lower and subsequently higher spring sea ice occurrence during the mediaeval warm period and the little ice age respectively comparisons are made between our proxy data with those obtained from other palaeo climate and sea ice studies for the caa

seeking a holocene drift ice proxy non clay mineral variations from the sw to n central iceland shelf trends regime shifts and periodicities quantitative x ray diffraction analysis of the 2 mm sediment fraction was carried out on 1257 samples from the seafloor and 16 cores from the iceland shelf west of 18 w all but one core b997 347pc were from transects along troughs on the nw to n central shelf an area that in modern and historic times has been affected by drift ice the paper focuses on the non clay mineralogy of the sediments excluding calcite and volcanic glass quartz and potassium feldspars occupy similar positions in an r mode principal component analysis and oligoclase feldspar tracks quartz these minerals are used as a proxy for ice rafted detritus ird accordingly the sum of these largely foreign minerals q k to icelandic bedrock is used as a proxy for drift ice a stacked equi spaced 100 a record is developed which shows both low frequency trends and higher frequency events the detrended stacked record compares well with the flux of quartz mg cm 2 a 1 at md99 2269 off n iceland the multi taper method indicated that there are three significant frequencies at the 95 confidence level with periods of ca 2500 445 and 304 a regime shift analysis pinpoints intervals when there was a statistically significant shift in the average q k weight and identifies four ird rich events separated by intervals with lower inputs there is some association between peaks of ird input less dense surface waters from 18o data on planktonic foraminifera and intervals of moraine building copyright 2009 john wiley sons ltd

climate induced changes in sedimentary regimes for organic matter supply on the continental shelf off northern norway abstract with this study i suggest that changes in biogeochemical processes in northern norwegian fjords during the last glacial interglacial transition 14 3 to 6 3 ka b p are predominantly climate induced variable strength in atlantic water inflow intrusion of arctic waters and sea ice coverage various nutrient supply as well as several re advances of continental ice sheets are recorded by both bulk organic and selected biomarkers in sediments of the andfjord stable isotope 13corg 15n and rock eval pyrolysis data indicate a strong supply of terrestrial organic matter during stadials e g younger dryas older dryas whereas enhanced input of marine organic matter prevailed during the interstadials bolling allerod profiles of selected biomarkers of marine origin show a characteristic climate induced variation during the whole time interval where relatively low concentrations of dinosterols and c37 alkenones may indicate similar to today a minor contribution of their respective plankton groups coccolithophorids dinoflagellates the prevalence of arctic waters and seasonal sea ice coverage during the younger dryas is indicated by a single maximum of 24 methylenecholesterol probably indicating the dominance of sea ice diatoms and or the prevalence of diatoms of thalassiosiraceae in surface waters the sediments of the allerod in contrast show a pronounced maximum in dinosterols indicating a better adaptation of dinoflagellates to an oceanic regime that is characterized by incipient intrusion of atlantic water highly variable sea surface temperatures and well stratified water masses the concentration of higher molecular weight n alkanes however follows the deglacial early holocene trend of climate amelioration from the last deglaciation to the middle holocene with maxima during ice advances stadials and minima during the middle holocene warm period these new results significantly improve the understanding of climate induced response on organic matter supply in fjords and provide a better knowledge of past variations of biogeochemical processes in high latitude coastal environments

historical variability of sea ice edge position in the nordic seas 1 historical ice observations in the nordic seas from april through august are used to construct time series of ice edge position anomalies spanning the period 1750 2002 while analysis showed that interannual variability remained almost constant throughout this period evidence was found of oscillations in ice cover with periods of about 60 to 80 years and 20 to 30 years superimposed on a continuous negative trend the lower frequency oscillations are more prominent in the greenland sea while higher frequency oscillations are dominant in the barents the analysis suggests that the recent well documented retreat of ice cover can partly be attributed to a manifestation of the positive phase of the 60 80 year variability associated with the warming of the subpolar north atlantic and the arctic the continuous retreat of ice edge position observed since the second half of the 19th century may be a recovery after significant cooling in the study area that occurred as early as the second half of the 18th century

complementary biomarker based methods for characterising arctic sea ice conditions a case study comparison between multivariate analysis and the pip 25 index abstract the discovery of ip25 as a qualitative biomarker proxy for arctic sea ice and subsequent introduction of the so called pip25 index for semi quantitative descriptions of sea ice conditions has significantly advanced our understanding of long term paleo arctic sea ice conditions over the past decade we investigated the potential for classification tree ct models to provide a further approach to paleo arctic sea ice reconstruction through analysis of a suite of highly branched isoprenoid hbi biomarkers in ca 200 surface sediments from the barents sea four ct models constructed using different hbi assemblages revealed ip25 and an hbi triene as the most appropriate classifiers of sea ice conditions achieving a 90 cross validated classification rate additionally lower model performance for locations in the marginal ice zone miz highlighted difficulties in characterisation of this climatically sensitive region ct model classification and semi quantitative pip25 derived estimates of spring sea ice concentration spsic for four downcore records from the region were consistent although agreement between proxy and satellite observational records was weaker for a core from the west svalbard margin likely due to the highly variable sea ice conditions the automatic selection of appropriate biomarkers for description of sea ice conditions quantitative model assessment and insensitivity to the c factor used in the calculation of the pip25 index are key attributes of the ct approach and we provide an initial comparative assessment between these potentially complementary methods the ct model should be capable of generating longer term temporal shifts in sea ice conditions for the climatically sensitive barents sea

semi quantitative reconstruction of early to late holocene spring and summer sea ice conditions in the northern barents sea semi quantitative estimates of early to late holocene spring sea ice concentration spsic and occurrence of summer sea ice for the northern barents sea have been obtained by analysing the biomarkers ip25 brassicasterol and a tri unsaturated highly branched isoprenoid lipid in a holocene marine sediment core sub surface water mass variations were derived from planktic foraminiferal assemblages and stable isotopes 18o 13c the record indicates paleoceanographic changes over three intervals during period i ca 9500 5900 cal a bp the study location experienced the lowest recorded spsic ca 25 with short spring seasons and long productive summers resulting partly from increased atlantic water inflow that caused a stronger ocean atmosphere heat exchange throughout period ii ca 5900 2700 cal a bp the winter sea ice margin migrated southwards and an overall cooling trend resulted in higher spsic ca 60 and increased delivery of cold arctic water during period iii ca 2700 cal a bp to present spsic increased further ca 75 and some sea ice remained during summer months a sub surface warming probably indicates a decoupling of heat exchange between the ocean and the atmosphere longer springs and shorter summers were accompanied by the most southerly location of the winter sea ice margin

230th normalization an essential tool for interpreting sedimentary fluxes during the late quaternary there is increasing evidence indicating that syndepositional redistribution of sediment on the seafloor by bottom currents is common and can significantly affect sediment mass accumulation rates notwithstanding its common incidence this process generally referred to as sediment focusing is often difficult to recognize if redistribution is near synchronous to deposition the stratigraphy of the sediment is not disturbed and sediment focusing can easily be overlooked ignoring it however can lead to serious misinterpretations of sedimentary fluxes particularly when past changes in export flux from the overlying water are inferred in many instances this problem can be resolved at least for sediments deposited during the late quaternary by normalizing to the flux of 230th scavenged from seawater which is nearly constant and equivalent to the known rate of production of 230th from the decay of dissolved 234u we review the principle advantages and limitations of this method notwithstanding its limitations it is clear that 230th normalization does provide a means of achieving more accurate interpretations of sedimentary fluxes and eliminates the risk of serious misinterpretations of sediment mass accumulation rates

biomarker distributions in surface sediments from the kara and laptev seas arctic ocean indicators for organic carbon sources and sea ice coverage studies of spatial and temporal changes in modern and past sea ice occurrence may help to understand the processes controlling the recent decrease in arctic sea ice cover here we determined concentrations of ip25 a novel biomarker proxy for sea ice developed in recent years phytoplankton derived biomarkers brassicasterol and dinosterol and terrigenous biomarkers campesterol and sitosterol in the surface sediments from the kara and laptev seas to estimate modern spatial seasonal sea ice variability and organic matter sources c25 hbi dienes and trienes were determined as additional palaeoenvironmental proxies in the study area furthermore a combined phytoplankton ip25 biomarker approach pip25 index is used to reconstruct the modern sea ice distribution more quantitatively the terrigenous biomarkers reach maximum concentrations in the coastal zones and estuaries reflecting the huge discharge by the major rivers ob yenisei and lena maxima in phytoplankton biomarkers indicating increased primary productivity were found in the seasonally ice free central part of the kara and laptev seas neither ip25 nor pip25 however shows a clear and simple correlation with satellite sea ice distribution in our study area due to the complex environmental conditions in our study area and the transportation process of sea ice diatom in the water column differences in the diene ip25 and triene ip25 ratios point to different sources of these hbis and different environmental conditions the diene ip25 ratio seems to correlate positively with sea surface temperature while negatively with salinity distributions

abrupt shifts of productivity and sea ice regimes at the western barents sea slope from the last glacial maximum to the bolling allerod interstadial abstract advanced knowledge of spatio temporal constraints on the barents sea ice sheet during the late weichselian glaciation overshadows relatively limited understanding of seasonal sea ice experiencing an annual advance retreat cycle and primary productivity trends accompanying massive abrupt climate changes during glacial deglacial cycles such paleo reconstructions are crucial prerequisites for improved comprehension and prediction of current and future climate change here we investigate sea ice and phytoplankton biomarker distributions in a barents sea sediment core covering ca 25 8 15 4 cal kyr bp to elucidate abrupt shifts of spring summer sea ice concentrations and relative sympagic pelagic productivity trends at the southwestern continental slope despite significant presence of seasonal sea ice the last glacial maximum lgm and initial shelf edge deglaciation sedg at the core site are characterised by occurrence of productive coastal polynya adjacent to the maximum ice sheet extent the onset of perennial i e multi year ice cover and near zero productivity during heinrich stadial 1 hs1 ca 18 0 16 3 cal kyr bp accompanies significant meltwater fluxes from ice sheet debuttressing and the consequent stagnation of thermohaline circulation rapid sea ice retreat and unprecedented pelagic productivity observed after 16 3 cal kyr bp coincides with areal ice sheet deglaciation and is potentially linked to the release of sub surface heat and nutrient reservoirs together with reinvigorated deep water circulation following millennial heating of the deep ocean during hs1 we find that a multivariate fingerprinting approach involving assessment of both downcore and surface biomarker distributions is able to distinguish relative ice algal and pelagic diatom productivity driven by sea ice dynamics

mid latitude southern indian ocean response to northern hemisphere heinrich events abstract the lack of temporal resolution and accurate chronology of southern ocean marine cores has hampered comparison of glacial millennial scale oscillations between the southern ocean antarctic ice and other records from both hemispheres in this study glacial climate variability is investigated over the last 50 ka using a multi proxy approach a precise chrono stratigraphy was developed on the high sedimentation rate core md94 103 indian southern ocean 45 35 s 86 31 e 3560 m water depth by geomagnetic synchronization between the later core and napis75 and 14c dates high resolution time series of 18o in planktonic foraminifera globigerina bulloides and neogloboquadrina pachyderma and sea surface temperatures ssts estimated from the alkenone uk 37 index and foraminifera assemblages have been generated temporal evolution of the two temperature proxy records is notably different during the last glacial period while foraminifera data indicate a consistent cooling towards the last glacial maximum anomalous warm glacial alkenone temperatures suggest a strong advection of warm detrital alkenones by surface waters of the agulhas current superimposed to this general trend during heinrich events foraminiferal ssts point to warmer surface waters while concurrent alkenone ssts exhibit apparent coolings probably caused by enhanced local alkenone production by analogy to modern observations possible influence of enso like conditions on the subantarctic southern ocean ssts is discussed

changes in sea ice cover and ice sheet extent at the yermak plateau during the last 160 ka reconstructions from biomarker records the yermak plateau is located north of svalbard at the entrance to the arctic ocean i e in an area highly sensitive to climate change a multi proxy approach was carried out on core ps92 039 2 to study glacial interglacial environmental changes at the northern barents sea margin during the last 160 ka the main emphasis was on the reconstruction of sea ice cover based on the sea ice proxy ip25 and the related phytoplankton sea ice index pip25 sea ice was present most of the time but showed significant temporal variability decisively affected by movements of the svalbard barents sea ice sheet for the first time we prove the occurrence of seasonal sea ice at the eastern yermak plateau during glacial intervals probably steered by a major northward advance of the ice sheet and the formation of a coastal polynya in front of it maximum accumulation of terrigenous organic carbon ip25 and the phytoplankton biomarkers brassicasterol dinosterol hbi iii can be correlated to distinct deglaciation events more severe but variable sea ice cover prevailed at the yermak plateau during interglacials the general proximity to the sea ice margin is further indicated by biomarker gdgt based sea surface temperatures below 2 5 c

quantifying the influence of atlantic heat on barents sea ice variability and retreat abstractthe recent arctic winter sea ice retreat is most pronounced in the barents sea using available observations of the atlantic inflow to the barents sea and results from a regional ice ocean model the authors assess and quantify the role of inflowing heat anomalies on sea ice variability the interannual variability and longer term decrease in sea ice area reflect the variability of the atlantic inflow both in observations and model simulations during the last decade 1998 2008 the reduction in annual july june sea ice area was 218 103 km2 or close to 50 this reduction has occurred concurrent with an increase in observed atlantic heat transport due to both strengthening and warming of the inflow modeled interannual variations in sea ice area between 1948 and 2007 are associated with anomalous heat transport r 0 63 with a 70 103 km2 decrease per 10 tw input of heat based on the simulated ocean heat budget it is found that the heat transport into the western barents sea sets the bou

the arctic sea ice biomarker ip25 a review of current understanding recommendations for future research and applications in palaeo sea ice reconstructions in recent years a novel proxy for the past occurrence of arctic sea ice has been proposed that is based on the variable marine sedimentary abundance of an organic geochemical lipid derived from sea ice diatoms in the spring this lipid termed ip25 ice proxy with 25 carbon atoms is a highly branched isoprenoid mono unsaturated alkene that appears to be sufficiently stable in sediments to permit meaningful palaeo sea ice reconstructions to be carried out over short to long term timescales since the first proposed use of ip25 as a proxy for palaeo sea ice by belt et al 2007 a number of laboratories have measured this biomarker in arctic sediments and it is anticipated that research activity in this area will increase further in the future the content of this review is divided into a number of sections firstly we describe the scientific basis for the ip25 proxy and its initial discovery in arctic sea ice sedimenting particles and sediments secondly we summarise the relatively few studies that have to date concentrated on examining the factors that influence the production and fate of ip25 and we identify some areas of future research that need to be addressed in order to improve our understanding of ip25 data obtained from sedimentary analyses what is clear at this stage however it that the presence of ip25 in arctic marine sediments appears to represent a proxy measure of past seasonal sea ice rather than permanent or multi year ice conditions thirdly we highlight the importance of rigorous analytical identification and quantification of ip25 especially if measurements of this biomarker are going to be used for quantitative sea ice reconstructions rather than qualitative analyses alone presence absence fourthly we review some recent attempts to make the interpretations of ip25 biomarker data more detailed and quantitative by combining sedimentary abundances with those of phytoplankton and other sea ice derived biomarkers thus the bases for the so called pip25 and dip25 indices are described together with an overview of potential limitations concluding that investigations into the use of these indices needs further research before their full potential can be realised in the final section we provide a summary of ip25 based palaeo sea ice reconstruction case studies performed to date these case studies cover different arctic regions and timescales spanning decades to tens of thousands of years

recent sediment accumulation rates for the western margin of the barents sea abstract we investigate patterns processes and rates of sediment accumulation within the marginal ice zone of the western barents sea the barents sea is among the most productive of the arctic marginal seas with approximately half of the sediment burial flux derived from marine rather than terrestrial sources sediment accumulation rates were quantified by 210 pb geochronology at 14 stations ranging in water depths from 173 to 503 m along a south north latitudinal gradient of 6 75 81 n the average sediment accumulation rate for all stations is 0 7 0 4 mm yr in general lower sediment accumulation rates are associated with coarser sediment fractions at shallower water depths 200 m where currents remove fine grained sediments and transport material to the deeper regions higher sediment accumulation rates are detected in deeper water stations and are largely associated with specific sedimentation events and or features of the barents seafloor although the c n ratio of surface sediments 0 2 cm from all stations indicates a predominance of sediments of marine origin c n 9 0 1 0 there is no distinct depositional pattern indicating preferential burial in areas more heavily influenced by the marginal ice zone we conclude that a combination of mixed sediment sources large shifts in the location of the marginal ice zone over time and the benthic boundary layer processes obscure the productivity signal preserved in these seafloor sediment deposits of the western barents sea

atlantic water advection to the eastern fram strait multiproxy evidence for late holocene variability a multiproxy data set of an ams radiocarbon dated 46 cm long sediment core from the continental margin off western svalbard reveals multidecadal climatic variability during the past two millennia investigation of planktic and benthic stable isotopes planktic foraminiferal fauna and lithogenic parameters aims to unveil the atlantic water advection to the eastern fram strait by intensity temperatures and salinities atlantic water has been continuously present at the site over the last 2 000 years superimposed on the increase in sea ice icebergs a strengthened intensity of atlantic water inflow and seasonal ice free conditions were detected at 1000 to 1200 ad during the well known medieval climate anomaly mca however temperatures of the mca never exceeded those of the 20th century since 1400 ad significantly higher portions of ice rafted debris and high planktic foraminifer fluxes suggest that the site was located in the region of a seasonal highly fluctuating sea ice margin a sharp reduction in planktic foraminifer fluxes around 800 ad and after 1730 ad indicates cool summer conditions with major influence of sea ice icebergs high amounts of the subpolar planktic foraminifer species turborotalia quinqueloba in size fraction 150 250 m indicate strengthened atlantic water inflow to the eastern fram strait already after 1860 ad nevertheless surface conditions stayed cold well into the 20th century indicated by low planktic foraminiferal fluxes most likely at the beginning of the 20th century cold conditions of the terminating little ice age period persisted at the surface whereas warm and saline atlantic water already strengthened hereby subsiding below the cold upper mixed layer surface sediments with high abundances of subpolar planktic foraminifers indicate a strong inflow of atlantic water providing seasonal ice free conditions in the eastern fram strait during the last few decades

rapid reductions and millennial scale variability in nordic seas sea ice cover during abrupt glacial climate changes constraining the past sea ice variability in the nordic seas is critical for a comprehensive understanding of the abrupt dansgaard oeschger d o climate changes during the last glacial here we present unprecedentedly detailed sea ice proxy evidence from two norwegian sea sediment cores and an east greenland ice core to resolve and constrain sea ice variations during four d o events between 32 and 41 ka our independent sea ice records consistently reveal a millennial scale variability and threshold response between an extensive seasonal sea ice cover in the nordic seas during cold stadials and reduced seasonal sea ice conditions during warmer interstadials they document substantial and rapid sea ice reductions that may have happened within 250 y or less concomitant with reinvigoration of deep convection in the nordic seas and the abrupt warming transitions in greenland our empirical evidence thus underpins the cardinal role of rapid sea ice decline and related feedbacks to trigger abrupt and large amplitude climate change of the glacial d o events

identification of paleo arctic winter sea ice limits and the marginal ice zone optimised biomarker based reconstructions of late quaternary arctic sea ice abstract analysis of 100 surface sediments from across the barents sea has shown that the relative abundances of the mono unsaturated sea ice diatom derived biomarker ip 25 and a tri unsaturated highly branched isoprenoid hbi lipid hbi iii are characteristic of the overlying surface oceanographic conditions most notably the location of the seasonal sea ice edge thus while ip 25 is generally limited to locations experiencing seasonal sea ice with higher abundances found for locations with longer periods of ice cover hbi iii is found in sediments from all sampling locations but is significantly enhanced in sediments within the vicinity of the retreating sea ice edge or marginal ice zone miz the response of hbi iii to this well defined sea ice scenario also appears to be more selective than that of the more generic phytoplankton biomarker brassicasterol the potential for the combined analysis of ip 25 and hbi iii to provide more detailed assessments of past sea ice conditions than ip 25 alone has been investigated by quantifying both biomarkers in three marine downcore records from locations with contrasting modern sea ice settings for sediment cores from the western barents sea intermittent seasonal sea ice and the northern norwegian sea ice free high ip 25 and low hbi iii during the younger dryas ca 12 9 11 9 cal kyr bp is consistent with extensive sea cover with relatively short periods of ice free conditions resulting from late summer retreat towards the end of the yd ca 11 9 11 5 cal kyr bp a general amelioration of conditions resulted in a near winter maximum ice edge scenario for both locations although this was somewhat variable and the eventual transition to predominantly ice free conditions was later for the western barents sea site ca 9 9 cal kyr bp compared to nw norway ca 11 5 cal kyr bp for both locations coeval elevated hbi iii but absent ip 25 potentially provides further evidence for increased atlantic water inflow during the early holocene but this interpretation requires further investigation in contrast ip 25 and hbi iii data obtained from a core from the northern barents sea demonstrate that seasonal sea ice prevailed throughout the holocene but with a gradual shift from winter ice edge conditions during the early holocene to more sustained ice cover in the neoglacial a directional shift that has undergone a reverse in the last ca 150 yr according to observational records our combined surface and downcore datasets suggest that combined analysis of ip 25 and hbi iii can provide information on temporal variations in the position of the maximum winter arctic sea ice extent together with insights into sea ice seasonality by characterisation of the miz combining ip 25 with hbi iii in the form of the previously proposed pip 25 index yields similar outcomes to those obtained using brassicasterol as the phytoplankton marker importantly however some problems associated with use of a variable balance factor employed in the pip 25 calculation are potentially alleviated using hbi iii

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

data assimilation with a coupled wind wave model a first attempt to assimilate observations into a coupled wind wave model system is presented a special feature of the wind model is that the drag coefficient depends on the wave age reflecting the dependence of the air flow on the wave state usually both wind and wave data are assimilated the assimilation is carried out by means of the adjoint technique this coupled wind wave data assimilation not only corrects successfully both model fields but their dynamical connection is retained furthermore the assimilation of only wave data results in enough information on the atmospheric state at the sea surface that it can correct both wave and wind fields as well moreover there is still some impact of the assimilation during the forecast period this persistence is found to be dependent on the typical relaxation time scale of the wind model and also to be related to the swell decay time scale due to wave breaking the computations reveal the importance of both the coupling and the coupled wind wave data assimilation scheme that has been developed

paleoceanographic development in the sw barents sea during the late weichselian early holocene transition abstract the late weichselian early holocene variability of the north atlantic current has been studied with focus on the zonal component of this meridional transport during the transition from glacial to interglacial conditions the investigated sediment core is from 409 m water depth in the sw barents sea eight accelerator mass spectrometry ams 14c dates show that the core covers the last 20 000 cal yr b p with a centennial scale resolution during late weichselian early holocene planktic foraminiferal assemblages were analyzed using the 100 m size fraction and foraminiferal planktic and benthic 13c and 18o isotopes were measured furthermore a range of physical and chemical analyses has been carried out on the bulk sediment samples four time periods have been identified which represent the varying oceanographic conditions in ingoydjupet a glacial trough located off the north coast of norway in the sw barents sea 1 the late glacial before ca 15 000 cal yr b p influenced by the nearby ice sheets with high amounts of sea ice or iceberg transported detritus 2 the late oldest dryas stadial and the bolling allerod interstadial ca 15 000 12 700 cal yr b p with cold surface water conditions influenced by the collapse of the nearby ice sheets high amounts of sea ice or iceberg transported detritus and melt water and weak subsurface inflow of atlantic water 3 the younger dryas cold stadial 12 700 11 650 cal yr b p with low primary productivity and extensive sea ice cover and 4 the preboreal and early holocene 11 650 6800 cal yr b p cal yr b p with strong influx of atlantic water into the area near absence of ice rafted debris and generally ameliorated conditions in both surface and bottom water masses as seen from a high flux of foraminifera and increased marine primary production

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

holocene cooling culminates in sea ice oscillations in fram strait a reconstruction of holocene sea ice conditions in the fram strait provides insight into the palaeoenvironmental and palaeoceanographic development of this climate sensitive area during the past 8500 years bp organic geochemical analyses of sediment cores from eastern and western fram strait enable the identification of variations in the ice coverage that can be linked to changes in the oceanic and atmospheric circulation system by means of the sea ice proxy ip25 phytoplankton derived biomarkers and ice rafted detritus ird increasing sea ice occurrences are traced along the western continental margin of spitsbergen throughout the holocene which supports previous palaeoenvironmental reconstructions that document a general cooling a further significant ice advance during the neoglacial is accompanied by distinct sea ice fluctuations which point to short term perturbations in either the atlantic water advection or arctic water outflow at this site at the continental shelf of east greenland the general holocene cooling however seems to be less pronounced and sea ice conditions remained rather stable here a major neoglacial increase in sea ice coverage did not occur before 1000 years bp phytoplankton ip25 indices pip25 index are used for more explicit sea ice estimates and display a mid holocene shift from a minor sea ice coverage to stable ice margin conditions in eastern fram strait while the inner east greenland shelf experienced less severe to marginal sea ice occurrences throughout the entire holocene highlights biomarker and ird data give insight into holocene sea ice conditions in fram strait we find increasing sea ice coverage off west spitsbergen throughout the holocene oceanic atmospheric variability caused neoglacial sea ice fluctuations ice conditions along east greenland shelf remain rather stable until 1000 years bp

mapping recent sea ice conditions in the barents sea using the proxy biomarker ip25 implications for palaeo sea ice reconstructions abstract an analysis of the sea ice proxy ip 25 and the open water phytoplankton indicator brassicasterol has been carried out for 93 surface sediments collected from the barents sea and some additional data from previous studies have been included to augment the analysis further consistent with a specific and selective sea ice diatom origin for ip 25 this biomarker was identified in virtually all sediments from seasonally ice covered locations but was absent from the majority of sites beyond the maximum sea ice extent msie for the period 1983 2002 in contrast brassicasterol was detected in virtually all sediments from the region and concentrations were not at all associated with the msie instead more localised regions of brassicasterol concentrations were identified and these likely reflect different influences on production and deposition when the ip 25 and brassicasterol concentrations were combined together in the form of the previously proposed p b ip 25 index the aforementioned association between ip 25 occurrence and the msie was clarified further and in addition provided more detailed descriptions of sea ice cover in particular p b ip 25 data indicated seasonal sea ice or marginal ice zone conditions for the region of the barents sea within the msie according to previously defined p b ip 25 ranges we also amalgamated the biomarker data from the current study with those derived previously by muller et al 2011 and compared these larger datasets with satellite derived mean spring sea ice concentrations significantly although the correlation between the combined ip 25 concentration dataset with the satellite data was very similar to that reported previously by muller et al 2011 the corresponding correlation using the p b ip 25 values was poorer with the larger dataset and some possible reasons for this are discussed finally in a small number of cases ip 25 was identified in sediments somewhat distal from the msie and it is hypothesised that the occurrence of ip 25 in these sediments results from allochthonous input following sediment advection between shelf and trough environments this is the first reported example that provides evidence for the allochthonous input of ip 25 into marine sediments and it is recommended that this should be considered carefully when carrying out palaeo sea ice reconstructions based on the occurrence of this biomarker in the future

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

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

a biomarker based reconstruction of sea ice conditions for the barents sea in recent centuries variations in sea ice occurrence for the barents sea since c ad 1700 have been determined by analysis of the abundance of the sea ice biomarker ip25 in three marine sediment box cores obtained from locations in the north southeast and southwest parts of the region depth age models for each core were established using excess 210pb activity profiles comparisons between these depth age models with those reported previously for the barents sea suggest that the proxy sea ice record may alternatively extend back to c ad 1500 1600 sedimentation accumulation rates and bulk densities were combined with ip 25 concentrations resulting in temporal changes to ip25 fluxes which have been interpreted in terms of sea ice variability the ip25 sea ice proxy data are also compared with other bulk organic geochemical parameters total organic carbon and c n ratios and with sediment particle size distributions the data indicate ice free conditions for the southwest barents sea for the past c 300 yr consistent

high resolution 3d seismic study of pockmarks and shallow fluid flow systems at the snohvit hydrocarbon field in the sw barents sea accepted manuscript version published version available at https doi org 10 1016 j margeo 2018 06 012 accepted manuscript version licensed cc by nc nd 4 0

convergence of lateral flow along a coastal plain estuary a set of velocity profiles obtained in the james river estuary with an acoustic doppler current profiler was used in combination with the results of an analytic tidal model to depict the appearance of surface lateral flow convergences v y during both flood and ebb stages of the tidal cycle the bathymetry of the estuary was characterized by a main channel and a secondary channel separated by relatively narrow shoals lateral surface flow convergences appeared over the edges of the channels and were produced by the phase lag of the flow in the channel relative to the shoals flood convergences developed in the late tidal stages and ebb convergences appeared soon after maximum currents most of these convergences caused fronts in the density field and flotsam lines that also appeared over the edges of the channel and that lasted 2 hours the transverse flows associated with the convergences were mostly in the same direction throughout the water column in fact the vertically averaged flow produced the same convergence patterns as those near the surface the analytic tidal model reproduced well the timing and location of the convergences as observed in the james river model results with different bathymetry emulated the results in other estuaries e g axial convergence in an estuary with a channel in the middle this work showed that the strength of lateral convergences along the estuary was proportional to the tidal amplitude and the channel steepness it also suggested that the convergences were produced mainly by the tidal flow interacting with the channel shoal bathymetry i e that they did not require the presence of density gradients however the analytic model underestimated the magnitude of the convergences and did not account for vertical circulations associated with fronts the formation of fronts resulted from the interaction of the tidal flow with the bathymetry and the density field

towards quantitative sea ice reconstructions in the northern north atlantic a combined biomarker and numerical modelling approach article i nfo organic geochemical analyses of marine surface sediments from the continental margins of east greenland and west spitsbergen provide for a biomarker based estimate of recent sea ice conditions in the northern north atlantic by means of the sea ice proxy ip25 and phytoplankton derived biomarkers e g brassicasterol and dinosterol we reconstruct sea ice and sea surface conditions respectively the combination of ip25 with a phytoplankton marker in terms of a phytoplankton marker ip25 index pip25 proves highly valuable to properly interpret the sea ice proxy signal as an under or overestimation of sea ice coverage can be circumvented a comparison of this biomarker based assessment of the sea ice distribution in the study area with 1 modern remote sensing data and 2 numerical modelling results reveal a good agreement between organic geochemical satellite and modelling observations the reasonable simulation of modern sea ice conditions by means of a regional ocean sea ice model demonstrates the feasibility to effectively integrate the complex atmospheric and oceanic circulation features as they prevail in the study area the good correlation between modelled sea ice parameters and the biomarker based estimate of sea ice coverage substantiates that linking proxy and model data occurs to be a promising concept in terms of a cross evaluation this combinatory approach may provide a first step towards quantitative sea ice reconstructions by means of ip25 future ip25 studies on marine surface sediments from the arctic realm however are recommended to extend and validate this new attempt of using ip25 in combination with a phytoplankton marker as a quantitative measure for sea ice reconstructions

late quaternary sea ice and sedimentary redox conditions in the eastern bering sea implications for ventilation of the mid depth north pacific and an atlantic pacific seesaw mechanism abstract on glacial interglacial and millennial timescales sea ice is an important player in the circulation and primary productivity of high latitude oceans affecting regional and global biogeochemical cycling in the modern north pacific brine rejection during sea ice freezing in the sea of okhotsk drives the formation of north pacific intermediate water npiw that ventilates the north pacific ocean at 300 m 1000 m water depth glacial intervals of the late quaternary however experienced a deepening of glacial npiw to at least 2000 m with the strongest ventilation observed during cold stadial conditions of the last deglaciation however the origin of the shifts in npiw ventilation is poorly understood numerical simulations suggest an atmospheric teleconnection between the north atlantic and the north pacific in response to a slowdown or shutdown of the atlantic meridional overturning circulation this leads to a build up of salinity in the north pacific surface ocean triggering deep ventilation alternatively increased sea ice formation in the north pacific and its marginal seas may have caused strengthened overturning in response to enhanced brine rejection here we use a multi proxy approach to explore sea ice dynamics sedimentary redox chemistry and benthic ecology at integrated ocean drilling program site u1343 in the eastern bering sea across the last 40 ka our results suggest that brine rejection from enhanced sea ice formation during early heinrich stadial 1 locally weakened the halocline aiding in the initiation of deep overturning additionally deglacial sea ice retreat likely contributed to increased primary productivity and expansion of mid depth hypoxia at site u1343 during interstadial conditions confirming a vital role of sea ice in the deglacial north pacific carbon cycle

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

source specific biomarkers as proxies for arctic and antarctic sea ice abstract over the last decade or so certain source specific c25 highly branched isoprenoid hbi lipid biomarkers have emerged as useful proxies for arctic and antarctic sea ice thus ip25 ice proxy with 25 carbon atoms and ipso25 ice proxy for the southern ocean with 25 carbon atoms represent binary measures of past seasonal sea ice in the arctic and antarctic respectively a further tri unsaturated hbi generally referred to as hbi iii appears to provide proxy evidence for the region of open water found adjacent to sea ice i e the marginal ice zone miz in both polar regions this review provides an update on current knowledge pertaining to each proxy the first section focuses on describing those studies that have aimed to establish the underlying features of each proxy including source identification and spatial distribution characteristics the second section presents some important analytical considerations pertinent to the accurate identification and quantification of hbi biomarkers the third section describes how each hbi proxy is normally interpreted within the sedimentary record for palaeo sea ice reconstruction purposes this includes the interpretation of individual and combined biomarker profiles such as the pip25 index and multivariate decision tree models a summary of all previous palaeo sea ice reconstructions based on hbis is also given which includes examples that clarify or reinforce our understanding of the individual or combined biomarker signatures some knowledge gaps and areas for future research are also briefly described

arctic sea ice proxies comparisons between biogeochemical and micropalaeontological reconstructions in a sediment archive from arctic canada boxcore 99lssl 001 from the southwest canadian arctic archipelago 68 095 n 114 186 w studied by multiproxy approaches sea ice diatom biomarker ip25 phytoplankton based biomarker brassicastero

distributions of highly branched isoprenoid alkenes and other algal lipids in surface waters from east antarctica further insights for biomarker based paleo sea ice reconstruction the occurrence and variable abundance of certain di and tri unsaturated c25 highly branched isoprenoid hbi biomarkers in antarctic marine sediments has previously been proposed as a possible proxy measure of paleo sea ice extent in the southern ocean in the current study we obtained 47 near surface ca 0 10 m water samples taken from locations in east antarctica with different sea ice settings and analysed them for their hbi sterol and fatty acid content sampling locations ranged from the permanently open ocean zone pooz with no seasonal sea ice cover the near shore summer sea ice zone siz where sea ice remains long into the summer melt season and the marginal ice zone miz located between the pooz and the siz and with a highly variable latitudinal sea ice edge throughout the season a di unsaturated c25 hbi diene ii was only identified in surface waters from the miz and the siz consistent with a sea ice diatom origin for this biomarker in contrast a tri unsaturated c25 hbi triene iii was detected in all samples from the pooz the miz and the siz and with a stable isotopic composition 13c 35 1 5 consistent with a phytoplankton source the highest concentrations of diene ii and triene iii were in samples from the siz and the miz respectively thus providing further insights into the sea ice conditions likely favourable for their production and how their relative abundances the ii iii ratio in underlying sediments might be better interpreted for paleo sea ice reconstruction in this respect relatively high ii iii might be a good indicator of extended into summer seasonal sea ice cover while lower ii iii may provide a better indicator of the miz however the observation of highly variable ii iii within the polynya setting of the siz may also have significant impacts on sedimentary values distributions of diatom sterols and fatty acids were also variable between the three sampling zones but these were not as distinctive as those observed for the hbis

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

distributional variations in marine crenarchaeotal membrane lipids a new tool for reconstructing ancient sea water temperatures it has recently been shown that membrane lipids of marine crenarchaeota a ubiquitous and abundant component of plankton occur in relatively high concentrations in recent and ancient sediments in this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments we especially focussed on temperature as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature indeed a significant linear correlation r2 0 92 is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures this suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives in turn archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments

field studies of the flow structure in a straight reach of the conwy estuary abstract synchronous measurements of dye distributions from a single point source surface injection and of the turbulent mean flow structure in a straight reach of the conwy estuary have been obtained for several tidal cycles the resulting two dimensional temporal y z t variations of velocity and salinity together with the three dimensional x y z dye distributions have been used to provide both a qualitative and quantitative description of the vertical stability and transverse flows caused by the interaction of the longitudinal solute induced density gradient and fluid shear the results show that the flow structure is temporally dependent due to velocity and depth changes and is spatially dependent due to channel topography

intratidal dynamics of fronts and lateral circulation at the shoal channel interface in a partially stratified estuary abstractin partially stratified shoal channel estuaries variations in bathymetry at the shoal channel interface generate horizontal shears and density gradients and foam lines characteristic of convergence fronts are frequently observed this study is based on transect data collected every 30 min across the shoal channel interface in south san francisco bay to analyze the dynamics of the transverse circulation and convergence fronts at this interface throughout a tidal cycle during the ebb a lateral density gradient develops as a result of the competition between differential advection of the longitudinal salinity gradient lateral variations in vertical mixing and nonlinear advection terms which are strongest when convergence fronts develop early and late in the ebb the lateral circulation over the slope is characterized by a large intratidal variability reversing three times during the ebb this variability is driven by a balance dominated by inertia and lateral baroclinic pressure gradient duri

sea ice and marine climate variability for nw iceland denmark strait over the last 2000 cal yr bp md99 2263 is a 46 cm box core collected from djupall a trough that cuts across the nw iceland shelf and ends above denmark strait we provide a multiproxy record that documents changes in the regional marine climate over the last 1700 yr the depth age model is based on seven calibrated radiocarbon dates on mollusk shells and on 210pb and 137cs sediment accumulation rates were variable 0 2 0 8 mm yr but increased dramatically ad 1500 grain size magnetic properties quantitative mineral composition of the 2 mm sediment fraction benthic foraminiferal composition benthic and planktic 18o ratios and abundances fluxes of the sea ice biomarker ip25 were determined to better compare the various proxies 12 of the critical climate proxies were co ordinated into 100 yr sample time series which were examined by principal component analysis the 1st axis explained 49 of the variance and the 2nd axis explained an additional 17 the variables most strongly associated with the 1st axis were sediment pr

abrupt climate changes for iceland during the last millennium evidence from high resolution sea ice reconstructions a high resolution account of icelandic sea ice over the last millennium has been constructed using a novel proxy based on the presence in sediments of a biomarker ip25 produced by sea ice algae comparison with historical sea ice records demonstrates a strong correlation between documented sea ice occurrences and the ip25 proxy an excellent agreement is also observed between the ip25 record and a diatom based sea surface temperature reconstruction obtained from the same core and the crowley and lowery northern hemisphere temperature reconstruction using this approach we provide new historical sea ice data for periods where records are scarce or absent and evidence for abrupt changes to sea ice and or climate conditions around iceland during the little ice age

striking similarities in temporal changes to spring sea ice occurrence across the central canadian arctic archipelago over the last 7000 years abstract a 7000 year spring sea ice record for victoria strait arc 4 and dease strait arc 5 in the canadian arctic archipelago caa has been determined by quantification of the sea ice diatom derived biomarker ip 25 in two marine sediment piston cores obtained in 2005 the chronologies of the arc 4 and arc 5 cores were determined using a combination of 14 c ams dates obtained from macrobenthic fossils and magnetic susceptibility measurements the ages of the tops of the piston cores were estimated by matching chemical and physical parameters with those obtained from corresponding box cores these analyses revealed that while the top of the arc 4 piston core was estimated to be essentially modern ca 60 cal yr bp a few hundred years of sediment appeared to be absent from the arc 5 piston core downcore changes to ip 25 fluxes for both cores were interpreted in terms of variations in spring sea ice occurrence and correlations between the individual ip 25 flux profiles for victoria strait dease strait and barrow strait reported previously were shown to be statistically significant at both 50 and 100 year resolutions the ip 25 data indicate lower spring sea ice occurrences during the early part of the record ca 7 0 3 0 cal kyr bp and for parts of the late holocene ca 1 5 0 8 cal kyr bp especially for the two lower latitude study locations in contrast higher spring sea ice occurrences existed during ca 3 0 1 5 cal kyr bp and after ca 800 cal yr bp the observation of consecutively lower and higher spring sea ice occurrence during two periods of the late holocene coincides broadly with the medieval warm period and little ice age epochs respectively the ip 25 data are complemented by particle size and mineralogical data although these may alternatively reflect changes in sea level at the study sites the ip 25 data are also compared to previous proxy based determinations of palaeo sea ice and palaeoclimate for the caa including those based on bowhead whale remains and dinocyst assemblages the spatial consistency in the proxy data which most notably indicates an increase in spring sea ice occurrence around 3 cal kyr bp provides a potentially useful benchmark for the termination of the holocene thermal maximum for the central caa

an assessment of biomarker based multivariate classification methods versus the pip25 index for paleo arctic sea ice reconstruction abstract the development of various combinative methods for arctic sea ice reconstruction using the sympagic highly branched isoprenoid hbi ip25 in conjunction with pelagic biomarkers has often facilitated more detailed descriptions of sea ice conditions than using ip25 alone here we investigated the application of the phytoplankton ip25 index pip25 and a recently proposed classification tree ct model for describing temporal shifts in sea ice conditions to assess the consistency of both methods based on biomarker data from three downcore records from the barents sea spanning millennial timescales we showcase apparent and potential limitations in both approaches and provide recommendations for their identification or prevention both methods provided generally consistent outcomes and within the studied cores captured abrupt shifts in sea ice regimes such as those evident during the younger dryas as well as more gradual trends in sea ice conditions during the holocene the most significant discrepancies occurred during periods of highly unstable climate change such as those characteristic of the younger dryas holocene transition such intervals of increased discrepancy were identifiable by significant changes of hbi distributions and correlations to values not observed in proximal surface sediments we suggest that periods of highly fluctuating climate that are not represented in modern settings may hinder the performance and complementary application of pip25 and ct based methods and that data visualisation techniques should be employed to identify such occurrences in downcore records additionally due to the reliance of both methods on biomarker distributions we emphasise the importance of accurate and consistent biomarker quantification

particle transport processes at slope environments event driven flux across the barents sea continental margin abstract recent studies of the vertical flux of organic matter into the deep ocean have prompted the search for key organic compounds biomarkers as tracers for its production flux and burial into the sediment particulate matter was collected with sediment traps moored at the barents sea continental margin 75 11 78 n 12 29 21 e water depth 2050 m at 610 1840 and 1950 m depth the compositions of the organic material in the two bottoms near traps differ significantly this difference cannot be the result of a change of the vertical sedimentation alone a combination of biomarker analyses quantitative microscopy and bulk parameter determinations on water and sediment trap samples is used in this study to demonstrate that a turbidity plume event at the shelf edge is a vehicle to transport organic and lithogenic particles at high velocities to the benthos of the lower continental margin it is suggested that fine particles were advected into the trap at 1850 m whereas the coarser fraction of higher settling velocities passing several resuspension loops entered the lower trap