clues to variability in arctic minimum sea ice extent received 11 august 2005 revised 20 september 2005 accepted 26 september 2005 published 2 november 2005 1 perennial sea ice is a primary indicator of arctic climate change since 1980 it has decreased in extent by about 15 analysis of new satellite derived fields of winds radiative forcing and advected heat reveals distinct regional differences in the relative roles of these parameters in explaining variability in the northernmost ice edge position in all six peripheral seas studied downwelling longwave flux anomalies explain the most variability approximately 40 while northward wind anomalies are important in areas north of siberia particularly earlier in the melt season anomalies in insolation are negatively correlated with perennial ice retreat in all regions suggesting that the effect of solar flux anomalies is overwhelmed by the longwave influence on ice edge position citation francis j a e hunter j r key and x wang 2005 clues to variability in arctic minimum sea ice extent geophys res lett 32 l21501 doi 10 1029 2005gl024376

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

holocene variability in sea surface temperature and sea ice extent in the northern bering sea a multiple biomarker study abstract the bering sea as a transition between the arctic and the pacific oceans plays an important role in global climate change and biogeochemical cycles here we examined a variety of biomarkers in a core br07 from the northern continental slope of the bering sea in order to reconstruct summer sea surface temperature sst and sea ice extent during the period 11 2 ka thousands of calendar years ago the tex 86 l derived sst gradually decreased ca 1 6 c from early to mid holocene 11 3 8 0 ka but did not show a cooling or warming trend afterwards our sst data do not support the hypothesis of a holocene seesaw in temperature between the north atlantic and the north pacific several algal biomarkers including ip 25 and its derived indicators for sea ice brassicasterol for diatoms and dinosterol for dinoflagellates suggest that the sea ice extent gradually increased from early to late holocene interrupted by rapid changes at ca 2 8 2 6 and 5 5 5 0 ka the synchronous evolution between ip 25 and sst indicates a strong coupling between sea ice cover and climate change in the holocene

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

arctic sea ice variability revisited this paper explores spatial and temporal relationships between variations in arctic sea ice concentration summer and winter and near surface atmospheric temperature and atmospheric pressure using multivariate statistical techniques trend empirical orthogonal function eof and singular value decomposition svd analyses are used to identify spatial patterns associated with covariances and correlations between these fields results show that 1 in winter the arctic oscillation still explains most of the variability in sea ice concentration from 1979 to 2006 and 2 in summer a decreasing sea ice trend centered in the pacific sector of the arctic basin is clearly correlated to an arctic wide air temperature warming trend these results demonstrate the applicability of multivariate methods and in particular svd analysis which has not been used in earlier studies for assessment of changes in the arctic sea ice cover results are consistent with the interpretation that a warming signal has now emerged from the noise in the arctic sea ice record during summer our analysis indicates that such a signal may also be forthcoming during winter

arctic palaeo river discharge and environmental change evidence from the holocene kara sea sedimentary record abstract in this paper we summarize data on terrigenous sediment supply in the kara sea and its accumulation and spatial and temporal variability during holocene times sedimentological organic geochemical and micropaleontological proxies determined in surface sediments allow to characterize the modern riverine terrigenous sediment input ams 14c dated sediment cores from the ob and yenisei estuaries and the adjacent inner kara sea were investigated to determine the terrigenous sediment fluxes and their relationship to paleoenvironmental changes the variability of sediment fluxes during holocene times is related to the post glacial sea level rise and changes in river discharge and coastal erosion input whereas during the late middle holocene most of the terrigenous sediments were deposited in the estuaries and the areas directly off the estuaries huge amounts of sediments accumulated on the kara sea shelf farther north during the early holocene before about 9 cal kyr bp the maximum accumulation at that time is related to the lowered sea level increased coastal erosion and increased river discharge based on sediment thickness charts echograph profiles and sediment core data we estimate an average holocene 0 11 cal kyr bp annual accumulation of 194 106 t yr 1 of total sediment for the whole kara sea based on late holocene modern sediment accumulation in the estuaries probably 12 106 t yr 1 of riverine suspended matter i e about 30 of the input may escape the marginal filter on a geological time scale and is transported onto the open kara sea shelf the high resolution magnetic susceptibility record of a yenisei core suggests a short term variability in siberian climate and river discharge on a frequency of 300 700 yr this variability may reflect natural cyclic climate variations to be seen in context with the interannual and interdecadal environmental changes recorded in the high northern latitudes over the last decades such as the nao ao pattern a major decrease in ms values starting near 2 5 cal kyr bp being more pronounced during the last about 2 cal kyr bp correlates with a cooling trend over greenland as indicated in the gisp 2 ice core extended sea ice cover in the north atlantic and advances of glaciers in western norway our still preliminary interpretation of the ms variability has to be proven by further ms records from additional cores as well as other high resolution multi proxy arctic climate records

sea ice and wind variability during the holocene in east antarctica insight on middle high latitude coupling abstract micropaleontological and biomarker data from two high accumulation marine sites from the coastal and continental shelf zone ccsz off east antarctica adelie land at 140 e and eastern prydz bay at 77 e are used to reconstruct holocene changes in sea ice and wind stress at the basin wide scale these data demonstrate congruent increase in sea ice concentration persistence and wind stress related sea surface turbulence in the two regions since 7 cal ka bp with a particularly strong signal since 4 5 3 5 cal ka bp comparison of these high latitude records with sea ice and turbulence records from the southern mid latitudes highlights distinctive climatic evolutions according to the different latitudinal bands sea ice persistence and turbulence increase in east antarctica ccsz are opposite to sea surface warming and sea ice retreat recorded after 4 5 3 5 cal ka bp in the east atlantic and indian sector between 55 and 45 s at the same period paleodata suggest sst cooling in all major coastal upwelling systems of the southern hemisphere caused by the northward transport of subpolar surface waters as a response to southern westerlies reinforcement we therefore propose as suggested for the northern hemisphere that holocene changes in the latitudinal insolation gradient primarily forced by obliquity and precession and amplified by sea ice and glacial ice expansions in the antarctic realm are responsible for the observed contrasted latitudinal patterns of southern latitudes

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

long term ice variability in arctic marginal seas abstract examination of records of fast ice thickness 1936 2000 and ice extent 1900 2000 in the kara laptev east siberian and chukchi seas provide evidence that long term ice thickness and extent trends are small and generally not statistically significant while trends for shorter records are not indicative of the long term tendencies due to large amplitude low frequency variability the ice variability in these seas is dominated by a multidecadal low frequency oscillation lfo and to a lesser degree by higher frequency decadal fluctuations the lfo signal decays eastward from the kara sea where it is strongest in the chukchi sea ice variability is dominated by decadal fluctuations and there is no evidence of the lfo this spatial pattern is consistent with the air temperature north atlantic oscillation nao index correlation pattern with maximum correlation in the near atlantic region which decays toward the north pacific sensitivity analysis shows that dynamical forcing wind or surfac

contributions of the siberian shelf polynyas to the arctic ocean intermediate and deep water the role of the open water regions or polynyas in the winter ice pack over the siberian continental shelves in the production of arctic ocean intermediate and deep water is examined through use of a combination of passive microwave satellite data coastal weather station data and oceanographic data the satellite data allow us to derive a time series of the open water areas of selected polynyas for the 1978 1982 winters the polynyas which occur north of svalbard around franz josef land along the west coast and north end of novaya zemlya and to the east of severnaya zemlya and the taymyr peninsula are the primary oceanographic contributors the open water time series for these polynyas are used in combination with coastal weather station data to estimate the heat loss from each polynya for the region north of svalbard which is historically known as whalers bay the study shows that the heat loss is sufficient to provide the observed cooling of the west spitsbergen current for the other polynyas the heat loss is used to compute the ice production rates and the oceanic salt flux we then use the historic oceanographic salinities with the salt fluxes to estimate the contribution of each polynya to the arctic ocean water masses if we assume that the salt contributes only to the arctic intermediate water our results show that the shelves are capable of producing about 20 60 of this water alternatively if the salt contributes only to the deep water of the eurasian basin then without consideration of the mixing of the bottom water with the greenland and norwegian sea water the contribution from the shelves yields a renewal time of about 100 years our results imply that there is insufficient water produced in the shelf polynyas to perform all of the roles that have been historically assigned to it

biomarker proxy shows potential for studying the entire quaternary arctic sea ice history recently a novel and promising biomarker proxy for reconstruction of arctic sea ice conditions was developed and is based on the determination of a highly branched isoprenoid with 25 carbons ip25 so far ip25 records have been restricted to the last 150 kyr bp here we present a biomarker record from ocean drilling program odp site 912 going back to the pliocene pleistocene boundary and indicating that sea ice of variable extent occurred in the fram strait southern yermak plateau area at least since about 2 2 ma furthermore our data support the idea that a combination of ip25 and open water phytoplankton biomarker data pip25 index may give more reliable and quantitative estimates of past sea ice cover at least for the study area this study reveals that the novel ip25 pip25 biomarker approach has potential for semi quantitative paleo sea ice studies covering the entire quaternary and motivate to carry out further detailed high resolution research on odp iodp material using this proxy

stable oxygen and carbon isotopes in modern benthic foraminifera from the laptev sea shelf implications for reconstructing proglacial and profluvial environments in the arctic measurements of 18o and 13c isotopes in three benthic foraminiferal species from surface sediments of the eastern laptev sea are compared to water 18o values and 13c values of dissolved inorganic carbon dic samples investigated originate from two environmentally contrasting core locations which are influenced by riverine freshwater runoff to a varying degree at the river distal site located within relatively stable marine conditions on the outer shelf elphidiella groenlandica haynesina orbiculare and elphidium excavatum forma clavata show a positive specific offset of 1 4 1 5 and 1 respectively in their 18o values relative to the expected value for inorganic calcite precipitated under equilibrium conditions at the site close to the lena river confluence with enhanced seasonal hydrographic contrasts calculated 18o offsets in e groenlandica and in h orbiculare remain about the same whereas e e clavata displays a distinctly negative offset of 1 8 the 18o variation in e e clavata is interpreted as a vital effect a finding which limits the potential of this species for reconstructing freshwater influenced shelf paleoenvironments on the basis of oxygen isotopes this interpretation gains support when comparing foraminiferal 13c with the 13cdic of the water while some of the difference in the carbonate 13c seems to be controlled by a riverine related admixture of dic clearly defined 13c ranges in each of the three foraminifera at the river proximal site shows that also the carbon isotopic signature in e e clavata is particularly affected by environmental factors

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

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

holocene variability in sea ice cover primary production and pacific water inflow and climate change in the chukchi and east siberian seas arctic ocean in this study we present new detailed biomarker based sea ice records from two sediment cores recovered in the chukchi sea and the east siberian sea these new biomarker data may provide new insights on processes controlling recent and past sea ice changes the biomarker proxy records show i minimum sea ice extent during the early holocene ii a prominent mid holocene short term high amplitude variability in sea ice primary production and pacific water inflow and iii significantly increased sea ice extent during the last ca 4 5k cal a bp this late holocene trend in sea ice change in the chukchi and east siberian seas seems to be contemporaneous with similar changes in sea ice extent recorded from other arctic marginal seas the main factors controlling the millennial variability in sea ice and surface water productivity are probably changes in surface water and heat flow from the pacific into the arctic ocean as well as the long term decrease in summer insolation the short term centennial variability observed in the high resolution middle holocene record is probably related to solar forcing our new data on holocene sea ice variability may contribute to synoptic reconstructions of regional to global holocene climate change based on terrestrial and marine archives

modern organic carbon deposition in the laptev sea and the adjacent continental slope surface water productivity vs terrigenous input sediment samples from the laptev sea taken during the 1993 rv polarstern expedition ark ix 4 and the rv ivan kireyev expedition transdrift i were investigated for the amount and composition of their organic carbon fractions of major interest was the identification of different processes controlling organic carbon deposition i e terrigenous supply vs surface water productivity long chain unsaturated alkenones derived from prymnesiophytes and fatty acids derived from diatoms and dinoflagellates were analysed by means of gas chromatography and mass spectrometry first results on the distribution of these biomarkers in surface sediments indicate that the surface water productivity signal is well preserved in the sediment data this is shown by the distribution of the 16 1 n 7 and 20 5 n 3 fatty acids indicative for diatoms and the excellent correlation with the chlorophyll a concentrations in the surface water masses and the biogenic opal content and increased hydrogen indices of the sediments the high concentration of these unsaturated fatty acids in shallow water sediments shows the recent deposition of the organic material in deep sea sediments on the other hand the concentrations are low this decreased content is typical for phytoplankton material which has been degraded by microorganisms or autoxidation in general the alkenone concentrations are very low suggesting low production rates by prymnesiophytes only at one station from the lower continental margin influenced by the inflow of atlantic water masses were some higher amounts of alkenones determined long chain n alkanes as well as high c n ratios and low hydrogen indices indicate the importance of fluvial supply of terrigenous organic matter

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

coastal environments of the western kara and eastern barents seas abstract satellite images from the kara sea show that until july fast ice extends along the coast and fills the estuaries of the ob and yenisey rivers it is separated from offshore drift ice by a region of open water comprising a flaw lead polynya by august much of the fast and drift ice has melted and retreated from the southwestern kara sea leaving behind a persistent patch of sea ice east of novaya zemlya because both the of and yenisey rivers discharge water throughout the winter the fast ice is likely to incorporate river borne contaminants by bottom adfreezing during peak river discharge in june the fast ice remains in place and is potentially influenced by the river outflow throughout the length of the estuary breakup and melting of the fast ice in july could release contaminants to the surface waters by late july and august when the fast ice has disappeared the river discharge is observed primarily along the shore in a zone that extends offshore more than 100 km in fall newly forming ice may incorporate contaminants from the river plume while in late winter convection penetrating to the sea floor may allow resuspended sediments to be entrained in ice forming in the flaw lead polynya drift ice formed in this region could then advect contaminants offshore the potential for exchange of water ice and contaminants with the barents sea through karskiye vorota south of novaya zemlya is discussed in the context of the temperature and turbidity distribution observed in the satellite images

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

can stable isotopes ride out the storms the role of convection for water isotopes in models records and paleoaltimetry studies in the central andes abstract globally changes in stable isotope ratios of oxygen and hydrogen o 18 and d in the meteoric water cycle result from distillation and evaporation processes isotope fractionation occurs when air masses rise in elevation cool and reduce their water vapor holding capacity with decreasing temperature as such o 18 and d values from a variety of sedimentary archives are often used to reconstruct changes in continental paleohydrology as well as paleoaltimetry of mountain ranges based on 234 stream water samples we demonstrate that areas experiencing deep convective storms in the eastern south central andes 22 28 s do not show the commonly observed relationship between o 18 and d with elevation these convective storms arise from intermontane basins where diurnal heating forces warm air masses upward resulting in cloudbursts and raindrop evaporation especially at the boundary between the tropical and extra tropical atmospheric circulation regimes where deep convective storms are very common 26 to 32 n and s the impact of such storms may yield non systematic stable isotope elevation relationships as convection dominates over adiabatic lifting of air masses because convective storms can reduce or mask the depletion of heavy isotopes in precipitation as a function of elevation linking modern or past topography to patterns of stable isotope proxy records can be compromised in mountainous regions and atmospheric circulation models attempting to predict stable isotope patterns must have sufficiently high spatial resolution to capture the fractionation dynamics of convective cells

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

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

identification of a c25 highly branched isoprenoid hbi diene in antarctic sediments antarctic sea ice diatoms and cultured diatoms abstract a highly branched isoprenoid hbi diene found in antarctic sea ice diatoms and surface layer 0 2 cm sediments from antarctica is identified as 2 10 14 trimethyl 6 methylene 7 3 methylpent 1 enyl pentadecane the identification was made by comparison of gc ms mass spectra and retention indices on both polar and apolar gc stationary phases with those of the diene authenticated by nmr after isolation from a laboratory culture of the diatom haslea ostrearia

post glacial variability of sea ice cover river run off and biological production in the western laptev sea arctic ocean a high resolution biomarker study abstract multi proxy biomarker measurements were applied on two sediment cores ps51 154 ps51 159 to reconstruct sea ice cover ip25 biological production brassicasterol dinosterol and river run off campesterol sitosterol in the western laptev sea over the last 17 ka with unprecedented temporal resolution the absence of ip25 from 17 2 to 15 5 ka in combination with minimum concentration of phytoplankton biomarkers suggests that the western laptev sea shelf was mostly covered with permanent sea ice very minor river run off and restricted biological production occurred during this cold interval from 16 ka until 7 5 ka a long term decrease of terrigenous riverine organic matter and a coeval increase of marine organic matter reflect the gradual establishment of fully marine conditions in the western laptev sea caused by the onset of the post glacial transgression intensified river run off and reduced sea ice cover characterized the time interval between 15 2 and 12 9 ka including the bolling allerod warm period 14 7 12 9 ka prominent peaks of the dip25 index coinciding with maximum abundances of subpolar foraminifers are interpreted as pulses of atlantic water inflow on the western laptev sea shelf after the warm period a sudden return to severe sea ice conditions with strongest ice coverage between 11 9 and 11 ka coincided with the younger dryas 12 9 11 6 ka at the onset of the younger dryas a distinct alteration of the ecosystem reflected in a distinct drop in terrigenous and phytoplankton biomarkers was detected during the last 7 ka the sea ice proxies reflect a cooling of the laptev sea spring summer season this cooling trend was superimposed by a short term variability in sea ice coverage probably representing bond cycles 1500 500 ka that are related to solar activity changes hence atmospheric circulation changes were apparently able to affect the sea ice conditions on the laptev sea shelf under modern sea level conditions

high resolution record of late glacial and deglacial sea ice changes in fram strait corroborates ice ocean interactions during abrupt climate shifts the transition from last glacial to deglacial and subsequently to modern interglacial climate conditions was accompanied by abrupt shifts in the palaeoceanographic setting in the subpolar north atlantic knowledge about the role that sea ice coverage played during these rapid climate reversals is limited since most marine sediment cores from the higher latitudes provide only a coarse temporal resolution and often poorly preserved microfossils here we present a highly resolved reconstruction of sea ice conditions that characterised the eastern fram strait a key area for water mass exchange between the arctic ocean and the north atlantic for the past 30 ka bp this reconstruction is based on the distribution of the sea ice biomarker ip25 and phytoplankton derived biomarkers in a sediment core from the continental slope of western svalbard during the late glacial 30 ka to 19 ka bp recurrent advances and retreats of sea ice characterised the study area and point to a hitherto less considered oceanic and or atmospheric variability a long lasting perennial sea ice coverage in eastern fram strait persisted only at the very end of the last glacial maximum i e from 19 2 to 17 6 ka bp and was abruptly reduced at the onset of heinrich event 1 coincident with or possibly even inducing the collapse of the atlantic meridional overturning circulation amoc further maximum sea ice conditions prevailed during the younger dryas cooling event and support the assumption of an amoc reduction due to increased formation and export of arctic sea ice through fram strait a significant retreat of sea ice and sea surface warming are observed for the early holocene

holocene sea subsurface and surface water masses in the fram strait comparisons of temperature and sea ice reconstructions highlights holocene sea subsurface temperatures after husum hald 2012 estimated from planktic foraminifer fauna in e fram strait biomarkers and ip25 derived indices including dip25 indicate surface water variability delayed onset of early holocene conditions in subsurface 10 6 ka compared to surface 11 7 ka water conditions warm atlantic layer likely occupied uppermost 200 m in eastern fram strait between 10 and 9 ka diverging late holocene trends in surface and subsurface conditions linked to presence of strong pycnocline stratification abstract two high resolution sediment cores from eastern fram strait have been investigated for sea subsurface and surface temperature variability during the holocene the past ca 12 000 years the transfer function developed by husum and hald 2012 has been applied to sediment cores in order to reconstruct fluctuations of sea subsurface temperatures throughout the period additional biomarker and foraminiferal proxy data are used to elucidate variability between surface and subsurface water mass conditions and to conclude on the holocene climate and oceanographic variability on the west spitsbergen continental margin results consistently reveal warm sea surface to subsurface temperatures of up to 6 c until ca 5 cal ka bp with maximum seawater temperatures around 10 cal ka bp likely related to maximum july insolation occurring at that time maximum atlantic water aw advection occurred at surface and subsurface between 10 6 and 8 5 cal ka bp based on both foraminiferal and dinocyst temperature reconstructions probably a less stratified ice free nutrient rich surface ocean with strong aw advection prevailed in the eastern fram strait between 10 and 9 cal ka bp weakened aw contribution is found after ca 5 cal ka bp when subsurface temperatures strongly decrease with minimum values between ca 4 and 3 cal ka bp cold late holocene conditions are furthermore supported by high planktic foraminifer shell fragmentation and high 18o values of the subpolar planktic foraminifer species turborotalita quinqueloba while ip25 associated indices as well as dinocyst data suggest a sustained cooling due to a decrease in early summer insolation and consequently sea ice increase since about 7 cal ka bp in surface waters planktic foraminiferal data including stable isotopes indicate a slight return of stronger subsurface aw influx since ca 3 cal ka bp the observed decoupling of surface and subsurface waters during the later holocene is most likely attributed to a strong pycnocline layer separating cold sea ice fed surface waters from enhanced subsurface aw advection this may be related to changes in north atlantic subpolar versus subtropical gyre activity

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

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

baffin bay paleoenvironments in the lgm and hs1 resolving the ice shelf question abstract core hu2008029 12pc from the disko trough mouth fan on the central west greenland continental slope is used to test whether an ice shelf covered baffin bay during the last glacial maximum lgm and at the onset of the deglaciation we use benthic and planktic foraminiferal assemblages stable isotope analysis of planktic forams algal biomarkers ice rafted detritus ird lithofacies characteristics defined from ct scans and quantitative mineralogy to reconstruct paleoceanographic conditions sediment processes and sediment provenance the chronology is based on radiocarbon dates on planktic foraminifers using a r of 140 30 14 c years supplemented by the varying reservoir estimates of stern and lisiecki 2013 that provide an envelope of potential ages hu2008029 12pc is bioturbated throughout sediments between the core base at 11 3 m and 4 6 m lgm through hs1 comprise thin turbidites plumites and hemipelagic sediments with greenlandic provenance consistent with processes active at the greenland ice sheet margin grounded at or near the shelf edge abundance spikes of planktic forams coincide with elevated abundance of benthic forams in assemblages indicative of chilled atlantic water meltwater and intermittent marine productivity ird and ip 25 are rare in this interval but brassicasterol an indicator of marine productivity reaches and sustains low levels during the lgm these biological characteristics are consistent with a sea ice covered ocean experiencing periods of more open water such as leads or polynyas in the sea ice cover with chilled atlantic water at depth rather than full ice shelf cover they do not support the existence of a full baffin bay ice shelf cover extending from grounded ice on the davis strait initial ice retreat from the west greenland margin is manifested by a pronounced lithofacies shift to bioturbated diatomaceous mud with rare ird of greenlandic origin at 467 cm 16 2 cal ka bp r 140 yrs within hs1 a spike in foraminiferal abundance and ocean warmth indicator benthic forams precedes the initial ice retreat from the shelf edge at the end of hs1 ip 25 brassicasterol and benthic forams indicative of sea ice edge productivity increase indicating warming interstadial conditions within the bolling allerod interstadial a strong rise in ip 25 content and ird spikes rich in detrital carbonate from northern baffin bay indicate that northern baffin bay ice streams were retreating and provides evidence for increased open water advection of atlantic water in the west greenland current and formation of an ird belt along the w greenland margin

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

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

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

deglacial environments in eastern prydz bay east antarctica abstract a high resolution continuous record of diatom census counts and diatom specific biomarkers in sediment core nbp0101 jpc24 allows assessment of oceanographic and environmental conditions in eastern prydz bay during the deglaciation 11 100 9000 cal yr bp at decadal timescale our study improves previous snapshots investigations based on resin embedded thin sections and presents a new proxy that compliments the diatom census counts our results suggest that the ice sheet retreat over the core site is dated at 11 100 cal yr bp setting the onset of local deglaciation and subsequent open marine conditions the glacial retreat in prydz bay is due to global warming initiated at 18 cal ka bp and the regional development of the prydz bay cyclonic gyre our results further demonstrate that the deglaciation in eastern prydz bay can be separated in four phases the first between 11 100 and 10 900 cal yr bp when the ice shelf was proximal and sea ice was almost perennial the second and the third phases between 10 900 10 400 cal yr bp and 10 400 9900 cal yr bp respectively when the ice shelf retreated and seasonal sea ice cycle consequently developed promoting warmer water to pump into the bay within the gyre which in turn forced the ice shelf recession and the yearly sea ice cycle establishment and the fourth between 9900 and 9000 cal yr bp when holocene condition were set with a recurrent seasonal sea ice cycle and a well established prydz bay gyre

high resolution paleoproductivity fluctuations during the past 24 kyr as indicated by benthic foraminifera in the marginal arctic ocean abstract analyses of benthic foraminifera in sediment cores taken at about 1000 m water depth at the yermak plateau and the barents sea slope adjacent to the position of the ice sheet edge during the last glacial maximum show that paleoproductivity was reduced to about a third of its present level during peak glacial stadials these reduced values are still higher than values for modern permanently ice covered regions suggesting that the core locations were at least partially ice free even during stadials paleoproductivity at the core locations was higher than or equal to that of today during initial deglaciations and warm substages peak paleoproductivity occurred in samples with low salinity surface waters as indicated by oxygen isotope values of planktonic foraminifera and slightly after increased abundance of atlantic species suggesting that enhanced advection of warmer waters from the atlantic supported the initial ice sheet retreat during the holocene climatic optimum productivity was much less than at present on the yermak plateau high at the barents sea site perhaps because of increased advection of atlantic water to the latter site and heavier ice coverage at the former after this optimum paleoproductivity at both sites was similar with slightly lower values during cold periods such as the little ice age

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

on the response of polarimetric gnss reflectometry to sea surface roughness reflectometry of global navigation satellite systems gnss signals from the ocean surface has provided a new source of observations to study the ocean atmosphere interactions we investigate the sensitivity and performance of the gnss reflectometry gnss r data to retrieve sea surface roughness ssr as an indicator of the sea state a data set of one year observations in 2016 is acquired from a coastal gnss r experiment in onsala sweden the experiment exploitstwo sea looking antennas with right and left hand circular polarizations rhcp and lhcp the interference of the direct and reflected signals captured by the antennas is used by a gnss r receiver to generate complex interferometric fringes we process the interferometric observations to estimate the contributions of direct signals and reflections to the total power the power estimates are inverted to the ssr using the state of the art model the roughness measurements from the rhcp and lhcp links are evaluated against match up wind measurements obtained from the nearest meteorological station the results report on successful roughness retrieval with overall correlations of 0 76 for both links however the roughness effect in lhcp observations is more pronounced the influence of surrounding complex coastlines and the wind direction dependence are discussed the analysis reveals that the winds blowing from land have minimal impact on the roughness due to limited fetch a clear improvement of roughness estimates with an overall correlation of 0 82 is observed for combined polarimetric observations from the rhcp and lhcp links the combined observations can also improve the sensitivity of gnss r measurements to the change of sea state

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

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

changes in arctic ocean paleoproductivity and hydrography during the last 145 kyr the benthic foraminiferal record the benthic foraminiferal record of two sediment cores at 900 and 2500 m water depth in the marginal arctic ocean reflects fluctuations in paleoproductivity ice sheet extent and atlantic water inflow highest paleoproductivity is observed in interglacial periods and at the termination of interstadials to stadials within oxygen isotope substages ois 6 3 5 3 5 1 3 1 and termination ia stable and high paleoproductivity at the ice edge during terminations is indicated by the melonis zaandami benthic foraminiferal association periods of glacial ice sheet advance or retreat from the core site are dominated by benthic foraminiferal associations related to seasonal organic carbon flux temperate saline atlantic water entered the arctic ocean within ois 6 3 5 5 and the holocene coincident paleoproductivity maxima are related to extended seasonal ice retreat during glacial periods of stagnating atlantic water advection unusual low paleoproductivity values are observed in the arctic ocean indicating increasing ice coverage deep water was poorly ventilated during these periods and the deeper site became exposed to corrosive bottom waters

holocene paleoenvironmental implications of diatom and organic carbon records from the southeastern kara sea siberian margin diatom assemblages and organic carbon records from two sediment cores located within an estuarian bay of the inner kara sea trace changes in yenisei river runoff and postglacial depositional environments paleosalinity and sea ice reconstructions are based on modern relationships of local diatom assemblages and summer surface water salinity approximately 15 500 cal yr b p rivers and bogs characterized the study area when sea level reached the 38 to 40 m paleo isobath approximately 9300 cal yr b p the coring site was flooded from 9300 9100 cal yr b p estuarine conditions occurred proximal to the depocenter of fluvially derived material and salinity was 7 8 paleosalinity increased to 11 13 by 7500 cal yr b p following postglacial sea level rise and the southward shift of the siberian coast sharp decreases in diatom accumulation rates total sediment and organic carbon also occurred suggesting the presence of brackish conditions and greater distance between the coast and study site maximum paleosalinity up to 13 was recorded between 7500 and 6000 cal yr b p which was likely caused by the enhanced penetration of atlantic waters to the kara sea stepwise decreases to modern salinity levels happened over the last 6000 cal yr

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

seasonal sea ice cover during the warm pliocene evidence from the iceland sea odp site 907 abstract sea ice is a critical component in the arctic and global climate system yet little is known about its extent and variability during past warm intervals such as the pliocene 5 33 2 58 ma here we present the first multi proxy ip25 sterols alkenones palynology sea ice reconstructions for the late pliocene iceland sea odp site 907 our interpretation of a seasonal sea ice cover with occasional ice free intervals between 3 50 3 00 ma is supported by reconstructed alkenone based summer sea surface temperatures as evidenced from brassicasterol and dinosterol primary productivity was low between 3 50 and 3 00 ma and the site experienced generally oligotrophic conditions the east greenland current and east icelandic current may have transported sea ice into the iceland sea and or brought cooler and fresher waters favoring local sea ice formation between 3 00 and 2 40 ma the iceland sea is mainly sea ice free but seasonal sea ice occurred between 2 81 and 2 74 ma sea ice extending into the iceland sea at this time may have acted as a positive feedback for the build up of the greenland ice sheet gis which underwent a major expansion 2 75 ma thereafter most likely a stable sea ice edge developed close to greenland possibly changing together with the expansion and retreat of the gis and affecting the productivity in the iceland sea

tracking the arctic s shrinking ice cover another extreme september minimum in 2004 1 satellite passive microwave observations document an overall downward trend in arctic sea ice extent and area since 1978 while the record minimum observed in september 2002 strongly reinforced this downward trend extreme ice minima were again observed in 2003 and 2004 although having three extreme minimum years in a row is unprecedented in the satellite record attributing these recent trends and extremes to greenhouse gas loading must be tempered by recognition that the sea ice cover is variable from year to year in response to wind temperature and oceanic forcings

lena river discharge events in sediments of laptev sea russian arctic abstract to reconstruct the variability of freshwater discharge to the arctic via the lena river 22 gravity cores were collected along two transects that extend from the delta floodplain onto the laptev sea shelf high magnetic susceptibility ms signals appear to be good indicators for river sediment deposition sedimentation of this terrestrial material forms fluvial units distinguished by coarse grain size and high ms signal produced by the magnetic properties from the river derived material the criteria to distinguish marine units are low magnetic susceptibility signals when compared with fluvial units lithological descriptions and granulometric analyses sedigraph granulometric analyses in combination with wet sieving analyses grain size 4 reveal changes in grain size distributions along the cores that are well correlated with magnetic susceptibility data fluvial and marine units were found to alternate sequentially along the cores data from cores comprising two transects in the laptev sea revealed 17 total fluvial events during the last 2000 years the lena river derived sediment bedload could be traced 34 5 47 5 km far from the delta edge of bykovskaya branch showing direct impact of lena river discharge to the laptev sea