quantitative mineralogy of surface sediments on the iceland shelf and application to down core studies of holocene ice rafted sediments abstract quantitative x ray diffraction analyses on the 2 mm sediment fraction from the iceland shelves are reported for subglacial diamictons seafloor surface sediments and the last 2000 cal yr bp from two cores the overall goal of the paper is to characterize the spatial variability of the mineralogy of the present day surface sediments 18 non clay minerals and 7 clay minerals compare that with largely in situ erosional products typified by the composition of subglacial diamictons and finally examine the late holocene temporal variability in mineral composition using multi mineral compositions the subglacial diamictons are dominated in the non clay mineral fraction by the plagioclase feldspars and pyroxene with 36 7 6 1 and 17 9 3 5 wt respectively with smectites being the dominant clay minerals the surface seafloor sediments have similar compositions although there are substantial amounts of calcite plus there is a distinct band of sites from nw to n central iceland that contain 1 6 wt of quartz this latter distribution mimics the modern and historic pattern of drift ice in iceland waters principal component analysis of the transformed wt log ratio non clay minerals is used to compare the subglacial surface and down core mineral compositions fifty eight percent of the variance is explained by the first two axes with dolomite microcline and quartz being important foreign species these analyses indicate that today the nw n central iceland shelf is affected by the import of exotic minerals which are transported and released from drift ice the down core mineralogy indicates that this is a process that has varied over the last 2000 cal yr bp

climate and oceanographic variability in the sw barents sea during the holocene the holocene section of the marine sediment core psh 5159n located in the sw barents sea has been studied at high resolution with a multiproxy approach a well stratified water column occurred at the site 11 9 8 ka bp the stratification was probably a result of a winter sea ice cover and or fresh warm surface waters during summer stratification and resultant reduction in air sea interaction allowed for warmer bottom water temperatures the general situation 11 9 8 ka bp could have been associated with an anomalous high pressure system over the nordic seas and the arctic ocean during the 11 10 5 ka bp interval the polar front was located close to the barents sea margin the polar front moved towards the site from 10 5 ka bp and from 9 8 to 7 5 ka bp it was probably located close to the site at 7 5 ka bp the polar front retreated eastwards as the present day oceanographic pattern established the mid holocene was in general characterized by rather stable conditions in contrast highly variable cond

oxygen isotope studies of carbonaceous chondrites abstract the carbonaceous chondrites display the widest range of oxygen isotopic composition of any meteorite group as a consequence of the interaction of primordial isotopic reservoirs in the solar nebula these isotopic variations can be used to identify the reservoirs and to determine conditions and loci of their interactions we present a comprehensive set of whole rock analyses of cv co ck cm cr ch and ci chondrites as well as selected components of some of these meteorites a simple model is developed which describes the isotopic behavior during parent body aqueous alteration processes the process of thermal dehydration also produces a recognizable effect in the oxygen isotopic composition

flux of ice rafted detritus from sea ice in the fram strait abstract a three year particle flux record from the eastern fram strait between greenland and svalbard revealed a rather untypical seasonal flux pattern compared to other particle flux studies from the nordic seas in the eastern fram strait this pattern is characterised by a sudden four to six fold increase of the particle flux in january when no daylight is available to support any biological productivity comparison with sea ice distribution maps led to the conclusion that the sudden increase in the flux is due to ice rafted detritus released from sea ice which originated from the svalbard archipelago and from the northern barents sea detailed grain size analyses of the silt fraction indicated the 10 m fraction of the lithogenic matter to be clearly enriched due to ird input even more important is the observation that lithogenic material 40 m occurs exclusively during the ice rafting event and therefore appears to be a suitable indicator for ird transported on sea ice thus in addition to coarse ird e g 500 m which is mainly derived from icebergs the analysis of fine ird 40 m in deep sea sediments can be used to reconstruct paleo sea ice extensions

effects of ice coverage and ice rafted material on sedimentation in the fram strait as little is known about pelagic sedimentation processes in arctic environments1 the interpretation of biological and chemical processes as well as the reconstruction of ancient conditions including those in the glacial north atlantic is difficult here we provide sediment trap results which show that the position of the sea ice boundary significantly influences the particle flux the seasonal variability of the particle flux differed markedly in the various sediment trap sites in fram strait depending on the behaviour of the sea ice under complete ice cover sedimentation is very low whereas maximum sedimentation is found at the ice margin the highest particle flux observed showing a large lithogenic component was observed at the ice edge where the water was warmer 2 c we find that high biogenic opal fluxes are characteristic of the summer ice margin indicating that the sedimentary record of opal fluxes may allow the position of ice margins in the past to be reconstructed

moisture supply for northern ice sheet growth during the last glacial maximum during the last ice age the barents sea ice sheet began to grow 22 kyr ago1 only 8 kyr before it began to disintegrate2 this implies that the ice must have grown very rapidly from the coast to the edge of the continental shelf such rapid growth of a large ice sheet requires significant amounts of moisture3 but the origin of this moisture has been unclear particularly as the climap climate reconstruction suggests4 5 that the greenland iceland norwegian gin seas were perennially ice covered during this period here we present data from deep sea sediment cores from the fram strait which suggest that relatively warm water from the north atlantic ocean was advected into the gin seas in two short term events 27 22 5 and 19 5 14 5 kyr ago we suggest that the resulting seasonally ice free waters were an important regional moisture source for the barents sea ice sheet and that the gin seas played a much more active role in climate during the last glaciation than has previously been supposed

pelagic processes and vertical flux of particles an overview of a long term comparative study in the norwegian sea and greenland sea pelagic processes and their relation to vertical flux have been studied in the norwegian and greenland seas since 1986 results of long term sediment trap deployments and adjoining process studies are presented and the underlying methodological and conceptional background is discussed recent extension of these investigations at the barents sea continental slope are also presented with similar conditions of input irradiation and nutrient conditions the norwegian and greenland seas exhibit comparable mean annual rates of new and total production major differences can be found between these regions however in the hydrographic conditions constraining primary production and in the composition and seasonal development of the plankton this is reflected in differences in the temporal patterns of vertical particle flux in relation to new production in the euphotic zone the composition of particles exported and in different processes leading to their modification in the mid water layers

scavenging of thorium isotopes in the canada basin of the arctic ocean abstract investigations on the distribution of thorium isotopes in the water column have been utilized as powerful tracers to investigate the geochemical pathways of particle reactive material in the ocean we measured th 228 th 230 th 232 th and 234 th isotopes in samples collected along a horizontal profile from barrow ak to the canada basin as well as two vertical profiles in the canada basin the suspended particle concentrations were also measured to investigate the role of suspended particulate matter spm in th scavenging the spm inventory is more than an order of magnitude higher than that reported for the alpha ridge ice station indicating that the spm inventories vary over an order of magnitude in the deep arctic basins the conditional partition coefficient of th isotopes between suspended particulate matter and dissolved phase generally appears to be higher than those in non polar regions and this is attributed to more reactive suspended particulate matter the residence times of total 230 th are significantly lower than those calculated for the alpha ridge station while higher than those found in the eurasian basin and beaufort sea in the canadian basin the calculated residence time in all the deep basins of the arctic ocean varied between 13 1 and 45 1 years a reversible scavenging model applied to the distribution of th isotopes 230 th 228 th in the deep waters and 234 th 228 th in the upper 100 m indicates that the forward removal rate constant is higher than the value reported for the alpha ridge while the reverse rate constant is comparable to the alpha ridge station suggesting faster removal onto particulate matter and slower desorption of th from the particulate matter

estimation of the catchment area of a sediment trap by means of current meters and foraminiferal tests abstract between june 1989 and july 1990 a mooring equipped with four current meters and one sediment trap was deployed in the fram strait 79 n from the material collected by the sediment trap two species of planktic foraminifera turborotalita quinqueloba and neogloboquadrina pachyderma were used to estimate the catchment area of the sediment trap for each species and size class the individual sinking velocity was used to determine the residence time in the water column the residence time is the major factor that determines the drift of the tests using current meter data trajectories were calculated to estimate the catchment area and the area of sedimentation the maximum distance the smallest tests have been transported while sinking from the surface 100 m to the sediment trap 1125 m is approximately 275 km with maximum trajectory lengths of up to 300 km depending mainly on the grain size of the tests the distances and trajectories have means lying between 25 and 50 km for n pachyderma and 50 and 100 km for t quinqueloba respectively considering the whole sampling period the estimated catchment areas are 23 900 km 2 for all n pachyderma tests and 33 300 km 2 for all t quinqueloba tests respectively the respective areas of sedimentation are estimated to range from 3400 km 2 to 3500 km 2

interception of atmospheric fluxes by arctic sea ice evidence from cosmogenic 7be 1 the natural cosmogenic radionuclide 7be t1 2 53 4 d is supplied to the surface ocean from the atmosphere and in the arctic ocean can be used as a tracer of the efficiency with which sea ice intercepts the atmospheric fluxes of chemical species and of the importance of ice as a transport mechanism for particulate matter and chemical species analyses of 7be in samples of surface water surface sea ice water beneath the ice sea ice sediments and precipitation from the eurasian basin of the arctic ocean show that the fraction of sea ice coverage determines the amount of 7be in the surface water when sea ice coverage is 80 the water column inventory drops to 58 20 bq m 2 the 7be inventory in sea ice is 39 23 bq m 2 and mass balance calculations show that sea ice can intercept 30 18 of the atmospheric flux of 7be during the studied period we suggest that other atmospherically transported contaminants should be similarly intercepted 7be in the ice also can be used to estimate that the annual transport and release of sediment to the ablation area of the fram strait is 500 g m 2 a value comparable to previously measured fluxes in sediment traps deployed in the area

association of sinking organic matter with various types of mineral ballast in the deep sea implications for the rain ratio 1 we compiled and standardized sediment trap data below 1000 m depth from 52 locations around the globe to infer the implications of the armstrong et al 2002 ballast model to the ratio of organic carbon to calcium carbonate in the deep sea the rain ratio we distinguished three forms of mineral ballast calcium carbonate opal and lithogenic material we concur with armstrong et al 2002 that organic carbon sinking fluxes correlate tightly with mineral fluxes based on the correlations seen in the trap data we conclude that most of the organic carbon rain in the deep sea is carried by calcium carbonate because it is denser than opal and more abundant than terrigenous material this analysis explains the constancy of the organic carbon to calcium carbonate rain ratio in the deep sea today and argues against large changes in the mean value of this ratio in the past however sediment trap data show variability in the ratio in areas of high relative calcium carbonate export mass caco3 mass ratio 0 4 unexplainable by the model leaving open the possibility of regional variations in the rain ratio in the past

mudstone sedimentation at high latitudes ice as a transport medium for mud and supplier of nutrients abstract controls on mudstone deposition at high latitudes are poorly known relative to low latitudes in recent sediments deposited in these environments ice significantly influences sediment transport and primary productivity the products of ice transport are relatively well known in glacimarine settings but are less well known from below melting sea ice this latter setting is significant as today it is associated with high primary organic productivity the aim of this study is to assess how sea ice might have controlled lithofacies variability and organic matter distribution and preservation in an ancient marine siliciclastic mudstone dominated succession deposited at high latitudes combined sedimentary logging optical and electron optical backscattered electron imagery geochemical and isotopic methods were used to determine sample variability in forty five samples collected from the lower cretaceous succession in the mikkelsen bay state 1 borehole north slope alaska the succession overall fines upward and contains muddy sandstones and sand and silt bearing clay rich mudstones towards its base in contrast to clay rich and clay dominated mudstones towards its top some of the mudstone units exhibit thin 5 mm relic beds that fine upward weakly in some units small 0 5 mm bed parallel silt filled microburrows disrupt depositional laminae whereas in others pervasive burrowing completely obliterates original depositional textures many of the units are pelleted these mudstones are unusual in that they contain minor but very striking outsize grains composed of subrounded to rounded sand and granule size material in addition they are good petroleum source rocks with between 2 8 and 5 9 wt total organic carbon of predominantly type ii kerogen the organic matter has an isotopic signature ranging from 25 4 13c to 28 1 13c thin tuffs 20 mm and carbonate cemented units are also present given the absence of significant polar ice in the early cretaceous the outsized grains are interpreted to have been deposited from a combination of melting dirty anchor and fast ice the mud fraction which forms the bulk of the sediment is interpreted to have been deposited from melting sediment laden frazil ice and fast ice after deposition sediments were partially reworked by bottom currents generated by brine rejection during sea ice formation sympagic organisms grazing on algae and bacteria both within and below the ice pelleted the sediment bioturbation which varies through the succession indicates that sedimentation probably occurred beneath a predominantly oxic or dys oxic water column in this setting productivity was fueled by nutrients released from melting sea ice in the marginal ice zone the good petroleum source potential of these mudstones is attributed to high organic productivity coupled to episodic and rapid sedimentation rather than existence of bottom water anoxia linked to upwelling because sea ice rafting was probably the dominant sediment transport mechanism it is not appropriate to use sequence stratigraphic methodology to predict lithofacies variability in this environment

importance of lateral transport processes to 210pb budget in the eastern chukchi sea during summer 2003 chinese ipy research program national natural science foundation of china 41125020 fujian natural science foundation 2009j06026 state oceanic administration of china 201105022 4 ministry of education of china

benthic prokaryotic community dynamics along the ardencaple canyon western greenland sea abstract the ardencaple canyon emanating from the eastern greenland continental rise over a distance of about 200 km towards the greenland basin was investigated to determine the effect of enhanced down slope transport mechanisms on deep sea benthic prokaryotic communities the concentration of viable bacterial cells live dead baclight and prokaryotic incorporation rates 3 h thymidine 14 c leucine increased with increasing distance from the continental shelf multidimensional scaling mds results from terminal restriction fragment length polymorphism t rflp analysis indicated a spatial coherence between the benthic bacterial community structure prokaryotic incorporation rates water content protein concentration and the total organic matter in the sediments the community complexity in sediments at 4 5 cm depth was lower in the central parts of the channel compared with the northern and the southern levees while richness in surface sediments of all stations was similar lacking any clear indications for a recent mass sediment transport or funneled shelf drainage flows high similarities between bacterial assemblages in sediments along the canyon course may thus be governed by a combination of an ice edge induced particle flux episodic down slope and canyon guided transport mechanisms

source to sink statistical identification of regional variations in the mineralogy of surface sediments in the western nordic seas 58 n 75 n 10 w 40 w the non clay and clay mineralogies of the 2 mm sediment fraction from 157 seafloor samples in the western nordic seas is calculated by quantitative x ray diffraction analysis our sample coverage includes the iceland shelf the ice impacted east greenland margin and the greenland iceland and irminger seas the bedrock geology of source areas includes precambrian basement rocks devonian red beds and younger marine and fluvial sediments and large outcrops of early tertiary to recent flood basalts and other volcanic facies sediment erosion and transport in the area are associated with ice sea ice and icebergs and glacial meltwater and fluvial sediment plumes we use principal component analysis fuzzy k means clustering and discriminant function analysis to reduce the original 31 minerals 157 sites matrix to more manageable 5 regional coherent clusters of sites which are well discriminated by the weight of six minerals namely quartz pyroxene illites magnetite and maghemite amorphous silica e g glass and muscovite the close spatial relationship between bedrock geology and discrete cluster membership stresses the importance of this variable and indicates that far distant sediment transport by sea ice icebergs or other mechanisms although occurring does not radically change the mineral composition of present day sea floor sediments our improved knowledge of the regional mineral assemblages allows for tracking distinct eastern greenland and icelandic sources

the supply and accumulation of silica in the marine environment rivers and submarine hydrothermal emanations supply 6 1 1014g sio2 yr to the marine environment approximately two thirds of the silica supplied to the marine environment can be accounted for in continental margin and deep sea deposits siliceous deep sea sediments located beneath the antarctic polar front convergence account for over a fourth 1 6 1014g sio2 yr of the silica supplied to the oceans deep sea sediment accumulation rates beneath the polar front are highest in the south atlantic with values as large as 53cm kyr during the last 18 000 yr siliceous sediments in the bering sea sea of okhotsk and subarctic north pacific accumulate 0 6 1014g sio2 yr or 10 of the dissolved silica input to the oceans the accumulation of biogenic silica in estuarine deposits removes a maximum of 0 8 1014g sio2 yr although estuarine silica versus salinity plots indicate extensive removal of riverine silica from surface waters the removal rates must be considered as maximum values because of dissolution of siliceous material in estuarine sediments and bottom waters siliceous sediments from continental margin upwelling areas e g gulf of california walvis bay or peru chile coast have the highest biogenic silica accumulation rates in the marine environment 69 g sio2 cm2 kyr despite the rapid accumulation of biogenic silica upwelling areas account for less than 5 of the silica supplied to the marine environment because they are confined laterally to such small areas

diagnostic study of the fram strait marginal ice zone during summer from 1983 and 1984 marginal ice zone experiment lagrangian observations from 1984 marginal ice zone experiment observations in fram strait three main results concerning large scale mesoscale and summer marginal ice zone miz features are presented and discussed in this paper regarding the large scale the main conclusion is that the east greenland current egc is a narrow stable current in contradiction with past results presenting the egc as a broad and unstable current in the mesoscale the west spitsbergen current wsc and the norwegian current are the main generators for eddies in fram strait these eddies propagate northwestward preferentially following topographic features like fracture zones which are quite abundant in this region in our opinion these wsc eddies represent an important part of the atlantic water recirculation in fram strait when approaching the east greenland continental slope they interact with the egc and they form well developed eddies these ice edge eddies associated with ice edge tongues are quite recognizable with remote sensing techniques the summer marginal ice zone in fram strait is clearly characterized by sea ice concentrations from 1 10 to 3 10 and floe sizes limited to 1 km or less there is a well defined limit which separates the pack ice from the miz where no big ice floes are ever recorded the breaking action of waves and swell propagating into the ice are likely to be the only mechanisms explaining such a drastic filtering effect according to their amplitudes and directions winds and eddies act in the miz in shrinking or stretching this zone

oceanic evidence for coherent fluctuations in fennoscandian and laurentide ice sheets on millennium timescales proxy temperature records from greenland ice cores1 2 and north atlantic sediment cores3 have provided evidence for a high degree of climate instability during the last glacial period much of this variability seems to be linked with the dynamics of the laurentide ice sheet that covered north america at this time3 which dis charged iceberg flotillas into the north atlantic that are now recorded in sediment cores as heinrich events4 how if at all this variability was manifested on the other side of the atlantic in the nordic seas and the ice sheets of northwest europe and scandinavia has been unclear here we present sediment micro fossil and oxygen isotope data from a sediment core in the norweg ian sea which reveal cooling events and iceberg discharges analogous to heinrich events we show that these climate fluctua tions in the norwegian sea were in phase or were phase locked with air temperatures over greenland suggesting that the rapid changes in heat fluxes in the north atlantic recorded in previous records3 were felt in this high latitude region the iceberg dis charges in our record seem to have come from the fennoscandian ice sheet implying that this and the laurentide ice sheets fluctu ated coherently on timescales shorter than those of milankovitch orbital cycles

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

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

coupling of air and sea surface temperatures in the eastern fram strait during the last 2000 years the arctic has undergone significant changes in the last 20 30 years the understanding of these changes is limited by the time span or resolution of existing climate records the main gateway of h

the white angel a unique wollastonite bearing mass fractionated refractory inclusion from the leoville cv3 carbonaceous chondrite we report the study of an unusual compact type a refractory inclusion named the white angel from the leoville cv3 meteorite the petrologic mineral chemical isotopic and traceelement signatures of this once molten ca al rich inclusion cai which contains large equant wollastonite crystals indicate a short multistage history that occurred very early before substantial decay of 26al magnesium in the inclusion is isotopically heavy with fmg reaching 18 amu in the range of fractionated and with unidentified nuclear effects fun inclusions however the absence of any nuclear anomalies in ca and ti and an inferred 26al 27al ratio of 5 5 0 9 10 5 indicate that the white angel belongs to the f inclusions silicon and oxygen are also mass fractionated in favor of the heavy isotopes but to a lesser extent the o isotopes show a range in 16o excesses on an o three isotope plot data points lie on a line parallel and to the right of the carbonaceous chondrite anhydrous mineral mixing line with wollastonite being the most 16o rich phase the chondritenormalized rare earth and trace element pattern of the whole inclusion is the complement of an ultrarefractory pattern indicating that precursor phases of the cai must have condensed in an al heavy rare earth element hree depleted reservoir melting of those precursor phases in an 16o rich environment and evaporation led to mass dependent isotopic fractionation of mg si and o partial isotopic exchange with a reservoir containing unfractionated mg took place at a later stage but before any measurable decay of 26al some minerals melilite and perovskite in the white angel equilibrated oxygen isotopes with a relatively 16o poor reservoir that was also mass fractionated toward the heavy isotopes different from that with which the normal or fun inclusions interacted

petrologic and almg isotopic clues to the accretion of two refractory inclusions onto the leoville parent body one was hot the other wasn t abstract two type b refractory inclusions found within several centimeters of each other in the foliated leoville meteorite differ greatly in their styles of deformation textures and mg al isotopic characteristics one is a subspheroidal type b1 with textures similar to those observed previously in many type b1s from other cv3 meteorites and whose deformation fracturing some granulation has been almost entirely brittle in nature its isotopic composition shows 26 mg 24 mg correlated with 27 al 24 mg which although disturbed indicates a lower limit for initial 26 al 27 al of 4 9 10 5 the other inclusion is a highly elongate l w 6 object whose long axis lies in the plane of foliation of the leoville meteorite it has a predominantly metamorphic texture but relict islands of an earlier and more normal type b precursor are preserved in its core the isotopic compositions of the two textural variants in this inclusion are different anorthite in the metamorphic region mostly showing little or no excess 26mg 26 al 27 al 0 6 that would be attributable to in situ decay of 26al whereas anorthite in the relict islands shows well resolved excess 26mg that gives a lower limit for initial 26 al 27 al of 4 6 10 5 the effects of shock metamorphism on the leoville meteorite are clearly seen in both inclusions including brittle deformation and local shock melting but are not responsible for the major textural differences between the two inclusions the most likely origin for the deformed and recrystallized features of the elongate inclusion is that it accreted onto the leoville parent body while still very hot and deformed into its present shape at the instant it impacted if the resetting of the al mg system occurred during this event it must have taken place at least 3 3 million years after formation of the precursor inclusion the possibility that other deformed leoville components accreted while hot should not be discounted

paleoceanography of the last interglacial glacial cycle in the polar north atlantic abstract using to its position close to the sites of waxing and waning of the major northern hemisphere ice sheets during the late quaternary climatic cycles the polar north atlantic plays a key role in driving global change therefore analyzing the present day sedimentation processes and reconstructing the late quaternary paleoceanography in this region has been a focus of major scientific interest through the last fifteen years this paper aims to combine the vast amount of new results about modern sediment fluxes surface sediment distribution and the paleoceanographic record and to present a comprehensive overview of the paleoceanography in the polar north atlantic through the last 200 000 years which is based on the basinwide analysis of carbonate and ice rafted detritus records during the last fifteen years the climap paleoceanographic view of the glacial polar north atlantic as an almost permanently isolated sea covered by heavy sea ice throughout the year has been shifted to a much more dynamic view of the environmental conditions a meridional current system similar to the present day conditions secured the exchange of water ice and heat between the polar north atlantic and the alantic and arctic oceans although affected by variations in strength and intensity this meridional current pattern resulted in an almost permanent presence of at least some seasonally ice free areas with all the consequences for e g marine life and deep water formation in addition the development of the continental ice sheets namely the fennoscandian and the barents sea ice sheets is closely related to this dynamic circulation pattern during the so called nordway events the pronounced inflow of temperate waters from the south provided moisture for the growth of the ice sheets the most prominent of these events stage 6 stage 4 and substage 3 1 2 ended in major glaciations reflected in the terrestrial sequences and in the deep sea ird records

efremovka 101 1 a cai with ultrarefractory ree patterns and enormous enrichments of sc zr and y in fassaite and perovskite inclusion 101 1 from the cv3 carbonaceous chondrite efremovka is a compact type a ca al rich inclusion cai highly enriched in ultrarefractory ur oxides it is the first complete cai with a ur rare earth element ree pattern found in a cv3 chondrite the inclusion is petrographically complex and was formed in a multistage process it consists of several lithologically unrelated units the core contains abundant y and zr perovskite sc and zr rich fassaite and metallic feni enclosed in melilite all mineral species except spinel in all lithological units exhibit the same basic ur ree pattern four different populations of perovskites are distinguished by different y zr ratios a few of the perovskites have y zr ratios similar to those obtained from crystal liquid fractionation experiments perovskites from the other three populations have either chondritic lower than chondritic y zr ratios or extremely low zr contents ca isotopic ratios differ among three perovskites from different populations demonstrating a variety of sources and formational processes most fassaites crystallized in situ through reaction between the cai liquid and preexisting perovskites this process induced redistribution of zr y sc and v between perovskite and fassaite thus overprinting the original abundances in perovskite fassaite reaction rims around feni metals are also encountered they are enriched in v which was gained from the metal through oxidation of v in metal during fassaite crystallization the relative abundances of zr y and sc in perovskites are complementary to the abundances of these elements in sc and zr fassaite indicating subsolidus partitioning of these elements between the two phases perovskites are enriched in y and depleted in sc and zr in comparison to fassaites the core contains two complete captured cais several sinuous fragments and fine grained polygonal refractory fragments an assemblage of andradite wollastonite hedenbergite and pure metallic iron is encoun tered as enclaves in the interior of some sinuous fragments metallic fe and wollastonite formed by reduction of preexisting andradite and hedenbergite nebular alteration products upon inclusion in the highly reduced cai melt numerous spinel clusters and framboids with varying v2o3 and cr2o3 concentrations are enclosed in individual melilite crystals in the host cai and captured cais the rim sequence of the host consists of six layers from the inside outward a feo poor spinel b sc bearing fassaite c al diopside d al and ca bearing olivine e pure diopside and f ca poor olivine like the constituents of the cai core all mineral layers of the rim sequence except spinel have the same ur ree pattern however the total ree abundances decrease systematically by 1 order of magnitude from layer 2 to layer 6 this feature strongly suggests formation of the rim sequence by successive condensation from a unique reservoir enriched in ur elements and excludes formation by flash heating petrography mineral chemistry ree refractory lithophile element abundances and ca isotopic compositions demonstrate the complex multistage formation history of a cai that on the surface looks like a regular type a inclusion copyright 2002 elsevier science ltd

depositional regimes in the norwegian greenland sea the last two glacial to interglacial transitions various models of surface and deep water circulation in the norwegian greenland sea ngs have been proposed for the last two glacial to interglacial transitions although much progress has been made in understanding the sedimentary response to climatic and oceanographic changes conflicting interpretations have been developed to clarify some of these discrepancies and to test or modify the existing circulation concepts a multiparameter approach is applied combining sedimentological micropaleontological organic geochemical and isotopic methods on the basis of indicative properties a combined litho and organofacies concept is developed and calibrated with modern depositional settings beneath different surface water masses sedimentary regimes are then derived for glacial and deglacial settings

the growth and decay of the late weichselian ice sheet in western svalbard and adjacent areas based on provenance studies of marine sediments the history of the late weichselian northwestern barents shelf including western svalbard has been investigated by provenance sedimentologist studies of five cores from the continental shelf and slope west of svalbard the chronostratigraphy of the cores is based on ams 14c dates and oxygen isotope analyses interpretations of the cores suggest that the ice sheets of western svalbard and northwestern barents sea experienced advances and retreats in two steps the first significant ice advance beyond the present coastline occurred ca 22 000 14c yr b p and was followed by an ice advance to the shelf edge ca 18 000 14c yr b p ice recession from the outer shelf and the southwestern barents sea began 14 800 14c yr b p and was followed by a second ice recession between 13 000 and 12 000 14 c yr b p during which ice withdrew from the inner shelf a minor readvance of the ice sheet on the shelf west of svalbard occurred close to 12 400 14c yr b p the first deglaciation event was associated with release of icebergs containing ice rafted detritus while the later episode also included significant amounts of meltwater and fine grained sediment

ocean circulation and iceberg discharge in the glacial north atlantic inferences from unmixing of sediment size distributions variability in iceberg discharge and deep ocean circulation in the north atlantic during the last glacial period is inferred from the grain size distribution and trace elemental composition of terrigenous sediments in a deep sea core taken on reykjanes ridge south of iceland end member modeling of the grain size distributions is used to unmix the signals of varying bottom current speed and iceberg discharge the size distribution within the silt fraction appears to be influenced by both factors based on th sc la relationship we established that during the ice rafted detritus events continental material of likely greenlandic origin increased to 87 and that bottom current derived material contains to 40 mid oceanic ridge fines probably of icelandic origin our results have important implications for the use of silt grain size as an indicator for paleocurrent speed in the glacial north atlantic we show that reconstructions of variations in bottom current speed based on the raw grain size data are opposite to inferences from the unmixed record the latter indicates that deep water convection decreased during periods of enhanced iceberg discharge which is in general agreement with paleoceanographic reconstructions of the north atlantic

glacial history and paleoceanography of the southern yermak plateau since 132 ka bp abstract the southern yermak plateau yp is situated at the entrance to the arctic ocean in the narrow marginal ice zone miz between the polar and arctic fronts north west of svalbard a gravity core jm10 02gc has been analysed in order to reconstruct paleoceanographic conditions and the movement of the sea ice margin as well as the glacier ice conditions of the svalbard barents sea ice sheet sbis during the last interglacial glacial cycle the distribution of planktic and benthic foraminifera planktic and benthic oxygen and carbon isotopes and variations in ice rafted debris ird has been investigated the sediment core covers the time interval from the marine isotope stage mis 6 5e transition termination ii c 132 ka bp to the early holocene during termination ii tii the sbis retreated and the sea ice margin was in distal position whereas during mis 5 to mis 4 the sea ice margin was close to the core site several core intervals interpreted as representing mis 5e mis 5c mis 5a mis 3 and mis 1 were barren of calcareous microfossils whereas the intervals representing mis 4 and mis 2 were characterised by high productivity hp of planktic and benthic foraminifera these glacial hp zones were associated with the open water conditions resulting from the advection of atlantic water aw and retreat of the sea ice margin the barren zones during mis 5 mis 3 and mis 1 resulted from the proximity of the sea ice margin whereas during mis 2 the likely cause was an advance of the sbis

the 2 6 ma depositional sequence from the challenger cold water coral carbonate mound iodp exp 307 sediment contributors and hydrodynamic palaeo environments during iodp expedition 307 the first complete sequence through a cold water coral carbonate mound a bio geological seafloor feature created through successive stages of cold water coral mediated sediment accumulation was successfully acquired the full recovery of the challenger mound one of the large ca 155 m high coral carbonate mounds along the ne atlantic continental margin belgica mound province eastern porcupine seabight facilitates for the first time the study of the entire development of a coral carbonate mound and hence allows the identification of the environmental conditions driving and maintaining the entire build up of these remarkable seafloor habitats in this study the different sediment contributors to the challenger mound are identified and assessed throughout its entire 2 6 ma long development high resolution siliciclastic particle size end member modelling and its ground truthing xrd quartz sand surface microtextures indicate the influence of an all dominant contour current system operating in variable energetic modes for most of the sediment accumulation history of the challenger mound only local short distance current controlled sediment re dispersal is evidenced while iceberg rafting is identified as an important depositional mechanism throughout the whole mound development period furthermore evidence for icebergs repeatedly reaching the eastern porcupine seabight continental margin even in the early stages of northern hemisphere glacial expansion is preserved in the mound sequence supporting the existing coral stratigraphy the challenger mound depositional sequence reveals a two phase development separated by a significant hiatus the lower mound phase m1 2 6 1 7 ma indicates a semi continuous steadily changing fast accumulating current controlled depositional environment the condensed upper mound phase m2 998 1 5 ka bears witness of a distinct shift to a more glacially influenced low accumulation environment most likely resulting from a reduced capacity to deposit and or preserve sediments cold water coral density at the site of deposition is assumed to play an essential role in sediment deposition and preservation on challenger mound it enabled the preservation of a unique higher resolution record in the lower m1 sequence in the otherwise erosive non depositional early pleistocene environment along the nw european continental margin the potential of coral carbonate mounds as intermediate water depth continental margin plio pleistocene palaeo archives is thereby showcased

oceanic and atmospheric variations during the last deglaciation in the fram strait arctic ocean a coupled high resolution organic geochemical and sedimentological study abstract from a high sedimentation rate core obtained from the yermak slope arctic ocean we deduced short term climatic fluctuations of the last deglaciation lasting from 17 000 to 9000 years bp by using a coupled organic geochemical and sedimentological approach we reconstructed near bottom current conditions and assessed their significance in relation with comparable global thermohaline circulation patterns and surface water conditions highest concentrations and fluctuations of specific marine phytoplankton biomarkers were obtained in the bolling allerod when the major deglaciation of the svalbard barents sea ice sheet sbis occurred the marine biomarker record and the sedimentological record are consistent with climate reconstructions obtained from greenland ice cores and thermohaline circulation variations however beginning with the younger dryas yd episode bottom currents decreased during this time period but surface waters remained very productive the atmospheric conditions of the western fram strait reconstructed from biomarker data and thermohaline circulation signals reconstructed from sedimentological data were decoupled in the yd maximum insolation values of solar radiation and fohn like winds enabled open water conditions and increased productivity values in the northern fram strait at least in summer

late quaternary stage 2 and 3 meltwater and heinrich events northwest labrador sea two major meltwater events are documented in cores from the nw labrador sea one occurred ca 20 000 14c yr b p in association with deposition of a major detrital carbonate unit both prior to and after this event 18o values of near surface planktonic foraminifera were 4 5 indicating fully enriched glacial values a younger event ca 14 000 14 c yr b p is characterized by a dramatic change in 18o from 4 5 to 2 0 and coincided with the retreat of ice from the outer se baffin shelf possibly into hudson strait these meltwater events coincide with heinrich h layers 1 and 2 from north atlantic sediments the 14 000 14c yr b p meltwater event indicates that the eastern margin of the laurentide ice sheet also underwent rapid retreat at approximately the same time as other ice sheet margins around the ne north atlantic a third major detrital carbonate event at the base of hu87 033 009 possibly correlative with heinrich layer 3 occurred ca 33 960 675 14 c yr b p however this is older than the accepted date for h 3 of 27 000 14c yr b p and may be h 4

reflection of scandinavian ice sheet fluctuations in norwegian sea sediments during the past 150 000 years the record of glacier fluctuations in western scandinavia as reconstructed from continental data has been correlated with records of ice rafted detritus ird from well dated sediment cores from the norwegian sea covering the past 150 000 yr b p the input of ird into the ocean is used as a proxy for ice sheet advances onto the shelf and thus for the calibration of a glaciation curve the marine results generally support land based reconstructions of glacier fluctuations and improve the time control on glacial advances the saalian ice sheet decayed very rapidly approximately 125 000 yr b p in the early weichselian a minor but significant ird maximum indicates the presence of icebergs in isotope substage 5b especially between 95 000 and 83 000 yr b p reduced amounts of calcareous nannofossils indicate that surface waters were influenced by meltwater discharges during isotope substages 5d and 5b an extensive build up of inland ice began again during isotope stage 4 but maximum glaciation was reached only in early stage 3 58 000 53 000 yr b p marine sediments have minimum carbonate content indicating strong dilution by lithogenic ice rafted material generally the ird accumulation rate was considerably higher in stages 4 2 than in stage 5 a marked peak in ird accumulation rates from 47 000 to 43 000 yr b p correlates well with a second middle weichselian ice sheet advance dated by the laschamp olby paleomagnetic event minimum ice extent during the alesund interstade 38 500 32 500 yr b p and several glacial oscillations during the late weichselian are also seen in the ird record of several late weichselian glacial oscillations on the shelf at least four correspond to the north atlantic heinrich events ice sheet behavior was either coupled or linked by external forcing during these events whereas internal ice sheet mechanisms may account for the noncoherent fluctuations

hibonite bearing microspherules a new type of refractory inclusions with large isotopic anomalies reported are petrographic descriptions major and trace element chemistry and mg ca and ti isotopic compositions of a new class of refractory inclusions that consist of spherules composed of hibonite and a silicate glass the distinctive features of these inclusions are excesses in 48ca and 50ti in both glass and hibonite and 26mg depletions relative to terrestrial isotopic compositions three spherules have been examined and analyzed one from the lance co3 meteorite and two from the murchison cm2 meteorite lance 3413 1 31 la3413 1 31 and murchison 7 228 mur7 228 have euhedral to subhedral hibonite crystals enclosed within glass murchison 7 753 mur7 753 has a rounded hibonite core with several small inclusions of perovskite a small fragment of glass is attached to the hibonite and an fe silicate rim is imperfectly preserved around the grain la3413 1 31 has a group ii ree pattern mur7 228 a refractory pattern with depletions in the relatively volatile elements sr ba nb v and eu and mur7 753 a pattern characterized by the prior removal of an ultrarefractory component and overall fractionation of all rees the partitioning of the lrees between hibonite and glass in mur7 228 is consistent with equilibrium hibonite liquid partition coefficients previously determined la3413 1 31 shows much less partitioning while mur7 753 shows no evidence for partitioning and preserves an unequilibrated refractory component highly enriched in gd all spherules have initial magnesium depleted in 26mg by around 3 relative to terrestrial mg but only mur7 228 shows evidence for in situ decay of 26al with an initial 26al27al of 1 7 0 7 10 5 both hibonite and glass in all three spherules show excesses of 48ca and 50ti ranging up to 40 and 20 respectively relative to terrestrial ca and ti spherules such as these are rare and the only other occurrence is in the unique chondrite alh85085 the hibonite in the spherules shows similarities to isotopically anomalous hibonite crystal fragments placs but it is unlikely that the spherules formed by remelting of placs the precursors include isotopically anomalous ca ti carriers but also isotopically normal refractory components that probably formed as condensates the spherules formed by melting of these precursors under disequilibrium conditions and rapid cooling after hibonite crystallization these inclusions must have formed early prior to the dilution of isotopic anomalies by mixing processes and in an area characterized by excesses of 48ca and 50ti depletions of 26mg and lack of 26al

two unusual type b refractory inclusions in the ningqiang carbonaceous chondrite evidence for relicts xenoliths and multi heating abstract two type b refractory inclusions consisting mainly of melilite fassaite and spinel anorthite were found in the anomalous ningqiang carbonaceous chondrite the composition of melilite varies from ak4 15 near the diopside rims to ak80 90 in the centers of these inclusions in addition melilite exhibits intergrowths with fassaite and or anorthite in the centers of the inclusions these observations suggest that both inclusions were once molten the na2o content of melilite is positively correlated with the ak content for ak beyond crystallization from melts the ningqiang type b refractory inclusions contain possible relict fassaite fragments these fragments are embedded in gehlenitic melilite and have corroded outlines surrounded by highly tio2 enriched fringes as distinguished from the fassaites intergrown with melilite in the centers of the inclusions in inclusion nqj331 most grains of anorthite occur as irregular coarse grained fragments distinct from those intergrown with melilite toward these anorthite fragments melilite shows a steep decrease in ak content we propose that these anorthite fragments are xenoliths and were probably injected into the host while the latter was crystallizing palisades occur only in nqj331 and are probably relicts too distinctly low v2o3 concentrations of the spinels from the palisade bodies and the presence of palisade bodies consisting of one or more corroded crystals of fassaite anorthite are new lines of the evidence for a relict origin of palisades the other type b refractory inclusion nqj354 contains a spherule consisting of a grossite core and a spinel mantle enclosing laths of hibonite the modal abundance and mineral chemistry of the spinel hibonite spherule are distinctly different from the host inclusion we propose that the spinel hibonite spherule crystallized from a sio2 poor melt at a very high temperature and was injected into the type b host before the latter was completely solidified this grossite bearing spinel hibonite spherule may be related to the spinel hibonite spherules in cm2 chondrites

a robust multisite holocene history of drift ice off northern iceland implications for north atlantic climate an important indicator of holocene climate change is provided by evidence for variations in the extent of drift ice a proxy for drift ice in iceland waters is provided by the presence of quartz q

holocene history of drift ice in the northern north atlantic evidence for different spatial and temporal modes 1 we present new high resolution proxy data for the holocene history of drift ice off iceland based on the mineralogy of the 2 mm sediment fraction using quantitative x ray diffraction these new data bolstered by a comparison with published proxy records point to a long term increasing trend in drift ice input into the north atlantic from 6 to 5 ka toward the present day at sites influenced by the cold east greenland current this feature reflects the late holocene neoglacial or cooling period recorded in ice cores and further terrestrial archives on greenland in contrast a decrease in drift ice during the same period is recorded at sites underlying the north atlantic drift which may reflect a warming of this region the results document that holocene changes in iceberg rafting and sea ice advection did not occur uniformly across the north atlantic centennial scale climate variability in the north atlantic region over the last 4 kyr is linked to the observed changes in drift ice input increased drift ice may have played a role in the increase of cold intervals during the late holocene e g the little ice age cooling

debris in icebergs and rates of glaci marine sedimentation observations from spitsbergen and a simple model debris distribution and content in spitsbergen icebergs varies but basal debris rich layers often 1 m thick are the most important sources of iceberg rafted material angular iceberg rafted clasts in the glaci marine record imply the presence of nunataks or valley walls rather than unbroken ice sheet surfaces indicating paleo ice mass configuration calculated iceberg melt rates imply that most iceberg rafted debris is released within spitsbergen fjords sedimentation from icebergs is calculated as 1 mm a 1 for inner mollerfjorden and 8 mm a 1 for inner kongsfjorden an order of magnitude lower than total sediment inputs turbid subglacial meltwater is a more important debris source a simple model is proposed to calculate the flux of basal debris in icebergs and iceberg sedimentation rates

a calcium aluminum rich inclusion from the essebi cm2 chondrite evidence for captured spinel hibonite spherules and for an ultra refractory rimming sequence abstract an unusual refractory inclusion was discovered in the essebi cm2 chondrite the inclusion has high concentrations of refractory lithophile and siderophile elements with strong enrichments of the most refractory elements lu sc hf in one part of the inclusion the inclusion consists of a melilite rich core partially surrounded by a very refractory rim which in turn is covered by a mantle enriched in si al fe mn cl and s melilite compositions vary from ak 10 26 in the core to ak 0 12 in the rim the core contains several complex framboids consisting of spinel fassaite or spinel hibonite these framboids are probably spherules of the types reported from murchison and were possibly captured by the molten inclusion before it solidified these findings may indicate a genetic link between framboids in cai s and the spinel rich spherules in murchison the rim sequence consists of the following five layers from inside to outside 1 1 hibonite spinel melilite 2 2 hibonite perovskite spinel melilite melilite in this layer is altered to sodalite nepheline calcite 3 3 a hibonite corundum solid solution 4 4 a spinel corundum solid solution as much as 0 1 mole fraction al 2 67 o 4 5 5 sc rich fassaite as much as 6 2 wt sc 2 o 3 spinel al 2 o 3 solid solution al rich diopside pt rich metal crystals occur only in the rim some of these metal crystals contain minor amounts of zr and hf indicating that they formed under reducing conditions the bulk mineral chemistry and texture of the essebi inclusion indicates a complex history involving capture of solid spinel and spinel hibonite spherules similar to the murchison type by a refractory melt droplet solidification of the droplet without obliteration of the spherule textures transportation of the composite object to hotter regions of the solar nebula where the very refractory rim condensed alteration of melilite to sodalite nepheline minor calcite and finally burial in the essebi parent body the cl s bearing mantle probably formed by reactions between the inclusion and liquid and gaseous phases in the parent body

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

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

the microstructure of minerals in coarse grained ca al rich inclusions from the allende meteorite abstract the microstructure and microchemistry of minerals in ca al rich coarse grained inclusions cai from the allende meteorite have been investigated with transmission electron microscopy tem spinels contain only low to moderate dislocation densities and are characterized by a ubiquitous fine black spotty texture believed to originate from a slightly non stoichiometric composition ti al pyroxenes are relatively featureless but contain veins of secondary phases apparently deposited in unhealed cracks chromite has been identified in the veins suggesting transport of oxidized iron during alteration melilites exhibit the greatest variety of microstructures and are the most heavily altered phase in cai high dislocation densities are common and crystals exhibit considerable internal strain indicating that they have not been annealed alteration occurs both as veins along cracks and in fronts extending across several grains plagioclase is commonly twinned but dislocations are rare the size and morphology of antiphase domains suggest a high temperature of formation with significant low temperature annealing submicron pyroxene precipitates are a ubiquitous and unusual feature of allende plagioclase whose properties are most consistent with prolonged slow cooling and equilibration after plagioclase crystallization the precipitates appear to be sufficiently abundant to contain the majority of mg present in plagioclase but do not easily account for na and ti abundances wollastonite needles from a cavity in a fluffy type a inclusion exhibit the growth habits and relatively perfect external surfaces indicative of direct condensation from a vapor alteration products are predominantly crystalline and alteration of melilite appears to have proceeded primarily by solid state diffusion at a temperature of approximately 920 k overall the tem observations suggest that cai formed under near equilibrium conditions characterized by slow cooling and that solid state bulk diffusion was the major process affecting their post crystallization history

a comparative study of melilite and fassaite in types b1 and b2 refractory inclusions abstract most of the petrologic data available for type b inclusions comes from type b1s relatively little comes from the b2s and there has not been a systematic comparison of the properties of their two most abundant minerals in this work we document the compositions and zoning patterns of melilite and fassaite in type b2 inclusions and compare and contrast them with the features of their counterparts in type b1 inclusions we find that melilite compositions in type b2 inclusions are similar to those of type b1s with maximum ak contents of 75 mol and a positive correlation between ak and na 2 o contents asymmetrically zoned melilite is common in type b2s as are melilite grains with reversely zoned regions and the reversely zoned portions of crystals are thicker than in b1s in b2s like b1s fassaite is zoned with decreasing ti sc and v oxide contents from cores to rims of grains approximately half of the ti is trivalent but unlike that in b1s within fassaite grains in b2s the ti 3 ti 3 ti 4 ratio does not decrease from core to rim and sharp enrichments spikes in ti 3 and v are not observed sector zoned fassaite is much more common in b2s than in b1s the differences we observed can be accounted for by the differences in bulk compositions between b1s and b2s type b2 inclusions tend to have higher sio 2 contents hence higher an ge component ratios than type b1s phase equilibria show that compared to b1s in b2s less melilite should crystallize prior to the appearance of fassaite so that in b2s a higher proportion of melilite cocrystallizes with fassaite causing more of the crystals to be reversely zoned more melilite crystallizes while adjacent to other crystals leading to asymmetrical zoning and with more liquid available transport of components to growing fassaite occurs more readily than in b1s facilitating crystal growth and giving rise to sector zoning the lack of zoning with respect to ti 3 ti tot and the absence of ti 3 v rich spikes suggest that type b2 melts maintained equilibrium with the nebular gas throughout crystallization while the interiors of b1s were probably isolated from the gas perhaps by their melilite mantles this makes the similarity of na ak relationships in b1 and b2 melilite difficult to understand but apparently enclosure by melilite mantles was not necessary for the retention of na 2 o during crystallization of type b refractory inclusions

crystallization sequences of ca al rich inclusions from allende an experimental study the equilibrium crystallization sequence at 1 atmosphere in air of a melt corresponding in composition to the average composition of type b ca al rich inclusions from the allende meteorite is spinel 1550 c melilite 1400 c ak22 anorthite 1260 c ti al rich clinopyroxene 1230 c ti fassaite the melilite becomes increasingly akermanitic with decreasing temperature the pyroxene is similar in composition to fassaites from type b inclusions preliminary results suggest that the crystallization sequence is similar at oxygen fugacities near the iron wustite buffer the results of these experiments have been integrated with available phase equilibrium data in the system cao mgo al 2o 3 sio 2tio 2 and a phase diagram for predicting the crystallization sequences of liquids with compositions of coarse grained ca al rich inclusions has been developed available bulk compositions of coarse grained inclusions form a well defined trend in terms of major elements extending from type a and bl inclusions near the spinel melilite join to more pyroxene rich type b2 inclusions the trend deviates from the expected sequence of solid condensates from a nebular gas at p 10 3 atm if pure diopside is assumed to be the clinopyroxene that condenses the type a b1 end of the trend is similar in composition to calculated equilibrium condensates at 1202 1227 c and the trend as a whole parallels the sequence of condensates expected from diopside condensation at 1170 c the trend is consistent to first order with the condensation of solid ti rich fassaite in place of pure diopside at higher temperatures than those at which pure diopside is predicted to condense partially molten condensates may be likely in this case or if the nebular pressure is higher than 10 3 atm

okhotsk sea ice coverage and kamchatka glaciation over the last 350ka evidence from ice rafted debris and planktonic δ18o high resolution records of ice rafted debris ird and oxygen isotope records spanning an e w trending transect across the okhotsk sea unravel the marine and terrestrial cryogenic history of ne siberia over the last 350 kyr ird predominantly dispersed basin wide by sea ice shows lowest fluxes during interglacial periods implying a reduced and seasonal sea ice coverage highest ird accumulation rates are observed during glacial and deglacial periods with a more extended but highly dynamic ice cover although being rather synchronous ird fluxes are on average higher in the western okhotsk sea than in the eastern part pointing to a persistent but mobile particle supplying sea ice cover even during full glacial conditions presumably less dense in the eastern parts mis 6 is exceptional in this respect asynchronous fluxes of ird which vary spatially reflect rapid paleoclimatic and paleo glaciomarine changes ird accumulation rates were by factor 2 3 higher during mis 6 as compared to the last glacial maximum and the ird depositional center shifted from the western okhotsk sea early mis 6 toward kamchatka late mis 6 synchronous to a distinct change in the ird mineral composition both the characteristic composition of late mis 6 ird originating from the sredinny mountain range of kamchatka and their significantly enhanced accumulation rates refer to intensified iceberg dispersal across the eastern part of the okhotsk sea at 138 ka 135 ka 129 ka and 128 ka bp this scenario affords the presence of extended mountain glaciers protruding down to sea level on the western side of kamchatka anomalously light planktonic stable oxygen isotopes during mis 6 3 termination ii and mis 5 5 5 4 suggest significant freshwater supply related to the westward drainage of kamchatka glaciers the intensified kamchatka glaciation observed during late mis 6 was repeated during mis 3 iceberg discharges into the eastern okhotsk sea are observed at 60 ka 51 ka 42 ka 38 ka 36 ka and 31 ka and may partly correspond to n atlantic heinrich events

sea ice impact on long term particle flux in the greenland sea s is odden nordbukta region 1985 1996 five sediment traps deployed in the greenland sea at a depth of 500 m between 72 n and 75 n by the sonderforschungsbereich 313 kiel germany provide the necessary data to compare particle flux with ambient ice regimes sedimentation in this seasonally ice covered region is dependent upon the following three basic parameters 1 ice concentration 2 duration of ice cover and 3 distance from the ice edge these factors vary significantly with time and space we develop algorithms that provide annual sedimentation amounts for the area contained by 71 n to 76 n the greenland coast and 10 e for a severe ice year the area of seasonal ice cover and an 80 km wide band extending along the maximum extent of the ice edge the biological marginal ice zone bmiz combine to provide 92 of the total sedimentation for particulate organic carbon and silica this zone accounts for 89 each of the total sedimentation in a light ice year the respective percentages are 84 for dry weight 87 for particulate organic carbon and 81 for biogenic particulate silica these figures are slightly less than sedimentation for a severe ice year if the is odden nordbukta region is replaced by open ocean for purposes of comparison the bmiz out produces the open ocean for poc by a factor of 3 2 projecting the algorithms for the is odden nordbukta region to the rest of the greenland sea we conclude that the is odden nordbukta region is a substantial producer of sedimentation

holocene variations in mineral and grain size composition along the east greenland glaciated margin ca 67 70 n local versus long distance sediment transport quantitative x ray diffraction qxrd analysis of the 2 mm sediment fraction from surface sea floor samples and marine sediment cores that span the last 10 12 cal ka bp are used to describe spatial and temporal variations in non clay mineral compositions for an area between kangerlussuaq trough and scoresby sund 67 70 n east greenland bedrock consists primarily of an early tertiary alkaline complex with high weight of pyroxene and plagioclase farther inland and to the north the bedrock is dominantly felsic with a high fraction of quartz and potassium feldspars principal component pc analysis of the non clay sediment compositions indicates the importance of quartz and pyroxene as compositional end members with an abrupt shift from quartz and k feldspar dominated sediments north of scoresby sund to sediments rich in pyroxene and plagioclase feldspars offshore from the early tertiary basaltic outcrop coarse 2 mm or 1 mm ice rafted sediments are largely absent from the trough sediments between 8 and 5 cal ka bp but then increase in the last 4 cal ka bp compositional unmixing of the sediments in grivel basin and kangerlussuaq trough indicate the dominance of local over long distance sediment sources with pulses of sediment from tidewater glaciers in kangerlussuaq and nansen fjords reaching the inner shelf during the neoglaciation the change in ird is more dramatic in the sediment grain size proxies than in the quartz wt forty to seventy percent of the variance in the quartz records from either side of denmark strait is explained by low frequency trends but the data from the grivel basin east greenland are distinctly different with an approximate 2500 yr periodicity

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

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

evolution of the norwegian current and the scandinavian ice sheets during the past 2 6 m y evidence from odp leg 104 biogenic carbonate and terrigenous records abstract records of biogenic and terrigenous components have been obtained from the interval corresponding to the last 2 6 m y of odp sites 643 and 644 in order to reconstruct surface and deep water regimes in the norwegian sea surface water regimes record long lasting moderate glacial conditions during the interval 2 6 1 0 ma small intrusions of atlantic water episodically penetrated into the norwegian sea forming a narrow tongue along the eastern margin which is documented at site 644 the polar front was most probably situated between the site 644 and 643 locations on the outer voring plateau during these time intervals deep water regimes reflect long term persistent corrosive bottom waters most probably due to a weakly undersaturated water column and a low rate of carbonate shell production in surface waters deep water production in the norwegian greenland sea may have operated in a different way e g brine formation during winter sea ice growth bottom waters were oxygenated throughout the entire period and deep water was exchanged persistently with the north atlantic increased glacial interglacial environmental contrasts are documented reflecting a strengthening of the norwegian current and intensified glaciations on the surrounding land masses during the interval 1 0 0 6 ma during this time a major shift in the mode of deep water production occurred the onset of large amplitudes in glacial interglacial environmental conditions with maximum contrasts in surface water regimes different modes of deep water production and intensified exchange with the north atlantic marks the last 0 6 ma a broad development of the norwegian current is observed during peak interglacials while during glacials seasonally variable sea ice cover and iceberg drift dominate surface water conditions

reconstruction of glaciation over the past 6 myr from ice borne deposits in the norwegian sea it is well known that a significant intensification of northern hemisphere glaciation occurred 2 5 myr ago in contrast to the much earlier onset 35 myr of glaciation in antarctica1 3 much less is known about the behaviour of the climate before 2 5 myr and it has remained unclear when sizeable glaciers first started to develop in the northern hemisphere here we deduce the history of high northern latitude glaciation over the past 6 myr from records of ice borne deposits in deep sea sediments of the norwegian sea we find that glaciers large enough to reach sea level were present in the norwegian sea area as early as 5 5 myr three million years before the intensification of glaciation at 2 5 myr fluctuations in ice volume can be deduced from the oxygen isotope record but this provides only a global average which may not reflect the history of ice sheet growth in specific regions from a comparison of the oxygen isotope records with the record of ice rafted material we derive an estimate of the relative contributions of southern and northern hemisphere glaciation to global variations in ice volume

muddled or mixed inferring palaeoclimate from size distributions of deep sea clastics abstract one of the outstanding problems of palaeoclimate reconstruction from physico chemical properties of terrigenous deep sea sediments stems from the fact that most basin fills are mixtures of sediment populations derived from different sources and transported to the site of deposition by different mechanisms conventional approaches to palaeoclimate reconstruction from deep sea sediments do not distinguish between provenance and dispersal related variations and therefore often fail to recognise the true significance of variations in sediment properties we formulate a set of requirements that each proposed palaeo environmental indicator should fulfil and focus on the intrinsic coupling between grain size and chemical composition a critical review of past achievements in grain size analysis serves to introduce a conceptual model of spatio temporal grain size variation based on dynamic populations each dynamic population results from a characteristic combination of production and transport mechanisms that corresponds to a distinct subpopulation in the data analysed the mathematical statistical representation of the conceptual model can be obtained by means of the end member modelling algorithm emma applications of the model to several ocean basins are discussed as well as methods to examine the validity of grain size based palaeoclimate reconstructions palaeoclimate reconstructions of a high and low latitude basin illustrate the common degree of complexity of deep sea grain size records

pb isotopes and geochemical monitoring of arctic sedimentary supplies and water mass export through fram strait since the last glacial maximum 1 elemental and pb isotope measurements were performed on leachates and residues from surface sediments and two 50 cm cores mc04 and mc16 collected along a ne sw transect through fram strait geochemical and isotopic properties of residues from surface sediments define three distinct spatial domains within the strait 1 the easternmost edge of the strait 2 the eastern part of the strait off the svalbard margins and 3 the western part of the strait influenced by supplies from svalbard the nordic seas with possible contributions from northwestern siberian margins and sea ice and water outflow from the arctic respectively core mc16 in the third domain beneath the outflowing arctic waters spans the last glacial maximum present interval sediments from this core were leached to obtain detrital residues and exchangeable leachates fractions detrital supplies to core mc16 are believed to originate mainly from melting of the overlying sea ice and thus can be used to document changes in arctic sedimentary sources detrital 206pb 204pb and 208pb 206pb ratios illustrate two mixing trends trends a and b corresponding to the pre and post younger dryas yd intervals respectively these trends represent binary mixtures with a common end member canadian margins and either a siberian trend a or greenland trend b margin end member the yd is marked by an isotopic excursion toward the canadian end member suggesting a very active beaufort gyre possibly triggered by massive drainage of the laurentide ice sheet pb isotope compositions of leachates thought to represent the signature of the overlying water masses define a unique linear trend coincident with trend a this suggests that water masses acquired their signature through exchange with particulate fluxes along the canadian and siberian continental margins

ecology of deep sea benthic foraminifera in the north atlantic during the last glaciation food or temperature control abstract in this study we explore the paleoecology of nineteen species and two species groups of deep sea benthic foraminifera in relation to bottom water temperature and food supply in the central north atlantic during the last glaciation 60 000 28 000 years bp the study is based on core so82 02ggc taken from 1730 m water depth on the western flank of reykjanes ridge the climate of the investigated period was extremely unstable interrupted by thirteen warmings and coolings the so called dansgaard oeschger events at so82 02ggc surface and bottom water temperatures varied with up to 5 c between the warm interstadials and the cold stadials surface productivity as indicated by the flux of planktic foraminifera varied with a factor of up to ten the dansgaard oeschger events had a significant impact on the benthic foraminiferal faunas which experienced up to 70 replacement between the interstadials and stadials multivariate analysis reveals that the investigated species can be separated into two groups group 1 including bulimina costata brizalina subspinescens epistominella decorata and trifarina angulosa was attracted to higher temperatures and high food supply group 2 including pullenia bulloides valvulineria laevigata and melonis barleeanus was attracted to colder water and low food supply three species belonging to the cold group cibicidoides wuellerstorfi oridorsalis umbonatus and eponides tumidulus are almost exclusively confined to sediments rich in ice rafted detritus a few species including nonionella iridea and epistominella vitrea show opportunistic behaviour most species are epifaunal to shallow infaunal and live today in oligotrophic to mesotrophic habitats our investigations indicate that temperature was the primary factor responsible for the relative abundance and main grouping of species however four species show little influence by temperature and several perhaps most were clearly also affected by food supply

entrainment and export of laptev sea ice sediments siberian arctic sea ice sediments sis sediments rafted by ice and shelf surface deposits from the siberian laptev sea were analyzed to study turbulent entrainment processes this study focused on the silt and clay fractions on average representing 63 4 and 30 4 total 93 7 of the bulk sis respectively generally the sis contains 50 more silt than the shelf deposits while the clay percentages in both sample groups are similar sand sized particles are less abundant in sis than in bottom sediment although sis is clearly enriched in silt no evidence was found for preferential ice entrainment of any silt subfraction coarse medium fine statistical tests of sis and shelf silt parameters and the similar clay mineral compositions of both sample groups provide evidence for entrainment of laptev bottom deposits into newly forming ice the entrainment is related to the mechanism known as suspension freezing accordingly coarser clasts sand and plant debris may be lifted upward by buoyant anchor ice while coarse silt particles are supposed to be transported to the surface by rising frazil aggregates additionally turbulent interaction of convergent langmuir circulation and near surface frazil ice streaks is proposed to support ice entrainment of the finest particles 6 4 phi 12 m entrainment and export of sis from the laptev sea were assessed for ten individual flaw leads extended narrow polynyas separating fast and drifting ice using particle concentrations in ice samples and new ice formation rates the results show that roughly 20 mt of sis can be annually exported from the laptev sea by lead ice only thus formation and export of sediment laden lead ice may play a major geological role in siberian arctic shelf erosion and coastal retreat

paleoceanographic changes and calcium carbonate dissolution in the central fram strait during the last 20 ka article i nfo article history received 31 october 2011 available online xxxx a deep sea sediment core covering thelast20 ka and located between thepolar and thearctic fronts in themar ginal ice zone miz of the central fram strait has been investigated for changes in paleoceanography and calcium carbonatepreservation the reconstructionisbased on the distribution patternsofplankticforaminifera mean shell weight and the degree of fragmentation of their shells stable isotopes and other geochemical and sedimentological data the results show that the planktic foraminifera shells are poorly preserved throughout most of the record only the intervals comprising the early holocene from 10 8 to 8 cal ka bp and the last 800 yr show improved preservation of caco3 the dissolution correlated with the extent of arctic water and the associated marginal ice zone miz and high organic productivity dissolution of planktic foraminifera is generally high during the late deglaciation mid and late holocene prior to 800 cal yr bp the abundance of small subpolar species increases in the surface sediments dating from the last century which could be interpreted as a large and significant surface water warming however this apparent high magnitude warming seems to be overestimated due to preservation changes in the youngest sediments

refractory inclusions in the prototypical cm chondrite mighei abstract refractory inclusions in the mighei cm2 meteorite are very abundant 35 being found in three thin sections of the meteorite the most common are pyroxene rimmed spinel rich inclusions that occur in a range of structural and textural types some inclusions are simple aggregates of crystals or rimmed crystals ranging from loose clusters of spinel grains to distended chains of pyroxene rimmed spinel knots others are more compact and may have experienced recrystallization or melting these include nodular spinel inclusions with polygonal granular textured spinel interiors and pyroxene rims ribbons of spinel in some cases with hibonite and or perovskite that are again rimmed by pyroxene and refractory spherules four inclusions are complex aggregates of several texturally distinct objects each collectively mighei inclusions are similar to those in murchison but appear to be somewhat more altered volatility fractionated and unfractionated trace element patterns similar to those found in refractory inclusions in other carbonaceous chondrites are represented in mighei inclusions and in addition some mighei inclusions have volatility fractionated pattern types not previously found in refractory inclusions in three of the complex aggregates fundamentally different trace element patterns are present within different portions of each inclusion meaning that these objects accreted from genetically different components that never equilibrated with one another subsequent to accretion bulk inclusion magnesium isotopic compositions show minor mass fractionation effects fmg values range from 2 3 to 7 5 but the average fmg value is indistinguishable from normal 1 8 1 2 there are no correlations between magnesium isotopic composition and textural type or trace element pattern type the diverse inclusion types in mighei represent a variety of origins and histories textures suggest that the nodular and banded inclusions may have experienced solid state recrystallization whereas the porous and chain like varieties and complex aggregates have not magnesium isotopic compositions and trace element abundances suggest that the mighei inclusions are unlikely to be evaporation residues and are more likely to be the products of condensation or recondensation processes

complexly zoned chromium aluminum spinel found in situ in the allende meteorite in addition to the mg al 16o rich spinels that are known to occur in refractory inclusions the murchison meteorite contains cr rich 16o poor spinels most of whose sources are unknown because they are rarely found in situ here we report the in situ occurrence in allende of cr rich spinels found in 13 chondrules and 4 olivine rich objects the allende spinels exhibit major and minor element contents isotopic compositions and zoning of cr2o3 contents like those of the cr spinels from murchison some chondrules contain patchy zoned spinel simon et al 1994 which suggests that such grains did not form by sintering but perhaps by formation of overgrowths on relic grains unlike the olivine rich objects phases in all three chondrules that were analyzed by ion microprobe have uniform near normal o isotopic compositions one olivine rich object alsp1 has a huge 1 mm fragment of chevron zoned spinel this spinel has near normal o isotopic compositions that are quite distinct from those of adjacent forsteritic olivine which are relatively 16o rich and plot on the calcium aluminum inclusion cai line like some isolated forsterite grains found in allende the spinel and olivine in this object are therefore not genetically related to each other another olivine rich object alsp11a contains a rectangular 150 s 100 m homogeneous spinel grain with 50 wt cr2o3 and 23 wt feo in a vuggy aggregate of finer grained 5 90 m feo rich fo47 55 olivine the magnesian core of one olivine grain has a somewhat 16o rich isotopic composition like that of the large spinel whereas the feo rich olivine is relatively 16o poor the composition of the spinel in alsp11a plots on the cai line the first cr rich spinel found to do so chevron zoned spinel has not been observed in chondrules and it is unlikely that either alsp1 or alsp11a were ever molten calculations show that a spinel with the composition of that in alsp1 can condense at 1780 k at a ptot of 10 3 atm and a dust gas ratio of 100 relative to solar the cr rich spinel in alsp11a could condense at 1420 k but this would require a dust gas enrichment of 1000 relative to solar the data presented here confirm that as in murchison the coarse cr rich spinels in allende are relatively 16o depleted and are isotopically distinct from the 16o enriched mgal2o4 from cais sample alsp11a may represent a third population one that is cr rich and plots on the cai line that the o isotopic composition of alsp1 is like those of cr rich spinels from chondrules indicates that o isotopic compositions cannot be used to distinguish whether grains from such unequilibrated objects are condensates or are fragments from a previous generation of chondrules

arctic ocean during the last glacial maximum atlantic and polar domains of surface water mass distribution and ice cover on the basis of 52 sediment cores analyzed and dated at high resolution the paleoceanography and climate of the last glacial maximum lgm were reconstructed in detail for the fram strait and the eastern and central arctic ocean sediment composition and stable isotope data suggest three distinct paleoenvironments 1 a productive region in the eastern to central fram strait and along the northern barents sea continental margin characterized by atlantic water advection frequent open water conditions and occasional local meltwater supply and iceberg calving from the barents sea ice sheet 2 an intermediate region in the southwestern eurasian basin up to 84 85 n and the western fram strait characterized by subsurface atlantic water advection and recirculation a moderately high planktic productivity and a perennial ice cover that breaks up only occasionally and 3 a central arctic region north of 85 n in the eurasian basin characterized by a low salinity surface water layer and a thick ice cover that strongly reduces bioproduction and bulk sedimentation rates although the total inflow of atlantic water into the arctic ocean may have been reduced during the lgm its impact on ice coverage and halocline structure in the fram strait and southwestern eurasian basin was strong

laminated sediments preceding heinrich event 1 in the northern north sea and southern norwegian sea origin processes and regional linkage abstract rapidly deposited laminated sediments dated between 18 and 21 cal ka bp have been observed at several core locations in the northern north sea and the southern norwegian sea sedimentation rates range from 20 cm ka up to 2000 cm ka compared to a normal background sedimentation rate in the area of 5 10 cm ka dropstones in situ paired bivalves and grain size distribution indicate a hemipelagic origin for the laminae in core md99 2291 from the upper continental slope of southern norway ams radiocarbon dating and cyclic changes in the number of planktonic foraminifera and lithological parameters suggest that the laminations in the core are annual varves the laminated sediments are interpreted to be suspension plume deposits and two phases of plume deposition have been dated to 21 5 and 18 6 cal ka bp large fluxes of meltwater were generated during this period as reflected in oxygen and carbon isotopes records from cores in the area the meltwater and the laminated plume deposits are interpreted to be associated with the presence and disintegration of the norwegian channel ice stream observations from other regions demonstrate that laminated high rate deposition is very widespread on glaciated continental margins around 18 6 cal ka bp increases in sediment fluxes also occurred on the barra fan the north sea fan the lofoten contourite drift and the svalbard margin preceding increased sediment and meltwater fluxes on the greenland margin and the labrador sea associated with heinrich event 1 warm water inflow to the norwegian sea together with rising sea level probably triggered the destabilisation of the ice streams of the fennoscandian ice sheet while a similar response of the laurentide ice sheet was delayed by 500 1000 yr