oxygen and carbon isotope record of east pacific core v19 30 implications for the formation of deep water in the late pleistocene north atlantic abstract a detailed oxygen and carbon isotope record has been obtained from benthic foraminifera in core v19 30 from the carnegie ridge on the south side of the panama basin expressing these records and the oxygen and carbon isotope records previously published for atlantic core m 12392 on a common timescale it is apparent that the oxygen isotope records are very similar but that the carbon isotope records are quite different by obtaining the carbon isotope gradient between the two sites as a function of time we show that the production of north atlantic deep water has varied over a wide range during the late pleistocene and that the pattern of variation is not simply related to the well known oxygen isotope record although the two oxygen isotope records are very similar changes in the interoceanic gradient are detectable and support the hypothesis that in the glacial mode the north atlantic was colder and less oxygenated than it is today shackleton s 1 1977 interpretation whereby the carbon isotope record from the atlantic core reflects changes in the terrestrial biomass is an over simplification however the record from the pacific core v19 30 probably can be explained in these terms since it probably approximates the carbon isotope record of global mean oceanic dissolved co 2

body wave traveltimes and a spherically symmetric p and s wave velocity model summary the derivation of a spherically symmetric reference earth model is a subject which has recently regained interest after a decade of studies on lateral heterogeneity we now have the tools to approach the problem an iaspei working group on traveltime tables was formed in 1988 with the goal of deriving a reliable and up to date radial model of seismic velocities following the guidelines developed by that working group we have investigated the body wave traveltimes for several branches frequently reported in the isc bulletins and propose here a model for p and s wave velocities consistent with these data approximately 16000 best recorded shallow focus earthquakes are selected from 24 years of isc bulletins 1964 1987 and relocated using among others corrections for lateral heterogeneity from this dataset we derive summary traveltime curves specified for each degree of epicentral distance for p pcp p pkpab pkpbc pkikp and s to constrain velocity at the top of the outer core we include data for sks and skks sks from hales roberts 1970 1971 our discrete time distance curves are obtained by evaluating the shape of the residual density distribution independently for each 1 interval to limit contamination due to the interference of other branches precursors or late readings in the upper mantle the resulting model sp6 differs from iasp91 kennett engdahl 1991 only by slightly higher p and s velocities between 410 and 660 km in the lower mantle new velocity profiles have lower velocity gradients this is also true in comparison with prem dziewonski anderson 1981 at the top of the outer core vp is smaller than in prem and the velocity jump at the inner core boundary is reduced to the value of 0 62 km s 1 the new inner core radius is 1215 km our model predicts traveltimes that differ from the iasp91 tables considerably although generally less than 1 s except for sks and skks for which the differences are greater

quaternary sediments and environments on the continental shelf off northern norway abstract based on lithologic palaeontologic and chronostratigraphic investigations of close to 200 gravity cores from troughs deep banks and shallow banks the following late quaternary environment can be outlined in the weichselian deposition of basal tills was followed by deposition of laminated clay in a sea ice environment later a pebbly pelite was deposited in the troughs at the same time as the banks were iceberg ploughed then 13 000 yrs b p a period with incipient winnowing occurred on the deep banks and deposition of sandy pelite took place in the troughs the holocene commenced with a marked environmental change due to intrusion of atlantic water the fauna changed from arctic to boreal high energy winnowing forming a lag deposit took place on the banks and high accumulation rates in the troughs occurred due to the winnowing and sediment influx from the downwasting continental icesheet during the later part of the holocene the winnowing diminished on the deeper banks on the shallow banks and on the shelf break it still prevails and in the troughs calcareous sandy mud is being deposited the surface sediments comprise three main facies bouldery and pebbly sand sand and sandy mud whose distribution mainly depends on the prevailing bottom current regime the composition of the older quaternary sediments is demonstrated by some selected seismic profiles

deep sea carbonates reading the carbon isotope signal the carbon isotope signal in deep sea sediments reflects a mix of 1 global changes in the rates of exchange of the ocean s carbon reservoir with biosphere soil and sediments 2 global and regional changes in surface water productivity 3 internal shifts in water mass structure and circulation basin basin fractionation oxygen minimum development and 4 organism specific fractionation effects due to changes in micro habitat and or ontogenic fractionation vital effects additional complications arise from differential preservation it is impossible to entirely isolate these various factors as a rule of thumb long period signals that are parallel for planktonic and benthic data reflect external global fractionation patterns whilst short period signals are more likely tied to internal patterns water mass fractionation the various approaches to interpretation are illustrated with three case studies the glacial holocene transition the messinian carbon shift and the miocene monterey excursion

deglacial warming of the northeastern atlantic ocean correlation with the paleoclimatic evolution of the european continent abstract isotopic micropaleontologic and pollen analyses of deep sea cores from the bay of biscay and the northeastern atlantic ocean show that the deglacial warming of this oceanic area was closely correlated with the paleoclimatic evolution of the adjacent european continent temperatures were at least as warm as those of today in the bay of biscay between 13 300 and 11 000 b p coinciding with the combined bolling allerod warm continental events a major spread of polar water occurred between 11 000 and 10 000 b p during this event which coincides with the younger dryas continental cold event marine temperatures were almost as low as those of the last glacial maximum the final deglacial warming of the norteastern atlatntic ocean occurred during the following 3000 yr

comment on wave propagation effects and the earth s structure in the lower mantle in a recent contribution haddon and buchbinder introduced a new shear velocity model for the lower mantle which combined with effects of velocity inhomogeneity at the base of the mantle they concluded to be consistent with observed sh arrivals preceding the core reflected phase scsh at distances beyond 70 o using kirchhoff wave theory they computed synthetic waveforms for the radially symmetric version of their model which has a 1 4 discontinuous velocity decrease at 2300 km depth that seem to match some sh data even without allowing for lateral heterogeneity however synthetic waveforms for this model computed using generalized ray theory and reflectivity do not match the kirchhoff synthetics or the data casting doubt upon the conclusions drawn in their study earlier models by lay and helmberger involving a 2 75 discontinuous velocity increase at a depth of about 2600 km require only slight modification in order to match all of the sh wave observations

a deglacial middle holocene record of biogenic sedimentation and paleoproductivity changes from the northern norwegian continental shelf 1 the relative proportions of marine organic carbon and biogenic carbonate in a high resolution record from a glacial trough on the northern norwegian continental shelf were used to decipher changes in biogenic sedimentation and paleoproductivity from the last deglaciation to the middle holocene decadal scale to century scale oscillations in biogenic sedimentation and surface ocean productivity recorded in the andfjorden sediments are synchronous with abrupt climate changes in open oceanic and atmospheric regimes of the high northern latitudes following several fluctuations during the bolling allerod interstadial the most dramatic drop in marine organic carbon and biogenic carbonate proportions occurred during the younger dryas however many short term and low amplitude events during the preboreal and the holocene have also affected biogenic sedimentation in the outer andfjorden apparently these abrupt changes in biogenic sedimentation were caused by the suppression of a potential upwelling center in the outer andfjorden by variable atlantic water inflow over the past 14 000 years the adjustment of decadal high productivity coastal systems to freshwater forced multiple cooling events during the late glacial to middle holocene highlights the impact of global climate changes on the climate sensitive local ecosystems off coastal norway

implications of a connection between clay mineral variations and coarse grained debris and lithology in the central norwegian greenland sea abstract a sediment core from the central norwegian greenland sea has been studied for sedimentary features and clay mineral composition during numerous events within isotope stage 6 relatively high contents of kaolinite as well as a distinctive dropstone association originating from the barents shelf were rafted to the southwest by rapidly melting ice causing the formation of dark diamictons the strong variations in the smectite content in glacial periods were controlled mainly by ice transport rather than by current transport the main source area is the shelf of the faeroe islands

evidence for an s velocity discontinuity in the lowermost mantle beneath the south eastern pacific basin we used tangential component sh waveforms with s scs ss and sscs arrivals of chilean earthquakes recorded by four seismographic stations located in antarctica to study the radial velocity structure at the core mantle boundary cmb beneath the south eastern pacific basin the selected station event pairs give information on two distinct close patches of d beneath the bellingshausen sea in one of these regions an anomalous arrival interpreted as a reflection at the top of d sds phase is seen between s and scs together with early arrivals of scs this observation is well fit by adding to global reference model sp6 a reflector 315 km above the cmb marking a 3 s velocity increase the new velocity model usb2 fits both sds and scs travel times and amplitudes available data do not provide clear evidence to confirm or refute the presence of a similar velocity discontinuity in the second patch

stable isotope stratigraphy and paleoceanography during the last deglaciation on the continental shelf off troms northern norway a stable oxygen and carbon isotope stratigraphy is established for a late weichselian holocene glaciomarine marine sequence in andfjorden and malangsdjupet on the continental shelf off troms northern norway the stratigraphy demonstrates that the global signals termination i b and possibly also i a upper parts are present and radiocarbon date to 10 3 9 7 kyr b p and 14 13 5 kyr b p respectively a temperature increase of 5 6 c and possibly a small salinity increase occurred during term i a near glacial environment between 13 and 14 kyr b p was characterized by poorly ventilated bottom waters followed by a meltwater pulse at circa 13 kyr b p during the beginning intrusion of atlantic water between 13 and 10 kyr b p the bottom water was characterized by somewhat fluctuating temperatures and salinities temperatures close to those of the present were established around 9 7 kyr b p and seem to have been rather stable since

foraminiferal stratigraphy and environment of late weichselian deposits on the continental shelf off troms northern norway abstract based on the analysis of 8 selected gravity cores from the upper sediment layers of andfjorden and malangsdjupet off northern norway six late weichselian foraminiferal assemblage zones are defined the two oldest assemblage zones 8 and 7 are found in basal tills and contain mixed faunas reworked and deposited by glaciers which reached the shelf edge during the early late weichselian during the earliest phase of the deglaciation of the continental shelf a sparse fauna characterized by buccella frigida zone 6 was deposited zone 5 is dominated by cassidulina laevigata and a fairly high content of planktic foraminifera indicating periods of ice free normal marine surface waters during a glacial advance between 14 000 and 13 000 b p the fauna zone 4 was dominated by elphidium excavatum this fauna reflects near glacial conditions characterized by unstable bottom water conditions the last c 500 years of this period suffered from oxygen depleted bottom waters zone 3 formed between 13 000 and 10 000 b p comprises several species e g cassidulina reniforme nonion barleeanum n labradoricum and cibicides lobatulus during the first 2000 years of this period the fauna reflects a climatic amelioration e g an increase in temperature salinity and current activity probably due to intrusion of atlantic water during the younger dryas zone 3 reflects a climatic deterioration

reconstruction of the last deglaciation deconvolved records of δ18o profiles micropaleontological variations and accelerator mass spectrometric14c dating bioturbation acts as a low pass filter in displacing and reducing the amplitudes of stratigraphic signals this often leads to a loss of high frequency events in the stratigraphic record in addition when considering an isotopic signal 18o 14c measured in stratigraphic carriers such as foraminifera bioturbation and carrier abundance changes can create artifacts which may be falsely interpreted as leads or lags in the paleoclimatic record

13c record of benthic foraminifera in the last interglacial ocean implications for the carbon cycle and the global deep water circulation the 13c 12c ratios of upper holocene benthic foraminiferal tests genera cibicides and uvigerina of deep sea cores from the various world ocean basins have been compared with those of the modern total carbon dioxide tco2 measured during the geosecs program the 13c difference between benthic foraminifera and tco2 is 0 07 0 04 for cibicides and 0 83 0 07 for uvigerina at the 95 confidence level 13c analyses of the benthic foraminifera that lived during the last interglaciation isotopic substage 5e about 120 000 yr ago show that the bulk of the tco2 in the world ocean had a 13c value 0 15 0 12 lower than the modern one at the 95 confidence level reflecting a depletion compared to the present value of the global organic carbon reservoir regional differences in 13c between the various oceanic basins are explained by a pattern of deep water circulation different from the modern one the antarctic bottom water production was higher than today during the last interglaciation but the eastward transport in the circumpolar deep water was lower

the east greenland continental margin 65 n since the last deglaciation changes in seafloor properties and ocean circulation nine gravity cores collected on the east greenland continental margin off kangerdlugssuaq fjord reveal a drastic decrease in average sedimentation rates from the cross shelf through the continental slope from 43 2 cm kyrs to 2 2 cm kyrs respectively since the last deglaciation beginning at 2g cm2kyrs at 4000 yrs b p both caco3 and non caco3 accumulation rates became high g cm2kyrs since 3000 yrs b p these rates distinctly decreased melting of glaciers and current activity which drastically changed in space and time controlled the terrigenous sediment input and thus the grain size distribution and the physical properties of sediments across the shelf these observations suggest that current winnowing on sediments is one of the dominant processes at present this is seen in the acoustic reflectivity and in the acoustically hard seafloor particularly at the upper continental slope in addition icebergs transported southward along the continental margin have scoured the sediment surface in water depths 350m

direct dating of the oxygen isotope record of the last deglaciation by 14c accelerator mass spectrometry major trends of quaternary global climate are reflected in the continental ice volume changes which have been reconstructed by oxygen isotope analysis1 2 18o records from deep sea sediments show that the net glacial build up occurs relatively slowly3 but that the end of an ice age occurs quickly in less than 10 000 yr implying a nonlinear response4 5 to simple milankovitch theory6 the latter observation suggests that the cause of the most recent deglaciation was the maximum in summer calorific radiation at the upper latitudes of the northern hemisphere centred around 11 000 yr ago a view supported by early studies7 later work has produced conflicting dates the main source of confusion being problems with obtaining accurate and reliable dates here by using accelerator mass spectrometry we have measured 14c for various species of foraminifera to produce a reliable timescale for the oxygen isotope record our results show that at the end of the last ice age continental ice sheets began to melt more than 4 000 yr before the northern hemisphere maximum of summer calorific radiation

two step deglaciation 14c dated high resolution δ18o records from the tropical atlantic ocean abstract eight box cores from the tropical atlantic were studied in detail with regard to foraminiferal oxygen isotopes radiocarbon and globorotalia menardii abundance a standard atlantic oxygen isotope signal was reconstructed for the last 20 000 yr it is quite similar to the west equatorial pacific signal published previously deglaciation is seen to occur in two steps which are separated by a pause onset of deglaciation is after 15 000 yr b p the pause is centered between 11 000 and 12 000 yr b p but may be correlative with the younger dryas 10 500 yr b p if allowance is made for a scale shift due to mixing processes on the sea floor step 2 is centered near 10 000 yr b p and is followed by a brief excursion toward light oxygen values this excursion the m event may correlate with the gulf of mexico meltwater spike

lateral variations in d thickness from long period shear wave data we explore global variations in d shear wave structure by examining 12 years of long period global digital seismograph network gdsn data to identify reflected phases from the d layer in the lowermost mantle we restrict our search to epicentral distances between 63 and 74 where a precritical d reflection will lie between the s and scs arrivals with gdsn long period records a d signal at these ranges is generally obscured by the stronger neighboring phases so to isolate the d reflections we develop a technique for stripping away the interfering s and scs waveforms we interpret travel time variations in the observed sds phases in terms of variations in d thickness and generate maps of inferred d thickness for areas of good seismic coverage the regions of observed d reflections are beneath australasia north central asia the arctic alaska and central america we find considerable variation in d structure in these regions a result consistent with previous studies which have found evidence for lateral heterogeneity in d on average the estimated d thickness is 260 km but there is a fairly uniform distribution of thicknesses between 150 km and 350 km a possible correlation is observed between d thickness and regions of predicted strong horizontal mantle flow

ocean circulation in the norwegian sea during the last deglaciation isotopic evidence abstract three cores from different depths in the southeastern norwegian sea have been investigated for benthic and planktonic foraminiferal stable isotope records the cores confirm that the last deglaciation occurred in two distinct steps the first step termination ia may have occurred at about 13 000 yr b p while the second step took place shortly after 10 000 yr b p the benthic oxygen isotopes reveal strong influence of deglacial intermediate waters possibly flowing in from the north atlantic with a maximum influence at about 12 000 yr b p both carbon and oxygen isotopic records show that bottom water formation in the norwegian sea was reinitiated after 12 000 yr b p during the first part of the deglaciation the deep water circulation pattern may have been opposite to that of the present the oxygen content in the norwegian sea deep water was low during the last glacial maximum and remained low during the first part of the deglaciation due to low vertical circulation rates the large variations in deep water circulation in the norwegian sea during the last deglaciation may have had important consequences for the interchange of co 2 between ocean and atmosphere

new faunal and isotopic evidence on the late weichselian holocene oceanographic changes in the norwegian sea downcore studies of planktonic and benthonic foraminifera and 18o and 13c in the planktonic foraminifer neogloboquadrina pachyderma sin in two piston cores from the southern part of the norwegian sea suggest large changes in the oceanic circulation pattern at the end of oxygenisotope stage 2 and in the early part of stage 1 prior to oxygen isotope termination ia 16 000 13 000 yr b p an isolated watermass with lower oxygen content and temperature warmer than today existed below a low salinity ice covered surface layer in the norwegian sea close to termination ia well oxygenated deep water probably with positive temperatures was introduced this deep water which must have had physical and or chemical parameters different from those of present deep water in the norwegian sea could have been introduced from the north atlantic or been formed within the basin by another mechanism than that which forms the present deep water of the norwegian sea a seasonal ice cover in the southern part of the norwegian sea is proposed for the period between termination ia and the beginning of ib close to 10 000 yr b p the present situation with strong influx of warm atlantic surface water and deep water formation by surface cooling was established at termination ib

macrofaunal palaeoecology and stratigraphy in late quaternary shelf sediments off northern norway abstract in a late pleistocene holocene glaciomarine marine sequence a minimum of 115 taxa macrofossils and trace fossils are recognized on the basis of 690 samples from gravity cores from andfjorden nine and malangsdjupet one the biostratigraphy is proposed on the basis of reconstructions of autochthonous macrofaunal assemblages a total of seven zones are defined five in the pleistocene and two in the holocene the ages of which are estimated by radiocarbon datings in ascending order the zones are mixed assemblage zone barren interzone arctinula greenlandica assemblage zone before 14 000 yr b p yoldiella intermedia assemblage zone 14 000 13 000 yr b p bathyarca glacialis assemblage zozne 13 000 yr b p bathyarca glacialis kelliella miliaris interval zone 10 000 ca 7800 yr b p and kelliella miliaris assemblage zone ca 7800 present the bathyarca glacialis zone is divided into three faunules i 13 000 12 000 yr b p ii 12 200 11 100 yr b p and iii 11 100 10 000 yr b p the palaeoecology of the faunal succession is elucidated by means of the sample frequency method two major environmental events have influenced the faunal history the first was the onset of the deglaciation of the thoughs the second the intrusion of the norwegian current bringing warm saline atlantic water into the troughs at 10 000 yr b p the pleistocene fossils demonstrate an arctic macrofaunal succession from a low order stage to a high order equilibrium stage that is in principle identical to that of a modern faunal development in fjords following a disturbance causing anoxia an estimated polychaete mollusc ratio together with changes in sediment influx depositional rates and grain size of substrate indicate the presence of different energy regimes where the inner and outer reaches of andfjorden are compared about 10 000 yr b p a major faunal change took place the previous arctic fauna was replaced by a boreal fauna which developed into the modern fauna the most important factor causing the replacement and renewed faunal succession were probably the rise in temperature and salinity as well as an increase in nutrient supply brought about by the intrusion of the norwegian current a comparison with shallower shelf areas indicates a somewhat different faunal composition in the pleistocene brought about by different depositional environments however a similar major faunal change took place at 10 000 yr b p and there are fewer discrepancies among the holocene faunas regional comparison indicates that some of the phases in the development of the fauna probably are rather local while other have a more regional nature

structure and timing of the last deglaciation oxygen isotope evidence foraminiferal oxygen isotope data from 24 tropical atlantic sediment cores constrained by 77 14c dates are stacked to form a composite record of isotopic termination 1 this record indicates that most of the isotopic transition at the end of the last ice age occurred between 14 ka bp and 6 ka bp minor isotopic expression of deglaciation is permitted as early as 16 ka bp but the most rapid rate of change occurred between 14 ka bp and 12 ka bp three steps of maximum change are present although they are close to the statistical limits of detection in the composite record the clear presence of the steps in individual records suggests that they are real we estimate their timing at 14 12 ka bp termination 1 a 10 9 ka bp termination 1 b and 8 6 ka bp termination 1 c centering of the termination near 11 ka bp is consistent with the milankovitch hypothesis that high summer insolation caused deglaciation in detail however maximum rates of change prior to the 11 ka bp insolation extreme and the inferred steps require additional mechanisms controlling the tempo of glacial interglacial climate change steps equivalent to those in 18o have not been detected in ice margin retreat data steps in the isotopic transition if real may record thinning of the ice sheets not accompanied by loss of area alternation between near equilibrium and near stagnant ice sheet profiles during deglaciation is hypothesized perhaps due to calving and unstable down draw of the ice sheets followed by partial re equilibration significant problems remain the effects of temperature on the isotope record are only partially constrained presently available data allow only semi quantitative intercalibration of ice volume sea level and isotopic estimates of glaciation

pyritization of tubes and burrows from late pleistocene continental shelf sediments off north norway four different types of pyritized tubes and three types of pyritized burrow fillings are described from pleistocene glaciomarine sediments in andfjorden northern norway the tubes and burrows probably originated from tubicolous and burrowing polychaetes respectively the decomposition of the organic matter in the tubes and burrows created a reducing micro environment favouring precipitation of pyrite by comparison with holocene tubes from marine sediments in andfjorden and fuglosyfjorden it is seen that pyritization commenced with isolated spherules these spherules with incipient pyrite crystals and framboids were formed mainly on the inner wall of the tube presence of a monosulphide in the holocene fugloyfjorden material suggests that the pyritization process has reached a later phase the final result would be a completely pyritized trace fossil it is shown that single pyrite crystals octahedra generally attain greater size in the burrow fillings than in the tubes the microstructure found in some of the pyritized tubes is interpreted as a reflection of the microstructure in the original wall finally the implications for the depositional environment in pleistocene in andfjorden is investigated with reference to the benthic skeletal macrofaunal assemblage in the sequence the pyritized trace fossils occur frequently in an opportunistic assemblage from a period c 14 000 13 000 yr bp characterized by some oxygen deficiency later 13 000 10 000 yr bp they play a minor role in an established assemblage under improved oxygen conditions

stable isotope fractionation in live benthic foraminifera from the southern california borderland live specimens of benthic foraminifera have been analyzed from surface sediment samples collected from 108 to 1134 m depth in the southern california borderland the temperature and isotopic composition of the ambient water and dissolved inorganic carbon have also been measured to permit comparison of foraminiferal compositions to expected equilibrium values the species analyzed break down into four groups which reflect the influence of mineralogy aragonite vs calcite biological fractionation vital effect and microhabitat effects on isotopic composition the aragonitic hoeglundina elegans show an enrichment in 18o relative to equilibrium calcite of 0 41 0 in shallower water increasing to at least 1 06 0 in deeper water the 13c enrichment of h elegans relative to the dissolved inorganic carbon dic is also depth dependent increasing from 1 27 0 at 108 m to 2 13 0 at 940 m this depth dependence results from the change in composition of the dic the 13c composition of h elegans remains constant with depth for some unknown reason one possible explanation is that the change in composition of the dic is balanced by an increase in hoeglundina hco 3 fractionation with decreased temperature the 13c values of the cassidulina species are almost identical to those of the ambient dissolved inorganic carbon dic and reflect the decrease in the 13c of the dic with depth the 13c values of species not in 18o equilibrium vary independently of the changing composition of the dic there is a correlation between 13c and 18o among coeval species consistent with the model which explains vital effect as the result of incorporation of isotopically light metabolic co2 into the shell the magnitude of disequilibrium is relatively constant for 18o but not for 13c suggesting that in isotopic stratigraphy studies it may be difficult to calibrate the 13c of different species as has been done with 18o there appears to be a relationship between taxonomic group and vital effect the foraminifera in approximate 18o equilibrium with the water including species of cassidulina bolivina uvigerina and globobulimina are members of the family cassidulinidae or superfamily buliminacea those not in 18o equilibrium including species of pyrgo quinqueloculina triloculina and lenticulina belong to the families miliolidae and vaginulinidae no disequilibrium species have been found as yet in the low oxygen environments of the borderland this observation and published findings on the ultrastructure of benthic foraminifera suggest that isotopic behavior may be related to a foraminifer s ability to exchange gases rapidly with its ambient water

a lower mantle s wave triplication and the shear velocity structure of d summary a lower mantle s wave triplication detected with short and longperiod wwssn and csn recordings indicates a substantial shear velocity discontinuity near 280 km above the core mantle boundary the triplication can be observed in rotated sh seismograms from intermediate and deep focus events throughout the distance range from 70 to 95 three distinct source region receiver array combinations that have been investigated in detail demonstrate consistent travel time and relative amplitude behaviour of the triplication with slight systematic shifts in the triplication indicating up to 40km variations in the depth of the discontinuity modelling of the observations with synthetic seismograms produced with the cagniard de hoop and reflectivity methods constrains the shear velocity increase to be 2 75 k 0 25 per cent comparable to upper mantle discontinuities short period observations indicate that the velocity increase may be a sharp first order discontinuity or may extend over a transition zone no more than 50 km thick the shear velocity gradient below the discontinuity within the d layer is not well constrained by the sh data but slightly positive or near zero velocity gradients are consistent with the long period amplitude ratios of scsh sh

carbon and oxygen isotopic disequilibria of recent deep sea benthic foraminifera abstract the carbon and oxygen isotopic compositions of 149 samples of benthic foraminifera from deep sea core tops indicate that none of the nine species studied secrete calcium carbonate in isotopic equilibrium with ambient bottom water uvigerina pyrgo murrhina and oridorsalis tener are the closest to 18o equilibrium with average deviations about 0 4 while planulina wuellerstorfi and p murrhina are the closest to 13c equilibrium with average deviations about 1 p wuellerstorfi shows the most systematic relationship between 13c and bottom water apparent oxygen utilization the intraspecific variabilities in 18o and 13c suggest that estimates of bottom water paleotemperatures can be made to a precision of 0 7 c while estimates of past apparent oxygen utilization aou can be made to 35 mol kg based on intraspecific comparisons of the recent samples with fossils no temporal changes in the degree of either 18o or 13c disequilibrium have been detected for planulina wuellerstorfi uvigerina oridorsalis tener and globocassidulina subglobosa

late weichselian deglaciation and early holocene development of a cold water coral reef along the lopphavet shelf northern norway recorded by benthic foraminifera and ostracoda cold water coral cwc settlement in northern norway is strongly related to the outlet glaciers of the fennoscandian ice sheet and dating of known cwc structures show clearly post glacial ages two gravity cores pos391 559 2 277 cm long and pos391 559 3 282 cm long were recovered on a cwc reef in the area of lopphavet northern norway detailed investigations on lithology sediment structures and composition micropaleontology foraminifera and ostracoda and ams 14c dating on the epibenthic foraminifera discanomalina coronata were performed on the two cores phosphorus analyses were performed only on core pos391 559 3 results indicate that the whole core pos391 559 2 is representative of a cwc reef environment the base of the core is dated at 10 600 120 cal yr bp thus representing one of the oldest ages of a norwegian coral reef core pos391 559 3 documents the passage from a proximal glacier environment characterized by fine silty sediments with intercalation of several dropstone layers to a cwc ecosystem the transition from the glacial to the interglacial stage is dated as old as 10 725 205 cal yr bp whereas the base of the core is dated to an age of 15 300 550 cal yr bp diversity of benthic foraminifera is higher within the cwc especially in the intervals containing coral framework five clusters are identified based on the bray curtis similarity term analyses and the interpretation of data shows that they are related to different ecological settings e g fluctuations of the sea ice cover influence of the warmer and more saline atlantic water masses transitional to a fully interglacial environment well oxygenated nutrient rich and high current setting being conducive to cwc ostracod assemblages show that these crustaceans may be also used to characterize sedimentary facies on cwc reefs

stable isotope composition of benthic foraminifera from the equatorial pacific when ranked according to deviation from isotopic equilibrium deep sea benthic foraminifera exhibit no correlation between the rankings for oxygen and for carbon both rank sequences are stable from east to west in the equatorial pacific fertility independent and from glacial to post glacial time independent records for the past 15 000 yr suggest marked changes in deep sea circulation during this time interval

mud volcanism an updated review abstract mud volcanism or sedimentary volcanism represents one of the most intriguing phenomena of the earth s crust with important implications in energy resource exploration seismicity geo hazard and atmospheric budget of greenhouse gases since the first review papers were issued at the beginning of 2000s a large amount of new geological geophysical and geochemical data has been acquired which clarified ambiguous concepts and significantly improved our knowledge of mud volcanism here we offer an updated review of the knowledge and implications of mud volcanoes with emphasis on the terminology used to describe different processes and structures the physical chemical and morphological characteristics of the several fluid emission structures the chemical properties of the released fluids in particular the molecular and isotopic composition of the gas the mud volcano formation dynamics and the several implications for petroleum exploration geo hazards and global atmospheric methane budget this review integrates new fluids data collected in azerbaijan and is complemented with field observations from various mud volcano provinces worldwide although the total number of mud volcanoes on earth is still uncertain 600 main onshore structures with a large variety in shapes and sizes are documented in recent global data sets and several thousand are assumed to exist in the oceans it is clear that a mud volcanoes are broadly distributed throughout the globe in active margins compressional zones of accretionary complexes thrust and overthrust belts passive margins deep sedimentary basins related to active plate boundaries as well as delta regions b they are specifically located in hydrocarbon bearing basins along anticline axes strike slips and normal faults and fault related folds in petroleum systems c they represent a specific category of natural gas oil seepage manifestation often related to deep and pressurised reservoirs d the main engine driving mud volcanism is given by a combination of gravitative instability of shales and fluid overpressure build up followed by hydrofracturing e hydrocarbons are generally of thermogenic origin while microbial gas is released in only a few cases mud volcanism on other planets e g mars and titan and microbial activity associated with gas seepage represent emerging issues and opportunities for future research

simulation of long period 3 d elastic responses for whole earth models summary improvements in gdsn seismic data quality and advances in numerical algorithms for solution of the wave equation now make it useful and feasible to simulate long period elastic responses for 3 d whole earth models the algorithm used is eighth order finite differencing on a staggered grid this allows stable computation at boundaries with large contrasts in poisson s ratio such as the core mantle boundary as the solution automatically generates all wave types it may lead to prediction of previously unobserved or misinterpreted phases and allow more detailed analysis of all phases simulations of large e g nuclear explosions and double couple earthquake sources reveal the effects on relative amplitudes of their respective radiation patterns in both wavefield snapshots and seismogram profiles a large number of phases are affected even by a single smooth bump on the core mantle boundary a 3 d whole earth model implicitly contains the travaltimes for all source receiver positions and for any source configuration the corresponding amplitudes of all phases thus 3 d numerical modelling of whole earth responses is a potentially valuable diagnostic and interpretive tool and a basis for globalization in contrast to regionalization of traveltime tables

stable isotopes in benthic foraminiferal calcite from a river influenced arctic marine environment kara and pechora seas oxygen and carbon stable isotope compositions of modern benthic foraminifera in the kara and pechora estuarine regions of the arctic continental shelf were compared with water 1 8 o 1 3 c d i c temperature and salinity the foraminiferal 1 8 o distribution is mostly similar to that of equilibrium calcite primarily controlled by mixing of runoff and seawater in near estuarine areas depth 15 20 m with additional temperature control seaward the 1 3 c composition is controlled by remineralization of organic matter mostly imported by rivers and by water mixing most analyses used the common arctic foraminifer elphidium excavatum forma clavata which yields depleted 1 3 c as expected for an infaunal species isotope records for sediment cores off the pechora and yenisey rivers show a decelerating rise in isotope values of up to 10 in 1 8 o over the last 10 kyr in a pattern similar to that of rising sea level and concomitant retreat of river mouths with local complexities probably resulting from glacio isostatic rebound and changes in sedimentation

paleoclimatic inferences from glacial fluctuations on svalbard during the last 20 000 years the climate history of western spitsbergen svalbard is deduced from variations of glaciers during the last 20 000 years a major depression of the regional equilibrium line altitude ela occurred during the late weichselian glacial maximum 18000 13000y ago when low summer temperatures may have caused year round snow accumulation on the ground this rapid expansion of the glaciers also indicates nearby moisture sources suggesting partly open conditions in the norwegian sea during the summers a rapid glacial retreat around 13 000 12 500 y bp was caused by a sudden warming during the younger dryas the ela along the extreme western coast of spitsbergen was not significantly lower than at present in contrast to fennoscandia the british isles and the alps there is no evidence for readvance of local glaciers during younger dryas on western spitsbergen this difference is attributed to a much dryer climate on spitsbergen and probably only slight changes in sea surface temperatures in addition summer melting in this high arctic area is more sensitive to orbitally increased insolation around 10 000 y bp another rapid warming occurred and during early and mid holocene the summer temperatures were significantly higher than at present a temperature decline during the late holocene caused regrowth of the glaciers which reached their maximum holocene position during the last century

evolution of seasonal stratification in the celtic sea during the holocene seasonal thermocline development in the shelf seas of nw europe results in the formation of pronounced frontal regions which separate stratified from well mixed water numerical m 2 palaeotidal modelling of the nw european continental shelf during successive stages of the holocene transgression indicates that seasonal stratification started to develop in the central celtic sea once a critical threshold water depth had been exceeded at around 9000 years bp this hypothesis has been tested through faunal isotopic and geochemical analysis of an ams 14 c dated british geological survey vibrocore from the celtic deep bathymetric basin a record which spans the last 12 000 years marked positive trends in the stable oxygen isotopic data from the benthic foraminifera ammonia batavus and quinqueloculina seminulum between 9000 and about 5000 years bp represent a 4 5 c cooling in summer bottom water temperature caused by the progressive replacement of tidally well mixed by stratified water stable carbon isotopic data from the same species measured through the same core intervals show a negative trend consistent with net oxygen utilization and decomposition of organic matter beneath the productive frontal zone these geological data indicate the progressive evolution of seasonally stratified water in the celtic sea during the earlier part of the holocene modern shelf sea frontal and thermocline development are known to influence biological productivity sedimentation rates the organic content of shelf sediments and the climate of surrounding landmasses hence these palaeodata have significance in defining the role of shelf sea environments in the climate system

stable isotope evidence for glacial lake drainage through the st lawrence estuary eastern canada 13 1 12 9 ka abstract postglacial varved and rhythmically laminated clays deposited during the transition from glacial lake vermont lv to the champlain sea cs record hydrological changes in the champlain st lawrence valley cslv at the onset of the younger dryas 13 1 12 9 ka linked to glacial lake drainage events oxygen isotope 18o records of three species of benthic foraminifera cassidulina reniforme haynesina orbiculare islandiella helenae from six sediment cores and the freshwater ostracode candona from one core were studied results show six large isotope excursions 0 5 to 2 in c reniforme 18o values five excursions in h orbiculare

evidence for a shear velocity discontinuity in the lower mantle beneath india and the indian ocean abstract sh and ssh seismograms are modeled to determine the shear velocity structure in the d region beneath india and the indian ocean the signals show waveform complexities similar to those observed in data sampling the d region beneath alaska the caribbean and eurasia lay and helmberger which have been attributed to a 2 7 shear velocity discontinuity 280 km above the core mantle boundary the new data set consists of long period tangential component recordings at wwssn stations in africa the middle east and europe for 11 intermediate and deep focus indonesian earthquakes in the distance range 70 82 the waveforms show an arrival between sh and scsh with systematic moveout from 89 to 94 there is a strong distortion of the sh waveforms indicating the arrival of several phases closely spaced in time the relative time shifts of similar complexity in the corresponding ssh phases requires a deep mantle origin the depth dependence and moveout of the interference effects are well predicted for both sh and ssh phases by a model with a lower mantle discontinuity alternative explanations of the interference as resulting from receiver reverberations sks contamination multiple source complexity or near source multipathing are ruled out by systematic tests while it is apparent that lateral variations in the lower mantle velocity structure prevent any single model from fitting all of the data synthetic waveform modeling using generalized ray theory and reflectivity shows that the data can be well fit by a model with a discontinuity similar in size and depth to that proposed for the previously investigated regions lay and helmberger but with a negative velocity gradient within the d layer

changes in the oceanic 13c 12c ratio during the last 140 000 years high latitude surface water records detailed records of the carbon and oxygen isotopic ratios of neogloboquadrina pachyderma are compared between nine high latitude sediment cores from the northern and southern hemispheres covering the last 140 000 yrs the strong analogies between the 13c records permit to define a 13c stratigraphic scale with three clear cut transitions simultaneous with the oxygen isotopic transitions 65 125 kyrs 54 65 kyrs and 21 13 kyrs the 13c records of n pachyderma in the high latitude cores which follow the changes in 13c of the surface water tco2 near areas of deep water formation present trends similar to the benthic foraminifera 13c records in cores v19 30 and m12 392 although amplitudes of the isotopic shifts are different this implies that a large part of the observed variations represents global changes in the carbon distribution between biosphere and ocean the 13c12c ratios of n pachyderma in the north atlantic cores display larger regional variations at 18 kyrs b p than at present to explain these differences we have plotted the 18 kyrs b p 13c values of n pachyderma from 17 cores distributed n of 40 n comparison with published surface water temperature distribution at 18 kyrs b p indicates that a strong divergent cyclonic cell centered approximatively 55 n and 15 w was active during most of the last ice age maximum this hydrology analogous to the present weddell sea explains the published evidences of bottom water formation if located on the northern flank of the gyre and the strong polar front on the southern flank probable location of intermediate water formation

origins of taiwan s mud volcanoes evidence from geochemistry abstract the supply of natural gas from mud volcanoes is commonly attributed to the migration of gas bearing fluids from a deeper source area however the relative importance of these gas sources is not well known onshore mud volcanoes in taiwan are mainly located in the foothills of southwestern taiwan and in the coastal range of eastern taiwan generally along structurally weak zones geochemical analyses of gases and sediments from 17 mud volcanoes were undertaken in this study using molecular and stable isotopic compositions hydrocarbon gases were characterized by type and source maturity source rock assessments and nanofossil analyses were carried out to evaluate the potential and to infer the origin of sediments a particular effort was directed towards determining the genetic relationships between mud volcanic gas and associated sediments gases from taiwan s mud volcanoes are predominantly ch4 enriched with the exception of a few mud volcanoes where co2 predominates the origins of hydrocarbon gases in these systems range from microbial to thermally over mature sources while excess co2 may be derived from an inorganic origin as indicated by measured 13 c co 2 values the integration of geochemistry and local geology has yielded models with which to evaluate possible mechanisms for the formation of mud volcanoes

production consumption and migration of methane in accretionary prism of southwestern taiwan to systematically quantify the production consumption and migration of methane along a continental margin 210 sediment cores were collected from offshore southwestern taiwan and analyzed for their gas and aqueous geochemistry these data combined with published results were used to calculate the diffusive methane fluxes across different geochemical transitions and to develop scenarios of mass balance to constrain deep microbial and thermogenic methane production rates within the accretionary prism the results showed that methane diffusive fluxes ranged from 2 71 10 3 to 2 78 10 1 and from 1 88 10 1 to 3 97 mmol m 2 d 1 at the sulfate methane transition zone smtz and sediment seawater interfaces respectively high methane fluxes tend to be associated with structural features suggesting a strong structural control on the methane transport a significant portion of ascending methane 50 is consumed by anaerobic oxidation of methane at the smtz at most sites indicating effective biological filtration gas compositions and isotopes revealed a transition from the predominance of microbial methane in the passive margin to thermogenic methane at the upper slope of the active margin and onshore mud volcanoes methane production and consumption at shallow depths were nearly offset with a small fraction of residual methane discharged into seawater the flux imbalance arose primarily due to the larger production of methane through deep microbial and thermogenic processes at a magnitude of 1 512 43 096 tg myr 1 methane and could be likely accounted for by the sequestration of methane into hydrate forms and clay absorption

the p wave velocity structure near the base of the mantle travel times from 16 events recorded at two temporary networks of short period seismometers deployed across australia have been used to study the p wave velocity structure of the mantle below depths of 1700 km the slowness distance curve derived from these times shows small deviations from the slownesses predicted from the preliminary reference earth model of dziewonski and anderson 1981 that may be significant the most important feature is a rapid decrease of more than 0 5 s degree between distances of 85 and 88 velocity filtering of seismograms from 5 nuclear explosions in kazakh recorded at these australian networks indicates the presence of two arrival branches at distances between 83 and 91 whose slownesses differ by 0 40 to 0 55 s degree and which intersect at a distance of 87 processed p wave seismograms from the yellowknife array in canada also indicate the presence of a similar phenomenon in the same distance range in two separate regions the results can be explained by a widespread rapid or sharp increase in velocity of 2 5 to 3 0 about 200 km above the core mantle boundary

evidence against a discontinuity at the top of d summary we investigate a recent suggestion of lay helmberger that there is a world wide discontinuity in 5 wave velocity about 250 300 km above the core mantle boundary with an increase of 2 5 3 per cent from above to below their model predicts pronounced pulse form changes of long period sh body waves in the epicentral distance range 95 120 a range which has not been studied by them similar pulse form changes are expected in p wave seismograms under the reasonable assumption of a similar increase in p velocity nine long period seismogram sections of sh and p waves from deepfocus earthquakes below fiji west brazil the sea of japan the sea of okhotsk and the banda sea are presented with practically no indication of the complications expected also the decay constants of pdiff as predicted by the new model differ strongly from observed values thus there is clear evidence against this model the pulse form peculiarities between mantle s and scs in transverse component seismograms at distances from 70 to 80 which lay helmberger interpreted as reflections from the discontinuity of their model must have a different cause

evidence of a lower mantle shear velocity discontinuity in s and ss phases teleseismic recordings of direct s and ss body wave phases and their core reflected counterparts scs and sscs from intermediate and deep focus earthquakes are used to analyze the lowermost mantle shear velocity structure beneath alaska a model with a 2 75 shear velocity increase 280 km above the core mantle boundary accurately matches waveform complexi ties in both the s and ss wavetrains variations in source depth produce systematic shifts in the timing of the triplication arrivals between the s and ss travel time branches that are readily ob served in long period wwssn tangential component recordings the systematic range and depth dependence of the observed shifts are well predicted by the discontinuity model and preclude explanations of the waveform complexity as resulting from multi ple ruptures at the source receiver reverberations or near source scattering from slab structure accurate models of the seismic velocity structure in the lower most 200 km of the mantle d region are essential for calcula tions of the thermal history and dynamics of the core and mantle several recent investigations of seismic body waves have indi cated the presence of velocity stratification above the core mantle boundary lay and helmberger 1983 wright et al 1985 while models of long wavelength lateral velocity variations in the lower mantle indicate strong heterogeneities in the d region dziewon ski 1984 clayton and comer 1983 current thermal models indicate a large temperature contrast of about 1000 o between the core and mantle requiring a thermal boundary layer at the base of the mantle jeanloz and richter 1979 loper 1984 this is consistent with the general decrease in velocity gradients observed in the lowermost mantle doornbos 1983 doornbos et al 1986 the combined effects of stratification lateral hetero geneity and decreased velocity gradients complicate interpreta tion of seismic data sampling the d region it is particularly important to resolve whether velocity discontinuities are actually present within d since compositional stratification would strongly affect the thermal boundary layer dynamics as well as the interpretation of the lateral velocity variations this paper presents an analysis of a combination of seismic body waves that is particularly sensitive to the presence of a velocity discontinuity in d lay and helmberger 1983 found evidence for a 2 75 shear velocity discontinuity about 280 km above the core in s waves from intermediate and deep focus earthquakes the long period tangential component seismograms they analyzed show wave form complexities in the distance range 75 o to 95 o that were attributed to a triplication produced by an abrupt velocity in crease this interpretation was criticized by schlittenhardt et al 1985 who argue that such a discontinuity is incompatible with

late cenozoic environments in the barents sea we examine the paleoceanography and paleogeography of the barents sea during the late cenozoic glacial regime by seismostratigraphy and core analysis during the smaller glaciations which probably dominated the first period of the glaciogenic regime approximately 2 5 0 8 ma glaciomarine processes with sediment influx from the adjacent mainland prevailed the barents sea has been covered by grounded ice sheets several five to 10 times during the late cenozoic we speculate that these glaciations occurred during the last 0 8 ma during these larger glaciations the margin of the ice sheet expanded to the shelf edge and the continental shelf break and slope acted as a depocenter and prograded rapidly frequent sediment gravity flows accumulated on the lower continental slope during interglacials the barents sea was converted to a starved continental margin most of the barents sea was glaciated during the maximum of the last glaciation 19 16 ka a two stepped deglaciation 16 to 13 ka and 13 to 10 ka occurred incipient atlantic water reached the western areas about 13 ka and totally replaced the arctic water by 10 ka these paleoceanographic events were delayed in the eastern barents sea

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

resolved measurements of 13cdh3 and 12cd2h2 from a mud volcano in taiwan abstract resolved measurements of the relative abundances of 13cdh3 and 12cd2h2 from a taiwan mud volcano confirm that thermogenic ch4 with a formation temperature of 150 c is bubbling from a pool of liquid mud analysis for both doubly substituted molecules provides confirmation that isotopic exchange equilibrium was achieved between methane isotopologues methane extracted from the headspace of core samples taken from sediments deposited proximal to the bubbling pool of mud shows small departures from isotopic equilibrium

core top evaluation of benthic foraminiferal isotopic ratios for paleo oceanographic interpretations abstract the benthic foraminifera cibicides wuellerstrofi oridforsalis tener and pyrgo rotalaria from twelve core tops in the norwegian greenland sea and c wuellerstorfi o tener and o umbonatus from four core tops on the rio grande rise were analysed for oxygen and carbon isotopes the norwegian greenland sea data yield statistically discrete means for both 18o and 13c for each species the interregional comparison of our data to published data from the east pacific rise shows that c wuellerstorfi 18o and 13c variations reflect oceanographic differences between sites whereas the data on oridorsalis and pyrgo do not we conclude that c wuellerstorfi is a reliable sensor of bottom water conditions whereas other taxa are of unproven utility supportive biological studies and the lack of positive covariance of 18o to 13c among deep sea benthic taxa lead us to reject models calling for incorporation of metabolic co2 to explain the isotopic variation among deep sea benthic foraminifera we propose a within sediment microhabitat hypothesis to explain the 13c variations among taxa

present seismic evidence for a boundary layer at the base of the mantle to improve the global coverage needed in investigating the observational consequences of boundary layer models the existing data set has been extended with long period diffracted p and sh from the sro network and short period diffracted p from the norsar array it was found that on average the amplitude decay of diffracted sh is relatively small in accordance with the majority of previously published wwssn data and consistent with the observed weakness in dispersion of this phase these results in combination with the apparent absence of anomalously high dt d can be explained by a relatively thin 100 km low velocity zone at the base of the mantle long period diffracted p wave data probably lack the required resolution for detecting a relatively thin transition zone such a zone with relatively low velocity is allowed by an average of travel time and amplitude data across the core shadow boundary and appears to be required by the norsar observations of short period diffraction far into the shadow however recent results of individual short period p wave studies pertaining to geographically limited regions only including also the norsar observations are partly conflicting unless lateral variations exist on balance current thermal models appear to be consistent with but not required by the present seismic evidence

quaternary shelf sea palaeoceanography recent developments in europe abstract high quality palaeoceanographic reconstructions based on sequences preserved in shallow marine environments demonstrate that these constitute significant archives of climatic and oceanographic change such sequences are important first because their often very high resolution sometimes laminated nature enables high frequency cycles to be resolved and provides the basis for establishing spatial and temporal variability in the marine radiocarbon reservoir effect second sea level index points from shelves are important for the validation of glacio hydro isostatic geophysical models and for understanding sea level change during early deglaciation third shallow marine sequences contain excellent records of land ocean interaction often preserving paired terrestrial marine proxies in the same stratigraphic sequence a new development in shelf sea palaeoceanography is documenting the long term dynamics of shelf sea stratification this is the dominant hydrodynamic phenomenon of tide dominated shelf seas in the middle and high latitudes and has a profound influence on productivity and therefore global change through the carbon cycle detailing the evolution of seasonal stratification during eustatic highstands is therefore of relevance to the climate system

sedimentary facies of glacial interglacial cycles in the norwegian sea during the last 350 ka sediment fluxes were highest in the norwegian sea during late glacial early deglacial periods i e at oxygen isotope transition 43 below transition 65 at various levels within stage 6 and below stage 9 dark diamictons deposited at these times reflect intense iceberg rafting in surface waters fed by surges along the front of the marine based parts of the continental ice sheets in the southeastern sector of the norwegian sea the high organic carbon content 0 5 1 3 in these layers reflects input from erosion of terrigenious matter rich sediments outcropping on the shelves partial oxidation of organic matter and decreased deep water renewal may explain the strong carbonate dissolution observed during these periods interglacial environments were strongly variable throughout the last 350 ka circulation patterns of stage 5e best resemble modern conditions while stage 7 and 9 sediments record a much weaker norwegian current

the dynamical structures of d and deep plumes in a non newtonian mantle the dynamical structures of the d layer and deep mantle plumes have been determined for a mantle with a power law creep rheology generalising recent newtonian analyses the lateral scales of d and plumes are determined by a balance between thermal diffusive thickening and lateral inflow the non newtonian effect of concentrating shear in regions of high stress acts to thicken the region of rapid flow in both d and plumes this effect is nearly counterbalanced by the increased lateral inflow in the non newtonian case resulting in a modest broadening of the lateral scales of the regions of rapid flow these changes are structurally unimportant and the essential physics of core cooling via convective flow in a thin d layer and narrow plumes is remarkably independent of mantle rheology

structure of the earth mantle and core the deep interior structure of the earth has been extensively analyzed using a wide variety of seismic phases and techniques during the last four years most studies have emphasized quantitative three dimensional mapping of the lateral velocity heterogeneity of the mantle and core these aspherical velocity variations are believed to be direct manifestations of thermal and compositional heterogeneity associated with convective processes a first generation of global models for the lateral velocity variations in the deep earth has been produced providing tantalizing images of large scale structures suggestive of a non steady state thermal convection system the upper 400 km of the mantle has the strongest lateral velocity variations of up to 10 for shear velocity surface wave analyses that do not require a priori regionalizations have demonstrated that there is a strong association between surface tectonic provinces and the uppermost mantle velocity variations thus the thermal and convective state of the upper 200 km of the mantle can be reliably interpreted in the context of plate tectonics the upper mantle models support the contention that continents have deep roots with differences in velocity structure from oceanic and active tectonic regions extending as deep as 400 km very long wavelength lateral velocity variations of a few percent have been detected in the transition zone at depths from 400 to 670 km as well as throughout the lower mantle these deep seated variations have little correspondence to surface tectonics and efforts to interpret their nature are just beginning the lowermost 200 km of the mantle d region has lateral velocity fluctuations comparable to those in the upper mantle and evidence has been presented for the presence of a sizable velocity discontinuity at the top of the d layer a combined thermal and compositional boundary layer roughly mirroring the lithosphere is a likely explanation for this anomalous zone the core mantle boundary appears to have significant 10 km long wavelength topography presumably sustained by dynamic stresses from deep mantle convection the inner core may have strong lateral heterogeneity or axially symmetric anisotropy suggesting a complex thermal and compositional state significant progress has been made in characterizing the frequency dependence of anelastic attenuation in the mantle in the short period body wave band models for teleseismic p wave attenuation operators have converged with t values of 0 7 1 0 s appropriate at 1 hz and t values of 0 4 0 6 s appropriate at 4 hz regional variations of attenuation are slowly being mapped out as well

meltwater and deglaciation se baffin shelf ne margin laurentide ice sheet between 13 5 and 7 ka from o and c stable isotopic data stable isotopic values on planktonic foraminifera in a suite of cores from basins across the se baffin shelf are used to extract a record of meltwater events during termination i deglaciation resolution and hatton basins lie on the se baffin shelf at water depths 500 m seaward of major conduits for ice drainage from the eastern sector of the laurentide ice sheet lis accelerator mass spectrometry 14c dates are used to constrain our chronology of events in ten cores in resolution basin three cores have 14c ams dates on foraminifera of 20 ka at their bases whereas hatton basin cores terminate in sediments 13 kyr sedimentation rates varied between 0 1 to 4 5 m ka stable oxygen and carbon isotopic ratios were obtained on 146 samples of the planktonic foraminifera neogloboquadrina pachyderma ehrenberg sinistral from seven of the ten cores no evidence was found to indicate that test morphology or size affected 18o between 7 and 13 5 ka the surface water on the shelf was on average 1 lower than the open ocean signal significant temporal variations were found in both 18o and 13c evidence for significant low 18o events occurred between 13 and 8 ka the 13c record from the planktonic foraminifera suggests a threefold division of events between 13 and 7 ka with positive values between 10 8 and 13 0 ka negative values between 9 and 10 8 ka and positive values from 7 to 9 ka the 18o data suggest the presence of meltwater on the shelf some 3 000 years prior to the first late glacial dates on terrestrial deglaciation at circa 10 4 ka hudson strait must be the real key to the importance of the calving process during deglaciation because it is potentially the largest marine outlet for the laurentide ice sheet and because it leads into the very center of the ice sheet the rates of calving through hudson strait during the period of initial 18o rise unfortunately are unknown w f ruddiman 1987 p 151

the 8200 cal yr bp event reflected in the arctic fjord van mijenfjorden svalbard detailed stratigraphic investigations of a high resolution sediment core from the arctic fjord van mijenfjorden svalbard reveal significant reductions in benthic foraminiferal 18o of 0 4 and 0 2 0 3 dated to c 8200 and 8450 cal yr bp respectively these reductions combined with changes in the benthic foraminiferal fauna and ird indicate substantial changes in the hydrography of the fjord such as freshening of the bottom water enhanced sea ice distribution and reduced biogenic production the age and duration 100 years of the youngest event is directly in phase with the 8200 cal yr anomaly in the 18o record gisp2 and ngrip of the greenland ice sheet the changes around 8450 cal yr bp compare well to the timing of the initial freshwater drainage of the proglacial lake agassiz therefore the proxy record of van mijenfjorden lends support to the theory explaining the 8200 cal yr bp event as a cumulative response to a freshwater forced reduction in the meridional overturning circulation in

late quaternary sedimentation in the eastern arctic basin stratigraphy and depositional environment abstract the late quaternary history of the arctic basin is poorly known because most sediment cores seemed to have accumulated very slowly based on magnetostratigraphy on the order of one to a few millimeters per thousand years two short sediment cores from the eurasian basin of the arctic ocean have now been dated by means of o and c isotopic ratios the o isotope stratigraphy suggests that these sediments accumulated much faster on the order of one to four centimeters per thousand years than in the central arctic ocean the cores penetrated sediments belonging to isotope stages 1 3 and allow a detailed description of the depositional environment under the arctic ice cover during the last ice age and the ensuing climatic warm interval

diagnostic criteria for reconstruction of tidal continental shelf regimes changing the paradigm abstract a biogeochemical flux paradigm is presented which provides a conceptual and numerical framework for reconstructing the dynamical and biogeochemical regimes of ancient tide driven continental shelves the paradigm links turbulence primary production and suspended particulate matter flux in the water column to microbiological and isotopic proxies in the sediment record and identifies the diagnostic signatures of sediments deposited in stratified frontal and mixed dynamic regimes of tidal shelves the critical governing processes in the water column and at the sediment water interface are temperature particulate organic carbon supply and benthic oxygen consumption which exhibit strong gradients across tidal mixing fronts the diagnostic proxies in the sediment record are microplanktonic e g dinoflagellate cysts and microbenthic e g foraminifera and their associated stable isotopic properties advanced numerical models are available which incorporate biophysical coupling in the water column and benthic boundary layer and which simulate biogeochemical and ecological processes and organic fluxes to the seabed these models offer potential advances for interpreting microbiological and isotopic proxies of biogeochemical regime preserved in the fine sediment record quaternary shelf deposits provide the best potential validation of the biogeochemical flux paradigm since most quaternary species are living today but the paradigm is applicable to ancient tidal shelf deposits the paradigm is particularly applicable to the fine sediment record which potentially preserves the most complete history of shelf evolution

variations in surface water mass conditions in the norwegian sea evidence from holocene coccolith and dinoflagellate cyst assemblages coccolith and dinoflagellate cyst assemblages have been investigated in five sediment cores from the norwegian sea and fram strait both fossil groups are characterized by similar patterns of composition the assemblages contain high proportions of single species the coccolith flora is of low diversity and consists almost entirely of coccolithus pelagicus and emiliania huxleyi the dinoflagellate cysts are generally dominated by operculodinium centrocarpum and nematosphaeropsis labyrinthus other species especially bitectatodinium tepikiense peridinium faeroense and impagidinium pallidum sometimes contribute considerably to the assemblages based on the abundance of the assemblages and the ratio change between the dominating species it has been possible to establish three intervals of distinct major changes in surface water mass conditions sparse occurrences of coccoliths and dinoflagellate cysts have been observed before 10 000 yrs b p indicating harsh environmental conditions with a distinct influence of meltwater and temporarily very slight inflow of atlantic water the modern surface water circulation pattern was reinitiated during termination ib the assemblages suggest slightly cooler and probably less saline surface water conditions than are present today until 7500 yrs b p solar insolation may have caused a first temperature peak which is responsible for the early holocene productivity maximum a considerable change in the composition of dinocyst and coccolith assemblages occurs corresponding approximately to the onset of the holocene climatic optimum this change was most probably linked to an almost synchronous reorganization of the hydrographic properties in the entire north atlantic realm after the ice sheets had vanished since 6000 yrs b p the norwegian current with its modern oceanographic and ecological properties has been fully established