ediacaran acritarch biota from the giles 1 drillhole officer basin australia and its potential for biostratigraphic correlation the remarkable diversification of single celled photosynthesising biota of algal and other as yet unknown affinities acritarchs followed by the diversification of metazoans occurred during the

radiation of meso neoproterozoic and early cambrian protists inferred from the microfossil record of china abstract marine protists can be affected by and reflect changes in the ecological environment based on available microfossil evidence from late mesoproterozoic early cambrian rocks of china radiations of protists and related changes in ecological environments are discussed in the paper remarkable development of protists had occurred by as early as the mesoproterozoic protist diversity significantly decreased in the middle neoproterozoic due to disruption of the ecological environment that may have been caused by global glaciations the doushantuo microfossil assemblage records high diversity and radiation of protists during the early to middle ediacaran an acritarch assemblage of asteridium comasphaeridium heliosphaeridium megathrix which is contemporaneous with the lowermost meishucunian small shelly fossil assemblage anabarites trisulcatus protohertzina anabarica is widely distributed in the lowermost cambrian strata of south china and the tarim basin and is useful for biostratigraphic correlation with baltica and other areas

mg ca ratios in the planktonic foraminifer neogloboquadrina pachyderma sinistral in the northern north atlantic nordic seas in core top samples in the nordic seas mg ca ratios of n pachyderma sin are generally consistent with previous high latitude calibration data but do not reflect the modern calcification temperature gradient from 2 c in the northwest to 8 c in the southeast this is because mg ca ratios in foraminiferal shells from the central nordic seas are 0 4 mmol mol higher than expected from calibrations of nurnberg 1995 and elderfield and ganssen 2000 the enhanced mg ca ratios are observed in an area with low sedimentation rates 5 cm kyr possible factors that may cause this include bioturbation holocene variability in old core tops dissolution pore water chemistry occurrence of volcanic ash and other natural variability the enhanced foraminiferal mg ca ratios in areas of the nordic seas and the northern north atlantic may also be linked with secondary factors related to the presence of fresher and colder water masses possibly combined with pore water chemistry in low sedimentation areas differing from high sedimentation areas

stratigraphy correlation and sedimentary history of adelaidean late proterozoic basins in australia abstract adelaidean late proterozoic time is represented by the precambrian portion of the thick sequence in the adelaide geosyncline its stratotype basin in south australia comparable adelaidean sedimentation including the deposition of glaciogenic sediments is recorded in other intracratonic and epicratonic basins extending northwards across australia in the adelaide geosyncline which lies to the east of the gawler craton and its cratonic platform cover the stuart shelf up to 15 km of mainly shallow water sediments accumulated partly in intracratonic troughs and perhaps partly on a miogeoclinal continental shelf the earliest sedimentation is associated with rifting and basic volcanism with an estimated age of ca 1100 ma it commenced with basal blanket sands shelf carbonates and basaltic volcanics followed by mixed carbonate clastic and evaporitic beds callanna beds the overlying burra group consists of a number of west derived possibly deltaic cycles and magnesite bearing platform carbonates the unconformably overlying late adelaidean umberatana group contains the lower glacial beds including the sturt tillite interglacial siltstone dated at about 750 ma and carbonate and the upper glacial beds the post glacial wilpena group commences with a distinctive cap dolomite above the upper glacials and contains mainly fine to medium clastics and the ediacara metazoan assemblage late adelaidean sedimentation patterns are sufficiently similar in the officer amadeus ngalia and georgina basins of central australia and in the kimberley region western australia to suggest interconnection with the adelaide geosyncline to the south in the amadeus basin the early adelaidean sequence is younger than about 1050 ma but cannot be directly correlated with the early adelaidean formations of the adelaide geosyncline however the late adelaidean glacial and younger sequences are readily correlated they include the lower glacial areyonga formation and the arumbera sandstone i containing elements of the ediacara assemblage in the georgina and ngalia basins mainly late adelaidean sequences including thick glacials can mostly be correlated with the amadeus basin in the kimberley region earliest adelaidean clastics may be represented but only the late adelaidean glaciogenic and associated sediments can be correlated with confidence the tillites commonly overlie glaciated pavements the lower glacials are represented only in a graben while the upper glacials and succeeding sequence are more widespread post glacial shales have been dated at ca 670 640 ma the dominantly carbonate and clastic sequences of the bangemall basin western australia cannot be directly correlated with any type adelaidean but geochronology suggests an earliest adelaidean age ca 1050 ma

carbon cycling and burial in the glacially influenced polar north atlantic 1 we have collated published records of carbon storage wt calcium carbonate and organic carbon in polar north atlantic sediments in order to assess the role that the glacial history of greenland and fennoscandia may have had on carbon cycling in this oceanographically important region the proportion of carbonate in sediment varies between 0 and 50 while that of organic carbon varies between 0 and 2 0 the spatial variation of the concentration and accumulation of both constituents is markedly different bulk accumulation shows a strong relationship with depth distance offshore and the location of major glacial outlets on neighboring landmasses therefore ice sheet dynamics and erosion influence carbon especially organic carbon storage strongly during the late weichselian 27 12 14c ka via their impact on sedimentation rates and constituents in contrast water mass characteristics are important in determining the pattern of carbon storage during the holocene carbonate fluxes to the polar north atlantic sediment column fall by 50 during glacials to 1 1 1013 kg kyr 1 but organic carbon storage is maintained at or greater than interglacial levels 4 6 1011 kg kyr 1 this represents a 100 change in the ratio of preserved inorganic to organic carbon when combined with reduced deep water ventilation respiration of this relatively greater organic carbon flux in both the water and sediment columns provides a good explanation for the observed periodic enhanced dissolution of carbonate in polar north atlantic late weichselian sections perhaps enhancing co2 storage in deep waters

reduced arctic sea ice extent during the mid pliocene warm period concurrent with increased atlantic climate regime abstract quantifying the contribution of poleward oceanic heat transport to the arctic ocean is important for making future sea ice and climate predictions to highlight its potential importance in a warmer world we present a new record of water mass exchange between the atlantic and the arctic oceans using the authigenic neodymium isotopic composition of marine sediments from the fram strait during the past 3 4 to 2 6 ma in this study we target the mid pliocene warm period mpwp 3 264 3 025 ma of the pliocene epoch the most recent geological analogue for future climate change we complement our semi quantitative water mass exchange reconstruction with estimates of spring sea ice concentration based on source specific biomarkers our estimates of volume transport of warm waters into the arctic ocean suggest long term secular changes from the lowest during the marine isotope stage m2 glacial 3 312 3 264 ma to near complete atlantification of the eurasian sector of the arctic ocean during the mpwp orbital forcing is found to be the dominant controlling factor for modulating northward volume transport of atlantic derived water masses with an associated reduction in arctic spring sea ice concentration of 30 35 current generation models often produce diverging results however and have not yet been validated against proxy data in northern high latitude settings during the mpwp our new results of northward volume transport and sea ice extent therefore provide much needed input for validation of current generation models aimed at improving the robustness of future climate modeling in the arctic

a chemostratigraphic overview of the late cryogenian interglacial sequence in the adelaide fold thrust belt south australia within the neoproterozoic sequence of the adelaide fold thrust belt south australia two of the most severe ice ages in earth history sturtian and marinoan are recorded in the glacigenic rocks which mark the base and top of the 4 5 km thick umberatana group the focus of the present chemostratigraphic study rock units from three drillholes and ten measured outcrop sections located in the southern and central flinders ranges and on the stuart shelf were sampled for isotopic analysis of their co existing calcite 13ccal dolomite 13cdol and kerogen 13corg strontium and sulphur isotopic analyses were also run on selected samples the sample sites are in tectonic domains where regional metamorphism has been insufficient to significantly alter the isotopic composition of the kerogen the resulting data when integrated with the lithostratigraphy of the umberatana group yield one of the most complete records of secular variation in the c isotope signature of the late cryogenian ocean between 750 and 680 ma its composite 13ccarb curve begins with a sharp positive excursion 3 to 1 5 in the dolomitic tindelpina shale which caps sturtian glacial diamictites wilyerpa formation then follows a steady climb through the shoaling upward tapley hill formation reaching 4 in the brighton limestone and culminating in a plateau of 13c enrichment within the platformal carbonates of the etina formation 8 to 10 the upper part of the temporal trend shows a decline to 6 to 7 in the stromatolite reef facies of the enorama shale and a dramatic drop to 8 to 9 5 followed by a recovery to 3 in the youngest carbonate unit trezona formation beneath the marinoan glacigenic elatina formation the latter is capped by a thin dolostone the nuccaleena formation which records a consistent up section decrease in 13c 1 to 3 superimposed on this overall pattern of c isotopic variation are second and third order fluctuations attributable to eustatic sea level change pyritic sulphur in the lower tapley hill formation 34s 9 to 40 is distinctly heavier than that in the underlying wilyerpa formation 4 to 20 minimum 87sr 86sr values obtained from the brighton limestone 0 7071 and etina formation 0 7076 are consistent with their late cryogenian age this sturtian to marinoan interglacial succession is more complete than equivalent sequences elsewhere and thus provides a useful reference for global chemostratigraphic correlation notable features of its c isotope curve are the strong post wilyerpa positive excursion also seen in key sections from svalbard and western mongolia the etina plateau of 13c enrichment which is remarkably similar to maxima in the terminal proterozoic c isotope records of western mongolia north western canada and brazil and the spectacular depletion of 13c in the lower trezona relative to similar carbonate facies in the underlying etina formation and enorama shale a preglacial offset in 13ccarb values of such proportions 14 is almost unprecedented except perhaps for that recently documented in the upper ombaatjie formation beneath tillites of the ghaub formation otavi group namibia it represents a key piece of evidence in the case presented by the proponents of a neoproterozoic snowball earth

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

dynamics of atlantic water advection to the norwegian greenland sea a time slice record of carbonate distribution in the last 300 ky abstract short term variability in volume and configuration of atlantic water advection to the norwegian greenland sea ngs has recently been identified as a new and significant element for northern hemisphere glacial interglacial climatic fluctuations the amount of salt heat and moisture transferred by atlantic waters to the high arctic effectively influences northern hemisphere climates and is critical for the overall oceanic turnover rate in particular determining the extent and duration of atlantic water intrusions in the ngs is essential because of 1 its effect on the climate of the nordic continents and 2 its trigger function on the stability of the ice sheets with a weak inflows of atlantic water during glacials promoting an increase in ice volume by moisture supply to polar areas and b positive feed back mechanisms of atlantic water intrusions during ice sheet decay in this study the dynamics of surface water mass regimes in the ngs have been reconstructed for the past 300 ky by means of time slice compilations of calcium carbonate distribution and micropaleontologic proxies in addition carbonate preservation records are used to quantify deep water ventilation and production rates in contrast to the climap scenario but in accordance with many recent publications results of this study indicate that atlantic water advection was also a common feature during most glacial periods but varied strongly in volume and configuration significant modes recognized are 1 the full interglacial mode with a wide inflow of warm atlantic waters covering a broad area in the eastern sector of the ngs and extending far north combined with excellent carbonate preservation and very efficient deep water formation stages 1 and 5 5 1 2 the moderate interglacial mode with a rather small extension of atlantic waters along a narrow corridor in the southeastern sector of the ngs but still very efficient deep water exchange stages 9 isotopic events 7 5 7 3 7 1 5 3 and 5 1 3 pronounced cool phases during interglacials with only a very narrow inflow of atlantic waters into the southeastern ngs while the coastal areas off norway were still affected by iceberg drift substages 7 4 and 5 2 carbonate preservation records indicate ongoing deep water formation in the ngs 4 the normal glacial mode characterized by a variable but persistent inflow of cool temperate atlantic water lower stage 8 repetitively during stages 6 4 3 1 and 2 carbonate preservation records indicate ongoing deep water formation in the ngs 5 short glacial and deglacial periods characterized by episodic high inputs of ird evidenced by a wide coverage of diamicton deposition and strong carbonate dissolution e g episodically within stages 10 6 and 2 the 6 5 4 3 and 2 1 transitions some of these ngs diamicton layers correlate with heinrich layers in the north atlantic but generally ngs diamicton layers occur more frequently than heinrich layers the role of atlantic water influence during these events remains enigmatic but atlantic water influence is frequently found just above and below these sections a scenario with rapid ice sheet disintegration induced by atlantic water advection via increase of the thermal regime along the ice margin possibly triggered by small scale sea level rise might be envisaged more obviously the short term cessation of deep water formation in the ngs as evidenced by the dissolution spikes may be correlated with contemporaneous ventilation minima in the north atlantic

evolution of atlantic pacific δ13c gradients over the last 2 5 m y the evolution of interocean carbon isotopic gradients over the last 2 5 m y is examined using high resolution 13c records from deep sea cores in the atlantic and pacific oceans over much of the northern hemisphere ice ages relative reductions in north atlantic deep water production occur during ice maxima from 2 5 to 1 5 ma glacial reductions in nadw are less than those observed in the late pleistocene glacial suppression of nadw intensified after 1 5 ma earlier than the transition to larger ice sheets around 0 7 ma at a number of times during the pleistocene 13c values at dsdp site 607 in the north atlantic were indistinguishable from eastern equatorial pacific 13c values from approximately the same depth odp site 677 indicating significant incursions of low 13c water into the deep north atlantic atlantic pacific 13c values converge during glaciations between 1 13 1 05 m y 0 83 0 70 m y and 0 46 0 43 m y this represents a pseudo periodicity of approximately 300 kyr which cannot easily be ascribed to global ice volume or orbital forcing this partial decoupling at low frequencies of the 18o and 13c signals at site 607 indicates that variations in north atlantic deep water circulation cannot be viewed simply as a linear response to ice sheet forcing

organic walled microfossils from earliest cambrian or latest proterozoic tindir group rocks northwest canada abstract uppermost tindir group limestones exposed in the headwaters of tindir creek yukon territory canada contain a diverse and abundant microbiota of mineralized and organic walled microfossils preserved primarily in chert modules and chert beds the organic walled forms include mat building cyanobacterial filaments and coccoids accompanied by less common bacteria fungi and forms of uncertain affinity as well as planktonic coccoidal cyanobacteria and acritarchs several lines of evidence support interpretation of an early cambrian age whereas others suggest a late proterozoic age of the 54 organic walled taxa recognized 12 are newly described yukonosphaeridion interior awramik n gen n sp microagglomeratus borealis awramik n gen n sp phacelogeminus lineatus awramik n gen n sp palaeoanacystis magna awramik n sp cephalophytarion majesticum allison n sp heliconema bulbosa allison n sp trachyhystrichosphaera magna allison n sp fusilabellum brevistriatum awramik n gen n sp sphaeranasillos irregularis allison n gen n sp hyalocyrillium clardyi allison n gen n sp eophycomyces herkoides allison n gen n sp and archeomyces dimakeloides allison n gen n sp

neoproterozoic stratigraphy of the centralian superbasin australia abstract the basement of central australia includes the arunta block and the 1200 1100 ma musgrave block succeeded by 1075 1000 ma bimodal volcanic rifts and dolerite dykes a regional hiatus at 1000 800 ma interpreted as reflecting a central post volcanic underplated upland was followed at 800 ma by a second swarm of dykes in the musgrave block gawler craton and stuart shelf associated with the crustal sagging that initiated the centralian superbasin the centralian superbasin is defined here to encompass the neoproterozoic fill of the amadeus georgina ngalia officer and savory basins the intra cratonic superbasin was disrupted internally 540 600 ma ago petermann ranges orogeny by a central uplift and associated thrusts and by mid carboniferous 320 ma tectonism alice springs orogeny to form the structural basins listed above the stratigraphy and sedimentology of the relatively well known areas can be used as a basis for predicting those of the poorly known regions new results from acritarch biostratigraphy and isotope chemostratigraphy in conjunction with conventional lithostratigraphy and sequence analysis allow better stratigraphic resolution than previously possible field observations in the recently discovered savory basin in western australia provide a basis for correlations with the adjacent basins

pleistocene δ13c variability of north atlantic intermediate water variations in the stable isotopic composition of benthic foraminifera from deep sea drilling project dsdp site 502b in the caribbean sea are used to reconstruct atlantic intermediate water circulation variability over the last 1 2 m y comparison of this record with other north atlantic benthic isotope records indicates that atlantic intermediate water circulation was relatively enhanced during glacial maxima when north atlantic deep water nadw production was reduced however a simple compensatory relationship between intermediate and deepwater circulation is not apparent geochemical models have shown that such changes in ocean circulation can affect atmospheric co2 levels by changing vertical nutrient and alkalinity profiles the 13c difference between caribbean site 502b and deep equatorial pacific site 677 is highly coherent and in phase with ice volume like the 18o record there is an increase in amplitude 40 and a large increase in 100 kyr power after 0 7 ma the 1 2 13c amplitude scales to 70 ppm v in atmospheric co2 using boyle s 1986 box model result the implied increase in co2 amplitude after 0 7 ma may suggest a positive feedback role in effecting the higher amplitude climatic fluctuations which characterize the last 0 7 m y

fast reconnaissance of carbonate dissolution based on the size distribution of calcareous ooze on walvis ridge se atlantic ocean we present a new index of carbonate fragmentation based on the size distribution of bulk sediments in core md962094 from walvis ridge se atlantic ocean the carbonate fragmentation index is constructed by taking a ratio of the two coarsest fractions in the grain size distributions of the bulk calcareous ooze the coarsest two fractions 25 90 small mu greekm and 90 small mu greekm of the bulk sediments consist primarily of complete shells and fragments of adult foraminifera shells and juvenile foraminifera shells and fragments respectively the ratio of the proportions of the two fractions is interpreted as a measure of fragmentation of the foraminifera shells caused by carbonate dissolution downcore changes in our carbonate fragmentation index compare very well with those in the coarse carbonate fragmentation index in sediments from a nearby core on walvis ridge the latter commonly used fragmentation index is defined as a ratio of foraminifera fragments over whole foraminifera in the 150 small mu greekm fraction as seen with a light microscope fragmentation is relatively high during glacial stages and relatively low during interglacial stages during the last 300 kyr caused by the combined effect of wind driven upwelling of corrosive water and increased production of organic matter decreasing the preservation potential of carbonates both during and after deposition the carbonate fragmentation index we present here provides a precise and fast method to establish a downcore fragmentation record it can be applied to bulk sediments that are carbonate rich caco3 68 and to all other deep marine sediments of which the grain size distribution of the carbonate free fraction is available

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

caco3 dissolution in california continental margin sediments the influence of organic matter remineralization in situ benthic flux chamber and oxygen microelectrode and shipboard porewater results have been used to quantify sea floor dissolution of caco3 on the continental rise adjacent to central california usa the porewater distributions and benthic fluxes of o2 no3 ta ca2 13c and tic are interpreted using a numerical simulation of organic matter remineralization and caco3 dissolution in marine sediments the processes considered in the simulation include organic matter oxidation by o2 no3 and so42 caco3 dissolution and precipitation hs and nh4 oxidation and sediment mixing and sediment accumulation calculated benthic fluxes of o2 no3 ta tic 13c and ca2 porewater concentrations of o2 no3 and nh4 and sediment distributions of organic carbon caco3 excess 210pb and 14c agree well with the measurements benthic fluxes of alkalinity and inferred caco3 dissolution rates cannot be explained on the basis of dissolution driven solely by bottom water undersaturation if the influence of metabolically produced co2 is included benthic fluxes are fully reconciled however this is in agreement with benthic chamber ca2 and 13c results that independently imply substantial caco3 dissolution in these sediments the above observations are in contrast to those reported by jahnke et al 1994 for the west african continental rise and the western equatorial pacific where 1 g diagenetic models predict dissolution fluxes larger than observed with benthic flux chambers we conclude that the extent of metabolic caco3 dissolution may vary regionally numerous factors such as the depth of metabolic co2 production and caco3 dissolution kinetics are known or predicted to influence metabolic dissolution among the factors that should be considered in reconciling these observations are l the extent to which sulfate reduction and reoxidation reactions may influence acid base properties in surface sediments and 2 the total sedimentary caco3 content of the sites that may influence porewater acidity through surface exchange reactions at the mineral surface

carbonate preservation records of the past 3 myr in the norwegian greenland sea and the northern north atlantic implications for the history of nadw production carbonate preservation records from a number of drill sites in the north atlantic and adjacent norwegian greenland sea ngs are used to reconstruct variations in north atlantic deep water nadw production over the past 3 myr before the initiation of major northern hemisphere glaciation good carbonate preservation was recorded in the north atlantic and the ngs supporting the superconveyor model of accelerated nadw formation in the late pliocene after the inception of main northern hemisphere glaciation nadw formation in the ngs was blocked off during the period 2 8 1 9 ma carbonate was only badly preserved due to 1 low production of carbonate shells in surface waters 2 sluggish renewal of deep waters induced by a rather stable sea ice cover and or 3 production of carbonate corrosive dense brines during sea ice formation e g sea ice dissolution mode in contrast contemporaneous good preservation in the adjacent north atlantic indicates efficient nadw production during the middle matuyama 1 9 1 4 ma the first intrusions of the proto norwegian current into a narrow corridor in the southeastern ngs are evidenced by much better carbonate preservation a decrease both in carbonate content and preservation towards the north and west of this corridor indicates the proximity of the polar front and gives evidence that nadw production was efficiently triggered by the atlantic water entrainment mode during the past 1 2 myr carbonate preservation patterns in the ngs clearly reflect major global events like the mid pleistocene transition and the mid brunhes dissolution event the onset of the mid pleistocene transition at 1 2 ma is characterized by a complete shift to higher carbonate contents in the southeastern ngs and labrador sea overall good preservation during both interglacials and glacials is only interrupted by high frequency short term dissolution spikes which were induced by ice sheet collapse and development of extensive meltwater lids as a consequence nadw was produced nearly continuously during glacials in the nordic seas however due to its lower density it was entrained into intermediate water levels in the north atlantic and thus enforced the intermediate water circulation loop whereas a decrease in lower nadw production is observed contemporaneously

a late holocene multi proxy record from the northern norwegian margin temperature and salinity variability manuscript published version available at the holocene 2016 doi 10 1177 0959683616675934

deep sea carbonate preservation in the western philippine sea over the past 1ma abstract in this paper we present a continuous record of calcium carbonate caco 3 content that covers the last 1 ma from core md06 3050 15 57 0943 n 124 46 7747 e water depth 2967 m which was collected in the western philippine sea wps the caco 3 content in this study core is characterized by maxima during deglaciations and minima during the onsets of glacial periods and generally shows pacific style patterns with relatively high and low values during glacial and interglacial periods respectively proxies of dissolution and primary productivity pp the caco 3 content and the oxygen isotope record from this core are compared throughout the 1 ma study interval to improve our understanding of the mechanisms that affected carbonate preservation and dissolution at this site the planktonic foraminifera shell fragmentation ratio shell fragment is used as a dissolution proxy in this study the shell fragment data from md06 3050 provide evidence of preservation maxima during most of the deglaciations whereas intense dissolution is recorded at the onsets of glacial periods within the past 1 ma the variations in shell fragments are similar to those seen in the caco 3 content which demonstrates that the bulk caco 3 content patterns were controlled by dissolution in deep seawater the primary productivity from the coccolith record shows limited similarity with the caco 3 content on glacial interglacial time scales since 1 ma which suggests that pp played a negligible role in the glacial interglacial caco 3 cycle however a bloom of the coccolithophores geophyrocapsa caribbeanica that extended from mis 9 to mis 12 likely contributed to the increased caco 3 content observed during the mid brunhes interval mbe over the glacial interglacial fluctuations therefore the caco 3 content should be used as a dissolution proxy with caution during the mbe in the tropical pacific especially for water depths that are shallower than the carbonate lysocline

shell size variation of the planktonic foraminifer neogloboquadrina pachyderma sin in the norwegian greenland sea during the last 1 3 myrs implications for paleoceanographic reconstructions we present measurements of the maximum diameter of the planktonic foraminifer neogloboquadrina pachyderma sin from six sediment cores ocean drilling program sites 643 644 907 909 985 and 987 from the norwegian greenland sea our data show a distinct net increase in mean shell size of n pachyderma sin at all sites during the last 1 3 ma with largest shell sizes reached after 0 4 ma external factors such as glacial interglacial variability and carbonate dissolution alone cannot account for the observed variation in mean shell size of n pachyderma sin we consider the observed shell size increase to mirror an evolutionary trend towards better adaptation of n pachyderma sin to the cold water environment after 1 1 1 0 ma probably the mid pleistocene climate shift and the associated change of amplitude and frequency of glacial interglacial fluctuations have triggered the evolution of this planktonic foraminifer oxygen and carbon stable isotope analyses of diverent shell size classes indicate that the observed shell size increase could not be explained by the functional concept that larger shells promote increasing sinking velocities during gametogenesis for paleoceanographic reconstructions the evolutionary adaptation of neogloboquadrina pachyderma sin to the cold water habitat has significant implications carbonate sedimentation in highest latitudes is highly dependent on the presence of this species in the norwegian greenland sea carbonate poor intervals before 1 1 ma are therefore not necessarily related to severe glacial conditions they are probably attributed to the absence of this not yet polar adapted species further transfer function and modern analog techniques used for the reconstruction of surface water conditions in high latitudes could therefore contain a large range of errors if they were applied to samples older than 1 1 1 0 myrs 2000 elsevier science b v all rights reserved

evolution of iceberg melting biological productivity and the record of icelandic volcanism in the irminger basin since 630 ka abstract planktic 18 o and 13 c records and point count records of biogenic volcanic and nonvolcanic terrigenous ice rafted debris ird sediment components from hole 919a in the irminger basin northern north atlantic provide a comprehensive dataset from which a paleoceanographic reconstruction for the last 630 kyr has been developed the paleoceanographic evolution of the irminger basin during this time contains both long term patterns and significant developmental steps one long term pattern observed is the persistent deposition of hematite stained ice rafted debris this record suggests that the modern and late pleistocene discharges of icebergs from northern redbed regions to the irminger sea lie in the low end of the range observed over the last 630 kyr in addition arctic front fluctuations appear to have been the main controlling factor on the long term accumulation patterns of ird and planktic biogenic groups the hole 919a sediment record also contains a long term association between felsic volcanic ash abundances and light 18 o excursions in both interglacial and glacial stages which suggests a causal link between deglaciations and explosive icelandic eruptions a significant developmental step in the paleoceanographic reconstruction based on benthic evidence was for diminished supply of denmark strait overflow water dsow beginning at 380 ka possibly initiated by the influx of meltwater from broad scale iceberg discharges along the east greenland coast there is also planktic evidence of a two step cooling of sea surface conditions in the irminger basin first at 338 309 ka and later at 211 190 ka after which both glacials and interglacials were colder as the arctic front migrated southeast of site 919 in addition to offering these findings this reconstruction provides a longer term geologic context for the interpretation of more recent paleoceanographic events and patterns of deposition from this region

a comparison between multiproxy and historical data ad 1990 1840 of drift ice conditions on the east greenland shelf 66 n the reduction in sea ice along the se greenland coast during the last century has severely impacted ice rafting to this area in order to reconstruct ice rafting and oceanographic conditions in the area of denmark strait during the last 150 years we conducted a multiproxy study on three short 20 cm sediment cores from outer kangerdlugssuaq trough 300 m water depth the proxy based data obtained have been compared with historical and instrumental data to gain a better understanding of the ice sheet ocean interactions in the area a robust chronology has been developed based on 210pb and 137cs measurements on core po175gkc 9 66 2 n 32 w and expanded to the two adjacent cores based on correlations between calcite weight percent records our proxy records include sea ice and phytoplankton biomarkers and a variety of mineralogical determinations based on the 2 mm sediment fraction including identification with quantitative x ray diffraction ice rafted debris counts on the 63 150 m sand fraction

dissolution of calcite in deep sea sediments ph and o2 microelectrode results abstract we present microelectrode profiles of oxygen ph and porosity measured at in situ depth across the sediment water interface from stations above and below the calcite saturation horizon in the equatorial atlantic resistivity electrode data indicate that the diffusion coefficient for solutes is attenuated by nearly a factor of two within the top centimeter of the sediment lattice oxygen and porosity data are used to estimate that the organic carbon respiration rate of the sediment is 10 15 mol cm 2 yr 1 in these locations comparison of the ph data with numerical model results reveals that sedimentary calcite dissolves in response to respiration in the top few centimeters of sediment even above the saturation horizon we calculate that the effective in situ dissolution rate constant for calcite required to explain these data is the neighborhood of 10 100 d 1 although more data are needed to confirm this result it appears to be at least an order of magnitude less than the rate observed in laboratory stirred reactor experiments

increased co2 uptake due to sea ice growth and decay in the nordic seas 1 the uptake rates of atmospheric co2 in the nordic seas are among the highest in the world s oceans this has been ascribed mainly to a strong biological drawdown but chemical processes within the sea ice itself have also been suggested to play a role the importance of sea ice for the carbon uptake in the nordic seas is currently unknown we present evidence from 50 localities in the arctic ocean that dissolved inorganic carbon is rejected together with brine from growing sea ice and that sea ice melting during summer is rich in carbonates model calculations show that melting of sea ice exported from the arctic ocean into the east greenland current and the nordic seas plays an important and overlooked role in regulating the surface water partial pressure of co2 and increases the seasonal co2 uptake in the area by approximately 50

the nature of the proterozoic cambrian transition in the northern amadeus basin central australia abstract the nature and completeness of the rock record is vital in determining whether evolution across the proterozoic cambrian boundary was episodic or explosive this study documents the nature of the neoproterozoic cambrian transition within the arumbera sandstone of the northern amadeus basin central australia and demonstrates an erosional surface close to this major stratigraphic boundary we are not able to recognise major facies differences between the largely unfossiliferous lower units i and ii and the rich trace fossil bearing beds of units iii iv horizons above and below the purported neoproterozoic cambrian transition were traced laterally and searched for both trace and body fossils in an attempt to locate a local boundary between the neoproterozoic and cambrian a single nonconformity bound sedimentary cycle above the major erosional surface dividing arumbera ii and iii is recognised the lowest sedimentary cycle of arumbera iii is devoid of trace fossils but at correlative levels in the ooraminna sub basin this horizon bears elements of the ediacara fauna reported for the first time herein we therefore suggest that contrary to previous studies the neoproterozoic cambrian transition is not coincident with the widespread seismic reflector but in areas of more complete sedimentation actually lies above it this study also presents new stratigraphic ichnological and palaeontological information from the neoproterozoic cambrian transition in central australia identifies areas of potentially continuous sedimentation and provides a basis for correlation of the arumbera sandstone with other neoproterozoic cambrian successions within australia and beyond

dinoflagellate cyst evidence for warm interglacial conditions at the northern barents sea margin during marine oxygen isotope stage 5 dinoflagellate cyst analysis has been conducted on a sediment core from the northern barents sea margin eastern arctic ocean to reconstruct sea surface conditions during marine oxygen isotope stage 5 cyst concentrations and composition of assemblages display a distinct variability reflecting deglacial warming and the onset of relatively warm interglacial conditions in early stage 5 dinoflagellate cyst assemblages of the last interglacial which corresponds broadly to substage 5e are comparable with those from recent sediments of the area but have lower abundances of cold water taxa such assemblages suggest that sea surface temperatures of the last interglacial were therefore at least as warm as today or even warmer after a distinct cooling relatively stable cold conditions with minor periods of surface water warming prevailed from mid substages 5d to 5b temperatures might have been similar in substages 5a and 5e but the different compositions of assemblages indicate a stronger stratification of surface waters probably owing to a larger meltwater supply in substage 5a these results are compared with previous studies on marine carbonate and calcareous microfossil records from the fram strait and yermak plateau area which show that the general view of a cold last interglacial in the eastern arctic ocean is untenable copyright 2001 john wiley sons ltd

rare earth elements rees in the tropical south atlantic and quantitative deconvolution of their non conservative behavior this study presents new concentration measurements of dissolved rare earth elements drees along a full depth east west section across the tropical south atlantic 12 s and uses these data to investigate the oceanic cycling of the rees enrichment of drees associated with the redox cycling of fe mn oxides is observed in the oxygen minimum zone omz off the african shelf for deeper waters a multi parameter mixing model was developed to deconvolve the relative importance of physical transport i e water mass mixing from biogeochemical controls on the dree distribution in the deep atlantic this approach enables chemical processes involved in ree cycling not apparent from the measurements alone to be distinguished and quantified results show that the measured dree concentrations below 1000 m are dominantly controlled 75 by preformed ree concentrations resulting from water mass mixing this result indicates that the linear correlation between drees and dissolved si observed in atlantic deep waters results from the dominantly conservative behavior of these tracers rather than from similar chemical processes influencing both drees and si minor addition of drees 10 of dnd and 5 of dyb is observed in the deep 4000 m brazil basin resulting from either remineralization of particles in situ or along the flow path greater addition of drees up to 25 for dnd and 20 for dyb is found at 1500 m and below 4000 m in the angola basin near the african continental margin cerium anomalies suggest that different sources are responsible for these dree addition plumes the 1500 m excess is most likely attributed to dree release from fe oxides whereas the 4000 m excess may be due to remineralization of calcite higher particulate fluxes and a more sluggish ocean circulation in the angola basin may explain why the dree excesses in this basin are significantly higher than that observed in the brazil basin hydrothermal venting over the mid atlantic ridge acts as a regional net sink for light rees but has little influence on the net budget of heavy rees the combination of dense ree measurements with water mass deconvolution is shown to provide quantitative assessment of the relative roles of physical and biogeochemical processes in the oceanic cycling of rees

marine calcium carbonate preservation vs climate change over the last two millennia in the fram strait implications for planktic foraminiferal paleostudies abstract we present a high resolution study of planktic foraminiferal distribution patterns in a deep sea core from the eastern fram strait position 78 55 n 06 46 e water depth 1497 m the sediment core is located below atlantic water masses flowing into the arctic ocean and spans the last 2400 years the investigation is based on planktic foraminiferal species distribution stable isotopes and sedimentological data the mean shell weight of neogloboquadrina pachyderma fragmentation organic and inorganic carbon content and the presence of benthic organic linings were also investigated as an indication of preservation changes the results indicate that the planktic foraminifera are affected by dissolution and point to five periods of especially poor preservation at 200 bce 300 650 ce 700 850 ce 1400 1500 ce and from 1800 ce to present in the last century small and fragile subpolar species turborotalita quinqueloba and globigerinita uvula are preserved the increased percentage of these subpolar species together with increases in the caco 3 toc and total foraminiferal flux would point to surface water warming however our data suggest that these fragile species may not have been preserved in sediments older than 1900 ce due to selective dissolution consequently the magnitude of the previously recorded recent surface water warming in the fram strait may be overestimated

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

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

recent benthic foraminifera of a transect from the north pole to the yermak plateau eastern central arctic ocean the recent distribution of living and dead benthic foraminifera of the arctic ocean proper has been examined in surface sediments that were sampled during the international arctic ocean expedition 1991 arctic 91 the samples represent the amundsen and nansen basins the morris jesup rise and the yermak plateau from 90 n to 79 42 4 n 05 15 6 e due to the technical difficulties of deep sea drilling in the arctic ocean these areas have until now been investigated only in very low density sampling the arctic 91 sites of this study cover a water depth range between 552 and 4375 m and represent three sites which are seasonally ice free although not yearly while the other sites are characterized by permanent sea ice there is a recent production of benthic foraminifera in the whole investigation area and all surface samples contain both benthic and planktonic foraminifera abyssal assemblages are recorded in the amundsen and nansen basins where stetsonia arctica dominates with high abundances it is however also possible to distinguish these two basins by the use of diagnostic species at intermediate water depths 500 to 2000 2500 m the faunas show higher diversities and higher abundances of atlantic species than the deep sea sites mixing of north atlantic water down to approximately 2500 m is suggested to explain the influx of atlantic species on the yermak plateau and the morris jesup rise the foraminiferal tests are well preserved within the investigation area and dissolution does not seem to be very obvious in the deeper areas there is no evidence from the recent foraminiferal faunas that the bottom waters of the eastern central arctic ocean are undersaturated with respect to calcium carbonate and the deep sea areas appear therefore to lie above the present ccd

the problems and potential of using animal fossils and trace fossils in terminal proterozoic biostratigraphy abstract despite the discovery of soft bodied megascopic fossils of late neoproterozoic age at numerous localities world wide there has been slow acceptance of their potential for intercontinental correlation the stratigraphic thickness of sediments separating individual occurrences of such fossils from the base of the cambrian is very varied basic questions have also been posed as to the classification of the organisms represented and hence their likely time significance recent geochronological studies support notions of a narrow time distribution well studied neoproterozoic sequences in eurasia eastern and western north america and southern australia show strikingly similar patterns of increase in the numbers and diversity of trace fossils and soft bodied megascopic remains up section though strata immediately preceding the cambrian are relatively barren other than for a sparse palynoflora and compressions of primitive plants trace fossils from australian sections relating to an early part of the ediacaran apparently overlap a time of abundance of large process bearing acritarchs and big leiosphaerids this overlap of early animal traces and distinctive acritarchs may prove to be of significant biostratigraphic importance rare discoveries of forms resembling rangea gurich in the flinders ranges of south australia precede the classical ediacara assemblage and may provide a possible correlation with occurrences of this genus in namibia the distinctive remains and trace fossils at this level constituting the rangeid hiemalora assemblage zone resemble a biota from the podolia region of the ukraine and show a similarity to finds in parts of the windermere supergroup of the northwest territories canada similarly the offshore frondose assemblage of newfoundland is comparable with the biota of charnwood forest england the type ediacara assemblage of the flinders ranges characterizing the dickinsonia costata assemblage zone is a climax biota with diverse taxa and large individual species as well as some 20 ichnogenera it closely correlates with a late redkinian or early kotlinian assemblage in the upper part of the section on the zimny gory coast of the white sea northern russia the trace fossils of these levels show that significant diversification began before the cambrian

recent calcium carbonate dissolution in the barents sea paleoceanographic applications abstract studies of benthic foraminifera in surface sediments of the arctic epicontinental barents sea show several indications of calcium carbonate dissolution low values of calcium carbonate correspond to low ratios of calcareous agglutinating foraminifera planktic benthic foraminifera high ratios of living dead foraminifera corroded calcareous foraminifera and high numbers of exposed organic linings of foraminifera dissolution increases eastwards and northwards in the study area we suggest that the dissolution is caused by the presence of dense cold saline and co 2 rich bottom water which is linked to sea ice production and the position of the oceanic polar front we also think calcium carbonate dissolution in this area indicates a sink for atmospheric co 2

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

modeling the calcite lysocline a numerical model of calcite dissolution in contact with sediment pore water is used to predict the depth and shape of the calcite lysocline in the deep sea model results are compared with lysocline data from 13 regions in the atlantic pacific and indian oceans the model lysocline shape is sensitive to the calcite dissolution rate constant the calcite organic carbon and refractory material rain rates and the rates of oxic versus anoxic organic carbon degradation in the sediment the model is able to reproduce the observed lysocline within the constraints of the sediment trap and calcite accumulation data using a calcite dissolution rate constant of 30 100 d 1 a molar ratio of organic carbon to calcite rain rates of 0 5 1 0 and an initial caco3 fraction of 90 excluding organic carbon this rate constant is consistent with microelectrode results presented by archer et al 1989 the model predicts that 30 50 of the calcite rain to the sea floor at the saturation horizon dissolves in response to organic carbon respiration consistent with previous modeling studies the range in the best fit value of the organic inorganic carbon rain rates arises from model sensitivity to uncertainty in the rate of anoxic carbon degradation in the sediment and in the rain rate of refractory material rather than from scatter in the data lysocline data from the western equatorial atlantic are anomalous to the rest of the data this anomaly may be explained by high rates of refractory material sedimentation from the amazon river

neoproterozoic carbon isotope stratigraphy of the amadeus basin central australia neoproterozoic shallow marine and carbonate rich strata of the northern amadeus basin central australia comprise a geochemical record of neoproterozoic seawater that facilitates correlation with other basins in australia and worldwide this study includes new carbon and oxygen isotope measurements of cryogenian and ediacaran carbonate in the northern amadeus basin that in combination with previous data from tonian strata of the bitter springs formation form a composite amadeus basin neoproterozoic c record key features of the cryogenian ediacaran portion of this record include 1 negative c excursions in cap carbonates overlying cryogenian glacigenic deposits of the areyonga and olympic formations i e the rasthof and maieberg excursions respectively 2 a mid cryogenian negative excursion in the ringwood member of the aralka formation seemingly correlative with the taishir excursion of sw mongolia 3 a subsequent mid cryogenian positive excursion the keele peak excursion in the limbla member of the aralka formation and 4 relatively low magnitude excursions in the ediacaran julie formation in comparison with other neoproterozoic stratigraphic successions key portions of the overall neoproterozoic c record that appear to be absent from the amadeus basin based on existing data include large magnitude negative excursions islay and trezona excursions that immediately preceded basaland terminal cryogenian i e sturtian and marinoan respectively glaciations these missing c excursions are associated with significant unconformities in the amadeus basin c and o from carbonate clasts in diamictite of the areyonga and olympic formations suggest that deposition of islay and trezona equivalent strata was limited or nonexistent in the amadeus basin as opposed to the possibility that these strata were deposited but subsequently removed by glacial erosion our new amadeus basin results refine cryogenian and early ediacaran correlations among the amadeus basin adelaide rift complex and namibia the lower part of the ringwood member which was deposited during early stages of the cryogenian nonglacial interlude includes two negative c excursions that are also evident in previous results from the tapley hill formation of the adelaide rift complex the upper part of the ringwood member contains abundant stromatolites and seems to correlate with cryogenian stromatolite reefs of the balcanoona formation in the adelaide rift complex the overlying limbla member in the amadeus basin correlates with the yankaninna etina amberoona and enorama formations of the adelaide rift complex as well as carbonate from other continents that record the keele peak excursion c from the early ediacaran olympic cap of the amadeus basin is 1 comparable to previous results from the maieberg and elandshoek formations in namibia and 2 consistent with diachronous deposition of marinoan cap dolostone in the amadeus basin additionally new c from the julie formation of the amadeus basin is similar to previous results from the late ediacaran kuibis subgroup in southern namibia these correlations underscore that ediacaran strata of namibia as well as the cryogenian nonglacial interlude strata of the adelaide rift complex are roughly an order of magnitude thicker than stratigraphic counterparts in the amadeus basin the wide disparity in sedimentation rates implied by this finding is likely attributable to fundamental differences in the neoproterozoic tectonic settings of the three locations

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

late quaternary calcium carbonate sedimentation and terrigenous input along the east greenland continental margin nine large box cores collected in the western greenland iceland norwegian gin sea were analyzed for calcium carbonate content and coarse fraction components stratigraphic control is based on oxygen isotope records performed on four of the cores all cores were correlated using oxygen and carbon isotope data fluctuations in calcium carbonate content coarse terrigenous particle content and volcanic ash beds glacial and interglacial cycles are documented by a number of terrigenous particle events and differentiated calcium carbonate production which can be correlated to major paleoceanographic and paleoclimatic shifts in the older core sections extensive deposition of ice rafted detritus ird persisted until about oxygen isotope stage 9 and document a relatively stable environment in this area strongly influenced by cold surface water masses the following interval was characterized by variations in the general surface water circulation pattern although high amounts of ird are still present in iceland sea sediments pronounced shifts in terrigenous input and pelagic carbonate records were identified close to the oxygen isotope stage full size image 1 k and full size image 1 k boundaries indicating massive melting of icebergs in the western gin sea these enormous inputs of debris were followed by an increase in calcium carbonate production caused by maximum intrusion of warm atlantic surface waters relatively high calcium carbonate contents also show that only little dilution by fine grained material and a minimum of ice melting occurred during these warm phases during oxygen isotope stage 5 conditions were more uniform indicating a less pronounced westward penetration of atlantic waters as compared to the holocene the last glacial stages 4 2 is characterized by the occurrence of heinrich like events although high ird contents were present throughout this interval a distinct contrast between the northernmost cores and the cores in the south is indicative of a rather strong westward penetration of atlantic water in the north and of an area dominated by cold water east of the kolbeinsey ridge during the holocene however conditions west of jan mayen seem to have remained constantly dominated by cold surface waters throughout the whole time investigated

a 1 0 myr record of glacial north atlantic intermediate water variability from odp site 982 in the northeast atlantic changes in the intermediate water structure of the north atlantic were reconstructed using benthic foraminiferal 13c at ocean drilling program odp site 982 for the past 1 0 myr during most terminations of the late pleistocene melting of icebergs and low salinity surface waters caused production of glacial north atlantic intermediate water to cease resulting in decreased ventilation of the middepth north atlantic poor ventilation of intermediate water masses lasted well into some interglacial stages until upper north atlantic deep water nadw production resumed under full interglacial conditions the magnitude of benthic 13c minima and ice rafted debris maxima at terminations at site 982 generally match the degree of glacial suppression of nadw inferred from site 607 these processes may be related and controlled by the spatial and seasonal extent of sea ice cover during glaciations in the nordic seas

microbiota from the neoproterozoic liulaobei formation in the huainan region northern anhui china abundant and well preserved acritarchs have been obtained from shales of the neoproterozoic liulaobei formation in the huainan region northern anhui province china this microfossil assemblage consisting of 9 genera 11 species and an undetermined form is dominated by sphaeromorphic acritarchs as well as filamentous cyanobacteria with the exception of a few new forms e g pololeptus rugosa yin c y comb nov p biacris yin c y comb nov and the undetermined taxon most components of this microbiota are well known from neoproterozoic deposits elsewhere in the world an integrational assessment of this microbiota in conjunction with the accompanying occurrence of the chuaria tawuia megafossil assemblage as well as radiometric datings tends to suggest that the liulaobei formation might be bracketed within a late riphean time range of 850 700 ma providing an useful reference for estimating the age of the overlying jiuliqiao formation which yields carbonaceous worm like fossils probably of a metazoan origin

aspects of problematic acid resistant organic walled microfossils acritarchs in the upper proterozoic of the north atlantic region abstract proterozoic acritarchs are a heterogeneous group of acid resistant organic walled microfossils of obscure biological affinities the acritarch record is regarded as strongly baised by a combination of mechanisms such as the character of the original ecosystems depositional conditions diagenetic history and thermal and tectonic events three distinctive acritarch assemblages are recognized in upper proterozoic sequences in scandinavia and greenland they can be compared with upper proterozoic upper riphean and vendian assemblages previously reported from the russian and siberian platforms china and elsewhere substantial taxonomic changes characterize these assemblages and are usually connected with the existence of major unconformities in the investigated rock sequences the acritarch assemblages can be traced over vast areas and are considered as constituting a promising tool for the biostratigraphic correlation of the upper proterozoic and lower cambrian

an isotopic biogeochemical study of neoproterozoic and early cambrian sediments from the centralian superbasin australia abstract organic matter from neoproterozoic and early cambrian sediments of the amadeus and officer basins of the centralian superbasin australia has been studied for biomarker distributions and the carbon isotopic compositions of kerogen and individual hydrocarbons these sediments represent both shallow and deep water marine facies in the older sections and marine and saline lacustrine carbonate deposits in the cambrian hydrocarbon biomarker patterns were found to be quite consistent with the known sedimentary environments and provide valuable insights into the biogeochemical changes which accompanied the transition from a microbially dominated ocean to the early stages of metazoan radiation in particular carbon isotopic data for n alkyl and isoprenoid lipids presented here and in earlier studies showed a reversal in carbon isotopic ordering between the proterozoic and phanerozoic by comparison with the 13c of kerogen n alkyl lipids from deep water proterozoic sediments were enriched in 13c and appear to be derived mainly from heterotrophs whilst open marine phanerozoic counterparts are 13c depleted and evidently derived mainly from autotrophs data from the samples studied here are consistent with a model invoking a change in the redox structure of the ocean possibly aided by the innovation of faecal pellets

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

latest proterozoic stratigraphy and earth history the end of the proterozoic eon was a time of pronounced biological biogeochemical climatic and tectonic change new bio and chemostratigraphic data provide an improved framework for stratigraphic correlation making possible a deeper understanding of latest proterozoic earth history and providing tools for a chronostratigraphic division of late proterozoic time

exceptional preservation of fossils in an upper proterozoic shale late proterozoic organisms must have been diverse and widely distributed but in general their fossil record is both taxonomically and environmentally limited exceptional preservation of proterozoic fossils is not unknown but it is usually associated with silicified carbonates from restricted peritidal or playa lake environments1 2 we report here an exceptionally well preserved and distinctive assemblage of late proterozoic fossils from subtidal marine shales in addition to the sphaeromorphic acritarchs and cyanobacterial sheaths routinely preserved in proterozoic rocks this assemblage includes multicellular algae seaweeds a diverse assortment of morphologically complex protistan vesicles and probable heterotrophic bacteria thus it provides one of the clearest and most taxonomically varied views of proterozoic life yet reported

marine core evidence for reduced deep water production during termination ii followed by a relatively stable substage 5e eemian we present oxygen and carbon isotope records of benthic foraminifera from the glacial stage 6 through interglacial substage 5e eemian sections of several cores from the subpolar north atlantic the cores range in water depth from 1451 to 2658 m in one core we generated estimates of sea surface temperature sst and of ice rafted detritus ird delivery for all of stage 5 we reconstruct bathymeric profiles of 13c for stage 6 termination ii and three time slices of substage 5e the 13c profiles indicate that local deep water geometry during stage 6 was similar to that of the last glaciation with glacial north atlantic intermediate water gnaiw overlying deeper waters partially of southern origin an anomalously large peak in ird coupled with planktonic 18o evidence for iceberg melting immediately precedes termination ii and is otherwise similar to stage 2 and 3 heinrich events during the termination low 13c values are observed in cores near and above 2 km providing evidence of reduced gnaiw production in association with deglacial melting in the shallowest cores low 13c values persist into early substage 5e indicating that the southward retreat of southern source waters was not completed until well after the beginning of the substage in contrast to termination i ssts remained cold until the end of the deglaciation this may be why there is little evidence from marine and terrestrial sequences for a pronounced climate reversal on termination ii despite what is now clear evidence of a significant reduction in ocean ventilation the faunal data suggest that ssts during early 5e were about 7 c warmer than during the glaciation sst rose several degrees from early to middle substage 5e peaked in middle substage 5e at about 10 c above glacial values and then gradually declined by about 5 c these changes were linked to variations in water mass configuration as interpreted from benthic 13c evidence most of the evidence suggests that oscillations superimposed on the gradual sst trend were 1 2 c in contrast to the larger sst changes 3 4 c documented for substage 5d

sub sea surface temperatures in the polar north atlantic during the holocene planktic foraminiferal mg ca temperature reconstructions holocene sea surface temperatures in the eastern fram strait are reconstructed based on mg ca ratios measured on the planktic foraminifer neogloboquadrina pachyderma sin the reconstructed sub sea surface temperatures ssstmg ca fluctuate markedly during the earliest holocene at 11 7 and 10 5 kyr bp this is probably in response to the varying presence of sea ice and deglacial meltwater between 10 5 7 9 kyr bp the ssstmg ca values are relatively high 4 c and more stable reflecting high insolation and intensified poleward advection of atlantic water after 7 9 kyr bp the ssstmg ca values decline to an average of 3 c throughout the mid holocene these changes can be attributed to a combined effect of reduced poleward oceanic heat advection and a decline in insolation as well as a gradually increased influence of eastward migrating arctic water the ssstmg ca values increase and vary between 2 1 c and 5 8 c from 2 7 kyr bp to the present this warming is in contrast to declining late holocene in

surface water conditions and calcium carbonate preservation in the fram strait during marine isotope stage 2 28 8 15 4 kyr 1 we present a high resolution record of calcium carbonate preservation alongside the distribution pattern of planktic foraminifera from the fram strait the record covers the marine isotope stage mis 2 28 8 to 15 4 kyr including the last glacial maximum lgm and the early deglaciation in multidecadal temporal resolution the investigation is based on the distribution patterns of planktic foraminifera stable isotopes mean shell weight of neogloboquadrina pachyderma the degree of fragmentation of planktic shells caco3 content and geochemical and sedimentological data the dissolution proxies indicate long lasting periods of markedly reduced preservation of calcium carbonate at 28 8 27 2 24 1 23 2 and 16 6 15 4 kyr in addition to a number of short lasting periods 300 year during the lgm these periods are accompanied by a simultaneous and significant reduction in specimens of subpolar planktic foraminifera indicating a southward expansion of arctic surface water masses prolonged periods with high abundances of subpolar foraminiferal species and good preservation of calcium carbonate are attributed to increased influence of atlantic water masses which appears to persist throughout most of the mis 2 comparison to holocene mis 1 shell weight records shows that the preservation during mis 2 was overall better even during the events of dissolution this was probably a reflection of the low concentration of atmospheric co2 at the time

contrasting glacial interglacial regimes in the western arctic ocean as exemplified by a sedimentary record from the mendeleev ridge distinct cyclicity in lithology and microfaunal distribution in sediment cores from the mendeleev ridge in the western arctic ocean water depths ca 1 5 km reflects contrasting glacial interglacial sedimentary patterns we conclude that during major glaciations extremely thick pack ice or ice shelves covered the western arctic ocean and its circulation was restricted in comparison with interglacial modern type conditions glacier collapse events are marked in sediment cores by increased contents of ice rafted debris notably by spikes of detrital carbonates and iron oxide grains from the canadian arctic archipelago composition of foraminiferal calcite n 18 o and n 13 c also shows strong cyclicity indicating changes in freshwater balance and or ventilation rates of the arctic ocean light stable isotopic spikes characterize deglacial events such as the last deglaciation at ca 12 14 c kyr bp the prolonged period with low n 18 o and n 13 c values and elevated contents of iron oxide grains from the canadian archipelago in the lower part of the mendeleev ridge record is interpreted to signify the pooling of freshwater in the amerasia basin possibly in relation to an extended glaciation in arctic north america unique benthic foraminiferal events provide a means for an independent stratigraphic correlation of sedimentary records from the mendeleev ridge and other mid depth locations throughout the arctic ocean such as the northwind and lomonosov ridges this correlation demonstrates the disparity of existing age models and underscores the need to establish a definitive chronostratigraphy for arctic ocean sediments 2003 elsevier b v all rights reserved

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

the mid pleistocene climate transition a deep sea carbon isotopic perspective five 13c records from the deep ocean extending back to 1 3 ma were examined in order to constrain changes in mean ocean carbon isotope composition and thermohaline circulation over the 41 to 100 ka climate transition these data show that significant perturbations in mean ocean carbon chemistry were associated with the mid pleistocene climate transition notable features of the last 1 3 myr are 1 a pronounced 0 3 decrease in mean ocean 13c between 0 9 and 1 0 myr followed by a return to pre 1 0 ma values by 400 ka b p which we propose was due to the onetime addition of isotopically depleted terrestrial carbon to the ocean possibly associated with an increase in global aridity and decrease in the size of the biosphere across the 41 to 100 ka transition 2 no change in the atlantic pacific a p 13c gradient over the last 1 3 myr suggesting no change in mean ocean nutrient content accompanied the addition of light carbon and 3 stronger vertical nutrient fractionation in the north atlantic in the middle pleistocene between sites 607 and 552 suggesting weaker north atlantic deep water formation at this time relative to the early and late pleistocene we also find evidence for a more pronounced deep recirculation gyre in the western north atlantic basin in the early brunhes as evidenced by aging of deep northern basin water site 607 relative to deep water in the equatorial atlantic site 664

prokaryotic and eukaryotic microfossils from a proterozoic phanerozoic transition in china cherts of the doushantuo formation in the yangtze gorges south china contain a superbly preserved heterogeneous assemblage of bacteria cyanobacteria planktonic algae submillimetre sized burrows and problematica the microbiota has a bearing on defining the precambrian cambrian boundary baltisphaeridium and associated spinose microfossils in the chert suggest an early cambrian age whereas other acritarchs vendotaenids and pretrilobite small shelly fossils from the conformably overlying the dengying formation indicate a late proterozoic age for the doushantuo this mixed benthic planktonic assemblage preserved in silicified laminated microbial mat like fabrics provides a unique sample of diverse microbiotic elements existing at the dawn of the phanerozoic and records the earliest evidence of meiofauna

variability in the deep and intermediate water circulation of the atlantic ocean during the past 25 000 years northern hemisphere modulation of the southern ocean the relative flux of north atlantic deep water nadw out of the atlantic can be monitored in the southern ocean where high 13c nadw mixes rapidly with low 13c recirculated pacific water before forming antarctic bottom water aabw by using 13c measured in benthic foraminifera as a water mass tracer it is shown that the southern ocean was dominated by pacific water with little nadw contribution during the last glaciation these tracer results document the direct physical connection between insolation controlled northern hemisphere oscillations and changes in the chemical and physical properties of southern ocean water the 13c records from the deep tropical atlantic document the transition from an atlantic dominated by southern ocean water during the last glaciation to an atlantic dominated by nadw during the holocene with more southern ocean water in the deep atlantic during the last glaciation the boundary between nadw and southern ocean water was north of its modern position allowing more southern ocean water to enter the eastern atlantic through the romanche fracture zone carbon isotope records from the caribbean and mediterranean seas suggest that the influence of mediterranean overflow water mow extended to the caribbean during the last glaciation and therefore was a volumetrically much more important water mass in the intermediate depth atlantic than it is today

diagenesis of early permian high latitude limestones lower parmeener supergroup tasmania the darlington sakmarian and berriedale artinskian limestones are neritic deposits that accumulated in high latitude environments along the south eastern margin of pangea in what is now tasmania these rocks underwent a series of diagenetic processes that began in the marine palaeoenvironment continued during rapid burial and were profoundly modified by alteration associated with the intrusion of mesozoic igneous rocks marine diagenesis was important but contradictory although dissolution took place there was also coeval precipitation of fibrous calcite cement phosphate and glauconite as well as calcitization of aragonite shells these processes are interpreted as having been promoted by mixing of shelf and upwelling deep ocean waters and enabled by microbial degradation of organic matter in contrast to warm water carbonates where meteoric diagenesis is important the darlington and berriedale limestones were largely unaffected by meteoric diagenesis only minor dissolution and local cementation took place in this diagenetic environment although mechanical compaction was ubiquitous correlation with burial history curves indicates that chemical compaction became important as burial depths exceeded 150 m promoting precipitation of extensive ferroan calcite this effect resulted from burial by rapidly deposited overlying thick late permian and triassic terrestrial sediments this diagenetic pathway was however complicated by the subsequent intrusion of massive mesozoic diabases and associated silicifying diagenetic fluids finally fractures most probably connected with cretaceous uplift were filled with late stage non ferroan calcite cement this study suggests that both carbonate dissolution and precipitation occur in high latitude marine palaeoenvironments and therefore the cold water diagenetic realm is not always destructive in terms of diagenesis furthermore it appears that for the early permian of southern pangea at least there was no real difference in the diagenetic pathways taken by cool water and cold water carbonates

stability of north atlantic water masses in face of pronounced climate variability during the pleistocene 1 geochemical profiles from the north atlantic ocean suggest that the vertical 13c structure of the water column at intermediate depths did not change significantly between glacial and interglacial time over much of the pleistocene despite large changes in ice volume and iceberg delivery from nearby landmasses the most anomalous 13c profiles are from the extreme interglaciations of the late pleistocene this compilation of data suggests that unlike today an extreme interglaciation the two primary sources of northern deep water norwegian greenland sea and labrador sea subpolar north atlantic had different characteristic 13c values over most of the pleistocene we speculate that the current open sea ice conditions in the norwegian greenland sea are a relatively rare occurrence and that the high 13c deep water that forms in this region today is geologically unusual if northern source deep waters can have highly variable 13c then this likelihood must be considered when inferring past circulation changes from benthic 13c records

recent and pleistocene carbonate dissolution in sediments of the norwegian greenland sea surface sediment samples from the norwegian greenland sea were investigated to reconstruct the spatial distribution of recent carbonate dissolution on the seafloor additionally carbonate dissolution records of ocean drilling program sites 985 and 987 are presented to outline the development of pleistocene carbonate preservation today well preserved carbonate tests can be observed along the inflow of warm atlantic surface water extending as far as into the northernmost norwegian greenland sea increased dissolution is indicated along the continental margins and in the deepest parts of the greenland basin factors favoring carbonate preservation were found to be supersaturation of the water column with respect to calcium carbonate high carbonate rain and probably excess alkalinity of bottom waters supplied by the arctic river discharge supralysoklinal dissolution is most important for recent carbonate dissolution in the norwegian greenland sea whereas the deepest parts of the greenland basin reaches the calcite saturation horizon pleistocene dissolution records show some prominent peaks of extreme carbonate dissolution during the brunhes chron carbonate dissolution maxima can be related to meltwater pulses which probably inhibited deep water formation in the norwegian greenland sea during deglaciation events long term severe carbonate dissolution is evident during the late matuyama chron this can be probably related to low carbonate rain due to a more eastwards located east greenland current and the nearly absence of the not yet polar adapted neogloboquadrina pachyderma sin during that period extreme dissolution events during the late matuyama indicate strongly reduced deep water formation

sequence stratigraphy and the interpretation of neoproterozoic earth history abstract the application of sequence stratigraphy to neoproterozoic successions is important for improving the resolution of time correlation within individual sedimentary basins and potentially at a global scale the methodology is illustrated in this paper by reference to two contrasting examples from the flinders ranges adelaide geosyncline of south australia where the younger part of the neoproterozoic to earliest cambrian succession 770 ma to 540 ma has been divided into thirteen unconformity bounded depositional sequences one of the most prominent sequence boundaries at or near the base of the wonoka formation is characterized by a series of buried canyons as much as 1 km deep high resolution sequence stratigraphic studies at umberatana syncline continue to support the view that the canyons were cut subaerially and filled by fluvial and shallow water sediments in contrast to the wonoka canyons sequence boundaries interpreted at the base of the nuccaleena formation seacliff sandstone and near the top of the abc range quartzite are relatively subtle with only limited evidence for erosion and valley incision four sequence boundaries at the level of the sturtian and marinoan varanger glacial deposits and in the vicinity of the precambrian cambrian boundary are thought to correlate with surfaces in the amadeus basin of central australia other prominent sequence boundaries including the wonoka canyons and surfaces within the upper part of the wonoka formation and at the base of the ediacara member of the rawnsley quartzite correspond with a relatively condensed section in the amadeus basin and their lateral persistence beyond the adelaide geosyncline is therefore difficult to evaluate given the lack of precision in biostratigraphy and isotope geochemistry in neoproterozoic rocks and in a marked departure from phanerozoic practice we recommend placement of a terminal proterozoic gssp at a sequence boundary a prime candidate in australia is the sequence boundary at the base of the nuccaleena formation seacliff sandstone immediately above the marinoan glacial rocks in the adelaide geosyncline and its likely correlative at or near the base of the gaylad sandstone in the amadeus basin

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

late quaternary changes in surface water and deep water masses of the nordic seas and north eastern north atlantic a review quantitative and semiquantitative proxy data based on more than 200 core top samples and 100 deep sea cores lead to important new insights about late quaternary changes in paleo oceanography climate and microfaunal habitats in the north eastern north atlantic and nordic seas insights resulting from a detailed investigation by the kiel research project sfb 313 132 summarized in this paper planktonic foraminifera species provide reliable tracers of past sea surface temperatures and currents the genus beella in particular was found to trace subtropical water masses up to the far north benthic foraminifera species served as sensors of bottom currents and local flux rates of organic matter new orders of time resolution are reached via stable isotope stratigraphy and accelerator mass spectrometry carbon 14 dating allowing the identification of meltwater events lasting a few hundred years and shorter a time range where however the yet unquantified role of bioturbation presents a growing problem based on this high resolution stratigraphy a number of time slices synoptic time intervals are defined to reconstruct the incursion of atlantic water masses to map paleocurrent patterns within the nordic seas and the north eastern north atlantic and to test alternative circulation models for example for the last glacial maximum lgm and various meltwater episodes these are clearly coeval with dansgaard oeschger events found in greenland ice cores with the actual cause of the flickering climate as yet unknown likewise there is ongoing controversy about the extent of past sea ice cover and about possible changes from the present anti estuarine to estuarine mode of deep water exchange between the north atlantic and the nordic seas during the lgm south of iceland however the history of deep water renewal over the last glacial cycle covering the last 30000 years was largely deciphered

patterns of phytoplankton radiation across the precambrian cambrian boundary late proterozoic and early phanerozoic phytoplankton comprise a wide array of microfossils of possibly bacterial and algal affinity their radiation patterns around the proterozoic cambrian boundary interval are becoming increasingly well known for numerous sequences in the east european and siberian platforms china baltoscandia and north america transgressive sequences in the east european platform and northern baltoscandia comprise alternating sandstones mudstones and claystones their sedimentology is well documented and microfossils acritarchs chitinous fossils sabelliditids shelly fossils and trace fossils are well represented rocks immediately overlying the transitional beds have yielded lower cambrian trilobite faunas that are utilized for regional correlations continuous successions of planktic microorganisms consisting of prokaryotic photoautotrophic cyanobacteria and algal protists are known from rocks comprising the transitional vendian cambrian sequence in the east european platform the rock sequence attributed to the lower cambrian platysolenites antiquissimus zone has yielded acritarchs of 9cambrian type9 abruptly replacing a morphologically simple proterozoic type microbiota recorded in beds of the upper proterozoic sabellidites vendotaenia zone the radiation of novel forms of phytoplankton appears to have been synchronous over a wide part of the late proterozoicarly cambrian shelf and is parallelled by the nearly contemporaneous emergence of cambrian shelly fossils and trace fossils along with new acritarch taxa the diagnostic acritarch assemblage of the platysolenites antiquissimus zone consists of widely distributed species occurring also in the lowermost cambrian deposits of the siberian platform baltoscandia greenland north america svalbard and scotland it is suggested that along with shelly faunas trace fossils and geochemical data the general radiation patterns of phytoplankton shed light on the events shaping the important biotic events around the precambrian cambrian boundary it is also believed that a better understanding of the regulatory mechanisms affecting the base of trophic chains may in turn be of significant importance in defining the precambrian cambrian boundary

changes in east atlantic deepwater circulation over the last 30 000 years eight time slice reconstructions using 95 epibenthic 13c records eight time slices were reconstructed to trace the distribution of east atlantic deepwater and intermediate water masses over the last 30 000 years our results show that there have been three distinct modes of deepwater circulation near the stage 3 2 boundary the origin of north atlantic deep water nadw was similar to today mode 1 however after late stage 3 the source region of the nadw end member shifted from the norwegian greenland sea to areas south of iceland mode 2 a reduced nadw flow persisted during the last glacial maximum with constant preformed 13c values the nutrient content of nadw increased markedly near the azores fracture zone from north to south probably because of the mixing of upwelled antarctic bottom water aabw from below which then advected with much higher flux rates into the northeast atlantic later the spread of glacial meltwater over the north atlantic led to a marked short term ventilation minimum below 1800 m about 13 500 14c years ago mode 3 the formation of nadw recommenced abruptly north of iceland 12 800 12 500 years ago and reached a volume approaching that of the holocene in the younger dryas 10 800 10 350 years b p another short term shutdown of deepwater formation followed between 10 200 and 9 600 years b p linked to a further major meltwater pulse into the atlantic each renewal of deepwater formation led to a marked release of fossil co2 from the ocean the likely cause of the contemporaneous 14c plateaus over the last 9000 years deepwater circulation varied little from today apart from a slight increase in aabw about 7000 14c years ago it is also shown that the oxygenated mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30 000 years

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

in situ analyses of phosphorus contents of carbonate minerals reconstruction of phosphorus contents of seawater from the ediacaran to early cambrian abstract the ediacaran and cambrian periods were one of the most important periods for the evolution of life the biodiversity drastically expanded in the period however the origins are still ambiguous because surface environmental changes through the time have not been well understood yet we conducted in situ analyses of the phosphorus contents of carbonate minerals with a laser ablation inductively coupled plasma mass spectrometer la icp ms to estimate the phosphorus contents of seawater from the ediacaran to the early cambrian carbonate rocks contain not only the carbonate minerals but also detrital and authigenic materials such as silicate and phosphate minerals therefore the whole rock compositions of carbonate rocks are not directly related with seawater composition to avoid the influence of the involvement of the phosphate minerals we performed the microscopic observation elemental mapping of si ca mg fe and p contents with an electron probe microanalyzer epma and investigation of time profiles of signal intensities of ca sr mn p la and ba with the la icp ms especially samples with low mn sr ratios and primary textures such as oolites are suitable to estimate the primary phosphorus contents of the carbonates the chemostratigraphy of the phosphorus contents of carbonates from the drill core and outcrop samples displays that the phosphorus contents decrease from ca 400 ppm in the ediacaran through ca 200 ppm around the terminal ediacaran and the beginning of the cambrian to ca 50 ppm in the early cambrian previous works on 87sr 86sr chemostratigraphy from the ediacaran to the cambrian sections suggested relatively high continental influx in the middle ediacaran and around the precambrian cambrian pc c boundary the high phosphorus content in the ediacaran was possibly due to the high continental flux on the other hand previous works on chemostratigraphy of carbon isotope values of carbonate carbon from the ediacaran to the cambrian sections showed some large negative anomalies in the ediacaran and around the precambrian cambrian pc c boundary and suggested that the negative anomalies were caused by remineralization and respiration of dissolved organic matter the degradation of the organic matter also accounts for the high phosphorus contents in the ediacaran the high phosphorus content of seawater favors enhancement of primary productivity and formation of phosphorites the high phosphorus contents in the seawater possibly led to the emergence of the large and motile organism through the enhancement of primary productivity and the consequent increase of oxygen content of the seawater

latest proterozoic plankton from the amadeus basin in central australia the plankton of the proterozoic is preserved mainly as microfossils known as acritarchs most of which are considered to be cysts of eukaryotic algae in recent studies of the diversity of proterozoic and early palaeozoic acritarchs a gradual increase in diversity from the middle into the late proterozoic has been shown to be followed by a sharp decrease in diversity in the latest proterozoic ediacarian or vendian and then a rise again in the early cambrian1 2 these observations have been interpreted in terms of the evolutionary diversification of eukaryotic algae and the ecological effects of the pre ediacarian glaciation occasional discoveries of complex acritarchs in ediacarian rocks3 6 have raised some doubts about these interpretations but more recent work seems to have supported this view7 here we report the discovery of a diverse assemblage of large and morphologically complex acritarchs from the ediacarian age upper pertatataka formation in the amadeus basin of central australia this with a recent report of similar fossils from the upper sinian of china8 provides a significant new perspective on the history of the plankton it is now necessary to suggest an earlier radiation at least in off shore environments or to question the reality of the postulated decrease in diversity in addition there may well have been an extinction event late in the ediacarian neither of these phenomena has been recognized previously

late cenozoic environmental changes along the norwegian margin abstract our ability to understand the rates and consequences of contemporary climate change is limited by the insufficient duration of instrumental records thus we are not able to fully understand the processes that provide a fundamental control in driving climate changes across different timescales palaeo climate archives like those preserved offshore norway provide our only real window through which to observe long term rates and styles of climate change this paper reviews the extensive geological and geophysical data available from the late cenozoic atlantic margin of norway along the margin periods of erosion and deposition have been controlled by agents including fluvial glacial and oceanographic processes current controlled sedimentation along the margin provides insight into the connection of the arctic and atlantic oceans from the miocene onward plio pleistocene shelf edge progradation of up to 150 km can be linked to the grounding of ice sheets on the continental shelf through observations of buried grounding zone wedges and mega scale glacial lineations the margin is also important for understanding the ability of glaciation to cause topographic relief changes and generate offshore geohazards such as the storegga slide which mobilised some 3000 km 3 of sediments during the holocene whilst the processes operating along the norwegian margin are well understood through the late cenozoic there is little geochronological control with which to constrain the environmental changes that have been observed concomitant with the wealth of knowledge and the extensive data that are currently available we propose that the norwegian margin is an ideal location to be considered for future ocean drilling the observations of multiple processes acting independently and together means ocean drilling could yield information of global significance due to the bridging location of norway s atlantic margin between the arctic and lower latitudes

organic walled microfossils from the chert phosphorite member tal formation precambrian cambrian boundary india the chert member also designated chert phosphorite member of the tal formation in the lesser himalaya contains well preserved organic walled microfossil assemblage the assemblage includes small 25 m acanthomorphic acritarchs sphaeromorphic acritarchs cyanobacterial filaments sponge spicules and thallophytic remains identified as micrhystridium lanceolatum m dissimilare m tornatum m lanatum cf lophosphaeridium sp paracymatiosphaera irregularis cymatiosphaera sp estiastra minima leiosphaeridia sp siphonophycus robustum thalloidal fragments and hexactinellid sponge spicules the present assemblage rich in small acanthomorphs appears to be best developed in upper nemakit daldynian beds based on acritarch biostratigraphy the present work suggests a nemakit daldynian to early tommotian age for the chert member which is in agreement with the formerly proposed age based mainly on small shelly fossils the assemblage is correlatable to the precambrian cambrian boundary microbiotic assemblage from china central asia and east european platform the assemblage shows low diversity of species the characteristic of inshore biota

paleoenvironmental changes in the norwegian sea and the northeast atlantic during the last 2 8 m y deep sea drilling project ocean drilling program sites 610 642 643 and 644 sedimentological isotopic and magnetostratigraphic investigations of ocean drilling program and deep sea drilling project sites 642 643 644 and 610 document the oceanographic and climatic evolution of the norwegian sea and the northeastern atlantic over the last 2 8 m y the results show that a major expansion of the scandinavian ice sheet to the coastal areas took place at about 2 56 ma relatively severe glacials appeared until about 2 ma the period 2 6 1 2 ma experienced in general cold surface water conditions with only a weak influx of temperate atlantic water as compared with late quaternary interglacials the norwegian sea was a sink of deep water through this period but deepwater ventilation was reduced and calcite dissolution was high compared with the holocene deep water formed by other mechanisms than it does today between 2 and 1 2 ma the glaciations in scandinavia were small a transition toward larger glacials took place during the period 1 2 to 0 6 ma corresponding to warmer interglacials and reduced calcite dissolution only during the last 0 6 m y has the oceanographic and climatic system of the norwegian sea varied in the manner described in previous studies of the late quaternary a strong thermal gradient was present between the norwegian sea and the northeastern atlantic during the matuyama 2 5 0 7 ma this is interpreted as a sign of a more zonal and less meridional climatic system over the region compared with the present situation