late eocene southern ocean cooling and invigoration of circulation preconditioned antarctica for full scale glaciation during the eocene oligocene transition eot 34 33 5 ma antarctic ice sheets relatively rapidly expanded leading to the first continent scale glaciation of the cenozoic declining atmospheric co2 concentrations and associated feedbacks have been invoked as underlying mechanisms but the role of the quasi coeval opening of southern ocean gateways tasman gateway and drake passage and resulting changes in ocean circulation is as yet poorly understood definitive field evidence from eot sedimentary successions from the antarctic margin and the southern ocean is lacking also because the few available sequences are often incomplete and poorly dated hampering detailed paleoceanographic and paleoclimatic analysis here we use organic dinoflagellate cysts dinocysts to date and correlate critical southern ocean eot successions we demonstrate that widespread winnowed glauconite rich lithological units were deposited ubiquitously and simultaneously in relatively shallow marine environments at various southern ocean localities starting in the late eocene 35 7 ma based on organic biomarker paleothermometry and quantitative dinocyst distribution patterns we analyze southern ocean paleoceanographic change across the eot we obtain strong indications for invigorated surface and bottom water circulation at sites affected by polar westward flowing wind driven currents including a westward flowing antarctic countercurrent starting at about 35 7 ma the mechanism for this oceanographic invigoration remains poorly understood the circum antarctic expression of the phenomenon suggests that rather than triggered by tectonic deepening of the tasman gateway progressive pre eot atmospheric cooling played an important role at localities affected by the antarctic countercurrent sea surface productivity increased and simultaneously circum antarctic surface waters cooled we surmise that combined these processes contributed to preconditioning the antarctic continent for glaciation

from greenhouse to icehouse organic walled dinoflagellate cysts as paleoenvironmental indicators in the paleogene abstract dinoflagellates are an important component of the extant eukaryotic plankton their organic walled hypnozygotic cysts dinocysts provide a rich albeit incomplete history of the group in ancient sediments building on pioneering studies of the late 1970s and 1980s recent drilling in the southern ocean has provided a wealth of new dinocyst data spanning the entire paleogene such multidisciplinary studies have been instrumental in refining existing and furnishing new concepts of paleogene paleoenvironmental and paleoclimatic reconstructions by means of dinocysts because dinocysts notably exhibit high abundances in neritic settings dinocyst based environmental and paleoclimatic information is important and complementary to the data derived from typically more offshore groups as planktonic foraminifera coccolithophorids diatoms and radiolaria by presenting case studies from around the globe this contribution provides a concise review of our present understanding of the paleoenvironmental significance of dinocysts in the paleogene 65 25 ma representing earth s greenhouse icehouse transition this episode holds the key to the understanding of extreme transient climatic change we discuss the potential of dinocysts for the reconstruction of paleogene sea surface productivity temperature salinity stratification and paleo oxygenation along with their application in sequence stratigraphy oceanic circulation and general watermass reconstructions

cenozoic ice rafting history of the central arctic ocean terrigenous sands on the lomonosov ridge the cenozoic ice rafted debris ird history of the central arctic is reconstructed utilizing the terrigenous coarse sand fraction in iodp 302 cores from 0 to 273 meters composite depth this holocene middle eocene quantitative record of terrigenous sand accumulation on the lomonosov ridge along with qualitative information on grain texture and composition confirms the interpretation that ice initiation sea ice and glacial ice occurred 46 ma in the arctic and provides a long term pattern of arctic ice expansion and decay since the middle eocene ird mass accumulation rates range from 0 to 0 13 g cm2 ka in the middle eocene and from 0 to 0 36 g cm2 ka in the neogene ird mass accumulation rate mar maxima in the miocene and pliocene cooccur with either glacial initiation or intensification in the sub arctic the 46 25 ma ird onset in the central arctic slightly precedes the earliest evidence of ice in the antarctic and compares in timing with a 1000 ppm decrease in atmospheric concentrations of co2 the decline of pco2 in the middle eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface arctic ocean especially during times of low insolation

past glacial and interglacial conditions in the arctic ocean and marginal seas a review past changes in the arctic ocean and its marginal seas have been profound even during the last 10 000 years understanding these changes such as those occurring during the transition from glacial to interglacial climates are important for research on modern processes because this knowledge provides a framework and unique perspective in which to view the modern physical and biological processes this paper discusses our current understanding of past environmental change and processes relative to those currently in progress special emphasis is placed on the most recent transition from a glacial state to the modern interglacial conditions

late eocene to early oligocene dinoflagellate cysts from the priabonian type area northeast italy biostratigraphy and paleoenvironmental interpretation abstract marginal marine late eocene through early oligocene dinoflagellate cyst successions have been studied from the type area of the priabonian stage northeast italy the results allow the recognition of dinoflagellate zones previously defined in bio and magnetostratigraphically well calibrated pelagic sequences from central italy thus providing a first order correlation of the priabonian stage to the standard chronostratigraphic scale with unprecedented precision within this detailed biostratigraphic framework successive shifts in the composition of the dinoflagellate cyst assemblages are interpreted in terms of sea level and sea surface temperature sst fluctuations the evaluation of ecologically and sedimentary controlled changes in the composition of dinoflagellate cyst assemblages in combination with sequence stratigraphic analysis allows the reconstruction of third and fourth order sea level fluctuations the third order sea level fluctuations appear to correspond to exxon cycles ta4 1 4 5 the stratigraphically and palaeoenvironmentally important late eocene dinoflagellate cyst species glaphyrocysta priabonensis sp nov is formally described

a novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids we propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high performance liquid chromatography mass spectrometry hplc ms analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol the characteristic membrane lipid of non thermophilic crenarchaeota which is especially abundant in the marine and lacustrine environment based on these findings an index was developed the so called branched and isoprenoid tetraether bit index based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol this bit index was applied to surface sediments from the angola basin where it was shown to trace the outflow of the congo river furthermore analyses of particulate organic matter from the north sea showed relatively higher bit indices in water column particulate organic matter near large river inputs a survey of globally distributed marine and lacustrine surface sediments shows that the bit index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable the new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 ma old

driftwood dropstones in middle miocene climate optimum shallow marine strata calvert cliffs maryland coastal plain erratic pebbles no certain proxy for cold climate abstract sparse lithic erratics pebbles to cobbles sampled from three shallow marine strata deposited during the middle miocene climate optimum mmco ca 16 14 ma along the western atlantic margin exposed in the calvert cliffs maryland suggest transport and deposition not from ice but from the roots of trees uprooted during floods and carried out to sea evidence for driftwood transport includes carbonized wood in the same strata more than half the ca 225 erratics were quarried in the largely metamorphic piedmont province including a few from the port deposit gneiss still outcropping on the lower susquehanna river the lowest sampled bed parker creek bone bed is assigned to the ca 15 7 15 5 ma peak warmth of the mmco which we attribute in part to co2 from the coevally erupted grande ronde flood basalts grfb the peak effusiveness episode of the columbia river flood basalts crfb the three sampled beds predate the ca 13 9 ma antarctic cryosphere expansion which may be recorded in the calvert cliffs by a unique buried channel

stable warm tropical climate through the eocene epoch earth s climate cooled from a period of extreme warmth in the early eocene epoch ca 50 ma to the early oligocene ca 33 ma when a large ice cap first appeared on antarctica evidence from the planktonic foraminifer oxygen isotope record in deep sea cores has suggested that tropical sea surface temperatures declined by 5 10 degrees over this interval eventually becoming much cooler than modern temperatures here we present paleotemperature estimates from foraminifer isotopes and the membrane lipids of marine crenarcheota from new drill cores in tanzania that indicate a warm and generally stable tropical climate over this period we reinterpret the previously published isotope records in the light of comparative textural analysis of the deep sea foraminifer shells which shows that in contrast to the tanzanian material they have been diagenetically recrystallized we suggest that increasingly severe alteration of the deep sea plankton shells through the eocene produced a diagenetic overprint on their oxygen isotope ratios that imparts the false appearance of a tropical sea surface cooling trend this implies that the long term eocene climatic cooling trend occurred mainly at the poles and had little effect at lower latitudes

variability in the length of the sea ice season in the middle eocene arctic finely laminated middle eocene sediments from the central arctic contain high abundances of the delicate sea ice dwelling fossil diatoms synedropsis spp and sea ice rafted debris sea ice ird establishing an offshore seasonal sea ice regime ca 47 ma synedropsis spp co occur with other diatom taxa and microfossils requiring open water this strongly indicates seasonality nonetheless seasonal reconstruction of the flux cycle cannot be resolved by standard bulk sediment analysis which destroys sedimentary fabrics and averages data within samples here we resolve and reconstruct seasonal scale flux events from these sediments using backscattered electron imagery bsei of resin embedded sediment a nondestructive technique that preserves the integrity of sedimentary microfabrics thus revealing discrete productivity flux events at ultrahigh e g 30 m resolution seasonality is expressed at the submillimeter scale by successions of discrete mono specific laminae and micro lenses of synedropsis spp terrigenous material sea ice ird and open water taxa indicating that first year ice existed in the central arctic further bsei reveals millimeter scale alternation of bundles of laminae and microlenses of two distinct types one characterized by synedropsis spp and terrigenous material the other by mainly open water taxa and little terrigenous material the sedimentation rate and preliminary assessment of annual cycles indicate suborbital variability on the order of multi decadal to centennial duration we argue that this reflects variations in the sea ice season length

paleogene record of elemental concentrations in sediments from the arctic ocean obtained by xrf analyses we present a high resolution x ray fluorescence xrf core scanner record for the expanded middle eocene section from integrated ocean drilling program iodp expedition 302 acex drilled on the lomonosov ridge central arctic ocean the division of the middle eocene into two units subunit 1 6 and unit 2 is seen in the cyclical behavior of the elements as well as the changing interelemental correlations and their relationship to physical property measurements of bulk sediment al ti and k strongly correlate throughout the record while the behavior of fe mn and si is more complex utilizing sediment geochemistry calibration to ground truth the xrf data we suggest the middle eocene arctic ocean was predominately euxinic although periodic oxygenation of bottom waters must have occurred during unit 2 49 7 45 4 ma initially the sediments are rich in biogenic silica unit 2 but there is a pronounced shift to terrigenous dominated sediment accumulation in subunit 1 6 we report changes in the elemental concentrations of these elements and investigate the relationship between fe content and pyrite additionally we explore the potential change in paleoenvironmental conditions across the unit boundary

ephemeral formation of perennial sea ice in the arctic ocean during the middle eocene arctic sea ice is a key component of the modern climate system marine sediment analyses suggest that perennial sea ice in the arctic ocean first formed transiently about 44 million years ago

salinity of the eocene arctic ocean from oxygen isotope analysis of fish bone carbonate stable isotope analysis was performed on the structural carbonate of fish bone apatite from early and early middle eocene samples 55 to 45 ma recently recovered from the lomonosov ridge by integrated ocean drilling program expedition 302 the arctic coring expedition the 18o values of the eocene samples ranged from 6 84 to 2 96 vienna peedee belemnite with a mean value of 4 89 compared to 2 77 for a miocene sample in the overlying section an average salinity of 21 to 25 was calculated for the eocene arctic compared to 35 for the miocene with lower salinities during the paleocene eocene thermal maximum the azolla event at 48 7 ma and a third previously unidentified event at 47 6 ma at the azolla event where the organic carbon content of the sediment reaches a maximum a positive 13c excursion was observed indicating unusually high productivity in the surface waters

introduction to special section on cenozoic paleoceanography of the central arctic ocean 1 in late summer 2004 the integrated ocean drilling program iodp conducted one of the most transformational missions in the almost 40 year history of scientific ocean drilling the arctic coring expedition acex backman et al 2006 moran et al 2006a this technically challenging expedition moran et al 2006b to the lomonosov ridge near 88 n recovered the first long term cenozoic sediment record from the arctic ocean extending previous records from 1 5 ma to an unprecedented 56 ma glimpses of the breadth of this transformation were seen during the acex cruise when the massulae from freshwater ferns azolla were found in 49 ma old sediments brinkhuis et al 2006 and the presence of apectodinium augustum confirmed that the paleocene eocene thermal maximum petm 55 ma was unexpectedly recovered sluijs et al 2006 2 soon after the expedition when the cores were opened and analyzed ice rafted debris was found in surprisingly old 46 ma sediments moran et al 2006a these middle eocene sediments are characterized also by their high organic carbon content stein et al 2006 the exciting early results attracted other investigators that expanded the scientific investigating team to more than 40 people analyses were extended to include studies that revealed surprisingly high arctic ocean surface water temperatures sluijs et al 2006 and an amplified hydrological system pagani et al 2006 during the petm initial analyses revealed an extensive hiatus encompassing about 26 million years that occurred below a short interval showing starkly alternating black and white layers that is now dubbed the zebra interval thus the time interval from the late early miocene 18 ma to the middle middle eocene 44 ma is missing although the hiatus is a lost window in time for the arctic paleoclimate record it spawned other studies that integrated the regional tectonic history with acex results revealing a major oceanographic reorganization at 17 5 ma ventilation of the arctic ocean to the north atlantic through the fram strait jakobsson et al 2007 in terms of ventilation and water mass history neogene neodymium isotope data reveal that arctic intermediate waters originate from brine formation on eurasian shelf areas between 15 and 2 ma and during glacial periods throughout pleistocene times haley et al 2008a they conclude that this mode of arctic circulation differs markedly from today s situation showing relatively high contributions of north atlantic intermediate water and minor input from brine formation 3 in this special section the transformation continues results from the large acex scientific family include a robust age model detailed analyses of the middle eocene that document a unique brackish water environment sea ice and iceberg history reconstructions as well as the provenance of ice rafted debris from the eocene to present evolution of depositional environments times of isolation and connection to the global ocean geochemical analyses of the organic carbon rich sediments and unique applications of high resolution proxies and cyclostratigraphy highlights from this special section are presented here

geomorphic processes and risk related to a large landslide dam in a highly urbanized mediterranean catchment genova italy abstract we present our research on the prato casarile landslide dam in genoa city to illustrate the interactions between slope instability processes and structural stabilization interventions aimed to reduce the hazard in a densely populated area analysis of the degradation of structural interventions constructed after flood events in 1953 1970 and 2014 contributed to an improved mitigation strategy at the same time the slope instability processes intensively advanced and regressive erosion quickly proceeded to the landslide dam threshold the discontinuity in human interactions in a geomorphic system after the initial hazard reduction resulted in an increased threat that combined with a rise in vulnerability due to urbanization expansion the research findings underline the necessity of constantly assessing the geomorphic evolution and active processes involved in order to determine the specific actions and interventions required to ensure the stability of the landslide dam finally and more generally we illustrated that anthropogenic interaction in the geomorphic system specifically when finalized for hazard mitigation needs to be continuously performed through both the monitoring and maintenance operation phases of the artificial structures

experimental evidence for high noble gas solubilities in silicate melts under mantle pressures abstract the solubilities of ar and xe in fe free synthetic haplogranitic and tholeiitic melts were experimentally determined in the pressure range of 1 11 gpa and at temperatures between 1500 and 2000 c experiments were performed in a piston cylinder apparatus 1 3 gpa and in a multi anvil apparatus 2 11 gpa the noble gas concentrations in the quenched glasses were determined with electron microprobe as a function of pressure ar solubility increases linearly up to about 4 5 gpa where it reaches about 4 0 and 0 8 wt for the haplogranitic and tholeiitic melt respectively at higher pressure the amount of dissolved ar remains constant suggesting that some threshold concentration is reached the xe solubility in tholeiite melt exhibits a very similar pattern it increases linearly up to about 6 gpa where a threshold concentration of 0 8 wt is reached a further increase of pressure up to 11 gpa does not result in changes in xe solubility the leveling off in noble gas solubility at high pressures may imply that the interstitial sites in the melt structure suitable for the accommodation of noble gas atoms are fully occupied indeed the experimental data can be successfully reproduced with the langmuir isotherm implying a solubility model in which the gas atoms occupy a certain population of interstitial sites however the data can be equally well described by a model assuming mixing of the noble gas atoms with the oxygen atoms of the silicate melt from a thermodynamic point of view the constant noble gas solubility at high pressures simply implies that the partial molar volumes of the respective noble gas in the fluid and in the melt are equal our results differ from those of chamorro perez et al earth planet sci lett 145 1996 97 107 nature 393 1998 352 355 who reported an abrupt order of magnitude drop of ar solubility in silica and olivine melt at around 5 gpa suggesting that melt densification results in an abrupt decrease of the hole size distribution a geochemical consequence of our results is that noble gases remain incompatible elements at pressure conditions covering most of the upper mantle therefore partial melting remains an efficient process in extracting noble gases and other volatiles from the earth s mantle

humidity estimate for the middle eocene arctic rain forest the exquisite preservation of fossilized metasequoia trees that grew near 808n latitude during the middle eocene ca 45 ma in nunavut canada allowed for dd and d 18 o analyses of cellulose techniques previously restricted to wood 30 000 yr old from the isotopic results we determined that the middle eocene arctic atmosphere contained 23 the water found in the region s atmosphere today this water vapor contributed to a middle eocene greenhouse effect that insulated the polar region during dark polar winters

quasi quadrennial and quasi biennial variability in the equatorial pacific evaluation of competing el nino southern oscillation enso theories requires one to identify separate spectral peaks in equatorial wind and sea surface temperature sst time series to sharpen this identification we examine the seasonal to interannual variability of these fields by the data adaptive method of multi channel singular spectrum analysis m ssa m ssa is applied to the equatorial band 4 n 4 s using 1950 1990 data from the comprehensive ocean and atmosphere data set two major interannual oscillations are found in the equatorial sst and surface zonal wind fields u the main peak is centered at about 52 months we refer to it as the quasi quadrennial qq mode quasi biennial qb variability is split between two modes with periods near 28 months and 24 months a faster 15 month oscillation has smaller amplitude the qq mode dominates the variance and has the most distinct spectral peak in time longitude reconstructions of this mode the sst has the form of a standing oscillation in the eastern equatorial pacific while the u field is dominated by a standing oscillation pattern in the western pacific and exhibits also slight eastward propagation in the central and western pacific the locations of maximum anomalies in both qb modes are similar to those of the qq mode slight westward migration in sst across the eastern and central and eastward propagation of u across the western and central pacific are found the significant wind anomaly covers a smaller region than for the qq the qq and qb modes together represent the enso variability well and interfere constructively during major events the sharper definition of the qq spectral peak and its dominance are consistent with the devil s staircase interaction mechanism between the annual cycle and enso

a siliceous microfossil view of middle eocene arctic paleoenvironments a window of biosilica production and preservation integrated ocean drilling program iodp expedition 302 the arctic coring expedition acex unearthed the most significant find of paleogene siliceous microfossils in nearly 2 decades 100 m of early middle eocene organic rich finely laminated sediments contain abundant marine and freshwater siliceous microfossils allowing intriguing insights into central arctic paleoenvironments during the start of cenozoic cooling largely endemic assemblages of marine diatoms and ebridians are preserved along with very high abundances of chrysophyte cysts the endogenously formed resting stage of freshwater algae an overall brackish environment is invoked but variations in group dominance suggest episodic changes in salinity stratification and trophic status with the backing of inorganic geochemistry we synthesize the sediment characteristics by hypothesizing an environmental model for the cooccurrence of these diverse siliceous microfossil groups we also report on initial insights into the composition of some of the laminations which may help explain the formation of this rich sediment archive

orbital forcing of arctic climate mechanisms of climate response and implications for continental glaciation progress in understanding how terrestrial ice volume is linked to earths orbital configuration has been impeded by the cost of simulating climate system processes relevant to glaciation over orbital time scales 10 3 10 5 years a compromise is usually made to rep resent the climate system by models that are averaged over one or more spatial dimensions or by three dimensional models that are limited to simulating par ticular snapshots in time we take advantage of the short equilibration time 310 years of a climate model consisting of a three dimensional atmosphere coupled to a simple slab ocean to derive the equilibrium climate response to accelerated variations in earths orbital configuration over the past 165 000 years prominent decreases in ice melt and increases in snowfall are sim ulated during three time intervals near 26 73 and 117 thousand years ago ka when aphelion was in late spring and obliquity was low there were also significant decreases in ice melt and increases in snowfall near 97 and 142 ka when eccentricity was relatively large aph elion was in late spring and obliquity was high or near its long term mean these glaciation friendly time intervals correspond to prominent and secondary phases of terrestrial ice growth seen within the marine d 18 o record both dynamical and thermal effects contribute to the increases in snowfall during these periods through increases in storm activity and the fraction of precipi tation falling as snow the majority of the mid to high latitude response to orbital forcing is organized by the properties of sea ice through its influence on radiative feedbacks that nearly double the size of the orbital forcing as well as its influence on the seasonal evolution of the latitudinal temperature gradient

eocene continental climates and latitudinal temperature gradients global climate during the mesozoic and early cenozoic is thought to have been warmer than at present but there is debate about winter temperatures paleontological data indicate mild temperatures even at high latitudes and in mid latitude continental interiors whereas computer simulations of continental paleoclimates produce winter temperatures closer to modern levels foliar physiognomy and floristic composition of 23 eocene floras from the interior of north america and australia indicate cold month means generally 2 c even where the mean annual temperature mat was

anoxia and high primary production in the paleogene central arctic ocean first detailed records from lomonosov ridge 1 except for a few discontinuous fragments of the late cretaceous early cenozoic climate history and depositional environment the paleoenvironmental evolution of the pre neogene central arctic ocean was virtually unknown prior to the iodp expedition 302 arctic ocean coring expedition acex drilling campaign on lomonosov ridge in 2004 here we present detailed organic carbon oc records from the entire ca 200 m thick paleogene oc rich section of the acex drill sites these records indicate euxinic black sea type conditions favorable for the preservation of labile aquatic marine algae type oc occur throughout the upper part of the early eocene and the middle eocene explained by salinity stratification due to freshwater discharge the superimposed short term milankovitch type variability in amount and composition of oc is related to changes in primary production and terrigenous input prominent early eocene events of algae type oc preservation coincide with global 13c events such as the petm and elmo events the elmo 13c event has been identified in the arctic ocean for the first time

climate sensitivity to arctic seaway restriction during the early paleogene abstract the opening and closing of ocean gateways affects the global distribution of heat salt and moisture potentially driving climatic change on regional to global scales between 65 and 45 million years ago ma during the early paleogene exchange between the arctic and global oceans occurred through two narrow and shallow seaways the greenland norway seaway and the turgai strait sediments from the arctic ocean suggest that during this interval the surface ocean was warm brackish and episodically enabled the freshwater fern azolla to bloom the precise mechanisms responsible for the development of these conditions in the paleogene arctic remain uncertain here we show results from an isotope enabled atmosphere ocean general circulation model which indicate that northern hemisphere climate would have been very sensitive to the degree of oceanic exchange through the arctic seaways we also present modelled estimates of seawater and calcite 18o for the paleogene by restricting these seaways we simulate freshening of the surface arctic ocean to 6 psu and warming of sea surface temperatures by 2 c in the north atlantic and 5 10 c in the labrador sea our results may help explain the occurrence of low salinity tolerant taxa in the arctic ocean during the eocene and provide a mechanism for enhanced warmth in the north western atlantic we propose that the formation of a volcanic land bridge between greenland and europe could have caused increased ocean convection and warming of intermediate waters in the atlantic if true this result is consistent with the theory that bathymetry changes may have caused thermal destabilisation of methane clathrates and supports a tectonic trigger hypothesis for the paleocene eocene thermal maximum petm

cyclicity in the middle eocene central arctic ocean sediment record orbital forcing and environmental response 1 continuous x ray fluorescence scanning of middle eocene 46 ma core m0002a 55x 236 241 m composite depth recovered during integrated ocean drilling program expedition 302 revealed a strong cyclical signal in some major and trace geochemical elements we performed a multiproxy study of the same core which included organic geochemical sedimentological and biological parameters and integrated our results with available geochemical and physical properties data the target was to look for cyclicity in the several proxies investigate their frequency and understand the environmental response to the potential forcing results indicate that a higher terrigenous component corresponds to lower organic carbon concentration smaller contributions by angiosperm pollen and spores organic walled dinoflagellate cysts and chrysophyte cysts lower productivity shorter growing season for flowering plants and lower stratification but higher contributions by bisaccate pollen and diatoms drier conditions on land more marine conditions and higher terrigenous sand ice rafted debris ird our investigation shows that physical proxy parameters hold cyclicity with periods of about 50 and 100 cm and that these frequency components are compatible with a milankovitchtype orbital forcing representing precession and obliquity respectively the longer 100 cm cyclicity is also present in the biological pollen dinoflagellate cysts and siliceous microfossils and in the sedimentological ird proxies the environmental signal derived from the integrated multiproxy analysis suggests that in an enclosed arctic ocean at time of ice sea ice and glacial ice initiation the biological proxies responded more strongly to growing season length darkness whereas the terrigenous components directly driven by sea ice and or glacial ice formation and extent responded more directly to seasonal insolation

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

spells of low frequency oscillations and weather regimes in the northern hemisphere abstract the low frequency variability in the midlatitudes is described through an analysis of the oscillatory phenomena in order to isolate nearly periodic components of the atmospheric flow the multichannel version of the singular spectrum analysis m ssa is developed and applied to an nmc 32 year long set of 700 hpa geopotential heights in the same way that principal component analysis identifies the spatial patterns dominating the variability m ssa identifies dynamically relevant space time patterns and provides an adaptive filtering technique three major low frequency oscillations lfos are found with periods of 70 days 40 45 days and 30 35 days the 70 day oscillation consists of fluctuations in both position and amplitude of the atlantic jet with a poleward propagating anomaly pattern the 40 45 day oscillation is specific to the pacific sector and has a pronounced pacific north american pna structure in its high amplitude phase the 30 35 day mode is confined over the atlantic region

the early miocene onset of a ventilated circulation regime in the arctic ocean deep water formation in the northern north atlantic ocean and the arctic ocean is a key driver of the global thermohaline circulation and hence also of global climate1 deciphering the history of the circulation regime in the arctic ocean has long been prevented by the lack of data from cores of cenozoic sediments from the arctic s deep sea floor similarly the timing of the opening of a connection between the northern north atlantic and the arctic ocean permitting deep water exchange has been poorly constrained this situation changed when the first drill cores were recovered from the central arctic ocean2 here we use these cores to show that the transition from poorly oxygenated to fully oxygenated ventilated conditions in the arctic ocean occurred during the later part of early miocene times we attribute this pronounced change in ventilation regime to the opening of the fram strait a palaeo geographic and palaeo bathymetric reconstruction of the arctic ocean together with a physical oceanographic analysis of the evolving strait and sill conditions in the fram strait suggests that the arctic ocean went from an oxygen poor lake stage to a transitional estuarine sea phase with variable ventilation and finally to the fully ventilated ocean phase 17 5 myr ago the timing of this palaeo oceanographic change coincides with the onset of the middle miocene climatic optimum3 although it remains unclear if there is a causal relationship between these two events

ocean and climate response to north atlantic seaway changes at the onset of long term eocene cooling abstract around the early middle eocene boundary the first occurrence of contourite drift sediments and widespread deep ocean erosion indicate changes in the north atlantic ocean circulation interestingly these changes coincide with the first steps of cenozoic cooling from the paleogene greenhouse climate towards the modern icehouse the cause for this ocean circulation reorganization is poorly understood since modern water mass tracers may have worked fundamentally different in the past and the paleoceanographic proxy record is limited in both time and space as a result it is challenging to reliably reconstruct the climatic and tectonic boundary conditions e g atmospheric greenhouse gas concentration and the depth and geometry of developing and closing passages between ocean basins in this study we attempt to identify thresholds in tectonic gateway passages and atmospheric co2 concentration using the fully coupled earth system model cosmos indeed the simulation of earth s past climates can unravel the physical processes driving deep water formation in a greenhouse world specifically we use cosmos to evaluate the impact of changes in the north atlantic gateways at the early middle eocene boundary on the north atlantic deep western boundary currents under low obliquity configuration we find that northern component waters start to form when the greenland scotland ridge reaches a threshold depth of deeper than 200 m while the arctic ocean is still shut off from the north atlantic in this scenario the relatively deep greenland scotland ridge allows for sufficient inflow of warm salty atlantic surface waters into the nordic seas to initiate convection during winter cooling opening the seaway towards the arctic leads to a cessation of northern component water formation as it allows for inflow of brackish surface waters into the northern nordic seas hindering northern component water formation

cortex a shipboard xrf scanner for element analyses in split sediment cores abstract the cortex corescanner texel is a non destructive xrf system for the logging of split sediment cores it is a seaworthy instrument that remains active during heavy weather conditions the scanner produces reliable counts for k to sr highly correlated with concentrations measured with atomic absorption spectrometry aas the option to scan al si and elements heavier than sr is in preparation a core section of 1 m can be scanned at 2 cm intervals within an hour a maximum resolution of 1 mm can be achieved at present each region and sedimentary environment requires separate calibration in the nearby future the generator settings will be standardized which may result in the development of a standard calibration procedure because of the high resolution of its semi quantitative records the cortex is a useful tool for detailed time series analysis inter core correlation and shipboard analysis

orbital scale variations and timescales from the arctic ocean we investigate geochemical measurements from the arctic coring expedition to derive sedimentation rates for selected intervals in the early and middle eocene this analysis is performed by quantifying cyclical variations in physical property data and elemental concentrations derived with an x ray fluorescence xrf core scanner our results show that physical properties and xrf derived elemental concentrations are coherent and correlated to each other changes in elemental concentrations occur on depth scales from decimeters to meters and correspond to varying contributions of detrital minerals and biogenic silica we confirm and refine sedimentation rates of the order of 10 to 25 m ma 1 these rates were obtained independently through biostratigraphic and magnetostratigraphic methods we observe a strong imprint of astronomically sourced cycles particularly through climatic precession this observation allows us to test recently proposed theoretical calculations of insolation

paleoceanographic and paleoclimatic constraints on the global eocene diatom and silicoflagellate record abstract eocene diatom and silicoflagellate biostratigraphy are summarized and correlated with the most recent geologic time scale as well as with the global oxygen isotope and eustatic sea level curves the global distribution of eocene diatom silicoflagellate bearing sediments varies considerably reflecting changing oceanic gateways and paleoceanography with changing patterns that are punctuated by four major depositional events event 1 49 million years ago ma at the end of the early eocene climatic optimum eeco saw the cessation of diatom silicoflagellate deposition in epicontinental regions of the north sea region and in the northern russia and the onset of biosilica deposition in the arctic event 2 46 ma which coincided with intensification of the middle eocene cooling trend marked the widespread expansion of diatom silicoflagellate deposition in both the north and south atlantic a shift of diatom silicoflagellate deposition from the atlantic to the pacific began at event 3 at the end of the middle eocene climatic optimum meco 40 ma that was likely tied to the initial opening of the drake passage between antarctica and south america event 4 39 ma coincided with a major sea level fall and a widespread deep sea hiatus in the latest middle eocene late eocene diatom silicoflagellate deposition became more concentrated in middle to high latitude regions and coastal upwelling regions particularly in the pacific ocean tabulation of the first and last occurrences of 132 biostratigraphically important diatoms suggests increased species turnover during the latest paleocene to earliest eocene that may be in part due to a monographic effect an increasing rate of evolution of new diatom species between 46 and 43 ma and after 40 ma coincides respectively with the widespread expansion of diatom deposition in the atlantic and with an increased pole to equator thermal gradient that witnessed the expansion of diatoms in high latitude oceans and coastal upwelling settings

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

episodic fresh surface waters in the eocene arctic ocean it has been suggested on the basis of modern hydrology and fully coupled palaeoclimate simulations that the warm greenhouse conditions that characterized the early palaeogene period 55 45 myr ago probably induced an intensified hydrological cycle with precipitation exceeding evaporation at high latitudes little field evidence however has been available to constrain oceanic conditions in the arctic during this period here we analyse palaeogene sediments obtained during the arctic coring expedition showing that large quantities of the free floating fern azolla grew and reproduced in the arctic ocean by the onset of the middle eocene epoch approximately 50 myr ago the azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of arctic surface waters during an approximately 800 000 year interval the abundant remains of azolla that characterize basal middle eocene marine deposits of all nordic seas probably represent transported assemblages resulting from freshwater spills from the arctic ocean that reached as far south as the north sea the termination of the azolla phase in the arctic coincides with a local sea surface temperature rise from approximately 10 degrees c to 13 degrees c pointing to simultaneous increases in salt and heat supply owing to the influx of waters from adjacent oceans we suggest that onset and termination of the azolla phase depended on the degree of oceanic exchange between arctic ocean and adjacent seas

paleoenvironmental implications of cenozoic sediments from the central arctic ocean iodp expedition 302 using inorganic geochemistry 1 integrated ocean drilling program iodp expedition 302 arctic coring expedition acex recovered a unique sediment record from the central arctic ocean revealing that this region underwent major environmental fluctuations since the late cretaceous major and trace element composition of 1 300 samples were determined using x ray fluorescence xrf the results show significant compositional variability of the sediments with depth that can be attributed to changes in a provenance and pathways of detrital material b paleoenvironmental conditions and depositional processes and c diagenetic overprint of the primary record in addition to existing lithological units we introduce new geochemical units for a more process related approach interpreting the acex record in detail via the geochemical signature of siberian flood basalts we are able to reconstruct the discontinuous rifting and deepening of the central lomonosov ridge during the paleogene accompanied by changing current regimes and the onset of sea ice eocene biosiliceous sedimentation took place in a relatively shallow setting under predominantly anoxic bottom water conditions causing a positive anoxia productivity feedback although water column stratification was repeatedly interrupted by ventilation events anoxic to sulfidic conditions were even more extreme after biosilica production ceased and significant amounts of pyrite were deposited on the lomonosov ridge especially in organic matter rich paleogene deposits diagenetic processes obscured the paleoenvironmental signals fundamental environmental changes occurred in the middle eocene but geochemical and micropaleontological proxies point not to the identical sediment depth after approximately 26 ma of non deposition or erosion the middle miocene record shows the transition to dominantly oxic bottom water conditions although suboxic diagenesis seemingly affected these deposits

continental ice in greenland during the eocene and oligocene the eocene and oligocene epochs approximately 55 to 23 million years ago comprise a critical phase in earth history an array of geological records supported by climate modelling indicates a profound shift in global climate during this interval from a state that was largely free of polar ice caps to one in which ice sheets on antarctica approached their modern size however the early glaciation history of the northern hemisphere is a subject of controversy here we report stratigraphically extensive ice rafted debris including macroscopic dropstones in late eocene to early oligocene sediments from the norwegian greenland sea that were deposited between about 38 and 30 million years ago our data indicate sediment rafting by glacial ice rather than sea ice and point to east greenland as the likely source records of this type from one site alone cannot be used to determine the extent of ice involved however our data suggest the existence of at least isolated glaciers on greenland about 20 million years earlier than previously documented at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher