amplitude and decay of long period coda of great earthquakes abstract the earthquake coda is the residual vibration energy long after the main arrivals of an earthquake previous studies of coda waves have focused on high frequencies and small earthquakes which are generally attributed to the scattering from the earth s internal heterogeneities here we examined the early coda of great earthquakes at long periods 50 to 300 s at time window of 10 000 to 50 000 s after the origin time we used 10 major earthquakes magnitude 8 0 in recent decades that were recorded at global seismic networks we found that the coda energy can be well represented by a simple exponential decay model for the early coda the variation of the initial coda energy with distance is dominated by the effect of geometric spreading suggesting that the scattering of the earth s internal heterogeneities contributes little to the long period early coda the energy decay rate is largely insensitive to earthquake source location magnitude focal mechanism or rupture process station location or 3d variation of the earth s internal structure making it ideal to constrain the average global attenuation structure a small modification of the quality factor based on a global reference model can fit the coda energy decay well the long period coda energy may potentially provide a new way to determine the seismic moment of a major earthquake

seismic detection of the lunar core despite recent insight regarding the history and current state of the moon from satellite sensing and analyses of limited apollo era seismic data deficiencies remain in our understanding of the deep lunar interior we reanalyzed apollo lunar seismograms using array processing methods to search for the presence of reflected and converted seismic energy from the core our results suggest the presence of a solid inner and fluid outer core overlain by a partially molten boundary layer the relative sizes of the inner and outer core suggest that the core is 60 liquid by volume based on phase diagrams of iron alloys and the presence of partial melt the core probably contains less than 6 weight of lighter alloying components which is consistent with a volatile depleted interior

topographic and boundary effects on steady and unsteady flow through straits an overview of topographic and boundary effects in flows through straits is presented the emphasis is on the various types of interaction of uniform and stratified flow with the topography of straits especially the interaction with sills the interaction of a single layer flow in a channel with a sill obstacle depends on the froude number of the flow and the relative height of the sill two classification schemes one steady and one pseudo steady are given for single layer flow in straits where the effects of rotation are important a further parameter the ratio of the channel width to a rossby radius is needed and a similar classification scheme as for the non rotating flows can be obtained unsteady flows often result in bores for single layer flows and internal bores in stratified flows and the behaviour of these is discussed the flow of stratified flow past sills may generate lee waves while the increased flow speeds at the sill may allow deep water to be drawn up and over the sill aspiration features of the strait topography away from the sill including slopes at the side of the channel and also downstream of the sill channel curvature and channel widening have important effects on the character of the flow and on mixing

surface wave tomography of the western united states from ambient seismic noise rayleigh and love wave phase velocity maps summary we present the results of rayleigh wave and love wave phase velocity tomography in the western united states using ambient seismic noise observed at over 250 broad band stations from the earthscope usarray transportable array and regional networks all available threecomponent time series for the 12 month span between 2005 november 1 and 2006 october 31 have been cross correlated to yield estimated empirical rayleigh and love wave green s functions the love wave signals were observed with higher average signal to noise ratio snr than rayleigh wave signals and hence cannot be fully explained by the scattering of rayleigh waves phase velocity dispersion curves for both rayleigh and love waves between 5 and 40 speriod were measured for each interstation path by applying frequency time analysis the average uncertainty and systematic bias of the measurements are estimated using a method based on analysing thousands of nearly linearly aligned station triplets we find that empirical green s functions can be estimated accurately from the negative time derivative of the symmetric component ambient noise cross correlation without explicit knowledge of the source distribution the average traveltime uncertainty is less than 1 s at periods shorter than 24 s we present rayleigh and love wave phase speed maps at periods of 8 12 16 and 20 s the maps show clear correlations with major geological structures and qualitative agreement with previous results based on rayleigh wave group speeds

allochthonous slope sequence at lobster cove head evidence for a complex middle ordovician platform margin in western newfoundland the upper part of an intact sequence of lower to middle ordovician deep water sediments which now form a large disrupted raft within the rocky harbour melange at lobster cove head is interpreted as having been deposited downslope from a drowned carbonate platform margin the entire 50 m thick section is arenig late canadian or ibexian to early whiterock in age graptolite biostratigraphy demonstrates a correlation with upper parts of the cow head group to the north the basal part of the section is a proximal facies of the cow head group shallow bay formation factory cove member beds 9 10 and part of bed 11 the upper part of the section consists of interbedded dolostone and shale and is unlike any other sequence in the cow head group this upper sedimentary sequence is defined as the lobster cove head member of the shallow bay formation cow head group contact between the two sedimentary packages is also marked by a faunal break and coincides with emplacement of megaconglomerate bed 12 at cow

high resolution probing of inner core structure with seismic interferometry increasing complexity of earth s inner core has been revealed in recent decades as the global distribution of seismic stations has improved the uneven distribution of earthquakes however still causes a biased geographical sampling of the inner core recent developments in seismic interferometry which allow for the retrieval of core sensitive body waves propagating between two receivers can significantly improve ray path coverage of the inner core in this study we apply such earthquake coda interferometry to 1846 usarray stations deployed across the u s from 2004 through 2013 clear inner core phases pkikp 2 and pkiikp 2 are observed across the entire array spatial analysis of the differential travel time residuals between the two phases reveals significant short wavelength variation and implies the existence of strong structural variability in the deep earth a linear n s trending anomaly across the middle of the u s may reflect an asymmetric quasi hemispherical structure deep within the inner core with boundaries of 99 w and 88 e

gas hydrate distribution and hydrocarbon maturation north of the knipovich ridge western svalbard margin a bottom simulating reflector bsr occurs west of svalbard in water depths exceeding 600 m indicating that gas hydrate occurrence in marine sediments is more widespread in this region than anywhere else on the eastern north atlantic margin regional bsr mapping shows the presence of hydrate and free gas in several areas with the largest area located north of the knipovich ridge a slow spreading ridge segment of the mid atlantic ridge system here heat flow is high up to 330 mw m 2 increasing towards the ridge axis the coinciding maxima in across margin bsr width and heat flow suggest that the knipovich ridge influenced methane generation in this area this is supported by recent finds of thermogenic methane at cold seeps north of the ridge termination to evaluate the source rock potential on the western svalbard margin we applied 1d petroleum system modeling at three sites the modeling shows that temperature and burial conditions near the ridge were sufficient to produce hydrocarbons the bulk petroleum mass produced since the eocene is at least 5 kt and could be as high as 0 2 mt most likely source rocks are miocene organic rich sediments and a potential eocene source rock that may exist in the area if early rifting created sufficiently deep depocenters thermogenic methane production could thus explain the more widespread presence of gas hydrates north of the knipovich ridge the presence of microbial methane on the upper continental slope and shelf indicates that the origin of methane on the svalbard margin varies spatially

antipodal focusing of seismic waves observed with the usarray we present an analysis of the mw 5 3 earthquake that occurred in the southeast indian ridge on 2010 february 11 using usarray data the epicentre of this event is antipodal to the usarray providing us with an opportunity to observe in details the antipodal focusing of seismic waves in space and time we compare the observed signals with synthetic seismograms computed for a spherically symmetric earth model prem a beamforming analysis is performed over the different seismic phases detected at antipodal distances direct spatial snapshots of the signals and the beamforming results show that the focusing is well predicted for the first p wave phases such as pkp or pp however converted phases sksp pps show a deviation of the energy focusing to the south likely caused by the earth s heterogeneity focusing of multiple s wave phases strongly deteriorates and is barely observable

graptolites from the lower middle ordovician st george and table head groups western newfoundland and their correlation with trilobite brachiopod and conodont zones faunal assemblages of the autochthonous shelf carbonate sequences belonging to the st george and table head groups are dominated by shelly macrofossils and conodonts rare usually monotypic graptolitic horizons enable correlation with the allochthonous cow head group which was deposited on the middle to lower slope and the shelly conodont and graptolitic zonal schemes elsewhere in north america the catoche formation of the st george group is of ibexian canadian age and yields graptolites indicative of the tetragraptus approximatus and tetragraptus akzharensis zones early arenig the basal aguathuna formation belongs to the pendeograptus fruticosus zone whereas higher parts span the ibexian whiterock boundary graptolites suggest that the table head group entirely postdates the cow head group this is supported by a whiterock early llanvirn trilobite conodont and brachiopod fauna

abiotic methane from ultraslow spreading ridges can charge arctic gas hydrates biotic gas generation from the degradation of organic carbon in marine sediments supplies and maintains gas hydrates throughout the world s oceans in nascent ultraslow spreading ocean basins methane generation can also be abiotic occurring during the high temperature 200 c serpentinization of ultramafic rocks here we report on the evolution of a growing arctic gas and gas hydrate charged sediment drift on oceanic crust in eastern fram strait a tectonically controlled deep water gateway between the subpolar north atlantic and arctic oceans ultraslow spreading ridges between northwest svalbard and northeast greenland permit the sustained interaction of a mid ocean ridge transform fault and developing sediment drift on both young 10 ma oceanic crust since the late miocene geophysical data image the gas charged drift and crustal structure and constrain the timing of a major 30 km lateral displacement of the drift across the molloy transform fault we describe the buildup of a 2 m y long lived gas hydrate and free gas charged drift system on young oceanic crust that may be fed and maintained by a dominantly abiotic methane source ultraslow spreading sedimented ridge flanks represent a previously unrecognized carbon reservoir for abiotic methane that could supply and maintain deep water methane hydrate systems throughout the arctic

effect of early pliocene uplift on late pliocene cooling in the arctic atlantic gateway despite the undisputed role of the arctic ocean in the modern and pliocene climate system the arctic has only recently attracted public awareness that ongoing fundamental change in the arctic cryosphere could be a response to global warming clarification of the arctic s role in global climate during the pliocene is however largely hampered by equivocal stratigraphic constraints from a well dated pliocene sequence from the yermak plateau off nw spitsbergen we present sedimentological and geochemical data indicating that 4 million years ago terrigenous sediment supply and sources changed abruptly in response to a regional tectonic uplift event we argue that this event together with contemporary uplift and tilting along the northwestern european continental margin preconditioned the landmasses for glacial ice build up during intensification of the northern hemisphere glaciation inhg our data further suggest that the final deepening widening of the arctic atlantic gateway the fram strait between 6 5 and 5 ma gradually caused increased deep water mass exchange which in turn likely contributed to the intensification of the north atlantic thermohaline circulation coupled to the north atlantic warm pool as a regional moisture source declining atmospheric co2 levels and other feedback mechanisms during the pliocene the regional tectonic activities in the high northern latitudes caused decreased summer ablation and thus allowed the initial build up of glacial ice both in scandinavia and the sub aerially exposed svalbard barents sea culminating in the first large scale coastline shelf edge glaciations at 2 75 ma

variable eocene miocene sedimentation processes and bottom water redox conditions in the central arctic ocean iodp expedition 302 abstract in 2004 integrated ocean drilling program expedition 302 arctic coring expedition acex to the lomonosov ridge drilled the first central arctic ocean sediment record reaching the uppermost cretaceous 430 m composite depth while the neogene part of the record is characterized by grayish yellowish siliciclastic material the paleogene part is dominated by biosiliceous black shale type sediments the lithological transition between paleogene and neogene deposits was initially interpreted as a single sedimentological unconformity hiatus of 26 ma duration separating eocene from miocene strata more recently however continuous sedimentation on lomonosov ridge throughout the cenozoic was proclaimed questioning the existence of a hiatus in this context we studied the elemental and mineralogical sediment composition around the paleogene neogene transition at high resolution to reconstruct variations in the depositional regime e g wave current activity detrital provenance and bottom water redox conditions already below the hiatus mineralogical and geochemical proxies imply drastic changes in sediment provenance and or weathering intensity in the hinterland and point to the existence of another earlier gap in the sediment record the sediments directly overlying the hiatus the zebra interval are characterized by pronounced and abrupt compositional changes that suggest repeated erosion and re deposition of material regarding redox conditions euxinic bottom waters prevailed at the eocene lomonosov ridge and became even more severe directly before the hiatus with detrital sedimentation rates decreasing authigenic trace metals were highly enriched in the sediment this continuous authigenic trace metal enrichment under persistent euxinia implies that the arctic trace metal pool was renewed continuously by water mass exchange with the world ocean so the eocene arctic ocean was not fully restricted above the hiatus extreme positive ce anomalies are clear signs of a periodically well oxygenated water column but redox conditions were highly variable during deposition of the zebra interval significant mn enrichments only occur above the zebra interval documenting the miocene establishment of stable oxic conditions in the arctic ocean in summary extreme and abrupt changes in geochemistry and mineralogy across the studied sediment section do not suggest continuous sedimentation at the lomonosov ridge around the eocene miocene transition but imply repeated periods of very low sedimentation rates and or erosion

diagenetic regimes in arctic ocean sediments implications for sediment geochemistry and core correlation dark brown sediment layers are a potential stratigraphic tool in quaternary arctic ocean sediments they are rich in mn fe and trace metals scavenged from the water column and were most likely deposited during interglacial intervals in this study we combine sediment and pore water data from sediment cores taken in different parts of the arctic ocean to investigate the influence of early diagenetic processes on sediment geochemistry in most studied cores mn co and mo are released into the pore waters from mn oxide dissolution in deeper 1 5 m sediment layers the relationship between sedimentary mn co and mo contents in excess of the lithogenic background elementxs shows thatcoxs moxs values are a diagnostic tool to distinguish between layers with diagenetic metal addition from the pore waters coxs moxs 10 and unaffected layers coxs moxs from 1 to 10 steady state calculations based on current pore water profiles reveal that in the studied cores the diagenetic addition of these metals from the pore water pool alone is not sufficient to produce the sedimentary metal enrichments however it seems evident that dissolution of mn oxides in the mn reduction zone can permanently alter the primary geochemical signature of the dark brown layers therefore pore water data and coxs moxs values should be considered before core correlation when this correlation is solely based on mn contents and dark sediment color in contrast to the mostly nonlithogenic origin of mn in the dark brown layers sedimentary fe consists of a large lithogenic 80 and a small non lithogenic fraction 20 our pore water data show that diagenetic fe remobilization is not currently occurring in the sediment the dominant fe sources are coastal erosion and river input budget calculations show that fe seems to be trapped in the modern arctic ocean and accumulates in shelf and basin sediments the fe isotopic signal 56fe of the solid phase is positive 0 2 to 0 3 in samples defined as the lithogenic background without significant fe enrichments with increasing non lithogenic fe contents in the sediment 56fe becomes more negative which indicates a shelf to basin export of an isotopically lighter fe fraction we assume that the same transport process is true for mn

basement structure of the north western yermak plateau 1 the separation of northeast greenland and svalbard was achieved by large strike slip movements in cenozoic times evidence for these movements can be found onshore both on north greenland and svalbard however the role of the yermak plateau in this process is quite speculative new multichannel seismic 10 km spacing and aeromagnetic data 7 5 km spacing across the north western part of the plateau show that the acoustic basement has a similar strike direction to that of the geological units onshore svalbard a prominent fault zone separates these most likely continental structures in the west from a more n s extended transitional crustal block in the eastern part of the plateau this part of the plateau is characterized by strong magnetic anomalies at least indicating highly intruded and stretched continental or even oceanic crust however the seismic data show that the plateau like bathymetry is quite young during most of its cenozoic history the yermak plateau had a rough topography similar to the topography onshore svalbard thus the paleo bathymetry might have played an important role for the water exchange between the arctic ocean and the north atlantic prior to the opening of the fram strait which is today the main pathway for the deep water masses

the heartbeat of the oligocene climate system a 13 million year continuous record of oligocene climate from the equatorial pacific reveals a pronounced heartbeat in the global carbon cycle and periodicity of glaciations this heartbeat consists of 405 000 127 000 and 96 000 year eccentricity cycles and 1 2 million year obliquity cycles in periodically recurring glacial and carbon cycle events that climate system response to intricate orbital variations suggests a fundamental interaction of the carbon cycle solar forcing and glacial events box modeling shows that the interaction of the carbon cycle and solar forcing modulates deep ocean acidity as well as the production and burial of global biomass the pronounced 405 000 year eccentricity cycle is amplified by the long residence time of carbon in the oceans

equatorial anisotropy in the inner part of earth s inner core from autocorrelation of earthquake coda the speed of seismic waves passing through the earth s inner core varies with direction analysis of earthquake seismic data suggests that this directional dependence differs between innermost and outer inner core

active synsedimentary tectonism on a mixed carbonate siliciclastic continental margin third order sequence stratigraphy of a ramp to basin transition lower sekwi formation selwyn basin northwest territories canada the lower part of the early cambrian sekwi formation in the selwyn basin of the northwest territories canada is composed of two regional unconformity bounded sequences s0 and s1 which record the first widespread carbonate deposition during the initial palaeozoic transgression onto the western margin of laurentia these early cambrian sequences are unique to the western north american cordillera representing the only record of primarily deep water deposition on a tectonically active mixed carbonate siliciclastic ramp during this period more specifically the geometry of the sekwi ramp changed during deposition of s0 and s1 from a shallowly dipping homoclinal ramp during the s0 transgressive systems tract to a steeply dipping tectonically modified ramp during the early highstand systems tract of s0 the steeply dipping ramp profile of s0 was preserved into the early transgressive systems tract of s1 the sekwi ramp returned to a gently sloping ramp during the late highstand systems tract of s1 and remained so throughout the remainder of sekwi deposition the evolving shape of the sekwi ramp is attributed to syndepositional down to the basin faulting during deposition of both s0 and s1 and is recorded by i the westward thickening irregular geometries of s0 and s1 ii geographical restriction of deep water facies including sediment gravity flow deposits iii the presence of large allochthonous blocks and iv the clast composition of sediment gravity flow deposits sediment gravity flow deposits play an unusually important role in the sequence stratigraphic interpretation of the lower sekwi formation as they delineate depositional packages including the maximum flooding zone the transitions between portions of systems tracts and the inferred locations of syntectonic extensional faults syntectonic faults increased accommodation basinward of an extensive ooid shoal complex that developed along the sekwi ramp crest greatly influencing sequence geometry and initiating the downslope motion of sediment gravity flows the syndepositional faulting probably was a continuation of extension that began during the latest neoproterozoic rifting of western laurentia the composition of sediment gravity flow deposits track changing accommodation space on the lower sekwi ramp and can be used to differentiate systems tracts that probably were related more to tectonism than eustasy

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

global propagation of body waves revealed by cross correlation analysis of seismic hum 1 seismic interferometry has now been applied to the exploration of the earth s interior at scales ranging from local to global most studies have used surface wave propagation recently some studies have focused on body wave propagation on local and regional scales but not on a global scale in this study we succeed in extracting global body wave propagation of p pp pkp s ss scs p p etc waves using seismic hum with frequency wave number filtering in the range of 5 to 40 mhz although the observed body wave propagation is similar to that of the corresponding components of green s functions there are two differences between them the lack of reflection phases in the observation and the dominance of shear coupled pl waves in the observation these differences originate from the dominance of shear traction sources on the earth s surface which causes the breakdown of equipartition among modes with different radial orders for further studies of body wave exploration by seismic interferometry these differences should be considered

transform marginal plateaus abstract numerous submarine plateaus form highstanding bathymetric highs at continent to ocean transitions due to their proximity to continents they have been frequently labelled marginal plateaus although this term has not been clearly defined or associated with a specific geology or geodynamic process until now these elevations have been interpreted as submerged thinned continental fragments detached from continents basaltic buildups formed by hotspots volcanic margins or oceanic plateaus many of these plateaus formed at transform margins connecting oceanic basins of contrasted ages we propose for the first time to define and review a class of marginal plateaus related to a specific tectonic setting transform marginal plateaus tmps based on a compilation of 20 tmps around the world we show that most of them have a polyphased history and have undergone at least one major volcanic phase our review highlights in particular a hitherto unrecognized close link between hotspots volcanic activity and transform margins we also propose that due to their polyphased history tmps may contain several successive basins and overlooked long lived sedimentary archives we finally highlight that because these tmps were transform plate boundaries perpendicular or oblique to surrounding rifts many of them were close to last contact points during final continental breakup and may have formed land bridges or bathymetric highs between continents therefore we discuss broader scientific issues such as the interest of tmps in recording and studying the onset and variations of oceanic currents or past biodiversity growth bio connectivity and lineage evolution

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

early development and flysch sedimentation in ordovician taconic foreland basin west central newfoundland during the early to late ordovician the taconic foredeep in west central newfoundland evolved from an underfilled to an overfilled state in response to cratonward advance thickening and erosion of the taconic orogen early orogen derived sediment in the foreland basin consisted of middle to lake arenigian deep water mudstones that accumulated on an inner craton facing slope prism uppermost parts of shallow bay and green point formations and correlative units these deposits are interbedded with and overlie passive margin slope sediments in the middle arenigian to early llanvirnian sand from the orogen formed several small sand rich submarine fans lower head formation and correlative units on the lower reaches of the inner slope and basin plain the fans may have been fed by closely spaced rivers draining the orogen as presently occurs in western south america only proximal portions of these fans are now exposed the flysch basin was narrow constricted by the inner slope and the passive ma

low frequency pliocene climate variability in the eastern nordic seas the pliocene 5 3 2 6 ma is often described as a relatively stable climatic period with warm temperatures characterizing high latitudes new suborbital resolved stable isotope records from ocean drilling program hole 642b in the eastern nordic seas document that the pliocene was not a stable period characterized by one climate rather seven distinct climate phases each lasting between 150 000 and 400 000 years are identified and characterized in the time interval 5 1 3 1 ma four of the transitions between the defined climate phases occurred close to an eccentricity minimum and a minimum in amplitude of change for northern hemisphere summer insolation while two occurred around an eccentricity maximum and a maximum in amplitude in insolation change hence a low frequency response of the nordic seas to insolation forcing is indicated in addition paleogeographic and related paleoceanographic changes expansion of the arctic sea ice cover and onset of northern hemisphere glaciation were important factors behind the evolving pliocene low frequency variability in the eastern nordic seas it is likely that the identified climate phases and transitions are important beyond the nordic seas due to their association with changes to both insolation and paleogeography however a strong and variable degree of diagenetic calcite overgrowth is documented for the planktic foraminifera especially influencing the planktic 18o results the absolute values and amplitude of change cannot be taken at face value

lateral heterogeneity imaged by small aperture scs retrieval from the ambient seismic field interpreting core related body wave travel times is challenging for seismologists because earth s heterogeneities are averaged over thousands of kilometers and the sparsity of earthquake measurements makes these heterogeneities difficult to localize we show how the ambient seismic wave field can be used to overcome these limitations we present a regional scale analysis of core mantle boundary reflections scs under mexico we show that body wave arrivals i e p and scs are retrieved from higher order cross correlations c3 a technique that provides a more uniform and controlled source distribution using the scattered waves of the coda of classical ambient field cross correlations c1 then we extract scs travel times along a dense linear array in mexico and find that lithospheric lateral heterogeneity such as the subducting cocos slab beneath mexico may have a strong impact on scs travel times in parallel we show that lateral heterogeneity such as a possible ultra low velocity zone ulvz near the core mantle boundary might also affect although to a lesser extent the travel time anomalies our results and interpretation are supported through numerical simulations that accounts for slab and ulvz properties

astronomically paced changes in deep water circulation in the western north atlantic during the middle eocene abstract north atlantic deep water nadw currently redistributes heat and salt between earth s ocean basins and plays a vital role in the ocean atmosphere co2 exchange despite its crucial role in today s climate system vigorous debate remains as to when deep water formation in the north atlantic started here we present datasets from carbonate rich middle eocene sediments from the newfoundland ridge revealing a unique archive of paleoceanographic change from the progressively cooling climate of the middle eocene well defined lithologic alternations between calcareous ooze and clay rich intervals occur at the 41 kyr beat of axial obliquity hence we identify obliquity as the driver of middle eocene 43 5 46 ma northern component water ncw the predecessor of modern nadw variability high resolution benthic foraminiferal 18 o and 13 c suggest that obliquity minima correspond to cold nutrient depleted western north atlantic deep waters we thus link stronger ncw formation with obliquity minima in contrast during obliquity maxima deep western boundary currents were weaker and warmer while abyssal nutrients were more abundant these aspects reflect a more sluggish ncw formation this obliquity paced paleoceanographic regime is in excellent agreement with results from an earth system model in which obliquity minima configurations enhance ncw formation

a methodology for targeting palaeo proxy data acquisition a case study for the terrestrial late miocene when planning the acquisition of new palaeo proxy data for reconstructing past climates many factors influence the decision of where the proxies are to be collected one such influence is the likelihood of recording a significant climate change relative to the modern another consideration which is less often considered is the desire to target regions in which there is significant uncertainty in numerical model predictions of past climate change new proxy data in these regions enables a more rigorous test of model simulations and results in better constraints on the various boundary conditions used to force the models in this paper we present a methodology for targeting new palaeo proxy data based on model simulations we use the terrestrial late miocene 11 6 to 5 3 ma as a case study the late miocene climate provides insights into future climate behavior as it is believed to have been considerably warmer than the modern we carry out a suite of late miocene atmosphere only general circulation model simulations which we initially evaluate relative to an example dataset of terrestrial temperature and precipitation in terms of targeting future data acquisition we locate those regions in the model which exhibit the largest change in temperature and or precipitation relative to the pre industrial we also locate those regions which display the largest variability between the model simulations because new data in these regions are most likely to provide a strict test of the reliability of the model results among other regions the amazon basin the chad basin central canada and northern india are identified as potentially useful areas to collect data

antipodal seismic observations of temporal and global variation at earth s inner outer core boundary 1 we have found two pairs of earthquake doublets closely located antipodally on one diametral axis between tonga algeria and several other events on other axes these doublets show significant correlation and exhibit seismic phases traversing the core that cannot be explained by a standard radial earth model such as prem the antipodal waveform data are highly variable between axes the observed variability of the waveforms indicates global variations in the structure above and below the inner outer core boundary region we have found evidence for a regional low velocity zone at the base of the outer core corresponding with a decadal temporal variation 0 55 s in seismic energy traversing the top of the inner core we propose an antipodal seismic array to constrain and to provide further progress for the study of the inner and outer core

seismic interferometry with antipodal station pairs in this study we analyze continuous data from all global seismographic network stations between year 2000 and 2009 and demonstrate that several body wave phases e g pp pcppkp sksp and pps propagating between nearly antipodal station pairs can be clearly observed without array stacking using the noise coda cross correlation method based on temporal correlations with global seismicity we show that the observed body waves are clearly earthquake related moreover based on single earthquake analysis we show that the earthquake coda energy observed between 10 000 and 30 000 s after a large earthquake contributes the majority of the signal we refine our method based on these observations and show that the signal can be significantly improved by selecting only earthquake coda times with our improved processing the pkikp phase which does not benefit from the focusing effect near the antipode can now also clearly be observed for long distance station pairs

arenig biostratigraphy of the pointe de levy slice quebec appalachians canada the pointe de levy slice includes a nearly complete arenig graptolite succession a conspicuous gap exists in the yapeenian ya to lower darriwilian da part ya 1 da 1 the lithological column is compiled from several sections at levis quebec that yield only parts of the complete succession the graptolite zonation can be compared closely with that from the cow head group of western newfoundland and the deep kill formation of eastern new york the shumardia limestone is differentiated into four graptolite zones and subzones of which the youngest zone clearly belongs to the llanvirn the araneograptus murrayi and holmograptus lentus zones are documented for the first time from the levis area the undulograptus dentatus zone of the latest arenig is introduced

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

lithostratigraphic and allostratigraphic framework of the cambrian ordovician potsdam group and correlations across early paleozoic southern laurentia the potsdam group is a cambrian to lower ordovician siliciclastic unit that crops out along the southeastern margins of the ottawa graben from its base upward the potsdam consists of the ausable hannawa falls and keeseville formations in addition the potsdam is subdivided into three allounits allounit 1 comprises the ausable and hannawa falls and allounits 2 and 3 respectively the lower and upper parts of the keeseville allounit 1 records early to middle cambrian syn rift arkosic fluvial sedimentation ausable formation with interfingering mudstone arkose and dolostone of the marine altona member recording transgression of the easternmost part of the ottawa graben rift sedimentation was followed by a middle cambrian climate change resulting in local quartzose aeolian sedimentation hannawa falls formation allounit 1 sedimentation termination coincided with latest middle cambrian tectonic reactivation of parts of the ottawa graben allounit 2 lower keeseville records mainly upper cambrian quartzose fluvial sedimentation with transgression of the northern ottawa graben resulting in deposition of mixed carbonate siliciclastic strata of the marine riviere aux outardes member sedimentation was then terminated by an earliest ordovician regression and unconformity development allounit 3 upper keeseville records diachronous transgression across the ottawa graben that by the arenigian culminated in mixed carbonate siliciclastic shallow marine sedimentation theresa formation the contact separating the potsdam group and theresa formation is conformable except locally in parts of the northern ottawa graben where the presence of localized islands and or coastal salients resulted in subaerial exposure and erosion of the uppermost potsdam strata and accordingly unconformity development

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

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

complex and variable crustal and uppermost mantle seismic anisotropy in the western united states deformation in the crust and mantle measured using seismic anisotropy is poorly constrained in the western united states because of inconsistencies in the existing data a three dimensional model that reconciles these discrepancies reveals that seismic anisotropy in the crust correlates with different geological provinces but is unrelated to anisotropy in the underlying mantle

analysis of intermediate period correlations of coda from deep earthquakes abstract we aim at assessing quantitatively the nature of the signals that appear in coda wave correlations at periods 20 s these signals contain transient constituents with arrival times corresponding to deep seismic phases these body wave constituents can be used for imaging to evaluate this approach we calculate the autocorrelations of the vertical component seismograms for the mw 8 4 sea of okhotsk earthquake at 400 stations in the eastern us using data from 1 h before to 50 h after the earthquake by using array analysis and modes identification we discover the dominant role played by high quality factor normal modes in the emergence of strong coherent phases as scs like and p p df like we then make use of geometrical quantization to derive the constituent rays associated with particular modes and gain insights about the ballistic reverberation of the rays that contributes to the emergence of body waves our study indicates that the signals measured in the spatially averaged autocorrelations have a physical significance but a direct interpretation of scs like and p p df like is not trivial indeed even a single simple measurement of long period late coda in a limited period band could provide valuable information on the deep structure by using the temporal information of its autocorrelation a procedure that could be also useful for planetary exploration

extracting stable seismic core phases from ambient seismic noise abstract ambient seismic noise correlation is a powerful tool for extracting the seismic core phases that propagate through the interior of the earth in this study we present and refine the root mean square stacking method to extract stable core phases e g pcp scs pcs scp and pkikp from within the central alborz region iran using empirical green s functions our studies on the extracted core phases using empirical green s functions indicated that the ambient seismic noise method is independent from global seismicity m 5 5 we also show that by dividing ambient seismic records into shorter i e 2700 s and overlapping 70 time windows before the cross correlation procedure we can improve the quality and stability of the empirical green s functions generated consequently 73 days equivalent to 22 of the total time period for the dataset of nonconsecutive ambient seismic noise time windows have been used to retrieve core phase empirical green s functions in a 5 10 s period band

arctic perennial ice cover over the last 14 million years knowledge of the long term history of the perennial ice is an important issue that has eluded study because the cenozoic core material needed has been unavailable until the recent arctic coring expedition acex detrital fe oxide mineral grains analyzed by microprobe from the last 14 ma 164 m of the acex composite core on the lomonosov ridge were matched to circum arctic sources with the same mineral and 12 element composition these precise source determinations and estimates of drift rates were used to determine that these sand grains could not be rafted to the acex core site in less than a year thus the perennial ice cover has existed since 14 ma except for the unlikely rapid return to seasonal ice between the average sampling interval of about 0 17 ma both north america and russia contributed significant fe grains to the acex core during the last 14 ma

changes in current patterns in the fram strait at the pliocene pleistocene boundary seismic reflection profiles from the northwestern and central part of the fram strait show thick packages of drift type sediments mainly along the western yermak plateau flank but also in the central flat part of the fram strait north of 80 5 n a large scale field of sediment waves along the yermak plateau rise separates a western lower from an eastern upper drift body these drift bodies were deposited by bottom currents most likely the northbound yermak branch of the west spitsbergen current but we cannot rule out that the western drift body may also have been influenced by southbound bottom currents a stratigraphic boundary is clearly visible within the drift bodies and even more pronounced within the sediment waves separating a lower package of waves migrating upslope at low angle 5 from an upper package with significantly increased wave crest migration 16 5 this stratigraphic boundary could be tracked along the seismic network and corresponds to the lithostratigraphic boundary between units ia and ib at odp leg 151 site 911 that was dated to 2 7 ma the increase in wave crest migration angle indicates a shift towards higher sedimentation rates at 2 7 ma which corresponds to the intensification of the northern hemisphere glaciation with a major expansion of the greenland scandinavian northern barents sea and north american ice sheets the subaerially exposed barents shelf and the expansion of the northern barents sea ice sheet as well as svalbard are likely sources for enhanced erosion and enhanced fluvial input along the pathway of the west spitsbergen current resulting in higher sedimentation rates in the fram strait

global cenozoic paleobathymetry with a focus on the northern hemisphere oceanic gateways abstract the evolution of the northern hemisphere oceanic gateways has facilitated ocean circulation changes and may have influenced climatic variations in the cenozoic time 66 ma 0 ma however the timing of these oceanic gateway events is poorly constrained and is often neglected in global paleobathymetric reconstructions we have therefore re evaluated the evolution of the northern hemisphere oceanic gateways i e the fram strait greenland scotland ridge the central american seaway and the tethys seaway and embedded their tectonic histories in a new global paleobathymetry and topography model for the cenozoic time our new paleobathymetry model incorporates northeast atlantic paleobathymetric variations due to iceland mantle plume activity updated regional plate kinematics and models for the oceanic lithospheric age sediment thickness and reconstructed oceanic plateaus and microcontinents we also provide a global paleotopography model based on new and previously published regional models in particular the new model documents important bathymetric changes in the northeast atlantic and in the tethys seaway at eocene oligocene transition 34 ma the time of the first glaciations of antarctica believed to be triggered by the opening of the southern ocean gateways i e the drake passage and the tasman gateway and subsequent antarctic circumpolar current initiation our new model can be used to test whether the northern hemisphere gateways could have also played an important role modulating ocean circulation and climate at that time in addition we provide a set of realistic global bathymetric and topographic reconstructions for the cenozoic time at one million year interval for further use in paleo ocean circulation and climate models

variations of north atlantic inflow to the central arctic ocean over the last 14 million years inferred from hafnium and neodymium isotopes the warm and saline north atlantic inflow to the arctic ocean is a major component of high northern latitude circulation and the main mechanism of deep water renewal in the arctic ocean knowledge of its past variability is critical for understanding the high latitude feedback mechanisms of the climate system here we present the first combined seawater hf and nd isotope compositions of past arctic intermediate water extracted from the authigenic fe mn oxyhydroxide fraction of two sediment cores recovered near the north pole to reconstruct changes in contributions from glacial brines of the eurasian shelf and past inflow of atlantic waters the hf and nd isotopic compositions obtained from leachates of the authigenic fraction show closely coupled and environmentally controlled variations over the past 14 million years an observed offset of these data from seawater ehf and end compositions from other ocean basins seawater array is interpreted as the result of continuously prevailing glacial weathering conditions on the high latitude eurasian continent in the late quaternary large amplitude hf and nd isotopic variations of arctic intermediate water aiw was characterized by more radiogenic isotope signatures generally prevailing under glacial conditions and less radiogenic values during interglacial periods on the basis of the close coupling between nd and hf isotopes we suggest that the evolution of hf isotope compositions of central arctic aiw has primarily been controlled by changes in ocean circulation and provenance of weathering inputs rather than changes in weathering regime

eocene silicoflagellate and ebridian paleoceanography in the central arctic ocean the silicoflagellate and ebridian assemblages in early middle eocene arctic cores obtained by iodp expedition 302 acex were studied in order to decipher the paleoceanography of the upper water column the assemblages in lithologic unit 2 49 7 45 1 ma one of the biosiliceous intervals were usually endemic as compared to the assemblages that occurred outside of the arctic ocean the presence of these endemic assemblages is probably due to a unique environmental setting controlled by the degree of mixing between the low salinity arctic waters and relatively high salinity waters supplied from outside the arctic ocean such as the atlantic and possibly the western siberian sea using the basin to basin fractionation model the early middle eocene arctic ocean corresponds to an estuarine circulation type which includes the modern day black sea the abundant down core occurrence of ebridians strongly suggests the past presence of low salinity waters and may indicate that low oxygen concentrations prevailed in the euphotic layer on the basis of the ecology of the modern ebridian hermesinum adriaticum

tomographic inversion for three dimensional anisotropy of earth s inner core abstract seismological studies generally suggest that the earth s inner core is anisotropic and the anisotropic structure changes significantly both laterally and with depth previous body wave studies of the inner core have relied on ray tracing or waveform modeling using one dimensional 1d models here we present non linear tomographic inversions of the inner core anisotropy using three dimensional 3d ray tracing spline parameterization and a large collection of pkp differential travel times we adapt a pseudo bending ray tracing pbr method in spherical coordinates for seismic rays that traverse the inner core pkp df phase the method iteratively perturbs each discontinuity point and continuous segment of the ray through 3d earth structure so that its travel time is minimum the 3d anisotropic structure of the inner core is approximated to the first order as 3d heterogeneous but isotropic structure for a given ray the data are corrected using a scaled mantle tomographic model the inner core anisotropy model obtained has the following major features 1 the model has strong hemispherical and depth variation the isotropic velocity in the topmost inner core is greater in quasi eastern hemisphere qeh 40 160 e than in quasi western hemisphere qwh other longitudes the anisotropy is weak in qeh to the depth of 600 700 km below the inner core boundary icb while in qwh the anisotropy increases at much shallower depth about 100 200 km below the icb to about 3 4 then remains at about 2 4 throughout the rest of the inner core 2 the anisotropy form changes abruptly over a depth range of about 150 km at the radius of about 600 km slightly less than half of the inner core radius forming a distinct inner inner core iic the velocity in the iic has maximums at equatorial and polar directions and minimum at an angle of about 40 from the equatorial plane the velocity in the outer inner core oic however changes little for ray directions 0 40 from the equatorial plane 3 despite large variation of the anisotropy the isotropic velocity voigt average throughout the inner core is nearly uniform the results suggest that the oic is likely composed of the same type of iron crystals with uniform chemistry but the iic may be composed of a different type of crystal alignment a different iron phase or a different chemical composition our tests on model parameterization mantle correction and linear and non linear inversion suggest the main features of our model are very robust however fine scale structures are likely to differ particularly in the major transition zones e g in the topmost qwh isotropy to anisotropy between oic and iic change in the form of anisotropy and between qeh and qwh in oic difference in anisotropy strength searches for possible waveform complications from these boundaries need to be aware of the directional dependence and geographical variation to be successful

shear properties of earth s inner core constrained by a detection of j waves in global correlation wavefield seismic j waves shear waves that traverse earth s inner core provide direct constraints on the inner core s solidity and shear properties however these waves have been elusive in the direct seismic wavefield because of their small amplitudes we devised a new method to detect j waves in the earthquake coda correlation wavefield they manifest through the similarity with other compressional core sensitive signals the inner core is solid but relatively soft with shear wave speeds and shear moduli of 3 42 0 02 kilometers per second and 149 0 1 6 gigapascals gpa near the inner core boundary and 3 58 0 02 kilometers per second and 167 4 1 6 gpa in earth s center the values are 2 5 lower than the widely used preliminary earth reference model this provides new constraints on the dynamical interpretation of earth s inner core

brachiopod biostratigraphy of the middle ordovician cow head and table head groups western newfoundland brachiopods from shallow water limestone boulders in beds 12 13 and 14 of the allochthonous cow head group belong in the earliest whiterockian orthidiella zone brachiopods of the autochthonous intertidal to deep water table head group are equivalent to those of the younger whiterockian anomalorthis zone the cow head is older than the table head integration of the brachiopod data from western newfoundland with those from the type whiterockian in nevada combined with the evidence of graptolites from both areas indicates that the orthidiella zone spans the australian castlemainian yapeenian and lower darriwilian dal zones

chondrites a trace fossil indicator of anoxia in sediments the trace fossil chondrites a highly branched burrow system of unknown endobenthic deposit feeders occurs in all types of sediment including those deposited under anaerobic conditions in some cases such as the jurassic posidonienschiefer formation of germany chondrites occurs in black laminated carbonaceous sediment that was deposited in chemically reducing conditions in other cases such as numerous oxic clastic and carbonate units throughout the geologic column chondrites typically represents the last trace fossil in a biotutbation sequence this indicates that the burrow system was produced deep within the sediment in the anaerobic zone below the surficial oxidized zone that was characterized by freely circulating and oxidizing pore waters

body wave imaging of earth s mantle discontinuities from ambient seismic noise ambient seismic noise correlations are widely used for high resolution surface wave imaging of earth s lithosphere similar observations of the seismic body waves that propagate through the interior of earth would provide a window into the deep earth we report the observation of the mantle transition zone through noise correlations of p waves as they are reflected by the discontinuities associated with the top 410 kliometers km and the bottom 660 km of this zone our data demonstrate that high resolution mapping of the mantle transition zone is possible without using earthquake sources

3 d crustal structure of the western united states application of rayleigh wave ellipticity extracted from noise cross correlations we present a new 3 d seismic model of the western united states crust derived from a joint inversion of rayleigh wave phase velocity and ellipticity measurements using periods from 8 to 100 s improved constraints on upper crustal structure result from use of short period rayleigh wave ellipticity or rayleigh wave h v horizontal to vertical amplitude ratios measurements determined using multicomponent ambient noise cross correlations to retain the amplitude ratio information between vertical and horizontal components for each station we perform daily noise pre processing temporal normalization and spectrum whitening simultaneously for all three components for each station pair amplitude measurements between cross correlations of different components radial radial radial vertical vertical radial and vertical vertical are then used to determine the rayleigh wave h v ratios at the two station locations we use all earthscope usarray tranportable array data available between 2007 january and 2011 june to determine the rayleigh wave h v ratios and their uncertainties at all station locations and construct new rayleigh wave h v ratio maps in the western united states between periods of 8 and 24 s combined with previous longer period earthquake rayleigh wave h v ratio measurements and rayleigh wave phase velocity measurements from both ambient noise and earthquakes we invert for a new 3 d crustal and upper mantle model in the western united states correlation between the inverted model and known geological features at all depths suggests good resolution in five crustal layers use of short period rayleigh wave h v ratio measurements based on noise cross correlation enables resolution of distinct near surface features such as the columbia river basalt flows which overlie a thick sedimentary basin

structural and tectonic evolution of the humber zone western newfoundland 2 a regional model for acadian thrust tectonics the humber zone of the western newfoundland appalachians represents a cambrian ordovician passive continental margin which was deformed in taconian mid ordovician and acadian silurian devonian orogenic events a deformation front is imaged in seismic reflection data offshore of western newfoundland structures associated with this deformation front are exposed on port au port peninsula where silurian rocks are strongly deformed but mississippian strata are flat lying indicating that latest thrusting was acadian a gravity low in the gulf of st lawrence corresponds to a sediment filled acadian foreland basin previous models suggest that the on land shelf succession is autochthonous to parautochthonous however two lithoprobe seismic reflection transects show sub horizontal reflections between 2 and 5 s two way travel time which extend up to 85 km east of the thrust front these are interpreted as autochthonous platform and basement in this model shallower reflectors and outcropping units include both allochthonous platform and basement comprising the acadian port au port allochthon the taconian humber arm allochthon was carried westward as a high structural slice during thrusting of this allochthon no major structural discontinuity exists between grenville age crystalline rocks of the long range massif and platform rocks interpreted as allochthonous in the northern seismic line a monocline at the southern extremity of the long range probably represents an oblique or lateral hanging wall ramp above the basal detachment within the long range thrust zone at the western margin of the massif the long range thrust shows only a few kilometers of displacement however the parsons pond thrust which we interpret to run offshore at green point juxtaposes contrasting successions with different structural and thermal histories it probably carries a much larger amount of the total displacement the basal decollement of the port au port allochthon is therefore interpreted to pass beneath the southern part of the long range massif

arctic warming through the fram strait oceanic heat transport from 3 years of measurements we present estimates of volume and heat transport through fram strait for the period 1997 to 2000 from data of moored instruments full depth volume transports at 78 55 n were in the order of 10 sv both northwards and southwards with an annual mean net transport between 2 and 4 sv to the south the temperature of the northward flow of atlantic water had a strong seasonality with a minimum in winter nevertheless the northward heat transport was highest in winter caused by the winter maximum of northward volume transport during the three years of observation the heat transport in the west spitsbergen current increased from 28 to 46 tw as a result of both increased speed and temperature in contrast to the west spitsbergen current the volume and heat transport of east greenland current remained fairly constant an integration over a subsection of the east greenland current showed similar values of volume transport to that obtained by measurements in the 1980s foldvik et al 1988 the southward heat transport through modified atlantic water weakened slightly between 1997 and 1999 despite increased temperatures

sediment deposition in the northern basins of the north atlantic and characteristic variations in shelf sedimentation along the east greenland margin abstract new seismic data off east greenland were acquired in the summer of 2002 between 77 n and 81 n north of the greenland fracture zone the data were combined with results from the greenland basin and odp site 909 and indicate a pronounced middle miocene unconformity within the deep sea basins between 72 n and 81 n seismic unit na 1 consists of sediments older than middle miocene age and unit na 2 contains sediments younger than the middle miocene classification of a thinly bedded succession in the molloy basin resulted in a subdivision into four units unit i unit ii unit iiia and unit iiib a comparison of volume estimations and sediment thickness maps between 72 n and 81 n indicates differences in sediment accumulation in the greenland boreas and molloy basins important controls on the variation of accumulation included different opening times of the basins as well as tectonic conditions and varying sources of sediment transport due to prominent basement structures and the varying reflection character of the sediments along the entire east greenland margin we defined an age model of shelf sediments on the basis of similar sediment deposit geometry and known results from other regions the seismic sequences on the shelf up to an age of middle miocene are divided into three sub units along the east greenland margin middle miocene middle late miocene su 3 middle late miocene pleistocene su 2 pleistocene su 1 the differences in the geometry of the sequences show more ice stream related sedimentation between 72 n and 77 n and more ice sheet related sedimentation north of 78 n the region south of 68 n is dominated by more aggradational sedimentary strata so that a glacio fluvial drainage seems the main transport mechanism due to the greenland inland ice borderlines we assume the glaciers between the scoresby sund and 68 n did not reach the shelf break a first comparison of the sediment structure of the northeast greenland margin with the southeast greenland margin made it possible to demonstrate significant differences in sedimentation along this margin

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

the lack of equipartitioning in global body wave coda correlation of the coda of large earthquakes can be used to retrieve body waves at teleseismic distances this retrieval depends on waves propagating with equal energy in all directions equipartitioning we carry out a beamforming analysis of body waves at periods of 10 and 40 s recorded at usarray and show that the late coda up to 10 h after the okhotsk earthquake is dominated by waves propagating in the great circle direction late coda waves are not equipartitioned this implies for seismic interferometry that teleseismic body waves can only be extracted from the coda when the earthquake and the receivers are located on a great circle this happens automatically when the employed stations are antipodal or when the autocorrelation of waves is used the use of long period ambient seismic noise relies on the distribution of sources because scattering only marginally randomizes directions this provides insight into recent observations of core phases extracted from seismic interferometry

seismic evidence for widespread western us deep crustal deformation caused by extension morgan moschetti and colleagues use ambient noise tomography data from the western united states to show that strong radial seismic anisotropy exists in the deep crust confined mainly to the geological provinces that have undergone significant extension during the cenozoic era since about 65 million years ago the coincidence of crustal radial anisotropy with these extensional provinces supports the hypothesis that the deep crust within these regions has undergone widespread and relatively uniform strain in response to crustal thinning and extension here a method of seismic wave imaging known as ambient noise tomography is used to generate high resolution images of seismic wave speeds in the crust and uppermost mantle the observations reveal strong and uniform anisotropy where waves travel through rock at different speeds depending on direction in the deep crust in areas of the western united states that have undergone significant extension during the past 65 million years laboratory experiments have established that many of the materials comprising the earth are strongly anisotropic in terms of seismic wave speeds1 observations of azimuthal2 3 and radial4 5 anisotropy in the upper mantle are attributed to the lattice preferred orientation of olivine caused by the shear strains associated with deformation and provide some of the most direct evidence for deformation and flow within the earth s interior although observations of crustal radial anisotropy would improve our understanding of crustal deformation and flow patterns resulting from tectonic processes large scale observations have been limited to regions of particularly thick crust6 here we show that observations from ambient noise tomography in the western united states reveal strong deep middle to lower crustal radial anisotropy that is confined mainly to the geological provinces that have undergone significant extension during the cenozoic era since 65 myr ago 7 8 the coincidence of crustal radial anisotropy with the extensional provinces of the western united states suggests that the radial anisotropy results from the lattice preferred orientation of anisotropic crustal minerals caused by extensional deformation these observations also provide support for the hypothesis that the deep crust within these regions has undergone widespread and relatively uniform strain in response to crustal thinning and extension9 10 11

seismostratigraphy of the siberian sector of the arctic ocean and adjacent laptev sea shelf a new seismostratigraphic model has been established within the arctic ocean adjacent to the east siberian shelf on the basis of multichannel seismic reflection data acquired along a transect at 81 n ages for the sedimentary units were estimated via links to seismic lines and drill site data of the us chukchi shelf the lomonosov ridge and the adjacent laptev shelf two distinct seismic units were mapped throughout the area and are the constraints for dating the remaining strata the lower marker unit a pronounced high amplitude reflector sequence hars is the most striking stratigraphic feature over large parts of the arctic ocean it indicates a strong and widespread change in deposition conditions probably it developed during oligocene times when a reorientation of arctic plates took place accompanied by the gradual opening of the fram strait and a widespread regression of sea level the top of the hars likely marks the end of oligocene early miocene 23ma an age estimate for the base of the sequence is less clear but likely corresponds to base of eocene 56ma the second marked unit detected on the seismic lines parallels the seafloor with a thickness of about 200ms two way travel time 160 m its base is marked by a change from a partly transparent sequence with weak amplitude reflections below to a set of continuous high amplitude reflectors above this interface likely marks the transition to large scale glaciation of the northern hemisphere and therefore is ascribed to the top miocene 5 3 ma

the earth s coda correlation wavefield rise of the new paradigm and recent advances abstract seismology has come a long way in providing insights into earth s internal structure and dynamics among many forward and inverse geophysical techniques developed full waveform modelling seismic tomography and receiver based studies enabled detailed imaging of earth s subsurface the invention of ambient noise tomography within the last two decades revolutionized studies of earth s subsurface based on the cross correlation of the earth s ambient noise that method in particular enabled imaging of earth structure in places where earthquakes or receivers do not exist at the same time progress in imaging the earth s deepest shells has been impeded by the lack of geometric coverage of body waves due to uneven global distribution of seismic sources and receivers and the fact that the ambient noise studies cannot reach deeper than the uppermost earth s shells near its surface in seeking the ways forward global seismologists started experimenting with cross correlating the part of the seismograms recorded many hours after the first arrivals of body waves the so called earthquake coda as in many science disciplines initial work on this topic resulted in controversies but also led to new realisations and discoveries that all contributed to the rise of a new paradigm the earthquake coda correlation wavefield which is the focus of this review paper we do not attempt here to provide a review of ambient noise correlation although we use some familiar concepts to introduce coda correlation our main goal is to review theoretical and observational work to date that resulted in a better understanding of the coda correlation wavefield both as a phenomenon and a powerful method the features in global correlograms exist due to many cross terms of reverberating body waves a principle fundamentally different from the reconstruction of surface waves in the ambient noise correlograms once the coda correlation wavefield is fully understood through theoretical developments the method becomes a powerful way to study earth s deep structure apart from providing a review of the most important results to date we scrutinise the process of making global correlograms and analyse their characteristics while taking into consideration various aspects such as the time after the earthquake the source receiver geometries the level of seismicity and the type of earthquake mechanism furthermore we provide practical examples on how to build correlograms and interpret correlogram features using programming language python our review seeks to promote the topic of coda correlation among already experienced researchers as well as students who embark on this interesting research which may play a central role in global and planetary seismology in the coming decades

evolution of the correlation wavefield extracted from seismic event coda abstract the seismic correlation wavefield constructed from stacked cross correlograms of event signals displays a wide range of features as a function of inter station distance the character of such correlation arrivals changes markedly with the segment of the wavefield employed all such correlation arrivals arise from the interaction of seismic phases that have a common slowness at the pair of stations being correlated it takes some time before a clear correlation field is established but after 1 h from event initiation a weak version of the regular wavefield emerges accompanied by many phases that have no counterpart in the direct source excitation such arrivals are produced by the interaction of seismic phases with common propagation legs and have time distance behaviour controlled by the differences in accumulated phase the regular phases fade with time and then distinct arrivals in the correlation field arise when there are many ways in which combinations of seismic phases have the same difference in propagation legs there are many more such possibilities for steeply travelling waves in the late coda so that a relatively stable correlation field develops the properties of the correlation field as a function of time can be well described by using a representation in terms of generalized rays supplemented by the contribution from the fundamental mode rayleigh wave

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

seismic stratigraphy and sediment thickness of the nansen basin arctic ocean summary a norwegian expedition to the western nansen basin yermak plateau and the hinlopen margin in 2001 acquired about 1100 km of 2 d multichannel seismic profiles and 50 wideangle sonobuoy record sections analysis of these data establishes a regional seismic stratigraphic framework for the western nansen basin integrating previously published stratigraphic schemes p wave velocities and sediment thickness were derived within 7 8 per cent uncertainty from 2 d seismic ray tracing models of each sonobuoy section sediment thickness reaches 2 km in the studied area and increases towards the depocentre of the giant franzvictoria fan on the barents kara continental margin high relief oceanic crystalline crust with 3 7 km s 1 average near top velocity is infilled by four seismic sediment units with typical velocities 2 4 2 2 2 0 and 1 8 km s 1 a prominent regional seismic horizon between units 2 and 3 is tentatively correlated by basement onlap and sedimentation rates to a miocene 10 ma palaeoceanographic event possibly the opening of the fram strait the youngest unit is correlated to prograding sequences on the margin and to the onset of major slope failure caused by intensified glacio fluvial drainage and ice sheet erosion during northern hemisphere glaciations 2 6 0 01 ma

enhanced preservation of marine derived organic matter in cenomanian black shales from the southern angola basin black shales possessing high concentrations of organic carbon1 were deposited in many parts of the proto south atlantic ocean during the cretaceous period2 the way such sediments accumulated is not fully understood but is likely to have occurred through a combination of low oxygen availability and abundant supply of organic matter thin centimetre thick layers of black shales are commonly interbedded with thicker layers of organic carbon deficient green claystones as found in strata of aptian to coniacian age at deep sea drilling project dsdp site 530 in the southern angola basin3 and elsewhere these differences in carbon content and colour reflect the conditions of deposition and possibly variations in the supply of organic matter4 5 we have compared using organic geochemical methods the compositions of organic matter in three pairs of closely bedded black and green cenomanian claystones obtained from site 530 kerogen analyses and distributions of biological markers show that the organic matter of the black shales is more marine and better preserved than that of the green claystones

correlations between the lomonosov ridge marvin spur and adjacent basins of the arctic ocean based on seismic data abstract seismic profiles across the lomonosov ridge marvin spur and adjacent basins acquired near the north pole by the drifting ice station np 28 provide a reflection image of the upper parts of the ridge that is readily correlatable with those acquired by the alfred wegner institute closer to the siberian margin a prominent flat lying composite reflection package is seen in most parts of the ridge at a few hundred meters below the sea bottom underlying reflections are variable in intensity and also in dip the base of this reflection package is often accompanied by a sharp increase in p velocity and defines a major angular discontinuity referred to here as the lomonosov unconformity the arctic coring expedition acex cored the first c 430 m section on the lomonosov ridge near the north pole in 2004 defining the deeper water character of the neogene and the shallower water paleogene sediments these boreholes penetrated the composite reflection package towards the base of the hole and identified sediments our unit iii of late paleocene and early eocene age campanian beds at the very base of the hole were thought to be representative of the units below the lomonosov unconformity but the p velocity data suggest that this is unlikely correlation of the lithologies along the top of the lomonosov ridge and to the marvin spur indicates that the marvin spur is a sliver of continental crust closely related to and rifted off the ridge this narrow 50 km wide linear basement high can be followed into beneath and across the makarov basin supporting the interpretation that this basin is partly resting on thinned continental crust in the makarov basin the paleogene succession is much thicker than on the ridge thus the condensed shallow water succession with hiati was deposited on the ridge during rapid eocene to miocene subsidence of the basin in the amundsen basin adjacent to the lomonosov ridge the sedimentary successions thicken towards the canadian margin and the reflections on the ridge are not readily identifiable the approximate ages of the sedimentary units are inferred from their relationships to the linear magnetic anomalies in the basin lomonosov acoustic basement dips gently into the basin over a distance of about 100 km and the linear negative anomaly previously thought to be chron 25 is probably related to a rift related mafic intrusive complex

between scylla and charybdis part 2 the sedimentary dynamics of the ancient early pleistocene messina strait central mediterranean based on its modern analogue abstract the 3 km wide messina strait divides sicily from the italian peninsula representing one of the most impressive examples of tide dominated marine passageway of the central mediterranean sea the tidal hydrodynamics governing the strait results from a semi diurnal phase inversion between two interlinked wider basins i e the tyrrhenian sea to the north and the ionian sea to the south due to the presence of a nodal tidal point in the centre of the strait this condition associated with coastal narrowing causes continuous water exchanges and a local phenomenon of tidal amplification producing collinear tidal currents up to 3 m s 1 in velocity in the point of tidal maxima of the strait centre currents follow bi directional patterns across the strait decelerating towards either opposite peripheries because of the progressive enlargement of the cross sectional areas tides exert a relevant influence on the strait bottom shaping characteristic erosional features governing the main sediment transport routes and promoting the migration of distinctive bedforms the textural and dimensional attributes of these bottom features vary according to the current velocity trends and main directions indicating a specific partition of the strait in individual sedimentary zones in the early pleistocene analogous conditions established across the same area and huge quantities of siliciclastic and bioclastic deposits accumulated in the ancient messina strait under a similar tidal hydrodynamics the 250 m thick strait fill succession which is magnificently exposed across the two opposite margins i e scylla and charybdis of the modern passageway represents a crucial correlative element in supporting the reconstruction of the sedimentary dynamics of the past strait based on the observation of the modern system in this work which represents the second part of a first article focused on the modern messina strait previous stratigraphic data are reviewed and integrated with new sedimentological observations carried out in both onshore and offshore key areas in particular outcrop analysis allows distinguishing a number of facies associations which are described and interpreted by taking into account the correspondent modern depositional strait setting the results of this study highlight a mutual correlation between the depositional zones detected in the modern messina strait and the individual facies associations recognised in the onshore margins the strait centre zone represented a bedload parting sector in the ancient system this zone which is one of the most difficult environment to detect in ancient straits due to a condensed sedimentary record is suggested to coincide with a structural palaeo high exposed in the southern sector of the investigated onshore area and continuing offshore in the modern strait this tectonic horst symmetrically separated two opposite highly depositional zones to the north and to the south hosting gravel and sand size siliciclastic and bioclastic deposits exhibiting diffuse motifs of large scale tidal cross stratification and a specific vertical facies stacking these characteristic tidal deposits which are believed to record the migration of several generations of tidal dunes forming extensive bedform fields in the strait reflect a tidal asymmetry between flood and ebb currents tidal asymmetry is referable to the oceanographic setting observable nowadays in the messina strait and deriving from a marked density driven water mass stratification between the two opposite flows in the ancient system tidal dunes transited down current to highly bioturbated fines including sporadic small scale tidal cross strata representing the distal periphery of the early pleistocene strait here bedforms followed migration pathways not always reflecting mutually evasive net gross sediment transport routes due to local conditions of current rotation occurring during each tidal phase inversion during these stages similar to slack water periods currents were weak enough to allow fine sediments to be settled from suspension reproducing a signature typical of other tide dominated coastal systems e g estuaries tidal flats etc these sedimentary zones of the ancient messina strait were laterally bounded by tectonically active margins where fan deltas clastic aprons and carbonate wedges developed under the constant interplay between mass transport processes and tidal currents the resulting architectural and sedimentary features observable in outcrop reveal impressive similarities with the morpho bathymetric features nowadays documented in the correspondent strait margin modern environments these considerations allow deciphering a general palaeo environmental reconstruction of the ancient strait which although suffering of limitations due to a partial preservation of the whole rock record discloses sedimentary processes and depositional environments of the ancient messina strait the process based analysis of this field based case study is crucial in predicting long term environmental changes and facies migration pathways and improves the state of knowledge on tidal straits which are the less understood among the most common tidal depositional systems

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

support for equatorial anisotropy of earth s inner inner core from seismic interferometry at low latitudes abstract anisotropy of earth s inner core provides a key role to understand its evolution and the earth s magnetic field recently using autocorrelations from earthquake s coda we found an equatorial anisotropy of the inner inner core iic in apparent contrast to the polar anisotropy of the outer inner core oic to reduce the influence of the polar anisotropy and reduce possible contaminations from the large fresnel zone of the pkikp 2 and pkiikp 2 phases at low frequencies we processed coda noise of large earthquakes 10 000 40 000 s after magnitude 7 0 from stations at low latitudes within 35 during 1990 2013 using a number of improved procedures of both autocorrelation and cross correlation we extracted 52 array stacked high quality empirical green s functions egfs an increase of over 60 from our previous study the high quality data allow us to measure the relative arrival times by automatic waveform cross correlation the results show large variation 10 9 s in the differential times between the pkikp 2 and pkiikp 2 phases the estimated influence of the fresnel zone is insignificant

response of marine palynomorphs to neogene climate cooling in the iceland sea odp hole 907a abstract the present study on odp leg 151 hole 907a combines a detailed analysis of marine palynomorphs dinoflagellate cysts prasinophytes and acritarchs and a low resolution alkenone based sea surface temperature sst record for the interval between 14 5 and 2 5 ma and allows to investigate the relationship between palynomorph assemblages and the paleoenvironmental evolution of the iceland sea a high marine productivity is indicated in the middle miocene and palynomorphs and ssts both mirror the subsequent long term neogene climate deterioration the diverse middle miocene palynomorph assemblages clearly diminish towards the impoverished assemblages of the late pliocene parallel with a somewhat gradual decrease of ssts being as high as 20 c at 13 5 ma to around 8 c at 3 ma superimposed palynomorph assemblages not only reflect middle to late miocene climate variability partly coinciding with the short lived global miocene isotope events mi events but also the initiation of a proto thermohaline circulation across the middle miocene climate transition which led to increased meridionality in the nordic seas last occurrences of species cluster during three events in the late miocene to early pliocene and are ascribed to the progressive strengthening and freshening of the proto east greenland current towards modern conditions a significant high latitude cooling between 6 5 and 6 ma is depicted by the supraregional decahedrella event coeval with lowest miocene productivity and a sst decline in the early pliocene a transient warming is accompanied by surface water stratification and increased productivity that likely reflects a high latitude response to the global biogenic bloom the succeeding crash in palynomorph accumulation and a subsequent interval virtually barren of marine palynomorphs may be attributed to enhanced bottom water oxygenation and substantial sea ice cover and indicates that conditions seriously affecting marine productivity in the iceland sea were already established well before the marked expansion of the greenland ice sheet at 3 3 ma