the role of midsummer urban aquifer recharge in stormflow generation using isotopic and chemical hydrograph separation techniques summary results dispute the traditional view that groundwater contribution to urban streams during storm events is too small to significantly influence stream flow rates the study used a two component hydrograph separation technique involving oxygen 18 and electrical conductivity to quantify event and pre event components of stream flow associated with a midsummer precipitation event in a highly urbanized formerly glaciated catchment isotopic separation results showed that only about 15 of the rainfall amount contributed to overland flow with groundwater accounting for 22 of the total stormflow elevated electrical conductivity values possibly associated with the flushing of urban contaminants during the storm suggested a slightly higher 30 groundwater contribution to total stormflow it was also demonstrated that nearly 6 of total rainfall contributed to aquifer recharge representing significant summer recharge in the urban catchment the findings are contrary to the prevailing assumption that stormflow in highly urban catchments is largely overland flow

breaking the glass ceiling for high resolution nd isotope records in early cenozoic paleoceanography abstract we report an optimized method for extracting neodymium nd from fossil fish teeth with a single stage column 125 l stem volume ln resin eichrom industries darien illinois for isotopic analysis by multi collector inductively coupled mass spectrometry mc icmps three reference materials basalt bcr 2 bhvo 2 phosphate fossil bone composite and splits of fossil fish teeth samples previously processed with existing two stage column methods were processed using the single stage column method 143 nd 144 nd values of reference materials agree within error with published values and the values for fish teeth correspond with sample splits processed with two stage columns precision to 0 23 e nd was achieved for 30 ng nd samples of reference materials and nd isotope measurements of fossil fish tooth sample replicates as small as 7 ng nd were reproducible within long term instrumental uncertainty we demonstrate the utility of the new method with the first high resolution nd isotope record spanning the 40 0 ma middle eocene climatic optimum which shows an excursion of 0 65 e nd during the peak warming at the study site ocean drilling program leg 119 site 738 30 kyr sample spacing from 40 3 to 39 6 ma ln resin is already used in standard methods for separating nd and nd isotopes are routinely measured by mc icpms with high efficiency inlet systems our innovation is a single small volume ln resin column for nd separation the streamlined approach results in a 10 increase in sample throughput

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

into the ice age there was minimal cooling in the north atlantic ocean during the oligocene inception of the antarctic ice sheet according to a sediment record this finding suggests asynchronous climate changes in the northern and southern hemispheres

global cooling during the eocene oligocene climate transition about 34 million years ago earth s climate shifted from a relatively ice free world to one with glacial conditions on antarctica characterized by substantial ice sheets how earth s temperature changed during this climate transition remains poorly understood and evidence for northern hemisphere polar ice is controversial here we report proxy records of sea surface temperatures from multiple ocean localities and show that the high latitude temperature decrease was substantial and heterogeneous high latitude 45 degrees to 70 degrees in both hemispheres temperatures before the climate transition were 20 c and cooled an average of 5 c our results combined with ocean and ice sheet model simulations and benthic oxygen isotope records indicate that northern hemisphere glaciation was not required to accommodate the magnitude of continental ice growth during this time

joint isotopic mass balance a novel approach to quantifying channel bed to channel margins sediment transfer during storm events the important role of floodplains and the broader riparian zone in providing temporary storage for a large fraction of the annual sediment load of rivers is well established but this understanding is largely based on observations of the long term average behavior of the catchment here we combine measurements of the fallout radionuclides 7be and 210pb and the stable isotopes of hydrogen in water to quantify fine sediment mobilization and storage in a stream and its channel margins during individual intermediate sized storm events with recurrence intervals of a few months or less we demonstrate this method using five storm events in a small 15 km2 undeveloped gravel bedded tributary of the connecticut river usa we estimate that in each storm the mass of sediment deposited onto the margins accounts for almost 90 of the sediment mobilized from the bed with the remainder of the mobilized bed sediment transported downstream as suspended load the result that the bed is a net source of sediment to the stream and the margins a net sink is robust but estimates of the mass of material eroded from the bed and deposited on the margins are less certain the source of sediment to the bed remains unclear as consistent with earlier studies we observe only limited deposition of sediment to the bed during the storm events the suspended sediment is organic rich and thus its source may be associated with in channel organic decay between storm events understanding the coupled interactions between discharge magnitude and frequency and sediment resupply at the event time scale has important implications for stream restoration efforts seeking to connect the channel and the broader riparian zone and for the development of accurate sediment budgets and predictions of sediment flux from a watershed copyright 2015 john wiley sons ltd

improved oxygen isotope temperature calibrations for cosmopolitan benthic foraminifera abstract despite decades of use as a paleoceanographic proxy considerable uncertainty still surrounds the temperature dependence of benthic foraminiferal 18o widely applied paleotemperature equations may mix non equilibrium foraminifera with equilibrium synthetic calcite resulting in temperature sensitivities that are too large warm water foraminiferal calibrations may give temperature sensitivities that are too small for very cold waters here we combine new core top measurements from the florida straits and the arctic ocean with published data to derive new 18o temperature relationships for three groups of benthic foraminifera we derive a quadratic equation for cibicidoides and planulina that agrees well with equilibrium synthetic calcite and that should be applicable over all oceanographic temperatures we find that uvigerina is not at equilibrium and is isotopically heavier than cibicidoides and planulina by 0 47 in contrast to the historically used 0 64 hoeglundina elegans is further enriched and appears to be slightly heavier than equilibrium aragonite finally we discuss the implications of the florida straits observations for the hypothesis that benthic foraminifera precipitate their shells from a ph dependent mixture of bicarbonate and carbonate ions

mixing of event and pre event water in a shallow entisol in sloping farmland based on isotopic and hydrometric measurements sw china

export of nutrient rich northern component water preceded early oligocene antarctic glaciation the onset of the north atlantic deep water formation is thought to have coincided with antarctic ice sheet growth about 34 million years ago ma however this timing is debated in part due to questions over the geochemical signature of the ancient northern component water ncw formed in the deep north atlantic here we present detailed geochemical records from north atlantic sediment cores located close to sites of deep water formation we find that prior to 36 ma the northwestern atlantic was stratified with nutrient rich low salinity bottom waters this restricted basin transitioned into a conduit for ncw that began flowing southwards approximately one million years before the initial antarctic glaciation the probable trigger was tectonic adjustments in subarctic seas that enabled an increased exchange across the greenland scotland ridge the increasing surface salinity and density strengthened the production of ncw the late eocene deep water mass differed in its carbon isotopic signature from modern values as a result of the leakage of fossil carbon from the arctic ocean export of this nutrient laden water provided a transient pulse of co2 to the earth system which perhaps caused short term warming whereas the long term effect of enhanced ncw formation was a greater northward heat transport that cooled antarctica

oligocene paleoceanographic changes based on an interbasinal comparison of cibicidoides spp δ18o records and a new compilation of data abstract oligocene paleoceanographic changes are useful for assessing future changes in the warming world because the levels of atmospheric pco2 in the oligocene were similar to those expected within the next century however the overall oligocene history is still unclear even though our understanding has been improved by previous studies in this paper we review the preexisting hypotheses for the eocene oligocene and oligocene miocene changes as well as the long term global changes based on newly compiled cibicidoides spp 18o 18ocib records we divide the oligocene paleoceanographic changes into five phases an abrupt increase in 18ocib values during the eocene oligocene transition eot phase 1 a gradual decrease in the early oligocene phase 2 a long term slow increase in the early to middle oligocene phase 3 a gradual decrease in the late oligocene phase 4 and an abrupt increase near the oligocene miocene transition omt phase 5 these recurring sequential changes in the global scale 18ocib profile following the eot are likely not directly connected to the strengthening and stratification of ocean currents during the oligocene as a result of the unidirectional strengthening of the antarctic circumpolar current acc and the northern component water ncw instead we suggest that the strengthened ocean currents contributed significantly to interbasinal differences in 18ocib values for a more robust explanation of oligocene long term 18ocib changes following the eot future studies will require high resolution and more reproducible records of changes in the volume of antarctic ice and atmospheric pco2 as well as information about the tectonic history

the assessment of ree patterns and 143nd 144nd ratios in fish remains abstract the ree content and isotopic composition of sr and nd have been determined in fish teeth ranging in age from the trias to the present and from various localities mostly around the atlantic these measurements have been carried out on selachian and teleost remains from the same locality in togo and show no appreciable difference which suggests with the help of a mass balance calculation of the ce anomaly that diagenetic effects are not responsible for the ree enrichment of biogenic phosphates one group of fossil teeth has about 3 times the ree abundances of shale and a shale normalized pattern with a minimum at sm it is thought to reflect deposition in the open sea environment a second group has ree concentration about 10 times higher than the first group with either a regular light ree enrichment or more frequently a maximum in the middle ree both being probably indicative of deposition in estuarine or near shore conditions the shape of the ree spectra and the size of the ce anomaly can be used semi quantitatively to determine the depth of deposition the results presented here on late cretaceous eocene fish teeth samples from morocco reflect an increasing influx of deep waters with a lowla yb ratio and strong negative ce anomaly which agrees well with the evolution of sediment chemistry and microfauna associations in contrast nd is typical of the water mass in which the fish debris decayed examples of nearly isolated basins identified with nd isotopes include the south atlantic prior to the lutetian nd 13 5 the miocene persian gulf nd 3 1 and bolivia during the late cretaceous nd 12 8 togo and guinea bissau results suggest that in the south atlantic the meridional oceanic circulation had not started before 45 ma ago combination of ree and nd data suggests that the assignment of jurassic cretaceous samples measured so far to open sea water masses is still ambiguous

atlantic dominance of the meridional overturning circulation north atlantic na deep water formation and the resulting atlantic meridional overturning cell is generally regarded as the primary feature of the global overturning circulation and is believed to be a result of the geometry of the continents here instead the overturning is viewed as a global energy driven system and the robustness of na dominance is investigated within this framework using an idealized geometry ocean general circulation model coupled to an energy moisture balance model various climatic forcings are tested for their effect on the strength and structure of the overturning circulation without winds or a high vertical diffusivity the ocean does not support deep convection a supply of mechanical energy through winds or mixing purposefully included or due to numerical diffusion starts the deep water formation once deep convection and overturning set in the distribution of convection centers is determined by the relative strength of the thermal and haline buoyancy forcing in the most thermally dominant state i e negligible salinity gradients strong convection is shared among the na north pacific np and southern ocean so while near the haline limit convection is restricted to the na the effect of a more vigorous hydrological cycle is to produce stronger salinity gradients favoring the haline state of na dominance in contrast a higher mean ocean temperature will increase the importance of temperature gradients because the thermal expansion coefficient is higher in a warm ocean leading to the thermally dominated state an increase in so winds or global winds tends to weaken the salinity gradients also pushing the ocean to the thermal state paleoobservations of more distributed sinking in warmer climates in the past suggest that mean ocean temperature and winds play a more important role than the hydrological cycle in the overturning circulation over long time scales

structural analysis of sheath folds with horizontal x axes northeast canada abstract early proterozoic supracrustal rocks occur below a thick nappe of archaean basement gneiss in the melville peninsula where sheath folds are exposed in a wide zone of middle proterozoic dynamothermal metamorphism outcrop patterns of truncated isoclinal sheath folds resemble cylindrical folds except in relatively small areas around the paraboloidal caps bulk extension axes are parallel to strike in the belt as shown by isoclinal sheath folds with horizontal central axes x axes as well as similarly aligned mullion structure and rotated scapolite prisms extension axes converge from northeast to southwest in the apparent flow direction

identifying the water source for subsurface flow with deuterium and oxygen 18 isotopes of soil water collected from tension lysimeters and cores the conventional identification of soil water with pre event water limits deep insights into the involvement of stationary and mobile soil water in subsurface hydrological processes in three tilled sloping field plots at a hilly area of southwestern china dominated by entisols soil water collected with a suction lysimeter was distinguished from the total soil water through an analysis of the stable isotopes deuterium and oxygen 18 differences in the depth profile of soil water before and after storm events were observed and used to examine how rainwater mixes with soil water and to identify the source contribution of different fractions of soil water in subsurface flow generation only water in the 0 10 cm soil layer was significantly affected by evaporation and infiltration water in the top 5 cm layer of the soil exhibited the lowest residence time because a storm can replace a substantial proportion of the pre event water soil water at the 10 20 cm depth showed the longest residence time as indicated by its high proportion of pre event water the isotopic signatures demonstrated that piston flow and preferential flow coexisted in this soil high antecedent soil water content and high rain intensity favor the formation of piston flow the water collected with the suction lysimeter represented the mobile fraction of the pre event water in the soil which effectively participates in the generation of subsurface flow newly infiltrated rainwater did not well mix with stationary pre event water in the soil the use of recent rainfall to represent mobile soil water may provide a practical solution for overcoming the negative effect of the spatial heterogeneity of the isotopic composition of soil water on hydrograph separation results bulk soil water and lysimeter water showed significant differences in isotopic composition under low soil water content or in the top soil layer stable isotopes in bulk and lysimeter soil water should be monitored synchronously to reveal the sources and pathways of soil water and their contributions to the generation of subsurface flow in the vadose zone c 2013 elsevier b v all rights reserved

neodymium isotopic reconstruction of late paleocene early eocene thermohaline circulation abstract high resolution fish tooth nd isotopic records for eight deep sea drilling project and ocean drilling program sites were used to reconstruct the nature of late paleocene early eocene deep water circulation the goal of this reconstruction was to test the hypothesis that a change in thermohaline circulation patterns caused the abrupt 4 5 c warming of deep and bottom waters at the paleocene eocene boundary the paleocene eocene thermal maximum petm event the combined set of records indicates a deep water mass common to the north and south atlantic southern and indian oceans characterized by mean nd values of 8 7 and different water masses found in the central pacific ocean nd 4 3 and caribbean sea nd 1 2 the geographic pattern of nd isotopic values before and during the petm suggests a southern ocean deep water formation site for deep and bottom waters in the atlantic and indian ocean basins the nd data do not contain evidence for a change in the composition of deep waters prior to the onset of the petm this finding is consistent with the pattern of warming established by recently published stable isotope records suggesting that deep and bottom water warming during the petm was gradual and the consequence of surface water warming in regions of downwelling

linking deformation migmatite formation and zircon u pb geochronology in polymetamorphic orthogneisses sveconorwegian province sweden absolute ages of migmatization in the polymetamorphic parautochthonous basement of the sveconorwegian province sweden have been determined using u pb ion probe analysis of zircon domains that formed in leucosome of migmatitic orthogneisses migmatite zircon was formed by recrystallization whereas dissolution reprecipitation and neocrystallization were subordinate the recrystallized migmatite zircon was identified by comparison of zircon in mesosomes and leucosomes it is backscatter electron bright u rich 800 4400 ppm with low th u ratios generally 0 01 0 1 unzoned or oscillatory ghost zoned and occurs as up to 100 m thick rims with transitional contacts to cores of protolith zircon protolith ages of 1686 12 and 1668 11 ma were obtained from moderately resorbed igneous zircon crystals generally th u 0 5 1 5 u 300 ppm in mesosomes protolith zircon is also present as resorbed cores in the leucosomes linkage of folding synchronous migmatization and formation of recrystallized zircon rims allowed direct dating of south vergent folding at 976 7 ma at a second locality similar recrystallized zircon rims in leucosome date pre sveconorwegian migmatization at 1425 7 ma an upper age bracket of 1394 12 ma for two overprinting phases of deformation upright folding along gently ssw plunging axes and stretching in ese was set by zircon in a folded metagranitic dyke lower age brackets for these events were set at 952 7 and 946 8 ma by zircon in two crosscutting and undeformed granite pegmatite dykes together with previously published data the present results demonstrate i tectonometamorphic reworking during the hallandian orogenesis at 1 44 1 42 ga resulting in migmatization and formation of a coarse gneissic layering ii sveconorwegian continent continent collision at 0 98 0 96 ga involving a emplacement of an eclogite unit b regional high pressure granulite facies metamorphism c southvergent folding subhorizontal east west stretching and migmatization all of which caused overprint or transposition of older mesoproterozoic and sveconorwegian structures the sveconorwegian migmatization and folding took place during or shortly after the emplacement of sveconorwegian eclogite and is interpreted as a result of north south shortening synchronous with east west extension and unroofing during late stages of the continent continent collision

comparison of atlantic and pacific paleochemical records for the last 215 000 years changes in deep ocean circulation and chemical inventories abstract detailed cd ca and 13 c data have been obtained for benthic foraminifera from western north atlantic and equatorial pacific sediment cores in the modern ocean both tracers are closely linked to nutrient distributions the sedimentary records for both tracers indicate that bottom waters overlying the atlantic site have been nutrient depleted relative to those at the pacific site over the last 215 000 years from this evidence it is reasonable to infer that there has been a continuous net flux of nutrient depleted water from the western north atlantic into the pacific this exchange has undergone significant fluctuations with the export of nutrient depleted atlantic water diminishing by about a factor of two relative to the inflow from southern ocean sources over the last 215 000 years carbon isotope fluctuations in both regions are dominated by variable storage of isotopically light carbon on continents with a lesser contribution from these deep ocean circulation changes the cadmium signal in the north atlantic is dominated by changes in deep ocean circulation patterns cadmium shows less variability in the pacific which may reflect changes in the global average cadmium content or minor changes in deep pacific circulation patterns using these records to estimate global averages it appears that glacial ocean water had 22 more cd and 0 46 less 13 c than the modern ocean these numbers are estimates which may be revised as more data become available although they are not likely to be as much as 20 in error for cd or 0 2 for 13 c relative north atlantic deep water nadw formation rates are modulated with a significant 41 kyr periodicity linked to obliquity induced variations in high latitude insolation nadw lags 8 2 kyr behind insolation however

erosion and physical transport via overland flow of arsenic and lead bound to silt sized particles understanding of the transport mechanisms of contaminated soils and sediment is essential for the sustainable management of contaminated lands in new england and elsewhere vast areas of agricultural lands are contaminated by the historical application of lead arsenate pesticides left undisturbed the physical and chemical mobility of as and pb in these soils is limited due to their strong affinity for adsorption onto solid phases however soil disturbance promotes erosion and overland flow during intense rainstorms here we investigate the event scale transport of disturbed as and pb contaminated soils through measurement of concentrations of as and pb in suspended sediment and changes in pb isotopic ratios in overland flow investigation of several rain events shows that where land disturbance has occurred physical transport of silt sized particles and aggregates is the primary transport vector of as and pb derived from pesticide contaminated soil although both as and pb are associated with similarly sized particles we find that solid phase as is more effectively mobilized and transported than pb our results demonstrate that anthropogenic land disturbance of historical lands contaminated with lead arsenate pesticides may redistribute through physical transport significant amounts of as and lesser amounts of pb to riparian and stream sediments where they are potentially more bioavailable

middle eocene large coccolithaceans biostratigraphic implications and paleoclimatic clues abstract a combined light microscope scanning electron microscope study of exceptionally well preserved calcareous nannofossil assemblages from clay rich middle eocene sediments recovered at iodp site u1410 nw atlantic ocean has enabled us to document a new evolutionary lineage within coccolithus like placoliths that have well developed near axial or diagonal cross bars in their central area based on our observations we describe a new genus pletolithus a new species pletolithus giganteus and four new combinations pletolithus opdykei pletolithus staurion pletolithus mutatus and pletolithus gigas the distinctive ultra structures of the different morphotypes and the presence of transitional morphologies suggest that pletolithus evolved from a morphological variant of coccolithus the evolution of this group of coccolithaceans is initially characterized by increasing size and the appearance of delicate axial cross bars in the central area size continues to increase in these coccoliths and the orientation of the cross bars shifts to asymmetric and diagonal in later representatives morphometric measurements on p gigas and the morphologically similar p giganteus provide evidence for the presence of two distinct populations allowing for an objective differentiation of these two species which in turn provides unambiguous taxonomic definition for the important biostratigraphic marker species p gigas these data improve the reliability of middle eocene biostratigraphy and show that this lineage appeared when a new equilibrium in the environmental conditions was reached and intriguingly it coincides with a remarkable change in the deep circulation of the north atlantic ocean

the use of stream flow routing for direct channel precipitation with isotopically based hydrograph separations the role of new water in stormflow generation abstract understanding the pathways by which event water contributes to stream stormflow provides insight into stormflow generation mechanisms we analyze the impact of storm size on the relative contribution of event water to stormflow by using natural variations in the oxygen isotopic composition of precipitation and stream water to separate multiple stormflow hydrographs from a single fourth order 1212 ha catchment we extend previous isotope based hydrograph separations by independently accounting for the contribution of event water via direct channel precipitation to the stream hydrograph the direct channel precipitation contribution is determined using a numerical model of stream flow routing though the catchment taking precipitation and digital elevation data as input variables for the range of storm sizes sampled having recurrence intervals ranging from less than a week to 4 months essentially all the event water in stream stormflow can be attributed to direct channel precipitation event water not directly falling on the stream channel indirectly contributes to stormflow by increasing the subsurface discharge of pre event water to the stream neither the hydrograph separation data field observations during the precipitation events nor experimental observations of flow in a large scale natural soil column extracted from the watershed are consistent with macropore flow or groundwater ridging as the primary mechanism responsible for increasing subsurface discharge results from a series of artificial rain experiments using the unsaturated natural soil column are consistent with a preferential kinematic flow model and indicate that the discharge of pre event water to the stream during a storm event may be controlled by kinematic flow processes within the watershed soils

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

topographic controls on shallow groundwater dynamics implications of hydrologic connectivity between hillslopes and riparian zones in a till mantled catchment hydrologic connectivity is regarded as one of the key controls in determining catchment rainfall run off response and has been linked to the export of solutes from uplands to streams we sought to identify the patterns of hydrologic connectivity within a small forested watershed by monitoring the shallow groundwater fluctuations of simple topographically defined landform sequences footslope backslope shoulder a spatially distributed instrument network was employed to continuously measure hydrometric responses of the shallow subsurface during seasonal wet up from summer through winter in a small till mantled research catchment we demonstrate that the spatial patterns of shallow water table extent and duration and therefore hydrologic connectivity had a strong seasonal signature during the low antecedent soil moisture conditions typically associated with the growing season water tables were patchy discontinuous and only the wettest near stream footslope areas were consistently hydrologically connected with the stream network during the dormant season footslopes and backslopes maintained water tables that persisted between storm events and were almost continuously connected with the stream network in the largest storm events the typically driest landforms shoulder slopes established shallow transient water tables suggesting that nearly the entire catchment was temporarily hydrologically connected with the stream network in addition we found significant differences p 0 05 in the magnitude and duration of groundwater responses to rainfall among landform groups both seasonally and during events these results have implications for using a similarity approach in representing characteristic hydrologic responses of topographically defined watershed elements determining hydrologic connectivity between watershed elements as well as for understanding solute transport in catchments copyright 2010 john wiley sons ltd

coeval folding and boudinage in four dimensions scaled analogue experiments have been carried out incrementally to demonstrate the growth of constrictional folds and boudins through space and time pure constriction acted on a single stiff layer that was embedded in a weak matrix with the layer trending parallel to the x axis of the constrictional strain ellipsoid the viscosity ratio between non linear viscous layer and matrix was set at ca 13 three dimensional images of the incrementally deformed layer have been obtained using computer tomography they yielded clear evidence that d1 folds and d1 boudins show striking interactions when growing simultaneously at low to moderate finite strain the axes of d1 folds are subparallel and the axes of d1 boudins are subperpendicular to the x axis of the constrictional strain ellipsoid the normalized wavelengths of d1 folds and d1 boudins and the amplitudes of d1 folds are fixed already at low finite strain 5 and do not significantly change as deformation proceeds the normalized wavelength of both structures is not so in line as suggested by theoretical studies at higher degrees of finite strain d1 boudins are affected by d2 folds and rotated limbs of the latter show d2 boudinage resulting in complex deformation patterns that are difficult to identify in the field the model results are important for the analysis and interpretation of deformation structures in rheologically stratified rocks undergoing dislocation creep under bulk constriction tectonic settings where constrictional folds and boudins may develop simultaneously are stems of salt diapirs subduction zones or thermal plumes

secular variation in the isotopic composition of nd in tethys seawater abstract this preliminary nd isotopic study of authigenic glauconites that are mineralogically chemically isotopically rb sr k ar and stratigraphically well characterized suggests that these minerals can be used to determine the nd isotopic evolution of ancient ocean water generally glauconites indicate the same evolutionary history of nd in tethys seawater as published data for marine phosphates e g fish remains mn ores and fossil debris the initial nd values define a smooth curve with lowest values of 9 to 10 for the cretaceous and lower tertiary highest nd values have been found for 150 200 ma tethys seawater that was influenced by both a nonradiogenic continental component and a greater input of young mantle derived material

cooling and ice growth across the eocene oligocene transition the eocene oligocene e o climate transition ca 34 ma marks a period of antarctic ice growth and a major step from early cenozoic greenhouse conditions toward today s glaciated climate state the transition is represented by an increase in deep sea benthic foraminiferal oxygen isotope 18o values occurring in two main steps that reflect the temperature and 18o of seawater existing benthic mg ca paleotemperature records do not display a cooling across the transition possibly reflecting a saturation state effect on benthic foraminiferal mg ca ratios at deep water sites here we present data from exceptionally well preserved foraminifera deposited well above the calcite compensation depth that provide the first proxy evidence for an 2 5 c ocean cooling associated with the ice growth this permits interpretation of e o 18o records without invoking northern hemisphere continental scale ice

the distribution of neodymium isotopes in arctic ocean basins nd concentration and isotope data have been obtained for the canada amundsen and makarov basins of the arctic ocean a pattern of high nd concentrations up to 58 pm at shallow depths is seen throughout the arctic and is distinct from that generally seen in other oceans where surface waters are relatively depleted a range of isotopic variations across the arctic and within individual depth profiles reflects the different sources of waters the dominant source of water and so nd is the atlantic ocean with lesser contributions from the pacific and arctic rivers radiogenic isotope nd signatures up to epsilon nd 6 5 can be traced in pacific water flowing into the canada basin waters from rivers draining older terrains provide very unradiogenic nd down to epsilon nd 14 2 that can be traced in surface waters across much of the eurasian basin a distinct feature of the arctic is the general influence of the shelves on the nd concentrations of waters flowing into the basins either from the pacific across the chukchi sea or from across the extensive siberian shelves water shelf interaction results in an increase in nd concentration without significant changes in salinity in essentially all waters in the arctic through processes that are not yet well understood in estuarine regions other processes modify the nd signal of freshwater components supplied into the arctic basin and possibly also contribute to sedimentary nd that may be subsequently involved in sediment water interactions mixing relationships indicate that in estuaries nd is removed from major river waters to different degrees deep waters in the arctic are higher in nd than the inflowing atlantic waters apparently through enrichments of waters on the shelves that are involved in ventilating the deep basins these enrichments generally have not resulted in major shifts in the isotopic compositions of the deep waters in the makarov basin epsilon nd similar to 10 5 but have created distinctive nd isotope signatures that were found near the margin of the canada basin with epsilon nd similar to 9 0 the deep waters of the amundsen basin are also distinct from the atlantic waters with epsilon nd 12 3 indicating that there has been limited inflow from the adjacent makarov basin through the lomonosov ridge c 2009 elsevier ltd all rights reserved

interfering folds in constrictional deformation abstract experiments on buckle folding indicate that in pure constriction 2 3 2 3 there is an association of domes and basins with nonplane noncylindrical folds the areas of domes and basins are reduced with increasing deformation there is a dominant fold trend perpendicular to 3 with a less dominant trend perpendicular to 3 folds at an angle to these two sets may also occur the divergent folds link up in smooth arcs or join up at a dome or a basin over a relatively large domain the interference pattern produced by general constriction can be recognized by the association of domes and basins with nonplane noncylindrical folds by occurrence of hair pin bends of hinge lines of open folds by occurrence of amoeboid outcrop patterns and by absence of a consistent overprinting relation among different sets of folds layers subparallel to the 3 axis of general constriction may give rise to two or more sets of coaxial cylindrical folds with orthogonal axial surfaces

cenozoic north atlantic deep circulation history recorded in contourite drifts offshore newfoundland canada abstract in the north atlantic ocean contour following deep currents have created regional erosional unconformities and deposited contourite drifts that exceed 2 km in thickness and extend for 100 s of km the stratigraphic records in the drifts have been used to reconstruct variations in north atlantic deep water circulation throughout the cenozoic however uncertainties remain about certain aspects of the timing intensity depth distribution and regional impact of these currents here we use an integrated dataset of seismic reflection profiles and iodp core data lithology biostratigraphy and magnetostratigraphy to document sedimentation history and the development of current effects in the cretaceous to present sedimentary record on the j anomaly ridge and southeast newfoundland ridge offshore newfoundland canada the newfoundland ridges are in a key location lying between well studied areas in the northern and western north atlantic and under the path of both the modern deep western boundary current and the gulf stream late cretaceous through early eocene sedimentation on the ridges was dominated by biogenic pelagic sedimentation but at 47 ma near the early middle eocene boundary well developed contourite drifts began to accrete in paleo water depths of 4000 4500 m accompanied by an order of magnitude increase in terrigenous sediment mass accumulation rates from this time forward drift deposition interrupted by brief episodes of erosion continued unabated this timing for the onset of persistent deep currents is coincident with reorganization of atlantic circulation inferred from a change from biosiliceous to non biosiliceous sedimentation in the western north atlantic horizon a c and with the current eroded intra eocene unconformity ieu in the northern north atlantic a change in sedimentation style occurred within the middle eocene to upper oligocene drift sequence and it likely was related to a shift to deeper more intense currents that eroded the widespread horizon a u along the margin of eastern north america about early oligocene time beginning in the late oligocene 25 ma a thick drift exhibiting seismically laminated mudwaves was deposited in a distinct belt at 3500 4500 m paleodepth on the southeast newfoundland ridge this development correlates with widespread late oligocene through miocene pliocene drift accumulation throughout the north atlantic the most recent phase of drift deposition since late pliocene time 3 ma occurred after a shift to the modern circulation system of deeper swifter currents and it includes mixed pelagic hemipelagic sediments and ice rafted debris that reflect glacial interglacial influences on sedimentation

kinematic and temporal relationships between parallel fold hinge lines and stretching lineations a microstructural and crystallographic preferred orientation approach folds with hinge lines subparallel to stretching lineation are common features in shear zones and represent extreme cases of fold modification however their microstructures and in particular their kinematic significance remain poorly understood here we describe the meso and micro scale structures and crystallographic preferred orientation cpo of quartz and muscovite from a metric scale shear modified fold from plattjen saas fee western internal alps the studied fold is of class 2 and the samples collected around the fold have essentially the same microstructures quartz c axes plotted in the tectonic coordinate system exhibit an apparent reverse obliquity on opposing limbs muscovite fabrics are controlled essentially by the orientation of 001 planes if the cpo data are plotted in a common reference frame e g either fold or geographical all samples exhibit essentially the same patterns for both minerals in particular relative to the fold axis and axial surface the reversal of quartz cpo obliquity on opposing limbs is no longer evident the small obliquity 15 between the intersection lineation of the two planes of 001 of muscovite and the fold axis results in the apparent reversal of shear sense on opposite limbs when viewing the cpo related to the macroscopic fabric the homogeneity of the microstructures and cpos of quartz and muscovite across the fold support the interpretation that the fold developed during simultaneous activation of heterogeneous and homogeneous simple shear with the former responsible for fold development and the latter responsible for fold rotation and the overwhelming of the heterogeneous deformation these processes led to the observed parallelism between fold hinge line and local stretching lineation

early oligocene initiation of north atlantic deep water formation dating the onset of deep water flow between the arctic and north atlantic oceans is critical for modelling climate change in the northern hemisphere1 2 and for explaining changes in global ocean circulation throughout the cenozoic era3 from about 65 million years ago to the present in the early cenozoic era exchange between these two ocean basins was inhibited by the greenland scotland ridge3 4 but a gateway through the faeroe shetland basin has been hypothesized3 5 previous estimates of the date marking the onset of deep water circulation through this basin on the basis of circumstantial evidence from neighbouring basins have been contradictory5 6 7 8 9 ranging from about 35 to 15 million years ago here we describe the newly discovered southeast faeroes drift which extends for 120 km parallel to the basin axis the onset of deposition in this drift has been dated to the early oligocene epoch 35 million years ago from a petroleum exploration borehole we show that the drift was deposited under a southerly flow regime and conclude that the initiation of deep water circulation from the norwegian sea into the north atlantic ocean took place much earlier than is currently assumed in most numerical models of ancient ocean circulation

sheath fold formation around slip surfaces terra nova 24 417 421 2012 abstract sheath folds are associated with shear zones and have been used as high strain indicators we present results from a three dimensional analytical study showing that the flow perturbation around a planar weakness acting as a slip surface in simple shear leads to the formation of sheath folds at low shear strain closed traces of marker layers are exhibited in cross sections cut perpendicular to the shear direction in the vicinity of the slip surface tip in cross sections cut parallel to the shear direction and normal to the shear plane flanking folds are observed our model captures the first order observations of natural sheath folds such as diversity of shapes and multiple eye structures natural equivalents of the planar weaknesses that we model include fractures veins and rheologically weak layers flow perturbation around these zones of weaknesses is proposed as an alternative mechanism of sheath fold formation which emphasizes the coeval operation of brittle and ductile processes in shear zones

high temperature deformation in the basal shear zone of an eclogite bearing fold nappe sveconorwegian orogen sweden ductile shear zones associated with emplacement of high pressure nappes are key features to resolve exhumation mechanisms the eastern segment of the sveconorwegian orogen hosts an eclogite bearing fold nappe whose basal shear zone shows structures associated with emplacement of the eclogite bearing nappe and decompression under high to intermediate pressure granulite and upper amphibolite fades conditions based on detailed structural mapping of a 4 km well exposed section of the basal shear zone we describe two major phases of deformation an early deformation stage d1 formed a penetrative gneissic foliation and tectonic layering including isoclinal folds f1 the sequence was subsequently affected by up to km scale tight south vergent folds f2 with sheared out limbs at the outcrop scale asymmetric f2 folds are commonly s vergent but symmetric folds with different degrees of tightness are also present melt was present at all stages of deformation and the structural relations demonstrate mutual feedback between melt localization and fold formation f2 folds have shallowly e plunging fold axis parallel to a stretching lineation defined by high grade mineral aggregates both constitute prominent structures of the basal shear zone f2 folds are associated with an axial planar fabric s2 defined by upper amphibolite and locally granulite facies mineral assemblages d2 shear structures are associated with top to the east kinematic indicators throughout the section the d1 episode was responsible for emplacement of the eclogite nappe into its present structural position the subsequently developed lineation parallel folds are interpreted to form by general shear where the structures reflect the regional e directed flow of the entire eclogite nappe c 2015 elsevier b v all rights reserved less

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

post eocene intensification of deep water circulation in the central south pacific micropalaeontological clues from dredged sites along the eastern manihiki plateau margin reconstruction of early cenozoic deep water circulation is one of the keys to modelling earth s greenhouse to icehouse surface evolution but it has long been hampered by the paucity of information from the central south pacific to help overcome this knowledge gap we present new micropalaeontological data from dredged carbonates r v sonne expedition so193 at several eastern volcanic salients of the manihiki plateau interestingly despite appreciable longitudinal separations among the dredged sites ages indicated by the foraminiferal assemblages are consistently around the middle eocene including mixed turonian late cretaceous eocene at a single site suggesting widespread post eocene cessation of the pelagic sedimentation by integrating with independent seismic and chronostratigraphic data deep sea drilling project leg 33 for large scale erosion of top eocene oligocene sedimentary units on the eastern manihiki plateau our results can be viewed as novel physical evidence for the intensification of central south pacific deep water circulation since the eocene oligocene climatic transition

acquisition of the neodymium isotopic composition of the north atlantic deep water the north atlantic deep water nadw neodymium isotopic composition nd ic is increasingly used in oceanography and paleoceanography to trace large scale circulation and weathering processes notably to investigate past variations of the global thermohaline circulation although the present day nadw nd ic is well characterized at nd 13 5 the acquisition of this isotopic signature in other words the causes of this value has so far been very sparsely documented such an understanding is however fundamental to the interpretation of paleo records nd ic and rare earth element concentrations were measured at 9 stations within the north atlantic subpolar gyre signature cruise summer 1999 the comparison of this data set with our understanding of water mass circulation provides a description of how the three layers constituting the nadw the labrador sea water lsw nd 13 9 0 4 north east atlantic deep water neadw nd 13 2 0 4 and north west atlantic bottom water nwabw nd 14 5 0 4 acquire their nd ic through distinct water mass mixings and lithogenic inputs these different mechanisms acting upon water masses from very diverse sources seem to bring the nd ic of the three nadw layers to values close together and similar to that of the nadw it is suggested that sediment seawater interactions significantly lower the neadw and nwabw nd ic along the south east greenland margin since these interactions do not significantly modify the nd content of these water masses sediment remobilizations leading to the nd ic variations are probably associated with nd removal fluxes from the water mass toward the sediment a process called boundary exchange on the other hand lsw seems to acquire its nd ic from the subpolar mode waters from which it is formed by deep convection and no other mechanism needs to be invoked its unradiogenic signature could ultimately be linked to fresh water runoff from the canadian shield these conclusions should allow more precise interpretations of paleoceanographic nd ic records taking into account the distinct histories of the three nadw layers including distinct water mass mixings and distinct lithogenic inputs

closure of the central american isthmus and its effect on deep water formation in the north atlantic modern ocean thermohaline driven circulation influences global climate by transporting heat to high latitudes1 2 and by affecting the exchange of co2 between ocean and atmosphere3 north atlantic deep water nadw plays a key role in this circulation and quaternary climate cycles have been linked to changes in nadw flow4 general circulation model simulations indicate that before closure some 3 4 million years ago of the central american isthmus the narrow strip of land linking north and south america the direct flow of low salinity water from the pacific to the atlantic ocean would have led to a smaller nadw flow5 6 sedimentation patterns7 and nutrient proxies8 11 support these model results by indicating an increase in nadw flow around the time of isthmus closure but these records do not allow changes in different nadw sources to be distinguished and the overall effect of closure on global ocean circulation is poorly known here we present nd pb and sr isotope records preserved by a hydrogenous ferromanganese crust from the nadw flow path in the western north atlantic ocean these records indicate that the isotopic signal associated with nadw strengthened around 3 4 million years ago showing that deep water that formed in the labrador sea made a gradually increasing contribution to nadw flow these data taken together with those from the central pacific ocean12 indicate an increased nadw flow since isthmus closure and suggest that the closure established today s general pattern of ocean circulation

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

evolution of atlantic thermohaline circulation early oligocene onset of deep water production in the north atlantic the flow of deep water masses is a key component of heat transport in the modern climate system yet the role of deep ocean heat transport during periods of extreme warmth is poorly understood the present mode of meridional overturning circulation is characterized by deep water formation in both the north atlantic and the southern ocean however a different mode of meridional overturning circulation operated during the extreme greenhouse warmth of the early cenozoic during which time the southern ocean was the dominant region of deep water formation the combination of general global cooling and tectonic evolution of the atlantic basins over the past 55 m y ultimately led to the development of a mode of overturning circulation characterized by both southern ocean and north atlantic deep water sources the change in deep water circulation mode may in turn have affected global climate however unraveling the causes and consequences of this transition requires a better understanding of the timing of the transition new nd isotope data from the southeastern atlantic ocean indicate that the initial transition to a bipolar mode of deep water circulation occurred in the early oligocene ca 33 ma the likely cause of significant deep water production in the north atlantic was tectonic deepening of the sill separating the greenland norwegian sea from the north atlantic

kilometre scale sheath fold at mattmark and implications for transport direction in the alps folds were the first tectonic features of rocks to be studied and as such are taken as a reference for the interpretation of other structures intuitively fold axes were assumed to be subperpendicular to the direction of transport nevertheless many studies of metamorphic belts showing intense ductile deformation describe folds with axes close to the transport direction in particular sheath folds1 9 are highly curvilinear folds elongated parallel to the direction of transport we discuss here a spectacular large sheath fold situated in a crustal shear zone in the monte rosa nappe swiss alps our analysis implies that both the geometry and significance of folds in the internal alps must be re examined we further demonstrate the existence of crustal ductile shear zones in an area of the alps where previously emphasis was generally placed on fold nappes the movements on these shear zones is often tens of kilometres

neodymium isotopic composition and concentration in the western north atlantic ocean results from the geotraces ga02 section the neodymium nd isotopic composition of seawater is commonly used as a proxy to study past changes in the thermohaline circulation the modern database for such reconstructions is however poor and the understanding of the underlying processes is incomplete here we present new observational data for nd isotopes and concentrations from twelve seawater depth profiles which follow the flow path of north atlantic deep water nadw from its formation region in the north atlantic to the northern equatorial atlantic samples were collected during two cruises constituting the northern part of the dutch geotraces transect ga02 in 2010 the results show that the different water masses in the subpolar north atlantic ocean which ultimately constitute nadw have the following nd isotope characteristics upper labrador sea water ulsw end 14 2 0 3 labrador sea water lsw end 13 7 0 9 northeast atlantic deep water neadw end 12 5 0 6 northwest atlantic bottom water nwabw end 11 8 1 4 in the subtropics where these source water masses have mixed to form nadw which is exported to the global ocean upper nadw is characterised by end values of 13 2 1 0 2sd and lower nadw exhibits values of end 12 4 0 4 2sd while both signatures overlap within error the signature for lower nadw is significantly more radiogenic than the traditionally used value for nadw end 13 5 due to the dominance of source waters from the nordic seas nwabw and neadw comparison between the concentration profiles and the corresponding nd isotope profiles with other water mass properties such as salinity silicate concentrations neutral densities and chlorofluorocarbon cfc concentration provides novel insights into the geochemical cycle of nd and reveals that different processes are necessary to account for the observed nd characteristics in the subpolar and subtropical gyres and throughout the vertical water column while our data set provides additional insights into the contribution of boundary exchange in areas of sediment resuspension the results for open ocean seawater demonstrate at an unprecedented level the suitability of nd isotopes to trace modern water masses in the strongly advecting western atlantic ocean

paleocean circulation during the last deglaciation a bipolar seesaw hughen et al 1998 have documented that during the first 200 years of younger dryas time the 14c content of atmospheric co2 increased by 50 and that during the remainder of this 1200 year duration cold event it steadily declined the initial increase in 14c c was likely the result of a reduction in the atlantic s conveyor circulation however were the subsequent radiocarbon decline due to the rejuvenation of this potent heat pump then it is difficult to understand why the climate conditions in the northern atlantic basin remained cold throughout the younger dryas modeling exercises by stocker and wright 1996 mikolajewicz 1998 and schiller et al 1998 show that if the conveyor is terminated the transfer of radiocarbon into the deep sea shifts to the southern ocean thereby stabilizing the atmospheric 14c c ratio paleoclimatic evidence from the antarctic continent suggests that this model based scenario might have been played out in the real world while the younger dryas cooling has been documented in many places around the world including new zealand denton and hendy 1994 sowers and bender 1995 using their 18o in o2 based correlation between the ice core 18o in ice records for antarctica and greenland have demonstrated that in antarctica the younger dryas was a time of maximum warming the point of this paper is that the steep rise in 18o rise in antarctic ice which commenced close to the onset of the younger dryas might have been caused by heat released to the atmosphere in response to an increase in deep sea ventilation in the southern ocean

kinematic models for soil moisture and solute transport the kinematic theory of soil moisture and solute transport in the vertical direction for unsaturated groundwater recharge is considered the general theory of kinematic models is reviewed and applied for an isolated wetting event wherein the soil starts at and eventually drains to field capacity analytical expressions are developed for the water content and moisture flux as a function of depth and time the approach is extended for an arbitrary sequence of surface flux or water content boundary conditions the transport of a solute with a general nonlinear sorption isotherm is also considered it is shown that for the general isotherm the vertical displacement of a solute isochore during an arbitrary wetting sequence depends only on the total depth of water infiltrated and not on how the infiltration rate varies with time

recumbent folds key structural elements in orogenic belts abstract this review has two main parts the first of them presents existing ideas and data related to recumbent folds reviewing aspects such as the physical conditions of the development of these folds the strain inside the folded layers the kinematic mechanisms of their formation the role of gravitational forces the tectonic context of their development and the structures associated with them in the second part the above ideas are discussed and possible mechanisms for the development of these folds are presented it is proposed that initial perturbations of the layers are essential to give rise to the asymmetry of recumbent folds these perturbations may be non planarities of the layering or may be linked to the existence of a core or basement of competent rock that hinders the normal propagation of the deformation this could explain why many large recumbent folds have a root zone deformation with an important component of simple shear is a general condition for the formation of recumbent folds in areas with very low grade metamorphism competent layers often play an active role during the deformation and undergo buckling with the development of an overturned fold limb which can be stretched and thinned to finally produce a pair of recumbent folds separated by a thrust in areas with low or medium metamorphism buckling under a simple shear regime is probably the most important mechanism for producing large folds with gentle or moderately dipping axial surfaces subsequent kinematic amplification by coaxial strain components with vertical maximum shortening is important for the formation of recumbent folds these components involve a sub horizontal stretching that can cause a problem of strain compatibility and give rise to a basal thrust in areas deformed under high p and t conditions recumbent folds can develop by flow perturbations and kinematic amplification of folds this is probably a common mechanism in ductile shear zones

hydrologic pathways and stormflow hydrochemistry at south creek northeast queensland abstract earlier investigations at south creek in northeastern queensland established the importance of overland flow as a hydrologic pathway in this tropical rainforest environment since this pathway is fast transmitting presumably new water its importance should be reflected in the stormflow chemistry of south creek the greater the volumentric contribution to the stormflow hydrograph the more similarity between the chemical composition of streamwater and of overland flow is to be expected water samples were taken during two storm events in an ephemeral gully gully a an intermittent gully gully b and at the south creek catchment outlet additional spot checks were made in several poorly defined rills the chemical composition of old water was determined from 45 baseflow samples collected throughout february the two events differed considerably in their magnitudes intensities and antecedent moisture conditions in both events the stormflow chemistry in south creek was characterized by a sharp decrease in ca mg na si cl ec anc alkalinity and total inorganic carbon ph remained nearly constant with discharge whereas k increased sharply as did sulfate in an ill defined manner in event 1 this south creek stormflow pattern was closely matched by the pattern in gully a implying a dominant contribution of new water this match was confirmed by the spot samples from rills gully b behaved like south creek itself but with a dampened new water signal indicating less overland flow generation in its subcatchment in event 2 which occurred five days later the initial new water signal in gully a was rapidly overwhelmed by a different signal which is attributed to rapid drainage from a perched water table this study shows that stormflow in this rainforest catchment consists predominantly of new water which reaches the stream channel via fast pathways where the ephemeral gullies delivering overland flow are incised deeply enough to intersect a perched water table a delayed old water like signal may be transmitted

early paleogene biosiliceous sedimentation in the atlantic ocean testing the inorganic origin hypothesis for paleocene and eocene chert and porcellanite abstract the widespread occurrence of lower eocene chert and porcellanite has been viewed as a major paleoceanographic issue since the advent of ocean drilling and both biotic and abiotic forcings have been proposed to explain it we present a reconstruction of indurated siliceous sediment iss and preserved biosiliceous sediment pbs occurrences in the atlantic ocean through the paleocene and eocene 66 through 34 ma iss and pbs distributions reveal dissimilar temporal trends with the peak of iss occurrences coinciding with the early eocene climatic optimum in line with previous studies pbs occurrences show a generally increasing trend culminating between 44 and 43 ma the common co occurrence of iss and pbs and their coherent geographic distribution lends strong support to the biogenic origin of the precursor to the widespread paleogene iss and argues against an inorganic mode of early cenozoic chert and porcellanite precipitation weight per cent biogenic opal records and trends in linear sedimentation rates indicate two plausible modes of silicification 1 silicification due to prolonged exposure of biogenic opal rich sediments to corrosive bottom waters and 2 silicification due to elevated pressures and temperatures caused by rapid burial of biogenic opal rich deposits the confinement of iss and pbs to proximal sites along continental margins points to the reliance of siliceous sedimentation through the paleocene and eocene on terrestrial supply of dissolved silicon consistent with this quantitative siliceous microfossil assemblage records from the blake nose in the nw atlantic indicate that the nutrient rich marginal rather than oligotrophic pelagic settings hosted the majority of siliceous plankton production through the early paleogene the inorganic sio2 precipitation model is unlikely to have been the dominant mechanism responsible for ubiquitous occurrences of early paleogene iss we favor the biogenic iss precursor scenario and reconcile it with the low productivity early cenozoic oceans by showing that large volumes of biogenic silica were supplied to the western north atlantic ocean from the north american margin through the paleocene and eocene dissolution of this surplus silica was facilitated by an early southwestward flow of young sio2 depleted waters from the north atlantic all these factors contributed to iss and pbs focusing in the western north atlantic through the early paleogene

flow path studies in forested watersheds of headwater tributaries of brush brook vermont an investigation was undertaken into how headwater tributaries of brush brook vermont could have average ph differences of almost two units 4 75 and 6 7 sampling along four tributaries revealed that most of one tributary below an area of seeps had consistently higher ph ca2 mg2 and k and lower al than other sites bedrock mapping showed numerous fractures in vicinity of the seeps a portion of this tributary s watershed and a portion of an acid tributary s watershed were intensively mapped for soil depth sampling showed the widespread existence of dense basal till in the watershed of the acid tributary but none in that of the near neutral stream lateral flow found above the dense till was chemically similar to that of the acid tributary and to solutions sampled from soil b horizons there were no differences in the average ph of nonseep soils sampled from either watershed flow paths are hypothesized to be through the b horizons in the acid tributaries and from below the soil profile in the near neutral tributary the acid catchment should be more sensitive to environmental change

integrated biomagnetochronology for the palaeogene of odp hole 647a implications for correlating palaeoceanographic events from high to low latitudes lower eocene to oligocene microfossil rich hemipelagic sediments in odp hole 647a southern labrador sea provide a strategic section for resolving the early history of high north atlantic climates and ocean circulation and for correlating with carbonate poor lower cenozoic sediments in the arctic and nordic seas our new integrated palaeomagneto and multigroup biostratigraphy 63 dinoflagellate cyst calcareous nannofossil planktonic foraminifer and diatom datums significantly improves site 647 chronostratigraphy and provides a framework for future studies this new age model coupled with provisional d18o analyses provides greater confidence in the location of significant ocean climate events at this site including the eocene oligocene transition and the middle eocene climatic optimum early eocene hyperthermals may also be present near the base of the section palaeomagnetic age control is significantly improved in the eocene but not in the oligocene revised estimates of sedimentation and biogenic flux indicate changes in supply and preservation that may be climatically controlled a lower to middle eocene hiatus is more precisely constrained with a c 4 million year duration age and depth errors quantify the age uncertainties throughout the section our revised age model will play an important role in stratigraphic correlation between very high latitude and lower latitude sites the geological society of london 2013

control of north atlantic deep water circulation by the greenland scotland ridge coherent bathymetric features along the reykjanes ridge indicate that there were significant changes in the flux of buoyant material within the icelandic hot spot during the neogene the radial extent of the topographic swell associated with this hot spot is of the order of 1000 to 2000 km and therefore these changes affected the greenland scotland ridge gsr at present sill depths along the gsr are generally less than 500 m with the deepest passage being less than 1000 m making the overflow water sensitive to even small changes in the ridge depths reconstructions of neogene mantle plume activity correlate with the deepwater circulation patterns in the north atlantic times of high mantle plume activity caused northern component water ncw production to cease ncw fluxes resumed once this phase of high mantle plume activity slowed the long term climate change during the neogene must be controlled by factors other than ncw production however climatic optima during the late early miocene and early pliocene appear to have been augmented by high ncw fluxes while subsequent middle miocene and middle pliocene coolings correlate with uplifts on the gsr and reduced ncw flux we suggest that reductions in ncw may have contributed to both of these cooling events

a laterally constricted shear zone system the nordre stromfjord steep belt nagssugtoqidian orogen w greenland many ductile shear zones are interpreted to operate by simple shear flow but some form under other flow regimes lineations and foliations in such shear zones can lie obliquely to those in simple shear zones which can lead to erroneous tectonic interpretations on the assumption of simple shear flow this paper describes a gently dipping shear zone system from the n central segment of the palaeoproterozoic nagssugtoqidian orogen of w greenland which operated with a lateral constriction component this resulted in the development of upright folds with axes parallel to the transport direction where the constriction component is weak where it is strong a linear fabric and even a subvertical foliation normal to the rotation axis of bulk flow developed this steep foliation is interpreted as the origin of the nordre stromfjord steep belt previously interpreted as a crustal scale sinistral transcurrent shear zone shear zones of this type may occur elsewhere and shear zone fabrics should therefore be carefully analysed before the direction of tectonic transpost can be determined

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

deep water temperature carbonate ion and ice volume changes across the eocene oligocene climate transition 1 paired benthic foraminiferal stable isotope and mg ca data are used to estimate bottom water temperature bwt and ice volume changes associated with the eocene oligocene transition eot the largest global climate event of the past 50 myr we utilized odp sites 1090 and 1265 in the south atlantic to assess seawater 18o w antarctic ice volume and sea level changes across the eot 33 8 33 54 ma we also use benthic 13c data to reconstruct the sources of the deep water masses in this region during the eot our data together with previously published records indicate that a pulse of northern component water influenced the south atlantic immediately prior to and following the eot benthic 18o records show a 0 5 increase at 33 8 ma eot 1 that represents a 2 c cooling and a small 10 m eustatic fall that is followed by a 1 0 increase associated with oi 1 the expected cooling of deep waters at oi 1 33 54 ma is not apparent in our mg ca records we suggest the cooling is masked by coeval changes in the carbonate saturation state co32 which affect the mg ca data to account for this the bwt ice volume and w estimates are corrected for a change in the co32 of deep waters on the basis of recently published work corrected bwt at sites 1090 and 1265 show a 1 5 c cooling coincident with oi 1 and an average w increase of 0 75 the increase in ice volume during oi 1 resulted in a 70 m drop in global sea level and the development of an antarctic ice sheet that was near modern size or slightly larger

early to middle eocene history of the arctic ocean from nd sr isotopes in fossil fish debris lomonosov ridge strontium and neodymium radiogenic isotope ratios in early to middle eocene fossil fish debris ichthyoliths from lomonosov ridge integrated ocean drilling program expedition 302 help constrain water mass compositions in the eocene arctic ocean between 55 and 45 ma the inferred paleodepositional setting was a shallow offshore marine to marginal marine environment with limited connections to surrounding ocean basins the new data demonstrate that sources of nd and sr in fish debris were distinct from each other consistent with a salinity stratified water column above lomonosov ridge in the eocene the 87sr 86sr values of ichthyoliths 0 7079 0 7087 are more radiogenic than eocene seawater requiring brackish to fresh water conditions in the environment where fish metabolized sr the 87sr 86sr variations probably record changes in the overall balance of river sr flux to the eocene arctic ocean between 55 and 45 ma and are used here to reconstruct surface water salinity values the nd values of ichthyoliths vary between 5 7 and 7 8 compatible with periodic or intermittent supply of nd to eocene arctic intermediate water aiw from adjacent seas although the norwegian greenland sea and north atlantic ocean were the most likely sources of eocene aiw nd input from the tethys sea via the turgay strait in early eocene time and the north pacific ocean via a proto bering strait also contributed

parallel stretching lineations and fold axes oblique to a shear displacement direction a model and observations abstract spatial variations in shear strain rate are expected in ductile shear zones where the variation is a change in shear strain perpendicular to the displacement direction the effect is to rotate the shear slip planes this is a mechanism for giving a rotation of fold axes into parallelism with the slip and extension direction in a rock if such a variation in shear strain affects rocks with a strong planar anisotropy it is possible to produce a fabric with an apparent stretching lineation parallel to fold axes but both significantly oblique to the slip direction a possible example of this is seen in strongly deformed quartz mica schists from syros greece where a stretching lineation is seen parallel to fold hinges over a range of fold axes orientations of at least 40

sheath folds formed by drag induced by rotation of rigid inclusions in viscous simple shear flow nature and experiment abstract natural examples of fold patterns associated with rotated boudins occur in the ossa morena zone s portugal and triggered the present study in ductile marbles with embedded competent mafic boudins the folds seem to have originated by rotation of these bodies and show differential development from gentle deflections to sheath folds this suggests a dependence of the structure type on the distance of the metamorphic layering to the rigid body the experimental work presented here was performed with rotating inclusions in bulk simple shear and introduces a new variable the distance of the marker layer from the rigid inclusion d expressed in terms of e the ratio between the spacing between marker layers d and the greater principal dimension of the inclusion a contrary to previous experimental work in the literature we used planar marker layers without concomitant boudinage our results show new processes of development of sheath folds from planar layers and also that some non cylindrical layer deflections are transient and thus that sheath folds do not originate from them when d is small and the inclusion starts with its longest axis normal to the shear plane sheath folds develop by drag pull processes on originally planar marker layers transient non cylindrical deflections develop on originally planar marker layers when the distance between the marker layers is smaller than the longest principal dimension of the rigid particle the monoclinic symmetry of the drag sheath fold patterns associated with rotating rigid inclusions indicate non coaxial flow and can be used as a shear sense criterion quarter structure

changing atmospheric co2 concentration was the primary driver of early cenozoic climate the early eocene climate optimum eeco which occurred about 51 to 53 million years ago was the warmest interval of the past 65 million years with mean annual surface air temperature over ten degrees celsius warmer than during the pre industrial period subsequent global cooling in the middle and late eocene epoch especially at high latitudes eventually led to continental ice sheet development in antarctica in the early oligocene epoch about 33 6 million years ago however existing estimates place atmospheric carbon dioxide co2 levels during the eocene at 500 3 000 parts per million and in the absence of tighter constraints carbon climate interactions over this interval remain uncertain here we use recent analytical and methodological developments to generate a new high fidelity record of co2 concentrations using the boron isotope 11 b composition of well preserved planktonic foraminifera from the tanzania drilling project revising previous estimates although species level uncertainties make absolute values difficult to constrain co2 concentrations during the eeco were around 1 400 parts per million the relative decline in co2 concentration through the eocene is more robustly constrained at about fifty per cent with a further decline into the oligocene provided the latitudinal dependency of sea surface temperature change for a given climate forcing in the eocene was similar to that of the late quaternary period this co2 decline was sufficient to drive the well documented high and low latitude cooling that occurred through the eocene once the change in global temperature between the pre industrial period and the eocene caused by the action of all known slow feedbacks apart from those associated with the carbon cycle is removed both the eeco and the late eocene exhibit an equilibrium climate sensitivity relative to the pre industrial period of 2 1 to 4 6 degrees celsius per co2 doubling 66 per cent confidence which is similar to the canonical range 1 5 to 4 5 degrees celsius indicating that a large fraction of the warmth of the early eocene greenhouse was driven by increased co2 concentrations and that climate sensitivity was relatively constant throughout this period

transient temperature asymmetry between hemispheres in the palaeogene atlantic ocean during the late palaeogene between 40 and 23 million years ago ma earth transitioned from a warm non glaciated climate state and developed large dynamic ice sheets on antarctica this transition is largely inferred from the deep sea oxygen isotope record because records from independent temperature proxies are sparse here we present a 25 million year long alkenone based record of surface temperature change from the north atlantic ocean our long temperature record documents peak warmth 29 c during the middle eocene a slow overall decline to the eocene oligocene transition eot 34 ma and high amplitude variability between 28 and 24 c during the oligo miocene the overall structure of the record is similar to that of the deep sea record but a distinct anomaly is also evident we find no evidence of surface cooling in the north atlantic directly coinciding with the eot when antarctica first became cold enough to sustain large ice sheets and subantarctic waters cooled substantially surface ocean cooling during the eot was therefore strongly asymmetric between hemispheres this transient thermal decoupling of the north atlantic ocean from the southern high latitudes suggests that antarctic glaciation triggered changes in ocean circulation driven heat transport and influenced the far field climate response

relative sea level variations in the chukchi region arctic ocean since the late eocene 1 relative sea level rsl variations are a result of tectonic activity changing of the water volume in ocean basins e g due to increasing decreasing of ice volume evaporation and variations in regional to global climate which influence erosional processes and material transport we present multi channel seismic data combined with dated sediment horizons from the chukchi shelf arctic ocean based on a series of prograding sequences in the upper 4 km of sediments and the method of seismic sequence stratigraphy we introduce the first rsl curve for the chukchi region beginning in the late eocene 40 ma the comparison of the chukchi rsl curve with the global rsl curve shows that rsl lowering events in the chukchi region do not correlate with global events for the eocene oligocene early miocene between the eocene oligocene and the late oligocene the chukchi rsl variations were small 100 m since the late oligocene the chukchi rsl increased until the opening of the fram strait in the early miocene we show that the chukchi rsl variations are representative for the arctic ocean and conclude that the arctic ocean was an isolated basin for the eocene oligocene early miocene

manganese carbonate overgrowths on foraminifera tests below the zone where manganese is remobilized as mn2 aq reductively cleaned foraminifera in deep sea sediments have much higher mnca than those in core tops and sediment traps mnca ranges from less than 20 10 6 in and above the mno2 maximum to as high as 700 10 6 in reducing panama basin sediments the most plausible explanation for this enrichment is that the tests are coated with mn carbonate overgrowths these coatings can account for a significant proportion of the mn in reduced deep sea sediments uptake of manganous ion by carbonate may explain the absence of mn nodules in areas of high carbonate accumulation extreme degrees of overgrowth can alter foram trace element values but this artifact can be avoided by avoiding foraminifera with high mn ca

the onset of modern like atlantic meridional overturning circulation at the eocene oligocene transition evidence causes and possible implications for global cooling a compilation of benthic 18o from the whole atlantic and the southern ocean atlantic sector shows two major jumps in the interbasinal gradient of 18o 18o during the eocene and the oligocene one at 40 ma and the second concomitant with the isotopic event of the eocene oligocene transition eot 33 7 ma ago from previously published circulation models and proxies we show that the first 18o jump reflects the thermal isolation of antarctica associated with the proto antarctic circumpolar current acc the second marks the onset of interhemispheric northern sourced circulation cell similar to the modern atlantic meridional overturning circulation amoc the onset of amoc like circulation slightly preceded 100 300 ky the eot as we show by the high resolution profiles of 18o and 13c previously published from dsdp odp sites in the southern ocean and south atlantic these events coincide with the onset of anti estuarine circulation between the nordic seas and the north atlantic which started around the eot and may be connected to the deepening of the greenland scotland ridge we suggest that while the shallow proto acc supplied the energy for deep ocean convection in the southern hemisphere the onset of the interhemispheric northern circulation cell was due to the significant eot intensification of deepwater formation in the north atlantic driven by the nordic anti estuarine circulation this onset of the interhemispheric northern sourced circulation cell could have prompted the eot global cooling

effect of the deepening of the tasman gateway on the global ocean 1 we examine the effect of the deepening of the tasman seaway at the end of the eocene in a climate model with realistic late eocene bathymetry and winds for this we have constructed an eocene numerical model based on the university of victoria climate model with wind forcing derived from a fully coupled eocene simulation the model climate state is characterized by an oceanic meridional overturning circulation moc involving southern hemisphere sinking and a northward atmospheric moisture transport across the equator the deepening of the tasman seaway in the presence of an open drake passage and the associated establishment of the antarctic circumpolar current acc have a limited climatic impact on antarctica nonetheless the antarctic deep sinking regions cool sufficiently to lead to a global deep ocean cooling of 3 c no initiation of northern component water is found indicating that this may require the development of a more mature acc previous studies suggest that the ross sea gyre cools the east coast of australia and expected the deepening of the tasman seaway to lead to a warming east of australia due to the introduction of warmer water from the australo antarctic gulf we here find that this warming is limited to close to the australian coast and that widespread cooling prevails further off shore

bipolar atlantic deepwater circulation in the middle late eocene effects of southern ocean gateway openings we present evidence for antarctic circumpolar current acc like effects on atlantic deepwater circulation beginning in the late middle eocene modern ocean circulation is characterized by a thermal differentiation between southern ocean and north atlantic deepwater formation regions in order to better constrain the timing and nature of the initial thermal differentiation between northern component water ncw and southern component water scw we analyze benthic foraminiferal stable isotope 18obf and 13cbf records from ocean drilling program site 1053 upper deep water western north atlantic our data compared with published records and interpreted in the context of ocean circulation models indicate that progressive opening of southern ocean gateways and initiation of a circum antarctic current caused a transition to a modern like deep ocean circulation characterized by thermal differentiation between scw and ncw beginning 38 5 ma in the initial stages of drake passage opening in addition the relatively low 18obf values recorded at site 1053 show that the cooling trend of the middle late eocene was not global because it was not recorded in the north atlantic the timing of thermal differentiation shows that ncw contributed to ocean circulation by the late middle eocene 1 4 myr earlier than previously thought we propose that early ncw originated in the labrador sea based on tectonic reconstructions and changes in foraminiferal assemblages in this basin finally we link further development of meridional isotopic gradients in the atlantic and pacific in the late eocene with the tasman gateway deepening 34 ma and the consequent development of a circumpolar proto acc

early oligocene glaciation and productivity in the eastern equatorial pacific insights into global carbon cycling the onset of sustained antarctic glaciation across the eocene oligocene transition eot marks a pivotal change in earth s climate but our understanding of this event particularly the role of the

axial directions of folds in rocks with linear planar fabrics abstract this paper examines the geological implications of an analysis of constraints on the orientation of fold axes in orthotropic materials we argue that rocks with penetrative linear and planar shape fabrics may have orthotropic anisotropic properties during deformation two forms of anisotropy rheological and structural could be potentially important in the control of fold axial directions we discuss a model of deformation of rocks with linear planar fabrics where in a single deformation event major fold axes need not be parallel to minor fold axes and neither need be perpendicular to the principal compressive stress direction geological and model examples of anistropic control on fold axial directions are given

a nd isotopic study of southern sourced waters and indonesian throughflow at intermediate depths in the cenozoic indian ocean we present nd isotopic data for fossil fish teeth recovered from the past 40 m y at odp site 757 currently located at 1650 m water depth on the ninetyeast ridge in the indian ocean although site 757 sits in a region strongly influenced by weathering inputs from the himalayas and volcanic inputs from the indonesian arc the pattern of nd isotopic variations does not appear to respond to these potential sources of nd instead secular variations correlate to changes in the composition of intermediate to deep water masses bathing the site and circulation patterns in the indian ocean from 40 to 10 ma nd values and the pattern of change at site 757 closely match those of odp site 1090 a deep water site in the atlantic sector of the southern ocean comparison to data from several fe mn crusts in the indian ocean suggests that intermediate to deep water flow paths were similar to the modern distribution of circumpolar deep water at approximately 10 ma nd isotopic values increase in a step function by 2 nd units suggesting that plate motions had carried site 757 into a region influenced by indonesian throughflow estimates of the vertical and horizontal position of this site at 10 ma imply that indonesian throughflow extended as far south as 20 s and to a depth of 1500 m from 10 to 0 ma nd isotopic variations at site 757 appear to record variations in indonesian throughflow from 10 to 5 5 ma values at site 757 overlap with those from crusts located in the southwest pacific indicating extensive flow through the indonesian seaway from 5 5 to 3 4 ma nd values become less radiogenic at site 757 and more radiogenic in the southwest pacific suggesting increasing closure of the seaway and concomitant rerouting of equatorial pacific waters beginning at 3 4 ma nd values become more radiogenic again at site 757 which may be attributed to enhanced opening of the seaway or to a change in the source of throughflow waters from a southern to a northern pacific region

tracing sources of summer streamflow in boreal headwaters using isotopic signatures and water geochemical components summary content of 18o 2h 3h and geochemical components in rainfall stream water peat water and bedrock groundwater in four headwater catchments were compared to reveal differences in sources of runoff and hydrological vulnerability to tunnel drainage during summer water previously stored within the catchments was the predominant component of streamflow during small and moderate events the proportion of event water increased at high discharge in autumn neither the isotopic nor the hydrochemical composition of stream water indicated any considerable contribution from old bedrock groundwater stream water hydrochemistry revealed clear influence of soil water pathways the differences in land cover could be seen in water quality and runoff generation water storage and mixing in lakes and lowland wetlands reduced fluctuations in runoff and water quality runoff retention and the solute trapping effect in peatlands were most efficient in flat areas near the catchment outlet in lowflow periods fluxes from hillslopes were of minor importance compared to discharges from wetland water storage water delivery from hillslopes with thin till cover

onset of north atlantic deep water production coincident with inception of the cenozoic global cooling trend here we show that the onset of deep water overflow from the norwegian greenland sea into the north atlantic interpreted to represent the onset of a modern style north atlantic deep water mass commenced close to the early to middle eocene boundary this finding is based on the identification of a large elongate contourite sediment drift the judd falls drift in the faeroe shetland basin through detailed mapping of high resolution two dimensional and three dimensional seismic data this sediment drift covers an area of 9000 km2 in one of the critical present day deep water gateways into the north atlantic ocean interpretation of the body as a contourite drift is based on standard seismic stratigraphic diagnostic criteria including tridirectional onlap lensoid sediment geometry upslope progradational configurations of stacked onlap units and an erosional base cut in a deepwater setting the internal reflection configuration indicates that the drift was deposited under a southwest flowing current regime which we propose represents the onset of north atlantic deep water production with continual deep water flow until at least the latest eocene ca 35 million years ago ma onset of drift deposition is dated by several key boreholes as occurring at ca 50 49 ma across the early to middle eocene boundary and is coincident with independent geochemical evidence for major changes in the configuration of deep sea circulation patterns global biological production and the onset of cenozoic climatic cooling these temporal concurrences suggest a strong link between the initiation of north atlantic deep water production and cenozoic global climate evolution

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

timing and climatic consequences of the opening of drake passage age estimates for the opening of drake passage range from 49 to 17 million years ago ma complicating interpretations of the relationship between ocean circulation and global cooling secular variations of neodymium isotope ratios at agulhas ridge southern ocean atlantic sector suggest an influx of shallow pacific seawater approximately 41 ma the timing of this connection and the subsequent deepening of the passage coincide with increased biological productivity and abrupt climate reversals circulation productivity linkages are proposed as a mechanism for declining atmospheric carbon dioxide these results also indicate that drake passage opened before the tasmanian gateway implying the late eocene establishment of a complete circum antarctic pathway

evolution of the neodymium isotopic signature of neritic seawater on a northwestern pacific margin new constrains on possible end members for the composition of deep water masses in the late cretaceous ocean the neodymium nd isotope composition of fish remains has beenwidely used to track past changes in oceanic circulation although the number of published nd isotope data for the cretaceous has markedly increased in the last years no consensus has been reached on the structure of the oceanic circulation and its evolution during the late cretaceous yet this period is characterised bymajor geodynamical and climatic changes andmarked by the disappearance of global oceanic anoxic events inwhich changes in oceanic circulation modesmay have played a significant role in this study we present the first record of nd isotopic composition of fish remains from continental margin environments on the northwestern pacific margin yezo group in the hokkaid area northern japan for the late cretaceous period this record interpreted in terms of nd isotopic composition of local neritic seafloor seawater is characterised by relatively radiogenic nd isotope compositions and presents variations of several e units from the turonian to the campanian ranging from 5 5 to 0 5 e units although most values remain in the 1 to 3 range conversely the local detrital fraction remains more constant and around 4 e units on the studied interval this new set of seawater nd data contains some of the most radiogenic values for the cretaceous published yet the more radiogenic seawater nd isotope values compared to that of the sediments points to an input of radiogenic seawater in the studied area by surface currents during the late cretaceous similarly to the modern configuration these radiogenic waters could have been conveyed in the studied area by a southward current comparable to the modern oyashio current bathing the hokkaid area our data are then consistent with the presence in the northern pacific of highly radiogenic seawater and support the northern and northwestern pacific as a possible radiogenic source for the deep parts of the basin as such this work represents a first step toward a better characterisation of the various end members that could have contributed to the nd isotopic signature of the deep water masses filling the cretaceous oceans

early cenozoic benthic foraminiferal isotopes species reliability and interspecies correction factors 1 oxygen and carbon isotope records are important tools used to reconstruct past ocean and climate conditions with those of benthic foraminifera providing information on the deep oceans reconstructions are complicatedby interspecies isotopic offsets that result from microhabitat preferences carbonate precipitation in isotopically distinct environments and vital effects species specific metabolic variation in isotopic fractionation we provide correction factors for early cenozoic benthic foraminifera commonly used for isotopic measurements cibicidoides spp nuttallides truempyi oridorsalis spp stensioina beccariiformis hanzawaia ammophila and bulimina spp showing that most yield reliable isotopic proxies of environmental change the statistical methods and larger data sets used in this study provide more robust correction factors than do previous studies interspecies isotopic offsets appear to have changed through the cenozoic either 1 as a result of evolutionary changes or 2 as an artifact of different statistical methods and data set sizes used to determine the offsets in different studies regardless of the reason the assumption that isotopic offsets have remained constant through the cenozoic has introduced an 1 2 c uncertainty into deep sea paleotemperature calculations in addition we compare multiple species isotopic data from a western north atlantic section that includes the paleocene eocene thermal maximum to determine the most reliable isotopic indicator for this event we propose that oridorsalis spp was the most reliable deepwater isotopic recorder at this location because it was best able to withstand the harsh water conditions that existed at this time it may be the best recorder at other locations and for other extreme events also

ocean overturning since the late cretaceous inferences from a new benthic foraminiferal isotope compilation 1 benthic foraminiferal oxygen isotopic d 18 o and carbon isotopic d 13 c trends constructed from compilations of data series from multiple ocean sites provide one of the primary means of reconstructing changes in the ocean interior these records are also widely used as a general climate indicator for comparison with local and more specific marine and terrestrial climate proxy records we present new benthic foraminiferal d 18 o and d 13 c compilations for individual ocean basins that provide a robust estimate of benthic foraminiferal stable isotopic variations to 80ma andtentatively to 110ma first order variations ininterbasinal isotopicgradients delineate transitions from interior ocean heterogeneity during the late cretaceous 65 ma to early paleogene 35 65 ma homogeneity and a return to heterogeneity in the late paleogene early neogene 35 0 ma we propose that these transitions reflect alterations in a first order characteristic of ocean circulation the ability of winds to make water in the deep ocean circulate we document the initiation of large interbasinal d 18 o gradients in the early oligocene and link the variations in interbasinal d 18 o gradients from the middle eocene to oligocene with the increasing influence of wind driven mixing due to the gradual tectonic opening of southern ocean passages and initiation and strengthening of the antarctic circumpolar current the role of wind driven upwelling possibly associated with a tethyan circumequatorial current in controlling late cretaceous interior ocean heterogeneity should be the subject of further research

heat transport deep waters and thermal gradients coupled simulation of an eocene greenhouse climate for the first time a coupled general circulation model with interactive and dynamical atmospheric oceanic and sea ice components is used to simulate an eocene 50 ma greenhouse climate we introduce efficient ocean spin up methods for coupled paleoclimate modeling sea surface temperatures ssts and salinities evolve unconstrained producing the first proxy data independent estimates for these eocene climate parameters tropical and extratropical model predicted ssts are warmer than modern values by 3 and 5 c respectively salinity driven deep water formation occurs in the north atlantic and tethys the zonal average overturning circulation is weaker than modern eocene ocean heat transport is 0 6 pw less than modern in the northern hemisphere and 0 4 pw greater in the southern hemisphere the model predicted near modern vertical and meridional eocene temperature gradients imply that the dominant theory for maintaining low gradients increased ocean heat transport is incorrect or incomplete and other mechanisms should be explored

neogene ice volume and ocean temperatures insights from infaunal foraminiferal mg ca paleothermometry antarctic continental scale glaciation is generally assumed to have initiated at the eocene oligocene transition yet its subsequent evolution is poorly constrained we reconstruct changes in bottom water temperature and global ice volume from 0 to 17 ma using 18o in conjunction with mg ca records of the infaunal benthic foraminifer o umbonatus from ocean drilling program odp site 806 equatorial pacific 2500 m considering uncertainties in core top calibrations and sensitivity to seawater mg ca mg ca sw we produce a range of mg ca temperature mg casw calibrations our favored exponential temperature calibration is mg ca 0 66 0 08 mg casw0 27 0 06 e 0 114 0 02 bwt and our favored linear temperature calibration is mg ca 1 21 0 04 0 12 0 004 bwt bottom water temperature mg casw 0 003 0 02 stated errors are 2 s e the equations are obtained by comparing o umbonatus mg ca for a paleocene eocene section from ocean drilling program odp site 690 weddell sea to 18o temperatures calculated assuming ice free conditions during this peak warmth period of the cenozoic this procedure suggests negligible effect of mg casw on the mg distribution coefficient dmg application of the new equations to the site 806 record leads to the suggestion that global ice volume was greater than today after the middle miocene climate transition 14 ma odp site 806 bottom waters cooled and freshened as the pacific zonal sea surface temperature gradient increased and climate cooled through the pliocene prior to the plio pleistocene glaciation of the northern hemisphere the records indicate a decoupling of deep water temperatures and global ice volume demonstrating the importance of thresholds in the evolution of the antarctic ice sheet

stable isotopic information for hydrological investigation in hailuogou watershed on the eastern slope of mount gongga china hydrological systems have been seriously affected by changes of glaciations and snow covers in mount gongga sichuan china but the relevance of ice snow melt for alpine river basin hydrology is so far not well known to better understand hydrological features of the hailuogou river changes of 18o and 2h were investigated by analyzing 117 water samples collected from may 2008 to november 2009 our results show that the stream water contains a relatively intermediate magnitude of isotopic variations with 18o ranging from 18 09 to 13 08 and 2h from 126 5 to 88 8 the average values are both higher than those of ice snow meltwater but lower than those of meteoric water these data also show a gradually increasing trend from upstream to downstream and these changes might document the fingerprint of ice snow melt in the headwater region and indicate the increasing recharge of heavy isotope enriched waters with flow distance the similarity in slopes of 2h and 18o relationship for meteoric waters and stream waters suggests that the isotopic signature of precipitation is well preserved in stream flow and during the rainfall and stream flow the evaporation is only minor based on 18o model the results suggested that the fraction of ice snow meltwater input over the total stream flow ranged from 84 50 to 86 52 in the headwater region but the fraction of ice snow meltwater input from upper basin downward was significantly decreased the study demonstrates that ice snow meltwater is a substantially important water source in alpine regions on the edge of tibetan plateau

enhanced weathering and co2 drawdown caused by latest eocene strengthening of the atlantic meridional overturning circulation on timescales significantly greater than 105 years atmospheric pco2 is controlled by the rate of mantle outgassing relative to the set point of the silicate weathering feedback the weathering set point has been shown to depend on the distribution and characteristics of rocks exposed at the earth s surface vegetation types and topography here we argue that large scale climate impacts caused by changes in ocean circulation can also modify the weathering set point and show evidence suggesting that this played a role in the establishment of the antarctic ice sheet at the eocene oligocene boundary in our simulations tectonic deepening of the drake passage causes freshening and stratification of the southern ocean strengthening the atlantic meridional overturning circulation and consequently raising temperatures and intensifying rainfall over land these simulated changes are consistent with late eocene tectonic reconstructions that show drake passage deepening and with sediment records that reveal southern ocean stratification the emergence of north atlantic deep water and a hemispherically asymmetric temperature change these factors would have driven intensified silicate weathering and can thereby explain the drawdown of carbon dioxide that has been linked with antarctic ice sheet growth we suggest that this mechanism illustrates another way in which ocean atmosphere climate dynamics can introduce nonlinear threshold behaviour through interaction with the geologic carbon cycle during the latest eocene declining atmospheric co2 levels led to the inception of the antarctic ice sheet simulations suggest that the deepening of the drake passage caused climate changes that enhanced continental weathering and co2 drawdown