marine derived 14c calibration and activity record for the past 50 000 years updated from the cariaco basin abstract an expanded cariaco basin 14c chronology is tied to 230th dated hulu cave speleothem records in order to provide detailed marine based 14c calibration for the past 50 000 years the revised high resolution cariaco 14c calibration record agrees well with data from 230th dated fossil corals back to 33 ka with continued agreement despite increased scatter back to 50 ka suggesting that the record provides accurate calibration back to the limits of radiocarbon dating the calibration data document highly elevated 14c during the glacial period carbon cycle box model simulations show that the majority of observed 14c change can be explained by increased 14c production however from 45 to 15 ka 14c remains anomalously high indicating that the distribution of radiocarbon between surface and deep ocean reservoirs was different than it is today additional observations of the magnitude spatial extent and timing of deep ocean 14c shifts are critical for a complete understanding of observed glacial 14c variability

crustal structure off norway 62 to 70 north abstract extensive geophysical surveys have been undertaken on the volcanic passive continental margin offshore norway between 62 and 70 n during the last 25 years three main margin segments have been identified the lofoten vesteralen margin the voring margin and the more margin the main features of the margins are prominent marginal highs including seaward dipping reflector sequences and an up to 22 km thick volcanic and transitional crust prominent escarpments the voring plateau escarpment and the faeroe shetland escarpment and up to 12 km deep post jurassic sedimentary basins east of the escarpments velocity depth solutions from about 250 sonobuoys expanding spread profiles and refraction profiles have been compiled and contoured isovelocity horizon contour maps and velocity transects outline a crust which broadly thickens from an oceanic crust with a normal oceanic type velocity structure to a ca 35 km thick continental crust with a continental velocity structure beneath the norwegian coast anomalous features include local crustal thickening below the more and vering marginal highs and high velocity bodies in the lower crust in the extension of the precambrian lofoten vesteralen archipelago the free air seasat derived gravity anomalies show a good correlation with the high velocity bodies and show prominent ne trending highs from the rockall plateau porcupine plateau region over the more voring and lofoten vesteralen margins to the southwestern barents sea

the deglacial evolution of north atlantic deep convection deepwater formation in the north atlantic by open ocean convection is an essential component of the overturning circulation of the atlantic ocean which helps regulate global climate we use water column radiocarbon reconstructions to examine changes in northeast atlantic convection since the last glacial maximum during cold intervals we infer a reduction in open ocean convection and an associated incursion of an extremely radiocarbon 14c depleted water mass interpreted to be antarctic intermediate water comparing the timing of deep convection changes in the northeast and northwest atlantic we suggest that despite a strong control on greenland temperature by northeast atlantic convection reduced open ocean convection in both the northwest and northeast atlantic is necessary to account for contemporaneous perturbations in atmospheric circulation

cenozoic and late mesozoic stratigraphy and subsidence history of the norwegian margin the stratigraphy of the passive continental margin off norway is mapped utilizing both deep sea drilling project dsdp data at five sites on the outer margin and multichannel seismic mcs data collected by lamont doherty geological observatory distinct units in the acoustic stratigraphy are tied to biostratigraphic and lithostratigraphic units in the drill data and mapped throughout most of the margin stratigraphy of the pre lower eocene section not encountered in drilling is inferred from depositional patterns and correlation with the continental shelf sequences the stratigraphy of which has been developed independently from detailed surveys the margin can be divided into three physiographic provinces two broad shelf and slope regions separated by the jan mayen fracture zone and the steep narrow shelf and slope off the lofoten islands each experienced a separate cenozoic subsidence history the voring plateau is partly underlain by oceanic crust it subsided nearly 1 000 m less than expected from thermal contraction but it did so following the development of a relatively deep water environment in the paleocene north of the voring plateau the margin may have subsided a few hundred metres more than thermal studies had predicted there is no evidence for a phase of extensional deformation associated with the inception of spreading the youngest faulted level occurs at the late jurassic level preceding sea floor spreading by nearly 100 ma and deformation in the cretaceous section is characterized by large uplift structures that may be of halokinetic origin the physiographic provinces as well as the cenozoic subsidence patterns along the margin appear to be related to the style and extent of mesozoic basin development and tectonics along the margin

a crustal study off lofoten n norway by use of 3 component ocean bottom seismographs abstract twenty four 3 component ocean bottom seismographs obs were used in august 1988 in a combined seismic refraction and reflection study off lofoten n norway the purpose of the experiment was to map the crustal structure from the continental shelf to the oceanic crust off lofoten the very high data quality is demonstrated by the strong p wave and shear wave reflections as well as converted waves from the moho observed on the continental shelf these arrivals are observed continuously from near vertical to wide angle incidence very high seismic sea floor velocities in this area 3 1 km s to 5 1 km s indicates absence or very thin sequences of mesozoic sediments the 5 1 km s refractor coincides with the base cretaceous reflection interpreted from the multichannel reflection data the crystalline continental crust is here divided in layers with velocities of 6 0 km s 6 4 km s and 6 8 km s respectively on the seaward side of the escarpment tertiary sediments varying in thickness from 1 0 1 5 km are situated on top of a 1 5 2 0 km thick layer of flood basalt containing seaward dipping reflectors a layer with velocity of 6 7 km s is observed above the lower crust which in this area is found to have a velocity as high as 7 3 km s these high velocities indicate that the crust in this area is of oceanic origin or alternatively the high velocity layer in the lower crust might represent a magmatic body underplating highly thinned and intruded continental crust seven obss were deployed in the area that was covered by landward flowing basalt deposited during the early eocene breakup between norway and greenland the survey was partly performed to investigate whether this method can be used to map structures below the basalt which is impenetrable with conventional seismic reflection techniques the obs data contain considerable information about structures below the flood basalt pre opening sediments up to 4 0 km thick are indicated below the 1 0 2 5 km thick landward flowing basalt the velocities of the crystalline portion of the crust are found to be similar to those observed under the continental shelf 6 0 6 8 km s which implies that the crust east of the escarpment is of continental origin the crystalline crust is strongly thinned in this area showing a minimum thickness of about 6 km the depth to the moho increases from about 15 km in the western part of the area to about 26 km on the continental shelf the success of the obs survey indicates that such measurements can become an important tool in investigations on passive volcanic margins and potentially in other areas where highly reflective surfaces make the reflection technique inefficient

reply to comment on compilation of geophysical geochronological and geochemical evidence indicates a rapid mediterranean derived submergence of the black sea s shelf and subsequent substantial salinification in the early holocene by a g yanchilina w b f ryan j f mcmanus p dimitrov d dimitrov k slavova m filipova marinova marine geology 383 2017 14 34 abstract soulet 2018 asserts that the calculation of the 14c reservoir age for the geochronology of the black sea sediments suffers from a fundamental flaw he contends that yanchilina et al 2017 obtained reservoir ages by first sorting the 18o and 13c values of the mollusks as a function of their corresponding 14c age before aligning the mollusk isotope curves to those of the nearby sofular cave sorting by 14c age would lead to an incorrect calendar age for each 18o and 13c measurement because it does not take into account changing reservoir ages we reply here that this sorting by 14c age was not the procedure taken the radiocarbon reservoir ages were derived after tuning the 18o and 13c composition of the mollusks sorted by their 18o 13c radiocarbon age and stratigraphic location in each core to the 18o and 13c composition of the u th dated sofular cave stalagmites as a function of calendar age shown to reflect black sea surface water 18o and 13c composition after the calendar age was derived for each mollusk it was then converted to a corresponding northern hemisphere atmospheric 14c age using reimer et al 2009 the 14c reservoir age was subsequently calculated from the difference between the measured 14c age of the mollusks and the calculated northern hemisphere atmospheric 14c age of the mollusks r t 14cshell t 14catm t e g ryan 2007 kwiecien et al 2009 jull et al 2013 philippsen 2013 soulet 2015 soulet et al 2016 the reimer et al 2009 calibration used in our original study differs

salt marsh hydrology implications for biogeochemical fluxes to the atmosphere and estuaries rates of gas emissions and solute fluxes from salt marsh sediments are influenced by sediment hydrology a comprehensive water balance study in a new england salt marsh reveals that evapotranspiration and infiltration during tidal inundation and precipitation are the dominant hydrological processes in the sediment on a marsh wide scale water loss by drainage through the sediment into tidal creeks is effectively limited to within 10 m to 15 m of the creek bank however drainage is responsible for 40 of the water loss within 10 m of the creek during nonflooding neap tide periods the rate and extent of advective transport by pore water drainage is controlled by the topography of the marsh surface tidal fluctuations in creek level drive larger oscillating water fluxes across the creek bank which results in a dispersive transport of the solutes in the sediment but these fluxes are attenuated in the first meter convexities in the marsh surface for example the crests of the creek banks are the location of maximum water loss by drainage and probably the highest degree of desaturation and aeration which can in turn increase gas emissions locally the spring neap tide cycle modulates wetting and drying of the sediment and by inference gas emissions in the interior of the marsh the limited extent of solute transport by drainage implies that an as yet undescribed mechanism is responsible for controlling the concentration of conservative solutes in salt marshes

the extent of lateral water movement in the sediments of a new england salt marsh models of depth averaged hydraulic head are used with data from a water balance study in a new england salt marsh to describe horizontal pore water water fluxes near a creek bank three hydrologically distinct regions are identified in the sediment in the marsh studied semidiurnal tides may drive an oscillating horizontal flux in the narrow region within about 2 5 m of the creek bank farther than 15 m from the creek there is essentially no horizontal water movement in the region between 2 5 and 15 m drainage to the creek is driven by alternating periods of surface flooding and nonflooding due to the spring neap variation in tidal amplitudes there is little or no input of fresh groundwater to the marsh sediment at this site the spatial extent of the drained region depends on the duration of the nonflooded period the morphology of the sediment surface and the ratio of hydraulic conductivity to specific storage of the sediment

seaward dipping reflectors and the continent ocean boundary at passive continental margins abstract the definition of the continent ocean boundary at passive continental margins has proved to be an elusive task even the relatively direct method of seismic refraction experiments has yielded results that cannot always be interpreted unequivocally multichannel seismic reflection profiles on many passive margins have revealed the presence of remarkable suites of arcuate reflectors dipping seaward to form a wedge shaped structure their general characteristics and velocity structure suggest that they may be largely volcanic in nature but there is no agreed upon model for their origin nevertheless it is generally thought that they lie at or close to the boundary between continent and ocean and as such they are extremely important structural markers that may yield important evidence concerning the structure and evolution of passive margins

comment on compilation of geophysical geochronological and geochemical evidence indicates a rapid mediterranean derived submergence of the black sea s shelf and subsequent substantial salinification in the early holocene by a g yanchilina w b f ryan j f mcmanus p dimitrov d dimitrov k slavova m filipova marinova marine geology 383 2017 14 34 abstract yanchilina et al 2017 describe a sequence of hydrological events that led to the abrupt submergence of the black sea shelf by mediterranean waters a key aspect of the study is an attempt to provide a reliable calendar chronological framework to interpret their set of geophysical and geochemical data however the approach used to build the calendar age framework suffers a fundamental methodological flaw in addition the reservoir age offsets appear to be miscalculated based on the data provided both observations cast doubt on the robustness of some of the conclusions drawn by yanchilina et al 2017

compilation of geophysical geochronological and geochemical evidence indicates a rapid mediterranean derived submergence of the black sea s shelf and subsequent substantial salinification in the early holocene abstract our knowledge of rate and processes in which semi enclosed environments alternate from lacustrine to marine is commonly limited because of the paucity of specific proxies for sea level and salinity here we investigate the timing rate and key mechanisms involved in the transformation of the previously isolated black sea lake to the modern partly enclosed marine sea using a suite of geophysical geochemical and geochronological methods cores were collected in transects across shelves of ukraine romania bulgaria and turkey biogenic carbonate from these cores was analyzed for radiocarbon and strontium oxygen and carbon isotopes strontium results indicate that the submergence of the black sea shelf at 9300 calendar years bp was caused by the ingress of mediterranean water and was abrupt taking radiocarbon years are calibrated to calendar years by tuning the oxygen and carbon isotope composition of the mollusk record to that of the u th dated sofular cave stalagmites the match shows a reduction of the lake s prior high reservoir age accompanying the inflow of the mediterranean water in 900 years the salinity reached a threshold that excluded all previous black sea lacustrine fauna these results imply that any substantial postglacial submergence of the black sea shelves did not occur prior to entry of mediterranean water

deep seismic and geochemical constraints on the nature of rift induced magmatism during breakup of the north atlantic abstract the deep crustal structure of the norwegian and east greenland conjugate passive margins has been investigated with two ship multichannel reflection and refraction techniques in the region from the iceland faeroe ridge to the greenland fracture zone the data demonstrate the presence of thick 15 20 km igneous crust that was emplaced along the conjugate margins during the initiation of seafloor spreading seaward dipping units comprise the uppermost 3 6 km of the thick crust the thickness of igneous crust diminishes seaward with oceanic layer 2 approaching normal thickness nearer to the margin than does oceanic layer 3 wide angle reflection techniques used in conjunction with expanded spread profiling reveal deep moho reflections beneath 20 km thick oceanic crust that continue seaward into the ocean basin margins that have experienced unusually prolific magmatic activity during breakup have been termed volcanic to distinguish them from non volcanic margins that have evolved into accreting plate boundaries without excessive volcanism the origin of volcanic margins cannot be determined from seismically derived crustal thicknesses alone however thermal and chemical properties of the mantle source may be revealed in the compositions of magmatic products emplaced within volcanic passive margins a combined investigation of crustal structure and associated basalt composition could better resolve processes that result in volcanic passive margins on the voring plateau of the norwegian margin seismic lines coincide with dsdp leg 38 drill sites whole rock major element abundances in the freshest basalts are compatible with moderate extents of partial melting of mantle much like that believed to underlie modern mid ocean ridge systems and would be expected to result in the emplacement of oceanic crust about 9 2 km thick this is about the thickness of oceanic crust located seaward of the dipping basaltic units off the hatton more and voring plateau margins and 10 km south of iceland on the reykjanes ridge these results together with regional heat flow depth gravity and geoid anomalies suggest that the mantle beneath this region has experienced a moderate long lived temperature increase compared to mantle beneath normal ocean basins the much greater thicknesses of igneous crust adjacent to the margins do not appear to reflect an unusually hot flux associated with their construction since this would lead to much greater extents of partial melting than are inferred from the basalt geochemistry evidently the difference between volcanic and non volcanic margins is not simply proximity to a hot spot instead we suggest that the magmatism is closely related to the continental rifting phase tectonism resulting in an abrupt transition from continental to oceanic lithosphere may induce small scale convection that results in the circulation of a greater amount of mantle material into the pressure temperature field where partial melting begins than would occur through passive upwelling alone initial crustal thicknesses are enhanced as a result of the convective partial melting crustal thickness is expected to diminish as this secondary convection slows but the degree of partial melting of the source should not change dramatically

magma productivity and early seafloor spreading rate correlation on the northern voring margin norway constraints on mantle melting abstract continental rifting at the voring margin off mid norway was initiated during the earliest eocene 54 ma and large volumes of magmatic rocks were emplaced during and after continental breakup in 2003 a marine survey collecting ocean bottom seismometer single channel reflection and magnetic data was conducted on the norwegian margin to constrain continental breakup and early seafloor spreading processes the profile described here crosses the northern part of the voring plateau and the crustal velocity model was constructed through a combination of ray tracing and forward gravity modeling the latter corrected for the thermal effects remaining from the seafloor spreading we found a maximum igneous crustal thickness of 18 km decreasing to 6 5 km over the first 6 m y after continental breakup both the volume and the duration of excess magmatism are about twice as large as that of the more margin south of the east jan mayen fracture zone which offsets the two margin segments by 170 km a similar reduction in magmatism occurs to the north over an along margin distance of 150 km to the lofoten margin but without a margin offset both the geochemical data and the mean p wave velocity indicate that there is active mantle upwelling combined with a moderate temperature increase during the earliest mantle melting at the voring margin the mean p wave velocity versus crustal thickness also indicates that there is a transition from convection dominated to temperature dominated magma production 2 m y after breakup the magnetic data were used to derive plate half spreading rates for the northern voring margin which are very similar to that obtained at the more margin there is a strong correlation between magma productivity and early plate spreading rate suggesting a common cause a model for the breakup related magmatism should be able to explain this correlation but also the magma production peak at breakup the along margin magmatic segmentation and the active mantle upwelling proposed end member hypotheses comprise elevated upper mantle temperatures caused by a hot mantle plume or edge driven small scale convection fluxing mantle rocks through the melt zone edge driven convection does not easily explain these observations but a mantle plume model in which buoyant plume material flows laterally to pond in the rift topography at the base of the lithosphere close to breakup time is promising when the continents break apart the hot and buoyant plume material can flow up into the rift zone from surrounding areas as the rift transits to drift and the excess temperature of this material will then cause excess magmatism which dies off as the rift restricted material is spent the buoyancy of the plume material may in addition cause active upwelling which can increase the melting furthermore and also increase the force on the plate boundaries to enhance plate spreading rate this conceptual model explains how both excess magmatism and spreading rate will be reduced similarly with time as the plume material is consumed by plate spreading and thus correlate

crustal structure beneath lofoten n norway from vertical incidence and wide angle seismic data summary a high quality multichannel seismic reflection line was acquired in 1987 along a 175 km long profile across the continental shelf off lofoten northern norway a seismic wide angle experiment was performed in 1988 along the same profile using seven three component ocean bottom seismographs obs with 20 25 km spacing and shotpoint intervals of 240 m the study of the data has shown that the combination of the multichannel reflection and the wide angle obs technique provides information about the crustal structure beneath the lofoten shelf that could not have been achieved using only one of the techniques the multichannel reflection data provide a detailed image of the shallow cretaceous structures which represents an important basis for inversion of the obs data the lower crust and the moho are also well mapped in some parts of the area with the multichannel reflection technique the obs data reveal that significant amounts of pre cretaceous sediments exist along almost the entire profile with a maximum thickness of about 5 km in the vestfjorden basin from the obs data the thickness of the lower crust is inferred to decrease from about 11 5 km under the rost high to about 2 km below the lofoten ridge the obs data indicate further that the moho position under the vestfjorden basin is considerably deeper than can be inferred from the reflection data about 10km below moho a strong dipping event is observed in the obs data this upper mantle reflection might be related to a possible seaward dipping master fault and or presence of layers of partially hydrated peridotite

hydrologic parameters of salt marsh peat because of their profound influence on water movement and nutrient cycling in salt marshes the two key physical properties of hydraulic conductivity and compressibility were studied in the great sippewissett marsh and in the ebben creek marsh in massachusetts hydraulic conductivity was the most variable property most frequently observed conductivities were of the order of 10 3 cm s 1 in both marshes but extremes ranged from about 10 1 to 10 5 cm s 1 compressibility was much less variable and contributed of the order of 10 3 cm 1 to the specific storativity of marsh sediment making compression a major mechanism for changes in water storage in the sediment surface sediments frequently exhibited below average conductivity in contrast to freshwater bog peats which are usually most conductive at the surface these measured properties may be applied to estimate the importance of many critical processes such as the extent of infiltration occurring on the marsh surface the hydrologic influence of the tidally varying creeks and the hydrologic response to spring neap tidal cycles

basin structure on the norwegian margin from analysis of digitally recorded sonobuoys during r v robert d conrad cruise 21 a large number of sonobuoys were recorded in the voring more and adjacent basins at the margin off norway the digital sonobuoy data have been transformed into the domain of intercept time tau and ray parameter p and inverted by the tau sum method to obtain better definition of the near seafloor velocities using also the precritical energy a move out correction has been applied to the tau p data conventional analyses of the x t data were also performed in general the various types of analyses complement each other and should be used interactively together with forward modeling to obtain the optimal velocity depth function the sonobuoy results have outlined in a regional sense the pre cenozoic sedimentary basin at the margin this basin attains a maximum sediment thickness of 8 10 km of which only the upper half is defined by seismic reflection profiling at the outer margin the marginal escarpments form major discontinuities in the lateral velocity distribution the survey has proven that sonobuoy profiles recorded during standard seismic reflection profiling in major marginal basins may provide important new information particularly about the deeper parts of the basins that is not directly available from the reflection profiles

structure of the earth oceanic crust and uppermost mantle the past four years have witnessed the introduction of a variety of new instruments and methods for the study of the seismic structure of the oceanic crust and lithosphere the application of these and existing tools has led to the discovery of a number of new phenomena and to a fuller understanding of the genesis and evolution of the oceanic ithosphere borehole seismic instrumentation has become more widely employed ocean bottom seismographs while generally decreasing in number have become significantly more reliable and useful and multichannel seismic systems have been employed in innovative experiments ranging from studies of fracture zones to the regular detection of magma chambers beneath rise axes the techniques available for the analysis of seismic data have become more sophisticated waveforms collected in seismic experiments can now be used directly in constructing and evaluating seismic velocity models and travel time data are regularly inverted directly for structure trial and error modeling has become increasingly unimportant marine seismologists are becoming increasingly involved in understanding the coupling between the ocean and the underlying oceanic lithosphere this has led to a more complete understanding of seafloor noise processes and the partitioning of energy between acoustic and elastic waves

structure of a volcanic continental margin derived from ocean bottom seismographic data the northern voring margin off norway this paper presents a crustal model derived from an ocean bottom seismograph obs study along the northern voring margin off norway the profile was acquired to map the crustal structure in the northernmost part of the voring basin and to link crustal models of the lofoten and central voring basin obtained by previous obs studies the voring margin as well as the lofoten margin to the north was created by continental breakup between norway and greenland in late paleocene early eocene the rifting and continental breakup process were accompanied by intense extrusive and intrusive magmatic activities the obs data provide the whole crustal structure along the northern voring margin in the area where the deep crustal structure cannot be resolved by conventional multichannel reflection data due to sill intrusions in the sedimentary sequence the shallow part of the crustal model is characterized by up to 10 km thick sediments a sequence of flood basalts and sill intrusions the p wave velocities in the flood basalts and sill intrusions are estimated to 5 0 km s and 4 7 5 8 km s respectively the model indicates an abrupt thickening of the upper crystalline crust from approx 3 km in the ne to about 10 km towards the se with velocities of 6 0 6 2 km s the lower crustal velocities are not well resolved due to lack of clear refraction arrivals from the lower crust however the observed amplitude versus offsets are best explained by a model with a change in lower crustal velocities from 6 8 to 7 2 km s beneath the bivrost lineament the modelling infers the presence of a lower crustal reflector beneath the lineament which represents the landward continuation of the bivrost lineament reflection arrivals from the moho reveal a moho depth of 23 km in the middle of the profile and 18 20 km in the northeastern part of the profile a 370 km long crustal section from the central part of the voring basin to the lofoten margin obtained by the results of this study and previous obs studies shows a simple thinned continental crust on the lofoten margin and a high velocity lower crust underlying an upper crust of varying thickness in the voring basin the transition between these structures is situated beneath the bivrost lineament in the lower crust and beneath the basement high about 40 km south of the lineament in the upper crust

estimating shallow subsidence in microtidal salt marshes of the southeastern united states kaye and barghoorn revisited abstract simultaneous measurements of vertical accretion and change in surface elevation relative to a shallow 3 5 m subsurface datum were made in selected coastal salt marshes of louisiana florida and north carolina to quantitatively test kaye and barghoorn s contention that vertical accretion is not a good surrogate for surface elevation change because of autocompaction of the substrate rates of subsidence of the upper 3 5 m of marsh substrate were calculated for each marsh as the difference between vertical accretion and elevation change measured with feldspar marker horizons and a sedimentation erosion table surface elevation change was significantly lower than vertical accretion at each site after 2 years indicating a significant amount of shallow subsidence had occurred ranging from 0 45 to 4 90 cm the highest rate of shallow subsidence occurred in the mississippi delta results confirm kaye and barghoorn s contention that vertical accretion is not generally a good surrogate for elevation change because of processes occurring in the upper few meters of the substrate including not only compaction but also apparently shrink swell from water storage and or plant production decomposition at some sites indeed surface elevation change was completely decoupled from vertical accretion at the florida site the assumption of a 1 1 relationship between vertical accretion and surface elevation change is too simplistic a generalization of the complex interactions between accretionary and substrate processes consequently the potential for coastal marsh submergence should be expressed as an elevation deficit based on direct measures of surface elevation change rather than accretion deficits these findings also indicate the need for greater understanding of the influence of subsurface and small scale hydrologic processes on marsh surface elevation

modelling shear waves in obs data from the voring basin northern norway by 2 d ray tracing three component recordings from an array of five ocean bottom seismographs in the northwestern part of the voring basin have been used to obtain a 2 d shear wave s wave velocity depth model the shear waves are identified by means of travel time differences compared to the compressional p waves and by analyzing their particle motions the model has been obtained by kinematic travel time ray tracing modelling of the obs horizontal components

accelerator mass spectrometry is the future bigger or smaller abstract since its inception in the late 1970s accelerator mass spectrometry has become a powerful tool for measurement of trace amounts of natural radionuclides in this paper we review recent advancements in ams and discuss future directions of this powerful technique we highlight some recent developments including the introduction of smaller accelerators novel detection systems and the development of new analytical capabilities we believe that the future prospects for ams measurements are practically unlimited and that ams has a vital role to play in the exploration of space where radionuclide measurements are a key factor in the understanding of processes on other planets

the aegir ridge structure of an extinct spreading axis in 1988 a reflection seismic survey was carried out by the alfred wegener institute for polar and marine research to study structure and development of the aegir ridge an extinct spreading axis in the norway basin a number of volcanolike structures were detected in the central ridge the emerging lava flows dip away from their source in ridge strike perpendicular to ridge strike we observed lava flows dipping towards the ridge center this pattern might represent a more general flow pattern at mid ocean ridges after spreading ceased sedimentation resulted in the deposition of 800 ms two way time twt to 1300 ms twt about 900 1400 m sediments in the central ridge distribution of the sediments indicate subsidence of the central ridge probably due to cooling after termination of spreading this subsidence started no later than late oligocene or early miocene we detected an area where migration of a fluid phase led to obstruction of the sedimentary layering and the formation of mounds and faults at the ocean bottom several sources for the fluid phase are discussed

possible shallow crustal shear wave anisotropy off lofoten norway inferred from three component ocean bottom seismographs summary p and s wave velocity models along two perpendicular profiles 145 and 175 km long on the undrilled continental shelf off lofoten northern norway have been obtained from the study of nine three component ocean bottom seismographs a vp vs ratio of 1 96 2 15 is found in the sedimentary layers along a ne sw profile these high values are consistent with shaly sediments which are identified in dredged bedrock samples along a nw se profile the s wave velocities in the sedimentary layers are 5 10 per cent higher than along a ne sw profile the most likely explanation for this velocity difference is seismic anisotropy which might be caused by liquid filled microfractures alligned along the direction of the present day maximum horizontal compressive stress the vp vs ratio in the upper crystalline crust is found to be 1 75 along both profiles if the inferred anisotropy described above is caused by aligned microcracks the lack of anisotropy in the crystalline basement indicates that these cracks are restricted to the sedimentary layers it must be emphasized however that the observed azimuthal difference in s wave velocities could be caused by lateral velocity variations in the sediments although the anisotropy hypothesis is considered more likely

vegetation change and surface elevation dynamics in estuarine wetlands of southeast australia vertical accretion and surface elevation trends were studied in mangrove and saltmarsh wetlands in southeast australia a total of 69 surface elevation tables each associated with three feldspar marker horizons was deployed in 10 wetlands across 7 estuaries and monitored for three years saltmarsh and mangrove vegetation distributions were mapped for the same estuaries and elevation characteristics of the wetlands were modelled rates of vertical accretion were found to correlate with tidal range no relationship was found between rates of vertical accretion and surface elevation increase a positive relationship was demonstrated between contemporary rates of saltmarsh surface elevation change and longer term rates of mangrove encroachment into saltmarsh we conclude that landward mangrove encroachment may be facilitated by local factors contributing to saltmarsh compaction during drought conditions

timing and climatic impact of greenland interstadials recorded in stalagmites from northern turkey a 50 kyr long exceptionally well dated and highly resolved stalagmite oxygen 18o and carbon 13c isotope record from sofular cave in northwestern turkey helps to further improve the dating of greenland interstadials gi 1 and 3 12 timing of most gi in the sofular record is consistent within 10 to 300 years with the iconic hulu cave record larger divergences 500 years between sofular and hulu are only observed for gi 4 and 7 the sofular record differs from the most recent ngrip chronology by up to several centuries whereas age offsets do not increase systematically with depth the sofular record also reveals a rapid and sensitive climate and ecosystem response in the eastern mediterranean to gi whereas a phase lag of 100 years between climate and full ecosystem response is evident finally results of spectral analyses of the sofular isotope records do not support a 1 470 year pacing of gi

vp vs ratio structure of the lofoten continental margin northern norway and its geological implications summary in 1988 an extensive seismic refraction and wide angle reflection study was performed at the lofoten passive continental margin off northern norway by using three component ocean bottom seismographs the lofoten margin was formed by continental rifting and sea floor spreading with extensive volcanism which is responsible for landward flood basalts and seaward dipping reflectors sdr the p wave structure beneath the seaward side of the voting plateau escarpment at the lofoten margin is characterized by a thick oceanic lower crust and the existence of an additional high velocity layer at the bottom of the crust in this study the distribution of the p wave velocity vp to s wave velocity vs ratio down to the uppermost mantle is obtained by studying p to s converted shear wave data vp vs ratios of 3 0 5 5 are obtained in the sedimentary layers these high ratios are attributed to unconsolidated sediments in the upper crust a significant difference in vp vs ratios is found between oceanic side profiles and land side profiles i e 1 86 oceanward of the sdrs and 1 76 landward of the sdrs this variation may have been caused by a difference in porosity due to the difference in extrusive processes the upper crust of the oceanic side of the sdrs was created by submarine eruptions while the land side of the sdrs was formed by submarian eruptions the vp vs ratios in the middle crust and lower crust are estimated as 1 76 1 78 and 1 80 respectively comparing vp and vsv data from the lower crust to those in previous studies clearly indicates the presence of mafic gneisses this result represents new seismic evidence for the hotspot hypothesis concerning the formation of passive volcanic continental margins clear s wave upper mantle refractions can be observed at offsets of up to 100 km even where p wave arrivals cannot be identified in order to model these s wave arrivals a vs 4 8 km s 1 layer is necessary 2 km below the moho

crustal structure of the northern part of the voring basin mid norway margin from wide angle seismic and gravity data abstract three regional ocean bottom seismograph obs profiles with a total of fifteen recovered obss were acquired in the northern part of the voring basin mid norway margin in 1996 the data have been modelled by inversion and forward modelling of the obs vertical components p waves the velocity is found to increase downwards within the sedimentary layers due to increasing depth of burial confining pressure within the two deepest sedimentary layers there seems to be an increase of 0 5 1 km s in velocity northwestwards this increase is most likely caused by high velocity sill intrusions in the sedimentary rocks emplaced during the rift episode leading to early eocene opening of the ne atlantic the presence of significant amounts of sills seems to terminate close to the nyk high along profile 5 dip profile and close to a dome northwest of the shelf edge along profile 6 dip profile the velocity in the top of this dome is anomalously high 3 4 km s at only 1 km depth beneath the seafloor suggesting that the high consists of volcanic rocks or heavily intruded sedimentary rocks the relatively low velocities derived from within the upper crystalline crust 5 9 6 2 km s confirms that the crust is of continental origin within the lower crust there seems to be a clear increase in velocity northwestwards from about 7 0 km s to about 7 4 km s suggesting that the amount of high velocity intrusions underplating in the lower crust decreases landwards the modelling of the strike profile profile 7 suggests that the transition from a lower crust dominated by magmatic intrusions to a more undisturbed continental lower crust is located approximately beneath this profile the model for profile 7 ties closely southwestwards to the models derived from obs data acquired in 1992 and northeastwards to lofoten obs data acquired in 1988 the models indicate that the thick magmatic intrusions in the sedimentary rocks and lower crust extend further landwards in the area of the 1992 survey and that the transition zone is related to the surt lineament the distribution of magmatic rocks thus seems to correlate strongly with pre breakup structures in addition to the p wave modelling gravity modelling has been performed along all profiles the gravity modelling confirmed all main aspects of the obs models and provided constraints on the crustal structures towards the ends of the profiles

pleistocene water intrusions from the mediterranean and caspian seas into the black sea the hydrological balance of the black sea is governed by riverine input and by the exchange with the mediterranean sea a speleothem record from a cave in northern turkey that tracks the isotopic signature of black sea surface water suggests an open connection to the mediterranean sea in at least twelve periods in the past 670 000 years

anomalous cenozoic subsidence along the passive continental margin from ireland to mid norway two dimensional flexural backstripping and thermal modelling assuming uniform stretching and cooling is applied to four interpreted depth converted seismic profiles across the rockall faroe shetland and voring basins along 1600 km of the atlantic continental margin of nw europe the results reveal a significant discrepancy between the modelled palaeo depths for the base of the cenozoic succession and those proven by geological evidence at control points subaerial conditions or depositional depth ranges in wells the discrepancy is of rm scale much larger than the possible range of parameter error determined by sensitivity tests up to 0 5 km assuming a cretaceous rift episode 100 ma the discrepancy is at least 1 7 km in the rockall basin up to 2 1 km in the faroe shetland basin and at least 1 km in the voring basin which also contains evidence of kilometre scale uplift of the inner margin assuming unproven a second rift in the early cenozoic 60 ma the discrepancy remains of kilometre scale in the rockall and faroe shetland basins the restorations also provide evidence of uplift both above compressive structures and across the modelled profiles as seaward rotations of palaeo bathymetric records the palaeo bathymetric discrepancy corresponds to an anomaly in subsidence that is the cumulative product of all the tectonic episodes that have affected the nw european margin and may incorporate both permanent effects of the last episode of lithospheric extension and transient responses to the interaction of the margin with mantle convective flow any explanation must accommodate both the large magnitude of anomalous subsidence along the margin and evidence of its episodic character

symmetric conjugation of continent ocean boundary structures along the norwegian and east greenland margins abstract a characteristic structural feature of the norwegian continental margin that has been described from multichannel seismic data as well as dsdp and odp drilling is a major buildup of layered extrusive basaltic rocks forming wedges that dip seaward along the entire margin models for their origin describe them as either products of a late stage intra continental rift phenomenon with the volcanic rocks overlying attenuated continental crust or as an integral component of the oceanic crust formed during the first few million years of seafloor spreading in the norwegian greenland sea from studies of the norwegian margin alone it was not possible to unequivocally distinguish between the two proposed models so an investigation of the conjugate portions of the east greenland margin was undertaken which used two ship multichannel seismic acquisition as its focus we found that the wedges were not only present on the east greenland margin but that details of their along strike variability are mirrored on both margins together with their spatial relationship to the oldest magnetic lineation pattern the wedges are relatively small in the northern part of the margin where they occur almost entirely landward of lineation 24 moving south we see that the wedges broaden encroach into the pattern of lineation 24 then develop into two separate wedges the seaward of which is associated with lineation 23 lineations 24 and 23 on both margins are distorted when associated with wedges we believe that these data lend strength to a tectonic association of the wedges with nascent plate boundary processes their observation in many margins throughout the world suggest that a prolific volcanic phase may be commonly associated with the inception of a divergent plate boundary and we believe that the most likely mechanism to generate the excess volcanism is the convective partial melting scheme recently proposed by mutter and buck 1986 and mutter et al in press

radiocarbon dating reservoir effects and calibration abstract we summarize how radiocarbon measurements are made using accelerator mass spectrometry we also discuss some complications inherent in the radiocarbon dating method when calibrating radiocarbon dates to calendar dates for example measurements of radiocarbon 14c in some types of materials are complicated by a reservoir effect caused by an apparent age of the source reservoir that differs from the contemporary atmospheric surface 14c value in other cases mobile carbon sources in nature can produce mixed sources of carbon we explore these effects and discuss their possible implications for 14c measurements and how we can deal with them

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

seismic anisotropy inferred from wide angle reflections off lofoten norway indicative of shear aligned minerals in the upper mantle abstract data from six three component ocean bottom seismographs situated on a 175 km long profile on the continental shelf off lofoten northern norway have been modelled using 2 d seismic ray tracing and p and s wave velocity models for the upper mantle are presented a dipping structure about 10 km below the moho causes strong p and s reflections as well as p to s conversions this upper mantle reflection might be related to a possible seaward dipping master fault and or the presence of partially hydrated peridotite the modelling of these arrivals reveals significant seismic anisotropy in the upper mantle the maximum p wave anisotropy is inferred to be in excess of 15 the maximum s wave anisotropy in the order of 5 10 and the axis of the fast velocity is inferred to be inclined at least 45 from the horizontal the strong anisotropy for p waves indicates that its cause is related to alignment of minerals we postulate that the inferred steep inclination of anisotropic minerals might be a result of shearing along faults and fractures during post caledonian extensional episodes it must be emphasized however that it cannot be excluded that more complicated anisotropic models with other geological implications can also explain the observations satisfactorily the study demonstrates the importance of incorporating s waves in analysis of seismic data because the strong p wave anisotropy would not have been discovered without the constraints given by the s waves

structure of the more basin mid norway continental margin abstract in the more basin offshore mid norway the basis of the cretaceous sequence reaches depths of more than 5000 m the basin is limited on its eastern margin by a system of extensional faults which probably were initiated in the triassic and which were active periodically throughout the aptian the internal basin floor is divided into subbasins by structural highs which are rotated fault blocks presumably rooted in the basement the main structuring of the basin started in late triassic and was followed by accelerating subsidence in the early cretaceous subsidence was interrupted by a mild phase of inversion in the latest cretaceous and a more pronounced inversional phase in the eocene miocene the latter developed folds with wavelengths in the order of kilometers and local low angle reverse faults and the inversion of depocenters

late pleistocene upland stratigraphy of the western delmarva peninsula usa abstract new pedological geological archaeological and geochronological data from the miles point site in eastern maryland are compared with similar data from other nearby sites to develop a framework for interpreting the upland stratigraphy in the western delmarva peninsula our results indicate the presence of two different intervals of loess deposition the earlier loess miles point loess was deposited between 41 and 25 ka a paleosol tilghman soil formed in this loess was initially developed in grasslands and boreal environments during a subsequent period of landscape stability between 25 and 18 ka between 18 and 12 8 ka the miles point loess and the tilghman soil were eroded in many areas as evidenced by diagnostic ca 12 8 ka clovis age artifacts lying unconformably on the tilghman soil cores adjacent to the deep channel area of the chesapeake bay confirm this erosional unconformity prior to 12 7 ka a relatively uniform terminal pleistocene loess paw paw deposited prior to the early archaic period buried clovis age lag artifacts and other archaeological remains older than 13 2 ka stratigraphic evidence from the late pleistocene lower susquehanna river valley suggests that the paw paw loess is the result of eolian redeposition and reworking of non glacial eroded upland sediments that filled the valley between 12 7 and 11 5 ka

black sea lake reservoir age evolution since the last glacial hydrologic and climatic implications abstract chronologies of sediments that document the last glacial history of the black sea lake are hampered by issues relating to reservoir age regulated by basin hydrology reservoir ages represent a tool that could potentially be used to better understand the response of black sea lake hydrology to climate change therefore deciphering reservoir age evolution is crucial both for better constraining the basin chronological framework and for providing new insights into our understanding of black sea lake hydrology by tuning a meaningful new high resolution geochemical dataset obtained from core md04 2790 to a climate reference record here we propose a reliable chronology spanning the last 32 kyr bp the chronology is compared to a large ams radiocarbon dataset n 51 pairs of calendar and radiocarbon ages allowed us to compute reservoir ages and to then reconstruct a high resolution quantitative reservoir age record for the last glacial history of the black sea lake the main factor controlling reservoir ages in lakes is the hard water effect hwe which is regulated by basin hydrology therefore changes in the reconstructed reservoir age record have been qualitatively interpreted in terms of the hydrologic responses of the black sea lake to climate change our results allowed us to determine periods of complete isolation or outflow for the black sea lake during heinrich event 2 he2 and during the last glacial maximum lgm the basin was strictly isolated whereas prior to he2 and during he1 it outflowed into the marmara sea following the onset of the bolling allerod factors other than the hwe are thought to have influenced the reservoir age preventing conclusive interpretations we also determined an undocumented to date phase of black sea lake stratification during the full glacial he2 and lgm our results indicate that reservoir age is a powerful tool for investigating and better understanding past hydrologic changes in lakes and inland seas

convective partial melting 1 a model for the formation of thick basaltic sequences during the initiation of spreading stretching and thinning of continental lithosphere during rifting and initiation of seafloor spreading cause upwelling of mantle rocks into a pressure temperature environment where partial melting occurs the amount of melt liberated is however insufficient to account for the thickness of igneous crust emplaced near the continent ocean boundary at some passive margins these igneous structures are known from seismic reflection and deep refraction studies on numerous passive margins worldwide seismic studies also suggest that the transition from continental to oceanic crust on these volcanic margins is relatively abrupt their evolution apparently does not include a prolonged extensional phase preceding the inception of spreading to account for these observations we propose a model for the generation of partial melt in which the lateral temperature contrasts evoked by rifting and asthenospheric upwelling drive convection in the upper mantle deep hot mantle material is transported upward by the convection and hence much larger volumes flow through the region where partial melting occurs than during passive upwelling numerical calculations show that convective partial melting can provide substantial additions to melting due to passive upwelling alone using this model we propose an evolutionary scheme for volcanic passive margins emphasize the contrast with nonvolcanic margins and describe conditions which might lead to the development of both types

cenozoic subsidence of the outer voring plateau abstract an idea on the subsidence history of the outer voring plateau on the norwegian continental margin is developed through the analysis of high resolution reflection seismic data subsidence of the outer voring plateau began after cessation of the volcanism of the earliest eocene and coastal onlap indicates that initially only the rim of the plateau was affected by subsidence subsidence of the entire outer voring plateau is inferred for the late eocene the plateau is assumed to have ascended in the oligocene when periods of erosion and non deposition took place this trend seems to have continued into the early miocene although at this time the northern part of the outer voring plateau experienced renewed subsidence this subsidence extended to the entire plateau during the middle miocene although the rates of subsidence were variable uniform subsidence began in the late miocene and probably continues today

pre bomb radiocarbon and the reservoir correction for calcareous marine species in the southern ocean four antarctic marine mollusc shells which were collected alive between 1917 and 1940 were analyzed by accelerator mass spectrometry to provide the first pre bomb radiocarbon measurements of biogenic carbonates from the southern ocean after correcting for the impact of fossil fuel combustion suess effect radiocarbon activities of the pre bomb shells averaged 149 8 10 4 in contrast the 14c values for post bomb molluscs echinoderms brachiopods and foraminifera averaged 96 1 25 2 these biogenic carbonate 14c values are nearly identical to pre bomb estimates 148 to 152 and post bomb measurements 98 4 22 0 of the surface waters in the southern ocean average radiocarbon ages of the biogenic carbonates before and after 1950 1303 84 years and 811 205 years respectively along with those from seals and penguins indicate that the antarctic marine radiocarbon reservoir has decreased in age by nearly 500 years during the second half of the 20th century marine species and seawater measurements firmly place the radiocarbon reservoir correction at 1300 100 years for calcareous marine fossils which are widespread abundant and well preserved organic materials for interpreting ice sheet climate and sea level impacts on the antarctic marine ecosystem during the holocene

a complete terrestrial radiocarbon record for 11 2 to 52 8 kyr b p radiocarbon 14c provides a way to date material that contains carbon with an age up to 50 000 years and is also an important tracer of the global carbon cycle however the lack of a comprehensive record reflecting atmospheric 14c prior to 12 5 thousand years before the present kyr b p has limited the application of radiocarbon dating of samples from the last glacial period here we report 14c results from lake suigetsu japan 35 35 n 135 53 e which provide a comprehensive record of terrestrial radiocarbon to the present limit of the 14c method the time scale we present in this work allows direct comparison of lake suigetsu paleoclimatic data with other terrestrial climatic records and gives information on the connection between global atmospheric and regional marine radiocarbon levels

carbon transfer dynamics from bomb 14c and δ13c time series of a laminated stalagmite from sw france modelling and comparison with other stalagmite records twenty two ams 14c measurements have been made on a modern stalagmite from sw france in order to reconstruct the 14c activity history of the calcite deposit annual growth laminae provides a chronology up to 1919 a d results show that the stalagmite 14c activity time series is sensitive to modern atmosphere 14c activity changes such as those produced by the nuclear weapon tests the comparison between the two 14c time series shows that the stalagmite time series is damped its amplitude variation between pre bomb and post bomb values is 75 less and the time delay between the two time series peaks is 16 years 3 a model is developed using atmosphere 14c and 13c data fractionation processes and three soil organic matter components whose mean turnover rates are different the linear correlation coefficient between modeled and measured activities is 0 99 these results combined with two other stalagmite 14c time series already published and compared with local vegetation and climate demonstrate that most of the carbon transfer dynamics are controlled in the soil by soil organic matter degradation rates where vegetation produces debris whose degradation is slow the fraction of old carbon injected in the system increases the observed 14c time series is much more damped and lag time longer than that observed under grassland sites the same mixing model applied on the 13c shows a good agreement r2 0 78 between modeled and measured stalagmite 13c and demonstrates that the suess effect due to fossil fuel combustion in the atmosphere is recorded in the stalagmite but with a damped effect due to som degradation rate the different sources of dead carbon in the seepage water are calculated and discussed

radiocarbon calibration beyond 20 000 14c yr b p by means of planktonic foraminifera of the iberian margin we present a new set of 14c ages obtained by accelerator mass spectrometry ams on planktonic foraminifera from a deep sea core collected off the iberian margin md952042 this site at 37 n is distant from the high latitude zones where 14c reservoir age is large and variable many independent proxies alkenones magnetic susceptibility ice rafted debris foraminifera stable isotopes abundances of foraminifera pollen and dinoflagellates show abrupt changes correlative with dansgaard oeschger and heinrich events of the last glacial period the good stratigraphic agreement of all proxies from the fine to the coarse size fractions indicates that the foraminifera 14c ages are representative of the different sediment fractions to obtain reliable 14c ages of foraminifera beyond 20 000 14c yr b p we leached the shells prior to carbonate hydrolysis and subsequent analysis for a calendar age scale we matched the iberian margin u37k profile with that of greenland summit 18o both are proxies for temperature which in models varies synchronously in the two areas the match creates no spurious jumps in sedimentation rate and requires only a limited number of tie points except for ages older than 40 000 14c yr b p greenland s gisp2 and grip records yield similar calendars the 14c and imported calendar ages of the iberian margin record are then compared to data from lacustrine annual varves and from corals and speleothems dated by u th previously used to extend the calibration beyond 20 000 14c yr b p the new record follows a smooth pattern between 23 000 and 50 000 cal yr b p we find good agreement with the previous data sets between 23 000 and 31 000 cal yr b p in the interval between 33 000 and 41 000 cal yr b p for which previous records disagree by up to 5000 cal yr the iberian margin record closely follows the polynomial curve that was previously defined by an interpolation of the coral ages and runs between the lake suigetsu and the bahamian speleothem data sets

alkali extraction of archaeological and geological charcoal evidence for diagenetic degradation and formation of humic acids charcoal forms a crucial source of archaeological and palaeoenvironmental data providing a record of cultural activities past climatic conditions and a means of chronological control via radiocarbon 14c dating key to this is the perceived resistance of charcoal to post depositional alteration however recent research has highlighted the possibility for alteration and degradation of charcoal in the environment an important aspect of such diagenesis is the potential for addition of exogenous humic acids has to affect the accuracy of archaeological and palaeoenvironmental reconstructions based upon chemical analyses of ha containing charcoal however the release of significant quantities of ha from apparently pristine charcoals raises the question whether some ha could be derived via diagenetic alteration of charcoal itself here we address this question through comparison of freshly produced charcoal with samples from archaeological and geological sites exposed to environmental conditions for millennia using elemental c h o and isotopic 13c measurements fourier transform infrared spectroscopy ftir and proton liquid state nuclear magnetic resonance 1h nmr the results of analyses show that the presence of highly carboxylated and aromatic alkali extractable ha in charcoal from depositional environments can often be attributable to the effects of post depositional processes and that these substances can represent the products of post depositional diagenetic alteration in charcoal

episodic cenozoic tectonism and the development of the nw european passive continental margin the north atlantic margins are archetypally passive yet they have experienced post rift vertical movements of up to kilometre scale the cenozoic history of such movements along the nw european margin from ireland to mid norway is examined by integrating published analyses of uplift and subsidence with higher resolution tectono stratigraphic indicators of relative movements including results from the stratagem project three episodes of epeirogenic movement are identified in the early mid and late cenozoic distinct from at least one phase of compressive tectonism two forms of epeirogenic movement are recognised referred to as tilting coeval subsidence and uplift rotations 1 over distances of 100s of kilometres and sagging strongly differential subsidence rotations up to 4 over distances 100 km each epeirogenic episode involved relatively rapid 10 ma km scale tectonic movements that drove major changes in patterns of sedimentation to find expression in regional unconformity bounded stratigraphic units early cenozoic tilting late paleocene to early eocene c 60 50 ma caused the basinward progradation of shelf slope wedges from elongate uplifts along the inner continental margin and from offshore highs mid cenozoic sagging late eocene to early oligocene c 35 25 ma ended wedge progradation and caused the onset of contourite deposition in deep water basins late cenozoic tilting early pliocene to present 4 0 5 ma again caused the basinward progradation of shelf slope wedges from uplifts along the inner margin including broad dome like features and from offshore highs the early mid and late cenozoic epeirogenic episodes coincided with atlantic plate reorganisations but the observed km scale tectonic movements are too large to be accounted for as flexural deflections due to intra plate stress variations mantle lithosphere interactions are implied but the succession of epeirogenic episodes of differing form are difficult to reconcile with the various syn to post rift mechanisms of permanent and or transient movements proposed in the hypothetical context of a plume beneath iceland the epeirogenic movements can be explained as dynamic topographic responses to changing forms of small scale convective flow in the upper mantle tilting as coeval upwelling and downwelling above an edge driven convection cell sagging as a loss of dynamic support above a former upwelling the inferred cenozoic succession of epeirogenic tilting sagging and tilting is proposed to record the episodic evolution of upper mantle convection during ocean opening a process that may also be the underlying cause of plate reorganisations the postulated episodes of flow reorganisation in the ne atlantic region have testable implications for epeirogenic movements along the adjacent oceanic spreading ridge and conjugate continental margin as well as on other atlantic type passive margins

ventilation of the deep southern ocean and deglacial co2 rise past glacial interglacial increases in the concentration of atmospheric carbon dioxide co2 are thought to arise from the rapid release of co2 sequestered in the deep sea primarily via the southern ocean here we present radiocarbon evidence from the atlantic sector of the southern ocean that strongly supports this hypothesis we show that during the last glacial period deep water circulating around antarctica was more than two times older than today relative to the atmosphere during deglaciation the dissipation of this old and presumably co2 enriched deep water played an important role in the pulsed rise of atmospheric co2 through its variable influence on the upwelling branch of the antarctic overturning circulation

marine radiocarbon reservoir effect along the northern chile southern peru coast 14 24 s throughout the holocene abstract through an extensive sampling and dating of pairs of associated shells and charcoal fragments combined with reanalysis of all the available previous data we reconstruct the evolution throughout the holocene of the regional marine radiocarbon reservoir effect r values along the northern chile southern peru area 14 24 s after elimination of the cases in which the terrestrial component yielded older ages than the marine shells to which they were associated the study is based upon data from 47 pairs of associated marine and terrestrial material our results suggest major changes in both the magnitude and variability range of r during the whole holocene period 1 between 10 400 and 6840 cal yr bp high values 511 278 yr probably result from a strengthened se pacific subtropical anticyclone and shoaling of equatorial subsurface waters during intensified upwelling events 2 between 5180 and 1160 cal yr bp lower values 226 98 yr may reflect a major influence of subtropical water and diminished coastal upwelling processes 3 during the last thousand years high values between 355 105 and 253 207 yr indicate an increased influence of 14 c depleted water masses and of enso for the early twentieth century a r value of 253 207 yr was calculated

ocean bottom seismographs used in a crustal study of an area covered with flood basalt off lofoten n norway seismic refraction measurements were made in august 1988 to study the crustal structure off lofoten northern norway twenty four 3 component ocean bottom seismographs obs were used of which seven were deployed in the area covered by landward flowing basalt deposited during the early eocene break up between norway and greenland the main purpose of the obs survey was to investigate whether this method can be used to map structures below the basalt which is not easy to penetrate with conventional seismic reflection techniques the records obtained showed that the obs data contain considerable information about structures below the flood basalt preopening sediments up to 4 0 km thick is indicated below the 1 0 2 5 km thick landward flowing basalt the success of the obs survey indicates that such measurements can become an important tool in investigations on passive volcanic margins and potentially in other areas where highly reflective boundaries make the reflection technique difficult to apply