changing atmospheric δ14c and the record of deep water paleoventilation ages we propose a new calculation method to better estimate the deep water ventilation age from benthic planktonic foraminifera 14 c ages our study is motivated by the fact that changes in atmospheric 14 c through time can cause contemporary benthic and planktonic foraminifera to have different initial 14 c values this effect can cause spurious ventilation age changes to be interpreted from the geologic data using a new calculation method 14 c projection ages we recalculate the data from the pacific ocean contrary to previous results we find that the pacific intermediate and deep waters were about 600 years older than today at the last glacial maximum in addition there are possible signals of ventilation age change prior to ice sheet melting and at the younger dryas however the data are still too sparse to constrain these ventilation transients

an evaluation of lohmann s foraminifera weight dissolution index down water column traverses of core top weights for three planktonic species confirm lohmann s 1995 relationship between foraminifera shell weight loss and bottom water carbonate ion content however they also suggest that the initial shell thickness varies with growth habitat and that the offset between bottom water and pore water carbonate ion concentration varies even on small space scales

pmc turbo studying gravity wave and instability dynamics in the summer mesosphere using polar mesospheric cloud imaging and profiling from a stratospheric balloon the polar mesospheric cloud turbulence experiment pmc turbo was designed to observe and quantify the dynamics of small scale gravity waves gws and instabilities leading to turbulence in the upper mesosphere during polar summer using instruments aboard a stratospheric balloon the pmc turbo scientific payload comprised seven high resolution cameras and a rayleigh lidar overlapping wide and narrow camera field of views from the balloon altitude of 38 km enabled resolution of features extending from 20 m to 100 km at the pmc layer altitude of 82 km the rayleigh lidar provided profiles of temperature below the pmc altitudes and of the pmcs throughout the flight pmcs were imaged during an 5 9 day flight from esrange sweden to n canada in july 2018 these data reveal sensitivity of the pmcs and the dynamics driving their structure and variability to tropospheric weather and larger scale gws and tides at the pmc altitudes initial results reveal strong modulation of pmc presence and brightness by larger scale waves significant variability in the occurrence of gws and instability dynamics on timescales of hours and a diversity of small scale dynamics leading to instabilities and turbulence at smaller scales at multiple times the overall field of view was dominated by extensive and nearly continuous gws and instabilities at horizontal scales from 2 100 km suggesting sustained turbulence generation and persistence at other times gws were less pronounced and instabilities were localized and or weaker but not absent an overview of the pmc turbo experiment motivations scientific goals and initial results is presented here

slope water current over the laurentian fan on interannual to millennial time scales the strength and position of surface and deep currents in the slope water south of newfoundland are thought to vary as a coupled system in relation to the dipole in atmospheric sea level pressure known as the north atlantic oscillation nao paleoceanographic data from the laurentian fan used as a proxy for sea surface temperature reveal that surface slope waters north of the gulf stream experienced warming during the little ice age of the 16th to 19th centuries and support the notion of an nao driven coupled system the nao may be a useful model for millennial scale ocean variability during interglacial climate states

experimental tests for particle size dependent bioturbation in the deep ocean the potential for particle size dependent bioturbation rates was experimentally tested at 1 240 m in the santa catalina basin eastern pacific spherical glass bead tracers in five size classes 816 17 31 32 62 63 125 and 126 420 m were spread over the sediment surface and tube cored 997 d later downcore concentrations of glass beads were enumerated in each of the five size categories and page s l test was used to test the null hypothesis of equal vertical penetration of all size classes of tracer in all cores the null hypothesis was rejected finer tracers penetrated deeper into the sediment in two of the three cores vertical biodiffusivities were computed from concentration profiles of downcore tracers these also showed size dependence with biodiffusivities ranging from 1 cm2 yr for the 8 1 6 pm fraction to 0 1 cm2 yr for the 1 25 420 pm size class these data demonstrate that vertical bioturbation rates are particle size dependent in santa catalina basin the likely cause is preferential ingestion and downward transport of fine particles by deposit feeders

deglacial radiocarbon history of tropical atlantic thermocline waters absence of co2 reservoir purging signal abstract a current scenario to explain much of the atmospheric co 2 increase during the glacial to holocene climate transition requires the outgassing of a deep old oceanic co 2 reservoir thought to be located in the southern ocean in this scenario co 2 rich and 14 c depleted subsurface antarctic sourced water ventilates the thermocline where it is purged to the atmosphere in the equatorial regions a view that has been met with conflicting results using a novel approach paired surface and deep dwelling planktonic foraminifer radiocarbon analyses we document that the equatorial atlantic thermocline did not see old 14 c depleted water which would be characteristic of the proposed isolated deep ocean co 2 reservoir data from several studies concur that during the deglaciation antarctic intermediate waters were contributing to atlantic thermocline waters even more than today therefore our observations challenge the current purging hypothesis together with other studies these results suggest that the mechanism responsible for the deglacial co 2 rise cannot invoke contemporary circulation modes and or thermocline ventilation pathways

on the horizontal and temporal structure of noctilucent clouds as observed by satellite and lidar at alomar 69n 1 simultaneous and common volume observations of noctilucent clouds nlc and polar mesospheric clouds pmc have been performed above the alomar research station in northern norway 69 n 16 e from ground and space respectively a detailed case study on august 5 2008 shows that the measured particle sizes and t matrix simulations of the optical properties allow to combine the two observation techniques from the ground the observations were performed by lidar sounding of the temporal evolution of the cloud at two locations separated by about 40 km before during and after the coincidence from space the cips instrument onboard the aim satellite observed the horizontal structure of the cloud using mesospheric radar wind measurements at alomar the advection of the cloud particles is calculated and the temporal evolution of the cloud as seen from ground is compared with the horizontal structure observed from satellite this comparison allows estimation of the timescales during which the clouds behave as passive tracers we find that during this case study cloud structures larger than about 5 km 5 km and oscillations slower than about one minute behaved like a passive tracer for up to one hour corresponding to horizontal scales of about 300 km however if the cloud shows wave structures with brightness modulations of 20 microphysical changes might take place on scales of minutes and kilometers

unmixing of stable isotope signals using single specimen δ18o analyses 1 the resolution at which foraminiferal stable isotopes are applied in paleo environmental studies is ever increasing resulting in continuous sampling of sediment cores the resolution of such continuously sampled records depends on the rate of sedimentation of foraminiferal shells in its relation to the intensity of bioturbation bioturbation essentially mixes sediment layers of different age altering the primary climate signal thereby impacting the accuracy of both the timing and magnitude of reconstructed climate changes a new approach to assess and correct the impact of bioturbation is investigated here based on the 18o of individual specimens of planktonic foraminifera globorotalia inflata from a series of boxcore samples in the eastern north atlantic average 18o values decrease southward from 1 62 to 1 07 with the exception of site t86 11 1 35 the 18o distribution of each station can be fitted with a uni to polymodal distribution a nonunimodal distribution strongly suggests admixing of bioturbated individuals quantification of these distributions allows deconvolving the original and bioturbated signals and subsequently provides a correction for bioturbation

the holocene preservation history of equatorial pacific sediments a model of the sediment mixed layer is used to quantify the glacial holocene changes in calcite preservation productivity minus dissolution at water depths that span the transition between lysocline and calcite compensation depth in the equatorial pacific the mean preservation fluxes required by the model to account for the observed changes in sediment composition indicate in most cases that calcite dissolution exceeds supply and that there has been net removal of calcite from surface sediments over the holocene the sediment mixed layer is therefore not at steady state with respect to caco3 fluxes the model is also used to show that an observed increase in the radiocarbon age of the core top sediments with increasing extent of dissolution cannot be explained by chemical erosion of underlying glacial material dissolution taking place at or just below the sediment water interface is the probable cause of this phenomenon

improving temperature estimates derived from mg ca of planktonic foraminifera using x ray computed tomography based dissolution index xdx 1 temperatures derived from mg ca ratios of the calcite tests of planktonic foraminifera are distorted when samples are partially dissolved and methods are required to quantify this source of inaccuracy here we compare a dissolution index xdx based on x ray computed tomography scans to mg ca of four species of foraminifera g ruber white g sacculifer without sac n dutertrei and p obliquiloculata from core top sediments from the tropical pacific atlantic and western indian ocean deepwater calcite saturation values co32 at the sites ranged from 55 to 23 mol kg an estimate of mg ca reduction in mg ca due to dissolution was made for each sample mg ca decreased linearly from deepwater co32 values of between 10 4 and 15 5 mol kg these values are minimum estimates of the threshold below which mg ca is affected by dissolution as they are limited by assumptions made in calculating mg ca sensitivity of mg ca to co32 was greatest for g ruber where mg ca decreased by 0 102 0 036 mmol mol per mol kg sensitivity was similar for g sacculifer 0 047 0 015 mmol mol per mol kg n dutertrei 0 037 0 010 mmol mol per mol kg and p obliquiloculata 0 040 0 008 mmol mol per mol kg sensitivity was similar at all sites for each species excepting an apparently greater response for n dutertrei from the caribbean compared to other sites calibrations between xdx and mg ca provide a means to estimate dissolution bias on mg ca poor correlation between xdx and 18o suggests that for the small sample size typical for analysis variability in initial 18o overwhelms dissolution effects

anomalous radiocarbon ages for foraminifera shells the causes for discordant radiocarbon results on multiple species of planktonic foraminifera from high sedimentation rate marine sediments are investigated we have documented two causes for these anomalous results one is the addition of secondary radiocarbon for which we have to date only one firm example it involves an opal rich sediment the other is the incorporation of reworked material again we have to date only one firm example it involves a rapidly deposited ocean margin sediment however we have three other examples where reworking is the most likely explanation on the basis of this study it is our conclusion that where precise radiocarbon dating of high deposition rate marine sediment is required a prerequisite is to demonstrate that concordant ages can be obtained on pairs of fragile and robust planktic shells for sediment rich in opal it is advisable to check for secondary calcite by comparing ages obtained on acid leached samples with those on unleached samples

radiocarbon age differences between coexisting foraminiferal species radiocarbon age measurements on single species of foraminifera from a core on the ceara rise demonstrate the importance of the joint effect of bioturbation and variable rain abundance of foraminifera the relatively high mixed layer ages for pulleniatina obliquiloculata reflect at least in part an early holocene peak in its abundance while the relatively young ages for globorotalia menardii reflect the delay until mid holocene of its reappearance in the atlantic ocean these results clearly demonstrate that core top sediment samples need not be representative foraminifera falling from today s surface ocean rather at least on the ceara rise such samples consist of a composite of changing species groupings these results also reconfirm the pitfalls associated with attempts to reconstruct the radiocarbon age of deep ocean water on the basis of benthic planktonic foraminiferal age differences

western equatorial pacific deep water carbonate chemistry during the last glacial maximum and deglaciation using planktic foraminiferal mg ca to reconstruct sea surface temperature and seafloor dissolution 1 we present a reconstruction of deep water carbonate saturation state co32 in the western equatorial pacific for the last glacial maximum lgm and deglaciation based on changes in the mg ca ratio of planktic foraminifers with increased water depth our data suggest there have been changes in bottom water co32 over the past 25 000 years at water depths as shallow as 1 6 km the co32 reconstruction for the lgm suggests co32 was similar or slightly higher than modern values between 1 6 and 2 0 km shifting sharply to lower values an average 30 mol kg lower below 2 5 km the shift in chemistry between 2 0 and 2 5 km supports a hypothesis that pacific overturning circulation occurred deeper during the lgm with a slightly more ventilated water mass above 2 0 km the data are not consistent with enhanced preservation in this region of the deep pacific at depths greater than 2 5 km suggesting that the long held view of better preservation throughout the glacial deep pacific must be reevaluated for the deglaciation we have evidence of a co32 maximum that suggests enhanced deglacial preservation between 1 6 and 4 0 km in comparison to the holocene and the lgm the deglacial co32 was as much as 28 mol kg higher than modern between 1 6 and 4 0 km results suggest carbonate burial rates were 1 5 times greater during the deglacial than the over the past 5 kyr

geometric test for late cretaceous paleogene intracontinental transform faulting in the canadian cordillera the tintina trench northern rocky mountain trench tt nrmt fault zone and the fraser river straight creek fr sc fault zone are separate en echelon concentric small circle fault segments of a composite intracontinental transform fault zone more than 2500 km long that cuts diagonally across the canadian cordillera from the outboard part of a tectonic collage of accreted foreign terranes in the south into the north american preaccretionary continental margin in the north most of the 450 km of right hand slip on the tt nrmt fault zone was transformed southward during the late cretaceous and paleocene into oblique convergence in the southern canadian rockies the remainder probably comprising less than 100 km was transformed southwestward during early and middle eocene time via a zone of distributed shear and east west crustal stretching into right hand slip on the en echelon fr sc fault zone these interpretations based on regional systematic mapping of geologic structures are in conflict with interpretations of paleomagnetic measurements that call for more than 1000 km of post mid cretaceous right hand displacement along the general locus of the tt nrmt fault zone involving foreign terranes and the parts of north america to which they had been accreted this paradox must be resolved

recent increase in pacific caco3 dissolution a mechanism for generating old 14c ages abstract western equatorial pacific box cores taken from water depths greater than 4 km show increased dissolution and anomalously old 14c ages in the upper 8 cm the temporal response of the vertical distribution of sediment carbonate fraction and 14c age to a decrease in the dissolved carbonate ion concentration of the deep sea is examined with a diffusion advection dissolution model the nature of this response is highly sensitive to both the magnitude of the dissolved carbonate ion decrease and the rate of mixing of the upper few centimeters of sediment if the sediment is initially calcareous and the increase in undersaturation is sufficient to eventually dissolve away most of the solid carbonate the system relaxes on a very long time scale greater than 10 000 years the dissolution flux in such a case temporally is greater than the total sedimentation input and chemical erosion occurs the cumulative erosion is about 4 times greater for strong sediment mixing d 200 cm 2 ka 1 than for weak mixing d 2 cm2 ka 1 the chemical erosion causes old carbonate to be transferred into the sediment mixed layer as the interface moves downwards thus the 14 c 12 c ratio initially decreases when erosion decreases because the surface carbonate content is diminished the 14c age of the sediment continues to become older in the case of weak mixing but reverses itself and becomes younger in the presence of moderate or strong mixing an attempt to predict the observed caco3 and 14 c 12 c in west equatorial pacific sediment suggests that beginning a few thousand years ago the deep pacific was 20 more undersaturated than today for about 1500 yrs this could possibly have been caused by late holocene growth of coral reefs following after the deglaciation

reconstruction of the last deglaciation deconvolved records of δ18o profiles micropaleontological variations and accelerator mass spectrometric14c dating bioturbation acts as a low pass filter in displacing and reducing the amplitudes of stratigraphic signals this often leads to a loss of high frequency events in the stratigraphic record in addition when considering an isotopic signal 18o 14c measured in stratigraphic carriers such as foraminifera bioturbation and carrier abundance changes can create artifacts which may be falsely interpreted as leads or lags in the paleoclimatic record

chronology for climate change developing age models for the biogeochemical ocean flux study cores we construct age models for a suite of cores from the northeast atlantic ocean by means of accelerator mass spectrometer dating of a key core bofs 5k and correlation with the rest of the suite the effects of bioturbation and foraminiferal species abundance gradients upon the age record are modeled using a simple equation the degree of bioturbation is estimated by comparing modeled profiles with dispersal of the vedde ash layer in core 5k and we find a mixing depth of roughly 8 cm for sand sized material using this value we estimate that age offsets between unbioturbated sediment and some foraminifera species after mixing may be up to 2500 years with lesser effect on fine carbonate 10 mu m ages the bioturbation model illustrates problems associated with the dating of instantaneous events such as ash layers and the heinrich peaks of ice rafted detritus correlations between core 5k and the other cores from the bofs suite are made on the basis of similarities in the downcore profiles of oxygen and carbon isotopes magnetic susceptibility water and carbonate content and via marker horizons in x radiographs and ash beds

how well would modern day oceanic property distributions be known with paleoceanographic like observations author s gebbie g streletz gj spero hj abstract 2016 american geophysical union all rights reserved compilations of paleoceanographic observations for the deep sea now contain a few hundred points along the oceanic margins mid ocean ridges and bathymetric highs where seawater conditions are indirectly recorded in the chemistry of buried benthic foraminiferal shells here we design an idealized experiment to test our predictive ability to reconstruct modern day seawater properties by considering paleoceanographic like data we attempt to reconstruct the known modern day global distributions by using a state estimation method that combines a kinematic tracer transport model with observations that have paleoceanographic characteristics when a modern like suite of observations practical salinity seawater 18o 13cdic po4 no3 and o2 is used from the sparse paleolocations the state estimate is consistent with the withheld data at all depths below 1500 m suggesting that the observational sparsity can be overcome physical features such as the interbasin gradients in deep 13cdic and the vertical structure of atlantic 13cdic are accurately reconstructed the state estimation method extracts useful information from the pointwise observations to infer distributions at the largest oceanic scales at least 10 000 km horizontally and 1500 m vertically and outperforms a standard optimal interpolation technique even though neither dynamical constraints nor constraints from surface boundary fluxes are used when the sparse observations are more realistically restricted to the paleoceanographic proxy observations of 13c 18o and cd ca however the large scale property distributions are no longer recovered coherently at least three more water mass tracers are likely needed at the core sites in order to accurately reconstruct the large scale property distributions of the last glacial maximum

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

the influence of microhabitats on the carbon isotopic composition of deep sea benthic foraminifera we report 13c and 18o values for rose bengal stained benthic foraminifera from a set of box cores from continental margin environments in the atlantic and pacific oceans these isotopic results are compared with foraminiferal distribution data and pore water 13c profiles to evaluate the importance of environmental microhabitat effects on the carbon isotopic composition of benthic foraminifera the 13c values of infaunal taxa are consistently lower than those of epifaunal taxa suggesting that microhabitat effects on test composition do exist the 13c differences between foraminiferal carbonate and bottom water dissolved inorganic carbon are not correlated with the 18o differences between benthic foraminifera tests and equilibrium calcite but they do correlate with variations in the chemistry of sediment pore waters however interspecific 18o differences as well as 13c differences between species with similar vertical distributions in the sediments indicate that taxon specific vital effects also influence test composition

paleomagnetism and tectonic significance of albian and cenomanian turbidites ochoco basin mitchell inlier central oregon 1 understanding continental growth and convergent margin dynamics associated with terrane accretion and modification of the cordilleran margin of north america is prevented by conflicts in paleogeographic models for major terranes oceanic plates and the north american margin we present new paleomagnetic data suggesting that the blue mountains superterrane located at an inboard portion of the cordilleran margin has undergone substantial northward translation and clockwise rotation relative to north america since mid cretaceous time positive baked contact conglomerate and fold tests provide evidence that the magnetization of these rocks dates from their deposition these results yield a mean direction of d 10 8 i 58 5 k 127 95 4 1 and n 11 comparison of magnetic inclinations and magnetic fabrics shows no evidence for inclination error a paleolatitude of 39 2 4 8 4 3 n is obtained indicating a paleolatitude anomaly of 15 9 4 1 northward translation of 1760 460 km and cw rotation of 37 7 3 with respect to north america since circa 93 ma application of an ad hoc 5 inclination error yields translation of 1200 460 km through comparison with other units in the western cordillera we infer that the mitchell inlier was located adjacent to the sierra nevada arc during mid cretaceous time and that the blue mountains province may correlate with the intermontane superterrane in british columbia other interpretations such as large inclination errors or an independent displacement history for the mitchell inlier are possible but unlikely more work is needed to fully test these hypotheses and resolve major questions of cordilleran tectonics

rapid transient changes in northeast atlantic deep water ventilation age across termination i 1 a sequence of accelerator mass spectrometry ams 14c dates performed on benthic and planktonic foraminifera from a northeast atlantic deep sea core md99 2334k 37 48 n 10 10 w 3146 m permit the reconstruction of deep water 14c ventilation ages across the last deglaciation the records from md99 2334k have been placed on the gisp2 timescale via the synchrony of temperature changes recorded in the greenland ice cores and in north atlantic planktonic 18occ calcite 18o on the basis of a range of estimates for past source water 14c this permits the estimation of 14c projection ventilation ages for comparison with benthic planktonic 14c age differences although the accurate estimation of past ventilation ages is precluded by unknown deep water 14c source signatures and by uncertainty regarding the extent of deep water mixing it is clear that deep water ventilation in the northeast atlantic was significantly reduced during the last glaciation increased abruptly coincident with the bolling allerod warming and rapidly became reduced again during the younger dryas cold reversal the character of these changes is consistent with a varying dominance of north atlantic deep water nadw versus antarctic bottom water aabw parallel benthic 13c deep water temperature tdw and deep water 18o 18odw estimates support this inference the fact that deglacial changes in the deep water radiocarbon content of the northeast atlantic run parallel to opposite changes in atmospheric radiocarbon content and in parallel with greenland temperature fluctuations unequivocally implicates changes in ocean circulation in deglacial climate evolution and illustrates the capacity for the deep ocean to respond and contribute to abrupt climate change

millennial scale ice rafting events and hudson strait heinrich like events during the late pliocene and pleistocene a review abstract various types of abrupt millennial scale climate variability such as dansgaard oeschger and heinrich events characterized the last glacial period over the last decade a number of studies demonstrated that such millennial scale climate variability was not limited to the last glacial but inherent to quaternary climate here we review the occurrence and origin of millennial ice rafting events in the north atlantic during the late pliocene and pleistocene last 3 4 ma with a special focus on north atlantic hudson strait hs heinrich like events we show that heinrich layers 5 4 2 and 1 in marine sediment cores from across the north atlantic all bear the organic geochemical fingerprint of the hudson area using this framework and combining previously published results detailed investigations into the organic and inorganic chemistry of ice rafted debris ird found across the north atlantic demonstrate that prior to mis 16 650 ka ird in the north atlantic did not originate from the hudson area of northern canada the signature of this early ird is distinctly different compared to that of hs heinrich layers rather ice rafting events during the late pliocene and early pleistocene predominantly emanated from the calving of the greenland and fennoscandian ice sheets and possibly minor contributions from local ice streams from the north american and british ice sheets compared to north atlantic hs heinrich events these early pleistocene ird events had a limited impact on surface water characteristics in the north atlantic north atlantic hs heinrich like events first occurred during mis 16 at the same time the dominant frequency in silicate rich ird accumulation shifted from the obliquity 41 ka to a 100 ka frequency across the north atlantic iceberg survivability or a change in iceberg trajectory likely did not control this change in ird regime these results lend further support for the existing hypothesis that an increase in size thickness of the laurentide ice sheet controls the occurrence of north atlantic hs heinrich events favoring an internal dynamic mechanism for their occurrence

grain scale deformation and the fold test evaluation of syn folding remagnetization the paleomagnetic fold test examines for pre syn or post folding re magnetization generally passive limb rotation is used to restore folded units to their original position and the position of the fisherian maximum deter mines the relationship between folding and magnetization in a more complete analysis the reorientation of material lines in different fold models is used however the magnetic vec tor should not be considered a material line as it represents the sum of vectors in individual magnetic carriers and does not cross grain boundaries therefore the role of grain scale deformation mechanisms was examined using two end mem bers rigid body rotation spin and homogeneous strain from this study it is concluded that 1 the fisherian maximum will in general occur before complete unfolding 2 the sign of the inclination may change during unfolding and consequently cross over unfolding is not representati ve of syn folding remagnetization 3 statistical analysis will not necessarily produce significant results a number of recommendations are given which include stepwise unfol ding and unplunging should be carried out routinely local rather than regional fold tests should be performed both limbs and the hinge of a single folded layer should be exa mined in order to determine the active deformation mecha

modelling planktic foraminiferal assemblage changes and application to sea surface temperature estimation in the western equatorial pacific ocean abstract calcite dissolution occurring on the sea floor impedes accurate sea surface temperature estimates from planktic foraminiferal assemblage compositions as an attempt to address this issue we devised a mathematical model to study the progressive modifications of species compositions by dissolution and to account for its effect on temperature estimates to calibrate the model planktic foraminiferal compositions and preservation were examined for a bathymetrie transect of samples from the ontong java plateau in the western equatorial pacific ocean along the transect variations in relative abundances of various species show depth related patterns and the preservation of foraminifera decreases with water depth assuming that the population of each foraminiferal species has a bell shaped response curve to dissolution the model numerically dissolves the well preserved shallowest sample to the levels that are indicated by the fragmentation levels of the samples from deeper water depths our results show that the model reproduces the observed depth related abundance variation patterns with remarkable accuracy after calibration the model is able to reconstruct the original species compositions for the samples from water depths above 3500 m by numerically adding back what has been dissolved this reduces the effect of dissolution on the sea surface temperature estimates from about 2 c to about 0 5 c for these samples we observed that the more dissolved samples on the ontong java plateau give higher sea surface temperature estimates a pattern opposite to what is observed in the south china sea we attribute the differing effects of dissolution on temperature estimates to regional differences in foraminiferal faunal compositions

oceanic radiocarbon separation of the natural and bomb components an improved method has been developed for the separation of the natural and bomb components of the radiocarbon in the ocean the improvement involves the use of a very strong correlation between natural radiocarbon and dissolved silica this method is applied to radiocarbon measurements made on samples collected during the geochemical ocean sections study geosecs transient tracers in the ocean tto and south atlantic ventilation experiment save expeditions on the basis of this new separation we provide not only an estimate of the global inventory of bomb 14c at the time of the geosecs survey but also the distribution of bomb radiocarbon along four thermocline isopycnals in each ocean we also document the evolution of the bomb 14c inventory and penetration along thermocline isopycnals in the north atlantic ocean between the times of the geosecs 1972 1973 and tto 1980 1982 surveys and in the south atlantic ocean between the times of the geosecs 1973 and save 1987 1989 surveys in addition we show that the bomb tritium to bomb 14c ratio expressed in the tritium unit tu 81 units 100 for waters entering the thermocline of the northern hemisphere is about 9 times higher than for those entering the southern hemisphere thermocline this contrast offers long term potential as an indicator of inter hemispheric transport of upper ocean waters

paleomagnetism of the methow region north central washington structural application of paleomagnetic data in a complexly deformed variably remagnetized terrane jurassic through paleocene rocks of the methow pasayten belt were studied in order to use paleomagnetic directions to resolve the question of cretaceous northward transport in the end circumstanc

major dextral transcurrent displacements along the northern rocky mountain trench and related lineaments in north central british columbia the northern rocky mountain trench and a number of other prominent lineaments along and east of the eastern margin of the intermontane belt mark faults along which dextral transcurrent movements have been dominant offsets of shelf to off shelf facies boundaries in lower paleozoic rocks indicate a cumulative displacement of at least 750 km and probably 900 km within the system of faults related to those in the northern rocky mountain and the tintina trenches farther west another system of faults appears to offset plutons and stratigraphic assemblages along the eastern margin of the intermontane belt by as much as 300 km these faults including the kutcho and the pinchi connect in part with the teslin suture zone in yukon territory and probably with the fraser river straight creek fault zone in southern british columbia although dextral transcurrent faulting may have taken place between the middle jurassic and early cenozoic the most convincing evidence points to middle cretaceous and particularly to early cenozoic eocene displacements the eocene movements were temporally related to plutonism volcanism lamprophyre dike emplacement high heat flow sedimentation in grabens and rapid uplift of northwesterly trending elongate ranges climactic episodes of granite emplacement particularly in and near the northern omineca crystalline belt at 100 m y 70 m y and 50 m y ago may have been facilitated by changes from dominantly compressional to dominantly transcurrent and related tensional strain

radiocarbon and stable isotope constraints on last glacial maximum and younger dryas ventilation in the western north atlantic 1 foraminiferal abundance 14c ventilation ages and stable isotope ratios in cores from high deposition rate locations in the western subtropical north atlantic are used to infer changes in ocean and climate during the younger dryas yd and last glacial maximum lgm the 18o of the surface dwelling planktonic foram globigerinoides ruber records the present day decrease in surface temperature sst of 4 c from gulf stream waters to the northeastern bermuda rise if during the lgm the modern 18o salinity relationship was maintained this sst contrast was reduced to 2 c with lgm to interglacial 18o changes of at least 2 2 ssts in the western subtropical gyre may have been as much as 5 c colder above 2 3 km glacial 13c was higher than today consistent with nutrient depleted younger bottom waters as identified previously below that 13c decreased continually to 0 5 about equal to the lowest lgm 13c in the north pacific ocean seven pairs of benthic and planktonic foraminiferal 14c dates from cores 2 5 km deep differ by 1100 340 years with a maximum apparent ventilation age of 1500 years at 4250 m and at 4700 m apparent ventilation ages are presently unavailable for the lgm 2 5 km because of problems with reworking on the continental slope when sea level was low because lgm 13c is about the same in the deep north atlantic and the deep north pacific and because the oldest apparent ventilation ages in the lgm north atlantic are the same as the north pacific today it is possible that the same water mass probably of southern origin flowed deep within each basin during the lgm very early in the yd dated here at 11 25 0 25 n 10 conventional 14c kyr bp equal to 12 9 calendar kyr bp apparent ventilation ages 2 3 km water depth were about the same as north atlantic deep water today below 2 3 km four yd pairs average 1030 400 years the oldest apparent ventilation age for the yd is 1600 years at 4250 m this strong contrast in ventilation which indicates a front between water masses of very different origin is similar to glacial profiles of nutrient like proxies this suggests that the lgm and yd modes of ocean circulation were the same

polar mesospheric cloud structures observed from the cloud imaging and particle size experiment on the aeronomy of ice in the mesosphere spacecraft atmospheric gravity waves as drivers for longitudinal variability in polar mesospheric cloud occurrence patterns and structures in polar mesospheric clouds pmcs around the summertime mesopause region which are qualitatively similar to structures seen in noctilucent clouds nlcs from ground based photographs the structures in pmc are generally considered to be manifestations ofupward propagating atmospheric gravity waves agws variability of agw effects on pmc reported at several lidar sites has led to the notion of longitudinal differences in this relationship this studycompares thelongitudinal variability in thecips observed wave occurrence frequency with cips measured pmc occurrence frequency and albedo along with mesospheric temperatures measured by the sounding of the atmosphere using broadband emission radiometry instrument on board the thermosphere ionosphere mesosphere energetics and dynamics spacecraft our results for the latitude ranges between 70 and 80 show a distinct anticorrelation of wave structures with cloud occurrence frequency and correlations with temperature perturbations for at least two of the four seasons analyzed supporting the idea of gravity wave induced cloud sublimation the locations of the observed wave events show regions of high wave activity in both hemispheres in the northern hemisphere while the longitudinal variability in observed wave structures show changes from the 2007 2008 seasons there exist regions of both low and high wave activities common to the two seasons these persistent features may explain some of the observed differences in pmc activity reported by ground based lidar instruments distributed at different longitudes the statistical distribution of horizontal scales increases with wavelength up to at least 250 km we also discuss the possibility of atmospheric tides especially the nonmigrating semidiurnal tide aliasing our observations and affecting the results presented in this analysis

remagnetization during cretaceous normal superchron in eastern san juan islands wa implications for tectonic history abstract the eastern san juan islands expose an island arc ophiolite sequence and one or more ocean floor terranes cover rocks of the former including red radiolarian tuff and arc derived sandstone have no penetrative fabric and lack high pressure minerals in contrast pillow basalts and ribbon cherts of the latter are strongly deformed and the overlying metagraywacke is folded with a penetrative axial plane cleavage all ocean floor rocks have aragonite in veins indicative of higher pressure conditions than experienced by the island arc rocks a downward magnetization is common to the ocean floor rocks consistent with widespread remagnetization during the cretaceous normal superchron this magnetization is carried by magnetite and in red rocks by hematite fluid flow during or after deformation and high p metamorphism likely facilitated remagnetization at low temperature the magnetic directions are somewhat scattered but most are moderately to steeply down to the southeast they are far from directions expected with or without northward transport of baja bc rotation of observed directions into agreement with those expected for either present or more southerly locations also rotate structural elements in the host rocks three alternative rotation histories explored here all produce structural reconstructions that differ considerably from the present structure a tectonic history of the eastern san juan islands based on any of these reconstructions would be superior to one based on present attitudes of structures this is because at least a constraint that the restored paleomagnetic directions match a paleomagnetic field direction is satisfied choices among alternative reconstructions would become clearer with better understanding of relative ages of specific structures and their magnetizations improved geologic understanding of the regional setting where the rocks could have been deformed and remagnetized would also help

the release of 14 c depleted carbon from the deep ocean during the last deglaciation evidence from the arabian sea article i nfo during the last deglaciation the concentration of co2 in the atmosphere increased and the radiocarbon activity 14 c of the atmosphere declined in two steps corresponding in timing to heinrich stadial 1 and the younger dryas these changes have been attributed to the redistribution of 14 c depleted carbon from the deep ocean into the upper ocean and atmosphere recently reconstructions of 14 c in intermediate waters of the eastern tropical pacific have revealed pulses of very old water during the deglaciation consistent with the release of 14 c depleted carbon from the deep ocean at this time here we present reconstructions of intermediate water 14 c from the northern arabian sea near the coast of oman these reconstructions record significant aging of intermediate waters in the arabian sea during heinrich stadial 1 and to a lesser extent during the younger dryas the timing and magnitude of 14 c depletion in the arabian sea during heinrich stadial 1 is very similar to that previously observed in the eastern north pacific near baja california indicating that similar mechanisms were involved in controlling 14 c at these two sites the most parsimonious explanation of the 14 c records from the arabian sea and baja california remains the release of 14 c depleted carbon from the deep ocean by renewal of upwelling and mixing in the southern ocean these

search for a glacial age 14c depleted ocean reservoir 1 measurements of the radiocarbon age difference between mixed benthic foraminifera and several coexisting planktic entities were made in hopes of finding evidence for the existence of an isolated glacial age abyssal ocean reservoir whose demise would explain the large drops in the 14 c to c ratio in atmosphere and surface ocean carbon which occurred during the period of deglaciation forty six new radiocarbon results were obtained at seven depths covering the full range of glacial time i e 27 to 15 14 c kyrs from an equatorial pacific sediment core at 4 4 km water depth even though age reversals for foraminifera but not for coccoliths at two of the eight depths and large age differences between g sacculifer and three submixed layer planktic species mar this data set there remains little likelihood that such a reservoir existed

decade time scale variability of ventilation in the north atlantic high precision measurements of bomb radiocarbon in banded corals the first high precision radiocarbon measurements for the upper ocean are presented for banded corals from two sites in the north atlantic ocean the striking dissimilarities between the post 1950 records at bermuda in the sargasso sea and the florida straits in the gulf stream illustrate the different mixing processes in the upper ocean at each site convective overturn associated with 18 degree water formation during late winter in the northern sargasso sea facilitates storage of considerable quantities of bomb radiocarbon at depth which accounts for the damping of the 14c signal at bermuda during the 1960s a multibox isopycnal mixing model is used to estimate the ventilation rate of the upper 700 m of the water column in the sargasso sea from 1950 to 1983 an inverse model is used that is the water mass renewal rate was calculated for the post bomb period in order to satisfy the bomb radiocarbon time history in the corals sea water radiocarbon measurements made during the geosecs 1972 1973 and transient tracers in the ocean 1980 1981 surveys are used to constrain the subsurface radiocarbon values calculated by the model results show that the rate of water mass renewal in the sargasso sea was high during 1963 1964 decreased during the late 1960s and remained low during most of the 1970s the 14c derived record of water mass renewal precedes by about 4 years that derived from isopycnal salinity in the sargasso sea jenkins 1982 illustrating that the coral 14c record is controlled to a large extent by changes in ocean circulation rather than by atmospheric exchange of co2

millennial scale climate variability in the subpolar north atlantic ocean during the late pliocene 1 large amplitude millennial scale climate oscillations have been identified in late pleistocene climate archives from around the world these oscillations appear to be of larger amplitude during times of enlarged ice sheets this observation suggests the existence of a relationship between large amplitude millennial variations in climate and extreme glacial conditions and therefore that the emergence of millennial scale climate variability may be linked to the pliocene intensification of northern hemisphere glaciation inhg here we test this hypothesis using new late pliocene high resolution 400 year records of ice rafted debris deposition and stable isotopes in planktic foraminiferal calcite globigerinoides ruber generated from integrated ocean drilling program site u1313 in the subpolar north atlantic a reoccupation of the classic deep sea drilling project site 607 our records span marine oxygen isotope stages mis 103 95 2600 to 2400 ka the first interval during inhg 3 5 to 2 5 ma in which large amplitude glacial interglacial cycles and inferred sea level changes occur our records reveal small amplitude variability at periodicities of 1 8 to 6 2 kyr that prevails regardless of inter glacial state with no significant amplification during the glacials mis 100 98 and 96 these findings imply that the threshold for the amplification of such variability to the proportions seen in the marine archive of the last glacial was not crossed during the late pliocene and in view of all available data likely not until the mid pleistocene transition

paleomagnetism of the upper cretaceous strata of mount tatlow evidence for 3000 km of northward displacement of the eastern coast belt british columbia this study contributes the first paleomagnetic data from dated cretaceous units of the coast belt 51 3 n 123 8 w in which paleohorizontal bedding surfaces can be identified with certainty we sampled 38 sites through a 1 5 km stratigraphic interval of cenomanian silverquick sedimentary strata and cenomanian to campanian powell creek volcanics in the tatlow syncline in the tyaughton methow basin magnetizations at 21 sites have high unblocking temperatures tub and pass the tilt test precision k 5 before untilting maximum k 48 after 100 untilting magnetic minerals of volcanics show original textures mean declinations in volcanic and sedimentary rocks are statistically identical and polarity is consistently normal the mean inclination 55 4 3 4 probability p 0 05 of this pretilting magnetization is 20 1 4 0 shallower than that expected if the rocks were deposited in their present position relative to cratonic north america field and laboratory observations rule out other causes for these anomalous shallow inclinations these rocks therefore have been displaced northward by 3000 500 km relative to cratonic north america since mid cretaceous time this displacement is almost 3 times greater than that estimated from mid cretaceous volcanics in the now adjacent intermontane belt evidently the two belts were not amalgamated until latest cretaceous or early tertiary time these results are inconsistent with all previous geologically based tectonic reconstructions of the cordillera magnetizations at eight sites in silverquick and powell creek beds have low tub and directional characteristics similar to those in three younger diorite intrusions reversed and normal polarities occur the rocks are commonly highly altered and maximum precision occurs after 40 untilting the magnetizations therefore are interpreted as overprints of latest cretaceous age acquired during folding

paleomagnetic evidence for displacement from the south of the coast plutonic complex british columbia the mid cretaceous spuzzum and porteau plutons of the coast plutonic complex of british columbia have two magnetizations a and b the a magnetization eight sites 83 specimens d 30 3 i 56 7 95 4 9 paleolatitude 37 5 n paleopole 65 0 n 14 9 w a95 6 2 is considered to have been acquired in the age range 105 90 ma this result differs from the field established for cratonic north america in this time range the difference could be caused either by previously undetected tilting about a horizontal axis of the plutons or by their rotation about a vertical axis and lateral displacement relative to the craton previously observed mid cretaceous magnetizations from other rock units from the western canadian cordillera and the cascades of washington united states are similarly discordant with respect to the craton this similarity over such a large area indicates that although local undetected tilting could be partly responsible it is unlikely to be the prime cause and we argue ther

cretaceous paleomagnetism of the methow pasayten belt washington detailed demagnetization experiments isolated a characteristic remanent magnetization in ten stable sites from the upper cretaceous winthrop and midnight peak formations in the methow pasayten belt of north central washington this remanence agrees best between opposite limbs of a fold the goat peak syncline when corrected for 46 of tilt this is consistent with magnetization acquired during deformation synfolding magnetization may have been facilitated by a thermo chemical event associated with synkinematic intrusions along the axis of folding the mean direction d 12 0 i 61 1 alpha 95 4 8 is highly discordant with respect to the expected direction for north central washington this discordance points to about 1 400 km of poleward transport and 48 of clockwise rotation between 93 and 45 48 ma

a possible 20th century slowdown of southern ocean deep water formation chlorofluorocarbon 11 inventories for the deep southern ocean appear to confirm physical oceanographic and geochemical studies in the southern ocean which suggest that no more than 5 x 10 6 cubic meters per second of ventilated deep water is currently being produced this result conflicts with conclusions based on the distributions of the carbon 14 carbon ratio and a quasi conservative property po 4 in the deep sea which seem to require an average of about 15 x 10 6 cubic meters per second of southern ocean deep ventilation over about the past 800 years a major reduction in southern ocean deep water production during the 20th century from high rates during the little ice age may explain this apparent discordance if this is true a seesawing of deep water production between the northern atlantic and southern oceans may lie at the heart of the 1500 year ice rafting cycle

post folding remagnetization that passes the fold test summary the palaeomagnetism of folded cretaceous redbeds in the methow pasayten belt of washington was studied in an attempt to resolve the tilt versus translation origin of shallow inclinations found in most cretaceous plutonic rocks of the pacific northwest after elimination of results from apparently strained overturned beds correction to palaeohorizontal of the high temperature dominant components produced two distinct directions one from each of two areas treated separately the magnetizations from these two areas appear to pass the fold test both directions are anomalously shallow which is typical of the region but the discrepancy between them casts doubt that both could have been acquired when the strata were horizontal instead we propose that they date from at least two episodes of remagnetization after the planar strata were tilted but before development of the tighter folds observed today our caution is that a positive fold test only establishes that a magnetization likely was acquired when strata in an area were planar other arguments are required to demonstrate that this planar surface was in fact horizontal during magnetization

remanence rotation due to rock strain during folding and the stepwise application of the fold test numerical modeling was conducted to determine the effects of simple models of folding strain on prefolding fisherian distributions of magnetization i found that the constant volume simple shear associated with flexural slip flexural flow folding can rotate a prefolding magnetization to have a maximum precision parameter k value at partial unfolding and thus appear to be synfolding in age if the magnetization is treated as a passive line marker this behavior only occurs for steep initial magnetizations the initial homogeneity of the fisherian precision parameters from each limb is degraded by this type of deformation and may be used to detect a strain modified remanence if the magnetization is carried by rigid mechanically active ellipsoidal or spherical particles a maximum k value at partial unfolding will occur for any initial inclination with the special case that rigid spheres will be rotated to cause a maximum k value at 50 unfolding for any initial inclination homogeneity of limb precisions is not affected in this case a discontinuous model of strain during folding in which pressure solution removes material at an axial planar spaced cleavage and causes limb dips steeper than bedding dips could also produce a maximum k value at partial unfolding strain and remanence studies of flexural slip folding in the allentown formation dolomite and the bloomsburg formation red sandstones and mudstones suggest that 1 the rigid grain model may be a more realistic model of magnetic particle behavior during shear strain and 2 about one quarter to one third of the theoretically predicted simple shear strain occurs in these rocks this amount of strain cannot explain the synfolding behavior observed in the allentown formation but could explain the maximum k values at 80 90 unfolding seen in the bloomsburg formation and perhaps other appalachian clastic rocks

bioturbation artifacts in zero age sediments 1 most seafloor sediments are dated with radiocarbon and the sediment is assumed to be zero age modern when the signal of atmospheric testing of nuclear weapons is present fraction modern fm 1 using a simple mass balance we show that even with fm 1 half of the planktonic foraminifera at the seafloor can be centuries old because of bioturbation this calculation and data from four core sites in the western north atlantic indicate that first during some part of the little ice age lia there may have been more antarctic bottom water than today in the deep western north atlantic alternatively bioturbation may have introduced much older benthic foraminifera into surface sediments second paleo based warming of sargasso sea surface waters since the lia must lag the actual warming because of bioturbation of older and colder foraminifera

comment on paleomagnetism of the upper cretaceous strata of mount tatlow evidence for 3000 km of northward displacement of the eastern coast belt british columbia by p j wynne et al and on paleomagnetism of the spences bridge group and northward

separating natural and bomb produced radiocarbon in the ocean the potential alkalinity method alkalinity method provides an estimate of surface ocean prebomb d 14 c concentrations predictions with the technique appear to be unbiased and have uncertainties which are less than previous techniques index terms 4860 oceanography biological and chemical radioactivity and radioisotopes 4894 oceanography biological and chemical instruments and techniques

enhanced sedimentation along the equator in the western pacific measurements on cores from the ontong java plateau demonstrate that on equator sediment accumulates more 230th than is produced in the overlying water column in contrast cores from 3 8 n accumulate an amount of excess 230th more nearly equal to that produced in the overlying water column taken together with the observation that both the caco3 and non caco3 components of the sediment accumulate at approximately twice the rate in on equator than in off equator cores broecker et al 1999 this requires either that the rain of the larger amount of organic matter generated above the equatorial upwelling plume entrains excess clay and 230th during its fall to the sea floor or that physical transport processes either in the upper ocean or near the sea bed redistribute sediments in such a way that they preferentially accumulate in a narrow 1 latitude equatorial centered belt

the correlation of magnetic anisotropy with strain in the chelmsford formation of the sudbury basin ontario abstract a quantitative correlation has been established between finite strain and the anisotropy of magnetic susceptibility ams in sandstones of the precambrian chelmsford formation of the sudbury basin ontario investigations of the progressive acquisition of isothermal remanent magnetization and its destruction with reverse field and thermal demagnetization as well as microscopic examination of polished thin sections show that both pyrrhotite and magnetite are present in the sandstone measurements of the ams have been carried out at 16 sites distributed throughout the chelmsford formation outcrop considerable variation in the shapes of the magnetic susceptibility ellipsoids axes k max k int k min exists within each site with the k max and k int axes contained in the cleavage planes where developed the magnitudes of the magnetic susceptibility axes have been quantitatively correlated with strain measurements carried out by clendenen et al this issue two different strain to magnetics correlations have been carried out between the site mean strain determined using deformed concretions and the mean values of the ams at each site and between individual specimen strain values determined at the microscopic scale and the individual specimen ams in both cases separate correlations were made between strain long intermediate and short axes and their corresponding magnetic k max k int and k min axes at 10 sites the site mean strain values were derived from strain analysis of the concretions and at an additional 6 sites the site mean strain values were derived from the ams to strain correlation 527 individual cores were converted to equivalent strain values using the ams structural correlation of individual specimens this study extends the use of ams methods to include strain determination in sandstones and provides an order of magnitude increase in the available number of such data for further structural analysis

horizontal winds derived from the polar mesospheric cloud images as observed by the cips instrument on the aim satellite a cloud pattern matching technique is applied to polar mesospheric cloud pmc images taken by the cloud imaging and particle size instrument cips to infer the wind velocities in the mesopause region cips measurements are analyzed to detect patterns that repeat from one orbit to the next but are displaced in location the displacement provides a measure of the wind velocity pattern matching is achieved by resampling the cips data to longitude and latitude grids with the grid box size forced at 5 km in both directions the correlated patterns are searched within a geographic region referred to as a frame of 500 km in longitude 400 km in latitude the histograms of the derived velocities indicate that easterly winds prevail with a mean zonal wind of 20 to 15 m s mean meridional winds are overall small but in late summer the histogram indicated a poleward wind of 20 30 m s the variability of cips cloud albedo on consecutive orbits is also examined at fixed geolocations the statistical results suggest that 86 of pairs underwent mean cloud albedo variation of 50 on consecutive orbits suggesting a moderate change it is also found that the correlation of the cloud structures between two consecutive orbits at a fixed location is generally poor these findings suggest that cloud patterns are subject to wind advection but the cloud patches are more extended in size than the movement that occurs cloud voids are found to be more likely to remain at the same geolocations

radiocarbon age offsets of foraminifera resulting from differential dissolution and fragmentation within the sedimentary bioturbated zone 1 shells of coexisting species of planktonic foraminifera from the ontong java plateau reveal radiocarbon age offsets of up to 2200 years similar offsets are found between fragments and whole shells of single species steady state modelling of dissolution and bioturbation within the sedimentary mixed layer predicts age differences of up to several kiloyears due to the interplay between differential dissolution and fragmentation of foraminifer shells and bioturbation the observation that fragile foraminiferal shells are systematically older than those of more robust species is more difficult to explain mechanisms of chemical erosion interface dissolution and sediment redistribution are all apparently unable to explain this phenomenon a possible solution is presented in which a particular species may be represented by two distinct classes of shells which are more or less robust in this case differential dissolution and fragmentation causes an increase in the mean age as the fragile class contributes less to the remaining intact shells this study highlights the vulnerability of low sedimentation rate cores to the effects of dissolution and bioturbation

spatial and temporal offsets between proxy records in a sediment drift chronologies for late quaternary marine sediment records are usually based on radiocarbon ages of planktonic foraminifera signals carried by other sedimentary components measured in parallel can provide complementary paleoclimate information a key premise is that microfossils and other indicators within a given sediment horizon are of equal age we show here that haptophyte derived alkenones isolated from bermuda rise drift sediments are up to 7000 years older than coexisting planktonic foraminifera this temporal offset which is apparently due to lateral transport of alkenones on fine grained particles from the nova scotian margin markedly influences molecular estimates of sea surface temperatures more broadly the observation raises questions about both the temporal and the geographic fidelity of paleoenvironmental records encoded by readily transported components of sediments

syntectonic remagnetization in the southern methow block resolving large displacements in the southern canadian cordillera 1 the upper cretaceous ventura member of the goat wall unit in the southern methow block of southern british columbia and northern washington state holds a syntectonic magnetization eight new sites from manning park in british columbia give a mean direction of d 27 5 i 60 1 k 304 7 95 3 2 after optimal partial tilt correction of five groups of bedded sites from farther south in the basin reported by bazard et al 1990 four have a syntectonic remanence with a direction similar to what we observe the exception is one group which has optimal concentration of remanence directions on 100 untilting and an abherent direction which must be rejected combining the accepted sites the optimal differential syntilting direction is d 11 8 i 61 5 k 39 3 95 3 4 n 47 giving a mean pole of 79 8 n 359 2 e k 19 5 and a95 4 8 the age of the remagnetization is constrained to be between 88 and 80 ma compared to cratonic north america this result indicates that the southern methow block was displaced from the south by 1800 500 km meaning it lay south of the sierra nevada subduction zone but well north of other paleomagnetically constrained cretaceous rock units from the insular superterrane including correlative strata of the mount tatlow area in the northern methow block among several possibilities to reconcile this discrepancy the most plausible has the whole methow block translated coherently but with the southern methow block strata remagnetized during transit

reply to comment on paleomagnetism of the upper cretaceous strata of mount tatlow evidence for 3000 km of northward displacement of the eastern coast belt british columbia by p j wynne et al and on paleomagnetism of the spences bridge group and northward displacement of the intermontane belt british columbia a second look by e irving et al

the chronology of the last deglaciation implications to the cause of the younger dryas event it has long been recognized that the transition from the last glacial to the present interglacial was punctuated by a brief and intense return to cold conditions this extraordinary event referred to by european palynologists as the younger dryas was centered in the northern atlantic basin evidence is accumulating that it may have been initiated and terminated by changes in the mode of operation of the northern atlantic ocean further it appears that these mode changes may have been triggered by diversions of glacial meltwater between the mississippi river and the st lawrence river drainage systems we report here accelerator mass spectrometry ams radiocarbon results on two strategically located deep sea cores one provides a chronology for surface water temperatures in the northern atlantic and the other for the meltwater discharge from the mississippi river our objective in obtaining these results was to strengthen our ability to correlate the air temperature history for the northern atlantic basin with the meltwater history for the laurentian ice sheet

cretaceous sedimentation and tectonics tyaughton methow basin southwestern british columbia the mesozoic tyaughton methow basin straddles the fraser yalakom pasayten straight creek fypsc strike slip fault zone between six tectono stratigraphic terranes in southwestern british columbia data from hauterivian cenomanian basin fill provide constraints for reconstruction of fault displacement and paleogeography the early cretaceous eastern margin of the basin was a region of uplifted jurassic plutons and active intermediate volcanism detritus shed southwestward from that margin was deposited as the marine jackass mountain group albian inner to mid fan facies of the jackass mountain group can be correlated across the yalakom fault suggesting 150 25 km of post albian dextral offset deposits of the jackass mountain group overlap the major strike slip zone fypsc if that zone represents the eastern boundary of the tectono stratigraphic terrane wrangellia then accretion of wrangellia to terranes to the east occurred before late early cretaceous time the western margin of the basin first b

core top 14c ages as a function of latitude and water depth on the ontong java plateau radiocarbon measurements on core tops from the ontong java plateau confirm a previous finding by berger and killingley 1982 that at any given water depth cores taken on the equator have higher accumulation rates and younger core top ages than their off equator counterparts further these new results fortify the conclusion by broecker et al 1991 that the increase in core top radiocarbon age with water depth rules out homogeneous dissolution within the pore waters as the dominant mechanism either most of the dissolution must occur prior to burial or it must occur during the first pass through the respiration co2 rich upper pore waters after which the calcite grains become armored against further dissolution a puzzling aspect of this new data set is that despite the sizable difference in accumulation rate the extent of dissolution as measured by either the caco3 content or the ratio of caco3 in the 150 m size fraction to that in the 63 m fraction is no different off than on the equator in order to reconcile the results of this study with those obtained by hales and emerson 1996 using in situ electrodes it is necessary to call upon calcite armoring

ventilation of the glacial deep pacific ocean measurements of the age difference between coexisting benthic and planktic foraminifera from western equatorial pacific deep sea cores suggest that during peak glacial time the radiocarbon age of water at 2 kilometers depth was no greater than that of today these results make unlikely suggestions that a slowdown in deep ocean ventilation was responsible for a sizable fraction of the increase of the ratio of carbon 14 14c to carbon in the atmosphere and surface ocean during glacial time comparison of 14c ages for coexisting wood and planktic foraminifera from the same site suggests that the atmosphere to surface ocean 14c to c ratio difference was not substantially different from today s

the influence of caco3 dissolution on core top radiocarbon ages for deep sea sediments radiocarbon ages on caco3 from deep sea cores offer constraints on the nature of the caco3 dissolution process the idea is that the toll taken by dissolution on grains within the core top bioturbation zone should be in proportion to their time of residence in this zone if so dissolution would shift the mass distribution in favor of younger grains thereby reducing the mean radiocarbon age for the grain ensemble we have searched in vain for evidence supporting the existence of such an age reduction instead we find that for water depths of more than 4 km in the tropical pacific the radiocarbon age increases with the extent of dissolution we can find no satisfactory steady state explanation and are forced to conclude that this increase must be the result of chemical erosion the idea is that during the holocene the rate of dissolution of caco3 has exceeded the rain rate of caco3 in this circumstance bioturbation exhumes caco3 from the underlying glacial sediment and mixes it with caco3 raining from the sea surface

spatial and temporal relations between early tertiary shortening and extension in nw washington based on geology of the pipestone canyon formation and surrounding rocks detailed mapping of the deformed paleocene pipestone canyon formation and surrounding cretaceous rocks in nw washington suggests that uplift erosion and unroofing of adjacent rocks was influenced by shortening at high angle to the continental margin during mid cretaceous circa 88 110 ma and early tertiary 47 65 ma time although significant shortening is mid cretaceous in age additional shortening expressed as reverse faults and major folds is early tertiary in the map area and regions to the west and northwest the skagit methow western okanogan area the shortening is essentially unmodified by extensional deformation whereas in regions east and northeast of the map area the omineca and eastern okanogan regions widespread eocene extension has obscured the shortening and caused additional unroofing as well the conglomeratic pipestone canyon formation lies unconformably on intruded early cretaceous rocks of the lower methow sequence approximately 3 5 km of mid cretaceous methow sequence strata are missing at the unconformity yet are present 15 km to the west and northwest these observations indicate late cretaceous erosion and unroofing in the southeastern methow area prior to deposition of the pipestone canyon formation furthermore conglomerate clasts in the pipestone canyon formation record sources resulting from relative uplift of the crystalline okanogan complex east of the basin and slightly later from relative uplift of the volcano sedimentary methow sequence and structurally underlying migmatitic skagit complex west to northwest of the basin following deposition which ended sometime between 55 and 65 ma the pipestone canyon formation and underlying methow sequence were tightly folded and faulted and juxtaposed with the okanogan complex by reverse faulting the map pattern of these folds and faults suggests ene wsw shortening and concomitant uplift crosscutting relations north of the map area constrain this deformation to be pre 47 ma similarity of pipestone canyon fold geometry to folds elsewhere in the methow and skagit areas supports the interpretation that a significant fold belt of circa 47 65 ma age developed in these areas and overprinted the mid cretaceous folding and thrusting regional data suggest the circa 47 65 ma folding formed a synclinorium in the methow area and an anticlinorium in the skagit area roughly concurrent with cooling ages for deep 8 9 kbar skagit rocks for the skagit methow western okanogan region as a whole the 47 65 ma shortening and unroofing were accompanied by uncertain amounts of fold belt parallel strike slip faulting timing estimates for shortening in the skagit methow western okanogan area are generally older but overlap with those established for extension farther east and northeast in the okanogan complex and omineca belt supporting interpretations that the belt of extension began to develop during or very soon after regional shortening existing thermal rheological models of extension immediately after shortening point to the need for heat sources other than mantle conduction and crustal radioactivity to facilitate the extension apparently the skagit methow fold belt failed to extend because it lacked the necessary heat

paleomagnetism and tectonics of the cretaceous mt stuart batholith of washington translation or tilt abstract the mt stuart batholith is a composite pluton of late cretaceous age that intrudes the crystalline north cascades terrane of northwestern washington its paleomagnetic direction d 10 0 i 45 5 95 4 9 is markedly different from the direction expected for cretaceous rocks from northwestern washington d 330 5 i 73 0 which means that the mt stuart batholith either has moved relative to the north american interior or has been tilted through a substantial angle or both since it acquired its magnetism either tilt or translation are possible geometrically but translation is more likely because 1 local geology apparently does not support tilt in the required direction 2 it probably is not possible for a panel of rock the size of the mt stuart batholith to tilt through the necessary angle ca 35 after its deeper parts have cooled sufficiently to retain remanent magnetization 3 the sense of paleomagnetic discordance found in the mt stuart batholith clockwise rotation of declination flattened inclination is identical to that found in nearly every other allochthonous terrane in the western north american cordillera including every other cretaceous batholith studied except the sierra nevada