a general rule for synoptic eddy feedback onto low frequency flow in this study scale interaction between synoptic eddies and low frequency flow is investigated it is demonstrated here that there is a general rule the left hand rule that describes synoptic eddy feedback onto low frequency flow the rule is that low frequency anomalies systematically stir and deform the transient eddies in such a way that the irrotational eddy vorticity fluxes are directed preferentially about 90 toward the left hand side of the low frequency flow thus this eddy feedback plays a positive role in maintaining and prolonging low frequency flow under the stormy atmosphere similarly we show that the irrotational eddy temperature and moisture fluxes are also directed preferentially about 90 toward the left hand side of the low frequency flow in the northern hemisphere the eddy temperature fluxes and their vertical structure play a positive role in reinforcing the low frequency flow in the low levels the moisture fluxes play a role in enhancing low frequency flow by providing eddy induced moisture convergence and divergence

dynamical feedbacks of the southern annular mode in winter and summer abstract the persistence of the southern annular mode sam is studied during austral winter june september and summer december march using observations of the three dimensional vorticity budget analysis of the relative vorticity tendency equation shows that convergence of eddy vorticity flux in the upper troposphere coupled with a secondary circulation constitutes a positive eddy feedback that acts to sustain the vorticity anomaly associated with the jet shift against drag the feedback exhibits a strong seasonality with summer months revealing a positive feedback through much of the hemisphere and winter months showing a positive feedback over the indian ocean but not over the western pacific results suggest that the lack of wintertime feedback over the western pacific is due to the weakness of the eddy driven midlatitude jet in that region

downslope propagation of normal modes in a shallow water wedge experimental results are presented for the downslope propagation of acoustic normal modes in a shallow water wedge with a penetrable bottom and a slope of up to 9 a 7 element line source was used to generate individual low order normal modes to obtain single modes in a wedge it was necessary to align the line source to form an arc of a circle centered on the wedge apex the resulting normal modes propagate with wave fronts which are also curved into arcs of circles centered on the wedge apex these wedge modes propagate without coupling the amplitudes mode functions and group velocities of the wedge modes are described by simple adiabatic normal mode theory but the wave front curvature is not

evidence for large scale eddy driven gyres in the north atlantic analysis of a recent climatological database for the north atlantic has detailed an extensive large scale recirculation system in the intermediate waters of the north atlantic basin the pressure fields that define this recirculation coupled with the potential vorticity fields associated with the recirculating flow provide observational evidence for basin scale eddy driven flow in the global ocean the recirculations are intimately tied to the waters carried southward by the deep western boundary current and are therefore likely to affect the distribution of climatic anomalies in the north atlantic

an analysis of the three dimensional sound field in a penetrable wedge with a stratified fluid or elastic basement a new analytical solution for the three dimensional sound field due to an harmonic point source in a broad class of penetrable wedges is presented the only restriction on the wedge basement is that it be horizontally stratified thus realistic models of the ocean floor such as a fluid or elastic sediment layer overlying a hard elastic substrate can be handled the wave theoretic solution is based on the method of source images in conjunction with an extension of brekhovskikh and lysanov s analysis of the reflection of a spherical wave field from a planar interface the new solution is accurate throughout the wedge including the normally difficult modal cutoff regions where energy propagates through the wedge at grazing angles close to the critical grazing angle and it is also valid through the hyperbolic caustics that border the region ensonified by each mode

interannual and decadal modulations recently observed in the pacific storm track activity and east asian winter monsoon abstract interannual variability of the north pacific storm track observed over 17 recent winters is documented the local storm track activity is measured by a meridional flux of sensible heat associated with the lower tropospheric subweekly fluctuations the interannual variability in the heat flux over the northwestern nw pacific is found to be strongest in midwinter the first empirical orthogonal function of the interannual variability in midwinter captures the decadal tendency toward the enhanced storm track activity in midwinter over the nw pacific in association with the decadal weakening of the east asian winter monsoon siberian high and the aleutian low that occurred in the late 1980s the most marked signature of this enhancement is that the midwinter minimum in the storm track activity which had been apparent in the early to mid 1980s almost disappeared afterward as opposed to linear theory of baroclinic instability the enhanced activity occurred despite the weakening of the pacific j

eddy mean flow interaction in the gulf stream at 68 w part ii eddy forcing on the time mean flow abstract data front the synop 68 w current meter array show a trough pattern in the 26 month mean gulf stream path at 68 w and a cyclone in the mean deep flow in order to determine whether eddies are controlling the speed and direction of the time mean gulf sream flow at 68 w a theory is developed that extends the eliassen palm theory for zonal mean flows to time mean flows the eddy force is evaluated as the three dimensional divergence of an eddy stress tensor and is equivalent to the eddy advection of momentum fmom and the rotated divergent eddy stretching potential vorticity flux ftherm the study region at 68 w is characterized by large amplitude trough formation events it is shown that ftherm is associated with the growth stage of the eddy trough formation events and tends to turn the upper level time mean flow southward into the trough pattern and accelerate and spin up the deep layer cyclone fmom has a vertically coherent pattern associated with the decay stage of the trough formation events

an evaluation of mesodon and other larger terrestrial gastropod shells for dating late holocene and historic alluvium in the midwestern usa abstract understanding the history of stream erosion and changes in channel morphology is important for managing and restoring unstable streams one of the significant challenges in this type of research is establishing accurate dating of late holocene and historic alluvium here we evaluate the potential of using 14c dating and amino acid racemization aar to date large terrestrial gastropod shells that are often preserved within alluvial sediments many terrestrial gastropods incorporate old carbon from limestone or other carbonate rocks into their shells and therefore are unsuitable for radiocarbon dating recent studies however have shown that some taxa avoid this limestone problem and can yield reliable 14c ages in this study we measured the 14c activity of specimens for the genera mesodon ventridens and allogona collected live and from alluvial sequences dated independently by dendrochronology 14c dating of wood and or 137cs analyses mesodon zaletus contained old carbon in similar concentrations up to 30 found in previous studies of other large taxa and should be avoided for 14c dating when possible in contrast shells of ventridens ligera and allogona profunda showed minimal limestone effects and therefore may be suitable for dating late holocene alluvium these results highlight the importance of taxonomic identification of gastropod taxa prior to their use for 14c dating and demonstrate that shell fragments that are not identifiable should be avoided we also measured d l ratios n 17 of aspartic and glutamic acid from eight different taxa of terrestrial gastropods recovered from four late holocene and historic stratigraphic sequences average d l ratios of aspartic and glutamic acid from historic sediments

the role of synoptic waves in the formation and maintenance of the western hemisphere circulation pattern abstractprevious studies have demonstrated that the nao the leading mode of atmospheric low frequency variability over the north atlantic could be linked to northeast pacific climate variability via the downstream propagation of synoptic waves in those studies the nao and the northeast pacific climate variability are considered as two separate modes that explain the variance over the north atlantic sector and the east pacific north american sector respectively a newly identified low frequency atmospheric regime the western hemisphere wh circulation pattern provides a unique example of a mode of variability that accounts for variance over the whole north atlantic north american north pacific sector the role of synoptic waves in the formation and maintenance of the wh pattern is investigated using the ecmwf reanalysis datasets persistent wh events are characterized by the propagation of quasi stationary rossby waves across the north pacific north american north atlantic regions and by associated s

big sites short time accumulation rates in archaeological sites large complex archaeological sites are often characterized by only a handful of radiocarbon dates this practice encourages indiscriminant dating of sites for the sole purpose of determining age if a more rigorous dating scheme is employed and accumulation rates are calculated otherwise invisible aspects of human behaviour become apparent issues central to settlement pattern analysis such as abandonment and reoccupation events population fluctuations building activities and activity areas are more easily identified when accumulation rates are calculated in this study accumulation rates are calculated for seven shell midden sites found in the san juan islands washington the collections are stored at the burke museum of natural history and culture university of washington seattle washington eighty two charcoal pieces were selected according to a comprehensive horizontal and vertical sampling regime and radiometrically dated accumulation rate calculations suggest that large archaeological sites like these shell middens do not always represent continuous human occupation characterized by gradual accumulation of material rather these large complex sites accumulated during short duration occupations that were repeated infrequently in the same area this research recommends that numerical accumulation rates be calculated using at least two calculations the excavation unit accumulation rate and the entire site accumulation rate and that the excavation unit accumulation rate is the more useful scale for interpreting settlement history calculations of these rates focus the multifaceted interaction between human behaviour and natural processes in a way that qualitative guesses cannot

testing and verification of a scale model acoustic propagation system this paper discusses the design and operation of a measurement apparatus used to conduct scale model underwater acoustic propagation experiments presents experimental results for an idealized waveguide and compares the measured results to data generated by two dimensional 2d and three dimensional 3d numerical models the main objective of this paper is to demonstrate the capability of the apparatus for a simple waveguide that primarily exhibits 2d acoustic propagation the apparatus contains a computer controlled positioning system that accurately moves a receiving transducer in the water layer above a scale model bathymetry while a stationary source transducer emits broadband pulsed waveforms experimental results are shown for a 2 133 m 1 219 m bathymetric part possessing a flat bottom bathymetry with a translationally invariant wedge of 10 slope along one edge beamformed results from a synthetic horizontal line array indicate the presence of strong in plane arrivals along with weaker diffracted and horizontally refracted arrivals a simulated annealing inversion method is applied to infer values for five waveguide parameters with the largest measurement uncertainty the inferred values are then used in a 2d method of images model and a 3d adiabatic normal mode model to simulate the measured acoustic data

the morphology of northern hemisphere blocking abstract the morphology of regional blocking in the northern hemisphere is discussed using the 40 yr ecmwf re analysis era 40 dataset and a measure of blocking based on the reversal at storm track latitudes of meridional contrasts on a potential vorticity pv surface representative of the tropopause the focus is on cyclonic and anticyclonic rossby wave breaking that is inherent to the blocking development and the extent to which this is determined by the climatological jet position and the ambient shears more generally the importance of the climatological planetary scale is discussed the approach is mainly through composite behavior but informed by consideration of many individual events a diversity of behavior is found with longitude in both winter and summer and there is a striking reversal of the sense of the wave breaking between the two seasons that is generally consistent with the difference in the jet locations preferred behaviors are found in various regions and seasons and retrogre

modeling three dimensional propagation in a continental shelf environment an acoustic propagation model is applied to predict measurements of three dimensional 3 d effects recorded off the southeast coast of florida the measured signal is produced by a low frequency source that is towed north parallel to the shelf from a fixed receiving array the acoustic data show the direct path arrival at the bearing of the tow ship and a second refracted path arrival as much as 30 inshore of the direct arrival notably the refracted arrival has a received level more than 25 db greater than that of the direct arrival a geoacoustic model of the environment is created to explain the data it is shown that the topography of the seafloor plays the largest role in controlling horizontal refraction effects whereas the range dependent sediment properties have the most influence on the received level the modeling approach is based on a 3 d adiabatic mode technique in which the horizontal refraction equation is solved using a parabolic equation in cartesian coordinates a modal decomposition of the field provides insight into the variability in the arrival angle and received level of the measured signal

assessing the role of precursor cyclones on the formation of extreme greenland blocking episodes and their impact on summer melting across the greenland ice sheet a 30 year climatology of north atlantic cyclones from 1979 to 2008 is examined within the context of extreme greenland blocking and accelerated surface melting across the greenland ice sheet gris a distinct class of north atlantic cyclones known as precursor cyclones was identified as any extratropical cyclones originating to the west of greenland blocks prior to the peak of blocking intensity composite map analysis reveals that precursor cyclones contributed to a significant intensification of extreme greenland blocking episodes gbes through the process of upper level wave amplification across all seasons most extreme gbes are associated with multiple precursor cyclones prior to peaking in intensity and a majority of these cyclones have continental rather than oceanic origins over both the western and eastern sectors of greenland daily meltwater production simulated by the modele atmospherique regional regional climate model is greater during extreme gbes accompanied by precursor cyclones compared to extreme gbes lacking a precursor cyclone based on an analysis of air parcel trajectories and north atlantic sst anomalies enhanced surface melting during the summer particularly over southern and western greenland is strongly linked to the combination of vigorous adiabatic warming generated by subsiding air within the blocking anticyclones and warm air advection supplied by the precursor cyclones with the increased frequency of extreme gbes accompanied by precursor cyclones observed during a strong positive phase of the atlantic multidecadal oscillation recent long term increases in gris surface melting can be partially attributed to the interaction of these atmospheric and oceanic processes

seasonal variations in the southern hemisphere storm tracks and jet streams as revealed in a reanalysis dataset abstract regional characteristics of the climatological seasonal variations in southern hemisphere sh storm tracks are examined based on a reanalysis dataset when differences in vertical structure between the subpolar and subtropical jet streams spj and stj respectively are considered the regional characteristics can be interpreted reasonably well from a potential vorticity perspective of baroclinic eddy growth and downstream development of a baroclinic wave packet eddy activity in the upper and lower tropospheres is strongest in the core region of the spj over the eastern south atlantic and indian ocean throughout the year even in austral winter when the intense stj forms over the indian ocean and south pacific showing its eddy driven nature the spj accompanies the strong surface westerlies along a well defined baroclinic zone above an intense oceanic frontal zone in this core region of the storm track low level eddy activity is strongly correlated with the local near surface baroclinicity

a computational method to predict and study underwater noise due to pile driving a hybrid modeling approach that uses the parabolic equation pe with an empirical source model is presented to study and predict the underwater noise due to pile driving in shallow inhomogeneous environments over long propagation ranges the empirical source model uses a phased point source array to simulate the time dependent pile source the pile source is coupled with a broadband application of a pe wave propagation model that includes range dependent geoacoustic properties and bathymetry simulation results are shown to be in good agreement with several acoustic observations of pile driving in the columbia river between portland or and vancouver wa the model is further applied to predict sound levels in the columbia river and study the effects of variable bathymetry and sediment configurations on underwater sound levels

book review biogeochemistry of amino acids edited by p e hare t c hoering and k king jr wiley 1980 538 pp 30 50

the ventilation of the world s oceans maps of the potential vorticity field abstract maps of potential vorticity q within four different density layers are presented for the north and south atlantic north and south pacific and indian oceans potential vorticity is evaluated as f 0 z a prescription that is valid for large slow scales and that allows its mapping from hydrographic data alone here f is the coriolis frequency p0 the potential density and z the vertical coordinate it is shown that the character of a layer within the thermocline of a subtropical gyre will vary greatly depending on the extent to which the layer is isolated from surface boundary conditions and forcing fluid particles recirculating within ventilated layers have their potential vorticity and other properties reset with virtually every circuit round the gyre when they pass through the outcrop zone by contrast particles within unventilated or dynamically isolated layers have time to share their properties with neighboring particles and approach a common homogenized state the north

on the interpretation of eddy fluxes during a blocking episode abstract using twice daily synoptic charts objectively analyzed at the national meteorological centre horizontal eddy fluxes of temperature and quasi geostrophic potential vorticity are computed for the month of july 1976 when a blocking anticyclone was centered over western europe the local time averaged eddy variance equations are used to provide a dynamical basis for interpreting the spatial pattern of eddy fluxes and their relation to mean gradients it is shown that a rotational non divergent flux can be identified the cross gradient component of which balances the mean flow advection of eddy variance the remaining flux is the dynamically significant one which helps maintain the block and can be understood in terms of a response to sources and sinks of eddy variance

isolating downward displacement the solutions and challenges of amino acid racemisation in shell midden archaeology shell middens are particularly susceptible to post depositional processes that can rework and redistribute material through a deposit as archaeological material is moved from its original primary context the assumption that a temporal connection exists with spatially associated material becomes tenuous it therefore becomes critical to identify displaced archaeological material within a deposit to ensure correct chronologies are being built radiometric dating techniques can identify individual displaced materials but are sometimes prohibitively costly to utilise on a large scale this study presents a new application of amino acid racemisation aar dating that identifies stratigraphically displaced midden shell from within a deposit from the northwest kimberley western australia low cost aar analysis of 72 samples identified a sample of downwardly displaced midden shell upon close inspection comparison of aar and ams radiocarbon determinations identified fine grained inconsistencies possible processes generating these discrepancies are considered with future avenues for research presented while an enormous amount of potential is contained within aar more work is required to bring the method to the same level of precision as other commonly utilised dating techniques in archaeological research

genesis and occupancy of a shell midden on parana state coast brazil abstract the publications related to pedological characterization of shell middens are rare and there are no comprehensive studies the objective of the present study was to understand habits and intensity of seasonal human occupancies and genesis of stratigraphic levels of an archaeological site on parana state coast brazil the formation of the shell midden by hunter fisher gatherer groups over thousands of years followed only a few patterns of interaction with the environment which would facilitate the studies of correlations with other middens of the brazilian coast in addition to strategies of searching food the amerindian also diversified their activities to improve life quality including cooking certain foods and the placement of insulating material on the midden the evolution of the genesis of layers was much more dependent on the depositional period than the post depositional interval during the post depositional period only the formation of silicate in the clay fraction of the more superficial layers was favored

an analytical model for the underwater sound pressure waveforms radiated when an offshore pile is drivena an analytical model has been developed for the pile vibration and consequent sound pressure and particle velocity radiated underwater when an offshore cylindrical pile is struck by a drop hammer the model which is based on the coupled equations of motion for axial and radial vibration of a thin cylindrical shell yields frequency dependent phase velocity and attenuation of these vibrations the amplitude of the pulse of axial and radial displacement that travels down a pile following an axial impact is described in terms of the hammer properties solutions are obtained for the radiated sound pressure and particle velocity using junger and feit s transform formulation of the pressure field of cylindrical radiators acoustical society of america new york 1993 p 216 the model is applied to published data on radiated noise from offshore driving of a steel pile the modeled pressure waveforms at 12 m horizontal range and at 9 hydrophone depths correlate significantly with the measured waveforms the modeled pressures of the initial positive peaks appropriately low pass filtered agree with data to within 1 db the initial negative peaks however exceed the data by up to 7 db and as hydrophone depth increases the model negative peaks have a maximum at 7 m whereas the data have a maximum at 9 m

the eddy radiation field of the gulf stream as measured by ocean acoustic tomography the gulf stream system is one of the most important components of the north atlantic circulation reciprocal acoustic transmissions have been analyzed to determine the structure and variability of temperature current velocity and relative vorticity in a region just south of the gulf stream observational evidence is presented that the gulf stream is the source of the energetic eddy variability found in the atlantic interior through highly nonlinear processes eddy activity energy radiates away from the stream southward via rossby wave packets

meanders of the gulf stream downstream from cape hatteras 1975 1978 abstract weekly gulf stream paths within 1000 km downstream of cape hatteras were obtained for 1975 78 from the navy s weekly eofa charts based on satellite ir imagery they displayed two dominant meander modes first a standing meander energetic over periods between 4 months and at least 4 years and second down stream propagating meanders that were most energetic at periods of several weeks the long period standing meander was confined between nodes located at the separation point near cape hatteras i e where the stream s mean path turns seaward and at a point about 600 km farther downstream the rms amplitude was 36 km at the antinode the amplitude of propagating meanders increased rapidly in the first 200 km downstream of the separation point where the capture of warm core eddies was common farther down stream the predominant meanders had a wavelength averaging 330 km a period averaging 1 5 month a phase speed averaging 8 cm s 1 a downstream group speed averaging 17 cm s 1 and downstrea

structure and mechanisms of the southern hemisphere summertime subtropical anticyclones abstract the three dimensional structure and dynamics of the climatological mean summertime subtropical anticyclones in the southern hemisphere sh are investigated as in the northern hemisphere nh each of the surface subtropical anticyclones over the south pacific south atlantic and south indian oceans is accompanied by a meridional vorticity dipole aloft exhibiting barotropic and baroclinic structures in its poleward and equatorward portions respectively in a manner that is dynamically consistent with the observed midtropospheric subsidence their dynamics are also similar to their nh counterpart it is demonstrated through the numerical experiments presented here that each of the sh surface anticyclones observed over the relatively cool eastern oceans can be reproduced as a response to a local near surface cooling heating couplet the cooling is mainly due to radiative cooling associated with low level maritime clouds and the heating to the east is due to sensible heat flux over the dry hea

northern hemisphere winter atmospheric transient eddy heat fluxes and the gulf stream and kuroshio oyashio extension variability abstractspatial and temporal covariability between the atmospheric transient eddy heat fluxes i e t and q in the northern hemisphere winter january march and the paths of the gulf stream gs kuroshio extension ke and oyashio extension oe are examined based on an atmospheric reanalyses and ocean observations for 1979 2009 for the climatological winter mean the northward heat fluxes by the synoptic 2 8 days transient eddies exhibit canonical storm tracks with their maxima collocated with the gs and ke oe the intraseasonal 8 days 3 months counterpart while having overall similar amplitude shows a spatial pattern with more localized maxima near the major orography and blocking regions lateral heat flux divergence by transient eddies as the sum of the two frequency bands exhibits very close coupling with the exact locations of the ocean fronts linear regression is used to examine the lead lag relationship between interannual changes in the northward heat fluxes by the transient

the impact of mid depth recirculations on the distribution of tracers in the north atlantic an interesting feature of the waters carried equatorward by the deep western boundary current in the north atlantic is their sharp vertical differentiation in tracer concentration and accordingly tracer age in this work i demonstrate that the strui ture and lateral extent of the recirculations in the intermediate and deep north atlantic have substantive differences with depth that can help explain the observed pattern of transient tracers such as tritium 3he and cfcs while recirculations are present at all depths spanned by the boundary current the distinct tracer minimum occurs at the depth where the recirculation extent is maximized overall the effect of the large scale recirculation at intermediate depths is to lengthen mixing pathways and to provide an alternate route for north atlantic deep waters to enter the subtropical basin

rapid racemization of aspartic acid in mollusc shells and potential for dating over recent centuries dating of deposits and materials less than 350 years old is hindered by the very poor time resolution of the radiocarbon method over this period1 2 fluctuations in atmospheric 14c levels result in the existence of several possible calendric ages for any given radiocarbon age for terrestrial samples in the marine record these fluctuations are dampened however only a small change in marine radiocarbon ages occurs over this period from ad 1700 to 1950 radiocarbon ages become only 100 yr younger2 consequently age resolution is poor furthermore there is an uncertainty in the amount of the correction for the reservoir effect the apparent radiocarbon age of modern marine carbon typically 400yr which reflects the average residence time of carbon in the oceans amino acid racemization epimerization analysis has been used primarily for dating samples older than the limit of radiocarbon dating 40 000 50 000 yr bp 3 4 here i show that aspartic acid asp in mollusc shells has racemized particularly rapidly over the past few centuries analyses done on land snails from deposits in the negev desert eolianites in madeira cave deposits in jamaica and from museum collections indicate racemization rates of 2 5 per century asp racemization thus provides a means of dating recent faunal assemblages of molluscs and other biogenic carbonates as well as recent terrestrial fluvial and marine sedimentary sequences that contain molluscs

on the predominant nonlinear response of the extratropical atmosphere to meridional shifts of the gulf stream abstractthe north atlantic atmospheric circulation response to the meridional shifts of the gulf stream gs path is examined using a large ensemble of high resolution hemispheric scale weather research and forecasting model simulations the model is forced with a broad range of wintertime sea surface temperature sst anomalies derived from a lag regression on a gs index the primary result of the model experiments supported in part by an independent analysis of a reanalysis dataset is that the large scale quasi steady north atlantic circulation response is remarkably nonlinear about the sign and amplitude of the sst anomaly chosen over a wide range of gs shift scenarios the nonlinear response prevails over the weak linear response and resembles the negative north atlantic oscillation nao the leading intrinsic mode of variability in the model and the observations further analysis of the associated dynamics reveals that the nonlinear responses are accompanied by the shift of the north atlantic eddy

further evidence of the complexity of the racemization process in fossil shells with implications for amino acid racemization dating abstract simulated aging experiments with shells of ostrea anadara and katelysia spp from modern holocene and pleistocene marine sediments in southern south australia give further insight into the difficulties in using d l ratios of amino acids for quantitative age determinations evidence is given that the progress of racemization as monitored by changes in d l ratios with time is not only non linear but also may be reversed demonstrating a decrease in the observed degree of racemization the observed changes in d l ratio with time differ according to the age and the genus of shell and the amino acid examined katelysia spp gives less variable values than ostrea or anadara and similarly valine racemization and isoleucine epimerization are far less variable than aspartic acid racemization

amino acid racemization dating of marine shells a mound of possibilities shell middens are one of the most important and widespread indicators for human exploitation of marine resources and occupation of coastal environments establishing an accurate and reliable chronology for these deposits has fundamental implications for understanding the patterns of human evolution and dispersal this paper explores the potential application of a new methodology of amino acid racemization aar dating of shell middens and describes a simple protocol to test the suitability of different molluscan species this protocol provides a preliminary test for the presence of an intracrystalline fraction of proteins by bleaching experiments and subsequent heating at high temperature checking the closed system behaviour of this fraction during diagenesis only species which pass both tests can be considered suitable for further studies to obtain reliable age information this amino acid geochronological technique is also applied to midden deposits at two latitudinal extremes northern scotland and the southern red sea results obtained in this study indicate that the application of this new method of aar dating of shells has the potential to aid the geochronological investigation of shell mounds in different areas of the world

observed changes in baroclinic wave activity during the life cycles of low frequency circulation anomalies abstract anomalous baroclinic wave activity during the onset and decay of blocking patterns in the northern hemisphere winter is investigated based upon a 30 year record of 500 mb height and sea level pressure a slowly varying envelope function is defined at each gridpoint in order to represent the modulation of the amplitude of baroclinic wave activity by the low frequency circulation anomalies related to blocking the envelope function fields and the low frequency circulation fields are composited relative to the onset and decay times of four persistent dipole patterns in low frequency circulation anomalies located downstream of the climatological mean stormtracks one polarity of the anomaly patterns corresponds to dipole or modon like blocking patterns over the eastern oceans and the other to strong zonal flow patterns each of the eight composites is comprised of more than 50 persistent blocking or zonal flow episodes the most striking common feature observed during the onset of blocking over th

assessing the reproducibility and reliability of estuarine bivalve shells saxidomus giganteus for sea surface temperature reconstruction implications for paleoclimate studies studies using oxygen isotopes y 18 o of mollusk shells to determine paleotemperature need to assume water y 18 o values which could severely influence calculated temperatures we analyzed aragonitic shells of the butter clam saxidomus giganteus deshayes 1839 to determine the reproducibility of the isotopic signal between individuals and to assess how precisely temperature could be calculated given known salinity and temperature furthermore carbon isotopes are also investigated as an environmental proxy the abundance of well preserved s giganteus shells in archeological and geological deposits in northwestern north america makes them a particularly suitable species for paleoclimate studies seasonally resolved stable oxygen isotope profiles in three s giganteus shells collected from the same site in puget sound washington usa were well correlated 0 77br 2 b0 87 although there were differences up to 0 58x in high resolution y 18 o profiles of the three shells the difference between the average y 18 o of each shell was less than half of this 0 19x and half of what has been reported for between colony coral variability y 13 c profiles on the other hand were more complex with shell y 13 c being about 2 5x lower than expected equilibrium values however this roughly conforms to the idea that about 10 of the shell carbon originates from metabolic co2 both y 18 o and y 13 c indicate that s giganteus do not grow during periods of reduced salinity despite the excellent reproducibility of y 18 o between shells and the fact that salinity effects were duly considered calculated temperature still differed from instrumental temperature applying different salinity y 18 o water relationships to average shell y 18 o and considering salinity from the shell collection site and a nearby offshore station resulted in calculated average water temperatures ranging from 1 7 to 6 4 8c warmer than measured although we could not determine if s giganteus precipitate their shells in isotopic equilibrium we believe that the difficulty in predicting temperature arose from not being able to accurately determine

the role of high and low frequency dynamics in blocking formation time evolutions of prominent blocking flow configurations over the north pacific and europe are compared based upon composites for the 30 strongest events observed during 27 recent winter seasons fluctuations associated with synoptic scale migratory eddies have been filtered out before the compositing a quasi stationary wave train across the atlantic is evident during the blocking amplification over europe while no counterpart is found to the west of the amplifying blocking over the north pacific correlation between the tropopause level potential vorticity pv and meridional wind velocity associated with the amplifying blocking is found to be negative over europe in association with the anticyclonic evolution of the low pv center but it is almost zero over the north pacific feedback from the synoptic scale eddies as evaluated in the form of 250 mb geopotential height tendency due to the eddy vorticity flux convergence accounts for more than 75 of the observed amplification for the pacific blocking and less than 45 for the european blocking this difference is highlighted in two types of contour advection with surgery experiments in one of them pv contours observed four days before the peak blocking time were advected by composite time series of the low pass filtered observational wind and in the other experiment they were advected by the low pass filtered wind from which the transient eddy feedback evaluated as above had been removed at every time step hence the latter data should be dominated by low frequency dynamics for the european blocking both experiments can reproduce the anticyclonic evolution of low pv air within a blocking ridge as observed for the pacific blocking in contrast the observed intrusion of low pv air into the higher latitudes cannot be reproduced without the transient feedback furthermore in a barotropic model initialized with the composite 250 mb flow observed three days before the peak time a simulated blocking development over the north pacific is more sensitive to the insertion of the observed transient feedback than that over europe these results suggest that the incoming wave activity flux associated with a quasi stationary rossby wave train is of primary importance in the blocking formation over europe whereas the forcing by the synoptic scale transients is indispensable to that over the north pacific

diagnoses of an eddy resolving atlantic ocean model simulation in the vicinity of the gulf stream part i potential vorticity abstract output of an eddy resolving model of the north atlantic is diagnosed in the vicinity of the gulf stream gs using quasigeostrophic potential vorticity qgpv ertel s potential vorticity pv and particle trajectories time series of qgpv show strong input of qgpv by the gs in the top 1000 m of the model ocean vigorous wave motions are observed in the vicinity of the model gs mixing qgpv in the region the time mean horizontal qgpv structures show qualitative similarity to those of large scale climatological pv calculated from hydrographic data by keffer and that of lozier the top 1000 m of the model ocean is characterized by a tongue or an elongated island of high mean qgpv along the gs it is demonstrated that the tongue is a product of strong qgpv input by the gs vigorous mixing by eddies and dissipation of qgpv along the path of the gs at the intermediate depths 1000 2500 m a large region of nearly homogenized mean pv or weakly varying mean qgpv is found to the west of the mid atla

diagnoses of an eddy resolving atlantic ocean model simulation in the vicinity of the gulf stream part ii eddy potential enstrophy and eddy potential vorticity fluxes abstract output of an eddy resolving model of the north atlantic is diagnosed in the vicinity of the gulf stream gs using quasigeostrophic potential vorticity qgpv quasigeostrophic potential enstrophy qgpe and modified divergent eddy potential vorticity flux v hq d a tongue or an elongated island of large mean qgpv along the model gs in the top 1000 m is associated with predominantly downgradient v hq d suggesting that the horizontal eddy fluxes are balancing a sink of eddy qgpe in most of the tongue or island by converting the mean qgpe into eddy qgpe some large upgradient v hq d is observed to the north of the center of the tongue or island however suggesting that some of the eddy fluxes in the northern half of the tongue or island of high qgpv are balancing a source of eddy qgpe there by converting eddy qgpe into the mean qgpe at the intermediate levels of the model under the gs eddy qgpe is small and the role of eddies appears to be mixed they are forcing the mean to some

dynamical feedbacks and the persistence of the nao the persistence of the north atlantic oscillation nao is studied using observations of the threedimensional vorticity budget in the atlantic sector analysis of the relative vorticity tendency equation shows that convergence of eddy vorticity flux in the upper troposphere counteracts the effect of anomalous largescale divergence at the upper level at low levels the convergence associated with this large scale vertical circulation cell maintains the relative vorticity anomaly against frictional drag the eddy vorticity flux convergence thus acts to sustain the vorticity anomaly associated with the nao against drag and increases the persistence of the nao vorticity anomaly the adiabatic cooling associated with the rising motion in the vorticity maximum sustains the thermal structure of the nao anomaly enhancing the baroclinicity and thus eddy generation this constitutes a positive eddy feedback that helps maintain the nao the positive eddy feedback occurs only in the midlatitude region and is strongest during the negative phase of the nao when the atlantic jet is displaced toward the equator with a high pressure anomaly to the north and a low pressure anomaly to the south the stronger feedback demonstrated during the negative phase is consistent with the greater persistence observed for this phase of the nao the positive feedback appears to be associated with anomalous northward eddy propagation away from the jet

earliest modern humans in southern africa dated by isoleucine epimerization in ostrich eggshell the oldest anatomically modern human remains are beyond the range of radiocarbon dating and associated deposits lack material suitable for most other dating methods consequently age estimates for early human skeletal material and correlative stratigraphic horizons in southern africa are frequently based on paleoclimatic correlations to the deep sea record and extrapolated sedimentation rates both of which incorporate a number of untested assumptions here we focus on one substage of the middle stone age of southern africa the howiesons poort industry a distinctive culture stratigraphic marker in sequences south of the zambezi anatomically modern human skeletal material has been found associated with or even older than the howiesons poort layer in stratified deposits at border cave and klasies river main site we have dated or bracketed the howiesons poort horizon at border cave boomplaas cave and apollo 11 cave three stratified cave sites in southern africa based on the extent of isoleucine epimerization in associated ostrich eggshells we conclude that the howiesons poort lithic industry is bracketed by limiting dates of 56 and 80 ka and is most likely centered on 66 5 ka anatomically modern human remains in deeper levels are more than 100 ka old lending support to the hypothesis of an african origin for homo sapiens

the structure dynamics and tropospheric signature of the polar annular mode 1 intraseasonal variability in the stratospheric polar vortex is intrinsically linked to concomitant tropospheric variability via the annular modes the primary mode the northern annular mode nam represents variability in the polar vortex strength while the second mode the lesser studied polar annular mode pam represents variability in the latitudinal position of the polar vortex the current study examines the structural evolution zonal mean dynamical forcing and tropospheric impact of discrete pam episodes occurring during boreal winter the analysis identifies large amplitude positive and negative pam events occurring in the absence of nam or sudden stratospheric warming events composite time evolution analyses are performed for both positive and negative pam events the onset of positive negative pam events is preceded by a weak and broad acceleration deceleration within the stratospheric polar vortex at midlatitudes during pam onset the canonical pam structure in zonal mean zonal wind develops over a 5 day period in association with robust stratosphere troposphere coupling zonal wind changes occurring during onset are induced by anomalous wave driving associated with low frequency rossby wave activity after pam onset the zonal wind anomaly features at high latitudes quickly weaken while those in the subtropics and midlatitudes persist for a period of 2 3 weeks during this time pam events provide a statistically significant impact upon the tropospheric circulation with large scale perturbations in a surface air temperature over north america and eurasia and b the structure and amplitude of the primary storm tracks

eddy mean flow interaction in the gulf stream at 68 w part i eddy energetics abstract from june 1988 to august 1990 twelve tall high performance current meter moorings measured the gulf stream s velocity and temperature fields at nominal depths of 400 m 700 m 1000 m and 3500 m along three lines centered at 68 w the overall eddy variability during the 26 month experiment was dominated by six large amplitude trough formation events with each event lasting approximately one month to determine the source s of energy for this eddy variability the eddy energy budget is evaluated traditionally the baroclinic conversion of mean potential energy to eddy potential energy is defined as a downgradient heat flux however because a nondivergent heat flux can be downgradient even under conditions in which there is no barolinic conversion occurring a better more dynamically correct definition of a baroclinic conversion rate is a downgradient horizontally divergent heat flux the horizontally divergent heat flux component is estimated to be approximately half the full horizontal hea

what do i do with all these shells basic guidance for the recovery processing and retention of archaeological marine shells abstract marine shells can be common on archaeological sites even forming sites and provide large amounts of information about the human past if recovered appropriately however guidance for appropriate recovery remains unformulated or not explicitly formulated leading to too many too few and too biased assemblages being excavated extracted processed and archived guidance is derived for minimum and maximum sample sizes field sampling methods and deposit priorities extracting shells from the matrix and accepting and retaining shells in archive

anatomy of synoptic eddy nao interaction through eddy structure decomposition abstracta method of eddy structure decomposition is proposed to detect how low frequency flow associated with the north atlantic oscillation nao organizes systematically synoptic eddy se activity to generate in phase and upstream feedbacks in this method a statistical eddy streamfunction ses field defined by the three point covariance of synoptic scale streamfunction is introduced to characterize spatiotemporal se flow structures the ses field is decomposed into basic and anomalous parts to represent the climatological se flow structure and its departure these two parts are used to calculate the basic and anomalous eddy velocity eddy vorticity and thus eddy vorticity flux fields in order to elucidate those two se feedbacks onto the nao this method is validated by the fact that the observed anomalous eddy vorticity flux field can be reproduced well by two linear terms the basic eddy velocity field multiplied by anomalous eddy vorticity field and the anomalous eddy velocity field multiplied

heat budget analysis of northern hemisphere high latitude spring onset events regional spring onset events are identified within 4 high latitude sectors the primary critical region over north siberia cr greenland north america g na east asia ea and alaska al to identify the primary forcing of the rapid temperature increases observed during spring onset the contributions to the near surface air temperature anomaly tendency are diagnosed within the thermodynamic equation for each of the 4 regional event categories for each region anomalous eddy heat flux convergence is the primary contributor to regional warming prior to and during the early stages of spring onset through day 5 thereafter horizontal advection of the climatological mean temperature by the large scale circulation anomaly field emerges as the leading contributor to regional warming during the later stages of spring onset a parallel diagnostic of storm track strength using the envelope function reveals a systematic weakening of eddy activity within each region leading to a reduction in the northward eddy heat flux out of the domain and an accumulation of heat within the region for cr g na and ea events an east west dipole structure in the sea level pressure anomaly field with lower higher pressure to the west east generates the anomalous southerly flow linked to late period linear warm advection our results indicate that anomalous dynamical processes associated with synoptic eddy activity and stationary wave patterns are the primary contributors to rapid temperature increase during arctic spring onset events with minimal contributions from anomalous diabatic processes

underwater mach wave radiation from impact pile driving theory and observation the underwater noise from impact pile driving is studied using a finite element model for the sound generation and parabolic equation model for propagation results are compared with measurements using a vertical line array deployed at a marine construction site in puget sound it is shown that the dominant underwater noise from impact driving is from the mach wave associated with the radial expansion of the pile that propagates down the pile after impact at supersonic speed the predictions of vertical arrival angle associated with the mach cone peak pressure level as function of depth and dominant features of the pressure time series compare well with corresponding field observations

the ksâr akil lebanon mollusc assemblage zooarchaeological and taphonomic investigations abstract shells of marine molluscs exploited by prehistoric humans constitute archives of palaeoecological and palaeoclimatic data as well as of human behaviour in coastal settings here we present our investigations on the mollusc assemblage from ks r akil lebanon a key site in southwestern asia occupied during the middle and upper palaeolithic the site plays an important role in understanding modern human dispersals into eurasia taxa from intertidal rocky shore subtidal soft bottom and rocky littoral habitats dominate the marine component of the invertebrate assemblage terrestrial snails indicate wooded and open half shaded habitats in the vicinity of the site species composition suggests that these habitats were present throughout the upper palaeolithic humans transported marine molluscs to the rockshelter as food packages for dietary purposes e g patella caerulea patella rustica phorcus turbinatus and shells of other taxa to be used as tools e g glycymeris sp or possibly for ornamental purposes e g nassarius gibbosulus and columbella rustica in the initial upper palaeolithic collection focussed on empty shells as raw material for utilitarian purposes in the subsequent early upper palaeolithic and later periods mollusc gathering was performed in an increasing number of habitats and shifted towards collection for human consumption which was the main reason for the introduction of shells to the site during the epipalaeolithic concurrent size shifts of live collected as well as beached specimens suggests that size changes were linked to environmental change rather than to potential overexploitation of dietary taxa by humans

coastal aminostratigraphy of the last interglaciation in southern australia abstract amino acid racemization data for marine molluscs of the last interglaciation from southern australia provide the basis for a predictive model for relative dating of late quaternary sequences genera analyzed include anadara sp katelysia sp glycymeris sp and fulvia sp that exhibit moderate racemization rates a genus effect on racemization is not evident in these taxa coefficients of variation for intershell d l ratio variation for each deposit are generally less than 12 the extent of racemization in molluscan fossils of the last interglaciation from temperate coastal settings in southern australia represents an exponential function of temperature and is in general accord with data from northern hemisphere sites with similar contemporary mean annual temperature values these data highlight the potential of amino acid racemization for global correlation programs the amino acid data from southern australia suggest however that a larger margin of variation may have to be accounted for in stratigraphic correlation as indicated by the greater scatter of data around the oxygen isotope substage 5e isochron these data have implications regarding the age resolving power of amino acid racemization

model simulation and projection of european heat waves in present day and future climates abstractthe synoptic behavior of present day heat waves hw over europe is studied using the gfdl high resolution atmospheric model hiram with 50 km grid spacing three regions of enhanced and coherent temperature variability are identified over western russia eastern europe and western europe the simulated hw characteristics are compared with those derived from climate forecast system reanalysis products composite charts for outstanding hw episodes resemble well known recurrent circulation types the hw region is overlain by a prominent upper level anticyclone which blocks the passage of synoptic scale transients the altered eddy vorticity transports in turn reinforce the anticyclone the anticyclone is part of a planetary scale wave train the successive downstream development of this wave train is indicative of rossby wave dispersion additional runs of hiram are conducted for the time slices of 2026 35 and 2086 95 in the climate scenario corresponding to representative concentration pathway

beam forming of the underwater sound field from impact pile driving observations of underwater noise from impact pile driving were made with a vertical line array previous studies reinhall and dahl j acoust soc am 130 1209 1216 2011 show that the dominant underwater noise from impact driving is from the mach wave associated with the radial expansion of the pile that propagates down the pile at supersonic speed after impact here precise estimates of the vertical arrival angles associated with the down and up going mach wave are made via beam forming and the energy budget of the arrival structure is quantified

aspartic acid racemization dating of holocene brachiopods and bivalves from the southern brazilian shelf south atlantic abstract the extent of racemization of aspartic acid asp has been used to estimate the ages of 9 shells of the epifaunal calcitic brachiopod bouchardia rosea and 9 shells of the infaunal aragonitic bivalve semele casali both taxa were collected concurrently from the same sites at depths of 10 m and 30 m off the coast of brazil asp d l values show an excellent correlation with radiocarbon age at both sites and for both taxa r2site 9 b rosea 0 97 r2site 1 b rosea 0 997 r2site 9 s casali 0 9998 r2site 1 s casali 0 93 the asp ratios plotted against reservoir corrected ams radiocarbon ages over the time span of multiple millennia can thus be used to develop reliable and precise geochronologies not only for aragonitic mollusks widely used for dating previously but also for calcitic brachiopods at each collection site bouchardia specimens display consistently higher d l values than specimens of semele thermal differences between sites are also notable and in agreement with theoretical expectations as extents of racemization for both taxa are greater at the warmer shallower site than at the cooler deeper one in late holocene marine settings concurrent time series of aragonitic and calcitic shells can be assembled using asp racemization dating and parallel multi centennial to multi millennial records can be developed simultaneously for multiple biomineral systems

seasonality and interannual variability of the westerly jet in the tibetan plateau region abstract in this study 40 yr ecmwf re analysis era 40 data are used for the description of the seasonal cycle and the interannual variability of the westerly jet in the tibetan plateau region to complement results based on the analysis of monthly mean horizontal wind speeds an occurrence based jet climatology is constructed by identifying the locations of the jet axes at 6 hourly intervals throughout 1958 2001 thus a dataset describing the highly transient and localized features of jet variability is obtained during winter and summer the westerly jet is located respectively to the south and north of the tibetan plateau during the spring and autumn seasons there are jet transitions from south to north and vice versa the median dates for these transitions are 28 april and 12 october the spring transition is associated with large interannual variations while the fall transition occurs more reliably within a 3 week period the strength of the jet exhibits a peculiar seasonal cycle during northw

evolution and dynamics of summertime blocking over the far east and the associated surface okhotsk high time evolution and dynamics of an upper level blocking ridge over the far east and the associated surface high over the sea of okhotsk that give rise to abnormal summertime coolness over eastern japan are investigated through a composite analysis applied to distinct surface high events the formation mechanism and vertical structure of the blocking differ fundamentally between may and july attributable to seasonal changes in the jet structure storm track activity over the far east and the land sea thermal contrast within the okhotsk region in may forcing from migratory eddies is strong enough for precursory anticyclonic anomalies retrograding slowly over the north pacific to develop into a blocking ridge the ridge remains equivalent barotropic under the weak land sea thermal contrast in the okhotsk region in contrast the eddy forcing is no longer the primary factor for the blocking formation in july in the presence of the weakened and split westerlies rather the propagation of a stationary rossby wave packet that has emanated from precursory anticyclonic anomalies over northern europe stagnates over the far east and the subsequent local breaking of the packet leads to the blocking formation in a particular case in july 1993 a wave packet involved in blocking formation could be traced back as far upstream as the east coast of north america over the two previous weeks acting on the strong thermal contrast in july between the cool sea surface and a warm land mass to the west the anomalous surface easterlies induced by the blocking ridge can build up a cold surface anticyclone through cold advection rendering the blocking anomalies distinctly baroclinic copyright 2004 royal meteorological society

comparison between theory and model scale measurements of three dimensional sound propagation in a shear supporting penetrable wedge laboratory experiments have been carried out to investigate underwater sound propagation over a sloping bottom which can support shear the model of the seafloor consisted of a sediment layer modeled experimentally by epoxy over a hard substrate made of concrete the sound field was measured in both the across slope and downslope directions for various frequencies and bottom slopes the experimental results have been compared with a new source image theory for sound propagation in an ocean wedge with an elastic shear supporting bottom and have shown very good agreement for both downslope and across slope propagation in particular the effect of shear waves on across slope propagation has been demonstrated both theoretically and experimentally further the effect of a sediment layer overlying a semi infinite substrate has been successfully incorporated into the source image theory for comparison with the experimental measurements

the response of the pacific storm track and atmospheric circulation to kuroshio extension variability an index of the kuroshio extension front strength is produced using a maximum covariance analysis between sea surface temperature sst and sea surface height ssh gradient observations and composites of the atmospheric state are presented during its positive and negative phases using reanalysis data 1992 2011 it is found that when the kuroshio extension is less more meandering with a stronger weaker sst front the atmospheric heat transport by transient eddies is increased in the western eastern pacific region consistent with an increase decrease in low level baroclinicity analysis of the eddy mean flow interaction shows that this zonal shift in heat transport forces anomalous barotropic flow in the eastern pacific where blocking frequency is strongly influenced the above relationships cannot be reconciled with the known response of the north pacific storm track to remote forcing from the tropical pacific nor can they be explained by the response of the ocean to atmospheric forcing via surface heat fluxes or winds rather the zonal shift in the storm track highlighted here and the associated changes in the large scale circulation are interpreted as a response to the interannual variability of the kuroshio extension front

archaeology of the continental shelf marine resources submerged landscapes and underwater archaeology we provide a critical review of the evidence for the long term use of marine resources and coastal environments in human evolution and later development we emphasise the importance of the coastal archaeological record in understanding patterns of human settlement and dispersal and draw attention to the large potential biases introduced by the destructive or obscuring effects of pleistocene sea level change we note that lowered sea levels have been the norm for most of the pleistocene and that periods of high sea level have been too short lived to provide other than a fragmentary coastal record and one that is beset with ambiguities and uncertainties we examine the geological processes of coastal uplift and underwater preservation that may help to mitigate these biases coastlines elevated by isostatic and tectonic processes or with very steep offshore drop offs at plate boundaries are important in providing a potential window into coastal landscapes and archaeology formed during periods of lowered sea level however we conclude that the opportunities afforded by these geological factors are too limited to obviate the need for underwater exploration we review the evidence now available from submerged landscapes across the africa eurasia interface from the atlantic coastlines of northwest europe to the southern red sea we show that geomorphological conditions for the preservation of archaeological and palaeoenvironmental data are commonly present that much material has already been discovered and that new techniques technologies and projects are providing the momentum for a rapidly expanding field of investigation the results do not simply add to what we already know from sites on land but are likely to produce qualitatively different evidence for coastal adaptations and landscapes that have no analogue on present day coastlines we note the strong probability that many coastal landscapes exposed at lowered sea level provided relatively fertile and productive refugia for plants land mammals and humans at a time when increased aridity would have reduced or deterred hinterland occupation we conclude that underwater investigation is essential if hypotheses of early human adaptation and dispersal are to be fully tested

left hand rule for synoptic eddy feedback on low frequency flow 1 in this study scale interaction between synoptic eddies and low frequency flow is investigated the synoptic eddy feedback is a key process in sustaining the low frequency flow we show clear evidence using ncep reanalysis data that there is a general underlying rule the left hand rule governing the synoptic eddy feedback onto low frequency flow this rule states that eddy vorticity fluxes are directed preferentially about 90 degrees toward their left hand side so that they converge into cyclonic flow and diverge from anticyclonic flow therefore the eddy vorticity flux plays a positive role in reinforcing low frequency flow citation kug j s and f f jin 2009 left hand rule for synoptic eddy feedback on low frequency flow geophys res lett 36 l05709 doi 10 1029 2008gl036435

a continuous multi millennial record of surficial bivalve mollusk shells from the sao paulo bight brazilian shelf abstract to evaluate the potential of using surficial shell accumulations for paleoenvironmental studies an extensive time series of individually dated specimens of the marine infaunal bivalve mollusk semele casali was assembled using amino acid racemization aar ratios n 270 calibrated against radiocarbon ages n 32 the shells were collected from surface sediments at multiple sites across a sediment starved shelf in the shallow sub tropical sao paulo bight sao paulo state brazil the resulting 14 c calibrated aar time series one of the largest aar datasets compiled to date ranges from modern to 10 307 cal yr bp is right skewed and represents a remarkably complete time series the completeness of the holocene record is 66 at 250 yr binning resolution and 81 at 500 yr binning resolution extensive time averaging is observed for all sites across the sampled bathymetric range indicating long water depth invariant survival of carbonate shells at the sediment surface with low net sedimentation rates benthic organisms collected from active depositional surfaces can provide multi millennial time series of biomineral records and serve as a source of geochemical proxy data for reconstructing environmental and climatic trends throughout the holocene at centennial resolution surface sediments can contain time rich shell accumulations that record the entire holocene not just the present

storm track organization and variability in a simplified atmospheric global circulation model a storm track is simulated in a coarse resolution multilevel primitive equation model with linear surface friction and heating terms a restoration temperature distribution consisting of a dipole embedded in a zonally symmetric profile forces the model to simulate the surface heating three simulations each with a different dipole orientation are performed to test the sensitivity of storm track organization to the external forcing field the climatological time mean circulation and the transient disturbances of the reference simulation agree well with observations of northern hemisphere wintertime storm tracks local energetics show that baroclinic instability is responsible for the enhanced eddy kinetic energy downstream of the jet and the downstream end of the storm track results from the barotropic conversions of eddy kinetic energy to the time mean flow low frequency fluctuations with a period of about 50 days associated with a retrograding large scale wave pattern are identified by a complex empirical orthogonal function analysis of the vertically averaged stream function a composite life cycle of the low frequency variability reveals the growth and decay of a blocking anticyclone downstream of the storm track a cyclogenesis initiated by an eastward propagating wave train is observed a few days before the amplitude of the low frequency anomaly attains its peak the net forcing of the high frequency eddies contributes to the growth and decay of the blocking anticyclone the results suggest that the occurrence of the blocking like event is part of the storm track dynamics

gulf stream path and thermocline structure near 74 w and 68 w the synoptic ocean prediction synop experiment had the goal of providing a physical understanding of energetic mesoscale eddy processes in the gulf stream in the synop inlet array off cape hatteras and in the central array near 68 w modred observations were collected from october 1987 through august 1990 the inlet array measured the surface path and bottom currents where the gulf stream leaves the continental margin to enter the deep water regime small amplitude propagating and growing meanders characterized the variability there the central array measured velocity and temperature as a proxy for density at four levels in the water column as well as the upper and deep level streamfunctions all with mesoscale resolution near 70 w the path envelope exhibited a relative node confined within a 40 km band 55 of the time near 68 w the path envelope was over 3 times as wide due to several elongated steep meander troughs and relatively steep meander crests the crests typically propagated downstream without much growth the troughs often stalled near 68 w steepened and persisted for one to several months two cases evolved into s shaped paths and subsequently formed rings even the time averaged fields showed a small trough in the mean path and thermocline structure whereas meanders of 20 to 60 day periods had similar spectral levels throughout 70 67 w meanders with long periods 85 day accounted for the local minimum in variance at 70 w bottom pressure and velocity observations revealed repeated periods of intense swirl speeds 0 30 m s 1 abyssal eddies the time averaged deep currents exhibited a mean cyclone centered 30 km offshore and downstream of the upper layer mean trough the cross stream slope of the thermocline steepened linearly with path curvature consistent with gradient wind balance structures are illustrated in the mapped fields consistent with baroclinic instability wherein troughs steepen and rings form

influence of the east asian winter monsoon on the storm track activity over the north pacific 1 we investigate the relationship between the east asian winter monsoon eawm and synoptic eddy activity over the north pacific ocean it is well known that the subtropical pacific jet becomes stronger during strong monsoon periods than during weak monsoons the storm track is generally expected to be active when the eawm is strong owing to the enhanced subtropical jet contrary to this expectation synoptic eddy activity is significantly reduced in strong eawm years and conversely significantly increased during weak years in addition we found that eawm induced lower level cooling brings about the reverse relationship a stronger jet but with weaker storm activities it is suggested that the local baroclinicity induced by the eawm modulates the variation of both the jet and north pacific storm track simultaneously in the interannual time scale because major lower level cooling is located in the western parts of both the subtropical jet and the storm track in longitudes and between the two central axes in latitudes it induces the opposite sign of anomalous local baroclinicity at the two active regions and causes this reverse relationship the wave seeding from east asia to the north pacific storm track is weakened owing to the anomalous lower level cooling in the northwestern pacific which also results in reduction of eddy generation and storm track activities

geoarchaeology in action a sedimentological analysis of anthropogenic shell mounds from the cape york region of australia abstract large mounded deposits of shell are prominent archaeological features across much of the north australian tropical coast many of the shell mounds are composed almost entirely of the bivalve anadara granosa linnaeus 1758 a food source for aboriginal people in the past a relatively long history of inquiry into the nature and significance of the shell mounds has focussed primarily on analysing the shell component as clues to australian aboriginal coastal economies in the past this paper presents results of new analyses on the non shell sediments examining the physical and chemical signatures of depositional and post depositional processes within shell mounds near weipa in far north queensland australia with a view to obtaining insights into how they formed and for what purposes and how their morphology structure and content may have changed since they ceased accumulating we also consider how such changes might relate to past and present environmental conditions physical and chemical analyses indicate that the primary purpose of mound building was most likely to discard the large volumes of shell resulting from a granosa harvesting and consumption post depositional diagenetic alteration has strongly influenced the present day composition and form of the shell mounds in particular the accession of carbon and silica to the mounds by environmental burning aided by strong leaching under the seasonal high rainfall conditions as such the mound chemistry is more likely to reflect modern environmental conditions rather than provide an archive of or an opening to the past

on the underwater sound field from impact pile driving arrival structure precursor arrivals and energy streamlines underwater noise from impact pile driving is studied through measurements using a vertical line array vla placed at range 120 m from the pile source water depth 7 5 m over which bathymetry varied gradually increasing to depth 12 5 m at the vla the data were modeled assuming the pile impact produces a radial expansion that acts as sound source and propagates along the pile at supersonic speed this leads to the conceptualization of the pile as a discrete vertical line source for which frequency and source depth dependent complex phasing is applied dominant features of the pressure time series versus measurement depth are reproduced in modeled counterparts that are linearly related these observations include precursor arrivals for which arrival timing depends on hydrophone depth and influence of a sediment sound speed gradient on precursor amplitude spatial gradients of model results are taken to obtain estimates of acoustic particle velocity and vector intensity for which active intensity is studied in the time domain evaluation of energy streamlines based on time integrated active intensity and energy path lines based on instantaneous or very short time integrated active intensity reveal interesting structure in the acoustic field including an inference as to the source depth of the precursor

a coupled mode solution for acoustic propagation in a waveguide with stepwise depth variations of a penetrable bottom a coupled mode solution is formulated for the problem of acoustic propagation in a cylindrically symmetric ocean divided in range into a finite number of adjoining pekeris waveguides of differing water depths attenuation is included in the bottom and the problem is discretized by assigning a pressure release boundary condition at a depth which is sufficiently far removed to prevent significant energy from returning to the water this formulation includes backscatter from the depth variations of the water column and full coupling between a finite number of modes propagating in the water column and in the bottom numerical results based on an implementation of this solution are presented

validation of finite element computations for the quantitative prediction of underwater noise from impact pile driving the acoustic radiation from a pile being driven into the sediment by a sequence of hammer strikes is studied with a linear axisymmetric structural acoustic frequency domain finite element model each hammer strike results in an impulsive sound that is emitted from the pile and then propagated in the shallow water waveguide measurements from accelerometers mounted on the head of a test pile and from hydrophones deployed in the water are used to validate the model results transfer functions between the force input at the top of the anvil and field quantities such as acceleration components in the structure or pressure in the fluid are computed with the model these transfer functions are validated using accelerometer or hydrophone measurements to infer the structural forcing a modeled hammer forcing pulse is used in the successive step to produce quantitative predictions of sound exposure at the hydrophones the comparison between the model and the measurements shows that although several simplifying assumptions were made useful predictions of noise levels based on linear structural acoustic models are possible in the final part of the paper the model is used to characterize the pile as an acoustic radiator by analyzing the flow of acoustic energy 2013 acoustical society of america

small slope simulation of acoustic backscatter from a physical model of an elastic ocean bottom an underwater acoustic experiment with a two dimensional rough interface milled from a slab of pvc was performed at a tank facility the purpose was to verify the predictions of numerical models of acoustic rough surface scattering using a manufactured physical model of an ocean bottom that featured shear effects nonhomogeneous roughness statistics and root mean square roughness amplitude on the order of the acoustic wavelength predictions of the received time series and interface scattering strength in the 100 300khz band were obtained from the bottom reverberation from inhomogeneities and surfaces small slope approximation boris ssa numerical scattering model the predictions were made using direct measurements of scattering model inputs specifically the geoacoustic properties from laboratory analysis of material samples and the grid of surface heights from a touch trigger probe boris ssa predictions for the amplitude of the received time series were shown to be accurate with a root mean squar

enhanced age resolution of the marine quaternary record in the arctic using aspartic acid racemization dating of bivalve shells abstract aspartic acid asp racemization occurs at a significantly higher rate than isoleucine epimerization and consequently provides better temporal resolution of arctic marine deposits from alaska spitsbergen and baffin island heating experiments at 100 c on the bivalvesmyaandhiatellashow the asp racemization rate decreases with increasing d l values as is typical for biogenic carbonates based on these experimental racemization rates and rates determined from racemization of samples radiocarbon dated to ca 10 000 12 000 yr b p activation energies formyaandhiatellaare estimated to be 30 6 and 30 0 kcal mol respectively for asp racemization and 29 0 and 29 5 for isoleucine epimerization analysis of a time series of plio pleistocenehiatellafrom the north coast of alaska shows that last interglacial mollusks can be readily distinguished from modern samples by asp but not by isoleucine d l asp values indicate a younger age for the fishcreekian transgression than does isoleucine epimerization for spitsbergen d l asp shows a slight age difference ca 12 000 yr between two units of the episode b interstadial and suggests that the age of these units may be closer to 65 000 than to 80 000 yr b p two possible ages suggested by other evidence the age of the loks land interstadial on baffin island is likely to be greater than that indicated by radiocarbon ages within deposits from each region d l asp values are less variable among individual shells than isoleucine epimerization values this may indicate better reliability of asp for geochronology

dependency of the north pacific winter storm tracks on the zonal distribution of mjo convection 1 we investigate the effects of the tropical madden julian oscillation mjo convection on the zonal location and intensity of storm activity during the boreal cool season nov 1 to feb 28 120 days over the pacific ocean as tropical convection shifts eastward from the eastern indian ocean to the western north pacific mjo induced local hadley circulation leads to an eastward displacement of extratropical rossby wave source rws consequently this influence leads to an eastward shift of the peak area of the storm track the storm track is strongest with the mjo convection over the eastern indian ocean phase 3 and it experiences the suppression when mjo convection is located over the maritime continents phase 4 and it increases again when the mjo propagates to the western pacific phase 5 after which it weakens again phase 6 the intensity of the storm track particularly over the western north pacific 120 e 180 is determined by the integrated effects of three factors the midlatitude convective forcing mcf the jet stream and rws these factors are associated with the locations of mjo convections it is estimated that mjo induced suppression accounts for only 2 5 of the total observed midwinter suppression mws however the pattern generated by the mjo is remarkably similar to the observed meridional displacement of north pacific storm track associated with sub seasonal variation we conclude that the spatial distribution of mjo affects the variation of the pacific storm track but is not a cause of the mws

dating pleistocene archeological sites by protein diagenesis in ostrich eggshell eggshells of the african ostrich struthio camelus ubiquitous in archeological sites in africa have been shown by laboratory simulation experiments to retain their indigenous organic matrix residues during diagenesis far better than any other calcified tissue yet studied the rate of l isoleucine epimerization to d alloisoleucine follows reversible first order kinetics and has been calibrated for local temperature effects and used to estimate the age range of stratified archeological sites age estimates are consistent with radiocarbon dates from several stratified archeological sites with adequate calibration this technique can provide accurate ages to within 10 to 15 percent for strata deposited within the last 200 000 years in the tropics and the last 1 000 000 years in colder regions such as china

comparison of simulations and data from a seismo acoustic tank experiment a tank experiment was carried out to investigate underwater sound propagation over an elastic bottom in flat and sloping configurations the purpose of the experiment was to evaluate range dependent propagation models with high quality experimental data the sea floor was modeled as an elastic medium by a polyvinyl chloride slab the relatively high rigidity of the slab requires accounting for shear waves in this environment acoustic measurements were obtained along virtual arrays in the water column using a robotic apparatus elastic parabolic equation solutions are in excellent agreement with data

mechanism for low frequency variability and salt flux in the mediterranean salt tongue the role of baroclinic instability in the generation of low frequency variability in the interior of ocean subtropical gyres and its possible importance in the zonal flux of salt and heat within the mediterranean salt tongue are discussed the observed zonal enhancement of the low frequency variability is interpreted as the signature of baroclinic instability of the large scale wind driven flow the zonal orientation results from the relatively weak vertical shear of the large scale upper ocean flow and the stabilizing influence of the planetary vorticity gradient there is a reversal in the vertical shear of velocity at middepths in the eastern basin of the north atlantic that results in a local middepth maximum in the zonal eddy flux of density linear theory predicts a vertical structure of this density flux that is nearly coincident with the observed vertical distribution of the warm salty water of the mediterranean salt tongue a primitive equation model is used to investigate the nonlinear large amplitude regime the zonal eddy density or salt flux averaged over several wavelengths and several cycles of wave growth and breaking indicates that this mechanism may be an important component in the overall salt balance in this region