new inferences of mantle viscosity from joint inversion of long wavelength mantle convection and post glacial rebound data we perform joint inversions for mantle viscosity of geophysical observables associated with both mantle convection and glacial isostatic adjustment gia our data include coefficients of the non hydrostatic geoid up to degree 8 and decay times associated with post glacial relative sea level rsl variations in hudson bay and fennoscandia we find that both data sets may be reconciled using a single profile of mantle viscosity which is characterized by a significant increase with depth across this region this result weakens previous arguments that the mantle rheology has significant transient effects the viscosity profiles we obtain are found to reconcile the observed free air gravity anomaly over hudson bay

the distribution of fe in the antarctic circumpolar current abstract the large scale distributions of dissolved and total fe in surface and deep waters of the antarctic circumpolar current exhibit strong relationships with hydrography and biological processes the mean dissolved fe concentrations are low in surface waters of the antarctic circumpolar current 0 31 0 49 nm with a minimum of 0 17 nm and higher averaging 1 11 9 nm in the polar frontal region enhanced dissolved surface water concentrations in the polar frontal region are attributed to input from the continental shelf and coincide with phytoplankton spring blooms of large diatoms the effects of sea ice melting and iceberg melting on the fe concentrations were relatively small dissolved deep water concentrations 400 m in the antarctic circumpolar current ranged from 0 4 to 2 8 nm circumpolar deep water has relatively high dissolved fe concentrations in the polar frontal region 0 4 2 8 nm compared with deep waters further to the south 0 6 1 1 nm similarly total dissolvable unfiltered fe concentrations in the upper circumpolar deep water tend to decrease southward from the polar frontal region in the lower circumpolar deep water total dissolvable fe concentrations are higher than in the upper circumpolar deep water due to the existing nepheloid layer and sources on the mid atlantic ridge dissolved and total dissolvable fe concentrations in the antarctic bottom water are higher than those of other water masses in the antarctic circumpolar current consistent with the nepheloid layer as well as diagenetic input from shelf sediments the high nutrient low chlorophyll areas of the antarctic ocean and northeast pacific ocean have different major fe input sources of similar magnitude in the antarctic circumpolar current upward transport of fe is the main input source whereas in the north pacific ocean aerosols are the dominant source

origin of a postglacial kettle fill sequence near georgetown ontario stratigraphic relationships radiocarbon dating and pollen and plant macrofossil analyses establish the origin and developmental history of a kettle near georgetown ontario the early inorganic s

transient diapycnal mixing and the meridional overturning circulation abstract an idealized three dimensional model of buoyancy forced flow in a single hemisphere is used to investigate whether transient diapycnal mixing can sustain the meridional overturning circulation in the annual mean mixing transience had little effect on the meridional overturning when mixing occurred on basin boundaries the overturning strength was found to be insensitive to mixing transience for mixing that was highly localized in space away from basin boundaries oceanic meridional mass and heat transport decreased as mixing became more transient the increased sensitivity in the highly localized case is likely due to the inhibition of surface heat flux into the thermocline the dynamic response to transient mixing featured large scale internal oscillations that increased in amplitude with the transience of mixing but were confined to the tropics and had little effect on the overturning cell through midlatitudes these results indicate that transient diapycnal mixing with a distribution sug

a complete formalism for the inversion of post glacial rebound data resolving power analysis summary a formal inverse theory for mantle viscosity based upon the data of glacial isostatic adjustment is here formulated and applied to synthetic data in this theory full account has been taken of the normal mode nature of the forward problem for realistic viscoelastic maxwell models of the planet since it is impossible to accurately infer the excitation and decay constants of the individual normal modes from the observations the formalism is cast in terms of the observed gross earth data in the time domain in this analysis expressions are required for the first order perturbations in both the modal amplitudes and relaxation times that are induced by an arbitrary radial perturbation to the starting viscosity profile a numerical technique is developed which enables us to accurately determine differential kernels for the modal amplitudes the analogous kernels for the modal decay times are derived analytically peltier 1976 and the complete set of kernels is shown to satisfy the physical constraint imposed by the uniqueness of the state of isostatic equilibrium for the viscously incompressible maxwell models that we employ when the problem is parametrized in terms of the logarithm of viscosity the kernels are capable of accurately predicting shifts in the normal mode characteristics for at least an order of magnitude variation in mantle viscosity using bayesian statistics a formal inversion is applied to a set of synthetically generated data these data chosen to reproduce the space time coverage of the actual observables include a subset related to the global gravity field and a large sequence of idealized relative sea level rsl curves it is found that even very weak a priori constraints can provide a stable and accurate inversion a resolving power analysis indicates a spatial resolution of approximately 1200km near the core mantle boundary cmb with a gradual improvement to better than 350km in the middle of the upper mantle subsets of the synthetic data are inverted in order to examine conditions on stability and accuracy and to determine their relative contributions to the spatial resolution data from progressively older beaches are shown to contribute most to the spatial resolution at all depths though the improvement in lower mantle resolution converges for data obtained from beaches formed within the last 5000 yr furthermore the rsl curves in the vicinity of the peripheral bulge of the ancient laurentide ice sheet are significant contributors to lower mantle resolution as demonstrated in previous analyses of the forward problem the inversion of this subset of the data also appears to be encouragingly stable

paleoclimatic implications of a late wisconsinan insect assemblage from rostock southwestern ontario the rostock site is situated in a peat covered wetland where fragments of a mammoth mammuthus primigenius were unearthed in 1982 excavation showed a descending sequence of peat silty marl gravel clayey silt and till approximately 300 kg of sediment was taken from the section for pollen invertebrate and geochemical analyses the peat marl transition is believed to be approximately contemporaneous with the spruce pine transition in southern ontario ca 10 600 years bp a date of 10 790 150 years bp on collagen from mammoth tusk fragments recovered from the same level substantiates this inference insects especially coleoptera were common throughout the marl and represent at least 2000 individuals from 16 different families on the basis of beetle ecologies and modern distributions the marl was subdivided into lower and upper horizons the lower horizon contains many species that are today restricted to western and northern north america they are typical residents of the northern boreal fore

lateral variations in mantle rheology implications for convection related surface observables and inferred viscosity models summary over the past decade numerous analyses of convection related observables such as horizontal surface divergence geoid or gravity anomalies and dynamic surface topography have been carried out in the context of tomography based mantle flow models one of the major objectives of this modelling has been the inference of the rheological structure of the mantle with few exceptions these studies have been conducted in the framework of a viscous flow theory which assumes that the mantle rheology may be represented in terms of an effective viscosity which varies with depth only here we present a detailed assessment of the impact of lateral variations in viscosity on global convection related observables using forward modelling of buoyancy induced flow in a 3 d spherical shell we find that the resulting dynamic topography at the surface and the core mantle boundary as well as the gravitational response of the earth are affected relatively little by the inclusion of lateral viscosity variations lvv when compared with results for a purely 1 d radial viscosity model in particular we found that the effect of lvv on the global observables is significantly smaller than the variability due to uncertainties in the current seismic tomography models we also quantify the effect of lvv in the context of the viscosity inverse problem using two synthetic data sets generated with a 1 d viscosity profile and with a fully 3 d viscosity model in which the lvv span across three orders of magnitude we compared the 1 d viscosity profiles recovered from the inversions and found that lvv have virtually no effect on our inversion results the synthetic viscosity inversion further revealed that the effect of lvv is small in comparison to the uncertainties arising from the seismic tomography models the inversions also suggest that the 1 d viscosity profiles derived from actual surface data represent the depth variation of the horizontally averaged logarithm of the 3 d viscosity distribution in the mantle intr o duction constraining the rheological properties of the mantle using surface geophysical data has traditionally involved separate treatments of short seismic intermediate solid earth tides long postglacial rebound and very long mantle convection timescale processes in each case the initial focus historically speaking has been on the inversion of the data to determine a one dimensional 1 d purely radial variation of the relevant rheological parameter e g elastic moduli intrinsic attenuation and viscosity which provides the best fit to the data it has long been recognized particularly in the context of the seismic inverse problem that the search for a 1 d earth model is subject to possible bias due to the presence of lateral variations in structure which may be as significant as the radial variations especially at shallow depths this paper is concerned with the mantle viscosity field the earliest inferences of the radial i e horizontally averaged profile of viscosity based on glacial isostatic adjustment gia data e g mcconnell 1968 parsons 1972 were characterized by a pronounced increase of viscosity with depth in the top half of the mantle however these were followed by two decades of gia research that argued for an essentially isoviscous

a mechanism for lack of sea ice reversibility in the southern ocean we find evidence that ocean processes during global warming may result in irreversible changes to the antarctic sea ice whereas the arctic sea ice changes appear to be reversible increased forcing gives rise to strong heat uptake in the southern ocean and existing pathways provide an increased transport of heat to the weddell sea as atmospheric concentrations of co2 are returned to preindustrial levels the antarctic ice extent at first recovers but a rapid change in the position of the an ocean front in the south atlantic maintains the heat transport into the weddell sea a cooling surface initiates deep convection accessing the stored heat resulting in a substantial loss of sea ice which has not recovered after a further 150 years at preindustrial co2

holocene paleoclimate and paleoecology determined from fossil coleoptera at brampton ontario canada an unusually rich and extensive 5 m sequence of organic rich sediments ca 13 000 to ca 4500 bp from a drained glacial kettle near brampton ontario has produced a large and varied assemblage of fossil insects coleoptera beetles from the base include species typical of northern boreal or tree line habitats today approximately one metre above the base of the section ca 11 500 bp there is an abrupt appearance of numerous bark beetles family scolytidae and other coleoptera that inhabit boreal forests temperate species whose ranges are predominantly or totally south of the ontario border appear beginning at ca 9500 bp suggesting environmental conditions similar to modern ones younger dryas and pre boreal oscillation cold events may be evident in lower parts of the boreal sequence although considerations of temporal and climatic resolution make interpretation somewhat ambiguous

postglacial rebound observed by lageos and the effective viscosity of the lower mantle sixty four observations of the orbital node made by the lageos satellite over a five year time interval reveal an acceleration of 8 1 or 1 8 x 10 to the 8 power arcseconds day 2 due to a source which is not presently modeled in the geodyn orbit determination computer program this acceleration cannot be explained by the ocean tide with 18 6 year period assuming it to be an equilibrium tide instead it seems to be due to postglacial rebound which changes the j 2 coefficient in the spherical harmonic expansion of the earth s gravitational field at the rate of 8 2 or 18 x 10 to the 19th power s this in turn accelerates the node this rate does not agree with the 32 x 10 to the 19th power s predicted by wu and peltier s 1982 l2 model which has upper and lower mantle effective viscosities of 10 to the 21st and 22nd powers pa s respectively it does agree well with their l1 model which gives about 10 x 10 to the 19th power s since the effective viscosity is 10 to the 21st power pa s throughout the entire mantle in the l1 model the results support the contentions that the efective viscosity is near 10 to the 21st power pa s everyhere in the mantle and this relatively low value for the effective viscosity may have permitted several degrees of polar wander due to glaciation during the quaternary ice age previously announced in star as n84 13705

thermal history of the earth a corollary concerning non linear mantle rheology abstract mantle rheology and the convective cooling process exert a close mutual control on one another so that the cooling rate can be calculated with only a rudimentary idea of the material properties of the mantle however the distinction between linear i e newtonian viscous behaviour and non linear or power law rheology in which the creep rate depends upon stress as n with n 1 it isportant we find that the present rate of loss of residual heat is almost twice as great with n 3 as it si tn the linear case n 1 since this net heat loss is simply the difference between the observed total mantle heat flux and the radiogenic heat input the radioactive content of the mantle is predicted to be substantially less in the non linear case an examination of the plausible ranges of the u th and k contents of the mantle shows that the requirement for radiogenic heat by the linear model us unreasonably high this observation strengthens an earlier very tentative conclusion based on temperatures of komatiite lavas that convective mantle rheology is non linear the alternative conclusion would be that the earth contains 30 ppb of u compared with carbonaceous chondrites 20 ppb or ordinary chondrites 15 ppb

the thickness of the continental lithosphere two independent sets of geophysical data are shown to be particularly sensitive to the thickness of the continental lithosphere both are connected with the response of the planet to the last deglaciation event of the current ice age the first set of data consists of relative sea level histories in the age range 0 10 kyr b p from sites along the eastern seaboard of north america such data appear to require a continental lithospheric thickness in excess of 200 km the second set of data consists of the ils record of the motion of the rotation pole over the time range 0 75 years b p which reveals a secular drift at the rate of 0 95 0 15 deg 106 years toward hudson bay when the viscosity profile of the mantle is fixed to that required to explain free air gravity and relative sea level data from within the ice margin and the observed nontidal acceleration of planetary rotation then these observations also suggest a continental lithospheric thickness of the same order

mantle phase transitions and the free air gravity anomalies over fennoscandia and laurentia the interpretation of free air gravity anomalies over present day centers of postglacial rebound has always been controversial we show that the observed gravity anomalies over both fennoscandia and laurentia and the associated relative sea level variations since deglaciation are explicable with a simple newtonian viscoelastic model of the earth if the earth model includes the density jumps in the mantle associated with the phase transitions at 420 and 670 km depth the result has important implications for mantle convection since the observed free air anomalies are very sensitive to the viscosity of the mantle beneath the deepest phase transition

comparison of shear measurements and mixing predictions with a direct observation of diapycnal mixing in the atlantic thermocline four sets of velocity and density profiles have been measured with an autonomous profiler during an upper ocean intentional tracer sf6 diapycnal diffusivity measurement the north atlantic tracer release experiment natre the tracer was injected near 310 m depth in the canary basin two profile sets were collected 6 months after tracer release and two were collected i year after release all within the horizontal boundaries of the sf6 patch shear and strain can be combined with turbulent kinetic energy dissipation and diffusivity measurements published elsewhere to test existing expressions for dissipation and diffusivity due to shear induced turbulence these expressions arise from internal wave decay modeling one expression of dissipation parameterized in terms of shear based on stochastic nonlinear internal wave interaction has fared well empirically its extension to estimate diffusivity is evaluated shear variance of the first two data sets was about 1 6 times gm76 and 2 5 to 3 0 times gm76 in the later sets the average parameterized mixing estimate computed using all of the temporally limited shear measurements overestimates annual mean natre diffusivity 1 5 x 10 m 2 s by a factor of 1 2 a modified parameterization gives an underestimate to first order this supports the present understanding of open ocean diffusivity in terms of fine scale shear and internal wave decay that is the slow diapycnal mixing was not a consequence of unusually low shear adjustment of the shear induced mixing models to better fit the data is not warranted because of the lack of direct comparability between the various measurements the expected natural variability of the shear and sampling errors

phase transition modulated mixing in the mantle of the earth and discussion recently published a priori analyses of the mantle convection process demonstrate that the influence of the endothermic phase transformation at 660 km depth could be profound and such as to enforce a strongly intermittent style of circulation in this phase transition modulated regime mass transfer across the 660 km horizon is inhibited leading to the formation of an internal thermal boundary layer that straddles the phase change interface this thermal boundary layer is itself episodically disrupted by convective instability leading to the development of intense avalanches of cold material from the transition zone into the lower mantle the consequences of such a circulation regime to the understanding of trace element geochemistry and the supercontinent cycle may be extremely important equally important are the implications for mantle viscosity since a circulation of this type would appear to allow reconciliation of a wide range of geodynamic data with a single viscosity model the relevant data include convection related observables such as the aspherical geoid and postglacial rebound related observables such as relative sea level histories and certain anomalies in earth rotation including the so called non tidal acceleration of rotation and the ongoing wander of the rotation pole towards greenland at a rate near 0 95 degrees per million years

wind driven internal waves and langmuir circulations in a numerical ocean model of the southern baltic sea 1 a one dimensional numerical ocean model of the southern baltic sea is used to investigate suitable parameterizations of unresolved turbulence and compare with available observations the turbulence model is a k e model that includes extra source terms piw and plc of turbulent kinetic energy tke due to unresolved breaking internal waves and langmuir circulations respectively as tides are negligible in the baltic sea topographic generation of internal wave energy iwe is neglected instead the energy for deepwater mixing in the baltic sea is provided by the wind at each level the source term piw is assumed to be related to a vertically integrated pool of iwe e0 and the buoyancy frequency n at the same level according to piw z e0n z this results in vertical profiles of e the dissipation rate of tke and kh the eddy diffusivity according to e n and kh n 2 below the main pycnocline earlier observations are inconclusive as to the proper value of and here a range of values of is tested in hundreds of 10 year simulations of the southern baltic sea it is concluded that 1 0 0 3 and that a mean energy flux density to the internal wave field of about 0 9 0 3 10 3 w m 2 is needed to explain the observed salinity field in addition a simple wind dependent formulation of the energy flux to the internal wave field is tested which has some success in describing the short and long term variability of the deepwater turbulence the model suggests that 16 of the energy supplied to the surface layer by the wind is used for deepwater mixing finally it is also shown that langmuir circulations are important to include when modeling the oceanic boundary layer a simple parameterization of langmuir circulations is tuned against large eddy simulation data and verified for the baltic sea

biological and chemical signs of upward motions in permanent geostrophic fronts of the western mediterranean upward motions are often invoked to explain the high productivity of permanent geostrophic fronts in the western mediterranean while physical evidence of such upward advections is seldom reported the goal of this study is to define biological and chemical criteria which can be used to localize such upward motions zones we use a one dimensional time dependent model of phytoplankton dynamics to test the effects of upward advection on the vertical distribution of phytoplankton biomass nutrients and dissolved oxygen simulations also include the effects of advective motions of the phytoplankton cells in the light field on phytoplankton growth in conformance with the continuity equation boundary conditions were defined to allow horizontal flow of the upwelled water within the upper mixed layer low upward advections 3 m d led to a shallowing and sharpening of the nitracline oxycline and deep maxima of phytoplankton biomass and oxygen and to an increase in phytoplankton biomass by confining the phytoplankton nutrient system in the surface mixed layer higher upward advections lead to homogeneous phytoplankton biomass and oxygen vertical distributions in the upper mixed layer the nitracline and the oxycline being then at the top of the pycnocline data collected during the prolig 2 cruise may 1985 on the heavy side of the liguro provenqal front are interpreted as an illustration of these numerical results computed primary production rates are compared with measurements conducted in the almer a oran front during the almofront i cruise april 1991 in a similar situation in both fronts upward advections of 1 2 m d would be sufficient to account for the observed vertical distributions and the increased primary production ecological implications for the phytoplankton nutrient system are discussed particularly the spatial uncoupling of phytoplankton biomass and primary production in permanent geostrophic fronts 1 introduction the liguro provengal front b thoux et prieur 1983 sournia et al 1990 and the almerfa oran front cheney and doblar 1982 tintor et al 1988 are permanent geostrophic structures in the western mediterranean both fronts are areas of high plankton biomass in contrast with two adjacent oligotrophic type systems lohrenz et al 1988 tintor et al 1988 sournia et al 1990 prieur et al 1993 claustre et al 1994b and show net change in both the specific composition of the autotrophic claustre et al 1994b and the heterotrophic boucher et al 1987 thibault et al 1994 communities several features indicate that the two fronts are sites of enhanced production in response to geostrophic frontal dynamics in addition to the main geostrophic flow a secondary circulation exists i e the ageostrophic flow which is characterized by enhanced vertical advections as shown for example by dewey et al 1991 in the california current it is thought that upward advections in the frontal zone upwell nutrients into the photic zone and enhance primary production lohrenz et al 1988 fideau et al 1994 the resulting high biomass is then downwelled by the conver paper number 98jc01537 0148 0227 98 98 jc 01537509 00 gent part of the ageostrophic circulation along the isopycnals claustre et al 1994a b fideau et al 1994 however physical evidence for upward advection in the two fronts is not well documented see however tintor et al 1991 and l iudez and tintor 1996 and poorly understood this paper defines criteria from the vertical distribution of parameters involved in primary production which can be used to localize with some confidence the upward motions in such frontal zones in a previous modeling study zakardjian and prieur 1994 two types of phytoplankton nutrient systems resulting from high and low turbulent regimes htr and ltr respectively were described with the ltr representing the ecological conditions in the waters adjacent to the liguro provengal and almerga oran fronts where the vertical structure is controlled by diffuse vertical fluxes we use a modified version of this previous one dimensional vertical model presented in section 2 to test the sensitivity of the ltr system when an upward advection term is added in section 3 we describe the steady state vertical distribution of phytoplankton biomass nutrients and dissolved oxygen obtained with upward advection values ranging from 0 to 5 m d effects of upward advection on the vertical distribution of primary production on phytoplankton growth and finally on the productivity indexes of the water column are detailed in section 4 we present multiparametric 27 849

a diverse late glacial mackinaw phase biota from leamington ontario a sand pit at leamington ontario in southeastern essex county in the southernmost part of canada has yielded many taxa of fossil animals and plants that are dated over 13 000 bp the fossils are of both terrestrial and freshwater origin and comprise a surprisingly diverse but coherent assemblage of molluscs ostracodes chironomidae coleoptera turbellaria trichoptera and a few fish bone fragments this is the oldest known postglacial occurrence in ontario for all animal groups paleoenvironments indicated by the taxa range from boreal forest to tundra taxa are an in situ assemblage with little transport or reworking although this site has yielded the richest fossil record of this age yet found in ontario previous finds at a few sites on the north edge of the eastern erie basin and in the southern huron basin indicate plants were well established in southwestern ontario by the time of the mackinaw phase interstadial when lowered lake levels likely facilitated their arrival from land areas to the south this discovery greatly improves the prospects of finding fossils of this age even though the known record is still extremely limited the site represents fortuitous preservation and discovery and amply demonstrates that glacial lakes of this time when much of the last ice sheet was still in existence were far from barren of life and that the migration of biota into the area was quite rapid during ice retreat resume de nombreux taxons d animaux et de plantes fossiles datant de plus de 13 000 ans avant le present ont ete trouves dans une carriere de sable a leamington en ontario dans le sud est du comte d essex dans la partie la plus meridionale du canada les fossiles ont des origines terrestres et d eau douce et ils comprennent un assemblage etonnamment diversifie mais coherent de mollusques d ostracodes de chironomes de coleopteres de turbellaries de trichopteres et de quelques fragments d os de poissons cet endroit constitue la plus ancienne occurrence postglaciaire en ontario de tous les groupes d animaux les paleoenvironnements signales par la plage des taxons varient de la foret boreale a la toundra les taxons constituent un assemblage in situ tres peu deplace ou retravaille bien que ce site ait produit le plus riche profil fossile de cet ge trouve a ce jour en ontario des decouvertes anterieures a quelques sites a la bordure nord de l est du bassin du lac erie et dans le sud du bassin du lac huron indiquent que des plantes etaient bien etablies dans le sud ouest de l ontario a l epoque de l interstadiaire mackinaw alors que les niveaux abaisses des lacs ont sans doute facilite leur arrivee en provenance de territoires plus au sud cette decouverte ameliore grandement les perspectives de trouver des fossiles de cet ge meme si les donnees sont encore tres limitees le site represente une conservation et une decouverte fortuites et demontre de maniere significative que les lacs glaciaires de cette epoque alors que la derniere nappe glaciaire existait encore etaient loin d etre steriles et que la migration du biote dans la region s est effectuee assez rapidement lors du retrait de la glace

boundary mixing in a rotating stratified fluid extension d une experience de laboratoire sur le melange en couche limite dans un fluide stratifie pour inclure les effets de rotation la combinaison du melange vertical a la frontiere et du melange horizontal par des tourbillons d echelle moyenne conduit a l affaiblissement du gradient de densite interieur

deglaciation induced vertical motion of the north american continent and transient lower mantle rheology the last deglaciation event of the current ice age which began approximately 18 000 years ago and ended about 7000 years ago continues to exert a profound influence on the vertical motion of the solid earth in and surrounding the regions which were once ice covered observations of such vertical motions may be employed to constrain the radial viscoelastic structure of the planet and therefore to contribute in an important way to the understanding of geodynamic processes in general in this paper both present day rates of vertical motion as recorded on tide gauges and long time scale records of vertical motion as recorded in 14c controlled relative sea level histories are employed to refine previously constructed models of the radial viscoelastic structure an interesting sidelight to this analysis is the demonstration that the lower mantle viscosity inferred from the vertical motion data could represent a transient rather than the steady state value a fact which would help considerably to reconcile the small viscosity stratification required by the glacial rebound data with the large stratification which seems to be required by some recent analyses of the geoid height anomalies associated with internal density heterogeneity of the mantle which has been revealed by application of seismic tomographic techniques a further product of these new analyses is obtained by the application of the glacial isostatic adjustment model to filter this signal from the secular trends of relative sea level observed on tide gauges from both the east and west coasts of the north american continent these results may be important in the context of recently proposed scenarios of climatic change

rheological models and interpretation of postglacial uplift accepted 1989 february 1 received 1989 january 28 in original form 1988 september 26 summary paper investigates four generalized maxwebl bodies gmbs and the classical maxwell body cmb with respect to their potential to explain postglacial uplift the gmbs are the lomnitz body defined by a logarithmic creep law the q power law body defined by a power law dependence of the quality factor on frequency the caputo body defined by a special stress strain relation with memory and the burgers body the burgers body is a 4 parameter model the other gmbs have 3 and the cmb has only 2 parameters theoretical uplift curves are calculated for simple space time models of the canadian and fennoscandian deglaciations and hedgehog inversion yields the successful model parameters the gmbs explain the data better than the cmb the parameters of the burgers body are only rather weakly constrained because of trade offs among them from the success of the gmbs we conclude that long time scale transient creep is a possible rheological behaviour of mantle rocks viscosity extrapolation from the time constant of postglacial uplift about 10 ka to the time constant of mantle convection roughly 100 ma is made with the effective viscosity and yields approximately ld2 pas q power law body loz3 pas caputo body and loz5 pas lomnitz body hence postglacial uplift does not strongly constrain the long time scale mantle viscosity it provides only a lower bound about loz1 pas this value follows from data interpretation with the cmb model in which steady state creep is present alone rayleigh number estimates for whole mantle convection are clearly supercritical for the cmb the q power law body and the caputo body but only about critical or even subcritical for the lomnitz body both postglacial uplift and mantle convection is satisfactorily explained by the cmb the q power law body and the caputo body

diapycnal mixing in western boundary currents in a previous study pelegri and csanady 1991 we found upward entrainment and two way exchange between the upper thermocline and surface layers of the gulf stream here we use isopycnic coordinates to analyze the mechanism of diapycnal shear induced mixing in western boundary currents a hydrographic section across the gulf stream off the mid atlantic bight is used for a case study it shows that the upper thermocline layers of the gulf stream are characterized by relatively small 16 m averaged gradient richardson numbers ri analysis of the jacobian j z p with z the depth and p the potential density total vorticity and potential vorticity fields shows that this region has low jacobian values associated with high values of potential vorticity as required theoretically for the case of dominant diapycnal mixing the density tendency wp dp dt is calculated from the vertical gradient of the reynolds density flux the latter parameterized as density eddy diffusivity divided by the jacobian we use munk and anderson s 1948 expression for the eddy diffusivity coefficient modified to conform to data of ueda et al 1981 maintaining a ri 3 2 dependence for large ri from this we obtain an explicit expression for wp in terms of the ri and j distributions the distributions of wp its diapycnal gradient wp p and the diapycnal velocity wd jwp are then calculated regions of high diapycnal convergence large negative wp p values coincide with the location of anomalously low jacobians in agreement with the idea that diapycnal mixing is the consequence of anomalies produced during frontogenesis in some phase of the meanders we suggest that this process taking place intermittently in space and time is responsible for two way exchange in western boundary currents

geoid anomalies in a dynamic earth in order to obtain a dynamically consistent relationship between the geoid and the earth s response to internal buoyancy forces we have calculated potential and surface deformation love numbers for internal loading these quantities depend on the depth and harmonic degree of loading they can be integrated as green functions to obtain the dynamic response due to an arbitrary distribution of internal density contrasts spherically symmetric self gravitating flow models are constructed for a variety of radial newtonian viscosity variations and flow configurations including both whole mantle and layered convection we demonstrate that boundary deformation due to internal loading reaches its equilibrium value on the same time scale as postglacial rebound much less than the time scale for significant change in the convective flow pattern by calculating relaxation times for a series of spherically symmetric viscous earth models for uniform mantle viscosity the geoid signature due to boundary deformations is larger than that due to internal loads resulting in net negative geoid anomalies for positive density contrasts geoid anomalies from intermediate wavelength density contrasts are amplified by up to an order of magnitude geoid anomalies are primarily the result of density contrasts in the interior of convecting layers density contrasts near layer boundaries are almost completely compensated layered mantle convection results in smaller geoid anomalies than mantle wide flow for a given density contrast viscosity stratification leads to more complicated spectral signatures because of the sensitivity of the dynamic response functions to model parameters forward models for the geoid can be used to combine several sources of geophysical data e g subducted slab locations seismic velocity anomalies surface topography to constrain better the structure and viscosity of the mantle

radial profile of mantle viscosity results from the joint inversion of convection and postglacial rebound observables we present new inferences of the radial profile of mantle viscosity that simultaneously fit long wavelength free air gravity harmonics associated with mantle convection and a large set of decay times estimated from the postglacial uplift of sites within previously glaciated regions hudson bay arctic canada and fennoscandia the relative sea level variation at these latter sites is constrained by age height pairs obtained by geological survey rather than the subjective trends which are commonly used in glacial isostatic adjustment gia studies our viscosity inferences are generated using two approaches first we adopt a relative viscosity profile which is known to provide a good fit to the free air gravity harmonics and determine an absolute scaling which yields a best fit to the gia decay time constraints second we perform an iterative nonlinear joint inversion of the two data sets in both cases our inferred profiles are characterized by a significant increase of viscosity 2 orders of magnitude with depth to values of 1022 pa s in the bottom half of the lower mantle the new viscosity profiles are shown to satisfy constraints based on the postglacial uplift of both fennoscandia the classic haskell 1935 number and hudson bay which have commonly been invoked to argue for an isoviscous mantle furthermore the models are used to predict a set of long wavelength signatures of the gia process these include predictions of gia induced variations in 1 the length of day over the late holocene period 2 the earth s precession constant and obliquity over the last 2 6 myr and 3 the present day zonal harmonics of the geopotential jl l 7 the predictions 1 and 3 bound the late holocene and ongoing mass flux between the large polar ice sheets greenland and antarctic and the global oceans to small values 0 4 mm yr equivalent eustatic sea level rise

interpreting paleoclimate from l8o and 2h in plant cellulose comparison with evidence from fossil insects and relict permafrost in southwestern ontario the oxygen isotope content of terrestrial plant cellulose is related to that of the source waters by a two step process involving evapotranspirative leaf water enrichment and equilibrium isotopic exchange between leaf water and atmospheric carbon dioxide a combination of two models that describe these steps yields consistent agreement between measured and predicted climatic and isotopic data humidity is the dominant influence on variations in the cellulose 18o enrichment relative to the source water a good first order approximation of the average daytime relative humidity during the growth season at a site can be based on the linear correlation that exists between humidity and cellulose enrichment without explicit consideration of factors such as temperature 18o of atmospheric vapour and leaf boundary layer dynamics the value of the combined model for paleoclimatic reconstruction has been tested using fossil wood from a late glacial site at brampton ontario estimates of the past relative humidity

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

abrupt climate oscillations during the last deglaciation in central north america evidence from stable isotopes and a variety of proxies from two ontario lakes demonstrate that many of the late glacial to early holocene events that are well known from the north atlantic seaboard such as the gerzensee killarney oscillation also known as the intra allerod cold period younger dryas and preboreal oscillation also occurred in central north america these results thus imply that climatic forcing acted in the same manner in both regions and that atmospheric circulation played an important role in the propagation of these events

evolution of the northern santa cruz mountains by advection of crust past a san andreas fault bend the late quaternary marine terraces near santa cruz california reflect uplift associated with the nearby restraining bend on the san andreas fault excellent correspondence of the coseismic vertical displacement field caused by the 17 october 1989 magnitude 7 1 loma prieta earthquake and the present elevations of these terraces allows calculation of maximum long term uplift rates 1 to 2 kilometers west of the san andreas fault of 0 8 millimeters per year over several million years this uplift in concert with the right lateral translation of the resulting topography and with continual attack by geomorphic processes can account for the general topography of the northern santa cruz mountains

consequences of experimental transient rheology recent analyses of transient creep data for lower crustal and upper mantle substances show that the parameters of the burgers body rheological model used up to now by geodynamicists have much lower ratios of the short term to long term viscosities than the laboratory values we have used these data to constrain the viscosity contrast across the 670 km discontinuity our results show that the previously inferred viscosity variations are now reduced by about a factor of ten in the new transient models this finding is in agreement with the revised viscosity estimate based on long wavelength geoid anomalies and seismic tomography we find that time dependent perturbations to the gravity field from recent ice movements are not at all small

biogeochemical cycling in the global ocean 1 a new analytical model with continuous vertical resolution and high latitude dynamics a new simple analytical model of ocean chemistry is presented which includes continuous vertical resolution high latitude dynamics air sea exchange and sea ice cover in this high latitude exchange interior diffusion advection hilda model ocean physics are represented by four parameters k and w an eddy diffusion coefficient and a deep upwelling velocity in the stratified interior q a rate of lateral exchange between the interior and a well mixed deep polar ocean and u an exchange velocity between surface and deep layers in the polar ocean first estimates are made of ice free and ice covered areas at high latitudes surface temperatures and air sea exchange velocities from available data then values of the physical parameters are estimated from simultaneous least mean square fits of model solutions for temperature t and abiotic carbon 14 14c to interior profiles of t and 14c and surface layer 14c values all derived from available data best fit values for k w q and u are 3 2 10 5 m2 s 1 2 0 10 8 m s 1 7 5 10 11 s 1 and 1 9 10 6 m s 1 respectively these results are interpreted in terms of modes of ocean circulation and mixing and compared with results from other simplier and more complex models in parts 2 and 3 of this series these values for k w q and u are taken as inputs for studying phosphorus oxygen and carbon cycling in the global ocean with the hilda model

late glacial climate and ecology of a kettle section at brampton ontario canada as determined from fossil coleoptera a 5 m sequence of organic rich sediments ca 13 000 years bp to ca 4500 bp from a drained glacial kettle pond near brampton ontario has yielded a rich and varied assemblage of coleopteran foss

the role of boundary mixing in the deep ocean recent laboratory studies demonstrate that mixing at the boundaries of stratified and rotating fluids can be described by a relatively simple parameterization these results are applied to the deep ocean and by using available field observations it is argued that mixing at the boundaries can lead to an apparent diapycnal diffusivity in the interior of the deep ocean whose magnitude has an upper bound of 3 10 5 m2 s 1

a new inference of mantle viscosity based upon joint inversion of convection and glacial isostatic adjustment data we present new profiles of mantle viscosity derived on the basis of non linear occam style joint inversions of an extensive set of data associated with mantle convection and glacial isostatic adjustment gia the convection related observables include satellite derived free air gravity harmonics the geodetically inferred excess ellipticity of the cmb and tectonic plate motions the gia constraints involve two classes of observables previously shown to be relatively insensitive to errors in the late pleistocene ice history the so called fennoscandian relaxation spectrum frs and a set of site specific decay times determined from the postglacial sea level history in hudson bay and sweden the inverted viscosity profiles show a significant three orders of magnitude increase from the upper mantle mean value of f4 10 20 pa s to a high viscosity 10 23 pa s peak at

new constraints on transient lower mantle rheology and internal mantle buoyancy from glacial rebound data a model of mantle rheology which has an explicit transient component of its relaxation spectrum is shown to reconcile two apparently conflicting inferences of lower mantle viscosity if recent analyses of isostatic geoid anomalies are correct in requiring a large increase of viscosity with depth then the weak viscosity stratification demanded by postglacial rebound data implies the importance of such rheological behaviour at least in the earth s lower mantle

north pacific upper ocean cold temperature biases in cmip6 simulations and the role of regional vertical mixing abstractsubstantial model biases are still prominent even in the latest cmip6 simulations attributing their causes is defined as one of the three main scientific questions addressed in cmip6 in t

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

observations of the structure of turbulent mixing across the kuroshio 1 the mean structure of turbulence intensity across the kuroshio in spring is presented by compositing microstructure profiles on a stream coordinate the composite mean of turbulent energy dissipation rate e was high near fronts on both cyclonic and anticyclonic sides on the cyclonic side e 10 8 w kg 1 vertical diffusivity of 3 10 5 m2 s 1 was observed in the region of strong vertical shear of geostrophic velocity depth averaged e within the depth range 50 150 m 150 250 m was significantly higher at 0 to 50 km 25 to 50 km compared with 50 km from the axis although lower than on the cyclonic side e at depths of 50 150 m on the anticyclonic side near the front was again enhanced on this side the total vertical shear of horizontal velocity was strong whereas the geostrophic shear was weak

changes in late quaternary vegetation and insect communities in southwestern ontario abstract the gage street site in kitchener ontario is a peat marl sequence representing continuous lacustrine sedimentation from the time of deglaciation ca 13 000 yr b p through 6900 yr b p insect pollen and plant macrofossil remains isolated from the sediments indicate that from ca 13 000 to 12 500 yr b p the region was characterized by parkland tundra vegetation existing within thermal conditions more analogous to those today of the midboreal forest the transition from parkland to coniferous forest at ca 12 500 yr b p occurred within a climate that was only gradually warming by the time of the spruce pine transition at 10 500 yr b p an insect fauna had become established that is typical of southwestern ontario today the replacement of this fauna at ca 8400 yr b p by one characteristic of the lowlands of the east central united states represents the beginning of hypsithermal conditions in southern ontario vegetation and insects indicate that the climate continued to gradually warm through the mid holocene

the lageos constraint on deep mantle viscosity results from a new normal mode method for the inversion of viscoelastic relaxation spectra the recently observed acceleration in the node of the orbit of the lageos satellite has previously been shown to provide a good constraint on the viscosity of the earth s mantle beneath the 670 km seismic discontinuity this paper explores the extent to which the previously inferred lower mantle viscosity may be traded off against variations of other properties of the radial viscoelastic structure we show explicitly that the nontidal acceleration of rotation inferred from the lageos data and predicted as a consequence of the earth s response to the last deglaciation event of the current ice age is relatively insensitive both to variations of lithospheric thickness and to the presence or absence of plausible chemical heterogeneity across the 670 km interface it therefore provides a high quality constraint on the viscosity of the deep mantle with the upper mantle viscosity fixed at the nominal value of 1021 pa s the bounds on lower mantle viscosity lm are such that 2 1021 pa s lm 6 1021 pa s even when allowance is made for the presence of a viscous boundary layer at the base of the upper mantle such as would exist if the mantle convective circulation were layered

glacial isostatic adjustment and the free air gravity anomaly as a constraint on deep mantle viscosity summary a gravitationally self consistent theory for relative sea level variations forced by pleistocene deglaciation events is employed to explore the extent to which rsl and free air gravity observations together constrain the viscosity of the mantle beneath the seismic discontinuity at 670 km depth a trade off is revealed between errors in the assumed deglaciation history and errors in the inferred value of the viscosity of the lower mantle taking full account of such uncertainty plausible values of the viscosity beneath the transition region are bounded above by 1023 poise cgs units the preferred value is at least a factor of 2 lower than this and is strongly constrained by the observed free air gravity anomaly over hudson bay the calculations described in detail here show for the first time that the relatively large gravity anomalies observed over sites of wurm wisconsin deglaciation do not require any pronounced increase of mantle viscosity with depth in order to explain them

vertical mixing in the baltic sea and consequences for eutrophication a review abstract in the transition area between the north sea and the baltic sea entrainment processes dominate the vertical mixing in the inflowing saline bottom water the hot spots of these processes are located at the darss sill and the bornholm channel in the western baltic sea in the central baltic sea the horizontal advection of saline water in deep layers below the permanent halocline dominate the temporal changes and associated transports this is accompanied by the turbulent vertical transport through the halocline into the surface layers the related vertical salt transport into the entire surface mixed layer estimated by various methods is slightly above 30 kg m 2 a during stagnation periods the residence time of the deep water in the eastern gotland basin increases roughly by a factor of five vertical mixing through the halocline is drastically reduced when inflows are lacking the potential processes of diapycnal mixing are discussed to the present knowledge the turbulent motion resulting from breaking internal waves is capable of turbulent transports through the halocline corresponding to the estimates of the salt transport into the surface mixed layer the actual knowledge about boundary mixing due to internal waves in the baltic sea is poor mesoscale eddies may contribute to the vertical mixing but it is not known whether they really do and which of the possible direct and indirect mixing mechanisms is most effective near bottom currents induced by inflow events likely enhance vertical mixing coastal upwelling certainly contributes to the vertical transport but the depth of its origin and the volume transport are hard to determine for large scale quantifications the short spatiotemporal scale of turbulent transports through the halocline resulting in a weakening of the halocline during summer together with the mixing of the entire surface layer down to the halocline in winter form a consistent description of the vertical salt transport it is hypothesised that the longer residence time of the deep water during stagnation periods results from the lack of energy imported by the inflows and directly or indirectly feeding the diapycnal mixing processes the vertical transport of nutrients such as the phosphate is quantitatively not sufficiently understood and needs further interdisciplinary research activities

transient creep in orthosilicates abstract an analysis of garnet olivine and ultramafic aggregate deformation data is performed using a burgers body rheology such that transient elasticities and viscosities can be obtained our results are indicative of transient shear moduli with magnitudes of about one tenth the isostatic shear moduli and transient viscosities of magnitudes 0 5 0 7 of the steady state viscosities these values differ significantly from those chosen by previous workers for burgers body parameters pertinent to transient creep in the lower mantle transient viscosity appears to have the same temperature dependence as the steady state viscosity which requires that the transient elastic modulus becomes rapidly weaker with increasing temperature hydrolytic weakening also seems to be accompanied by a weaker transient elastic modulus implying a longer relaxation period of the transient strains in water weakened experiments a discrepancy between previously reported transient behavior in dunite and the data analyzed here can be attributed to errors in the dunite experimental data

subducted slabs and the geoid constraints on mantle rheology and flow geoid anomalies are primarily the result of the density contrasts driving mantle convection and plate motion the total geoid anomaly resulting from a given density contrast in a convecting earth is affected by the mass anomalies associated with the flow induced deformation of the upper surface and internal compositional boundaries as well as by the density contrast itself these boundary deformations and hence the total gravity field depend on the radial distribution of effective viscosity if the internal density contrasts can be estimated as is the case for subducted slabs useful constraints can be placed on the depth and on the variation of viscosity with depth of the convecting system the degree 4 9 components of the observed long wavelength geoid are highly correlated with those predicted by a density model for seismically active subducted slabs the positive sign of the correlation requires that the effective viscosity increases with depth by a factor of 30 or more the amplitude of the correlation cannot be explained by the density contrasts associated with just the seismically active parts of subducted slabs however the amplitude can be explained if the density contrasts associated with subduction extend into the lower mantle or if old lithosphere is piled up at the base of the upper mantle beneath subduction zones to a thickness in excess of 350 km over horizontal distances of thousands of kilometers mantlewide convection in a mantle that has a viscosity increasing with depth provides a simple explanation of the long wavelength geoid anomalies over subduction zones

mantle rheology viscomagnetic coupling at the core mantle boundary and differential rotation of the core induced by pleistocenic deglaciation summary the influence of the viscomagnetic coupling at the core mantle boundary cmb on the differential rotation of the core and non tidal acceleration induced by the pleistocenic deglaciation is investigated for stratified mantle models with steadystate or transient rheologies for a realistic modelling of the viscomagnetic coupling the time dependent viscoelastic topography at the cmb induces a westward drift of the core with respect to the mantle that can be correlated to the zonal component of the secular drift of the geomagnetic field starting from a reference model based on the maxwell rheology and a viscosity profile inferred from j2 data and non tidal acceleration with 1021 pas and 5 x 1021 pas for upper and lower mantle respectively we study first the effects of the hardening of the upper mantle in the transition zone between 420 and 670 km depth this hardening is responsible for a 30 per cent reduction in the westward drift with respect to a uniform upper mantle the impact of a viscosity decrease on the top of the lower mantle is considered next the softening of the lower mantle beneath the 670 km discontinuity counteracts the effects of the transition zone enhancing the differential rotation of the core the d layer is also implemented in order to analyse the influence of the decoupling at the bottom of the mantle responsible for faster relaxation of the topography if lower mantle viscosity is increased beyond the threshold of 10 pas we obtain a differential rotation of the core in the opposite direction or an eastward drift we also analyse the impact of a burgers rheology for the lower mantle to simulate transient effects for this rheology steady state viscosities in the lower mantle higher than pa s in agreement with estimates from long wavelength geoid anomalies and recent findings from true polar wander allow a westward drift of the core non tidal acceleration is generally less affected by rheological variations than the differential rotation changes in the non tidal acceleration induced by the various rheological models are on the other hand comparable with the error bounds in the observed values

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

assessing meteoric water composition and relative humidity from18o and2h in wood cellulose paleoclimatic implications for southern ontario canada abstract an empirical model is presented that derives the initial isotopic composition of water used by terrestrial plants and the relative humidity that prevailed during photosynthesis from the isotopic composition of oxygen and carbon bound hydrogen in the plant cellulose the model uses fixed values for the fractionation factors that describe the evapotranspirative isotopic enrichment of leaf waters and the biochemical fractionations occurring during cellulose synthesis when applied to cellulose extracted from fossil plant matter the model can be used to generate quantitative estimates of the temperature and moisture regimes of the past the application of the model is demonstrated by consideration of 18o and 2h results on cellulose from fossil wood collected at brampton ontario the brampton data yield records of systematic changes in the temperature and moisture regimes of the eastern great lakes region over the past 11 500 a both mean annual temperature and photosynthetic humidity increased substantially from values much lower than the present at the end of the wisconsin stage to values higher than the present in the mid holocene the phase relation of the paleotemperature and paleohumidity curves engenders differentiation of the climatic history at brampton into four characteristic zones i a period of ameliorating climate predominantly much colder and drier than now lasting until about 7400 b p ii an early hypsithermal period of warm and dry conditions that transformed after 6000 a b p into iii the main hypsithermal time of warmth and pronounced moistness subsequent climatic detrioration led to establishment of iv cool moist conditions like the present sometime within the last few thousand years

microstructure measurements in the mid depth waters of the north pacific 1 microstructure measurements from the surface down to maximum depths of 2000 m were carried out at 28 locations in the interior of the north pacific special attention was directed to the diapycnal diffusivities k in the significant generation regions of the semidiurnal internal tide such as the aleutian ridge the hawaiian ridge and the izu ogasawara ridge in the profiles obtained near the aleutian ridge only a few turbulent patches with 10 9 wkg 1 were detected and k was generally less than 10 5 m2s 1 in the profiles obtained near the hawaiian ridge many turbulent patches with 10 9 wkg 1 were observed although k was generally of the order of 10 5 m2s 1 along the izu ogasawara trough running in parallel with the izu ogasawara ridge in contrast remarkably intense turbulent mixing 10 8 wkg 1 k 10 4 10 3 m2s 1 was common throughout the observed water depth

observations of boundary mixing over the continental slope observations of mixing over the continental slope using a towed body reveal a great lateral extent several kilometers of continuously turbulent fluid within a few hundred meters of the boundary at depth 1600 m the largest turbulent dissipation rates were observed ove ra5k mhorizontal region near a slope critical to the m2 internal tide over a submarine landslide perpendicular to the continental slope enhanced mixing extended at least 600 m above the boundary increasing toward the bottom the resulting vertical divergence of the heat flux near the bottom implies that fluid there must be replenished intermediate nepheloid layers detected optically contained fluid with u s properties distinct from their surroundings it is suggested that intermediate nepheloid layers are interior signitures of the boundary layer detachment required by the near bottom flux divergance

continental lithospheric thickness and deglaciation induced true polar wander the secular drift of the earth s rotation pole which is evident in ils data is a memory of the planet of the last deglaciation event of the current ice age in order to fit the observed rate and direction of drift with an earth model whose viscosity profile is capable of reconciling the free air gravity and relative sea level data of postglacial rebound requires a lithospheric thickness which is substantially in excess of that which might be considered an appropriate average thickness for the entire planet this required thickness which is greater than 250 km is nevertheless in accord with independent estimates of the thickness of the continental lithosphere

near boundary mixing above the flanks of a midlatitude seamount fine scale velocity and density profile data with concurrent turbulent velocity and temperature dissipation estimates obtained above the flanks of fieberling guyot a seamount in the eastern north pacific ocean are examined for evidence of near bottom boundary mixing fine scale shear and strain spectral levels were elevated over the flanks of the seamount in a 500 m thick stratified layer above the bottom the velocity shear was horizontally isotropic clockwise and counterclockwise with depth shear spectral levels were comparable and no significant correlation between shear and strain was observed above the steepest bottom slopes near the seamount summit rim excess vertical strain relative to shear was observed as compared to the background internal wave field suggesting the presence of high frequency internal waves these signals may have been the product of wave reflections from the steep flanks of the seamount and or wave generation from tidal currents flowing over the rough bottom associated with the enhanced shears and strains were more frequent occurrences of low 10 m richardson number events increased overturning scales and larger estimated turbulent eddy diffusivity relative to observations 15 km or more from the seamount in particular turbulent diffusivity estimates increased from o 0 1 10 4 m2 s 1 in the ocean interior to 1 5 10 4 m2 s 1 within 500 m vertically 1 3 km horizontally of the seamount flank a simple geometric scaling argument suggests that boundary mixing of this intensity has relevance to the large scale circulation at abyssal depths where a large fraction of the ocean waters is in close proximity to the bottom

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

viscous gravitational relaxation summary this paper is concerned with a detailed examination of the response of maxwell models of the planet to surface mass loads particular attention is devoted to an examination of the factors which determine the isostatic response since the understanding of this response is crucial in a number of different geodynamic problems one particular example which we discuss in detail is concerned with the prediction of free air gravity anomalies produced by large scale deglaciation events using the methods developed here we are able to provide the first direct assessment of the importance of initial isostatic disequilibrium on the observed relative sea level variations and free air gravity anomalies forced by the melting of the laurentide ice sheet we are therefore able to estimate the extent to which such initial disequilibrium might influence the inference of mantle viscosity from isostatic adjustment data our calculations establish that free air gravity data although they are sensitive to the degree of initial disequilibrium provide an extremely high quality constraint upon the viscosity of the lower mantle

pleistocene deglaciation and the earth s rotation a new analysis summary this paper is concerned with an analysis of the effect of the pleistocene glacial cycle upon the earth s rotation we demonstrate that two important geophysical observables may be explained as aspects of the rotational response to surface mass loading by ice sheets these are the astronomically observed non tidal component of the acceleration of planetary rotation and the secular drift of the rotation pole relative to the surface geography which is evident in the ils pole path the former observation is shown to provide an unambiguous constraint upon the viscosity of the planetary mantle and requires a depth dependence of this parameter which is the same as that which has previously been inferred in studies of the relative sea level variations and free air gravity anomalies associated with post glacial rebound the observed secular drift of the pole cannot provide an independent estimate of the viscosity of the mantle because it depends jointly upon mantle viscosity and lithospheric thickness with the viscosity profile fixed by the rebound data the observed speed of polar wander suggests a continental lithospheric thickness which is in excess of that appropriate for old ocean basins but nevertheless in accord with independent constraints

pleistocene deglaciation and the global gravity field the present day global geoid and free air gravity anomaly signals induced by pleistocene deglaciation have been computed along with their secular variations a revised green function has been derived for the free air gravity anomaly and we find that an earth model with a lower mantle viscosity moderately larger than the upper mantle value satisfies observations of the anomaly over both hudson s bay and fennoscandia using this preferred earth model the predicted global geoid anomaly map is characterized by peak negative values of 36 7 9 4 and 21 9 m over hudson s bay northern europe and antarctica respectively and by a smooth small amplitude 2 5 m upwarping over the major ocean basins although the field has an order of magnitude less power than the observed there is a significant spatial correlation between the two inferences of mantle viscosity based upon comparisons between the observed geoid and the computed deglaciation induced anomaly are hampered by the large contribution from the convective circulation in the earth s mantle we have subtracted a predicted convection signal based on seismic tomography from the observed field however the residual geoid thus obtained is still too inaccurate to allow a useful comparison in contrast a filtered version of the observed geoid over canada which retains harmonic coefficients in the degree range 10 22 provides a relatively uncontaminated by convection datum that is indeed satisfied by the preferred earth model secular variations in the earth s gravitational field are naturally dominated by the signal from pleistocene deglaciation in this respect we compute zonal harmonics in the expansion of the present day rate of change of the geopotential and in particular we predict amplitudes comparable to that for the previously analysed j2 for j4 j5 j7 and j9 all of which reflect in large part the response due to the melting of the massive laurentide ice sheet this analysis suggests that measurement of these higher order secular variations of the zonal harmonics based upon analysis of long time series of lageos ranging data could provide very useful additional constraints on the radial variation of mantle viscosity these constraints along with all others described in this paper are shown to be relatively insensitive to assumptions concerning the deflection during the glacial isostatic adjustment process of the 400 and 670 km density discontinuities within the mantle

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

viscoelastic relaxation of a burgers half space implications for the interpretation of the fennoscandian uplift summary we investigate the load induced response of a burgers earth model in particular using the incremental field equations and interface conditions of viscoelastodynamics we give closed form solutions for a two layer half space subjected to surface loading in the special case of homogeneity the solution shows that the burgers half space is characterized by two fundamental normal modes mo and m they correspond to the short and long time viscosities o and which describe the creep behaviour of the transient burgers rheology at short and long times after the onset of loading in the more general case of a burgers substratum overlain by an elastic layer the number of normal modes increases to four mo lo m l values of the parameters specifying the burgers substratum are estimated by predicting the observed post glacial uplift in fennoscandia with a simple model of the pleistocene glaciation history the calculations return the following results 1 an upper bound on cannot be determined 2 a comparison with uplift curves for a steady state maxwell substratum shows that the marginal and peripheral regions of the fennoscandian ice sheet are most sensitive to transient creep in the earth s mantle and 3 an estimate of cannot be obtained without a priori knowledge of the other parameters of burgers rheology

distribution of fine scale shear in the deep waters of the north pacific obtained using expendable current profilers 1 recent numerical experiments hibiya et al 1996 1998 2002 predicted that the energy cascade across the internal wave spectrum down to small dissipation scales was under strong control by parametric subharmonic instabilities that transfer energy from the low vertical wave number double inertial frequency wave band to a high vertical wave number near inertial frequency wave band to test whether or not the numerically predicted energy cascade process is actually dominant in the real deep ocean we deployed a total of 106 expendable current profilers over a large area in the north pacific to examine the spatial distribution of high vertical wave number vertical wavelength 25 m shear at midlatitudes significant enhancement of the 25 m vertical shear was found over prominent generation regions of semidiurnal internal tides such as the hawaiian ridge and the izu ogasawara ridge where the semidiurnal tidal frequency exceeds twice the local inertial frequency at high latitudes in contrast no significant enhancement of the 25 m vertical shear was found to occur even over another prominent generation region of semidiurnal internal tides the aleutian ridge where the semidiurnal tidal frequency is less than twice the local inertial frequency we find that the spatial distribution of the intensity of the 25 m vertical shear correlates very well with that of the low vertical wave number double inertial frequency internal wave energy numerically predicted by nagasawa et al 2000 and niwa and hibiya 2001a 2001b this is the first in situ evidence for the dominant role of parametric subharmonic instability in transferring deep ocean internal wave energy down to small dissipation scales this study provides a theoretical framework for future attempts to determine the large scale structure of mixing over the world s oceans

on the driving processes of the atlantic meridional overturning circulation because of its relevance for the global climate the atlantic meridional overturning circulation amoc has been a major research focus for many years yet the question of which physical mechanisms ultimately drive the amoc in the sense of providing its energy supply remains a matter of controversy here we review both observational data and model results concerning the two main candidates vertical mixing processes in the ocean s interior and wind induced ekman upwelling in the southern ocean in distinction to the energy source we also discuss the role of surface heat and freshwater fluxes which influence the volume transport of the meridional overturning circulation and shape its spatial circulation pattern without actually supplying energy to the overturning itself in steady state we conclude that both wind driven upwelling and vertical mixing are likely contributing to driving the observed circulation to quantify their respective contributions future research needs to address some open questions which we outline

plate tectonics and aspherical earth structure the importance of poloidal toroidal coupling we derive poloidal flow internal loading green functions for incompressible fluid models of the mantle consisting either of a single constant viscosity spherical shell or of two adjacent spherical shells having different viscosities from the green function we obtain kernels connecting the surface divergence the geoid and the surface topography fields to the lateral density heterogeneity inferred on the basis of the application of seismic tomographic imaging techniques and with these kernels we argue that both the surface divergence and geoid fields consisting of harmonic degrees 2 5 may be reasonably fit with only a factor of 8 viscosity increase at a depth of 1200 km we point out however that the coupling from poloidal to toroidal flow which is required to understand surface velocity spectra may allow these observations to be understood in terms of a viscosity increase at depth which is smaller than required by nonhydrostatic geoid data in the context of pure poloidal models using the observed kinetic energy in the surface plate motions as a constraint allows us to infer a value for the steady state upper mantle viscosity of 2 0 0 5 1021 pa s we comment on the implication of the difference between this number and the somewhat lower value 1 1021 pa s which has been derived on the basis of analyses of signatures of the glacial isostatic adjustment process

mixing in the main thermocline abstract a series of profiles of velocity microstructure along 152 e in the western north pacific ocean were collected in may june 1982 large averaged turbulent dissipation rates found in the main thermocline 400 to 1000 m were determined by a combination of large independent estimates of and a greater rate of occurrence of turbulent events in the main thermocline than elsewhere concurrently we find that averaged values of exhibit a positive dependence on the buoyancy frequency n and that form an is best fit by 1 when only the data below 400 m are considered of the more than 5000 m of data collected below 1000 m depth 12 showed measurable turbulence and dominated the depth averages a deep ocean estimate of an upper bound to the eddy coefficient for vertical diffusion k is 10 4 m2 s 1 and not significantly different from the value estimated by munk the inferred dependence of the mass flux with depth indicates the relative significance of vertical mixing in the main thermocli

viscosity estimates for the crust and upper mantle from patterns of lacustrine shoreline deformation in the eastern great basin the deformed shorelines of lake bonneville constitute a classic source of information on lithospheric elastic thickness and upper mantle viscosity we describe and apply a new model to a recently augmented data set new data better constrain both the complex spatio temporal pattern of the lake load and the crustal deformation response to that load the history of lake level fluctuations has been significantly refined and somewhat modified this is due to both more radiocarbon dates from within the bonneville basin and to an improved calibration of the radiocarbon timescale itself the data which constrain the crustal deformation pattern consist of ages and shoreline elevations from several hundred points which sample three major levels of lake bonneville and corresponding elevations from the high stands of three smaller lakes situated to the west of lake bonneville the data from the smaller lakes help elucidate the pattern of deflection which occurred beyond the edge of the big lake the geometry of the earth model incorporates an arbitrary number of layers overlying a half space and the rheology of each level can accommodate an arbitrary number of maxwell viscoelastic elements in parallel the inverse modeling comprises three complementary approaches for the simplest configurations we performed a direct search of the parameter space and delineated the irregular boundary of the subspace of acceptable models for more complex configurations we constrained the elastic parameters to their seismically determined values and then solved for viscosity versus depth profiles by either expressing the log viscosity versus log depth profile as a series of specially constructed orthogonal polynomials or by allowing each of 8 10 layers plus the half space to have an independently determined viscosity we found that the data do not strongly support nor can they conclusively exclude a more complex rheology than simple maxwell viscoelasticity the orthogonal polynomial solution exhibits an essentially monotonic decrease in viscosity with depth the most rapid change occurs at shallow depths decreasing from 1023 pa s at 3 km to 102o pa s at 30 km the decrease is much more gradual below with only another factor of 5 decrease between 30 and 300 km depth the unconstrained solution exhibits a rapid decrease in viscosity with depth from 2x 10 24 pa s in the top 10 km to 4x 1017 pa s at a depth of 40 km a nearly isoviscous asthenospheric region extends from 40 to 150 km and is underlain by a mantle lithospheric region with increased viscosity 2x 102o pa s extending from 150 to 300 km depth and by a uniform viscosity 1019 pa s half space below