oxygen and carbon isotope record of east pacific core v19 30 implications for the formation of deep water in the late pleistocene north atlantic abstract a detailed oxygen and carbon isotope record has been obtained from benthic foraminifera in core v19 30 from the carnegie ridge on the south side of the panama basin expressing these records and the oxygen and carbon isotope records previously published for atlantic core m 12392 on a common timescale it is apparent that the oxygen isotope records are very similar but that the carbon isotope records are quite different by obtaining the carbon isotope gradient between the two sites as a function of time we show that the production of north atlantic deep water has varied over a wide range during the late pleistocene and that the pattern of variation is not simply related to the well known oxygen isotope record although the two oxygen isotope records are very similar changes in the interoceanic gradient are detectable and support the hypothesis that in the glacial mode the north atlantic was colder and less oxygenated than it is today shackleton s 1 1977 interpretation whereby the carbon isotope record from the atlantic core reflects changes in the terrestrial biomass is an over simplification however the record from the pacific core v19 30 probably can be explained in these terms since it probably approximates the carbon isotope record of global mean oceanic dissolved co 2

oxygen isotope analyses and pleistocene ice volumes abstract the oxygen isotope record from fossil foraminifera in deep sea sediments is commonly used as a proxy for global ice volume the linkage between 18 o and ice volume however is probably nonlinear we have developed a simple numerical model of the isotopic response of the oceans to ice volume change the major features it simulates are 1 the changing mean isotopic composition of snow as a function of ice volume colder snow temperatures forced by climate change and higher elevation accumulation areas imply more negative mean 18 o 2 the nonequilibrium isotopic composition of ice sheets the past history of an ice sheet is integrated into its mean isotopic composition which introduces a lag of isotopic ice volume i e the measured 18 o record scaled to ice volume units behind true ice volume 3 selective preservation of isotopically more negative colder higher latitude ice this geographic effect can selectively amplify or dampen the isotopic response to the ice volume signal we illustrate the response of our model to simple hypothetical ice volume transitions of ice growth and ice decay sensitivity tests are illustrated for all model parameters the results suggest that oxygen isotope records reproduce the general patterns of ice volume change fairly accurately the foraminiferal isotope record however may misrepresent the true amplitude of the ice volume signal and lag true ice volume by 1000 to 3000 yr

two basin filling boxes the convection induced by turbulent buoyant plumes in a rectangular filling box baines and turner 1969 is extended to situations where the lower depths of the box are divided into two basins by a vertical barrier the barrier restricts horizontal spreading and allows the interbasin exchange of water to occur only in the common region above the barrier height one and two plume systems are considered in the two plume case it is assumed that each of the plumes arises from an independent buoyancy source above each basin the resulting two basin circulation is characterized by different stratifications in each basin and by an overflow from one basin into the other the spreading depths of the plumes and ambient stratification depend on the barrier height relative basin sizes and in the two plume case the relative strengths of the two buoyancy fluxes these results may be of relevance to multibasin seas and oceans where the circulation produced by near surface sources of intermediate and deep water is influenced by underwater ridges

multiphase plumes in a stratified ambient we report on experiments of turbulent particle laden plumes descending through a stratified environment we show that provided the characteristic plume speed b 0 n 1 4 exceeds the particle fall speed where the plume buoyancy flux is b 0 and the brunt vaisala frequency is n then the plume is arrested by the stratification and initially intrudes at the neutral height associated with a single phase plume of the same buoyancy flux if the original fluid phase in the plume has density equal to that of the ambient fluid at the source then as the particles sediment from the intruding fluid the fluid finds itself buoyant and rises ultimately intruding at a height of about 0 58 pm 0 03 of the original plume height consistent with new predictions we present based on classical plume theory we generalise this result and show that if the buoyancy flux at the source is composed of a fraction f s associated with the buoyancy of the source fluid and a fraction 1 f s from the particles then following the sedimentation of the particles the plume fluid intrudes at a height 0 58 0 22f s pm 0 03 h t where h t is the maximum plume height this is key for predictions of the environmental impact of any material dissolved in the plume water which may originate from the particle load we also show that the particles sediment at their fall speed through the fluid below the maximum depth of the plume as a cylindrical column whose area scales as the ratio of the particle flux at the source to the fall speed and concentration of particles in the plume at the maximum depth of the plume before it is arrested by the stratification we demonstrate that there is negligible vertical transport of fluid in this cylindrical column but a series of layers of high and low particle concentration develop in the column with a vertical spacing which is given by the ratio of the buoyancy of the particle load and the background buoyancy gradient small fluid intrusions develop at the side of the column associated with these layers as dense parcels of particle laden fluid convect downwards and then outward once the particles have sedimented from the fluid with a lateral return flow drawing in ambient fluid as a result the pattern of particle rich and particle poor layers in the column gradually migrates upwards owing to the convective transport of particles between the particle rich layers superposed on the background sedimentation we consider the implications of the results for mixing by bubble plumes for submarine blowouts of oil and gas and for the fate of plumes of waste particles discharged at the ocean surface during deep sea mining

filling box flows in porous media we report upon a theoretical and experimental investigation of a porous medium filling box flow by specifically examining the details of the laminar descending plume and its outflow in a control volume having an impermeable bottom boundary and sidewalls the plume outflow initially comprises a pair of oppositely directed gravity currents the gravity currents propagate horizontally until they reach the lateral sidewalls at y pm l the flow then becomes of filling box type with a vertically ascending first front separating discharged plume fluid below from ambient fluid above the flow details are described analytically by first deriving a new similarity solution for darcy plumes with mathit pe o 1 where mathit pe is the peclet number from the similarity solution so obtained we then derive expressions for the plume volume flux and mean reduced gravity as functions of the vertical distance from the source regarding the plume outflow a similarity solution adopted from huppert woods j fluid mech vol 292 1995 pp 55 69 describes the height and front speed of the gravity currents whereas a semi implicit finite difference scheme is used to predict the first front elevation versus time and horizontal distance as with high reynolds number filling box flows that studied here is an example of a coupled problem the gravity current source conditions are prescribed by the plume volume flux and mean reduced gravity conversely discharged plume fluid may be re entrained into the plume be it soon or long after reaching the bottom impermeable boundary to corroborate our model predictions analogue laboratory experiments are performed with fresh water and salt water as the working fluids our experiments consider as independent variables the porous medium bead diameter and the plume source volume flux and reduced gravity predictions for the gravity current front position and height compare favourably against analogue measured data good agreement is likewise noted when considering either the mean elevation or the profile of the first front results from this study may be adopted in modelling geological plumes for example our equations can be used to predict the time required for discharged plume fluid to return to the point of injection in the case of aquifers closed on the sides and below by impermeable boundaries

post glacial rebound and transient lower mantle rheology summary although post glacial rebound data have been conventionally interpreted as being governed by the steady state component of the mantle viscosity spectrum the radial profile of this parameter which is then inferred by fitting a model to observations is characterized by the fact that it exhibits rather slight variation with depth this disagrees with expectations based upon microphysical models of the solid state creep process it also disagrees with very recent inferences of the viscosity stratification based on isostatic geoid anomalies expected on the basis of the internal lateral heterogeneity of mantle density obtained from seismic tomographic analyses the new calculations of the signatures of post glacial rebound reported here show that these two types of information are easily reconciled if the previously inferred value of the lower mantle viscosity is interpreted as a transient value as originally suggested by weertman on the basis of qualitative considerations in these new models considered here the steady state creep resistance of the lower mantle is not constrained at all by post glacial rebound observations it can be futed only by an appeal to other geophysical data whether such models are actually required by the data should become clear in the very near future

the pleistocene glaciations in the dutch sector of the north sea c laban publisher university of amsterdam 1995 proefschrift phd thesis 194 pp isbn 90 9008587 4

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

quaternary correlations in arctic canada in the hudson bay james bay lowlands along the coasts of banks island and along the eastern coast of baffin island are continuous and extensive sections in quaternary sediments these sections are rich in marine fossils buried peats and soils and contain a wide variety of glaciagenic sediments together with glacial marine units and littoral deposits lake muds are also fairly common all three areas possess very long records that may extend to the early quaternary and pliocene the events of the last glaciation wisconsinan foxe amundsen are interpreted in terms of lithostratigraphy biostratigraphy and aminostratigraphy relative and absolute dating control is provided by radiocarbon dating of events that span the last 50 ka and in particular the last 11 ka and some age control is also provided by several u series dates on marine molluscs regional correlations are based on comparisons of amino acid ratios from marine shells suggested correlations during the last glaciation wisconsinan foxe amundsen are ka banks island hudson bay lowland baffin island 8 tyrrell sea sediments inugsuin regression 10 russell stade upper tills baffinland stade 40 friday creek sediments iron stand event till 80 fawn river gravels quajon interstade m clure stade adam till ayr lakde stade 120 cape collinson interglaciation missinaibi formation kogalu cape broughton interglaciation

effect of melting glaciers on the earth s rotation and gravitational field 1965 1984 summary yearly mass balance data for 85 glaciers in 13 of the 31 mountain glacier systems designated in meier s 1984 paper are averaged for the years 1965 1984 average rates of volume change for the 13 regions are compared to meier s 1984 estimates of glacial melting these data cover regions that account for about 74 per cent of the volume change estimated to have occurred in all the 31 mountain glacier systems from 1900 to 1984 the volume changes in the 13 regions tend to be less than those calculated by using changes in the volume of glaciers between 1900 and 1961 meier 1984 although the reason for this difference is not well known it could result from melting during the first half of the 20th century of ice accumulated during earlier periods or a decrease in the rise in atmospheric temperatures from 1945 to 1980 spatial and temporal empirical orthogonal functional analysis is used to bring out the similarities and differences among the 13 regions and identify those regions contributing most to the variance of the data set these regions are not necessarily those with the greatest average rates of volume change enough spatial variability is present to support the hypothesis that satellites may eventually be able to discern changes in the earth s glaciers through the gravitational field even though the signal from the mass change is small and changes in the gravitational field of the earth are contaminated with gravity signals from other mass changes on the earth s surface and interior zonal coefficients of the spherical harmonic expansion of the gravitational potential are calculated for yearly mass changes for these 13 regions up to i 8 there is little similarity at decadal periods between the polar motion excitation from mountain glacier systems and the observed excitation the majority of observed polar motion excitation could be due to other surface mass changes including continental water storage see for example chao 1988 the amplitude of the interannual excitation due to the glacial signal computed here is less than 10 per cent of the observed excitation and the secular trend of the excitation from melting glaciers in the 13 regions is about one quarter of that of the observed excitation yearly changes in the length of day lod are calculated from the glacial signals and compared to the observed yearly alod excess lod signal the contribution of glaciers to the total excess lod signal is less than one part in 150 of the observed signal as alod is caused mainly by core mantle coupling at decadal periods and atmospheric coupling at shorter periods the contributions to displacement of the centre of mass of the solid earth as seen by a satellite tracked from the earth s surface are calculated for the mountain glaciers and an 80 year record of global sea level for the glaciers the average displacements are as much as 1 mm over 20 years and for sea level the z coordinate of the average displacement is 5mm over its 80 year record interannual signals

the great cenozoic ice sheet abstract ocean floor sediments contain a record of quaternary continental glaciations in which global cooling prevails over a 100 000 year cycle and the intensity of the last glacial maximum is as strong as any of the earlier glaciations yet the areal extent of quaternary glacial drift in north america and eurasia during the last glaciation is much less extensive than during several earlier glaciations in an attempt to explore this problem two versions of a great cenozoic ice sheet were reconstructed the minimum version transformed a frozen bed beneath high interior ice domes and along southern margins during the last glaciation into a thawed bed during more extensive earlier glaciations this allowed thinner ice to cover a larger area with little change in ice volume thereby satisfying both the continental and oceanic records of quaternary glaciation the maximum version extended frozen basal conditions beneath high interior ice domes and along southern margins so that a greater areal extent could only be accommodated by thicker ice a greater ice volume is required in this case and would seem to put the great cenozoic ice sheet in the late tertiary where some evidence for global cooling on a 400 000 year cycle exists and might provide the longer timespan needed to produce a larger ice sheet

late weichselian and holocene relative sea level history of broggerhalvoya spitsbergen abstract radiocarbon dated whalebones from raised beaches record a relative sea level history for broggerhalvoya western spitsbergen that suggest a two step deglaciation on svalbard at the end of the late weichselian glaciation the late weichselian marine limit was reached at about 13 000 yr b p and was followed by relatively slow emergence until about 10 000 yr b p either in response to ice unloading in the barents sea initial retreat of local fjord glaciers or some combination of the two rare whale skeletons dating between 13 000 and 10 000 yr b p indicate that the norwegian sea was at least seasonally ice free during that interval deglaciation of spitsbergen is recorded by the rapid emergence of broggerhalvoya after 10 000 yr b p this was followed by a transgression during the mid holocene here named the talavera transgression and another in modern times raised beach morphologies suggest striking differences in nearshore depositional processes before and after 10 000 yr b p that are probably related to changes in the rate of uplift and in sea ice conditions

glacial isostatic adjustment i the forward problem summary the isostatic adjustment of a radially stratified visco elastic spheroid is treated using space time green functions for the associated surface mass load boundary value problem these impulse response functions are convolved with a heaviside function to give the time dependent deformation of the planet which would be produced by a unit point mass brought up from infinity at t 0 and allowed to remain on the surface the resulting heaviside green functions can be employed to simulate all of the important signatures of glacial isostatic adjustment given a space time dependent surface mass load consisting of ice sheet ablation histories and a model of the simultaneous filling of the ocean basins these source terms are simply convolved with the heaviside green function appropriate to a specific response signature a realistic model of the spatial distribution of the main late pleistocene ice loads and of their temporal disintegration is constructed the response of two visco elastic earth models is computed and compared to a global set of relaxation data relative sea level curves on the basis of this initial comparison of theory and observation the possibility that the lower mantle has a viscosity which is significantly in excess of the viscosity of the upper mantle is excluded in addition clear evidence of the presence of the lithosphere has been found in relaxation data from sites which were near the edge of the laurentide ice sheet such data should therefore prove useful as a basis for analysis of lateral variations in lithosphere thickness further extensions of the calculation are suggested

sensitivity experiments with a model of the ice age cycle the response to milankovitch forcing abstract we address the question of the extent to which a simple one dimensional time dependent climate model is able to explain the fluctuations of continental ice volume which have occurred during the last quarter of the pleistocene epoch the model includes explicit ice physics based on the glen flow law and explicit glacial isostatic adjustment based on a realistic viscoelastic field theory when the model is forced by the milankovitch variations of insulation it delivers ice volume fluctuations which are very similar to those implied by the specmap 18o record in particular the model appears capable of explaining the observed correlation between eccentricity and ice volume variations the dominance of the 105 year period in the power spectrum of the ice volume time series and the thickness and latitudinal extents of the continental ice sheets which existed at wurm wisconsin maximum 18 000 years ago

emptying filling boxes the fluid mechanics of natural ventilation this paper describes the fluid mechanics of the natural ventilation of a space connected to a large body of stationary ambient fluid the flows are driven by buoyancy differences between the interior and exterior fluids connections with the ambient fluid are high level and low level openings two main forms of ventilation are identified mixing ventilation and displacement ventilation mixing ventilation occurs when the incoming ambient fluid mixes with the fluid within the space as is the case if dense fluid enters through a high level inlet in this case vertical stratification is weak displacement ventilation occurs when dense fluid enters at low levels and displaces the lighter fluid within the space out through high level openings a strong stable stratification develops in this case and there is little mixing between the incoming fluid and that in the interior both of these modes of ventilation are studied theoretically and the results are compared with laboratory experiments transient draining flows which occur when a space initially contains fluid of a density different from the ambient are examined the presence of internal sources of buoyancy allows steady states to be established and the effects of point line and vertically distributed sources are studied these steady states are extensions of filling box models with the addition of continuous exchange of fluid with the environment outside the space a major result of this work is that the form of the stratification within the space depends on the entrainment caused by the convective elements plumes produced by the buoyancy sources but is independent of the strength of the sources the strength of the stratification and the magnitudes of the velocities do however depend on the source strength the effects of opening size s and configurations are determined and criteria for producing a particular stratification within the space are established applications of this work to the ventilation of buildings are presented

assessing the global meltwater spike abstract l v worthington 1968 meteorological monographs 8 63 67 hypothesized that a low salinity lid covered the entire world ocean by deconvolving isotopic curves from the western equatorial pacific and equatorial atlantic w h berger r f johnson and j s killingley 1977 nature london 269 661 663 and w h berger 1978 deep sea research 25 473 480 reconstructed meltwater spikes similar to those actually observed in the gulf of mexico and thus apparently confirmed the worthington hypothesis it is shown that this conclusion is unwarranted the primary flaw in the reconstructed meltwater spikes is that the mixing intensity used in the deconvolution operation is overestimated as a result structure recorded in the mixed isotopic record becomes exaggerated in the attempt to restore the original unmixed record this structure can be attributed to variable ice volume decay during deglaciation effects of differential solution on planktonic foraminifera temporal changes in abundance of the foraminifera carrying the isotopic signal and analytical error an alternative geographic view to the global low salinity lid is offered a map showing portions of the ocean potentially affected by increased deglacial meltwater at middle and high latitudes and by increased precipitation induced runoff at low and middle latitudes

land motion estimates from gps at tide gauges a geophysical evaluation summary space geodesy applications have mainly been limited to horizontal deformations due to a number of restrictions on the vertical component accuracy monitoring vertical land motion is nonetheless of crucial interest in observations of long term sea level change or postglacial rebound measurements here we present a global vertical velocity field obtained with more than 200 permanent gps stations most of them colocated with tide gauges tgs we used a state of the art homogeneous processing strategy to ensure that the reference frame was stable throughout the observation period of almost 10 yr we associate realistic uncertainties to our vertical rates taking into account the time correlation noise in the time series the results are compared with two independent geophysical vertical velocity fields 1 vertical velocity estimates using long term tg records and 2 postglacial model predictions from the ice 5g vm2 adjustment the quantitative agreement of the gps vertical velocities with the internal estimates of vertical displacements using the tg record is very good with a mean difference of 0 13 1 64 mm yr 1 on more than 100 sites for 84 per cent of the gps stations considered the vertical velocity is confirmed by the tg estimate to within 2 mm yr 1 the overall agreement with the glacial isostatic adjustment gia model is good with discrepancy patterns related either to a local misfit of the model or to active tectonics for 72 per cent of the sites considered the predictions of the gia model agree with the gps results to within two standard deviations most of the gps velocities showing discrepancies with respect to the predictions of the gia model are however consistent with previously published space geodesy results we in turn confirm the value of 1 8 0 5 mm yr 1 for the 20th century average global sea level rise and conclude that gps is now a robust tool for vertical land motion monitoring which is accurate at least at 1 mm yr 1

turbulent fountains in an open chamber the flow and density distribution produced by injecting dense fluid upwards at the bottom of a homogeneous fluid have been investigated experimentally and theoretically both axisymmetric and line sources have been studied using small scale laboratory experiments in which salt water is injected into a tank of fresh water the turbulent fountain formed in this way rises to a maximum height which can be related to the froude number of the inflow and then falls back and spreads out along the floor continuing the inflow builds up a stable stratification in a similar manner to that discussed earlier for the plume filling box model of baines turner 1969 which is complementary to the present work the fountain flows considered here have the important new feature that the volume of the inflow is significant so the total volume of fluid in the open container increases with time the evolution is determined by the rate of entrainment into the fountain from its surroundings which is found directly by experiment re entrainment of fluid into the fountain continually changes the density profile in the mixed fluid collecting at the bottom of the chamber below the level of the fountain top and controls the rate of rise of a front of marked fluid the top of the fountain rises linearly in time at a rate which for axisymmetric fountains has been shown both experimentally and theoretically to be close to half the rate of rise of the free surface due to the inflow thus at a certain time the front rises above the top of the fountain once the mixed fluid at the bottom of the chamber has risen above the fountain its density profile remains unchanged the front velocity the fountain height and the density profile have all been obtained as functions of time using a theory which is in good agreement with the experimental results for a large range of input froude numbers for line fountains the results are less precise owing to an instability which causes the flow to switch irregularly from a symmetrical state to one in which the downflow occurs on one side only and with a smaller maximum height in concluding we discuss the applications which motivated the work particularly the development of a stratified hybrid layer in magma chambers replenished from below and the dynamically identical but inverted problem of heating large buildings through ducts located near the roof

quasi steady states in natural displacement ventilation driven by periodic gusting of wind we investigate the natural displacement ventilation of a space connected to a body of warm fluid through high and low level vents the space is subject to discrete periodic gusts of wind entering at high level from a cold exterior the cold exterior air entering the space produces buoyancy differences between the space and the body of warm fluid driving a ventilation flow initially we examine the case of a series of identical gusts of wind modelled as turbulent buoyant thermals new laboratory experiments show that an approximately two layer stratification is established and the height of the interface is quasi steady if the period between thermals is much less than the draining time of the space but longer than the fall time of individual thermals experiments also show that the interface height depends on the average buoyancy flux associated with the wind gusts the time between thermals as well as the geometric properties of the vents this contrasts with the case of a continuous source of buoyancy where the interface height depends only on the geometric properties of the vents and is independent of the buoyancy flux we develop a quasi steady two layer model of the flow based on the classical theory of turbulent thermals and show that it is consistent with our new experimental data we generalize the model to explore the sensitivity of the results to temporal variations in the size of thermals we then extend the model to explore the effects of longer interval times between successive thermals and find a two layer stratification still develops but that the interface height now varies cyclically in time we then discuss the implications of these results for the ventilation of a shopping mall subject to gusts of wind

emptying filling boxes free turbulent versus laminar porous media plumes we examine the transient evolution of a negatively buoyant laminar plume in an emptying filling box containing a uniform porous medium in the long time limit unicode stix x1d70f rightarrow infty the box is partitioned into two uniform layers of different densities however the approach towards steady state is characterized by a lower contaminated layer that is continuously stratified the presence of this continuous stratification poses non trivial analytical challenges we nonetheless demonstrate that it is possible to derive meaningful bounds on the range of possible solutions particularly in the limit of large unicode stix x1d707 where unicode stix x1d707 represents the ratio of the draining to filling time scales the validity of our approach is confirmed by drawing comparisons against the free turbulent plume case where unlike with porous media plumes an analytical solution that accounts for the time variable continuous stratification of the lower layer is available baines turner j fluid mech vol 37 1969 pp 51 80 germeles j fluid mech vol 71 1975 pp 601 623 a separate component of our study considers time variable forcing where the laminar plume source strength changes abruptly with time when the source is turned on and off with a half period unicode stix x0394 unicode stix x1d70f the depth and reduced gravity of the contaminated layer oscillate between two extrema after the first few cycles different behaviour is seen when the source is merely turned up or down for instance a change of the source reduced gravity leads to a permanent change of interface depth which is a qualitative point of difference from the free turbulent plume case

antarctic ice volume and contribution to sea level fall at 20 000 yr bp from raised beaches the contribution of the antarctic ice sheets to global sea level fall at the last glacial maximum lgm depends largely on how the extent and thickness of peripheral ice changed model studies1 3 suggest that there was widespread thickening from 500 m to more than 1 000 m of the ice sheet margins sufficient to induce a drop in sea level of at least 25 m geological evidence4 5 on the other hand indicates only limited ice expansion and a sea level fall of just 8 m here we use recent data on the altitudes and ages of raised beaches from the ross embayment and east antarctica to investigate the timing and extent of antarctic deglaciation these indicate that the ice margin during the lgm was thinner and less extensive than has been formerly thought and that its contribution to the drop in sea level was only 0 5 2 5 m deglaciation was well advanced by 10 kyr bp and was complete by 6 kyr bp these findings imply either that sea level during the lgm fell less than present estimates suggest or that an ice volume considerably greater than currently accepted must have been present in the northern hemisphere

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

total meltwater volume since the last glacial maximum and viscosity structure of earth s mantle inferred from relative sea level changes at barbados and bonaparte gulf and gia induced j2

late pleistocene eolian sand sheets in alaska abstract nonglaciated lowlands in central and southwestern alaska contain extensive deposits of upper quaternary eolian sand derived largely from major outwash rivers although surface dunes are common deep exposures consistently reveal that subhorizontally stratified sand and silt deposits dominate over dune cross strata we hypothesize that 1 many of the subhorizontally stratified deposits represent full glacial eolian sand sheets formed when sand supply was limited by seasonally variable combinations of ice cementation snow cover high groundwater tables and vegetation and 2 many surface dunes reflect late glacial and postglacial reworking under conditions of increased short term availability of loose sand the morphology of some surface dunes may therefore reflect mainly the intensity of reworking since the last glacial maximum rather than full glacial paleowind vectors or the age of the bulk of the underlying deposits

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

present day antarctic ice mass changes and crustal motion the peak vertical velocities predicted by three realistic but contrasting present day scenarios of antarctic ice sheet mass balance are found to be of the order of several mm a one scenario predicts local uplift rates in excess of 5 mm a these rates are small compared to the peak antarctic vertical velocities of the ice 3g glacial rebound model which are in excess of 20 mm a if the holocene antarctic deglaciation history portrayed in ice 3g is realistic and if regional upper mantle viscosity is not an order of magnitude below 10 exp 21 pa s then a vast geographical region in west antarctica is uplifting at a rate that could be detected by a future global positioning system gps campaign while present day scenarios predict small vertical crustal velocities their overall continent ocean mass exchange is large enough to account for a substantial portion of the observed secular polar motion omega m bar and time varying zonal gravity field j sub 1

natural ventilation in interconnected chambers ventilation of adjacent connected chambers forced in one chamber by an isolated point source of buoyancy is investigated there are floor and ceiling level external openings in the forced and unforced chambers respectively while the partition between the chambers has both a floor and ceiling level opening the flow evolves on the time scale over which the volume flux associated with the plume at the ceiling would fill both chambers the steady state in the forced chamber is analogous to the single chamber flow described by linden lane serff smeed j fluid mech vol 212 1990 p 309 with a well mixed buoyant upper layer which is deeper than in the single chamber flow due to the extra pressure drop at the upper interior opening the steady state in the unforced chamber inevitably exhibits vertical stratification and depends on the transient flow all the opening areas and the relative plan area of the two chambers as is verified by laboratory experiments when the upper interior opening is relatively large the buoyant layer in the unforced chamber is deeper than the buoyant layer in the forced chamber which contradicts model predictions based on the assumption that the layers are always well mixed

contribution of glacial isostatic adjustment to the geocenter motion abstract the geocenter motion describes the surface net displacement of the entire solid earth with respect to the center of mass of the entire earth including surface masses therefore it resembles an integrative quantity of surface displacement and mass redistribution inside the earth as well as at its surface seasonal variations of this quantity are understood to originate mainly from mass redistribution in the water cycle in contrast a secular trend of the geocenter motion is possible to result also from the dynamics of the earth s interior one mechanism inducing a secular geocenter motion is the glacial isostatic adjustment describing the deformation and mass redistribution in the earth s interior due to glaciations during the pleistocene focusing on this contribution we compute the geocenter motion from the displacement and gravity potential fields calculated for a spherical self gravitating incompressible and viscoelastic earth model loaded by the last pleistocene glacial cycle we discuss the fluid core approximation usually adopted and assess the influence of a list of modelling parameters which are the upper and lower mantle viscosity lithosphere thickness and glaciation history we find a rather robust geocenter motion with respect to parameter variations which is directed towards northeast canada and shows velocities that vary between 0 1 and 1 mm yr depending on the adopted earth model and glaciation history parameterizations

secular variations in zonal harmonics of earth s geopotential and their implications for mantle viscosity and antarctic melting history due to the last deglaciation

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

potential and limits of combining studies of coarse and fine grained sediments for the coastal event history of a caribbean carbonate environment the coastal deposits of bonaire leeward antilles are among the most studied archives for extreme wave events ewes in the caribbean here we present more than 400 electron spin resonance esr and radiocarbon data on coarse clast deposits from bonaire s eastern and western coasts the chronological data are compared to the occurrence and age of fine grained extremewave deposits detected in lagoons and floodplains both approaches are aimed at the identification of ewes the differentiation between extraordinary storms and tsunamis improving reconstructions of the coastal evolution and establishing a geochronological framework for the events although the combination of different methods and archives contributes to a better understanding of the interplay of coastal and archive related processes insufficient separation superimposition or burying of coarse clast deposits and restricted dating accuracy limit the use of both fine grained and coarse clast geoarchives to unravel decadal to centennial scale events at several locations distinct landforms are attributed to different coastal flooding events interpreted to be of tsunamigenic origin coastal landforms on the western coast have significantly been influenced by sub recent hurricanes indicating that formation of the coarse clast deposits on the eastern coast is likely to be related to past events of higher energy

measurements of past ice sheet elevations in interior west antarctica a lateral moraine band on mount waesche a volcanic nunatak in marie byrd land provides estimates of past ice sheet surface elevations in west antarctica helium 3 and chlorine 36 surface exposure ages indicate that the proximal part of the moraine up to 45 meters above the present ice surface was deposited about 10 000 years ago substantially later than the maximum ice extent in the ross embayment the upper distal part of the moraine may record multiple earlier ice sheet high stands a nonequilibrium ice sheet model predicts a delay of several thousand years in maximum ice levels at mount waesche relative to the maximum ice extent in the ross sea the glacial geologic evidence coupled with the ice sheet model indicates that the contribution of the ross sea sector of the west antarctic ice sheet to holocene sea level rise was only about 3 meters these results eliminate west antarctic ice as the principle source of the large meltwater pulse during the early holocene

structural inheritance control on intraplate present day deformation gps strain rate variations in the saint lawrence valley eastern canada structural inheritance is one of the key factors commonly proposed to control the localization of strain and seismicity in continental intraplate regions primarily on the basis of a first order spatial correlation between seismicity and inherited tectonic structures in this paper we present new gps global positioning system velocity and strain rate analyses that provide strong constraints on the magnitude and style of present day strain localization associated with the inherited tectonic structures of the saint lawrence valley eastern canada we analyze 143 continuous and campaign gps stations to calculate velocity and strain rate patterns with specific emphases on the combination of continuous and campaign velocity uncertainties and on the definition of robustness categories for the strain rate estimations within the structural inheritance area strain rates are on average 2 11 times higher than surrounding regions and display strong lateral variations of the style of deformation these gps velocity and strain rate fields primarily reflect ongoing glacial isostatic adjustment gia their comparison with gia model predictions allows us to quantify the impact of the structural inheritance and the associated lithosphere rheology weakening outside of the major tectonic inheritance area gps and gia model strain rates agree to first order both in style and magnitude in contrast the saint lawrence valley displays strong strain amplification with gps strain rates 6 28 times higher than model predicted gia strain rates our results provide the first quantitative constraints on the impact of lithospheric scale structural inheritance on strain localization in intraplate domains

will earthquake activity in eastern canada increase in the next few thousand years knowledge of whether earthquake activity will increase in the next few thousand years is important for the planning of nuclear waste repositories assuming that fault instability portends earthquak

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

interstitial fluid chemistry of sediments underlying the north atlantic gyre and the influence of subsurface fluid flow abstract the western flank of the mid atlantic ridge is a region underlying the oligotrophic waters of the central atlantic the seafloor along portions of this ridge is characterized by sediment filled depressions which are surrounded by steep basaltic outcrops we present pore fluid and sediment solid phase chemical data from fourteen gravity cores from north pond a sediment pond where previous drilling work indicated directed flow of seawater within the basement sediment lithology is broadly characterized as a nannofossil pelagic sediment containing varying amounts of clay foraminifers and mn micronodules and typically contains less than 0 3 organic carbon and 70 calcium carbonate consistent with its location within an oligotrophic ocean gyre oxygen and nitrate penetrated deeply into the sediment package however there is significant spatial variability in the pore fluid nitrate and oxygen profiles with oxygen generally lower and nitrate higher toward the center of the basin as compared to the edges in addition oxygen increased with sediment depth at a number of sites toward the edges of the pond where sediment cover was thinnest we interpret these oxygen distributions to indicate that there is upward diffusion of dissolved oxygen from the underlying basaltic basement fluid and the sediment package and this process appears to be regionally pervasive pore fluid molybdenum generally decreases with depth and exhibits spatial variability similar to dissolved oxygen and nitrate molybdenum is likely being taken up at depth via adsorption onto manganese oxides as these sediments are rich in manganese 300 3000 ppm mn and molybdenum 2 14 ppm mo the strong geographical variations in pore fluid chemistry coupled with the co variation between molybdenum and oxygen two species that we would not necessarily expect to be coupled suggest that diffusion of dissolved constituents into the sediment package from below plays an important role in determining the chemistry of the overlying sediment

merging of two or more plumes arranged around a circle a model is presented of merging turbulent plumes from sources evenly spaced around a horizontal circle in a quiescent unstratified background this follows the previously developed method of i identifying the boundaries of interacting plumes with velocity potential contours of line sinks and ii closing the generalised plume equations with an entrainment assumption based on the integrated flux across the plume boundaries it includes the simplest case of two merging plumes as well as being applicable to plume flows in restricted corner configurations the model is shown to display the expected limiting behaviour for the source plumes and the merged plume consideration of the plume fluxes in the merging region leads to a revision of the entrainment assumption the resulting revised model compares satisfactorily with previous estimates of volume flux in two merging plumes

the ventilated filling box containing a vertically distributed source of buoyancy this paper describes the fluid mechanics within a box containing a vertical plane distributed source of buoyancy a theoretical analysis is presented that models the development of plumes from such sources in an unconfined ambient of uniform density two extensions are considered the first concerns a sealed box and the second involves the more general situation where the box is ventilated by openings at top and bottom in the sealed box the stratification develops in much the same way as for a filling box containing a single point source of buoyancy on the floor an initial front descends from the ceiling of the box and an asymptotic stratification eventually develops which is continuous in the vertical direction in the case of the ventilated box it is found that a complex stratification develops where one or more horizontal intrusions are formed by detachment of the plume boundary layer from the vertically distributed source where the buoyancy of the plume is less than or equal to that of the stratified ambient at a given height experimental results are presented to demonstrate the validity of the theory the findings are relevant to both forced and naturally ventilated buildings containing non adiabatic vertical surfaces

the formation and evolution of stratification during transient mixing ventilation we investigate the buoyancy driven ventilation of an enclosed volume of buoyant fluid which is connected to the exterior through two openings at the top of the enclosure an exchange flow becomes established with outflow through one opening being matched by an equal and opposite inflow through the other vent the inflowing flux of dense exterior fluid develops a turbulent buoyant plume which mixes with the interior fluid as it cascades to the base of the fluid volume an upward return flow gradually stratifies the confined volume of fluid with a first front of relatively dense plume fluid advancing to the top of the space initially the exchange flow is steady but as the first front rises above the inflow opening the flow rate wanes the initial development of the exchange flow and interior stratification follows the classical filling box work of baines turner j fluid mech vol 37 1969 p 51 with a plume of constant buoyancy flux once the first front exits the space the volume flux rapidly asymptotes to the form q q0 t from the initial value q0 where is the buoyancy driven draining time based on the initial density contrast with the environment the vertical structure of the interior density stratification asymptotes to a profile of constant shape whose amplitude decays in time as t 2 and we identify conditions under which the vertical variation in density is comparable to the difference between mean interior density and the exterior this generalises the analysis presented by linden lane serff smeed j fluid mech vol 212 1990 p 309 who assumed that the interior fluid is well mixed new laboratory experiments of the process are shown to be consistent with our predictions of the evolution of the flow the interior stratification and the migration of contaminants we also develop our analysis for situations where there are multiple stacks and show how this improves the mixing efficiency for a given ventilation flow the model has relevance for the design of transient mixing ventilation in a building especially when the effect of vertical stratification is important for ensuring thermal comfort

lithospheric thickness antarctic deglaciation history and ocean basin discretization effects in a global model of postglacial sea level change a summary of some sources of nonuniqueness the global model of postglacial relative sea level variations that has been developed over the past decade is employed to investigate the constraints that it may be invoked to place on the timing of the deglaciation of west antarctica the analyses presented here confirm the suggestion of p wu and w r peltier 1983 geophysical journal of the royal astronomical society74 377 450 that the model of this event employed inj a clark and c s lingle 1979quaternary research11 279 298 may be simply modified to rectify the misfits between theory and observation that are otherwise obtained at southern hemisphere sites a large number of southern hemisphere relative sea level data are shown to require that the retreat of antarctic ice substantially lagged the retreat of northern hemisphere ice if the deglaciation of antarctica was abrupt the time of onset of antarctic deglaciation is thereby shown to coincide with the time of most rapid northern hemisphere deglaciation sensitivity tests are performed which demonstrate that this result is relatively insensitive to the discretization employed to represent the ocean basins the only exception to this general rule obtains at some coastal sites at which a trade off is revealed between the delay of west antarctic melting and the thickness of the lithosphere required to reconcile the observed local variations of relative sea level at such sites which are all in the far field of the ice sheets some attention must be paid to the accuracy of the local finite element representation of the oceans and to the details of the antarctic deglaciation history

a 10 000 yr b p extensive ice shelf over viscount melville sound arctic canada abstract late wisconsinan age glacial landforms and deposits indicate that an ice shelf of at least 60 000 km 2 flowed northwestward into viscount melville sound probably from the m clintock dome of the laurentide ice sheet the ice shelf overlapped coastal areas and laid winter harbour till up to 125 m above present sea level on the southern coast of melville island to 135 m on byam martin island to possibly 90 m on the northeast tip of banks island and to 150 m on the north coast of victoria island the contemporary sea level was 50 to 100 m higher than present it now rises eastward a maximum age of 10 340 150 yr b p for the till and thus the ice shelf advance is provided by shells in marine sediments which underlie it whereas a minimum age of 9880 150 yr b p is provided by overlying shells that postdate the ice advance the major advance of shelf ice into viscount melville sound may be the result of the rapid disintegration of the m clintock dome while the climate ameliorated in the western arctic

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

on postglacial sea level summary an exact method is presented for calculating the changes in sea level that occur when ice and water masses are rearranged on the surface of elastic and viscoelastic non rotating earth models the method is used to calculate the instantaneous elastic and delayed vi scoelastic sea level changes following the partial melting of late quaternary ice sheets we find that there can be large errors in the usual assumption that changes in sea level are uniform over the ocean basins if a quantity of ice equivalent to a uniform 100 m rise in sea level melts from the laurentide and fennoscandian ice sheets then in the south pacific the instantaneous rise in sea level can be as large as 120m in the north atlantic the instantaneous rise is always less than 100 m there is a zone in the north atlantic with almost no sea level change and near greenland and norway the sea level falls rather than rises by over 100 m one thousand years after the melting a forebulge migrating towards the ice loads causes water to flow from the south pacific into the north pacific suggesting that raised beaches should occur in the south pacific the gravitational attraction of an ice mass upon a nearby ocean tends to hold sea level high in the vicinity of the ice this extra load near the ice may have a significant influence on postglacial isostatic adjustment

scalings for submarine melting at tidewater glaciers from buoyant plume theory abstractrapid dynamic changes at the margins of the greenland ice sheet synchronous with ocean warming have raised concern that tidewater glaciers can respond sensitively to ocean forcing understanding of the processes encompassing ocean forcing nevertheless remains embryonic the authors use buoyant plume theory to study the dynamics of proglacial discharge plumes arising from the emergence of subglacial discharge into a fjord at the grounding line of a tidewater glacier deriving scalings for the induced submarine melting focusing on the parameter space relevant for high discharge tidewater glaciers the authors suggest that in an unstratified fjord the often quoted relationship between total submarine melt volume and subglacial discharge raised to the power is appropriate regardless of plume geometry provided discharge lies below a critical value in these cases it is then possible to formulate a simple equation estimating total submarine melt volume as a function of discharge fjord temperature

natural ventilation of an enclosure containing two buoyancy sources this paper describes experiments and theoretical modelling of a naturally ventilated enclosure containing two point sources of buoyancy previous work on the flow and stratification that develop in a space owing to the presence of a single source of buoyancy has been extended to cover two sources of positive or negative buoyancy in an attempt to produce more realistic models of practical problems examples include naturally ventilated buildings and industrial or medical processes involving dispersal of contaminants by air currents the experimental technique involves the use of a water filled enclosure with salt solution injected at two points these sources of negative buoyancy form turbulent plumes within the enclosure two sources of unequal strength are found to produce a vertical density profile consisting of three distinct fully mixed layers the paper describes a theoretical model that successfully predicts the depths and densities of these layers the positions of the interfaces between the three layers were found to be a function only of the effective area a of the enclosure openings the height of the enclosure h and the ratio of the strengths of the two sources of buoyancy b 1 b 2 the behaviour of a system with one source of positive buoyancy at the lower boundary and one of negative buoyancy at the upper boundary of the enclosure is also examined this case has particular relevance to the prediction of thermal stratification in rooms with both cold and warm surfaces present again the height of the interfaces is dependent only on the geometry of the enclosure and the source strength ratio three distinct types of flow pattern are predicted and observed

buoyancy driven unbalanced exchange flow through a horizontal opening buoyancy driven exchange flows occur in a variety of natural and industrial situations including nuclear and hydraulic engineering oceanography and building ventilation balanced exchange flows whereby there is simultaneously an equal volume flux transferred vertically upwards and downwards through a horizontal opening have previously been described theoretically however until now there has been no theoretical description of unbalanced exchange flows whereby the volume flux in one direction through an opening exceeds that in the other the model developed herein examines the growth of perturbations on the density interface at an opening made in a horizontal plane that connects buoyant fluid below with denser fluid above by considering the interface as it is advected away from the plane of the opening by a bulk flow imposed in the vertical we quantify the exchange for the unbalanced case the model successfully predicts the froude number criterion which corresponds directly to the minimum dimensionless flow rate of the imposed flow for the onset of unbalanced exchange across circular openings found experimentally additionally comparisons made between the exchanges predicted and measured show excellent agreement across the entire range of possible flows from unidirectional flow through unbalanced exchange to balanced exchange consideration is given to applications of the model to ocean outfall design and to the prediction of building ventilation flows for natural ventilation the theoretical model we derive for unbalanced exchange bridges the gap in the prediction of air flow rates between displacement flows where the flow is unidirectional and balanced exchange flows

isostatic adjustments in a full glacial sea during the last glaciation an ice free corridor existed between the northeast ellesmere island and northwest greenland ice sheets this corridor constituted a peripheral depression in which the marine limit marks the uppermost extent of a full glacial sea the full glacial sea is characterized by 1 14c dates on in situ marine shells that predate initial emergence unloading followed by 2 synchronous emergence from the marine limit throughout the peripheral depression relative sea level curves from the full glacial sea confirm previous morphostratigraphic and glacioisostatic evidence for limited ice extent during the last glaciation these curves also document the history of glacial unloading and the form of the relative sea level curve that one would theoretically expect in the peripheral depression the form of the curves presented here is unlike any other published emergence curves from arctic canada or from fennoscandia the relative sea level curves for northeast ellesmere island show three segme

evidence from fram strait 78 n for early deglaciation recent syntheses of the history of the last northern hemisphere glaciation and deglaciation illustrate that understanding of the mechanisms and timing of deglaciation before approximately 12 000 years bp1 5 is limited after 12 000 yr bp however there is sufficient evidence from radiocarbon dated moraines raised beaches varved lake sediments and pollen records to provide a reasonable temporal and geographic picture of the decay of the ice sheets here we report on the first oxygen isotope record from the norwegian greenland sea that is radiocarbon dated directly by accelerator mass spectrometry a significant light oxygen isotope event is recorded at approximately 15 000 years bp which suggests that the marine based barents shelf ice sheet disintegrated rapidly at this time recent studies6 7 have estimated that the decay of this ice sheet could have contributed as much as 15 metres to eustatic sea level rise the decay of the barents shelf ice sheet is the earliest major deglacial event yet dated and may have triggered subsequent deglacial events through eustatic sea level effects