ice age simulations with a calving ice sheet model abstract variations of ice sheet volume during the quaternary ice ages are simulated using a simple ice sheet model for the northern hemisphere the basic model predicts ice thickness and bedrock deformation in a north south cross section with a prescribed snow budget distribution shifted uniformly in space to represent the orbital perturbations an ice calving parameterization crudely representing proglacial lakes or marine incursions can attack the ice whenever the tip drops below sea level the model produces a large 100 000 yr response in fair agreement correlation coefficient up to 0 8 with the 18o deep sea core records to increase confidence in the results several of the more uncertain model components are extended or replaced using an alternative treatment of bedrock deformation a more realistic ice shelf model of ice calving and a generalized parameterization for such features as the north atlantic deglacial meltwater layer much the same ice age simulations and agreement with the 18o records as with the original model are still obtained the model is run with different types of forcing to identify which aspect of the orbital forcing controls the phase of the 100 000 yr cycles first the model is shown to give a 100 000 yr response to nearly any kind of higher frequency forcing although over the last 2 million yrs the model phase is mainly controlled by the precessional modulation due to eccentricity over just the last 500 000 yr the observed phase can also be simulated with eccentricity held constant a definite conclusion on the phase control of the real 100 000 yr cycles is prevented by uncertainty in the deep sea core time scales before 600 000 yr b p the model is adapted to represent west antarctica and yields unforced internal oscillations with periods of about 50 000 yr

the younger dryas an intrinsic feature of late pleistocene climate change at millennial timescales abstract a box model of the north atlantic ocean exhibits self sustained oscillations of the large scale ocean circulation which are reminiscent of dansgaard oeschger do style oscillations the freshwater forcing of this ocean model depends on mean climate state represented by global ice volume this is computed by a one dimensional ice sheet model subject to changes in high latitude northern hemisphere summer insolation at low large ice volume the ocean ice system stays in a permanent interstadial stadial mode millennial scale do style oscillations result at intermediate ice volume values which thus define a do window during an interglacial to glacial transition this do window is crossed sufficiently slow to allow for sustained do style oscillations to develop in contrast during a glacial termination the system moves relatively rapid through the do window resulting in an intermittent re appearance of do style oscillations which resemble the sequence of events surrounding the younger dryas yd when forced with modeled ice volume evolution over the last 800 thousand years our model predicts younger dryas type cooling events for each major glacial termination accordingly the younger dryas does not appear to be a one time event

topographic advection of dense bottom water the time development of a dense eddy placed on a varying topography in a rotating system is the subject of this paper it is shown that if the bathymetric variations are comparable with the thickness of the eddy these will induce a first order time development in the water mass large amplitude geostrophic theory shows that the water is advected along the depth contours with a speed that is proportional to the slope of the bottom the results are applied to a laboratory experiment with a rotating parabolic channel according to theory an initially circular eddy placed in the centre of the channel becomes elliptical while shifting its axis along the channel the outcome of the experiment is in accordance with theory and the importance of topographic advection in the ocean is discussed it is suggested that the mechanism may be important for moving water from deep water formation sites and into the global deep water circulation

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

on too fast baroclinic planetary waves in the general circulation abstract recent altimetric observations of the ocean surface reveal signatures of long planetary waves near the annual frequency band comparisons of the observed wave speeds and those predicted by standard linear theory suggest that the latter is inadequate as it yields different westward speeds than those measured in the extratropical latitudes the predicted speeds are typically slower than the observations here the problem of long baroclinic wave propagation in a forced stratified ocean is considered theoretically with a view toward explaining these observations of too fast planetary waves from a quasigeostrophic analysis it is argued that baroclinic waves in a sheared environment are accelerated to the west via their interactions with both the mean advective field and the mean potential vorticity field conditions under which the ratio of actual to linear phase speeds matches the observed ratio are computed and found to be typical of the open ocean extensions of these ideas to continuously st

antarctic ice and sediment flux in the oligocene simulated by a climate ice sheet sediment model abstract a model of deforming sediment is added to a climate ice sheet model and applied to the eocene oligocene transition in antarctic ice volume around 34 ma the coupling between the global climate and ice sheet models is asynchronous with a climate simulation performed once every 10 000 years and only for the first 40 000 years these global climate model solutions are re used to perform runs of 400 000 years in length with orbital forcing and different levels of co2 the sediment model includes bulk transport under ice generation of sub ice till and river transport and predicts the continental scale evolution of sediment thickness and coastal discharge for the first few 10 000 s of years after the onset of substantial ice triggered by co2 falling below 3 pre industrial level sediment discharge to the ocean is relatively uniform around the coast derived from nearby pre existing regolith after that most discharge is concentrated into 4 sites at the mouths of major trough systems with orbitally paced pulses on 104 yr scales these sites and the average magnitudes of the fluxes agree generally with those deduced from offshore seismic and core data although longer 10 my integrations are needed to model the real sediment evolution

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

translational velocity of warm core rings relative to the slope water abstract five warm core rings were examined during short time intervals using thermal infrared satellite imagery a total of 12 pairs of observations of these rings were made all east of 72 w the observations concentrated on the translational velocity of the rings and the mean velocity of the surrounding slope water the mean translational velocity of the rings was found to be 8 5 3 1 cm s 1 at 282 from north the mean velocity of the surrounding slope water determined from a combination of in situ observations with a depth weighting based on theoretical arguments was 5 2 0 3 cm s 1 at 258 the difference i e the velocity of the ring relative to the slope water was 4 6 3 0 cm s 1 at 208 or in component form these rings were found to move relative to the surrounding slope water with a mean northward component of 2 8 1 7 cm s 1 and a mean westward component of 3 2 2 3 cm s 1 the observations presented here are in disagreement with previous observations of ring displacements which s

glacial terminations in the oxygen isotope record of deep sea cores hypothesis of massive antarctic ice shelf destruction abstract glacial terminations i and ii in the deep sea core foraminiferal oxygen isotope ratios though not similar in form are each characterized by a short interval of about 3 ka during which a large negative change occurred in the ratios after correcting for temperature effects we estimate that each change was equivalent to a glacial disintegration capable of causing a 50 60 m eustatic sea level rise in the termination i interval 16 13 ka b p the estimated equivalent sea level rise is much larger than that suggested by the best evidence of deglacial ice loss from the laurentide ice sheet which is thought to dominate pleistocene glacial ice volume changes moreover in termination ii about 125 ka b p the estimated equivalent sea level rise is much larger than that inferred from the stratigraphy of coral reefs and beaches on new guinea and other locations which suggests quite high sea levels for 10 ka prior to this termination to reconcile these severely conflicting lines of evidence we propose that the rapid negative isotope ratio changes were largely caused by the disintegration of massive floating antarctic ice shelves which masqueraded as land ice in the oceanic isotope ratios but which contributed no sea level change we propose that such shelves were formed when oceanic circulation changes in the north atlantic under glacial conditions greatly reduced the formation of relatively warmer north atlantic deep water and its injection into circumpolar antarctic regions and that the shelves disintegrated rapidly with the resumption of large scale formation of this deep water and its input into the antarctic we find that high sea levels in the 125 135 ka b p interval prior to termination ii which imply very little northern ice then are well supported by dated coral reef stratigraphy although these ages were not accepted by the climap study of the last interglacial ocean minimal northern ice volumes at that time imply that strong milankovitch summer insolation is not always required for northern deglaciation a promising additional deglacial mechanism is the prolonged viscous depression of the crust beneath the laurentide ice sheet combined with atmospheric oceanic circulation factors

the interaction of a two layer isolated mesoscale eddy with bottom topography abstract the propagation of an isolated mesoscale eddy onto a western bounding topographic slope is examined through the use of a two layer primitive equation numerical model variable parameters in the study are sense of rotation cyclonic anticyclonic vertical structure baroclinic barotropic and layer thickness ratio h1 h2 eddy size and strength rotational velocity and frictional parameterization are fixed dispersion in the isolated eddy is induced by planetary and topographic beta effects giving the eddy an asymmetric distribution this asymmetric distribution allows for nonlinear self advective propagation tendencies these nonlinear tendencies play a key role in the direction of propagation of the eddy specifically in a quiescient background an anticyclone can have eastward propagation tendencies which can overcome planetary and topographic beta effects conversely cyclones can have westward propagation velocities which are augmented greater than maximum rossby wave phase speed b

oceanic mechanisms for amplification of the 23 000 year ice volume cycle situated adjacent to the largest northern hemispher ice sheets of the ice ages the mid latitude north atlantic ocean has an important role in the earth s climate history it provides a significant local source of moisture for the atmosphere and adjacent continents forms a corridor that guides moisture bearing storms northward from low latitudes and at times makes direct contact along its shorelines with continental ice masses evidence of major ice ocean air interactions involving the north atlantic during the last 250 000 years is summarized outflow of icebergs and meltwater initially driven by summer insolation over the ice sheets affects midlatitude ocean temperatures summer heat storage winter sea ice extent and global sea level these oceanic responses in turn influence the winter moisture flux back to the ice sheets as well as ablation of land ice by calving spectral data indicate that the oceanic moisture and sea level feedbacks in part controlled by glacial melt products amplify milankovitch insolation forcing of the volumetrically dominant mid latitude ice sheets at the 23 000 year precessional cycle

numerical simulations of the baroclinic dynamics of density driven coupled fronts and eddies on a sloping bottom numerical simulations of the baroclinic dynamics of density driven coupled fronts and eddies are described the simulations are based on a two layer intermediate length scale model which filters out barotropic instability and focuses on the subinertial baroclinic evolution of density driven flows within the context of allowing finite amplitude height variations in the lower layer the baroclinic destabilization of a bottom trapped coupled front on a sloping bottom is described in the overlying fluid the instability takes the form of amplifying topographic rossby waves in the coupled front the perturbations to the downslope incropping are preferentially amplified compared to those on the upslope incropping the perturbations to the downslope incropping develop into downslope propagating plumes which eventually evolve into relatively coherent along slope propagating domes we discuss the propagation characteristics of these domes we also simulate the evolution of density driven eddies or domes the first eddy simulation we describe is for an initial eddy configuration which satisfies a zero topographic rossby wave condition in the upper layer we show that these traveling solutions remain remarkably coherent over a period of about 40 eddy circulation times or about 250 days for typical continental slope values for a sufficiently large initial eddy height upper layer fluid parcels can be transported in the along slope direction by the baroclinic eddy we also simulate the evolution of an initial eddy configuration which does not satisfy a zero topographic rossby wave condition in the upper layer a relatively intense cyclonic circulation develops in the overlying fluid over the traveling dome as does a topographic rossby wave tail however even these solutions remain surprisingly coherent over many eddy circulation times

growth of large sulfide structures on the endeavour segment of the juan de fuca ridge abstract mapping and sampling with dsrv alvin has established that sulfide blocks 0 5 m across dredged from the axial valley of the endeavour segment at 47 57 n are samples of unusually large sulfide structures the steep sided structures up to 30 m in length 20 m in height and 10 15 m across are localized by venting along normal faults at the base of the western axial valley wall and are distributed for about 200 m along strike paralleling the 020 trend of the ridge crest high temperature fluids 350 to more than 400 c pass through the massive sulfide structures and enter seawater through small concentric nozzle like features projecting from the top or the sides of the larger vent structures diffuse low temperature flow is pervasive in the vicinity of the active sulfide structures exiting from basalt and sulfide surfaces alike evidence of recent volcanic activity is sparse the two largest samples taken with the dredge would not have been recoverable using the submersible these samples represent massive complex portions of the sulfide structures which were not closely associated with rapid high temperature fluid flow at the time of sampling they contain textural evidence of sealed hydrothermal fluid exit channels mineralogy is dominated by fe sulfides nnd amorphous silica pyrite marcasite wurtzite chalcopyrite and iss are the most common sulfide phases pyrrhotite galena and sphalerite are present in trace amounts barite amorphous silica and chalcedony are the only non sulfide phases anhydrite is not observed in any of the dredge samples although it is common in the chimney like samples recovered by alvin specific mineralogical textural zones within the dredge samples are anaoogous to individual layers in east pacific rise at 21 n and southern juan de fuca ridge samples with two exceptions a coarse grained highly porous fe sulfide rich interior containing sulfidized tubeworm casts and a 2 5 cm thick zone near the outer margin of the samples dominated by late stage amorphous silica the porous interior may have formed by dendritic crystal growth from a slowly circulating fluid within a large enclosed chamber the amorphous silica deposited from a seawater hydrothermal fluid mixture percolating slowly through the walls of the enclosed chamber conductive cooling of the fluid as it traversed the walls allowed amorphous silica to precipitate these silica rich zones are the densest most durable portions of the structures and may be responsible for the lasting stability of the large sulfide features observations in these samples are consistent with two distinct phases of development phase 1 is analogous to chimney growth and construction at 21 n and ends when flow channels become sealed to rapid flow of through going fluid the flow is evidently redirected within the structure phase 2 includes dissolution of anhydrite and precipitation of amorphous silica during conductive cooling of sluggishly circulating hydrothermal fluid or seawater hydrothermal fluid mixtures evolution of vent structures through phase 2 allows lateral and vertical growth of unusually large structures

tidal dynamical considerations constrain the state of an ocean on enceladus abstract in previous work solutions to the non dissipative laplace tidal equations lte were used to provide bounds on the heat generated by the response of a subsurface ocean on enceladus to an obliquity component of tidal forces here we improve these bounds using solutions from the lte with a generic dissipation term explicitly added we find solutions for a wider range of ocean tidal responses that include both unstratified barotropic and stratified baroclinic flow responses to obliquity as well as eccentricity components of the tidal forces we consolidate the results in three ocean tidal scenarios on enceladus that can explain the high heat fluxes 7 mw m 2 globally averaged inferred from measurements by the cassini spacecraft 1 a deep 1 50 km barotropic ocean responding to obliquity tidal forces where obliquity is at least 0 1 2 a shallow 360 m barotropic ocean responding to eccentricity tidal forces 3 a stratified baroclinic ocean responding to eccentricity tidal forces where the density weighted equivalent depth typically much smaller than the ocean s physical depth is near 360 m the ocean is assumed to be global but extensions for a semi global case are also described a more general result which is independent of the specific scenarios proposed is that an ocean attempting to freeze with an associated decrease in its liquid depth which affects the ocean s dynamical response to the tidal forcing must first pass through resonant configurations with a greatly increased generation of ocean tidal heat exceeding 1 w m 2 to 1 kw m 2 that would act to halt further freezing and stagnate the ocean state in this configuration so long as there is still orbital energy to provide the tidal forces with an additional assumption that the ocean has evolved from a more energetic state where the depth of the liquid ocean was greater we obtain the three scenarios proposed

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

a paleoclimate model of northern hemisphere ice sheets abstract a model for predicting the growth and decay of ice sheets based on the astronomical theory of climate change is presented the purpose of the study in part is to isolate the role of the ice sheet physics and earth response under varying ice load by simplifying to the extreme the role of the hydrosphere atmosphere ice sheet physics and the response of the lithosphere asthenosphere under the ice load are modeled explicitly insolation anomalies taken at a fixed latitude directly force latitudinal displacement of the snow line accumulation rate a and ablation rate a evaluated at mean sea level are specificed as external constants a a decrease linearly with ice sheet elevation rough tuning of the model to the general shape of the ice volume record of the last two major glacials determines the external constants model predictions of the ages of several events in the last major glaciation compare well with the radiological ages the six glacial terminatios i vi over the last 600 000 yr are identified and the predicted ages compare reasonably well with the 18 o record for two deep sea cores a direct comparison of model power spectra of ice volume as a function of period with spectra of the 18 o record shows apparent underprediction of power near 100 000 yr when a quantitative but heuristic method for taking into account the red noise spectrum evident in the geological records is used a much more favorable comparison is possible the model prediction lends support to the hypothesis that the nonlinearity of the ice sheet physics is responsible for the 100 000 yr periodicity in the geological record of the late pleistocene

brunhes matuyama magnetic reversal dated at 790 000 yr b p by marine astronomical correlations abstract the presence of the brunhes matuyama magnetic reversal in deep sea core sediments makes possible an alternative to the usual k ar radioistope method of dating the reversal as found in rocks the alternative method uses correlations of northern hemisphere summer insolation with oxygen isotope ratios from tropical cores the latitude dependent insolation variations are calculated from planetary mechanics and thus provide a highly accurate astronomical time scale the insolation variations strongly influence glacial ice volume fluctuations that dominate the oxygenisotope ratio changes recorded in core sediments the summer half year insolation variations are identified with corresponding isotope ratio changes in cores from the present through glacial stage 20 misleading effects of discontinuities or major nonuniformities of sediment deposition are avoided by an analysis of the uniformity of v28 238 and v28 239 the principal cores studied and by comparisons with other cores the top section stages 1 to 10 of v28 238 is uniformly deposited and for this section an isotope ratio time scale is chosen that agrees with the thorium uranium date for the high sea stand of the last interglacial extreme over this interval major glacial extremes strong isotope ratio minima coincide consistently with major insolation minima at times of low orbital eccentricity in addition interstadials are directly associated with precessional insolation peaks and the envelope of isotope ratio peaks resembles the envelope of precessionally dominated insolation peaks the assumption that the glacial extremes depended similarly on insolation minima during stages 10 to 20 permits minor age shifts of strong isotope ratio minima in the two cores relative to ages based on uniform overal deposition to match the ages of low eccentricity insolation minima the age shifts reflect residual nonuniformities of deposition the validity of this matching procedure is supported by a resulting consistent identification of principal isotope ratio peaks with high and low latitude coincident insolation maxima the brunhes matuyama reversal is found intinterglacial stage 19 and is dated on the astronomical time scale at 790 000 5000 yr b p

a climate model with cryodynamics and geodynamics we present a highly simplified zero dimensional model of the climatic system the model attempts to incorporate mechanisms important on the time scale of glaciation cycles namely 104 105 years in particular the radiation balance of the ocean atmosphere the plastic flow of continental ice sheets and the viscous flow of the upper mantle are taken into account the stress is on the interaction between the cryosphere ice sheets and the asthenosphere upper mantle which had not been taken into account in previous energy balance or ice sheet models of climate weertman 1976 kallen et al 1979 the model exhibits free self sustained oscillations of an amplitude and period comparable to those found in the paleoclimatic record of glaciations viz o 10 deg k and o 104 years respectively such oscillations had already been found in the simpler model of kallen et al 1978 1979 the fact that nonlinear self sustained oscillations also obtain for the present slightly more complex model is interesting it offers mild support to the idea that unforced oscillations can actually exist in the real climatic system itself these oscillations are characterized by a quarter phase lag between ice extent and global temperature given that the climatic system is a nonlinear oscillator with a period of o 104 years it is expected that astronomical forcing at 19 000 23 000 and 41 000 years will lead to subharmonic oscillations with a period close to 100 000 years the dominant period of glaciation cycles such effects have already been noticed in the work of birchfield and weertman 1978 with an even simpler model including only glacial dynamics the careful study of the interplay between internal mechanisms and external forcing with comparable time scales represents an interesting challenge to the theory of ice ages the results of such theoretical studies can also provide guidance for observational work in particular periodicities of o 104 years in the climate record and phase lags between ice volume and temperature appear to be supported by the most recent paleogeochemical investigations ruddiman and mclntyre 1981

a simple ice sheet model yields realistic 100 kyr glacial cycles records of global ice volume for the past 700 kyr based on oxygen isotopic data from deep sea cores and reflecting mainly the changing northern hemispheric ice sheets show a dominant cycle of roughly 100 kyr period the records also show smaller amplitude oscillations with spectral peaks at roughly 40 and 20 kyr periods which are well correlated with the milankovich insolation variations due to perturbations in the earth s orbital parameters however no model has accurately simulated the 100 kyr glacial cycle recently birchfield et al 1 and oerlemans2 have obtained encouraging agreement with some features of the glacial cycle by using a simple ice sheet model with a realistic time lag in the response of the bedrock to the ice load this study extends their basic model first by including topography to represent high ground in the north improved results can then be obtained but only with unrealistic parameter values and for some aspects of the record further improvements areobtained by crudely parameterizing possible calving at the equatorward ice sheet tip during deglaciation by proglacial lakes and or marine incursions from the atlantic as emphasized by andrews3 the resulting ice volume curves agree fairly well with the observed records and their power spectra over the past 700 kyr

carbonate time series of the quaternary and late miocene sediments in the pacific ocean a spectral comparison abstract the variance of the quaternary carbonate record of core rc11 209 from the equatorial pacific is almost twice as large as that for the upper miocene of dsdp site 158 from the same region spectral analysis of the carbonate time series shows that the miocene record is dominated by very low frequency components with a concentration of variance near the frequency corresponding to a period of about 400 kyr the quaternary record is also dominated by low frequency components but has in addition concentrations of variance spectral peaks at frequencies corresponding to periods near 100 and 40 kyr cross spectral analysis indicates that both records are coherent with the calculated record of eccentricity of the earth s orbit and that the quaternary record in addition shows coherence with the calculated record of axial tilt these variations in the earth s orbital parameters can then be used to tune the time scales of these two records based on the similarity in the amount of variance in the two records near the 400 kyr period and the observed relationship between carbonate fluctuations and variations in global ice volume as indicated by oxygen isotope measurements it is proposed that the dominant 400 kyr cycle has been associated directly or indirectly with long term fluctuations in the antarctic ice cap since its formation in mid miocene times the major difference in the quaternary carbonate spectrum lies in the marked increase in variance at frequencies associated with the 100 kyr period this increase is thought to be linked directly or indirectly with glacial to interglacial fluctuations of the northern hemisphere ice sheets

abrupt changes heinrich events in late quaternary north atlantic marine environments a history and review of data and concepts in the last several years evidence has mounted that a series of abrupt changes in sediment delivery and palaeoceanography effected the north atlantic they are recorded in a variety of proxy records but most dramatically in changes of grain size and mineralogy associated with postulated iceberg rafting events specifically heinrich h events this review paper examines the evidence for such evidence prior to the development of the heinrich event concept 1988 1992 and then examines the explosion of data and correlations that stemmed from the acceptance and use of this paradigm specific attention is focused on ideas pertaining to the cause s of glaciological mechanisms sediment delivery and sediment source and major gaps in our understanding of the underlying glaciological glacial geological and glacial marine processes are stressed abrupt changes across boundaries associated with h 2 in the labrador sea are illustrated from core hu87033 009lcf the case is made that correlations between records need to be more rigorous especially within the range of radiocarbon dating but it appears that abrupt changes in the delivery of iceberg rafted debris which characterize these intervals are multisourced it is unclear how global climate can simultaneously influence the abrupt behaviour of ice margins in different parts of the world for marine based margins changes in relative sea level are one possibility a qualitative model is presented for triggering h events which includes global changes in mass balance changes in relative sea level at ice margins due to glacial isostasy and changes in the basal thermal regime of tidewater ice streams 1998 john wiley sons ltd

westward motion of mesoscale eddies abstract since the pioneering work of nof the determination of the westward drift of mesoscale eddies under the planetary beta effect has been a recurrent theme in mesoscale oceanography and several different formulae have been proposed in the literature here recpatiulation is sought and within the confines of a single layer model a generalized formula is derived although it is similar to nof s the present formula is established from a modified definition and with fewer assumptions it also recaptiulates all other formulae for the one layer model and applies to a wide variety of situations including cases when the vortex develops a wake of rossby waves or undergoes axismmetrization following the derivation of the formula a physical interpretation clarifies the migration mechanism which can be divided between a self induced propulsion and a reaction from the displaced ambient fluid numerical simulations with primitive and geostrophic equations validate the formula for a variety of length sc

heating of enceladus due to the dissipation of ocean tides abstract given cassini observations of a large and unexplained endogenic heat source the subsurface ocean on enceladus is an important test bed for modeling icy satellite ocean tides and the dissipative heat generated here we revisit and expand estimates of the ocean tidal power heating rate to describe how the power depends on input parameter and process assumptions the approach taken in this and previous work by this author is that the dissipation process in enceladus ocean is unknown and cannot be reliably modeled from first principles considered instead are generic dissipation forms that cover specific physical dissipation processes as special cases specific cases described here include linear nonlinear drag eddy viscosity viscoelastic ice coupling and vertical wave damping the justification for basing conclusions primarily on the generic rather than specific dissipation forms is that whatever the ocean dissipation process it must draw from the stored energy kinetic or potential in the ocean tidal response and this process must have an associated time scale for the dissipation to take place by treating this time scale as well as the lamb number wave speed as free parameters millions of tidal solutions are calculated to sample the full domain of tidal scenarios that arrive from different combinations of these two parameters as well as the assumed dissipation form conclusions drawn from the general behavior in this larger solution domain are then considered to be more robust than conclusions drawn from the subdomain that assumes the validity of a specific physical dissipation process the results show plausible states whereby the ocean tides even if enceladus is covered with thick ice generate the observed heat flux while the same results show that low power non resonant states are also allowed an argument is presented that these low power states may not be stable in the presence of secular trends e g cooling stratification rather self tuned resonance stabilizes the tidal configuration in a near resonant forced state with high power and dissipative heat

multiple instabilities and modes of glacial rhythmicity in the plio pleistocene a general theory of late cenozoic climatic change it has been noted that several distinct modes of glacial oscillation have existed during the past few million years ranging from low amplitude high frequency oscillations in the early pliocene through relatively high amplitude predominantly near 40 ky period oscillations in the late pliocene and early pleistocene to the major near 100 ky period oscillations of the late pleistocene in addition to other plausible mechanisms suggested previously to explain aspects of this multirhythmic phenomenon we now illustrate another possible contributor to this type of behavior based on the hypothesis that the slow response climatic system is bistable and that two kinds of internal instability may be operative along with externally imposed forcing due to earth orbital milankovitch radiation changes and slow tectonically induced changes in atmospheric carbon dioxide these two instabilities have been discussed previously one is due to positive feedback in the global carbon cycle leading to near 100 ky free oscillations of the ice sheets and the other is due to the potential for ice calving catastrophes associated with bedrock variations that can lead to oscillations of a period near 40 ky independent of obliquity forcing within the framework of a dynamical model containing the possibility for these two instabilities as well as for stable modes we show 1 how milankovitch radiative changes or stochastic forcing influencing ice sheets can induce aperiodic chaotic transitions between the possible stable and unstable modes and more significantly 2 how progressive long term tectonically induced changes in carbon dioxide acting in concert with earth orbital radiative variations in high northern hemisphere latitudes can force systematic transitions between the modes such systematic changes can result in an ice mass chronology for the past 5 my that is qualitatively similar to the observed record of global ice mass in essence we have constructed a minimum dynamical model of the late cenozoic climatic changes containing what are believed to be the main physical factors determining these changes ice mass bedrock depression atmospheric carbon dioxide concentration deep ocean thermohaline state milankovitch radiation forcing and slow tectonically induced carbon dioxide forcing this model forms the basis for a coherent theory for the complex climatic events of this long period

coherent baroclinic eddies on a sloping bottom a coherent and stable baroclinic eddy in a rotating fluid was produced on a sloping bottom by releasing a dome of salt water into the ambient fresh water a strong cyclonic vortex is produced above the heavy dome the entire eddy system moves north westward with the up slope direction designated north as a taylor column the eddy system displays long lifetimes but it is shown that a theory of isolated systems cannot account for the experimental observations instead it is demonstrated that the vortex flow above the lens is along the lines of constant depth producing a net pressure force on the lens which approximately balances the buoyancy force when ekman friction is also included it accounts for the northward motion of the dome

deep planetary circulation and topography simple models of midocean flows abstract the presence of broad flowing water masses in the deep ocean requires dynamical explanation vertical density diffusion and effect are invoked in classical theories here we show how topographic potential vorticity can control broad baroclinic flows with diffusion playing a secondary role the theory and numerical experiments involve a zonal flow over topography such as one finds in the southern ocean although similar effects occur in source sink flows at middle latitudes a 1 layer model that is one active deep layer beneath a thick upper layer of the deep circulation shows intense interactions with both small scale o 500 km wide and large scale o 2500 km wide seafloor slopes broad gentle slopes can block an initially uniform flow expelling the circulation to an outer rim defined by hyperbolic characteristics where it forms into jets with smaller scale topography planetary scale flow encountering a midocean ridge develops transient distortions of the flow and density fields whi

a string function for describing the propagation of baroclinic anomalies in the ocean the authors derive a string function that describes the propagation of large scale potentially large amplitude baroclinic energy anomalies in a two layer ocean with variable topography and rotation parameter the generality of the two layer results allows results for the 1 layer 1 5 layer inverted 1 5 layer lens and dome models to be produced as limiting cases the string function is a scalar field that acts as a streamfunction for the propagation velocity in the linear case the string function is simply c2o f where co is the background baroclinic shallow water wave speed and typically describes propagation poleward on the eastern boundaries westward with some topographic steering over the middle ocean and equatorward on the western boundaries in the more general nonlinear case the string function is locally distorted by the anomaly in the fully nonlinear examples of a lens or dome there is no rest or background string function the string function is generated entirely by the disturbance and propagation is due to asymmetric distribution of the anomalous mass over the string function contours it is shown that conventional beta topographic propagation results e g beta drift of eddies the nof speed of cold domes can be obtained as limiting cases of the string function the string function provides however more general propagation velocities that are also usually simpler to derive the first baroclinic mode string function for the global oceans is calculated from hydrographic data the westward propagation speeds in the ocean basins as derived from the meridional gradient of the string function are typically two to five times faster than those expected from standard theory and agree well with the propagation speeds observed for long baroclinic rossby waves in the topex poseidon data

long periodic variations in the earth s obliquity and their relation to third order eustatic cycles and late neogene glaciations abstract evolutive spectra of four high resolution climatic proxy records reveal that the spectral power in the obliquity frequency band increases during five well defined intervals in the last 5 3 million years these intervals correspond to periods of high amplitude variations in the tilt obliquity of the earth s axis connected with a 1 2 myr cycle and to sea level lowstands of third order eustatic cycles in the haq et al 1987 curve this implies that the development of major plio pleistocene glaciations proceeded episodically and that third order cycles are glacio eustatically controlled in at least two of these intervals sinistrally coiled neogloboquadrinids entered the mediterranean at times of glacial periods one interval starts around 2 8 ma and is characterized by the first occurrence of n atlantica s another interval begins at the plio pleistocene boundary around 1 8 ma and is characterized by the common occurrence of sinistrally coiled n pachyderma also during the late miocene third order cycles correlate well with the 1 2 myr cycle of obliquity a significant drop in the third order eustatic curve starting at the tortonian messinian boundary for instance coincides with a period of high amplitude variations in the obliquity time series connected with the 1 2 myr cycle

asthenospheric ice load effects in a global dynamical system model of the pleistocene climate in a previous dynamical model the late cenozoic climate variations were simulated taking into account free and forced variations of atmospheric carbon dioxide acting in concert with changes in global ice mass and the deep ocean thermal state all under the influence of the known earth orbital radiative changes this model is now extended by adding another relevant variable bedrock asthenosphere depression including its associated ice calving effects within the context of this extended model we 1 demonstrate the main results of previous bedrock ice sheet models in what we believe is the simplest possible manner 2 show how these previous models can exhibit the mid pleistocene transition with the inclusion of co2 effects 3 discuss the limitations of these previous bedrock models and 4 illustrate the possibility of removing some of these limitations and accounting for further aspects of the paleoclimate record by using the full dynamical system that includes forced and free effects of co2 as well as effects of bedrock depression and milankovitch forcing as one example of a new possibility with bedrock effects included in the full system we can obtain a solution characterized by irregularly spaced intermittent episodes in which the behavior is dominated either by near 40 kyr period oscillations or by near 100 kyr periods such as prevailed over the pleistocene

long extratropical planetary wave propagation in the presence of slowly varying mean flow and bottom topography part i the local problem one of the most successful theories to date to explain why observed planetary waves propagate westward faster than linear flat bottom theory predicts has been to include the effect of background baroclinic mean flow which modifies the potential vorticity waveguide in which the waves propagate barotropic flows are almost everywhere too small to explain the observed differences that theory accounted for most but not all of the observed wave speeds a later attempt to examine the effect of the sloping bottom on these waves without the mean flow effect did not find any overall speedup this paper combines these two effects assuming long geostrophic waves and slowly varying mean flow and topography and computes group velocities at each point in the global ocean these velocities turn out to be largely independent of the orientation of the wave vector a second speedup of the waves is found over that for mean flow only almost no eastward oriented group velocities are found and so features that appear to propagate in the same sense as a subtropical gyre would have to be coupled with the atmosphere or be density compensated in some manner

the destruction of lenses and generation of wodons abstract since midocean eddies migrate westward they eventually reach the western boundaries it is therefore of interest to find out what happens after the eddies collide with the walls an isopycnic two layer primitive equation model on a plane and a simple analytical model on an f plane are constructed to investigate the meridional migration of an oceanic eddy along a western wall on a plane three factors determine the eddy s migration along a western meridional wall first the image effect pushes an anticyclonic cyclonic eddy northward southward second the force resulting from the larger coriolis force on the northern side of the eddy pulls an anticyclonic cyclonic eddy southward northward third after an anticyclonic cyclonic eddy collides with the wall parts of the anticyclonic eddy s interior fluid leak out southward northward along the wall forming a thin jet in an analogy to a rocket this jet pushes the eddy northward southward our aim is to investigate in whi

a coupled climate ice sheet model applied to the quaternary ice ages a coupled climate ice sheet model is used in an attempt to simulate the northern hemispheric ice sheet volume variations implied by deep sea core records over the last several 105 years the climate model consists of a global one level diffusive energy balance equation with seasonal variation and land ocean contrast using a severely truncated series of associated legendre functions the ice sheet model uses a standard vertically averaged flow law and predicts ice thickness in a north south cross section bedrock deformation under the ice is included as linear flow confined to a thin asthenospheric channel the climate model is tuned to the modern climate and tested against results from atmospheric general circulation models for 18 000 and 10 000 yr b p it is suggested that the lack of sea ice variations causes the biggest departures from the gcm results the sensitivities to the orbital perturbations of the coupled model and of the ice sheet model alone with a prescribed snow budget distribution are examined some qualitative differences are found in the latitudinal forms of these sensitivities despite these differences however the two types of models produce similar ice age simulations over the last 700 thousand years in response to the orbital perturbations in particular fairly realistic simulations with strong 100 kyr cycles similar to those obtained by adding an ice calving mechanism to the ice sheet model in pollard 1982a are again produced in the coupled model

abrupt climatic change related to unstable ice sheet dynamics toward a new paradigm ice streams are fast currents of ice that drain some 90 of present day ice sheets and probably drained a similar percent of ice from former ice sheets ice streams may have life cycles akin to but much longer than surge cycles of certain mountain glaciers the floating tongues of marine ice streams coalesce to form floating ice shelves that buttress marine ice sheets and the grounded lobes of terrestrial ice streams stabilize terrestrial ice sheets ice shelves and ice lobes form during the life cycles of ice streams and disintegrate rapidly to initiate new life cycles successive life cycles continue until the ice sheet collapses a new paradigm is postulated in which abrupt climatic change is driven by iceberg outbursts associated with life cycles of marine ice streams and dust storms associated with life cycles of terrestrial ice streams for pleistocene northern hemisphere ice sheets these mechanisms regulated north atlantic surface temperatures and salinity and perhaps planetary albedo and atmospheric co2 and thereby drove climatic change which tended to be abrupt because ice stream life cycles began and ended abruptly ice streams proliferated along the margins of northern hemisphere ice sheets after they advanced beyond the crystalline shields of north america and eurasia and spread over softer sedimentary rocks overlain by thick ice cemented sediments that progressively thawed especially along river valleys and marine troughs an increasing fraction of these ice sheets was then subjected to the unstable life cycles of ice streams as seen in the pronounced spikiness of the late glacial oxygen isotope stratigraphy in the greenland ice core at dye 3 life cycles of greenland ice streams during the holocene seem to be linked to episodes of regional climatic cooling most recently the little ice age when superimposed on the present milankovitch hemicycle of reduced insolation over the north atlantic this could abruptly initiate a new worldwide glaciation cycle in the aftermath of present day co2 greenhouse warming proliferation of antarctic ice stream life cycles during the period of greenhouse warming may also trigger global climatic change by forcing a reorganization of circumpolar thermohaline circulation in the southern ocean