direct correlation of millennial scale changes in western north american vegetation and climate with changes in the california current system over the past 60 kyr terrestrial pollen and marine climate proxies from seven sediment cores taken on the continental margin of western north america between 32 and 43 n show systematically related short term changes superposed on milankovitch scale oscillations of the past 60 kyr during oxygen isotope stage 3 brief warming events in california and oregon appear correlative with interstadial events in waters offshore as do the rapid climate oscillations of the last glacial transition 14 10 ka estimated temperature depression of the coastal lowlands ranges from 10 c in southern california to 5 c in oregon during the last glacial the absence of long distance migration of pacific coastal plant assemblages concurs with marine evidence that southward movement of the polar front during the last glacial maximum was limited correlative changes in terrestrial and marine ecosystems imply that broad reorganizations of circulation in the northeast pacific ocean were synchronous with reorganizations of atmospheric circulation over western north america

residual mean solutions for the antarctic circumpolar current and its associated overturning circulation abstract residual mean theory is applied to the streamwise averaged antarctic circumpolar current to arrive at a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane simple solutions are found in which transfer by geostrophic eddies colludes with applied winds and buoyancy fluxes to determine the depth and stratification of the thermocline and the pattern of associated residual meridional overturning circulation

salinity driven thermocline transients in a wind and thermohaline forced isopycnic coordinate model of the north atlantic abstract an isopycnic coordinate oceanic circulation model formulated with the aim of simulating thermodynamically and mechanically driven flow in realistic basins is presented special emphasis is placed on the handling of diabatic surface processes and on thermocline ventilation the model performance is illustrated by a 30 year spinup run with coarse horizontal resolution 2 mesh in a domain with north atlantic topography extending from 10 to 60 n latitude the vertical structure encompasses 10 isopycnic layers in steps of 0 2 units capped by a thermodynamically active mixed layer from an initially isohaline state with isopycnals prescribed by zonally averaged climatology the model is forced by seasonally varying wind stress radiative and freshwater fluxes and by a thermal relaxation process at the surface after a mechanical spinup time of about 15 years a quasi stationary pattern of mean circulation and annual variability ensues characterized by pronounced subtropical mode water formation

enhancement of mesoscale eddy stirring at steering levels in the southern ocean abstract meridional cross sections of effective diffusivity in the southern ocean are presented and discussed the effective diffusivity keff characterizes the rate at which mesoscale eddies stir properties on interior isopycnal surfaces and laterally at the sea surface the distributions are obtained by monitoring the rate at which eddies stir an idealized tracer whose initial distribution varies monotonically across the antarctic circumpolar current acc in the absence of observed maps of eddying currents in the interior ocean the advecting velocity field is taken from an eddy permitting state estimate of the southern ocean sose a three dimensional advection diffusion equation is solved and the diffusivity diagnosed by applying the nakamura technique on both horizontal and isopycnal surfaces the resulting meridional sections of keff reveal intensified isopycnal eddy stirring reaching values of 2000 m2 s 1 in a layer deep beneath the acc but rising toward the surface on the equatorward flank

biomarker temperature estimates for modern and last glacial surface waters of the california current system between 33 and 42 n sea surface temperature sst estimates were made using data for c37 39 alkenones analyzed in modern and glacial age intervals of sediment cores collected along an east west 42 n from 125 to 132 w and a north south 41 33 n transect of the california current system ccs the prymnesiophyte biomarker results suggest that surface waters warmed significantly throughout this region since the last glacial maximum lgm but the magnitude of warming varied spatially stratigraphic profiles from four sediment cores along the north south transect indicate the warming period was confined to the glacial interglacial transition 15 10 ka with sst reaching a maximum value at 10 ka and maintaining a uniformly high value throughout the holocene comparison of estimates derived from analysis of modern and lgm sediment intervals indicates the magnitude of the sst change was minimal for locations south of about 36 n 1 2 c and increased significantly 3 5 c north of this latitude using a simple heat balance model we calculate from the latitudinal gradient in sst that southward flow in the california current system during the lgm was about 60 of that measured today at 36 n our findings support the conclusion of others based on pollen data that coastal upwelling in the region of the northeast pacific off northern california was significantly reduced or even completely shutdown during the lgm

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

tracer dating and ocean ventilation the interpretation of transient tracer observations depends on difcult to obtain information on the evolution in time of the tracer boundary conditions and interior distributions recent studies have attempted to circumvent this problem by making use of a derived quantity age based on the simultaneous distribution of two complementary tracers such as tritium and its daughter helium 3 the age is defined with reference to the surface such that the boundary condition takes on a constant value of zero we use a two dimensional model to explore the circumstances under which such a combination of conservation equations for two complementary tracers can lead to a cancellation of the time derivative terms an interesting aspect of this approach is that mixing can serve as a source or sink of tracer based age we define an idealized ventilation age tracer that is conservative with respect to mixing and we explore how its behavior compares with that of the tracer based ages over a range of advective and diffusive parameters transient tracers such as tritium and tritiugenic helium 3 chlorofiuorocarbons especially cfc 11 and cfc 12 and radiocarbon produced by nuclear bomb tests have entered the oceans primarily during the past 30 years the inherent time scale of these tracers matches very well typical time scales for thermocline ventilation as well as other important oceanic processes such as deep water formation they have been used with some success to study the time scales of thermocline ventilation e g sarrniento 1983 jenkins 1987 and oxygen utilization rates our e g jenkins 1977 1980 1982 1987 as well as other processes such as equatorial upwelling rates broecker et al 1978 quay et al 1983 wunsch 1984 and transport of upper north atlantic deep water weiss et al 1985 the problem of coping with the nonsteady state aspect of these tracers has been dealt with in many ways few of them truly satisfactory for example rooth and ostlund 1972 chose to estimate the diapycnic diffusivity in a region where there was some evidence that the tracer distributions were approximately in steady state at the time of their measurements wunsch 1984 used a similar steady state assumption in his study of equatorial upwelling using bomb radiocarbon such an argu ment cannot be applied in most regions of the ocean however indeed one can question whether it applies even in the above situations therefore one generally would expect that it would be necessary to know something about the evolution of the tracer concentration in time as well as the time history of the boundary conditions for that tracer over the same span of time for example sarrniento s 1983 tritium box model of the thermocline solved the conserva tion equation for the period of time between 1952 before nuclear bomb tests had injected a significant amount of tritium into the oceans and 1972 when a single realization of the tracer field was obtained by a series of field studies the surface concentration time history of dreisigacker and roether 1978 was used as a boundary condition such an l now at deutsche forschungs und versuchasanstalt ftir luft

apparent synchroneity of submillennial scale climate events between greenland and santa barbara basin california from 30 10 ka abstract evidence is presented from odp hole 893a santa barbara basin for possible synchroneity between greenland and california margin submillennial climate change records during termination 1 and the last glacial maximum lgm planktonic foraminiferal isotope and faunal records are compared to the gisp2 18o records greenland for the interval between 30 and 10 ka using a new chronology based on 38 planktonic 14c dates apparent synchronous climatic events include interstadial is events 2 3 and 4 a broad warming trend between 21 and 19 ka and a broad cooling trend between 19 and 17 ka bolling and allerod warm episodes separated by the cooler older dryas event younger dryas cool episode and the preboreal the resulting tight correlation supports an intimate teleconnection between santa barbara basin surface waters and greenland air temperatures differences between greenland and santa barbara basin suggest that some regional variations were superimposed on the global pattern of climate change e g the pre bolling warming

stable isotope evidence for a foggy climate on santa cruz island california at 16 600 cal yr b p abstract in this study we use stable isotope analysis to investigate the climate in southern coastal california during the last 10 000 years of the pleistocene by comparing the carbon and oxygen stable isotope ratios of preserved douglas fir pseudotsuga menziesii wood from santa cruz island to modern douglas fir wood from northern california ams age determination indicates that the preserved trees grew at about 16 600 270 cal yr b p after isolating cellulose from both the modern and pleistocene wood to remove any potential bias due to differential decomposition rates of wood components loader n j robertson i mccarroll d 2003 comparison of stable carbon isotope ratios in whole wood cellulose and lignin of oak tree rings palaeogeography palaeoclimatology palaeoecology 196 395 407 we find that the pleistocene douglas fir wood has significantly greater carbon isotope discrimination and significantly more enriched 18 o than the modern douglas fir wood which suggests that the douglas fir trees growing on santa cruz island at 16 600 cal yr b p experienced less moisture stress and used more enriched water from fog than douglas fir trees at point reyes today

transit time distributions in a global ocean model abstract results from a simulation of the ocean transit time distribution ttd for global and regional ocean surface boundary conditions are presented based on a 5000 yr integration using the parallel ocean program ocean general circulation model the ttd describes the probability that water at a given interior point in the ocean was at some point on the ocean surface a given amount of time ago it is shown that the spatial distribution of ocean ttds can be understood in terms of conventional wisdom regarding time scales and pathways of the ventilated thermocline and the thermohaline circulation driven deep ocean circulation the true mean age from the model the first moment of the ttd is demonstrated to be very large everywhere because of very long tailed distributions regional ttd distributions are presented for distinct surface boundary subregions and it is shown how these can help in the interpretation of the global ttd the spatial structure of each regional ttd is shown to become essential

transit time and tracer age distributions in geophysical flows transport in the atmosphere and in the ocean is the result of the complex action of time dependent and often highly turbulent flow a useful diagnostic that summarizes the rate at which fluid elements are transported from some region to a point or the reverse via a multiplicity of pathways and mechanisms is the probability density function pdf of transit times the first moment of this pdf often referred to as mean age has become an important transport diagnostic commonly used by the observational community this paper explores how to probe the flow with passive tracers to extract transit time pdf s as a foundation the literal tracer age is defined as the elapsed time since tracer was injected into the flow and the corresponding tracer age distribution z as the fractional tracer mass in a given interval of tracer age the distribution z has concrete physical interpretation for arbitrary sources but is only equivalent to a tracer independent transit time pdf of the flow in special cases the transit time pdf is a propagator g9 of boundary conditions the age spectrum of t m hall and r a plumb applied over a control surface v the propagator g9 is shown to be the flux into v resulting from a unit mass injected into the time reversed flow through explicit construction of the transit time pdf using the concept of tracer age the special cases for which z and g9 coincide are established this allows a direct physical demonstration of g9 and its adjoint g9 as the pdf s of transit times since fluid at point r had last contact with v and until fluid at r will have first contact with v respectively in the limit as v is shrunk to a point point to point transit time pdf s are well defined but their mean transit time and higher order moments become infinite several concrete geophysical examples are considered to illustrate under what conditions characteristics of tracer age and transit time pdf s can be inferred from observations in the atmosphere or the ocean

on ocean transport diagnostics the idealized age tracer and the age spectrum abstract the idealized age tracer is commonly used to diagnose transport in ocean models and to help interpret ocean measurements in most studies only the steady state distribution the result of many centuries of model integration has been presented and analyzed however in principle the transient solution provides more information about the transport here it is shown that this information can be readily interpreted in terms of the ventilation histories of water masses a simple relationship is derived valid for stationary transport between the transient evolution id r t of the idealized age tracer and the age spectrum g r t the distribution of times t since a water mass was last ventilated namely g r t tt id r t implications of the relationship are discussed and the relationship is illustrated with an idealized model

pore fluid effects on elastic wave velocities of serpentinite and implications for estimates of serpentinization in oceanic lithosphere abstract recent seismic refraction surveys at various outer rise regions have identified low seismic velocities in the uppermost mantle which is indicative of mantle hydration serpentinization related to water infiltration along bending related faults prior to subduction serpentinization could lead to the development of pore spaces during hydration reaction which influences seismic velocity here we measured the elastic wave velocity of low temperature serpentinites with various porosities and reevaluated the degree of serpentinization of the oceanic mantle in outer rise regions accounting for pore fluid effects experimental results show that the elastic wave velocity of serpentinite decreases with increasing porosity this relationship indicates that the estimated degree of serpentinization decreases with increasing serpentinite porosity we then applied these experimental data to the geophysical observations of the outer rise regions to reevaluate the amount and the type of water carried into earth s interior at subduction systems

a generalized transport theory water mass composition and age abstract a general theory to describe and understand advective and diffusive ocean transport is reported it allows any passive tracer field with an atmospheric source to be constructed by superposing sea surface contributions with a generalized green s function called the boundary propagator of the passive tracer equation the boundary propagator has the interpretation of the joint water mass and transit time distribution from the sea surface the theory thus includes the classical oceanographic idea of water mass analysis and extends it to allow for a distribution of transit times from the sea surface the joint water mass and transit time distribution contains complete information about the transport processes in the flow it captures this information in a more accessible way than using velocity and diffusivity fields however at least for the case of sequestration and transport of dissolved material by the ocean circulation the boundary propagator is thus the natural quantity to consider when discus

on the factors controlling the eddy induced transport in the antarctic circumpolar current abstractthis study examines eddy driven material transport by analyzing trajectories of lagrangian particles in an idealized model of the southern ocean the main focus is on the direction of the transport in the latitude depth plane as well as on the magnitudes of the vertical and meridional particle dispersion in particular this transport is along the mean isopycnals in the control simulation but changes its direction and intensity in a series of sensitivity experiments with artificially modified currents the main new conclusion is that the direction of the transport is determined by the three dimensional interplay between the zonal background flow and the transient eddies the stationary meanders play a secondary role the key parameter here is the strength of the zonal advection relative to the eddy magnitudes whereas the mean vertical shear in the zonal velocity is of secondary importance in particular stronger mean zonal advection leads to steeper orientation of the eddy fluxes and deeper pe

antarctic intermediate water and subantarctic mode water formation in the southeast pacific the role of turbulent mixing abstract during the 2005 austral winter late august early october and 2006 austral summer february mid march two intensive hydrographic surveys of the southeast pacific sector of the southern ocean were completed in this study the turbulent kinetic energy dissipation rate diapycnal diffusivity and buoyancy flux jb are estimated from the ctd o2 and xctd profiles for each survey enhanced of o 10 3 to 10 4 m2 s 1 is found near the subantarctic front saf during both surveys during the winter survey enhanced was also observed north of the subduction front the northern boundary of the winter deep mixed layer north of the saf in contrast the summer survey found enhanced across the entire region north of the saf below the shallow seasonal mixed layer the enhanced below the mixed layer decays rapidly with depth a number of ocean processes are considered that may provide the energy flux necessary to support the observed diffusivity the observed buoyancy flux 4 0 10 8 m2 s 3 surr

anomalous chlorofluorocarbon uptake by mesoscale eddies in the drake passage region the role of mesoscale eddies in the uptake of anthropogenic chlorofluorocarbon 11 cfc 11 gas is investigated with a 1 20 eddy resolving numerical ocean model of a region of the southern ocean with a relatively fast air sea equilibrium time scale about a month the air sea cfc 11 flux quickly responds to the changes in the mixed layer cfc 11 partial pressure pcfc 11 at the mesoscale significant correlations are observed between pcfc 11 anomaly anomalies in sea surface temperature sst net heat flux and mixed layer depth an eddy centric analysis of the simulated cfc 11 field suggests that anticyclonic warm core eddies generate negative pcfc 11 anomalies and cyclonic cold core eddies generate positive anomalies of pcfc 11 surface pcfc 11 is modulated by mixed layer dynamics in addition to cfc 11 air sea fluxes a negative cross correlation between mixed layer depth and surface pcfc 11 anomalies is linked to higher cfc 11 uptake in anticyclones and lower cfc 11 uptake in cyclones especially in winter an almost exact asymmetry in the air sea cfc 11 flux between cyclones and anticyclones is found

the effects of mesoscale eddies on the stratification and transport of an ocean with a circumpolar channel abstract the effects of eddies in a primitive equation ocean model configured in a single hemisphere domain with circumpolar channels at their poleward ends are investigated in particular two regimes for the mass balance in the channel are investigated with small overlying winds the channel stratification is largely set by diffusion operating in the gyre portion of the domain the depth scale varies with a fractional power of the diffusivity but has little dependence on the wind stress as the winds are increased the depth becomes increasingly controlled by a tendency toward small residual circulation in this limit a scaling theory is derived for the stratification in the channel that predicts the overall depth of the thermocline as a power of the wind stress and that allows the eddy length scale to differ from the channel length scale the predicted depth depends on the details of the closure chosen for the eddy buoyancy flux but in general it varies as some fractional power of the wind stress a

localized subduction of anthropogenic carbon dioxide in the southern hemisphere oceans the southern ocean makes a substantial contribution to the oceanic carbon sink observationally based estimates of carbon subduction suggest that carbon sequestration depends on physical properties such as mixed layer depth ocean currents wind and eddies that are potentially sensitive to climate variability and change

comparison of subantarctic mode water and antarctic intermediate water formation rates in the south pacific between ncar ccsm4 and observations average formation rates for subantarctic mode water samw and antarctic intermediate water aaiw in the south pacific are calculated from the national center for atmospheric research community climate system model version 4 ncar ccsm4 using chlorofluorocarbon inventories cfc 12 when compared to observations ccsm4 accurately simulates the southeast pacific as the main formation region for samw and aaiw formation rates for samw in ccsm4 are 3 4 sverdrup sv about half of the observational rate due in part to shallow mixed layers a thinner samw layer and insufficient meridional transport a formation rate of 8 1 sv for aaiw in ccsm4 is higher than observations due to higher inventories in the southwest and central pacific and surface concentrations within ccsm4 also a lack of data in the southwest pacific may bias the observational rate low this model observation comparison is useful for understanding the uptake and transport of other gases e g co2 by the model

isolating the role of mesoscale eddies in mixing of a passive tracer in an eddy resolving model 1 this study examines the role of mesoscale eddies in distribution of chlorofluorocarbon cfc in a numerical model of the north atlantic our main conclusions are based on a comparison of two eddy resolving experiments one with and one without eddy advection of cfc the cfc distributions in these two experiments exhibit substantial differences within the subpolar gyre in particular in the presence of eddies the horizontal distribution of cfc in the upper 1000 m is more uniform and the cfc concentration is lower in the lower 1500 m our analysis demonstrates that these basin wide differences are caused by the interactions of eddy advection with convection and mean advection in several isolated locations the corresponding eddy flux divergence terms are spatially non uniform in magnitude their effects are often nonlocal and sometimes work against the spreading of cfc being carried out by the mean advection these conclusions are further confirmed by a third experiment in which the eddy advection was replaced by a down gradient diffusive parameterization our results demonstrate that advection by mesoscale eddies is crucial to the mixing of atmospheric gasses into the ocean and outline difficulties in representing eddies by the down gradient diffusion

importance of mesoscale eddies and mean circulation in ventilation of the southern ocean this study examines the relative importance of the mean advection and mesoscale currents in the property exchange between the southern ocean mixed layer and downstream in the upper 2000 meters this exchange is referred to as ventilation a new highly efficient offline tracer model employed here uses pre calculated velocities to advect dynamically passive tracers two idealized tracers are considered the boundary impulse response bir tracer which helps to determine the ventilation pathways and time scales and the transient surface tracer tst which is relevant to transient atmospheric tracers the importance of eddies is isolated by contrasting the control simulation with a simulation without mesoscale currents the analysis reveals complex three dimensional ventilation pathways controlled by the interplay between the mean advection and eddy induced spreading the mean currents carry the tracers eastward within acc and contribute to the formation of the antarctic intermediate water aaiw in the south pacific and south atlantic the main effect of eddies is to disperse tracers away from the mean pathways and this dispersion acts to retain the bir tracer in the atlantic and indian sectors and reduce the upstream influence of these regions on the south pacific in addition the eddy induced along isopycnal spreading within acc increases the ventilated depth and the inventory of tst the results can be used to interpret distribution of tracers in the ocean in numerical simulations and observations this article is protected by copyright all rights reserved

characterizing the chaotic nature of ocean ventilation ventilation of the upper ocean plays an important role in climate variability on interannual to decadal timescales by influencing the exchange of heat and carbon dioxide between the atmosphere and ocean the turbulent nature of ocean circulation manifest in a vigorous mesoscale eddy field means that pathways of ventilation once thought to be quasi laminar are in fact highly chaotic we characterise the chaotic nature of ventilation pathways according to a nondimensional filamentation number which estimates the reduction in filament width of a ventilated fluid parcel due to mesoscale strain in the subtropical north atlantic of an eddy permitting ocean model the filamentation number is large everywhere across three upper ocean density surfaces implying highly chaotic ventilation pathways and increases with depth by mapping surface ocean properties onto these density surfaces we directly resolve the highly filamented structure and confirm that the filamentation number captures its spatial variability these results have implications for the spreading of atmospherically derived tracers into the ocean interior