the ventilated ocean abstractadiabatic theories of ocean circulation and density structure have a long tradition from the concept of the ventilated thermocline to the notion that deep ocean ventilation is controlled by westerly winds over the southern ocean this study explores these ideas using a recently developed lagrangian ocean model lom which simulates ocean motions by computing trajectories of water parcels a unique feature of the lom is its capacity to model ocean circulations in the adiabatic limit in which water parcels exactly conserve their densities when they are not in contact with the ocean surface the authors take advantage of this property of the lom and consider the circulation and stratification that develop in an ocean with a fully adiabatic interior with both isopycnal and diapycnal diffusivities set to zero the ocean basin in the study mimics that of the atlantic ocean and includes a circumpolar channel the model is forced by zonal wind stress and a density restoring at the surface despite the

resolution analysis of finite fault source inversion using one and three dimensional green s functions 2 combining seismic and geodetic data using numerical tests for a prescribed heterogeneous earthquake slip distribution we examine the importance of accurate green s functions gf for finite fault source inversions which rely on coseismic gps displacements and leveling line uplift alone and in combination with near source strong ground motions the static displacements while sensitive to the three dimensional 3 d structure are less so than seismic waveforms and thus are an important contribution particularly when used in conjunction with waveform inversions for numerical tests of an earthquake source and data distribution modeled after the 1994 northridge earthquake a joint geodetic and seismic inversion allows for reasonable recovery of the heterogeneous slip distribution on the fault in contrast inaccurate 3 d gfs or multiple 1 d gfs allow only partial recovery of the slip distribution given strong motion data alone likewise using just the gps and leveling line data requires significant smoothing for inversion stability and hence only a blurred vision of the prescribed slip is recovered although the half space approximation for computing the surface static deformation field is no longer justifiable based on the high level of accuracy for current gps data acquisition and the computed differences between 3 d and half space surface displacements a layered 1 d approximation to 3 d earth structure provides adequate representation of the surface displacement field however even with the half space approximation geodetic data can provide additional slip resolution in the joint seismic and geodetic inversion provided a priori fault location and geometry are correct nevertheless the sensitivity of the static displacements to the earth structure begs caution for interpretation of surface displacements particularly those recorded at monuments located in or near basin environments

does stommel s mixed layer demon work abstract stommel argued that the seasonal cycle leads to a bias in the coupling between the surface mixed layer and the main thermocline of the ocean he suggested that a demon operated that effectively only allowed fluid at the end of winter to pass from the mixed layer into the main thermocline in this study stommel s hypothesis is examined using diagnostics from a time dependent coupled mixed layer primitive equation model of the north atlantic cme the influence of the seasonal cycle on the properties of the main thermocline is investigated using two methods in the first the rate and timing of subduction into the main thermocline is diagnosed using kinematic methods from the 1 resolution cme fields in the second tracer diagnostics of the cme and idealized experiments using a date tracer identifying the timing of subduction are performed over the subtropical gyre both approaches generally support stommel s hypothesis that fluid is only transferred from the mixed layer into the main therm

ams radiocarbon dating and varve chronology of lake soppensee 6000 to 12000 14c years bp for the extension of the radiocarbon calibration curve beyond 10000 14c y bp laminated sediment from lake soppensee central switzerland was dated the radiocarbon time scale was obtained using accelerator mass spectrometry ams dating of terrestrial macrofossils selected from the soppensee sediment because of an unlaminated sediment section during the younger dryas 10000 11000 14c y bp the absolute time scale based on counting annual layers varves had to be corrected for missing varves the soppensee radiocarbon verve chronology covers the time period from 6000 to 12000 14c y bp on the radiocarbon time scale and 7000 to 13000 calendar y bp on the absolute time scale the good agreement with the tree ring curve in the interval from 7000 to 11450 cal y bp cal y indicates calendar year proves the annual character of the laminations the ash layer of the vasset killian tephra massif central france is dated at 8230 140 14c y bp and 9407 44 cal y bp the boundaries of the younger dryas biozone are placed at 10986 69 cal y bp younger dryas preboreal and 1212 86 cal y bp allerod younger dryas on the absolute time scale the absolute age of the laacher see tephra layer dated with the radiocarbon method at 10 800 to 11200 14c y bp is estimated at 12350 135 cal y bp the oldest radiocarbon age of 14190 120 14c y bp was obtained on macrofossils of pioneer vegetation which were found in the lowermost part of the sediment profile for the late glacial the offset between the radiocarbon 10000 12000 14c y bp and the absolute time scale 11400 13000 cal y bp in the soppensee chronology is not greater than 1000 years which differs from the trend of the u th radiocarbon curve derived from corals

source process of the 1923 kanto earthquake considering subduction interface geometry and amplification effects caused by the large scale and 3d complex sedimentary basin abstract the 1923 kanto earthquake occurred along the sagami trough central japan causing severe damage in the tokyo metropolitan area this study was able to characterize the source process for this event using geodetic teleseismic and strong motion data the kanto region is located above a large scale sedimentary basin therefore 3d green s functions and a curved fault modeling the subduction interface geometry were used to account for 3d complex wave propagation inside the basin the later phases of the 3d green s functions with long paths inside the basin had large amplitude and long duration primarily because of amplification effects caused by the lateral heterogeneity of sedimentary layers however 3d static displacements were large mainly because of amplification effects caused by the presence of thick soft sedimentary layers in the basin the geodetic inversions with 3d and 1d green s functions had smaller seismic moments than half space ones this suggests that wave amplifications caused by large scale sedimentary basins exert significant effects on seismic moment determinations the joint inversion with 3d green s functions showed two large slip areas with a maximum slip of 6 m and an estimated total seismic moment of about 4 1 10 20 n m m w 7 7 strong motions were recovered very well even for the later phases by slips in shallow areas furthermore by comparing various source processes inverted by two fault models of 70 or 280 subfaults 3d or 1d green s functions and a curved or planar fault model we verified these assumptions based on the inversion results

three dimensional finite difference simulations of long period strong motions in the tokyo metropolitan area during the 1990 odawara earthquake mj 5 1 and the great 1923 kanto earthquake ms 8 2 in japan utilizing a crustal velocity model that includes the complexity of the irregular subsurface structure of the kanto basin we have performed three dimensional 3d finite difference fd simulations of near source long period strong ground motions in the tokyo metropolitan area for the 1990 odawara mj 5 1 and the 1923 kanto ms 8 2 earthquakes constraints on the development of the 3d velocity model come from available geological and geophysical data as well as our previous 1d waveform modeling results sato et al 1998a the simulation of the moderate sized odawara earthquake demonstrates that the 3d velocity model works quite well at reproducing the recorded long period t 3 33 sec strong motions including basin generated surface waves for a number of sites located throughout the kanto basin region using this validated 3d model along with the variable slip rupture model of wald and somerville 1995 we then simulate the long period t 4 sec ground motions in this region for the 1923 kanto earthquake the simulation results for the 1923 event show that the largest ground motions occur east of the epicenter along the central and southern part of the boso peninsula these large motions arise from strong rupture directivity effects and are comprised of relatively simple source controlled pulses with a dominant period of about 10 sec north of the epicentral region in the tokyo area 3d basin generated phases are quite significant and these phases produce large amplitude late arriving pulses in the ground motions at station hongo hng which is the only site having digitized and restored near fault strong motion records for this event our 3d simulations compare quite well with the ground motions of the restored imamura seismogram for the restored ewing record our 3d simulations reproduce the phase and amplitude of the initial pulses of motion however the dominant period of the large amplitude later phases is noticeably shorter in the simulations about 5 to 6 sec than in the observation 13 sec these results suggest that the restored imamura seismogram may be a better representation of the gross features of the actual motion than the restored ewing seismogram although the first clipped and restored part of the imamura seismogram may still underestimate the strength of the actual motion

inferring the subduction rate and period over the north atlantic abstract the annual rate at which mixed layer fluid is transferred into the permanent thermocline that is the annual subduction rate sann and the effective subduction period x1d4af eff is inferred from climatological data in the north atlantic from its kinematic definition sann is obtained by summing the vertical velocity at the base of the winter mixed layer with the lateral induction of fluid through the sloping base of the winter mixed layer geostrophic velocity fields computed from the levitus climatology assuming a level of no motion at 2 5 km are used the vertical velocity at the base of the mixed layer is deduced from observed surface ekman pumping velocities and linear vorticity balance a plausible pattern of sann is obtained with subduction rates over the subtropical gyre approaching 100 m yr twice the maximum rate of ekman pumping the subduction period x1d4af eff is found by viewing subduction as a transformation process converting mixed layer fluid into stratified thermocline fluid the effective

comparison between instrumental observational and high resolution proxy sedimentary records of late holocene climatic change a discussion of possibilities abstract variability of the north atlantic region is a key factor in the workings of global climate changes related to orbital factors and to the thermohaline circulation thc occur on timescales ranging from 1000 to 100 000 years whereas subdecadal decadal and multidecadal trends are associated with changes in atmospheric circulation sea surface temperature sst and salinity long term changes are known only from proxies whereas shorter periodicities are identified in instrumental and other observational data between lies a range of less well known centennial periodicities too long to be recorded observationally and too short for all but the highest resolution proxy records such as tree rings atmospheric 14c and varved lake sediments numerous investigations of such periodicities involve comparisons between the proxy and the observational record however results depend on the length of the datasets being analysed the relative strength of the periodicities present whether data are stationary or non stationary the degree to which they have been smoothed in order to remove particular fluctuations and the methods of analysis employed ideally comparisons should be between datasets of equal length and of similar properties but these criteria are not always easy to fulfill a search for periodicities in a range of well known multidecadal datasets reveals that whilst some frequencies previously identified in the central england temperature cet record and in the koch sea ice index are statistically significant those found by several authors in the index of the north atlantic oscillation nao are not as the index approximates to white noise instead decadal periodicity of the nao described by several authors appears to be result of smoothing of the raw data periodicities of 6 1 33 9 and 213 years identified in a proxy record from laminated sediments from loch ness scotland appear respectively to be related to a subdecadal variations in sst and salinity in the north atlantic ocean b multidecadal interactions between the nao and the north atlantic thc and c a well known centennial solar periodicity

western north atlantic evidence for millennial scale changes in ocean circulation and climate two late quaternary series of high resolution percent carbonate data from western north atlantic sediment drifts bermuda rise and bahama outer ridge show millennial scale oscillations superimposed on the familiar longer period oscillations of orbital origin the dominant high frequency oscillation in these records has a quasi period of about 4000 years these percent caco3 changes most likely result from the influence of climate change on the flux of terrigenous material from eastern canada the resuspension of continental margin sediment by deep eddy kinetic energy and carbonate dissolution sediment is transported to the bermuda rise by deep recirculating gyres and to the bahama outer ridge by the deep western boundary current system stable isotope results on foraminifera across several of these oscillations from interstadial climate conditions and from a glacial inception display variability similar to that of percent caco3 oxygen isotope ratios of planktonic foraminifera suggest large variations in near surface temperature and or salinity and carbon isotope ratios of benthic foraminifera indicate that there were significant oscillations in the flux of north atlantic deep water nadw these data support models which couple surface ocean conditions in the north atlantic production of nadw north atlantic heat flux and evidence for temperature oscillations in ice cores

the laminated sediments of loch ness scotland preliminary report on the construction of a chronology of sedimentation and its potential use in assessing holocene climatic variability abstract two sediment cores ca 6 m long have been recovered from the north basin of loch ness scotland each consists of ca 4 5 m of laminated gyttja terminating in a basal grey unlaminated clay a suite of three 14c ams dates have been obtained and place the base of the gyttja at ca 9500 yr b p investigations into the structure composition and formation of the laminae are in progress analysis by backscatter scanning electron microscopy bsem has demonstrated that they consist of couplets comprising dark clay rich sediments thought to be deposited from spring to autumn and pale silt rich layers believed to represent sedimentation through winter the laminae are thus thought to record incidence and intensity of streamflow into the loch over the past nine millennia and thus illustrate environmental change over the region for most of the holocene x ray densitometry has been utilised in order to count the laminations and test the hypothesis that they are varves it has however proved difficult to obtain a continuous sequence of countable laminations although it has been possible to construct a fragmented floating chronology which indicates that the hypothesis may be correct examination of lamination thickness reveals that although the average rate of sedimentation throughout the time periods studied seems to have remained fairly constant significant variations have occurred as loch ness is located on the northwest oceanic fringe of europe any climatic signal which the laminations contain will be closely related to even larger scale events over and within the north atlantic ocean which is a major controller of global climate preliminary statistical investigation of sequences of laminae is being carried out in order to search for periodicity of sedimentation which may then be related to appropriate climatic indices

earthquake source fault beneath tokyo devastating earthquakes occur on a megathrust fault that underlies the tokyo metropolitan region we identify this fault with use of deep seismic reflection profiling to be the upper surface of the philippine sea plate the depth to the top of this plate 4 to 26 kilometers is much shallower than previous estimates based on the distribution of seismicity this shallower plate geometry changes the location of maximum finite slip of the 1923 kanto earthquake and will affect estimations of strong ground motion for seismic hazards analysis within the tokyo region

cooling spirals and recirculation in the subtropical gyre abstract the influence of cooling in a western boundary current on the recirculation of parcels in the subtropical gyre and their eventual transfer into the subpolar gyre is investigated it is shown that heat loss to the atmosphere and the resulting vertical convection of dense water in the gulf stream of a general circulation primitive equation model forces a counterclockwise spiral of the velocity vector with depth a cooling spiral parcels that pass through this region of cooling are forced to cross under the upper level trajectories from south to north in opposite sense to the beta spiral experienced in the interior of the subtropical gyre this crossing of trajectories is an important consequence of the cooling in the western boundary current as it influences both scale and structure of the subtropical gyre recirculation a simple expression is derived that relates the spatial scale of the recirculation to the cooling rate in the western boundary current and the wind forcing in the subtropical gyre

a lagrangian method to isolate the impacts of mixed layer subduction on the meridional overturning circulation in a numerical model large differences in the atlantic meridional overturning circulation amoc exhibited between the available ocean models pose problems as to how they can be interpreted for climate policy a novel lagrangian methodology has been developed for use with ocean models that enables a decomposition of the amoc according to its source waters of subduction from the mixed layer of different geographical regions the method is described here and used to decompose the amoc of the centre national de recherches meteorologiques cnrm ocean model which is approximately 4 5 sv 1 sv 106 m3 s 1 too weak at 26 n compared to observations contributions from mixed layer subduction to the peak amoc at 26 n in the model are dominated by the labrador sea which contributes 7 51 sv but contributions from the nordic seas the irminger sea and the rockall basin are also important these waters mostly originate where deep mixed layers border the topographic slopes of the subpolar gyre and nordic seas the too weak model amoc can be explained by weak model representations of the overflow and of irminger sea subduction these are offset by the large labrador sea component which is likely to be too strong as a result of unrealistically distributed and too deep mixed layers near the shelf

what controls the mean east west sea surface temperature gradient in the equatorial pacific the role of cloud albedo abstractthe mean east west sea surface temperature gradient along the equator is a key feature of tropical climate tightly coupled to the atmospheric walker circulation and the oceanic east west thermocline tilt it effectively defines tropical climate conditions in the pacific its presence permits the el nino southern oscillation phenomenon what determines this temperature gradient within the fully coupled ocean atmosphere system is therefore a central question in climate dynamics critical for understanding past and future climates using a comprehensive coupled model community earth system model cesm the authors demonstrate how the meridional gradient in cloud albedo between the tropics and midlatitudes sets the mean east west sea surface temperature gradient in the equatorial pacific to change in the numerical experiments the authors change the optical properties of clouds by modifying the atmospheric water path but only in the shortwave radiation scheme of the model when is va

the seasonal cycle over the tropical pacific in coupled ocean atmosphere general circulation models abstract the seasonal cycle over the tropical pacific simulated by 11 coupled ocean atmosphere general circulation models gcms is examined each model consists of a high resolution ocean gcm of either the tropical pacific or near global means coupled to a moderate or high resolution atmospheric gcm without the use of flux correction the seasonal behavior of sea surface temperature sst and eastern pacific rainfall is presented for each model the results show that current state of the art coupled gcms share important successes and troublesome systematic errors all 11 models are able to simulate the mean zonal gradient in sst at the equator over the central pacific the simulated equatorial cold tongue generally tends to be too strong too narrow and extend too far west ssts are generally too warm in a broad region west of peru and in a band near 10 s this is accompanied in some models by a double intertropical convergence zone itcz straddling the equator over the eastern pacific and in others

a coupled theory of tropical climatology warm pool cold tongue and walker circulation abstract based on results from analytic and general circulation models the authors propose a theory for the coupled warm pool cold tongue and walker circulation system the intensity of the coupled system is determined by the coupling strength the local equilibrium time and latitudinal differential heating most importantly this intensity is strongly regulated in the coupled system with a saturation level that can be reached at a modest coupling strength the saturation west east sea surface temperature difference and the associated walker circulation corresponds to about one quarter of the latitudinal differential equilibrium temperature this regulation is caused primarily by the decoupling of the sst gradient from a strong ocean current the author s estimate suggests that the present pacific is near the saturation state furthermore the much weaker walker circulation system in the atlantic ocean is interpreted as being the result of the influence of the adjacent land which is able to extend

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

geophysical surveys of the sediments of loch ness scotland implications for the deglaciation of the moray firth ice stream british irish ice sheet we present results from three geophysical campaigns using high resolution sub bottom profiling to image sediments deposited in loch ness scotland sonar profiles show distinct packages of sediment providing insight into the loch s deglacial history a recessional moraine complex in the north of the loch indicates initial punctuated retreat subsequent retreat was rapid before stabilisation at foyers rise formed a large stillstand moraine here the calving margin produced significant volumes of laminated sediments in a proglacial fjord like environment subsequent to this ice retreated rapidly to the southern end of the loch where it again deposited a sequence of proglacial laminated sediments sediment sequences were then disturbed by the deposition of a thick gravel layer and a large turbidite deposit as a result of a jo kulhlaup from the spean roy ice dammed lake these sediments are overlain by a holocene sheet drape data indicate i a former tributary of the moray firth ice stream migrated back into loch ness as a major outlet glacier with a calving margin in a fjord like setting ii there was significant sediment supply to the terminus of this outlet glacier in loch ness and iii that jo kulhlaups are important for sediment supply into proglacial fjord lake environments and may compose 20 of proglacial sedimentary sequences

global climate variations connected with sea surface temperature anomalies in the eastern equatorial pacific ocean for the 1958 73 period abstract the sea surface temperature anomalies in the eastern equatorial pacific ocean are shown to demarcate a key region new 130 w for observed variations in the global general circulation various techniques are used to describe global conditions during warm and cold sea surface conditions in the key region based on a global 15 year set of surface and upper air analyses earlier work is confirmed that during warm episodes 1 the westerly jets in both hemispheres are strengthened and 2 some of the semi permanent circulation features such as the intertropical convergence zone the subtropical high over the western and central pacific and the aleutian low increase in strength and vice versa for cold episodes the time series of monthly mean atmospheric temperature averaged over the entire man of the northern hemisphere is found to be highly correlated with the sea surface temperature anomalies in the key region the highest correlation of r 0 65 is found when the atmosphere lags the ocean by 6 m

dynamics and heat balance of steady equatorial undercurrents abstract a two dimensional in a vertical and meridional plane model for steady equatorial undercurrents is described compared to the primitive equation model the zonal pressure gradient and associated zonal temperature gradients both vary vertically are prescribed in this model and all other terms involving zonal variations are ignored with zonal pressure gradients resembling actual ocean gradients model undercurrents agree well with observations as far as the main features are concerned in particular the model simulates a stronger undercurrent in the pacific than in the atlantic suggesting that a weaker zonal wind stress a shallower thermocline a more surface confined zonal pressure gradient and an associated larger magnitude of near surface zonal temperature gradient around 30 w in the atlantic than around 150 w in the pacific which is related to the longitudinal structure of the zonal wind stress and longitudinal basin extent are the cause of this difference an argument based on geost

effects of the mixed layer time variability on kinematic subduction rate diagnostics abstract an eddy resolving primitive equation general circulation model is used to estimate water mass subduction rates in the north atlantic ocean subtropical gyre the diagnostics are based on the instantaneous kinematic approach which allows the calculation of the annual rate of water mass subduction at a given density range following isopycnal outcrop positions over the annual cycle it is shown that water mass subduction is effected rapidly 1 2 months as the mixed layer depth decreases in spring consistent with stommel s hypothesis and occurs mostly over the area of deep late winter mixed layers 150 m across the central north atlantic in the density range 26 27 2 annual subduction rates o 100 200 m yr 1 are found south and east of the gulf stream extension in the density range of subtropical mode waters from roughly 26 2 to 26 6 in the northeastern part of the subtropical gyre annual subduction rates are somewhat larger o 250 m yr 1 from a density of about 26 9 east of the nort

understanding the structure of the subtropical thermocline closing a gyre with a western boundary current imposes a constraint on its vertical structure that requires there to be no net vertical flux of potential vorticity through any closed pressure contour in steady state this constraint resembles the traditional similarity balance for the internal thermocline with additional terms representing friction in the western boundary current and convection in the mixed layer the terms in the integral constraint are diagnosed in a planetary geostrophic ocean model and are used to understand the coexistence of ventilated and internal thermoclines within the subtropical gyre

constraints on paleoproterozoic atmospheric oxygen levels the oxygenation of earth s surface environment dramatically altered key biological and geochemical cycles and ultimately ushered in the rise of an ecologically diverse biosphere however atmospheric oxygen partial pressures p o 2 estimates for large swaths of the precambrian remain intensely debated here we evaluate and explore the use of carbonate cerium ce anomalies ce ce as a quantitative atmospheric p o 2 proxy and provide estimates of proterozoic p o 2 using marine carbonates from a unique precambrian carbonate succession the paleoproterozoic pethei group in contrast to most previous work we measure ce ce on marine carbonate precipitates that formed in situ across a depth gradient building on previous detailed sedimentology and stratigraphy to constrain the paleo depth of each sample measuring ce ce across a full platform to basin depth gradient we found only minor depleted ce anomalies restricted to the platform and upper slope facies we combine these results with a ce oxidation model to provide a quantitative constraint on atmospheric p o 2 1 87 billion years ago ga our results suggest paleoproterozoic atmospheric oxygen concentrations were low near 0 1 of the present atmospheric level this work provides another crucial line of empirical evidence that atmospheric oxygen levels returned to low concentrations following the lomagundi event and remained low enough for large portions of the proterozoic to have impacted the ecology of the earliest complex organisms

the freshening of surface waters in high latitudes effects on the thermohaline and wind driven circulations abstract the impacts of a freshening of surface waters in high latitudes on the deep slow thermohaline circulation have received enormous attention especially the possibility of a shutdown in the meridional overturning that involves sinking of surface waters in the northern atlantic ocean a recent study by fedorov et al has drawn attention to the effects of a freshening on the other main component of the oceanic circulation the swift shallow wind driven circulation that varies on decadal time scales and is closely associated with the ventilated thermocline that circulation too involves meridional overturning but its variations and critical transitions affect mainly the tropics a surface freshening in mid to high latitudes can deepen the equatorial thermocline to such a degree that temperatures along the equator become as warm in the eastern part of the basin as they are in the west the tropical zonal sea surface temperature gradient virtually disappears and permanently warm conditions prevail

processes controlling the mean tropical pacific precipitation pattern part i the andes and the eastern pacific itcz abstract the question of why the intertropical convergence zone itcz is generally north of the equator in the tropical pacific is addressed experiments with an atmospheric general circulation model coupled to idealized representations of the ocean show that the presence of the andes is enough to lower sea surface temperature sst off the west coast of south america through evaporation thus promoting a north south asymmetry with the itcz north of the equator which is amplified by interactions between the ocean and the atmosphere the evaporative cooling results mainly from the subsidence of low specific humidity air which is due in turn to the mechanical effect of the andes on the zonal mean flow the positive feedback from low level clouds on sst is an important factor for the efficiency of the mechanism described west of 120 w the presence of the rockies and himalayas produces a comparable forcing to that of the andes but this is not enough to reverse or neutralize the north south asymmetry se

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

ventilation of the north atlantic and north pacific subduction versus obduction abstract ventilation in the north atlantic and north pacific is examined by analyzing the levitus climatological data and the hellerman and rosenstein wind stress data ventilation between the permanent pycnocline and the overlying seasonal pycnocline and mixed layer consists of two physical processes subduction and obduction subduction takes place mainly in the subtropical basin where surface water is irreversibly transferred into the permanent pycnocline below obduction takes place in the subpolar basin where water from the permanent pycnocline is irreversibly transferred into the mixed layer above veatilation in the north atlantic and north pacific can be clarified into four physically different regions the subductive region the obductive region the ambiductive region where both subduction and obduction take place and the insulated region where neither subduction nor obduction occurs although the total subduction rates in these two oceans are comparable the total obduction rates are considera

kinematics of the pacific equatorial undercurrent an eulerian and lagrangian approach from gcm results abstract three dimensional monthly velocity fields from an ocean general circulation model are used to study the annual mean mass balance of the pacific equatorial undercurrent euc eulerian diagnostics are used to evaluate the various meridional vertical and zonal mass fluxes related to the euc there are several distinct regimes along the equator showing clear asymmetries between the western and eastern parts of the basin and between the northern and southern edges of the euc meridional fluxes are decomposed into pure ekman divergence and geostrophic convergence and it is shown that the asymmetries are mainly related to the spatial structure of the ekman divergence and thus to that of the trade winds lagrangian calculations are used to evaluate accurately the mass transfers between various sections of the euc and between the euc domain and the tropics the authors show that geostrophic convergence only ventilates the upper layers of the euc and that the euc really is a tongue of water flowing

the chronology of the last deglaciation implications to the cause of the younger dryas event it has long been recognized that the transition from the last glacial to the present interglacial was punctuated by a brief and intense return to cold conditions this extraordinary event referred to by european palynologists as the younger dryas was centered in the northern atlantic basin evidence is accumulating that it may have been initiated and terminated by changes in the mode of operation of the northern atlantic ocean further it appears that these mode changes may have been triggered by diversions of glacial meltwater between the mississippi river and the st lawrence river drainage systems we report here accelerator mass spectrometry ams radiocarbon results on two strategically located deep sea cores one provides a chronology for surface water temperatures in the northern atlantic and the other for the meltwater discharge from the mississippi river our objective in obtaining these results was to strengthen our ability to correlate the air temperature history for the northern atlantic basin with the meltwater history for the laurentian ice sheet

ocean atmosphere interaction and the tropical climatology part ii why the pacific cold tongue is in the east abstract the influence of coupled process on the climatology of the tropical pacific is studied in a model for the interaction of equatorial sst the associated component of the walker circulation and upper ocean dynamics in this part the authors show how different physical mechanisms affect the spatial pattern of the pacific warm pool and cold tongue in this coupled climatology when model parameters give a suitable balance between effects of upwelling and thermocline depth on sea surface temperature and for suitable atmospheric parameters a good prototype for the observed cold tongue configuration is produced this is largely determined by coupled ocean atmosphere processes within the basin presence of an easterly wind s component produced by factors external to the pacific basin can be important in setting up a cooling tendency but this is magnified and modified by a chain of nonlinear feedbacks between trade winds and ocean dynamics affecting the sst gradient within the basin these feedbacks d

a comprehensive mass flux scheme for cumulus parameterization in large scale models abstract observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large scale models but this approach through the introduction of a spectral cloud ensemble leads normally to rather complex schemes in this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions this is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection gate marshall islands tradewind cumuli atex bomex and extratropical organized convection sesame 79 and then in a nwp model the scheme considers a population of clouds where the cloud ensemble is described by a one dimensional bulk model as earlier applied by yanai et al in a diagnostic study of tropical convection cumulus scale downdrafts are included various types of convection are represented i e penetrative convection in c

a theory for the surface atlantic response to thermohaline variability abstract the response of the upper warm limb of the thermohaline circulation in the north atlantic to a rapid change in deep water formation at high latitudes is investigated using a reduced gravity ocean model changes in deep water formation rate initiate kelvin waves that propagate along the western boundary to the equator on a timescale of months the response in the north atlantic is therefore rapid the southern hemisphere response is much slower limited by a mechanism here termed the ldquo uatorial buffer since to leading order the flow is in geostrophic balance the pressure anomaly decreases in magnitude as the kelvin wave moves equatorward where the coriolis parameter is lower together with the lack of sustained pressure gradients along the eastern boundary this limits the size of the pressure field response in the southern hemisphere interior adjustment is by the westward propagation of rossby waves but only a small fraction of the change in thermohaline circulation strength is commun

rupture history of the 1984 morgan hill california earthquake from the inversion of strong motion records near source strong motion velocity records and teleseismic short period p waveforms are modeled to obtain the spatial and temporal distribution of slip for the 1984 morgan hill earthquake both forward modeling and constrained least squares inversion techniques are used to interpret the strong motion velocity waveforms in the frequency range of approximately 0 2 to 2 0 hz these data support a nearly unilateral rupture to the southeast with a rupture propagation velocity of nine tenths of the local s wave velocity the majority of the slip occurs over a fault length of 25 km and to a first approximation can be interpreted as two main source regions each with an extent of about 5 km with their centers separated by about 12 km however each of the sources has detailed structure of its own and a simple two point source model is not an accurate representation of the morgan hill earthquake the second source occurs about 4 5 sec after the first and is approximately 3 times larger the maximum dislocation on the fault plane is about 1 m the total moment of the earthquake is estimated to be 2 1 10 25 dyne cm the morgan hill earthquake offers convincing evidence for very inhomogeneous slip and stress distributions on shallow strike slip faults

variable slip rupture model of the great 1923 kanto japan earthquake geodetic and body waveform analysis abstract the available geodetic and teleseismic data sets for the 1923 kanto earthquake m s 8 1 have been combined into a joint inversion for both temporal and spatial slip variations we assumed an initial faulting model to be consistent with the geometry determined by kanamori 1971 on the basis of first motion data aftershock area and the amplitude of surface waves at teleseismic distances and also to enclose the slipped area estimated by matsu9ura et al 1980 from the geodetic data employed here we then inverted for a heterogeneous distribution of slip of the fault plane the leveling routes and triangulation stations used consisting of 225 bench marks and 31 triangulation points are from matsu9ura et al 1980 we chose to first determine the overall static slip distribution by inverting the geodetic data alone we then proceeded to gradually increase the importance of the teleseismic data always requiring a good fit to the geodetic leveling and horizontal displacements in this way we could provide a constraint on the overall static slip characteristics from the geodetic data and provide stability for the teleseismic inversion yet determine the degree of slip heterogeneity and time history most suitable for matching the waveform data and for simulating strong ground motions our analysis yields a seismic moment of 7 to 8 10 27 dyne cm m w 7 8 to 7 9 with a maximum slip of approximately 8 m the most concentrated slip is in the shallow central and western portion of the fault the location of the concentrated slip on the fault plane has important consequences for the amplitude duration and frequency content of the resulting ground motions as documented by takeo and kanamori 1993

the eastern subtropical pacific origin of the equatorial cold bias in climate models a lagrangian perspective abstractglobal climate models frequently exhibit cold biases in tropical sea surface temperature sst in the central and eastern equatorial pacific here lagrangian particle back trajectories are used to investigate the source regions of the water that upwells along the equator in the ipsl climate model to test and confirm the hypothesis that the sst biases are caused by remote biases advected in from the extratropics and to identify the dominant source regions water in the model is found to be sourced primarily from localized regions along the western and eastern flanks of the subtropical gyres however while the model sst bias is especially large in the northwestern subtropical pacific about 5 c it is found that the eastern subtropics contribute to the equatorial bias the most this is due to two distinct subsurface pathways connecting these regions to the equator the first pathway originating in the northwestern subtropical pacific has relatively long advection time scales close to or exceed

solar variance recorded in lacustrine deposits from the devonian and proterozoic of scotland abstract continental lacustrine laminites deposited in low latitudes have been examined from the devonian and torridonian mesoproterozoic strata of northern scotland to investigate the consistency of sunspot periodicity through geological time the thicknesses of 2448 annual laminae were measured from the middle devonian c 388 ma achanarras limestone member lower caithness flagstone group and of 2821 laminae from the mesoproterozoic 1 2 ga poll a9mhuilt member of the stoer group time series analysis resolved periodicities of 13 8 and 13 9 years in the complete devonian and mesoproterozoic datasets respectively when sedimentological variance was considered and the data were examined as evolutive spectra those sections consisting of the most robust data consistently yielded periodicities between 8 6 and 13 7 years for the devonian section and 9 2 and 10 6 years for the mesoproterozoic section these correspond well to schwabe cycles evidence for the presence of the longer hale cycles 20 years was also recognized in the devonian time series the sunspot periodicities identified within the devonian and mesoproterozoic show little variance from published examples from the quaternary and eocene and therefore provide evidence for the consistency of solar processes and solar atmospheric interactions for the past 1 2 ga

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr