temperature and salinity staircases in the northwestern weddell sea abstract temperature and salinity data obtained from the northwestern weddell sea during march 1986 reveal numerous thermohaline staircases in the thermocline separating warm deep water from the overlying colder lower salinity winter water staircases in the upper steeper portion of the thermocline were characterized by layers having vertical extents of 1 5 m layer thicknesses in the deeper weaker portion of the thermocline were far greater sometimes exceeding 100 m the former staircases are referred to as type a and the latter as type b vertical gradients in temperature and salinity decreased abruptly across the boundary between type a and type b staircase regions mean density ratios r were 1 52 and 1 36 over the depth intervals containing type a and type b staircases respectively type a staircases were present at all sites sampled whereas type b staircases were present over approximately the central 50 of the area sampled laboratory derived results show that the observed time and vertical

evolution of the southern ocean winter mixed layer and sea ice open ocean deepwater formation and ventilation an analytical model has been developed to describe the nature of the winter ocean sea ice interaction in the southern ocean to determine the principal processes responsible for maintaining stability in this marginally stable region and to predict the response to changes in the external forcing and initial conditions the model accurately describes the sparse winter observations and the general temporal evolution of the ice mixed layer depth and salinity for the period following the elimination of the seasonal pycnocline by rapid fall ice growth a scale analysis and sensitivity study reveal the system parameter dependence this indicates that the magnitude of entrainment is proportional to fst h0 s where fs is the external salt flux h0 the depth of the winter mixed layer and s the salinity gradient through the pycnocline thermodynamic ice growth reflects predominantly the competition between the oceanic diffusive heat gain across the base of the mixed layer and the loss to the atmosphere through the ice and leads a strong thermal gradient across the pycnocline leads to a significant diffusive flux which balances most of the heat lost to the atmosphere this limits the amount of ice growth possible and plays the principal role in maintaining the system stability since the ice growth is required for destabilization through haline rejection during the growth process the system is also sensitive to the large ratio of heat to salt in the pycnocline this introduces a negative feedback where increasing ice growth induces entrainment by the associated salt flux which in turn drives an entrainment heat flux which compensates for heat lost to the atmosphere this moderates the ability to grow ice and drive further entrainment the absolute strength of the salinity gradient on the other hand dictates the effectiveness which a same magnitude external salt flux will have in driving entrainment the effectiveness with which changes in these parameters as well as several other external parameters can influence the southern ocean stability is explicitly evaluated through the sensitivity study and analysis

polar water column stability abstract an expression is derived for the surface salt input needed to induce complete convective overturning of a polar water column consisting of 1 a layer of sea ice 2 a freezing temperature mixed layer 3 a pycnocline with linearly varying temperature and salinity and 4 deep water with fixed temperature and salinity this quantity has been termed the bulk stability by martinson the bulk stability is found to consist of three components the first two make up martinson s salt deficit and are the salt input needed to increase the density of the mixed layer and the pycnocline layer to that of the deep water the mixed layer stability and pycnocline layer stability respectively the third component is martinson s thermal barrier the potential for pycnocline heat to melt ice reducing the surface salinity it is found that when the pycnocline density gradient due to temperature offsets more than one half of that due to salinity the pycnocline layer stability is negative consequently it is poss

on the linkage between antarctic surface water stratification and global deep water temperature the suggestion is advanced that the remarkably low static stability of antarctic surface waters may arise from a feedback loop involving global deep water temperatures if deep water temperatures are too warm this promotes antarctic convection thereby strengthening the inflow of antarctic bottom water into the ocean interior and cooling the deep ocean if deep waters are too cold this promotes antarctic stratification allowing the deep ocean to warm because of the input of north atlantic deep water a steady state deep water temperature is achieved such that the antarctic surface can barely undergo convection a two box model is used to illustrate this feedback loop in its simplest expression and to develop basic concepts such as the bounds on the operation of this loop the model illustrates the possible dominating influence of antarctic upwelling rate and antarctic freshwater balance on global deep water temperatures

evidence for widespread nonlinear strong ground motion in the mw 6 9 loma prieta earthquake we exploit 55 repeating microearthquake sequences on the san andreas fault just south of the rupture zone of the 1989 m w 6 9 loma prieta earthquake to search for time dependent properties of the earth s crust using moving window waveform cross correlation we identify clear and systematic delays as large as 20 msec for the direct s wave and exceeding 50 msec in the early s wave coda following the loma prieta mainshock others have also identified phase delays velocity reductions associated with damaging earthquakes and they have suggested a myriad of possible causal mechanisms here we present new evidence for a mechanism to produce velocity reductions correlated in time and space with an earthquake a strong correlation between the spatial patterns of s delays and the intensity of strong ground motion in the loma prieta earthquake suggests that physical damage the formation or growth of cracks during strong ground motion to the earth s shallow crust is responsible for the observed velocity reductions the strong spatial variability in s delays over short distances and the strong correlation of the magnitude of delays with surface geology indicate that the phase delays accumulate primarily near the receiver the effect is stronger at stations on young soft rocks than at stations on old hard rock disproportionately larger s coda delays than p coda delays suggest that the cracks formed by the strong shaking are fluid filled in the 10 years after loma prieta the initial increase in travel times reduces logarithmically with respect to time often back to the premainshock levels we attribute this behavior to the same slow dynamic healing observed in laboratory studies of the recovery of materials from transient nonlinear strain manuscript received 14 january 2004

sensitivity of simulated salinities in a three dimensional ocean general circulation model to vertical mixing of destabilizing surface fluxes we present simulations performed with a three dimensional global ocean general circulation model which show that simulated salinities and amounts of convective mixing are very sensitive to vertical mixing of surface buoyancy fluxes if as usual surface buoyancy fluxes are placed entirely in the topmost model level our model produces excessive convective mixing in the southern ocean this results in poor stimulated salinity in the southern ocean in this simulation we assume as usual that both surface buoyancy forcing and vertical mixing are homogeneous within each grid cell if on the other hand destabilizing surface fluxes are instantaneously mixed into the subsurface ocean the model produces much less convective mixing and much more realistic salinities the vertical mixing of surface buoyancy fluxes performed in this simulation is equivalent to assuming that those fluxes affect only a small fraction of each grid cell and cause vertical mixing only in that limited area our interpretation of these results is that the usual assumption that both surface buoyancy forcing and vertical mixing are uniform within each grid cell has a detrimental effect on model results these results could be significantly improved by good parametrizations which treat the horizontal inhomogeneity of surface buoyancy forcing and of vertical mixing

on the abruptness of bolling allerod warming abstractprevious observations and simulations suggest that an approximate 3 5 c warming occurred at intermediate depths in the north atlantic over several millennia during heinrich stadial 1 hs1 which induces warm salty water wsw lying beneath surface cold freshwater this arrangement eventually generates ocean convective available potential energy ocape the maximum potential energy releasable by adiabatic vertical parcel rearrangements in an ocean column the authors find that basin scale ocape starts to appear in the north atlantic 67 5 73 5 n and builds up over decades at the end of hs1 with a magnitude of about 0 05 j kg 1 ocape provides a key kinetic energy source for thermobaric cabbeling convection tcc using a high resolution tcc resolved regional model it is found that this decadal scale accumulation of ocape ultimately overshoots its intrinsic threshold and is released abruptly 1 month into kinetic energy of tcc with further intensification from cabbeling tcc has convective

impact of atmospheric forcing on antarctic continental shelf water masses the antarctic continental shelf seas feature a bimodal distribution of water mass temperature with the amundsen and bellingshausen seas flooded by circumpolar deep water that is several degrees celsius warmer than the cold shelf waters prevalent in the weddell and ross seas this bimodal distribution could be caused by differences in atmospheric forcing ocean dynamics ocean and ice feedbacks or some combination of these factors in this study a highly simplified coupled sea ice mixed layer model is developed to investigate the physical processes controlling this situation under regional atmospheric forcings and parameter choices the 10 yr simulations demonstrate a complete destratification of the weddell sea water column in winter forming cold relatively saline shelf waters while the amundsen sea winter mixed layer remains shallower allowing a layer of deep warm water to persist applying the weddell atmospheric forcing to the amundsen sea model destratifies the water column after two years and applying the amundsen forcing to the weddell sea model results in a shallower steady state winter mixed layer that no longer destratifies the water column this suggests that the regional difference in atmospheric forcings alone is sufficient to account for the bimodal distribution in antarctic shelf sea temperatures the model prediction of mixed layer depth is most sensitive to the air temperature forcing but a switch in all forcings is required to prevent destratification of the weddell sea water column

evidence for stability in coda q associated with the egion central greece earthquake of 15 june 1995 one hundred seventy two seismograms recorded at one seismological station located close to the source region of the egion ms 6 2 15 june 1995 earthquake were used to measure values of q from the decay of the earthquake coda the collected data were compared between events that occurred before and after the main event the analysis showed no significant temporal variation in the value of coda q for the region

temporal change in coda q before the tangshan earthquake of 1976 and the haicheng earthquake of 1975 a new earthquake precursor called coda q is demonstrated for the tangshan earthquake of 1976 and for the haicheng earthquake of 1975 the precursor is based on the measurement of coda decay rate for small local earthquakes in the general area that is preparing for a major earthquake during the 3 year period preceding the tangshan earthquake the coda q was about 3 times lower than it was before or after this period a comparable change also occured at the time of the haicheng earthquake the observed change cannot be due to the change in the source parameters such as the focal depth or the source spectrum the coda q precursor appears to detect the same physical process detected by other precursors such as b value quiescence radon water quality vp vs and animal behavior but has advantages over them in its clearer physical mechanism easier sampling and better defined anomalous region

transient sea ice polynya forced by oceanic flow variability abstract in the weddell sea during the winters of 1974 1976 a significant opening in the sea ice cover occurred in the vicinity of a large bathymetric feature the maud rise seamount the event is commonly referred to as the weddell polynya aside from such a large scale relatively persistent polynya in the weddell sea transient small scale polynya can also appear in the sea ice cover at various times throughout the winter and at various locations with respect to the maud rise the underlying causes for the occurrence of such transient polynya have not been unambiguously identified we hypothesize that variations in the mean ocean currents are one major contributor to such variability in the sea ice cover analysis of the sea ice equations with certain idealized patterns of ocean currents serving as forcing is shown to lead to ekman transports of sea ice favorable to the initiation of transient polynya aside from the actual spatial pattern of the idealized ocean currents many other factors need also be taken into account when looking at such transient polynya two other such factors discussed are variations in the sea ice thickness field and the treatment of the sea ice rheology simulations of a sea ice model coupled to a dynamical ocean model show that the interaction of dynamical oceanic currents with large scale topographic features such as the maud rise does lead to the formation of transient polynya again through ekman transport effects this occurs because the seamount has a dynamic impact on the three dimensional oceanic flow field all the way up through the water column and hence on the near surface ocean currents that are in physical contact with the sea ice further simulations of a sea ice model coupled to a dynamic ocean model and forced with atmospheric buoyancy fluxes show that transient polynya can be enhanced when atmospheric cooling provides a positive feedback mechanism allowing preferential open ocean convection to occur the convection which takes hold at sites where transient polynya have been initiated by sea ice ocean stress interaction has an enhancing effect arising from the convective access to warmer deeper waters to investigate all of these effects in a hierarchical manner we use a primitive equation coupled sea ice ocean numerical model configured in a periodic channel domain with specified atmospheric conditions we show that oceanic flow variability can account for temporal variability in small scale transient polynya and thus point to a plausible mechanism for the initiation of large scale sustained polynya such as the weddell polynya event of the mid 1970s

antarctic sea ice simulations with a coupled ocean sea ice model on a telescoped grid results from a century long integration of a coupled ocean sea ice model covering the southern hemisphere are discussed the model has a refined grid in a 60 sector south of australia and is driven by climatological atmospheric variables the ocean sea ice system evolves into a thermal mode behaviour i e strong vertical mixing produces a well mixed weakly stratified upper ocean in the sea ice zone resulting in a thin ice cover with multiple polynyas in southern winter the time evolution of total ice area however is close to estimates from satellite observations the relative extrema of total sea ice area are somewhat underestimated

temporal variation of coda q during hualien earthquake of 1986 in eastern taiwan the may 20 1986 hualien earthquake sequence occurred on the northeastern coast of taiwan them 6 1 gs mb mainshock was followed by a large number of closely clustered aftershocks with the largest being anm 5 5 event one seismic station twd of the taiwan telemetered seismographic network is located in the surface projection of the source region and provides excellent recordings of the entire earthquake sequence these recordings plus events occurring in the same source area preceding the mainshock offer a unique opportunity to study the spatial and temporal variations of codaq in a region of active subduction a simple technique is devised that uses the envelope of the coda waveform to enable a quick determination of the codaq from drum records for recordings with a peak power at about 8 hz the following findings have been obtained 1 the ambient codaq near an active subduction region was as low as 145 2 there was no significant decrease in codaq within the period beginning one year and four months prior to the mainshock 3 there was a significant drop of codaq immediately after the mainshock this drop lasted approximately two days before returning to the ambient level 4 codaq values varied with focal depth

warm weddell deep water west of maud rise a pool of relatively warm 1 0 c weddell deep water wdw immediately west of maud rise appears to be a quasi stationary feature the warm pool is derived from the flow of warm wdw around the flanks of maud rise an austral spring 1989 expedition of the r v akademik fedorov obtained detailed measurements of the warm pool it displays the general regional relationship of temperature maximum t max warmth to shallowness of the pycnocline as well as mixed layer oxygen concentration well below full saturation depression of oxygen values is a product of injection of wdw into the mixed layer during the ice covered winter period associated with this transfer are high vertical fluxes of heat and salt which limit the thickness of the sea ice cover in the winter the atmosphere is sufficiently cold to remove the wdw heat without massive sea ice melting though the regional ice thickness is restricted in the spring the atmospheric conditions cannot remove the ocean heat and ice melting ensues before the atmospheric heat budget alone can account for the ice melt this is clearly seen in the warm pool as very low mixed layer oxygen which is a reflection of high wdw entrainment and vertical heat flux and is normally associated with high mixed layer salinity here it is coupled instead with reduced salinity a result of approximately 0 5 m of ice melt the fedorov data confirm the role of oceanic heat flux in early removal of southern ocean sea ice at the end of winter in that the region of highest wdw entertainment is associated with greater amounts of melt water

horizontal mixing in lakes horizontal mixing in the upper hypolimnion of lakes far from the boundaries was studied in lake basins with surface areas between 5 and 220 km 2 by observing the growth of the concentration distribution of the fluorescent dye sodium fluorescein uranin in each of the eight experiments between 0 2 and 2 kg of uranin was instantaneously released into the lake in the appropriate depth between 15 and 25 m in such a way to keep the initial cloud size as small as possible the horizontal extension of the cloud was repeatedly determined by integration of numerous vertical profiles these surveys served to test theoretical models for horizontal mixing the temporal development of the size and of the variances along the principal axes of the tracer concentration distribution was the main property considered here the experiments cover a range of cloud sizes between 3 x 10 2 and 3 x 10 5 m 2 none of them support the hypothesis that cloud size grows with elapsed time raised to the power of 3 as predicted by the inertial subrange turbulence model first applied to dispersion by batchelor 1950 the shear diffusion model of carter and okubo 1965 was found to provide a good description of the development of cloud size with time this model also accounts for the fact that the tracer distributions were not radially symmetric effective horizontal diffusivities lie between 0 02 and 0 3 m 2 s 1 reevaluation of published data from experiments in lake ontario e g murthy 1976 and in the ocean e g okubo 1971 supports both the applicability of the shear diffusion model and the doubts raised against the appropriateness of the inertial subrange model for scales up to 1000 m

sea ice switch mechanism and glacial interglacial co2 variations 1 a physical mechanism is proposed for the glacial interglacial variations in the rate of vertical mixing and in sea ice cover in the southern ocean such variations were postulated without an explanation by toggweiler 1999 and stephens and keeling 2000 who used them to explain the glacial interglacial co2 variations in the physical mechanism explored here initially given by gildor and tziperman 2001b changes in the stratification of the southern ocean due to the cooling of north atlantic deep water nadw during glacial maxima reduce the rate of vertical mixing of the surface water with the deep water the changed temperature of the nadw arriving to the southern ocean and the reduced vertical mixing there also increase the southern ocean sea ice cover during glacial maxima these vertical mixing and sea ice cover changes are shown to be a natural result of the sea ice switch mechanism of the glacial cycles a box model of the climate system is used to demonstrate the above physical mechanism and its effect on the atmospheric co2 because of the uncertainties in the exact dependence of the vertical mixing on vertical stratification it is impossible to quantify the exact separate contribution of reduced vertical mixing and larger sea ice cover to the glacial co2 variations the co2 variations are not essential to the existence of the glacial cycles in the sea ice switch mechanism yet they are shown to amplify the glacial interglacial variability consistent with the view of the role of co2 deduced from proxy observations

on the parameterisation of oceanic sensible heat loss to the atmosphere and to ice in an ice covered mixed layer in winter abstract in high latitude oceans with seasonal ice cover the ice and the low salinity mixed layer form an interacting barrier for the heat flux from the ocean to the atmosphere the presence of a less dense surface layer allows ice to form and the ice cover reduces the heat loss to the atmosphere the ice formation weakens the stability at the base of the mixed layer leading to stronger entrainment and larger heat flux from below this heat transport retards and perhaps stops the growth of the ice cover as much heat is then entrained from below as is lost to the atmosphere this heat loss further reduces the stability and unless a net ice melt occurs the mixed layer convects two possibilities exist 1 a net ice melt sufficient to retain the stability will always occur and convection will not take place until all ice is removed the deep convection will then be thermal deepening the mixed layer 2 the ice remains until the stability at the base of the mixed layer disappears the mixed layer then convects through haline convection into the deep ocean warm water rises towards the surface and the ice starts to melt and a new mixed layer is reformed the present work discusses the interactions between ice cover and entrainment during winter when heat loss to the atmosphere is present one crucial hypothesis is introduced when ice is present and the ocean loses sensible heat to the atmosphere and to ice melt the buoyancy input at the sea surface due to ice melt is at a minimum using a one dimensional energy balance model applied to the artificial situation where ice melts directly on warmer water it is found that this corresponds to a constant fraction of the heat loss going to ice melt it is postulated that this partitioning holds for the ice cover and the mixed layer in the high latitude ocean when a constant fraction of heat goes to ice melt at least one deep convection event occurs before the ice cover can be removed by heat entrained from below after one or several convection events the ice normally disappears and a deep reaching thermal convection is established conditions appropriate for the weddell sea and the greenland sea are examined and compared with field observations with realistic initial conditions no convection occurs in the warm regime of the weddell sea a balance between entrained heat and atmospheric heat loss is established and the ice cover remains throughout the winter at maud rise convection may occur but late in winter and normally no polynya can form before the summer ice melt in the central greenland sea the mixed layer generally convects early in winter and the ice is removed by melting from below as early as february or march this is in agreement with existing observations

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

the isotopic composition of diatom bound nitrogen in southern ocean sediments treatment of diatom microfossils from southern ocean sediments with hot perchloric acid leaves a diatom bound n fraction which is 0 4 lower in 15n than the bulk sediment typically 3 lower in recent antarctic diatom ooze results from southern ocean surface sediments indicate that early diagenetic changes in bulk sediment n content and 15n are not reflected in diatom bound n suggesting that diatom bound n is physically protected from early diagenesis by the microfossil matrix a meridional transect of multicores from the indian sector of the southern ocean shows a northward increase in the 15n of diatom bound n suggesting that diatom bound 15n like bulk sedimentary 15n varies with nitrate utilization in the overlying surface waters the 15n of diatom bound n is 3 4 higher in glacial age antarctic sediments than in holocene sediments supporting the hypothesis previously based on bulk sediment 15n that nitrate utilization in the surface antarctic was higher during the last ice age while there are important uncertainties the inferred range of utilization changes could potentially explain the entire 80 ppm amplitude of observed glacial interglacial variations in atmospheric co2

a mechanism for the formation of the weddell polynya in 1974 abstract the formation of the weddell polynya is investigated with a one dimensional convective mixed layer model using in situ data from late summer 1974 as initial conditions we propose that a high salinity mixed layer in summer resulted in the formation of the weddell polynya in 1974 the model results show that the high salinity allows deep convection driven by surface cooling alone and the resulting upward transfer of heat and salt prohibits sea ice formation throughout the winter subject to the freshwater input less than 0 4 m yr 1 because of the uncertainty of amount of the actual freshwater input in 1974 whether sea ice formed is ambiguous however the occurrence of the deep convection during the 1974 polynya formation is confirmed by summer data from 1975 showing the modification of deep water to be colder fresher and richer in oxygen than in 1974 the upward heat flux through the deep convection resulted in the formation of the weddell polynya in 1974

hypocenter migration as an explanation for temporal changes in coda q in the 1993 earthquake swarm near the norris lake community georgia qc coda q and b value exhibit systematic temporal variations on a scale of months and hours the long term monthly variations correlate with the swarm s growth and decay examination of the hypocenters demonstrates that q is a strong function of hypocenter and the temporal variations of q reflect a systematic migration of hypocenters the b value appears to vary in this swarm because the method of magnitude determination is dependent on qc throughout the duration of the swarm the active areas migrated from a high qc area eastward to a low qc area variations of qc over periods of hours were explained by a shifting ofhypocenters between high and low qc areas significant changes in qc occur for hypocenters that are separated by distances 10 km the nonuniform fractal distribution of relative scattering coefficients plays a major role in determining the spatial dependence of q by using forward coda modeling on the distribution of relative scattering coefficients derived for this earthquake swarm we can reproduce seismic coda with the same spatial dependence on q as found in the earthquakes throughout the swarm the relative locations of earthquakes associated with different q values and our ability to model different q values from a known distribution of relative scattering coefficients confirm that the migration of hypocenters and not a temporal change in attenuation properties determines the temporal variation of qc observed during the norris lake community earthquake swarm

weddell gyre temperature maximum stratum at depths below 200 m relatively warm salty water spreads poleward from the antarctic circumpolar current acc this deep water mass is cooled through interaction with the atmosphere feeding the formation of dense bottom water which in turn influences much of the world ocean significant poleward spreading is accomplished within the weddell gyre of the atlantic sector of the southern ocean an extensive data set obtained in the 1980s within the weddell gyre provides a detailed view of the subsurface temperature maximum t max stratum defining the top of the deep water mass the seasonal sea ice growth and retreat pattern reflects the t max distribution there is evidence for subdivision of the t max into two cold centers which may reflect secondary circulation features within the gyre the primary inflow of warm deep water is derived from the southern edge of the acc near 20 30 e the inflow spreads to the west along 65 s and is divided into smaller pools of relatively warm water west of maud rise with a cold feature directly over the rise in a manner shown by models of topographically generated eddies variability of the t max stratum in the vicinity of maud rise arising from changes in the vigor of the large scale circulation may influence the regional vertical heat fluxes and be related to interannual variability of the sea ice cover and to the recurring polynya feature typical of the region

a possible link between the weddell polynya and the southern annular mode abstract shortly after the advent of the first imaging passive microwave sensor on board a research satellite an anomalous climate feature was observed within the weddell sea during the years 1974 1976 a 250 103 km2 area within the seasonal sea ice cover was virtually free of winter sea ice this feature the weddell polynya was created as sea ice formation was inhibited by ocean convection that injected relatively warm deep water into the surface layer though smaller less persistent polynyas associated with topographically induced upwelling at maud rise frequently form in the area there has not been a reoccurrence of the weddell polynya since 1976 archived observations of the surface layer salinity within the weddell gyre suggest that the weddell polynya may have been induced by a prolonged period of negative southern annular mode sam during negative sam the weddell sea experiences colder and drier atmospheric conditions making for a saltier surface layer with reduced pycnocline stability t

a model study of upper ocean sea ice interactions abstract a thermodynamic sea ice model including leads has been coupled to a one dimensional oceanic mixed layer model in order to investigate the upper ocean sea ice interactions the oceanic heat flux at the base of the ice layer fb is predicted not imposed assuming a thermodynamic equilibrium between the bottom of the ice and the water just below for testing of the model the annual cycle of the arctic sea ice and upper ocean is simulated along longitude 169 5 w the model produces a realistic evolution of the sea ice thickness and extent and of the upper mean salinity and temperature profiles the major deficiencies in the simulation are linked to the absence of ocean and ice dynamics the modeled value of fb is far from being constant below thin ice it can be larger than 5 w m 2 due to the important fraction of the solar irradiance that is transmitted through the ice absorbed in the mixed layer and then returned to the ice below the thicker perennial sea ice fb takes values between 0 and

seasonality of southern ocean sea ice the sea ice cover of the southern ocean undergoes a rapid decrease from mid november to mid january the atmosphere to ocean heat flux is insufficient to account for this melting even in the presence of the high percentage of open water characteristic of the southern ocean sea ice it is estimated that sea air heat exchange in the 60 to 70 s zone can account for roughly 50 of the required spring heating the remainder must be supplied by the relatively warm deep water residing below the southern ocean pycnocline deep to surface water heat flux is accomplished by upwelling of the pycnocline due to the regional ekman divergence of the surface layer and by cross pycnocline mixing it is estimated that the required vertical mixing coefficient for the pycnocline is 1 5 cm2 s this value is considered as realistic in view of the relatively weak pycnocline which is a consequence of low levels of fresh water input to the surface layer it is suggested that the magnitude of fresh water input is a major factor in determining the degree of seasonality of southern ocean sea ice

a preliminary study of coda q in california and nevada the decay rate of local earthquake coda is characteristic of the area in which the epicenter and stations are located aki 1969 aki and chouet 1975 rautian and khalturin 1978 tsujiura 1978 aki 1980 interpreted the coda decay rate in terms of the attenuation property of s waves in the lithosphere under the area the q of s waves inferred from coda waves is called coda q recently several papers reported temporal changes in coda q prior to the occurrence of large earthquakes they are 1 the tangshan earthquake m 7 8 of 1976 and the haicheng earthquake m 7 4 of 1975 jin and aki 1986 2 three earthquakes m 8 in the kuril kamchatka region gusev and lemzikov 1985 3 the kalapana hawaii earthquake m 7 2 of 1975 wilson et al 1983 and 4 the eastern yamanashi japan earthquake m 6 0 of 8 august 1983 sato 1986 in all these cases the coda q was reported to be anomalously low before the occurrence of the earthquake however in a detailed study by chouet 1979 a strong fluctuation of coda q with time was observed in bear valley california which was not followed by a significant earthquake a recent coda q study in the adak seismic zone by scherbaum and kisslinger 1985 also did not find significant coda q changes that could be related to a mb 5 8 earthquake which occurred in the area of investigation in order to evaluate the feasibility of using coda q for earthquake prediction research in california and nevada we began a systematic study of coda q using digital waveform data from the regional microearthquake networks operated by the u s geological survey and the university of nevada

a convective model for the weddell polynya abstract mechanisms are considered which may induct the large over 105 km2 area of open water or polynya which frequently occurs within the weddell sea winter sea ice we propose that when surface cooling and ice formation decrease the temperature and increase the salinity of the surface water the latter by salt rejection during ice formation in a preconditioned area static instability with intense vertical mixing can occur the upwelled warm salty deep water can then supply enough heat to melt the ice or prohibit its formation even in the middle of winter a simple two level model is derived to test this theory and is found to agree well with observations the process is found to be irregular due to different times of ice onset from one year to the next and to a lesser extent from variations in surface heating and cooling further it is shown that unless the freshwater input exactly balances the increased salinity from the overturn each year the system will either gain or lose salt yearly an

impact of sea ice formation on the properties of antarctic bottom water it is generally accepted that fresh water fluxes due to ice accretion or melting profoundly influence the formation of antarctic bottom water aabw this is investigated by means of a global three dimensional ice ocean model two model runs were conducted at the high southern latitudes the control experiment exhibits positive i e towards the ocean fresh water fluxes over the deep ocean and large negative fluxes over the antarctic continental shelf because of the intense ice production taking place in this region the salinity of shelf water can increase in such a way that deep water formation is facilitated the simulated net fresh water flux over the shelf has an annual mean value of 1 m a 1 this flux induces a transport of salt to bottom waters which corresponds to an increase of their salinity estimated to be around 0 05 psu in the second model run the fresh water fluxes due to ice melting or freezing are neglected leading to a rearrangement of the water masses in particular the aabw formation rate decreases which allows the influence of north atlantic deep water nadw to increase as nadw is warmer and saltier than aabw the bottom water salinity and temperature become higher

effects of glacial meltwater inflows and moat freezing on mixing in an ice covered antarctic lake as interpreted from stable isotope and tritium distributions perennially ice covered lakes in the mcmurdo dry valleys have risen several meters over the past two decades due to climatic warming and increased glacial meltwater inflow to elucidate the hydrologic responses to changing climate and the effects on lake mixing processes we measured the stable isotope al80 and 6d and tritium concentrations of water and ice samples collected in the lake fryxell watershed from 1987 through 1990 stable isotope enrichment resulted from evaporation in stream and moat samples and from sublimation in surface lake ice samples tritium enrichment resulted from exchange with the postnuclear atmosphere in stream and moat samples rapid injection of tritiated water into the upper water column of the lake and incorporation of this water into the ice cover resulted in uniformly elevated tritium contents 3 0 tu in these reservoirs tritium was also present in deep water suggesting that a component of bottom water was recently at the surface during summer melted lake ice and stream water forms the moat water excluded from ice formation during fall moat freezing enriched in solutes and tritium and depleted in iso and 2h relative to water below 15 m depth may sink as density currents to the bottom of the lake seasonal lake circulation in response to climate driven surface inflow is therefore responsible for the distribution of both water isotopes and dissolved solutes in lake fryxell

thermobaric deep convection baroclinic instability and their roles in vertical heat transport around maud rise in the weddell sea 1 numerical experiments with two and three dimensional nonhydrostatic models in a rotating frame have been executed to investigate thermobaric deep convection subsequent baroclinic instability and their roles in vertical heat transport using hydrographic data around maud rise in the weddell sea antarctica overturning of the water column due to thermobaric convection is apt to occur on the southern and northern flanks of the rise and induces upward heat transport the depth of overturning is two times larger on the northern flank 1 5 km than on the southern flank 0 7 km to the contrary no overturning occurs over the top of the rise in 90 days baroclinic instability develops at a density front formed between the overturned and unoverturned regions since a density contrast at the front is enhanced by thermobaricity heat transport due to baroclinic instability is similarly upward and at peak becomes comparable to that due to the overturning applicability of the results to the cooling events previously reported is also discussed

restriction of convective depth in the weddell sea 1 the depth open ocean convection can reach around maud rise in the weddell sea is estimated based on the entrainment assumption using hydrographic data obtained in winter 1986 during which no distinct polynya was observed while the water column is stable at all ctd stations when observed additional cooling makes the mixed layer water heavier than the underlying water at any depth in an adiabatic sense however convective plume cannot reach the ocean bottom since it loses positive density anomaly due to thermobaricity by entraining the warm deep water wdw on its downward way the deeper convection is located over maud rise where the maximum temperature of the wdw max is about 0 5 c while the shallower one in the warm water cell region where max is more than 1 0 c the mean convective depth is much shallower than the ocean depth and the ventilated depth during the weddell polynya years 3 4 km

sensitivity of simulated cfc 11 distributions in a global ocean model to the treatment of salt rejected during sea ice formation we show that simulated oceanic absorption of an atmospheric gas is very sensitive to the representation of a process that occurs beneath sea ice as sea ice forms salt is rejected locally increasing surface sea water density this dense water can sink to the pycnocline at the base of the mixed layer previous studies have not considered the impact of this subgrid scale process on transient tracers in the ocean to assess the potential importance of this process to the oceanic absorption of atmospheric gases we performed two idealized simulations a control simulation in which salt rejected during sea ice formation is placed in the model s 25 m thick surface layer and a test simulation in which salt rejected during sea ice formation is distributed uniformly through the upper 160 m beneath the forming sea ice our treatment of rejected salt is highly idealized and is intended to demonstrate the need for a physically based parameterization of subgrid scale convection for use in ocean general circulation models that takes into account the subgrid scale heterogeneity of surface buoyancy forcing distributing rejected salt more deeply during periods of ice formation helps to maintain vertical density gradients inhibiting grid scale convection especially in the southern ocean this greatly diminishes simulated ocean uptake of cfc 11 and generally improves simulated cfc 11 and salinity fields the modeled global ocean inventory of cfc 11 for year 1990 is about 30 lower and modeled column inventories in the southern ocean are up to 90 lower in our test simulation relative to our control simulation we infer that a more detailed treatment of subgrid scale processes occurring beneath sea ice may diminish simulated oceanic absorption of anthropogenic co2 especially in the southern ocean

water mass transformation by sea ice in the upper branch of the southern ocean overturning sea ice formation is a key factor in the lower branch of the southern ocean overturning circulation observation based data in conjunction with a water mass transformation framework reveal that sea ice plays a central role in the upper branch too

temporal change in attenuation intensity before and after the eastern yamanashi earthquake of 1983 in central japan a crutal earthquake of magnitude 6 0 took place on august 8 1983 in the middle of the kanto tokai microearthquake observation network of the national research center for disaster prevention in central japan by analyzing vertical seismograms of microearthquakes occurring in a small volume in the aftershock region we measured temporal change in attenuation intensity for a period from 22 months before to 9 months after the main shock attenuation change was estimated by using two different kinds of analyses in the first analysis station magnitude calculated from the maximum amplitude at each station was compared with the average of station magnitudes deviations of station magnitude from the average magnitude at five stations in the vicinity of the aftershock area are found to have increased after the main shock compared with that before in the second analysis s coda duration from the origin time was measured and was compared with the average magnitude the increase of s coda duration for the same average magnitude is found after the main shock at two stations close to the main shock epicenter the simplest interpretation of the results is that the attenuation intensity in the upper crust in the close vicinity of the focal region decreased after the main shock for frequencies f from 2 to 20 hz qs 1 1 4 10 2f 1 since other precursors appeared in the preparation stage it is possible to interpret the change in qs 1 as a precursor the attenuation intensity would have been anomalously large before the main shock

antarctic circumpolar current s role in the antarctic ice system an overview abstract the antarctic circumpolar current acc provides fundamental control on the antarctic ice system the tilt of the isopycnals of the acc in response to strong westerlies serves to thermally isolate the antarctic continent from directly receiving the overwhelming subtropical ocean surface heat this same tilt provides the northern boundary of the polar seas as such it contains the statically stable cold fresh surface polar waters required for sea ice formation in this manner it effectively sets the northern limit for seasonal sea ice formation the isopycnal tilt also allows warm deep water to upwell to the surface near the continental margin in western antarctica where the acc skirts the continental shelf leading to excessive ocean heat flux to the atmosphere in winter and providing heat to melt the underside of the glacial ice

the ice thickness distribution across the atlantic sector of the antarctic ocean in midwinter during the first leg of the winter weddell sea project antarktis v 2 cruise of f s polarstern the entire width of the antarctic sea ice zone was traversed in the vicinity of 0 longitude in the period july 18 to september 10 1986 ice thicknesses were measured by direct drilling and by helicopter profiling using an exstar 100 mhz impulse radar system in addition aerial photography of the ice cover was done from 100 to 2000 m altitude using a 70 mm aerial camera mounted in the helicopter the results of the point measurements drilling are reported in this paper together with an indication of how the radar and photography data will be used to extend them so as to yield area averaged ice thickness distributions it was found that the main ice type across the entire width of the ice cover was consolidated pancake ice occurring in vast floes this formed out of a 250 km wide band at the advancing ice edge which comprised a concentrated field of individual pancakes in a matrix of frazil ice preferred thicknesses of undeformed floes were 40 60 cm of ice covered with 5 15 cm of snow the individual pancakes attained almost all of this thickness before consolidation subsequent congelation growth was slow estimated at 0 4 cm d 1 the floes contained much small scale roughness on the upper and lower surfaces due to rafting of pancakes at the time of consolidation but pressure ridging was modest except in the far south a few very thick 8 11 m multiyear floes were observed embedded in the pack at latitudes beyond 66 s

time space variation of seismic s wave coda attenuation qc 1 and magnitude distribution b values for the petatlan earthquake average s wave coda q qc at 6 hz and to about 10 sec after the s wave arrival shows 1 temporal variation positively correlated with the magnitude distribution parameter b for foreshocks and aftershocks of the 1979 petatlan mexico earthquake 2 spatial variation through the aftershock area positively correlated with b high qc b values at the two activity centers intermediate values in between and landward and low values toward the middle america trench which remain low for two weeks after the main shock and 3 five foreshock average qc 135 1 6 and eleven aftershock average qc 175 1 3 for the eastern asperity the b values and possibly qc values seem to correlate with the level of aftershock activity

a coupled one dimensional sea ice ocean model a prognostic one dimensional mixed layer pycnocline model describing the vertical structure of the upper ocean is coupled to a thermodynamic sea ice model the coupled prognostic model is compared with the more usual sea ice model overlying a fixed mixed layer with constant oceanic heat flux and is then applied to investigate the effect of temporal and regional variations of the entrained oceanic heat flux on the sea ice cover in both polar regions in the southern ocean a standard simulation is compared with two perturbation experiments which both describe the occurrence of a polynya in the arctic ocean the effect of possible soviet river diversions is investigated finally the response of the coupled model to paleoclimatic forcing and boundary conditions is presented

the southern ocean at the last glacial maximum a strong sink for atmospheric carbon dioxide analysis of satellite ocean color sea surface temperature and sea ice cover data reveals consistent patterns between biological production iron availability and physical forcings in the southern ocean the consistency of these patterns in conjunction with information on physical conditions during the last glacial maximum lgm enables estimates of export production at the lgm the lgm southern ocean experienced increased wind speeds colder sea surface and atmospheric temperatures increased deposition of atmospheric dust and a greatly expanded winter sea ice cover these variations had strong effects on southern ocean ecology and on air sea fluxes of co2 the seasonal ice zone siz was much larger at the lgm 30 million km2 than at present 19 million km2 the antarctic polar front pf likely marked the northern boundary of this expanded siz throughout the southern ocean as it does today in the drake passage region a large northward shift in the position of the pf during glacial times is unlikely due to topographic constraints north of the pf the increased flux of aeolian dust during glacial times altered phytoplankton species composition and increased export production and as a result this region was a stronger sink for atmospheric co2 than in the modern ocean south of the pf interactions between the biota and sea ice strongly influence air sea gas exchange over seasonal timescales the combined influence of melting sea ice and increased aeolian dust flux with its associated iron increased both primary and export production by phytoplankton over daily monthly timescales during austral spring summer resulting in a strong flux of co2 into the ocean heavy ice cover would have minimized air sea gas exchange over much of the rest of the year thus an increased net flux of co2 into the ocean is likely during glacial times even in areas where annual primary production declined we estimate that export production in the southern ocean as a whole was increased by 2 9 3 6 gt c yr 1 at the lgm relative to the modern era altered seasonal sea ice dynamics would further increase the net flux of co2 into the ocean thus the southern ocean was a strong sink for atmospheric co2 and contributed substantially to the lowering of atmospheric co2 levels during the last ice age

temporal stability of coda q 1 in southern california some studies of coda q 1 have found temporal changes that may be associated with earthquake activity but these analyses are subject to biases due to differences in source locations and other nonstationary behavior in earthquake catalogs these biases can be greatly reduced by using clusters of repeating earthquakes studies using this approach have generally found no resolvable changes in coda q 1 we examine coda q 1 variations across southern california using 22 similar event clusters identified from a recent large scale waveform cross correlation project to improve earthquake locations these clusters are found across the region and span the time period between 1981 and 2005 we apply the method of beroza et al 1995 to compute differential coda q 1 using waveforms from similar earthquake pairs and analyze the results to constrain any possible temporal variations results from individual event pairs show a great deal of scatter in differential coda q 1 but exhibit no clear temporal variations or changes associated with large earthquakes application of a median filter to smooth the results shows that any persistent large scale changes in coda q 1 during this time period are less than about 30

vertical eddy diffusivity determined with 222rn in the benthic boundary layer of ice covered lakes concentration gradients of 222rn and 226ra were analyzed in the benthic boundary of seven icecovered lakes to investigate vertical eddy diffusivity k sediment free samples retrieved with a tubing sampler from as close to the bottom as 14 cm showed that sharp 222rn gradients persist over the sediments a three dimensional analytical mixing model indicated horizontal mixing would not supply significant amounts of 222rn to midlake profiles in some flat bottomed lakes under ice cover one dimensional analysis of the profiles permitted observation of change in k with height above the sediments computed k values usually decreased in a given lake toward the sediments the range in k from all lakes studied was 0 30 cm2 s l at 3 6 1 m above the bottom to 3 2 x 1o 4 cm2 s l at 0 23 m both in lake mendota the correlation between k and the buoyancy density n2 was computed k 1 2 x 1o 5 n2 63 this relationship indicates turbulcnce arising from shear flow influences the vertical mixing in the winter boundary layer retarded mixing in the profundal boundary layer restricts vertical solute transport in some ice covered lakes

winter convection transports atlantic water heat to the surface layer in the eastern arctic ocean a 1 yr 2009 10 record of temperature and salinity profiles from ice tethered profiler itp buoys in the eurasian basin eb of the arctic ocean is used to quantify the flux of heat from the upper pycnocline to the surface mixed layer the upper pycnocline in the central eb is fed by the upward flux of heat from the intermediate depth 150 900m atlanticwater aw layer thisfluxisestimatedtobe 1wm 22 averaged over one year release of heat from the upper pycnocline through the cold halocline layer to the surface mixed layer is however seasonally intensified occurring more strongly in winter this seasonal heat loss averages 3 4wm 22 between january and april reducing the rate of winter sea ice formation this study hypothesizes that the winter heat loss is driven by mixing caused by a combination of brine driven convection associated with sea ice formation and larger vertical velocity shear below the base of the surface mixed layer sml enhanced by atmospheric storms and the seasonal reduction in density difference between the sml and underlying pycnocline

the thermodynamic balance of the weddell gyre the thermodynamic balance of the weddell gyre is assessed from an inverse estimate of the circulation across the gyre s rim the gyre experiences a weak net buoyancy gain that arises from a leading order cancellation between two opposing contributions linked to two cells of water mass transformation and diapycnal overturning the lower cell involves a cooling driven densification of 8 4 2 0 sv of circumpolar deep water and antarctic bottom water near the gyre s southern and western margins the upper cell entails a freshening driven conversion of 4 9 2 0 sv of circumpolar deep water into lighter upper ocean waters within the gyre interior the distinct role of salinity between the two cells stems from opposing salinity changes induced by sea ice production meteoric sources and admixture of fresh upper ocean waters in the lower cell which contrasts with coherent reductions in salinity associated with sea ice melting and meteoric sources in the upper cell

southern ocean frontal structure and sea ice formation rates revealed by elephant seals polar regions are particularly sensitive to climate change with the potential for significant feedbacks between ocean circulation sea ice and the ocean carbon cycle however the difficulty in obtaining in situ data means that our ability to detect and interpret change is very limited especially in the southern ocean where the ocean beneath the sea ice remains almost entirely unobserved and the rate of sea ice formation is poorly known here we show that southern elephant seals mirounga leonina equipped with oceanographic sensors can measure ocean structure and water mass changes in regions and seasons rarely observed with traditional oceanographic platforms in particular seals provided a 30 fold increase in hydrographic profiles from the sea ice zone allowing the major fronts to be mapped south of 60 s and sea ice formation rates to be inferred from changes in upper ocean salinity sea ice production rates peaked in early winter april may during the rapid northward expansion of the pack ice and declined by a factor of 2 to 3 between may and august in agreement with a three dimensional coupled ocean sea ice model by measuring the high latitude ocean during winter elephant seals fill a blind spot in our sampling coverage enabling the establishment of a truly global ocean observing system

properties of scattered elastic waves in the lithosphere of kamchatka parameters and temporal variations abstract records of near earthquakes from the shipunsky station were used to estimate s wave absorption for seven frequency bands ranging from 0 4 to 24 hz three techniques were employed and three rows of consistent estimates were obtained two of the three techniques give estimates that are independent of q anisotropic scattering was studied by observing the broadening of the s wavelet the estimates obtained show that anisotropic scatter may be significant the time variation of the coda envelope shape was studied using the records of 1 s regional seismographs three epicentral regions were chosen in the kurile kamchatka zone where m 8 earthquakes have occurred time series of the parameter which is the anomaly of the logarithmic steepness of coda envelope were constructed for vertical and horizontal channels of several stations pronounced forerunner type variations of were revealed we show that the probable cause of these variations is a qs decrease in the vicinity of impending m 8 earthquake this decrease is about 20 with a lead time of about a year the forerunner anomaly is not of the bay type and recovers 1 2 years after a large earthquake

dynamic and double diffusive instabilities in a weak pycnocline part i observations of heat flux and diffusivity in the vicinity of maud rise weddell sea abstractan expedition to study the stability of the weakly stratified water column in the eastern weddell sea was undertaken in the austral winter of 2005 a regional ctd survey around maud rise delineated water mass boundaries associated with flow around the seamount and identified areas most susceptible to overturning a downstream region of the seamount taylor column was found least stable with a potential density difference across the pycnocline less than 0 018 kg m 3 intensive water column measurements including 1300 profiles of temperature conductivity and fast response microconductivity were made during a series of 13 drift stations to investigate vertical turbulent transports and the evolution of water column stability the dependence of pycnocline turbulent diffusivity kt on froude number fr turbulence generated by internal wave shear and density ratio r turbulence generated by diffusive layering and possibly diapycnal cabbeling is investigated the fr alone cannot explain completely t

field investigation of winter thermo and hydrodynamics in a small karelian lake during late winter 18 march 7 april 1994 temperature and current measurements were made in lake vendyurskoe russia including three surveys at six cross sections of the lake also the temperature profile evolution was registered with two thermistor chains at two stations bottom depths of 7 6 and 11 5 m until the time of ice breakup temperature gradients were measured just below the ice cover and in the upper 1 ocm layer of the bottom sediments the isotherms were found to be almost horizontal and evenly spaced vl rtically so no conditions for largescale density induced currents existed the heat flux from sediments to water ranged from 0 6 to 2 0 w m 2 these values were inversely related to the depth the heat flux from water to ice ranged from 0 7 to 1 2 w rn2 when water heating from solar radiation penetration became apparent this flux increased by a factor of two when solar radiation increased convection occurred in the upper layers of the water column when solar radiation heating became significant at the beginning of spring the average net heat flux at the ice water interface during daytime was 7 7 w m 2 weak currents few mm s l with a seiche like character were observed which most likely resulted from ice cover oscillations winter thermo and hydrodynamics in dimictic lakes have only been sparsely studied and are far from being well understood because dimictic lakes can be ice covered for several months the influences of water temperature currents and mixing during this period play an important role for the water quality and ecological state of the lake the dynamic processes are different when the lake is ice covered than when it is not thermal regime the thermal regime is rather stable during winter having small horizontal temperature differences the vertical temperature structure has a continuous increase from 0 c at the ice water interface to 4 c and higher in the bottom layers hutchinson 1957

ocean heat flux in the central weddell sea during winter abstract seasonal sea ice which plays a pivotal role in air sea interaction in the weddell sea a region of large deep water formation with potential impact on climate depends critically on heat flux from the deep ocean during the austral winter of 1994 an intensive process oriented field program named the antarctic zone flux experiment measured upper ocean turbulent fluxes during two short manned ice drift station experiments near the maud rise seamount region of the weddell sea unmanned data buoys left at the site of the first manned drift provided a season long time series of ice motion mixed layer temperature and salinity plus a truncated high resolution record of temperature within the ice column direct turbulence flux measurements made in the ocean boundary layer during the manned drift stations were extended to the ice ocean interface with a mixing length model and were used to evaluate parameters in bulk expressions for interfacial stress a rossby similarity drag law and ocean to

thermobaric cabbeling over maud rise theory and large eddy simulation abstract a large eddy simulation les of the wintertime upper ocean below seasonal antarctic ice cover over maud rise was carried out using observed time dependent surface forcing from 1994 antarctic zone flux experiment anzflux observations surface ice formation increases the density of the cold fresher surface mixed layer sml that overlies warmer saltier weddell deep water wdw this reduces the stability of the thermocline until it reaches a critical point for instabilities arising from the nonlinear equation of state nes for seawater density this simulation was intended to model the thermobaric detrainment of sml fluid a nes instability predicted to result from the dependence of seawater density on the product p of temperature and pressure instead model results demonstrate a different instability arising from the combination of thermobaricity with cabbeling the nes effect due primarily to the dependence of on 2 this combined thermobaric cabbeling instability drives turbulent convection in a deep interior mixed layer iml that may grow hundreds of meters thick below the thermocline largely decoupled from sml dynamics in the les thermobaric cabbeling and iml convection shoals the sml through entrainment from below until ice motion increases in the observationally based model forcing increased upper ocean model heat flux due to higher ice speed melts surface ice increasing thermocline stratification and eventually bringing the simulated instability to a halt in an auxiliary simulation the lull preceding strong ice motion in field observations is artificially extended by temporarily holding model surface forcing constant until the sml shoals entirely bringing the modified wdw of the iml 2 c above freezing directly to the surface subsequently reverting to the observed surface forcing and its attendant strong ice motion melts the ice cover entirely demonstrating a possible mechanism for open ocean antarctic polynya formation the same process as halted prematurely in the les using the forcing observed may also be responsible for thick deep internal layers and localized chimney structures observed in the weddell sea

temporal change in coda associated with the round valley california earthquake of november 23 1984 seven thousand seismograms of small earthquakes in the mammoth lakes bishop area were used to measure values of q from the decay of the earthquake coda these measurements were compared between events that occurred before and after the round valley earthquake m 5 7 we found that in regions near the main shock epicenter measurements of coda q 1 for earthquakes that occurred after the main shock were higher than for those earthquakes that occurred prior to the main shock the opposite behavior was found for regions farther away from the main shock namely lower coda q 1 after the main shock than before measurements of coda q 1 in the long valley caldera outside of the immediate source region of the earthquake were higher than in surrounding areas before the main shock but the difference disappeared after the occurrence of the main shock this indicates that the temporal variation in coda q 1 is comparable to its spatial variation the doughnut model seismicity quiescence surrounded by a zone of activity which was invoked for explaining the precursory seismicity pattern appears to be similar with the observed coda q 1 variation associated with the round valley earthquake the observed spatial variations in coda q 1 also help to reconcile conflicting results published in previous studies of the coda q 1 precursor

the role of deep ocean circulation in setting glacial climates the glacial cycles of the pleistocene involve changes in the circulation of the deep ocean in important ways this review seeks to establish what were the robust patterns of deep sea water mass changes and how they might have influenced important parts of the last glacial cycle after a brief review of how tracers in the modern ocean can be used to understand the distribution of water masses i examine the data for biogeochemical circulation rate and conservative tracers during glacial climates some of the robust results from the literature of the last 30 years include a shoaled version of northern source deep water in the atlantic expanded southern source water in the abyss and deep ocean salt rather than heat stratification of the last glacial maximum lgm deep sea and several lines of evidence for slower overturning circulation in the southern deep cell we combine these observations into a new idea for how the ocean atmosphere system moves from interglacial to glacial periods across a single cycle by virtue of its influence on the melting of land based ice around antarctica cooling north atlantic deep water nadw leads to a cold and salty version of antarctic bottom water aabw this previously underappreciated feedback can lead to a more stratified deep ocean that operates as a more effective carbon trap than the modern helping to lower atmospheric co 2 and providing a mechanism for the deep ocean to synchronize the hemispheres in a positive feedback that drives the system to further cooling

preconditioning of antarctic maximum sea ice extent by upper ocean stratification on a seasonal timescale this study uses an observationally constrained and dynamically consistent ocean and sea ice state estimate the author presents a remarkable agreement between the location of the edge of antarctic maximum sea ice extent reached in september and the narrow transition band for the upper ocean 0 100 m depths stratification as early as april to june to the south of this edge the upper ocean has high stratification which forbids convective fluxes to cross through consequently the ocean heat loss to the atmosphere is an efficient way to cool the surface ocean to the freezing point during april to september to the north the upper ocean has low stratification such that the ocean heat loss to the atmosphere is not efficient to cool the upper ocean the upper ocean is instead cooled mainly through mixing with the colder inflow carried by northward ekman transport but cannot reach the freezing point due to the nature of mixing therefore upper ocean stratification dominated by salinity here provides an important constraint on the northward expansion of antarctic sea ice to its maximum

supercooled southern ocean waters in cold polar waters temperatures sometimes drop below the freezing point a process referred to as supercooling however observational challenges in polar regions limit our understanding of the spatial and temporal extent of this phenomenon we here provide observational evidence that supercooled waters are much more widespread in the seasonally ice covered southern ocean than previously reported in 5 8 of all analyzed hydrographic profiles south of 55 s we find temperatures below the surface freezing point potential supercooling and half of these have temperatures below the local freezing point in situ supercooling their occurrence doubles when neglecting measurement uncertainties we attribute deep coastal ocean supercooling to melting of antarctic ice shelves and surface induced supercooling in the seasonal sea ice region to winter time sea ice formation the latter supercooling type can extend down to the permanent pycnocline due to convective sinking plumes an important mechanism for vertical tracer transport and water mass structure in the polar ocean

spin down of baroclinic eddies under sea ice a linear model is used to examine the spin down of a baroclinic eddy under the sea ice for anti cyclonic eddies the ice stress besides directly spinning down the azimuthal flow within the mixed layer generates an ekman divergence that raises the pycnocline near the eddy axis for eddies of the size of the baroclinic radius of deformation based on the unperturbed mixed layer depth h and the density jump across the pycnocline the doming reaches a quasi stationary state on the frictional time scale t defined as h where is the resistence coefficient at the ice water interface which generally is of the order of days upward entrainment of the fluid across the pycnocline causes a flow convergence below the mixed layer that continues to spin down the deeper flow and flatten the dome the erosion of the dome however occurs over a much longer time scale of n 1t where and n are dimensionless parameters characterizing the entrainment rate and the deep stratification using realistic parameter values for the polar eddies this time scale is of the order of a year or longer the pycnocline dome observed over the antarctic warm cells is thus likely to survive into the following freezing season and provide a preconditioning for the deep convection in the weddell sea

thermohaline stratification below the southern ocean sea ice the end of winter stratification within the cold cyclonic trough of the weddell gyre near 60 s between 5 e and the greenwich meridian is resolved with the mikhail somov data set the temperature maximum of the weddell deep water wdw is for the most part less than 0 5 c but warmer cells of wdw are found these warm wdw cells have temperature salinity and oxygen properties similar to the wdw characteristic of the weddell gyre inflow which is situated to the southeast of the mikhail somov study region the warm wdw cells are accompanied by domes in the pycnocline of 40 m amplitude over the surrounding pycnocline while deeper isopycnals are depressed anticyclonic shear below the 27 83 isopycnal within the warm wdw cells is compensated by the cyclonic shear associated with the pycnocline dome the pycnocline domes are exposed to about 50 greater entrainment by the turbulently active winter mixed layer relative to the regional entrainment rate this entrainment can significantly erode the warm cells in a single winter season introducing excess heat and salt into the mixed layer while the heat is lost to the atmosphere the excess salt is not necessarily compensated by increased fresh water introduction it is hypothesized that the warm wdw cells within the weddell gyre trough are derived from instability within the frontal zone which extends from maud rise to the northeast separating the weddell warm regime from the cold regime greater than normal injection of warm wdw cells into the weddell gyre trough would increase the surface salinity which would tend to destabilize the pycnocline increasing the probability of deep convection and polynya events

regionalization of crustal coda q in the continental united states a contour map of crustal q sub 0 values for the entire united states is presented based on a scattering model to explain the coda waves of local and near regional earthquakes these coda q sub 0 values are in good agreement with q of lg waves data are obtained from over 250 local earthquakes with most magnitudes between 3 0 and 5 0 recorded by 25 wwssn and 27 lrsm stations throughout the continental united states these two sets of data provide a range of frequencies from 0 5 to 3 5 hz a frequency dependence of q is observed in the range of frequencies considered a power law dependence of the form q q sub 0 f f sub 0 sup eta is assumed the value of frequency dependence eta is found to be maximum in the tectonically active western united states and least in the stable regions of the central and south central united states the lowest q sub 0 values are obtained in the western united states with values ranging from 140 to 200 in the coastal plains average crustal q sub 0 values for the basin and range province vary from 200 to 300 increasing gradually to 400 in the colorado plateau region q sub 0 valuesmore in the columbia plateau vary from 200 to 400 q sub 0 values increase very rapidly along the central and southern rocky mountains from 400 to 800 east of the rocky mountains q sub 0 values increase gradually in the interior plains to a maximum value of around 1300 in the mississippi embayment region farther east q sub 0 values decrease gradually to an almost constant value of 1000 along the appalachian mountains coastal regions of eastern and northeastern united states have a crustal q sub 0 value between 900 to 700 regions of north central and gulf coastal plains show low q sub 0 values ranging from 600 to 400 and less the source factor b f sub p a measure of the intensity of scattering was obtained for several different regions of the continental united states regions of high q sub 0 values exhibit low intensity of scattering less

southern ocean winter mixed layer austral winter 1986 observations from the polarstern along the greenwich meridian from the ice edge to the antarctic margin show the mixed layer beneath the winter sea ice cover to be significantly depressed in oxygen saturation incorporation of weddell deep water wdw into the winter mixed layer responsible for this undersaturation also introduces heat and salinity into the surface layer which strongly influences the mixed layer sea air exchanges and sea ice formation processes the total wdw transfer into the mixed layer averages 45 myr 1 implying a residence time for the surface water of 2 5 years the associated winter heat flux is 41 w m 2 which limits ice thickness to about 0 55 m agreeing quite well with observations the air temperatures during the cruise are just sufficient to remove the wdw heat input in the presence of observed ice thickness and concentration this suggests that the sea ice cover and wdw heat input into the mixed layer are in approximate balance by midwinter the annual heat flux from wdw to the surface layer and hence into the atmosphere is estimated as 16 w m 2 extrapolation of the greenwich meridian wdw entrainment value to the full circumpolar 60 70 s belt yields total up welling of 24 106 m3 s 1 similar extrapolation of the heat flux value gives a circumpolar total of 2 8 1014 w as a consequence of circulation topography interaction the maud rise water column stands out as an anomaly relative to the surrounding region with a significantly more saline and dense mixed layer below the mixed layer the water column over the crest of the rise is identical to that over the flanks if the latter water column is upwelled by 400 m this uplifting is believed to be a response of the upstream flow encountering the rise increased upstream flow would be expected to increase maud rise upwelling and the dependent salinity density of the mixed layer slight increases in the mixed layer density could trigger a convective mode and generation of a polynya it is hypothesized that spin up of the weddell gyre s barotropic circulation induced by an increase of the regional wind stress curl would enhance the probability of polynya development over maud rise

water properties on the west antarctic peninsula continental shelf a model study of effects of surface fluxes and sea ice abstract a vertical and time dependent numerical mixed layer and sea ice model is used to analyze processes responsible for sea ice and surface mixed layer water properties on the continental shelf on the west side of the antarctic peninsula atmospheric observations from faraday and palmer stations along with satellite sea ice observations and shipboard water observations four hydrographic cruises between january 1993 to february 1994 are used for forcing and verification the focus of this study is the year 1993 during which the best observations exist however a 16 year simulation is completed to analyze interannual variations of ice thickness and mixed layer depth this model study shows that surface waters of the west antarctic peninsula are heated in the summer by solar radiation and cooled in the winter by sensible heat losses diffusive convection is important for upward heat flux across the pycnocline ice melt in the spring is due to solar warming of open water which then melts ice the direct melting for ice by solar heating is negligible the near closure of surface heat and salt budgets over 1 year supports the minor importance or at least the compensation of near surface lateral exchanges intrusion of upper circumpolar deep water from the antarctic circumpolar current onto the subpycnocline shelf is a critical element of both salt and heat budgets a 16 year simulation 1978 1993 reproduces most high and low ice years as observed by satellite microwave measurements thus supporting the major contribution of thermodynamic local processes in creating sea ice and mixed layer properties

the impact of a downslope water transport parametrization in a global ocean general circulation model the impact of a downslope water transport parametrization on the circulation and water mass characteristics of a global depth level ocean general circulation model is investigated the spreading of dense water from the formation regions into the deep ocean is known to be poorly represented in depth level models with no bottom boundary layer resolved or attached the new scheme is simple and intends to parametrize the effects of various oceanographic processes rather than the processes themselves that help dense water to descend topographic slopes by which the formation regions are separated from the world ocean the new scheme significantly improves the large scale properties of the north atlantic deep water changes in the north atlantic circulation however are rather small in the southern ocean the exchange between the dense water formation regions on the continental shelves and the deep ocean is strengthened at the expense of deep water mass formation by open ocean convection in all three ocean basins the density of the deep and bottom water is higher with the new parametrization which brings the simulations closer to observations in the atlantic and indian oceans in the pacific ocean however where the density has already been well reproduced without the downslope transport it becomes slightly too high the results are in agreement with those from other model studies

convectively driven transport in temperate lakes penetrative convection in the surface layer of a midsize temperate lake 5 km2 was investigated in both summer and winter using a conductivity temperature depth ctd logger mounted on an autonomous underwater vehicle auv flown repeatedly along horizontal transects at selected depths in summer the epilimnion cooled differentially during a calm evening 240 and 297 w m22 on the east and west sides of the lake respectively these cooling rates agree well with the average net heat flux of 270 w m22 estimated from meteorological data density currents were driven by this differential cooling in winter ctd profiles during a sunny day showed four distinct thermal layers beneath the ice 50 cm thick consistent with radiative penetrative convection a stratified diffusive layer just beneath the ice top 1 6 m a well mixed convective layer that deepens at 1 14 m d21 and warms at 0 015u cd 21 during the observation period an entrainment layer 1 5 m thick and a weakly stratified quiescent layer to bottom auv transects flown at constant depths in each layer revealed a 150 m wide region displaying evidence of penetrative convection surrounded by regions with negligible heat changes these high resolution horizontal ctd measurements provided insight into previously unresolved physical dynamics of the well mixed layer of a temperate lake in quasi shear free conditions that would have been difficult to quantify during summer months and impossible under winter ice cover without the use of an auv platform in temperate lakes during periods of little or no wind exposure penetrative convection driven by a destabilizing buoyancy flux will be the dominant source of vertical mixing in the upper layers of the water column above the temperature of maximum density penetrative convection

last glacial benthic foraminiferal δ18o anomalies in the polar north atlantic a modern analogue evaluation modern processes are evaluated to understand the possible mechanisms behind last glacial benthic foraminiferal 18o anomalies that occurred concurrent with meltwater events in the polar north atlantic such anomalies in the nordic seas were recently interpreted to be caused by brine formation despite intensive sea ice production on circumarctic shelves modern data show that brines ejected from sea ice formation containing low 18o water do not significantly contribute to deep waters in the arctic ocean today assuming that this process was nevertheless responsible for 18o anomalies in nordic seas deep water during the last glaciation a broad shallow shelf area adjacent to the nordic seas such as the barents sea had to be seasonally free of sea ice in order to serve as an area for brine formation another process which may explain 18o depleted water at depth is found in the weddell sea today where a low 18o signal in deep waters originates from ice shelf interactions if temperature were considered the main mechanism for the low benthic 18o values an increase of 4 c must have occurred in the deep water an analogous situation with a reversed water temperature pattern due to a subsurface inflow of warm atlantic water is found today in the eastern arctic ocean and deep water warming is observed in the greenland gyre in the absence of deep convection because paleoproxy data also indicate an atlantic water inflow into the nordic seas during such benthic 18o anomalies temperature as a principal mechanism of changing 18o cannot be excluded

sea ice ocean feedbacks in the antarctic shelf seas abstractobserved changes in antarctic sea ice are poorly understood in part due to the complexity of its interactions with the atmosphere and ocean a highly simplified coupled sea ice ocean mixe

icesat measurements of sea ice freeboard and estimates of sea ice thickness in the weddell sea 1 sea ice freeboard heights in the weddell sea of antarctica are derived from the ice cloud and land elevation satellite icesat laser altimeter measurements which have a unique range precision to flat surfaces of 2 cm within 70 m footprints spaced at 172 m along track although elevations of flat surfaces can be obtained to an accuracy of 10 cm 1s per footprint direct determination of freeboard heights is precluded by errors in knowledge of the geoid and temporal variability of the ocean surface therefore freeboards are determined relative to an ocean reference level detected over areas of open water and very thin ice within the sea ice pack using an along track filtering method the open water thin ice selections show good agreement in the combined analysis of icesat segments and envisat synthetic aperture radar sar imagery the average residual between the icesat measured ocean level and the egm96 geoid is 1 4 m estimates of snow depth on the sea ice from amsr e passive microwave data along with nominal densities of snow water and sea ice are used to estimate sea ice thickness four periods of icesat data in may june fall and october november late winter of 2004 and 2005 between longitudes 298e and 360e are analyzed in the fall the mean freeboards are 0 28 m in 2004 and 0 29 m in 2005 and the mean thicknesses are 1 33 m in 2004 and 1 52 m in 2005 in late winter the freeboards grew to 0 37 m in 2004 and 0 35 in 2005 and the thicknesses grew to 2 23 m in 2004 and 2 31 m in 2005 the interannual differences in freeboard are small and the larger interannual change in estimated thickness mainly represents differences in the snow depth estimates seasonal changes in the spatial patterns of freeboard and thickness over the 4 months correlate with the expected circulation of sea ice in the weddell sea as indicated by sea ice velocity fields

some properties of currents and mixing in a shallow ice covered lake a study on characteristics of currents and mixing in a shallow ice covered russian lake is presented the current velocity data are separated into four main components mean velocity uninodal longitudinal and transverse seiche currents and high frequency velocity fluctuations using digital filters the analysis of components shows that mean currents are most pronounced in early winter and are of the order of 1 10 mm s 1 all three oscillatory components are on average of the same magnitude 0 1 1 mm s 1 and about the same as mean currents in midwinter and do not show any pronounced differences during winter mean currents increase during the convective period in late winter up to several millimeters per second apart from possible local hydrodynamic instability induced by salt fluxes at the ice and bottom boundaries and local turbulence near the boundaries in early winter the vertical mixing in early winter and midwinter in the lake appears to be determined solely by molecular processes

the influence of sea ice on ocean heat uptake in response to increasing co2 two significant changes in ocean heat uptake that occur in the vicinity of sea ice cover in response to increasing co2 are investigated with community climate system model version 3 ccsm3 a deep warming below 500 m and extending down several kilometers in the southern ocean and warming in a 200 m layer just below the surface in the arctic ocean ocean heat uptake caused by sea ice retreat is isolated by running the model with the sea ice albedo reduced artificially alone this integration has a climate response with strong ocean heat uptake in the southern ocean and modest ocean heat uptake in the subsurface arctic ocean the arctic ocean warming results from enhanced ocean heat transport from the northern north atlantic at the time of co2 doubling about 1 3 of the heat transport anomaly results from advection of anomalously warm water and 2 3 results from strengthened inflow at the same time the overturning circulation is strengthened in the northern north atlantic and arctic oceans wind stress changes cannot explain the circulation changes which instead appear related to strengthened convection along the siberian shelves deep ocean warming in the southern ocean is initiated by weakened convection which is mainly a result of surface freshening through altered sea ice and ocean freshwater transport below about 500 m changes in convection reduce the vertical and meridional temperature gradients in the southern ocean which significantly reduce isopycnal diffusion of heat upward around antarctica the geometry of the sea ice cover and its influence on convection have a strong influence on ocean temperature gradients making sea ice an important player in deep ocean heat uptake in the southern ocean