integration of ice core marine and terrestrial records for the australian last glacial maximum and termination a contribution from the oz intimate group the degree to which southern hemisphere climatic changes during the end of the last glacial period and early holocene 30 8 ka were influenced or initiated by events occurring in the high latitudes of the northern hemisphere is a complex issue there is conflicting evidence for the degree of hemispheric teleconnection and an unresolved debate as to the principle forcing mechanism s the available hypotheses are difficult to test robustly however because the few detailed palaeoclimatic records in the southern hemisphere are widely dispersed and lack duplication here we present climatic and environmental reconstructions from across australia a key region of the southern hemisphere because of the range of environments it covers and the potentially important role regional atmospheric and oceanic controls play in global climate change we identify a general scheme of events for the end of the last glacial period and early holocene but a detailed reconstruction proved problematic significant progress in climate quantification and geochronological control is now urgently required to robustly investigate change through this period copyright c 2006 john wiley sons ltd

reconstructing paleoenvironment eruption mechanism and paleomorphology of the pliocene pula maar hungary abstract pula maar is a partially eroded pliocene maar diatreme volcano part of the mio pliocene bakony balaton highland volcanic field the surficial remnant of the maar diatreme volcano consists of 1 a distinct depression with a thick post eruptive lacustrine alginite sediment infill interbedded with coarse grained volcaniclastic sediments 2 a narrow marginal zone inside the depression consisting of primary pyroclastic rock units that are interpreted to be partly collapsed and subsided blocks of entire sections from the tephra ring formerly surrounding the maar crater depression and 3 coarse grained volcaniclastic debris flow deposits closely associated with the collapsed primary pyroclastic rock units in the marginal zone the presence of coherent lava rocks below the crater fill units their distribution pattern and their association with scoriaceous beds indicate that after the maar diatreme forming phreatomagmatic explosive activity small 100 m scale scoria and or spatter cones erupted in the maar crater these cones are the likely source of the lava flows that partially filled the maar crater basin the widespread dm to m thick basaltic sand and or silt units at the base of the post eruptive crater filling sedimentary succession are interpreted to be reworked volcaniclastic material from the intra maar scoria spatter cones as well as from the tephra ring based on comparative analyses of 53 core descriptions this study reveals that the original maar crater basin was larger than previously suggested the deep level of the maar crater is reconstructed to be a northeast southwest elongated depression currently forming a c 50 m deep basin geomorphological considerations suggest that most of the phreatomagmatic pyroclastic rocks are composed of base surge and tephra fall deposits around the deep maar depression these allochthonous rock units form a 50 400 m wide zone of proximal tuff ring sequences the formation of this zone is inferred to be a result of a combination of syn eruptive subsidence due to mass deficit in the rigid triassic dolomite basement caused by the phreatomagmatic explosions as well as post eruptive subsidence of the crater and diatreme filling successions due to diagenetic compaction the facies in the centre of the maar lake is a soft laminated alginite mainly botryococcus colonies diatom frustles calcium carbonate crystals clay minerals in the section exposed in the pula open cast mine a single turbiditic layer is present this layer originated in a landslide which possibly could have been caused by either syn eruptive earthquake and or a sudden post eruptive subsidence event of the diatreme fill

subsurface fine scale patterns in an anticyclonic eddy off cap vert peninsula observed from glider measurements glider measurements acquired along four transects between cap vert peninsula and thecape verde archipelago in the eastern tropical north atlantic during march april 2014 were used to investigate fine scale stirring in an anticyclonic eddy the anticyclone was formed near 12 n off the continental shelf and propagated northwest toward the cape verde islands at depth between 100 and 400 m the isolated anticyclone core contained relatively oxygenated low salinity south atlantic centralwater while the surrounding water masses were saltier and poorly oxygenated the dynamical and thermohaline subsurface environment favored the generation offine scale horizontal and vertical temperature and salinity structures in and around the core of the anticyclone these features exhibited horizontal scales of o 10 30 km relatively small with respect to the eddy radius of o 150 km the vertical scales of o 5 100 m were associated to density compensated gradient spectra of salinity and oxygen along isopycnals revealed a slope of around k 2in the 10 to 100 km horizontal scale range further analyses suggest that the fine scale structures are likely related to tracer stirring processes such mesoscale anticyclonic eddies and the embedded fine scale tracers in and around them could play a major role in the transport of south atlantic central water masses and ventilation of the north atlantic oxygen minimum zone

fine scale variability of isopycnal salinity in the california current system this paper examines the finescale structure and seasonal fluctuations of the isopycnal salinity of the california current system from 2007 to 2013 using temperature and salinity profiles obtained from a series of underwater glider surveys the seasonal mean distributions of the spectral power of the isopycnal salinity gradient averaged over submesoscale 12 30 km and mesoscale 30 60 km ranges along three survey lines off monterey bay point conception and dana point were obtained from 298 transects the mesoscale and submesoscale variance increased as coastal upwelling caused the isopycnal salinity gradient to steepen areas of elevated variance were clearly observed around the salinity front during the summer then spread offshore through the fall and winter the high finescale variances were observed typically above 25 8 kg m 3 and decreased with depth to a minimum at around 26 3 kg m 3 the mean spectral slope of the isopycnal salinity gradient with respect to wavenumber was 0 19 0 27 over the horizontal scale of 12 60 km and 31 to 35 of the spectra had significantly positive slopes in contrast the spectral slope over 12 30 km was mostly flat with mean values of 0 025 0 32 an increase in submesoscale variability accompanying the steepening of the spectral slope was often observed in inshore areas e g off monterey bay in winter where a sharp front developed between the california current and the california under current and the lower layers of the southern california bight where vigorous interaction between a synoptic current and bottom topography is to be expected

ventilation of the subtropical north pacific the shallow salinity minimum abstract the shallow salinity minimum of the subtropical north pacific is shown to be a feature of the ventilated wind driven circulation subduction of low salinity surface water in the northeastern subtropical gyre beneath higher salinity water to the south causes the salinity minimum variation of salinity along surface isopycnals causes variations in density and salinity at the minimum a model of ventilated flow is used to demonstrate how the shallow salinity minimum can arise the model is modified to account for nonzonal realistic winds it is also extended to examine the three dimensional structure of the western shadow zone the boundary between the subtropical and subpolar gyres is given by the zero of the zonal integral of ekman pumping the western shadow zone fills the subtropical gyre at the base of the ventilated layers and decreases in extent with decreasing density for parameters appropriate to the north pacific the eastern shadow zone is of very limited extent observations of salini

on sampling the ocean using underwater gliders surface to 1000 m and back took 5 6 h and covered 5 3 km resulting in a horizontal speed of 0 26 m s 1 seasoar undulated between the surface and 400 m completing a cycle in 11 min while covering 2 6 km for a speed of 3 9 m s 1 adjacent profiles of temperature and salinity are compared between the two platforms to prove that each is accurate spray and seasoar data are compared through sections isopycnal spatial series and wave number spectra the relative slowness of the glider results in the projection of high frequency oceanic variability such as internal waves onto spatial structure the projection is caused by doppler smearing because of finite speed and aliasing due to discrete sampling the projected variability is apparent in properties measured on depth surfaces or in isopycnal depth no projected variability is seen in observations of properties on constant density surfaces because internal waves are intrinsically filtered wave number spectra suggest that projected variability affects properties at constant depth at wavelengths shorter than 30 km these results imply that isobaric quantities like geostrophic shear are valid at wavelengths longer than 30 km while isopycnal quantities like spice may be analyzed for scales as small as a glider measures

frontal surveys with a towed profiling conductivity temperature depth measurement package seasoar in april 1986 rv oceanus participated in the frontal air sea interaction experiment fasinex1 in the region 27 29 n 68 71 w the objective was to survey a pronounced oceanic front2 4 and its effect on the oceanic and atmospheric boundary layers although moorings have yet to be recovered and much of the data analysis is as yet only preliminary it is possible to report here the typical density structure of a front as derived from seasoar5 6 fig 1a observations which were analysed within a few hours of collection previously unreported detail is revealed including subducted pycnostads areas of weak vertical density gradient with anomalous temperature salinity signature splitting of the frontal jet and three dimensional structure not apparent in the surface temperature field

seismic attenuation and velocity dispersion in heterogeneous partially saturated porous rocks summary using a numerical approach we explore wave induced fluid flow effects in partially saturated porous rocks in which the gas water saturation patterns are governed by mesoscopic heterogeneities associated with the dry frame properties the link between the dry frame properties and the gas saturation is defined by the assumption of capillary pressure equilibrium which in the presence of heterogeneity implies that neighbouring regions can exhibit different levels of saturation to determine the equivalent attenuation and phase velocity of the synthetic rock samples considered in this study we apply a numerical upscaling procedure which permits to take into account mesoscopic heterogeneities associated with the dry frame properties as well as spatially continuous variations of the pore fluid properties the multiscale nature of the fluid saturation is taken into account by locally computing the physical properties of an effective fluid which are then used for the larger scale simulations we consider two sets of numerical experiments to analyse such effects in heterogeneous partially saturated porous media where the saturation field is determined by variations in porosity and clay content respectively in both cases we also evaluate the seismic responses of corresponding binary patchy type saturation patterns our results indicate that significant attenuation and modest velocity dispersion effects take place in this kind of media for both binary patchy type and spatially continuous gas saturation patterns and in particular in the presence of relatively small amounts of gas the numerical experiments also show that the nature of the gas distribution patterns is a critical parameter controlling the seismic responses of these environments since attenuation and velocity dispersion effects are much more significant and occur over a broader saturation range for binary patchy type gas water distributions this analysis therefore suggests that the physical mechanisms governing partial saturation should be accounted for when analysing seismic data in a poroelastic framework in this context heterogeneities associated with the dry frame properties which do not play important roles in wave induced fluid flow processes per se should be taken into account since they may determine the kind of gas distribution pattern taking place in the porous rock

an australian holocene climate reconstruction using chironomidae from a tropical volcanic maar lake abstract holocene sediments from lake barrine on the atherton tableland in tropical north east queensland australia 17 15 s 145 38 e 721 m asl reveal 10 assemblage shifts in subfossil aquatic immature chironomidae remains over the past 9000 years using the program canoco 3 12 and ordination analyses we examined relationships between the physico chemistry of multiple local and regional water bodies and their chironomid fauna to assess the relative importance of various environmental and climatic parameters on the distribution of australian chironomids to derive palaeoclimates we used an extant assemblage to test reconstructions over 50 calibrated radiocarbon dates from a 7 5 m sediment record and the correlative distribution modelling programs domain and bioclim to construct and overlap climate envelopes of species in comparison with contemporary climate reconstructed conditions were warmer annually by 2 5 c from 4650 calendar years before present cal yr bp to more recent times annual temperatures were slightly cooler between 5130 to 4650 cal yr bp and may have been cooler in the warmest quarter by 6 6 c between 6890 and 6090 cal yr bp precipitation estimates although subject to greater errors were reconstructed in the wettest quarter to be drier by around 500 mm at 5130 4650 and 6890 6090 cal yr bp the inferred sensitivity of chironomidae to climatic and environmental conditions at lake barrine suggests that australian midges are reliable and informative biological indicators faunal changes were correlated with fluctuations in water levels sediment influx organic material oxygen availability and nutrient status mediated by changes in the local climate and a shift from dry sclerophyll vegetation to rainforest within the catchment

compensation and alignment of thermohaline gradients in the ocean mixed layer the surface mixed layer of the ocean is often characterized by thermohaline compensation and alignment that is temperature and salinity gradients tend to be parallel and to cancel in their contribution to density in this paper a combination of theoretical arguments and numerical simulations is presented to investigate how compensation and alignment emerge as a result of processes at work within the mixed layer the dynamics of the mixed layer is investigated through a simple model that couples a nonlinear diffusive parameterization for the horizontal transports of temperature and salinity with stirring by mesoscale eddies it is found that stirring quickly aligns the temperature and salinity gradients and that nonlinear diffusion creates compensation neither process by itself is sufficient to reproduce the observations

warm season temperatures since 1600 bc reconstructed from tasmanian tree rings and their relationship to large scale sea surface temperature anomalies we describe an improved tree ring reconstruction of mean warm season november april temperatures for tasmania from huon pine this record extends back to 1600 bc and is based on a tree ring chronology that was processed to retain as much low frequency variance as possible the resulting reconstruction explains 46 6 of the variance and verifies significantly when compared to withheld instrumental data cross spectral analysis of actual and estimated temperatures over the 1886 1991 common period indicates that most of the unexplained variance is at periods 12 years the squared coherency ranges between 0 6 0 8 and the cross spectral gain indicates that the amplitude of the reconstruction is a nearly unbiased estimate of the true temperature amplitude therefore this reconstruction should be especially useful for studying multi decadal temperature variability in the tasmanian sector of the southern hemisphere over the past 3592 years to this end we examined the time evolution of low frequency temperature amplitude fluctuations and found evidence for a 35 amplitude reduction after ad 100 that persisted until about ad 1900 since that time the low frequency temperature amplitude has systematically increased we also show how this reconstruction is related to large scale sea surface temperatures sst in the indian ocean and eastward to the dateline pointwise correlations between the tasmanian record and ssts reveal a relationship that extends across the southern indian ocean and towards the arabian sea this pattern is largely determined by inter decadal temperature variability with correlations in this 10 year bandwidth commonly exceeding 0 6 over most of the southern indian and southwestern pacific sectors a rotated empirical orthogonal function analysis reveals that the pattern of pointwise correlations found between the temperature reconstruction and ssts is largely explained by the linear combination of three orthogonal modes of sst variability

time lapse sonic logs reveal patchy co2 saturation in situ 1 based on time lapse sonic and neutron porosity logs from the nagaoka co2 sequestration experiment a p wave velocity saturation relation at reservoir depth is retrieved it does not coincide with either of the end member models of uniform and patchy saturation but falls in between even if realistic error estimates for the host rock properties are considered assuming a random distribution of co2 patches it is shown that the mechanism of wave induced flow can be evoked to explain this velocity saturation relation characteristic co2 patch size estimates range from 1 to 5 mm such mesoscopic heterogeneity can be responsible for attenuation and dispersion in the well logging frequency band

comparison of p wave attenuation models of wave induced flow abstract wave induced oscillatory fluid flow in the vicinity of inclusions embedded in porous rocks is one of the main causes for p wave dispersion and attenuation at seismic frequencies hence the p wave velocity depends on wave frequency porosity saturation and other rock parameters several analytical models quantify this wave induced flow attenuation and result in characteristic velocity saturation relations here we compare some of these models by analyzing their low and high frequency asymptotic behaviours and by applying them to measured velocity saturation relations specifically the biot rayleigh model considering spherical inclusions embedded in an isotropic rock matrix is compared with white s and johnson s models of patchy saturation the modeling of laboratory data for tight sandstone and limestone indicates that by selecting appropriate inclusion size the biot rayleigh predictions are close to the measured values particularly for intermediate and high water saturations

seismic attenuation and pore fluid viscosity in clay rich reservoir sandstones the frequency dependence of seismic attenuation in a suite of clay rich reservoir sandstones was investigated in the laboratory compressional and shear wave velocities vp and vs and quality factors qp and qs were measured as functions of pore fluid viscosity at an effective pressure of 50 mpa and at an experimental frequency of about 0 8 mhz using the pulse echo technique the experimental viscosity ranged from 0 3 to 1000 centipoise which gives equivalent frequencies for a water saturated sandstone of 2 6 mhz to 780 hz assuming a global flow loss mechanism two types of behavior were observed high permeability greater than 100 millidarcies sandstones tend to show variable qp and qs which are similar in magnitude to those predicted by the biot theory over the viscosity range 0 3 to about 20 centipoise equivalent frequency range 2 6 mhz to about 39 khz low permeability less than 50 millidarcies sandstones tend to show almost constant qp and qs over the experimental viscosity range that are

observation of the surface horizontal thermohaline variability at mesoscale to submesoscale in the north eastern subtropical atlantic ocean the seasonal variability of the surface horizontal thermohaline structure is investigated in the north eastern atlantic surface salinity maximum ssm at length scales from five to hundreds of kilometers i e at submesoscale to mesoscale the near surface temperature and salinity data from merchant ship thermosalinograph tsg transects across the atlantic are used to compute the horizontal temperature salinity and density fluctuations and the density ratio during late winter in the north eastern ssm thermohaline compensation is observed for wavelengths from 5 km to more than 200 km in spite of large and sharp surface thermohaline fronts a weak density surface horizontal gradient is observed temperature and salinity exhibit an energetic spectra in k 2 slope scale between 20 100 km scale and a steeper slope at shorter wavelengths while density spectra exhibit lower energy level with a clear k 3 slope below 20 km consistent with interior quasigeostrophic turbulence during summer in the north eastern ssm salinity and temperature gradients are no longer compensated due to strong atmospheric heating of the upper ocean in comparison with winter the surface density spectrum is enhanced with a flatter slope between k 2 and k 1 between 5 and 20 km

low mode internal tides and balanced dynamics disentanglement in altimetric observations synergy with surface density observations the performance of a tentative method that disentangles the contributions of a low mode internal tide on sea level from that of the balanced mesoscale eddies is examined using an idealized high resolution numerical simulation this disentanglement is essential for proper estimation from sea level of the ocean circulation related to balanced motions the method relies on an independent observation of the sea surface water density whose variations are 1 dominated by the balanced dynamics and 2 correlate with variations of potential vorticity at depth for the chosen regime of surface intensified turbulence the surface density therefore leads via potential vorticity inversion to an estimate of the balanced contribution to sea level fluctuations the difference between instantaneous sea level presumably observed with altimetry and the balanced estimate compares moderately well with the contribution from the low mode tide application to realistic configurations remains to be tested these results aim at motivating further developments of reconstruction methods of the ocean dynamics based on potential vorticity dynamics arguments in that context they are particularly relevant for the upcoming wide swath high resolution altimetric missions swot

lateral dispersion over the continental shelf analysis of dye release experiments lateral dispersion over the continental shelf was examined using dye studies performed as a part of the coastal mixing and optics experiment four experiments performed at intermediate depths each lasting 2 5 5 days were examined in some cases the dye patches remained fairly homogeneous both vertically and horizontally throughout an experiment in other cases significant patchiness was observed on scales ranging from 2 to 10 m vertically and a few hundred meters to a few kilometers horizontally the observations showed that the dye distributions were significantly influenced by shearing and straining on scales of 5 10 m in the vertical and 1 10 km in the horizontal superimposed on these larger scale distortions were simultaneous increases in the horizontal second moments of the dye patches with corresponding horizontal diffusivities based on a fickian diffusion model of 0 3 4 9 m 2 s 1 analysis of the dye data in concert with shear estimates from shipboard acoustic doppler current profiler observations showed that the existing paradigms of shear dispersion and dispersion by interleaving water masses cannot account for the observed diffusive spreading of the dye patches this result suggests that some other mechanisms provided an additional diffusivity of order 0 2 4 6 m 2 s 1 an alternative mechanism dispersion by vortical motions caused by the relaxation of diapycnal mixing events may explain the observed dispersion in some cases

the mutual climatic range method of palaeoclimate reconstruction based on insect fossils new applications and interhemispheric comparisons abstract the mutual climatic range mcr method of palaeoclimate reconstruction has been employed in europe for the last decade a quantitative calibrated method mcr has many advantages over qualitative methods more recent applications deal with eastern and central north america and the method is also being developed for desert and arctic faunas the climate envelopes for north american beetles have been compiled using a 25 km gridded north american climate database that pairs climate parameters with modern collection sites modern tests of the reliability of the mcr method for north american species yielded similar results to prior european tests linear regressions of predicted on observed values yielded equations used to calibrate the mcr estimates work is under way to develop mcr estimates of mean annual precipitation for fossil assemblages from the desert southwest where moisture conditions may play a more important role in determining beetle species ranges an examination of british and north american mean july temperature reconstructions during the late wisconsinan glacial interval compares and contrasts three sets of records the north american records show no indication of the younger dryas cooling that is clearly marked in records from northwest europe the mcr method adds vigour to our reconstructions and allows us to compare between regions and with other palaeoenvironmental methods

holocene and modern sediment storage in the subtropical macrotidal fitzroy river estuary southeast queensland australia the fitzroy river estuary is a macrotidal tide dominated estuary located in the dry tropics of central queensland and represents the major source of terrestrial sediment to the southern great barrier reef gbr lagoon the estuary currently receives most of its sediment during large episodic floods that are typically associated with cyclones mean annual sediment budgets for such systems are difficult to estimate due to the sporadic nature of flood discharge events which are highly seasonal and vary greatly in magnitude between years we have estimated the quantity and long term rate of accumulation of catchment derived sediment in the estuarine floodplain using the holocene stratigraphic sequence determined from a series of sediment cores dated with radiocarbon and optically stimulated luminescence osl methods approximately 13 760 million tonnes mt of fluvial sediment has accumulated in the fitzroy estuary during the past 8000 years which equates to an average of 1720 kt yr 1 sediment has accumulated in the fitzroy estuary during the past 8000 years which equates to an average of 1720 kt yr 1 over the past 100 years sediment accumulation has been focused around mangrove and tidal creek environments which cover an area of 13 0 km 2 cores from the tidal creeks dated using cs c 137 pb 210 and osl provide sedimentation rates of approximately 15 mm yr 1 for the past 45 120 years or sediment mass accumulation of 1700 kt yr 1 which includes a component that is reworked into the estuary by tidal currents combined with the small amount of sediment that accumulates on the floodplain during floods similar to 1 mm yr 1 640 kt yr 1 we estimate that approximately 2350 kt yr 1 of sediment is trapped in the modem lower floodplain and estuary this estimate of sediment storage suggests that greater than 50 of the modem mean annual sediment discharge of the fitzroy river 4162 kt yr 1 may be retained in the lower floodplain and estuary these results provide useful insights into the spatial pattern of sedimentation long term rates of accumulation and estimates of sediment trapping in a tropical macrotidal sedimentary system crown copyright c 2007 published by elsevier b v all rights reserved

when mixed layers are not mixed storm driven mixing and bio optical vertical gradients in mixed layers of the southern ocean author s carranza mm gille st franks pjs johnson ks pinkel r girton jb abstract 2018 american geophysical union all rights reserved mixed layers are defined to have homogeneous density temperature and salinity however bio optical profiles may not always be fully homogenized within the mixed layer the relative timescales of mixing and biological processes determine whether bio optical gradients can form within a uniform density mixed layer vertical profiles of bio optical measurements from biogeochemical argo floats and elephant seal tags in the southern ocean are used to assess biological structure in the upper ocean within the hydrographically defined mixed layer the profiles show significant vertical variance in chlorophyll a chl a fluorescence and particle optical backscatter biological structure is assessed by fitting chl a fluorescence and particle backscatter profiles to functional forms i e gaussian sigmoid exponential and their combinations in the southern ocean which characteristically has deep mixed layers only 40 of nighttime bio optical profiles were characterized by a sigmoid indicating a well mixed surface layer of the remaining 60 that showed structure 40 had a deep fluorescence maximum below 20 m depth that correlated with particle backscatter furthermore a significant fraction of these deep fluorescence maxima were found within the mixed layer 20 80 depending on mixed layer depth definition and season results suggest that the timescale between mixing events that homogenize the surface layer is often longer than biological timescales of restratification we hypothesize that periods of quiescence between synoptic storms which we estimate to be 3 5 days depending on season allow bio optical gradients to develop within mixed layers that remain homogeneous in density

seasonal evolution of upper ocean horizontal structure and the remnant mixed layer 1 we discuss the seasonal evolution of upper ocean thermohaline structure at small horizontal scales the upper 350 m of a 1000 km long section in the subtropical north pacific was observed in winter spring and summer with 3 14 km horizontal resolution four vertical regions had distinct density and salinity structure the mixed layer remnant mixed layer high stratification layer and permanent thermocline the remnant mixed layer consists of water from the winter mixed layer left over after restratification the remnant mixed layer was most similar to the mixed layer in winter and spring and most similar to the high stratification layer below in summer the high stratification layer had elevated stratification that varied seasonally the permanent thermocline varied little seasonally and was horizontally and vertically uniform in comparison in all seasons density ratios showed that mixed layer s differences tended to compensate in density with the strongest tendency toward compensation in winter density ratios were temperature dominated in the remnant mixed layer consistent with salt fingering salinity anomalies were largest at the surface and decayed with depth in all seasons spectra of isopycnal depth and s anomalies along isopycnals are compared between the three seasons and four vertical layers isopycnal depth variance at 30 46 km wavelengths decreased from winter to spring to summer by a factor of 2 10 in stratified regions by treating salinity anomalies as a tracer the effective isopycnal diffusivity in the remnant mixed layer was estimated to be 1 4 m2 s 1 over 30 46 km wavelengths

strontium content of ostracods indicates lacustrine palaeosalinity individual non marine ostracod valves contain sr in proportion to the sr content of their host lake water two commonly coexisting large planktonic species mytilocypris praenuncia and australocypris robusta have a sr distribution coefficient kd sr ca of 0 082 which is independent of temperature in the range 10 18 c if the relationship between salinity and the sr content of a hydrologically simple lake is known palaeosalinities can be calculated from fossil ostracods we present here palaeosalinities for the past 10 000 yr for lake keilambete victoria calculated from ostracod sr ca of fossil material which are in striking agreement with independent interpretations of palaeosalinity the range of salinity spans 14 95 we also show that a reliable quantitative continuous indicator of lacustrine palaeosalinity is important for the elucidation of continental palaeoenvironments for palaeoclimatology and archaeology and ocean continent climatic correlations and interactions

towed thermistor chain observations of fronts in the subtropical north pacific a thermistor chain was towed 1400 km through the eastern north pacific subtropical frontal zone in january 1980 the observations resolve surface layer temperature features with horizontal wavelengths of 0 2 200 km and vertical scales of 10 70 m the dominant features which have horizontal wavelengths of 10 100 km amplitudes of 0 2 1 0 c and random orientation likely arise from baroclinic instability associated with them is a plateau below 0 1 cpkm in the horizontal temperature gradient spectrum strong temperature fronts o 1 2 c 3 10 km are observed near 33 n 31 n and 27 n temperature variability is partially density compensated by salinity with the fraction of compensation increasing northward there is evidence of vertical mixing during high winds temperature at 15 m depth is roughly normally distributed around the climatological surface mean with a standard deviation of approximately 0 5 c the standard deviation would correspond to an adiabatic meridional displacement of 80 100 km in the mean gradient horizontal temperature gradient at 15 m depth has maximum values in excess of 0 25 c 100 m and kurtosis near 80 in the band 0 10 1 cpkm the 15 m gradient spectrum is inversely proportional to wave number consistent with predictions from geostrophic turbulence theory while the spectrum at 70 m depth has additional variance that is consistent with garrett munk internal wave displacements

characterizing horizontal variability and energy spectra in the arctic ocean halocline energy transfer from the atmosphere into the upper arctic ocean is expected to become more efficient as summer sea ice coverage decreases and multiyear ice thins due to recent atmospheric warming however relatively little is known about how energy is transferred within the ocean by turbulent processes from large to small scales in the presence of ice and how these pathways might change in future this study characterises horizontal variability in several regions of the eurasian arctic ocean under differing sea ice conditions historic along track ctd data collected by a royal navy submarine during summer 1996 allows a unique examination of horizontal variability and associated wavenumber spectra within the arctic ocean halocline spectral analysis indicates that potential energy variance under perennial sea ice in the amundsen basin is o 100 less than within the marginal ice zone miz of fram strait spectra from all regions show a transition in scaling at wavelengths of approximately 5 to 7 km at scales greater than the transition wavelength to 50 km energy spectra are consistent with a k 3 scaling where k is wavenumber and interior quasi geostrophic dynamics the scaling of spectra at these scales is extremely similar between regions suggesting similar dynamics and energy exchange pathways the k 3 scaling is steeper than typically found in regions of mid latitude open ocean at scales below the transition wavelength to 300 m spectra are close to a k 5 3 scaling or flatter indicating a change in dynamics which is potentially due to internal waves dominating variability at small scales this article is protected by copyright all rights reserved

four views of a portion of the north atlantic subtropical gyre abstract data from four cruises to the triangle centered at 27 n 32 30 w were smoothed by fitting second degree polynomials at each of about 30 different density surfaces the density intervals were p 0 3 corresponding to about 50 db intervals in pressure from the polynomials determination was made of central values horizontal derivatives and laplacians of the fields of pressure salt oxygen and dynamic height in addition maps of the fits and deviations of each nation from the smoothed fits were produced from the steady advective diffusive equation and the smoothed fits to the age oxygen and dynamic height fields the lateral isopycnal diffusivity as estimated to be kh 0 5 103 m2 s 1 although the salt field was reasonably stable from cruise to cruise the variability of the baroclinic velocity shear was found to be as large as the baroclinic shear itself the maps suggest a wobble of the gyre the standard deviation of the fluctuations at each nation from the smoothed fits when norma

thermohaline variability in the upper ocean the main goal of this exploratory study is to determine how the temperature salinity relationship changes with horizontal length scale and depth in the ocean temperature and salinity were measured on a range of scales from 4 m to 1000 km towing a seasoar along isobars and isopycnals in the subtropical gyre of the north pacific during the winter of 1997 the wavelet transform technique is used to compute the horizontal density ratio and thermohaline variability as a function of scale and location measurements along an isobar in the mixed layer show that the horizontal density ratio is 1 at all scales observed that is horizontal temperature and salinity gradients tend to cancel each other in their effect on density thermohaline variability at small scales is intermittent and clusters around large scale thermohaline anomalies below the base of the mixed layer horizontal gradients of temperature are only partially opposed by salinity and the density ratio is close to 2 in the thermocline the distribution of thermohaline variability is uniform along isobars but intermittent and colocated at different scales along isopycnals density compensated variability ubiquitous in the mixed layer is reduced along deeper isopycnals compensation of horizontal temperature and salinity gradients supports recent theoretical ideas that mixing in the winter mixed layer depends on horizontal density gradients

rock anelasticity due to patchy saturation and fabric heterogeneity a double double porosity model of wave propagation heterogeneity of rock s fabric can induce heterogeneous distribution of immiscible fluids in natural reservoirs since the lithological variations mainly permeability may affect fluid migration in geological time scales resulting in patchy saturation of fluids therefore fabric and saturation inhomogeneities both affect wave propagation to model the wave effects attenuation and velocity dispersion we introduce a double double porosity model where pores saturated with two different fluids overlap with pores having dissimilar compressibilities the governing equations are derived by using hamilton s principle based on the potential energy kinetic energy and dissipation functions and the stiffness coefficients are determined by gedanken experiments yielding one fast p wave and four slow biot waves three examples are given namely muddy siltstones clean dolomites and tight sandstones where fabric heterogeneities at three different spatial scales are analyzed in comparison with experimental data in muddy siltstones where intrapore clay and intergranular pores constitute a submicroscopic double porosity structure wave anelasticity mainly occurs in the frequency range 104 107 hz while in pure dolomites with microscopic heterogeneity of grain contacts and tight sandstones with mesoscopic heterogeneity of less consolidated sands it occurs at 103 107 hz and 101 103 hz seismic band respectively the predicted maximum quality factor of the fast compressional wave for the sandstone is the lowest approximately 8 and that of the dolomite is the highest the results of the diffusive slow waves are affected by the strong friction effects between solids and fluids the model describes wave propagation in patchy saturated rocks with fabric heterogeneity at different scales and the relevant theoretical predictions agree well with the experimental data in fully and partially saturated rocks

changes in the rates of floodplain and in channel bench accretion in response to catchment disturbance central queensland australia analysis of the changes in rates of catchment sediment storage can provide material evidence of the impact of landscape disturbance on catchment sediment flux a number of studies have suggested increased sediment yields from the rivers draining to the great barrier reef since european settlement in the mid nineteenth century many of these predictions which indicate increases between four to ten times the pre disturbance estimates are based on large scale catchment modelling that make some critical assumptions about pre disturbance erosion rates and or sediment delivery ratios in addition the majority have not been validated by empirical data this study uses single grain osl dating and 137cs depth profiles to determine pre and post floodplain accretion rates in theresa creek a subcatchment of the dry tropical fitzroy river basin we demonstrate that floodplain accretion rates have increased by three to four times since european settlement ca a d 1850 decreased rates of floodplain accretion since the mid twentieth century at sites contributed to by gullied terrain suggest a decrease in the supply of sediment derived from gully networks in contrast floodplain accretion rates from areas dominated by cultivation remain high widespread in channel benches deposited since european settlement are stable and appear to be important stores of large volumes of sediment low magnitude increases in post disturbance floodplain sedimentation rates 3 to 4 times in comparison to those reported from mainly temperate climates 10 to 100 times are attributed to the naturally high sediment loads typical of dry tropical catchments consequently previous predictions of large post disturbance increases in sediment yields from large dry tropical catchments draining to the great barrier reef are likely to be overestimates

seismic attenuation due to heterogeneities of rock fabric and fluid distribution jing ba 1 2 jose m carcione3 and weitao sun4 1school of mathematics and statistics xi an jiaotong university 710049 xi an china e mail jba uh edu 2department of earth and atmospheric sciences university of houston houston tx 77204 usa 3istituto nazionale di oceanografia e di geofisica sperimentale ogs borgo grotta gigante 42c sgonico trieste i 34010 italy 4zhou pei yuan center for applied mathematics tsinghua university 100083 beijing china

the frequency of lamination in the sediments of lake barrine tropical north east australia during the last five millennia abstract at lake barrine 17 15 s 145 38 e 721 m a s l under water 55 m deep the uppermost sediment is composed of alternating detritus poor and detritus rich laminae the former are interpreted as the continuous sedimentation mostly plankton from the undisturbed water body the latter as redeposition during turbulent periods induced by unusually cold winters of material previously accumulated under shallower water a continuous 4 5 m long stratigraphic record from beneath the deepest water 67 m consists of about 3000 individual laminations punctuated by characteristic relatively thick marker bands each lamina was measured and allocated to one of the two categories a chronology based on 28 radiocarbon dates monotonically decreasing in age with decreasing depth established a span from 5 ka cal bp to 1987 ad the collection year the plot of the durations of detritus poor laminations hence the return times of laminating events is divisible into 20 sections laminating events are not annual but 80 of return times lie between 1 and 6 years apart from the lowermost three sections 5 ka 3 9 ka having a greater number of long return times than the rest there is no systematic change in the modes or ranges of the relative frequencies of return times between sections prediction of the characteristics of a section from those of its predecessor is impossible nor within a section is any return time a good predictor of the subsequent one extreme events are indicated most obviously by the marker bands which represent periods of unusual turbulence in the water body perhaps by the occurrence of several consecutive very cold winters or the passage of a cyclonic wind directly over the lake long placid periods evidenced by thick detritus poor laminae spanning 10 years are not systematically distributed through time except for their absence from 3 0 ka to 2 3 ka and their concentration from 5 0 ka to 4 4 ka uncertainties imposed by the methods used are discussed as are those relating to their palaeoclimatic application

3h and 3he in the beta triangle observations of gyre ventilation and oxygen utilization rates abstract isopycnal maps of 3h 3he age with about 100 km resolution have been obtained for a 1000 km scale area in the eastern subtropical north atlantic the midscale texture of the maps is consistent with isopycnal diffusivities of order 500 m 2 s 1 analysis of the distributions within the context of advection diffusion equations reveals that the larger scale 3h 3he age gradients observed within the area are not seriously affected by mixing on those surfaces that outcrop in the region of ekman downwelling thus isopycnal velocities can be estimated from 1 but record only the velocity component normal to the outcrop the velocities thus obtained agree well with geostrophic estimates although the comparison is flawed by the fundamental mismatch in timescales between the two techniques backward extrapolation of the maps to zero age outcrop positions indicate that the contribution of unventilated older recirculated water to the gyre flow above 600 m depth is small in this area no more than 20

thermohaline structure in the california current system observations and modeling of spice variance 1 upper ocean thermohaline structure in the california current system is investigated using sustained observations from autonomous underwater gliders and a numerical state estimate both observations and the state estimate show layers distinguished by the temperature and salinity variability along isopycnals i e spice variance mesoscale and submesoscale spice variance is largest in the remnant mixed layer decreases to a minimum below the pycnocline near 26 3 kg m 3 and then increases again near 26 6 kg m 3 layers of high low meso and submesoscale spice variance are found on isopycnals where large scale spice gradients are large small consistent with stirring of large scale gradients to produce smaller scale thermohaline structure passive tracer adjoint calculations in the state estimate are used to investigate possible mechanisms for the formation of the layers of spice variance layers of high spice variance are found to have distinct origins and to be associated with named water masses high spice variance water in the remnant mixed layer has northerly origin and is identified as pacific subarctic water while the water in the deeper high spice variance layer has southerly origin and is identified as equatorial pacific water the layer of low spice variance near 26 3 kg m 3 lies between the named water masses and does not have a clear origin both effective horizontal diffusivity h and effective diapycnal diffusivity v are elevated relative to the diffusion coefficients set in the numerical simulation but changes in h and v with depth are not sufficient to explain the observed layering of thermohaline structure

evidence for early postglacial warming in mount field national park tasmania abstract situated between the western pacific warm pool to the north and antarctica to the south tasmania is an ideal location to study both postglacial and holocene paleoclimates few well dated quantitative temperature reconstructions exist for the region so that important questions about the occurrence and magnitude of events such as the antarctic cold reversal and younger dryas in tasmania remain unanswered here we provide chironomid based reconstructions of temperature of the warmest quarter twarm for two small subalpine lakes eagle and platypus tarns mount field national park shortly after deglaciation twarm reached modern values by approximately 15 000 cal a bp and remained high until 13 000 cal a bp after which temperatures began to cool steadily reaching a minimum by 11 100 10 000 cal a bp these results are consistent with sea surface temperature sst reconstructions from south of tasmania but are in stark contrast to temperature inferences drawn from vegetation reconstructions based on pollen data that indicate cool initial temperatures followed by a broad warm period between 11 600 6800 cal a bp 10 000 6000 14c a bp the chironomid record broadly matches the summer insolation curve whereas the vegetation record and associated climate inferences mirror winter insolation the antarctic cold reversal and younger dryas cold events are not evident in the chironomid inferred temperatures but the antarctic cold reversal is evident in the loss on ignition curves

the significance of maar volcanoes for palaeoclimatic studies in china abstract the sediments of maar lakes often provide paleoenvironmental records which are highly suitable for palaeoclimatic studies the main advantages of the records from maar lakes compared with other lacustrine records are as follows first the presence of varves annually laminated layers and tephra layers as well as other materials like terrestrial plant macrofossils charcoals organic carbon organic shells suitable for isotopic dating like ams 14c 210pb 137cs 238u 230th 40ar 39ar provides the possibility of developing several independent chronologies enabling the development of robust high resolution chronologies second maars and maar lakes can provide continuous sedimentary records spanning tens of thousands of years tianyang maar in china is hosted the longest known record spanning at least 400 kyr bp that are ideal for the investigation of climate change on different timescales including orbital millennial centennial and annual decadal third recent studies of biomarkers based on long chain alkenones lcas and glycerol dialkyl glycerol tetraethers gdgts have demonstrated the potential of maar lakes for quantitative paleotemperature reconstruction in this study we review some of the more significant achievements of palaeoclimatic research based on maar lake sediment sequences from china with the focus on chronology multiple timescales and quantitative paleoclimatic reconstruction

holocene sediments of lake barrine north east australia and their implications for the history of lake and catchment environments abstract lake barrine 17 15 s 145 38 e 721 m a s l lies in a maar crater surrounded by tropical rainforest its surface area is 1 km2 and its maximum depth 67 m it has no inflow streams and an outlet only active in the wet summer months the sediments underlying the lake have been investigated by numerous mackereth cores and in situ frozen slabs in addition to lithological descriptions selected samples have been analysed for grain size bulk density and combustible content mineralogy and chemistry palaeomagnetism pollen and charcoal a chronology was established from radiocarbon dating of 211 sediment samples the deposits are divisible into three main strata between about 16 ka and 9 7 ka cal bp they are mainly inorganic representing occasional very energetic inwash from the lightly vegetated inner walls of the crater only a few small enclaves were perennially flooded between 9 7 and 5 4 ka cal bp sediments were for the most part finely grained with a substantial organic component their indications are of a water level rising overall but not at a constant rate from time to time erosion and redeposition of marginal materials and older sediments took place by 7 3 ka bp as rainforest began to cover the catchment the water level had risen sufficiently for reducing conditions to be established in its deeps and subsequent deposits indicated pedogenesis beneath the forest and reduced runoff to the lake between 9 7 and 7 3 ka cal bp the catchment erosion rate was 859 kg dry wt ha 1 ka 1 but this fell to 267 kg ha 1 ka 1 from 7 3 to 5 4 ka cal bp from 5 4 ka cal bp to the present the sediments beneath 55 m of the modern lake are strongly and finely laminated this was the result of intermittent relocation of detritus from shallower to deeper water when the lake s thermal stability was reduced by unusually low winter temperatures the resultant lamination being preserved under a persistent monimolimnion lamination counts indicate that this has happened more than a thousand times in the last 5 4 ka by 3 2 ka cal bp the water level had reached the modern outlet and its oscillations thereby minimised between 5 4 ka cal bp and 3 2 ka cal bp the catchment sediment yield was 112 kg ha 1 ka 1 rising to 146 kg ha 1 ka 1 thereafter in the period between 9 7 and 3 2 ka cal bp the lake volume increased from virtually nothing to almost 36 gl

smos salinity in the subtropical north atlantic salinity maximum 2 two dimensional horizontal thermohaline variability the horizontal thermohaline seasonal variability of the surface ocean is investigated in the subtropical north atlantic surface salinity maximum sssmax region satellite sea surface temperature and salinity are used along with high resolution thermosalinograph data and argo interpolated products to study the horizontal two dimensional field of density and thermohaline variability during late winter compensated temperature and salinity gradients at large and mesoscale are observed northeast of the sssmax in the azores front current region in spite of the large and sharp surface thermohaline fronts satellite measurements reveal a rather weak surface horizontal density gradient during summer the front is dominated by salinity gradients south of the sssmax at large scales the density ratio is controlled by the salinity gradient and the horizontal density gradient is enhanced by a constructive contribution of opposite salinity and temperature gradients

on the density ratio balance in the central water abstract an equation for the conservation of density ratio on isopycnal surfaces is derived it is shown that a vertical shear can modify the density ratio if salinity and temperature gradients exist along isopycnals the mixing processes of turbulence salt fingering and lateral isopycnal mixing are evaluated for possible balances with the shear term in the rp constant central waters it is found that turbulence cannot provide a balance and that isopycnal mixing can balance only with a particular vertical variation in the mixing rate salt firm however provide a simple balance between the shear term and the vertical variation of flux divergence since beat and salt are transported at different rates the conservation of density ratio should provide a useful constraint on mixing estimates from hydrographic data in both double diffusive and non double diffusive regimes and could be applicable to modelling studies of the temperature salinity relation in the thermocline

mixed layer instabilities and restratification abstract the restratification of the oceanic surface mixed layer that results from lateral gradients in the surface density field is studied the lateral gradients are shown to be unstable to ageostrophic baroclinic instabilities and slump from the horizontal to the vertical these instabilities which are referred to as mixed layer instabilities mlis differ from instabilities in the ocean interior because of the weak surface stratification spatial scales are o 1 10 km and growth time scales are on the order of a day linear stability analysis and fully nonlinear simulations are used to study mlis and their impact on mixed layer restratification the main result is that mlis are a leading order process in the ml heat budget acting to constantly restratify the surface ocean climate and regional ocean models do not resolve the scales associated with mlis and are likely to underestimate the rate of ml restratification and consequently suffer from a bias in sea surface temperatures and ml depths in a

pore fluid effects on s wave attenuation caused by wave induced fluid flow we studied seismic attenuation of p and s waves caused by the physical mechanism of wave induced fluid flow at the mesoscopic scale stress relaxation experiments were numerically simulated by solving biot s equations for consolidation of 2d poroelastic media with finite element modeling the experiments yielded time dependent stress strain relations that were used to calculate the complex moduli from which frequency dependent attenuation was determined our model consisted of periodically distributed circular or elliptical heterogeneities with much lower porosityandpermeabilitythan thebackgroundmedia which contained 80 of the total pore space of the media this model can represent a hydrocarbon reservoir where the porous background is fully saturated with oil or gas and the low porosity regions are always saturated with water three different saturation scenarios were considered oil saturated 80 oil 20 water gas saturated 80 gas 20 water and fully water saturated media varying the dry bulk and shear moduli in the background and in the heterogeneities a consistent tendency was observed in the relative behavior of the s wave attenuation among the different saturation scenarios first in the gas saturated media the s wave attenuation was very low and much lower than in the oil saturated or in the fully water saturated media second at low frequencies the s wave attenuation was significantly higher in the oil saturated media than in the fully water saturated media the p wave attenuation exhibited a more variable relative behavior among the different saturation degrees based on the mechanism of wave induced fluid flow and on our numerical results we suggest that s wave attenuation could be used as an indicator of fluid content in a reservoir additionally we observed that impermeable barriers in the background can cause a significant increasein s waveattenuation thissuggests that s wave attenuation could also be an indicator of permeability changes in a reservoir due to for example fracturing operations

along isopycnal variability of spice in the north pacific two hydrographic surveys in the gulf of alaska and the north pacific subtropical gyre are presented both surveys are roughly perpendicular to lateral temperature gradients and were collected in the summer when there was a shallow mixed layer and a seasonal thermocline isopycnal displacements and horizontal velocities are dominated by internal waves spice anomalies along isopycnals are examined to diagnose lateral stirring mechanisms the spectra of spice anomaly gradients along near surface isopycnals roughly follow power laws of kx0 6 0 2 variance spectra power laws of kx 1 4 0 2 and in most cases the spectra become redder at depth the near surface spectra are possibly consistent with the predictions of quasi geostrophic turbulence theory when surface buoyancy effects are accounted for but the spectra at depth are inconsistent with any quasi geostrophic theory probability distributions of spice gradients exhibit a large peak at low gradients and long tails for large gradients symptomatic of fronts vertical coherence of the spice signal falls off with a decorrelation depth scale that has a maximum of about 80 m at 100 km wavelengths and depends on horizontal wavelength with a power law of approximately kx 1 2 lateral decorrelation length scales are 20 40 km close to the baroclinic rossby radius lateral stirring occurs over large scales with average lateral displacements of about 200 km in the upper 75 m decreasing to 100 km at greater depths the depth variation of the statistics indicates that time history of tracer stirring on each isopycnal is important or that there are unconsidered depth dependent stirring mechanisms

submesoscale water mass spectra in the sargasso sea submesoscale stirring contributes to the cascade of tracer variance from large to small scales multiple nested surveys in the summer sargasso sea with tow yo and autonomous platforms captured submesoscale water mass variability in the seasonal pycnocline at 20 60 m depths to filter out internal waves that dominate dynamic signals on these scales spectra for salinity anomalies on isopycnals were formed salinitygradient spectra are approximately flat with slopes of 20 2 6 0 2 over horizontal wavelengths of 0 03 10km while the two to three realizations presented here might be biased more representative measurements in the literature are consistent with a nearly flat submesoscale passive tracer gradient spectrum for horizontal wavelengths in excess of 1km a review of mechanisms that could be responsible for a flat passive tracer gradient spectrum rules out i quasigeostrophic eddy stirring ii atmospheric forcing through a relict submesoscale winter mixed layer structure or nocturnal mixed layer deepening iii a downscale vortical mode cascade and iv horizontal diffusion because of shear dispersion of diapycnal mixing internal wave horizontal strain appears to be able to explain horizontal wavenumbers of 0 1 7 cycles per kilometer cpkm but not the highest resolved wavenumbers 7 30cpkm submesoscale subduction cannot be ruled out at these depths though previous observations observe a flat spectrum well below subduction depths so this seems unlikely primitive equation numerical modeling suggests that nonquasigeostrophic subinertial horizontal stirring can produce a flat spectrum the last need not be limited to mode one interior or surface rossby wavenumbers of quasigeostrophic theory but may have a broaderband spectrum extending to smaller horizontal scales associated with frontogenesis and frontal instabilities as well as internal waves

sub mesoscale lateral density structure in the oceanic surface mixed layer 1 we investigate the horizontal scales of density variability in the surface mixed layer sml in the north pacific subtropical front stf during a period of highly variable atmospheric forcing wavelet analysis shows that horizontal density variability is not restricted to scales l 10 km as previously suggested but extends to l 2 km the limiting l varies strongly with location and corresponds to a local internal rossby radius that accounts for transient stratification above the seasonal thermocline density compensation in the sml achieved when temperature and salinity effects cancel in their effect on density occurs at 30 n at the climatological front associated with the northern boundary of the stf where large thermohaline gradients are observed at 28 n however temperature gradients within the sml are not compensated by salinity and horizontal density gradients result in 2 l 10 km our observations suggest dynamic processes restratify the sml at scales rarely resolved by numerical models of the sml

quantifying climate change in huelmo mire chile northwestern patagonia during the last glacial termination using a newly developed chironomid based temperature model abstract the development of quantitative temperature reconstructions in regions of paleoclimate interest is an important step for providing reliable temperature estimates in that region fossil chironomid assemblages have been studied in patagonia showing great promise for reconstructing paleotemperatures however there is still a lack of robust temperature inference models in that area to contribute to the understanding of climate change a transfer function using chironomids preserved in 46 lakes in chile and argentina was developed the best performing model to infer the mean air temperature of the warmest month was a 3 component wa pls model with a coefficient of correlation r 2 jack of 0 56 a root mean square error of prediction rmsep of 1 69 c and a maximum bias of 2 07 c this model was applied to the chironomids preserved in the sediment of the huelmo mire 41 31 s 73 00 w in the lake district of northwestern patagonia the reconstruction showed several cold spells one at 13 200 to 13 000 cal yr bp and a cooling trend between 12 600 and 11 500 cal yr bp associated with the younger dryas and or huelmo mascardi cold reversal hmcr our findings support climate models proposing fast acting inter hemispheric coupling mechanisms including the recently proposed bipolar atmospheric and or bipolar ocean teleconnections rather than a bipolar see saw model

the spatial distribution and annual cycle of upper ocean thermohaline structure 1 observations of the spatial distribution and persistence of thermohaline structure are presented and show how advection and diffusion affect a passive tracer more than two years of underwater glider observations in the central subtropical north pacific showed thermohaline variability over horizontal scales from 5 to 1300 km thermohaline fluctuations along isopycnals spice fluctuations were elevated in layers throughout the water column with the largest fluctuations near the surface and subtropical frontal regions fluctuations were uncorrelated between the layers but stirred by the same velocity field spice variance had local extrema in the vertical because of differences in source water properties and the influence of neighboring water masses spice variance spanned about three orders of magnitude along deeper isopycnals with larger variance where different water masses met and where velocity and vorticity variance were elevated horizontal wave number spectra of spice had slopes of 2 everywhere in the upper 1000 m submesoscale spice fluctuations had slopes in physical space near the ratio of the coriolis parameter to the buoyancy frequency f n consistent with predictions of quasi geostrophic theory in the mixed layer thermohaline structure had a significant annual cycle with smaller interannual differences thermohaline fluctuations left behind during restratification and isolated from the mixed layer decayed with time because of diffusion along isopycnals horizontal diffusivity estimates in the remnant mixed layer were 0 4 m2 s 1 at 15 28 km wavelengths and 0 9 m2 s 1 at 35 45 km wavelengths

mesoscale to submesoscale transition in the california current system part i flow structure eddy flux and observational tests in computational simulations of an idealized subtropical eastern boundary upwelling current system similar to the california current a submesoscale transition occurs in the eddy variability as the horizontal grid scale is reduced to o 1 km this first paper in a series of three describes the transition in terms of the emergent flow structure and the associated time averaged eddy fluxes in addition to the mesoscale eddies that arise from a primary instability of the alongshore wind driven currents significant energy is transferred into submesoscale fronts and vortices in the upper ocean the submesoscale arises through surface frontogenesis growing off upwelled cold filaments that are pulled offshore and strained in between the mesoscale eddy centers in turn some submesoscale fronts become unstable and develop submesoscale meanders and fragment into roll up vortices associated with this phenomenon are a large vertical vorticity and rossby number a large vertical velocity relatively flat horizontal spectra contrary to the prevailing view of mesoscale dynamics a large vertical buoyancy flux acting to restratify the upper ocean a submesoscale energy conversion from potential to kinetic a significant spatial and temporal intermittency in the upper ocean and material exchanges between the surface boundary layer and pycnocline comparison with available observations indicates that submesoscale fronts and instabilities occur widely in the upper ocean with characteristics similar to the simulations

mixing of a tracer in the pycnocline a patch of sulfur hexafluoride was released in may 1992 in the eastern north atlantic on an isopycnal surface near 300 m depth and was surveyed over a period of 30 months as it dispersed across and along isopycnal surfaces the diapycnal eddy diffusivity k estimated for the first 6 months was 0 12 0 02 cm2 s while for the subsequent 24 months it was 0 17 0 02 cm2 s the vertical tracer distribution remained very close to gaussian for the full 30 months as the root mean square rms dispersion grew from 5 to 50 m lateral dispersion was measured on several scales the growth of the rms width of the tracer streaks from less than 100 m to approximately 300 m within 2 weeks implies an isopycnal diffusivity of 0 07 m2 s at scales of 0 1 to 1 km larger than expected from the interaction between vertical shear of the internal waves and diapycnal mixing teasing of the overall patch initially about 25 km across into streaks with an overall length of 1800 km within 6 months supports predictions of exponential growth by the mesoscale strain field at a rate of 3 0 5 10 7 s 1 the rms width of these streaks estimated as 3 km and maintained in the face of the streak growth indicates an isopycnal diffusivity of 2 m2 s at scales of 1 to 10 km much greater than expected from internal wave shear dispersion the patch was painted in albeit streakily by 12 months confirming expectations from analytical and numerical models homogenization of the patch continued during the subsequent 18 months while the patch continued to spread with an effective isopycnal eddy diffusivity on the order of 1000 m2 s acting at scales of 30 to 300 km

the characteristics and source of laminated mud at lake barrine northeast australia abstract in a small 1 km 2 crater lake in the australian upland tropics 17 15 s 145 38 e 721 m a s l laminated mud has accumulated throughout the past 5 ka it is limited to a central region below 50 67 m of water where it is protected by a monimolimnion the contents of the laminae e g total lake products organic detritus diatoms pollen grains vivianite crystals distinguish two contrasting types namely detritus rich and detritus poor judged against radiocarbon dates over long sequences these couplets are not annual gravimetric mineralogical and chemical observations on the mud and on suspended organic and inorganic matter caught through several periods indicate some diagenetic changes across the mud water interface diatom analyses do not assist in relating mud type to source or period of origin the most likely mechanism of lamination is that continuous deposition of clay with small and varied detrital accompaniment is periodically enhanced by greater detrital input this occurs in some but not all periods of winter isothermy when ground temperatures fall to zero and below on several consecutive nights this leads to the stirring of sediments in water shallower than 50 m and their relocation in the deeper meromictic zone fine variations in e g diatom content partly independent of lamination type probably contain a wealth of detail about the lake s environmental history

horizontal density structure and restratification of the arctic ocean surface layer ice tethered profiler itp measurements from the arctic ocean s canada basin indicate an ocean surface layer beneath sea ice with significant horizontal density structure on scales of hundreds of kilometers to the order 1 km submesoscale the observed horizontal gradients in density are dynamically important in that they are associated with restratification of the surface ocean when dense water flows under light water such restratification is prevalent in wintertime and competes with convective mixing upon buoyancy forcing e g ice growth and brine rejection and shear driven mixing when the ice moves relative to the ocean frontal structure and estimates of the balanced richardson number point to the likelihood of dynamical restratification by isopycnal tilt and submesoscale baroclinic instability based on the evidence here it is likely that submesoscale processes play an important role in setting surface layer properties and lateral density variability in the arctic ocean

establishing a chronology for the last 1000 years of laminated sediment accumulation at lake barrine a tropical upland maar lake northeastern australia radiocarbon dates from the uppermost 115 cm of laminated mud beneath the centre of a small crater lake are affected by the residence time in the marginal shallows of the organic detritus which after transport to deep water forms alternate layers in the sediment column the delay is estimated from radiocarbon ages of source materials trapped seston and the upper levels of the sediment column based on the post bomb atmospheric radiocarbon flux the contaminating component does not reside uniquely in any specific fraction of a mud sample defined by alkali solubility and particle size but is generally associated with the detrital layers the lead 210 method together with proxy indications from charcoal exotic solanum pollen and meteorological correlations effectively replace radiocarbon for the dating of the sediment column from ad 1987 back to 1965 beyond that the selection of the youngest radiocarbon age from those in each of eight depth intervals leads to an acceptable estimate of accumulation rate to ad 1060

eddy stirring and horizontal diffusivity from argo float observations geographic and depth variability stirring along isopycnals is a significant factor in determining the distribution of tracers within the ocean salinity anomalies on density surfaces from argo float profiles are used to investigate horizontal stirring and estimate eddy mixing lengths eddy mixing length and velocity fluctuations from the ecco2 global state estimate are used to estimate horizontal diffusivity at a 300 km scale in the upper 2000 m with near global coverage diffusivity varies by over two orders of magnitude with latitude longitude and depth in all basins diffusivity is elevated in zonal bands corresponding to strong current regions including western boundary current extension regions the antarctic circumpolar current and equatorial current systems the estimated mixing lengths and diffusivities provide an observationally based data set that can be used to test and constrain predictions and parameterizations of eddy stirring

horizontal stratification during deep convection in the labrador sea abstractdeep convection the process by which surface waters are mixed down to 1000 m or deeper forms the primary downwelling of the meridional overturning circulation in the northern hemisphere high resolution hydrographic measurements from seagliders indicate that during deep convection though water is well mixed vertically there is substantial horizontal variation in density over short distances tens of kilometers this horizontal density variability present in winter january february contains sufficient buoyancy to restratify the convecting region to observed levels 2 5 months later as estimated from argo floating platforms these results highlight the importance of small scale heterogeneities in the ocean that are typically poorly represented in climate models potentially contributing to the difficulty climate models have in representing deep convection

the greenland sea tracer experiment 1996 2002 horizontal mixing and transport of greenland sea intermediate water in summer 1996 a tracer release experiment using sulphur hexafluoride sf6 was launched in the intermediate depth waters of the central greenland sea gs to study the mixing and ventilation processes in the region and its role in the northern limb of the atlantic overturning circulation here we describe the hydrographic context of the experiment the methods adopted and the results from the monitoring of the horizontal tracer spread for the 1996 2002 period documented by 10 shipboard surveys the tracer marked greenland sea arctic intermediate water gsaiw this was redistributed in the gyre by variable winter convection penetrating only to mid depths reaching at most 1800 m depth during the strongest event observed in 2002 for the first 18 months the tracer remained mainly in the greenland sea vigorous horizontal mixing within the greenland sea gyre and a tight circulation of the gyre interacting slowly with the other basins under strong topographic influences were identified we use the tracer distributions to derive the horizontal shear at the scale of the greenland sea gyre and rates of horizontal mixing at 10 and 300 km scales mixing rates at small scale are high several times those observed at comparable depths at lower latitudes horizontal stirring at the sub gyre scale is mediated by numerous and vigorous eddies evidence obtained during the tracer release suggests that these play an important role in mixing water masses to form the intermediate waters of the central greenland sea by year two the tracer had entered the surrounding current systems at intermediate depths and small concentrations were in proximity to the overflows into the north atlantic after 3 years the tracer had spread over the nordic seas basins finally by year six an intensive large survey provided an overall synoptic documentation of the spreading of the tagged gsaiw in the nordic seas a circulation scheme of the tagged water originating from the centre of the gs is deduced from the horizontal spread of the tracer we present this circulation and evaluate the transport budgets of the tracer between the gs and the surroundings basins the overall residence time for the tagged gsaiw in the greenland sea was about 2 5 years we infer an export of intermediate water of gsaiw from the gs of 1 to 1 85 sv 1 sv 106 m3 s 1 for the period from september 1998 to june 2002 based on the evolution of the amount of tracer leaving the gs gyre there is strong exchange between the greenland sea and arctic ocean via fram strait but the contribution of the greenland sea to the denmark strait and iceland scotland overflows is modest probably not exceeding 6 during the period under study

overview of the frontal air sea interaction experiment fasinex a study of air sea interaction in a region of strong oceanic gradients from 1984 to 1986 the cooperative frontal air sea interaction experiment fasinex was conducted in the subtropical convergence zone southwest of bermuda the overall objective of the experiment was to study air sea interaction on 1 to 100 km horizontal scales in a region of the open ocean characterized by strong horizontal gradients in upper ocean and sea surface properties ocean fronts provided both large spatial gradients in sea surface temperature and strong jetlike flows in the upper ocean the motivation for and detailed objectives of fasinex are reviewed then the components of the field program are summarized finally selected results are presented in order to provide an overview of the outcome of fasinex

the dynamics of chironomid assemblages and vegetation during the late quaternary at laguna facil chonos archipelago southern chile abstract we compare high resolution pollen and chironomid records from the last 15 000 yr in laguna facil southern chile major vegetation and chironomid changes are recorded between ca 14 900 and 14 700 cal yr bp during the lateglacial changes in the chironomid stratigraphy lag behind changes in the pollen stratigraphy suggesting that the chironomids are responding to changes in the tree canopy or in soil chemistry brought about by vegetational development at about 7200 cal yr bp there is a change in the chironomid stratigraphy in advance of changes in the vegetation this suggests that the response is to regional climatic change the relatively close correlation of the chironomid and pollen stratigraphies with changes in charcoal concentrations also implicates the importance of fire and or vulcanism in influencing the dynamics of forest and limnological systems there is no clear evidence of cooling during the younger dryas chronozone in laguna facil

the significance of chironomid analysis insecta diptera for paleolimnological research abstract consideration of the dipteran family chironomidae is an important aspect of microfossil analysis of lake sediments because chironomids provide information on the ecological characteristics of an earlier period of lake development chironomids are of particular interest because some species are typical of the profundal zone of eutrophic lakes and other of oligotrophic lakes as a result the major part of the literature on chironomid analysis deals with the use of these animals as indicators of trophic states during earlier periods of lake histories indeed some studies have shown that an oligotrophic profundal fauna was completely replaced by eutrophic species during lake development the chironomid fauna is not only influenced by factors connected with eutrophication but also by other events occurring during lake development such as changing climatic conditions which until now have hardly been discussed

shallow pycnoclines and mode water subduction in the eastern north atlantic abstract a lagrangian one dimensional model is used to study the subduction of subpolar mode water in the eastern north atlantic and to analyze recently observed hydrological features related to this process considering a southward moving column of mode water subduction occurs when the upper part of the column starts gaining buoyancy in an annual budget the seasonal pycnocline on top of the column can no longer be completely eroded in winter and it is shown how its remnant forms a shallow secondary pycnocline at about 200 m depth which isolates the lower part of the fluid column from the atmosphere this mechanism for the subduction of subpolar mode water induces a strong meridional gradient in the winter mixed layer depth the various components of the buoyancy input are thoroughly studied horizontal advection in the shallow ekman layer and vertical advection along the column are shown to modify significantly both the thermal and haline contents of the column with magnitudes comparable to the ai

a chironomid based transfer function for reconstructing summer temperatures in southeastern australia we present a new chironomid based temperature transfer function which was developed from a training set of 33 natural and artificial lakes from southeast australia from subtropical queensland to cool temperate tasmania multivariate statistical analyses cca pcca were used to study the distribution of chironomids in relation to the environmental and climatic variables seven out of eighteen available variables were significantly p 0 05 related to chironomid species variation and these were mean february temperature 9 5 ph 9 5 specific conductance 8 2 total phosphorous 8 potential evapotranspiration 8 chlorophyll a 6 9 and water depth 6 2 further pcca analyses show that mean february temperature mft is the most robust and independent variable explaining chironomid species variation the best mft transfer function was a partial least squares pls model with a coefficient of determination r2jackknifed of 0 69 a root mean squared error of prediction rmsep of 2 33 c and maximum bias of 2 15 c chironomid assemblages from actively managed reservoirs appear to match assemblages from equivalent natural lakes in similar climates and therefore can be included in the development of the chironomid transfer function although we cannot completely rule out some degree of endemism in the tasmanian chironomid fauna our analyses show that the degree of endemism is greatly reduced therefore integrating the existing chironomid transfer function for tasmania rees et al 2008 with this new model is a real possibility

forced imbibition into a limestone measuring p wave velocity and water saturation dependence on injection rate quantitative interpretation of time lapse seismic data requires knowledge of the relationship between elastic wave velocities and fluid saturation this relationship is not unique but depends on the spatial distribution of the fluid in the pore space of the rock in turn the fluid distribution depends on the injection rate to study this dependency forced imbibition experiments with variable injection rates have been performed on an air dry limestone sample water was injected into a cylindrical sample and was monitored by x ray computed tomography and ultrasonic timeof flight measurements across the sample the measurements show that the p wave velocity decreases well before the saturation front approaches the ultrasonic raypath this decrease is followed by an increase as the saturation front crosses the raypath the observed patterns of the acoustic response and water saturation as functions of the injection rate are consistent with previous observations on sandstone the results confirm that the injection rate has significant influence on fluid distribution and the corresponding acoustic response the complexity of the acoustic response that is not monotonic with changes in saturation and which at the same saturation varies between hydrostatic conditions and states of dynamic fluid flow may have implications for the interpretation of time lapse seismic responses

subtropical mode water in the northeast pacific basin a new type of mode water in the upper thermocline of the eastern subtropical north pacific is identified and examined using data from world ocean circulation experiment high resolution repeat expendable bathythermograph xbt section px37 and archives of historical xbt data this water mass labeled eastern subtropical mode water is characterized by a subsurface potential vorticity minimum and is located east of hawaii northeast pacific basin in a density range of 24 25 4 it is a distinct water mass from the classical subtropical mode water stmw of the western pacific eastern stmw is formed as a relatively deep late winter mixed layer associated with the subtropical subpolar water mass boundary near 25 30 n 135 140 w and is capped and subducted into the permanent thermocline along a section between san francisco and honolulu eastern stmw production is seen in every year for which there is adequate data in this section the volume of eastern stmw formed each winter and the temperature of the potential vorticity minimum are similar during the periods 1970 1979 and 1991 1997

a chironomid inferred summer temperature reconstruction from subtropical australia during the last glacial maximum lgm and the last deglaciation abstract a chironomid based mean february temperature reconstruction from welsby lagoon north stradbroke island australia covering the last glacial maximum lgm and deglaciation between c 23 2 and 15 5 cal ka bp is presented mean february temperature reconstructions show a maximum inferred cooling of c 6 5 c at c 18 5 cal ka bp followed by rapid warming to near holocene values immediately after the lgm the inferred timing magnitude and trend of maximum cooling and warming display strong similarities to marine records from areas affected by the east australian current eac the warming trend started at c 18 1 cal ka bp and is consistent with the start of deglaciation from antarctic records near holocene values are maintained through the deglaciation to 15 5 cal ka bp these records suggest that changes in the australian subtropics are linked to southern high latitudes

shallow salinity minima in the north pacific abstract ctd std data from 24 cruises in the north pacific are studied for their vertical salinity structure and compared to bottle observations a triple salinity minimum is found in two separated regions in the eastern north pacific in the first region bounded by the northern edge of the subarctic frontal zone and the 34 n front between 160 and 150 w a middle salinity minimum is found below the permanent pycnocline in the density range of 26 0 and 26 5 this middle minimum underlies reid s shallow salinity minimum and overlies the north pacific intermediate water npiw in the second region southeast of the first a seasonal salinity minimum appears above the shallow salinity minimum at densities lower than 25 1 the shallow salinity minimum and the npiw can be found throughout year while the seasonal minimum only appears in summer and fall the middle and shallow salinity minima as well as the seasonal minimum originate at the sea surface in the northeast pacific the properties at the m