dinoflagellate cyst based modern analogue technique at test a 300 year record from the gulf of taranto eastern mediterranean abstract to test the performance of dinoflagellate cyst based palaeoenvironmental reconstructions derived via the modern analogue technique mat and a non quantitative method we have compared reconstructions of mixed layer temperature sea surface temperature and mixed layer salinity of a well dated site from the gulf of taranto to instrumental data of air temperature precipitation and river discharge two hypotheses are tested the reconstructions of dinoflagellate cyst based mat improve when a a local reference dataset rather than an extra regional reference dataset is used b the reference and downcore datasets are corrected for species specific preservation prior to analysis this is achieved by executing four experiments based on different reference datasets 1 a north atlantic dataset including all species 2 a north atlantic dataset including degradation resistant species 3 a mediterranean dataset including all species 4 a mediterranean dataset including degradation resistant species only we show that mat based reconstructions improve when a local rather than an extra regional reference dataset is used exclusively including species resistant to degradation improves the reconstruction if an extra regional reference dataset is used but leads to considerable loss of variability if the local reference dataset is used both mat based and qualitative reconstructions correlate to instrumental data for industrial times for pre industrial times mat reconstructions of variability in temperature and salinity do not co vary with variability in the instrumental data whereas qualitative reconstructions provide a relatively good fit we suggest this to be a result of the anthropogenic influence on coastal marine ecosystems existing today at the majority of the coastal sample sites in the reference dataset as a result conditions at these sites do not correspond to pre industrial conditions we advise users of dinoflagellate cyst transfer functions to pay more attention to this aspect

winter to summer oceanographic observations in the arctic ocean north of svalbard oceanographic observations from the eurasian basin north of svalbard collected between january and june 2015 from the n ice2015 drifting expedition are presented the unique winter observations are a key contribution to existing climatologies of the arctic ocean and show a 100m deep winter mixed layer likely due to high sea ice growth rates in local leads current observations for the upper 200m show mostly a barotropic flow enhanced over the shallow yermak plateau the two branches of inflowing atlantic water are partly captured confirming that the outer yermak branch follows the perimeter of the plateau and the inner svalbard branch the coast atlantic water observed to be warmer and shallower than in the climatology is found directly below the mixed layer down to 800m depth and is warmest along the slope while properties inside the basin are quite homogeneous from late may onwards the drift was continually close to the ice edge and a thinner surface mixed layer and shallower atlantic water coincided with significant sea ice melt being observed this article is protected by copyright all rights reserved

late quaternary fluvial dynamics and landscape evolution at the lower shulaveris ghele river southern caucasus the southern caucasus was intensively settled through the neolithic period to present studies of late quaternary fluvial dynamics and landscape development at the lower shulaveris ghele river in southeastern georgia aid understanding of the quaternary history of this region our studies show that following river aggradation to form a fan shaped alluvial surface during the late pleistocene fluvial sedimentation shifted west leaving a fan surface subject only to local fluvial and colluvial processes as well as late neolithic settlement at about 6 ka the river avulsed to the east and eroded some late neolithic settlements occupying the eastern portion of the fan the avulsion was followed by 3 distinct episodes of aggradation at about 6 ka 3 2 ka and since 1 0 ka no such aggradation is evident in the early holocene regional holocene fluvial activity in this area was apparently influenced by vegetation dynamics possibly controlled by regional climatic and or anthropogenic factors and significantly differs from the eastern mediterranean region all late neolithic settlements were originally built far from an active river possibly indicating late neolithic water management systems

south indian countercurrent and associated fronts a striking feature of the south indian ocean circulation is the presence of the eastward south indian countercurrent sicc that flows in a direction opposite to that predicted by the classical theories of wind driven circulation several authors suggest that the sicc resembles the subtropical countercurrents stccs observed in other oceans which are defined as narrow eastward jets on the equatorward side of subtropical gyres where the depth integrated flow is westward these jets are associated with subsurface thermal fronts at thermocline depths by the thermal wind relation however the subsurface thermal front associated with the sicc has not been described to date other studies conjecture an important role for salinity in controlling the sicc in the present work we analyze three argo based atlases and data from six hydrographic cruises to investigate whether the sicc is accompanied by permanent thermal and density fronts including salinity effects the seasonal cycle of these fronts in relation to the sicc strength is also investigated we find that the sicc is better described as composed of three distinct jets which we name the northern central and southern sicc we find that the southern sicc around 26 s has an associated thermal front at subsurface depths around 100 200 m with salinity being of secondary importance the southern branch strength is related to mode waters poleward of the front similar to a stcc like current however the sicc multiple jet structure seems to be better described as resulting from pv staircases

can we map the interannual variability of the whole upper southern ocean with the current database of hydrographic observations with the advent of argo floats it now seems feasible to study the interannual variations of upper ocean hydrographic properties of the historically undersampled southern ocean to do so scattered hydrographic profiles often first need to be mapped to investigate biases and errors associated both with the limited space time distribution of the profiles and with the mapping methods we colocate the mixed layer depth mld output from a state of the art 1 12 drakkar simulation onto the latitude longitude and date of actual in situ profiles from 2005 to 2014 we compare the results obtained after remapping using a nearest neighbor nn interpolation and an objective analysis oa with different spatiotemporal grid resolutions and decorrelation scales nn is improved with a coarser resolution oa performs best with low decorrelation scales avoiding too strong a smoothing but returns values over larger areas with large decorrelation scales and low temporal resolution as more points are available for all resolutions oa represents better the annual extreme values than nn both methods underestimate the seasonal cycle in mld mld biases are lower than 10 m on average but can exceed 250 m locally in winter we argue that current argo data should not be mapped to infer decadal trends in mld as all methods are unable to reproduce existing trends without creating unrealistic extra ones we also show that regions of the subtropical atlantic indian and pacific oceans and the whole ice covered southern ocean still cannot be mapped even by the best method because of the lack of observational data

seaglider observations of equatorial indian ocean rossby waves associated with the madden julian oscillation during the cindy dynamo field campaign of september 2011 january 2012 a seaglider was deployed at 80 e and completed 10 north south sections between 3 and 4 s measuring temperature salinity dissolved oxygen concentration and chlorophyll fluorescence these high resolution subsurface observations provide insight into equatorial ocean rossby wave activity forced by three madden julian oscillation mjo events during this time period these rossby waves generate variability in temperature o 1 c salinity o 0 2 g kg 1 density o 0 2 kg m 3 and oxygen concentration o 10 mol kg 1 associated with 10 m vertical displacements of the thermocline the variability extends down to 1000 m the greatest depth of the seaglider observations highlighting the importance of surface forcing for the deep equatorial ocean the temperature variability observed by the seaglider is greater than that simulated in the ecco jpl reanalysis especially at depth there is also marked variability in chlorophyll fluorescence at the surface and at the depth of the chlorophyll maximum upwelling from rossby waves and local wind stress curl leads to an enhanced shoaling of the chlorophyll maximum by 10 25 m in response to the increased availability of nutrients and light this influence of the mjo on primary production via equatorial ocean rossby waves has not previously been recognized

lateral eddy mixing in the subtropical salinity maxima of the global ocean abstracta suite of observationally driven model experiments is used to investigate the contribution of near surface lateral eddy mixing to the subtropical surface salinity maxima in the global ocean surface fields of salinity are treated as a passive tracer and stirred by surface velocities derived from altimetry leading to irreversible water mass transformation in the absence of surface forcing and vertical processes the transformation rate can be directly related to the integrated diffusion across tracer contours which is determined by the observed velocities the destruction rates of the salinity maxima by lateral mixing can be compared to the production rates by surface forcing which act to strengthen the maxima the ratio of destruction by eddy mixing in the surface layer versus the surface forcing exhibits regional differences in the mean from 10 in the south pacific to up to 25 in the south indian furthermore the regional basins show seasonal and interannual variability in eddy mixing th

physical and biogeochemical controls on the variability in surface ph and calcium carbonate saturation states in the atlantic sectors of the arctic and southern oceans polar oceans are particularly vulnerable to ocean acidification due to their low temperatures and reduced buffering capacity and are expected to experience extensive low ph conditions and reduced carbonate mineral saturations states in the near future however the impact of anthropogenic co2 on ph and will vary regionally between and across the arctic and southern oceans here we investigate the carbonate chemistry in the atlantic sector of two polar oceans the nordic seas and barents sea in the arctic ocean and the scotia and weddell seas in the southern ocean to determine the physical and biogeochemical processes that control surface ph and high resolution observations showed large gradients in surface ph 0 10 to 0 30 and aragonite saturation state ar 0 2 to 1 0 over small spatial scales and these were particularly strong in sea ice covered areas up to 0 45 in ph and 2 0 in ar in the arctic sea ice melt facilitated bloom initiation in light limited and iron replete dfe 0 2 nm regions such as the fram strait resulting in high ph 8 45 and ar 3 0 along the sea ice edge in contrast accumulation of dissolved inorganic carbon derived from organic carbon mineralisation under the ice resulted in low ph 8 05 and ar 1 1 in areas where thick ice persisted in the southern ocean sea ice retreat resulted in bloom formation only where terrestrial inputs supplied sufficient iron dfe 0 2 nm such as in the vicinity of the south sandwich islands where enhanced ph 8 3 and ar 2 3 were primarily due to biological production in contrast in the adjacent weddell sea weak biological uptake of co2 due to low iron concentrations dfe 0 2 nm resulted in low ph 8 1 and ar 1 6 the large spatial variability in both polar oceans highlights the need for spatially resolved surface data of carbonate chemistry variables but also nutrients including iron in order to accurately elucidate the large gradients experienced by marine organisms and to understand their response to increased co2 in the future

chronology of neogene and quaternary uplift and magmatism in the caucasus constraints from k ar dating of volcanism in armenia abstract the greater caucasus is one of earth s highest actively uplifting mountain ranges the adjoining caspian sea basin contains a substantial proportion of its hydrocarbon reserves like other parts of the former soviet union the neogene and quaternary chronology of these important regions has not previously been well defined it has thus been impossible to obtain reliable estimates for rates of processes such as uplift of the caucasus and sedimentation in the caspian sea previous studies have established the relative timings of events in the region using correlation schemes between volcanism glaciations and the stratigraphy of the caspian basin however a range of absolute chronologies has previously been proposed for these sediments and igneous rocks based mainly on different interpretations of their magnetostratigraphic records by k ar dating we determine the ages of volcanism at three localities in armenia as 1 1 0 8 and 0 8 ma using these data and other evidence we propose a revision to the chronology of this region in which a distinctive brief interval of normal magnetic polarity in the local sedimentary and volcanic magnetostratigraphic records is matched to the cobb mountain event in the global record rather than the olduvai event or an earlier subchron as had previously been thought we thus interpret a 1 5 ma timing for the start of volcanism in the lesser caucasus and also suggest a 1 2 ma timing for the late akchagyl transgression of the caspian sea a key event in the regional stratigraphy when this water body reached its greatest extent we tentatively correlate this transgression with the melting event following glaciation during stage 36 of the oxygen isotope timescale which was thus the first time during the pleistocene when eastern europe was covered by a lowland ice sheet time averaged since 1 ma the flanks of the eastern greater caucasus mountains are shown to have uplifted at 0 6 mm a 1 and the lesser caucasus at 0 3 mm a 1 we show that the rate and spatial scale of this uplift are too great to be the result of plate convergence and suggest instead that this uplift is caused by crustal thickening due to inward lower crustal flow to beneath these mountain ranges at the start of magmatism in both the greater and lesser caucasus the estimated crustal thickness was 45 km we thus suggest that this magmatism has been caused by heating of the mantle lithosphere due to earlier crustal thickening the temperature rise required to initiate magmatism being the same in both cases

reply to comment on empirical stochastic ground motion prediction for eastern north america by behrooz tavakoli and shahram pezeshk by kenneth w campbell the shape of earthquake source spectrum and how it is scaled with earthquake parameters e g seismic moment stress parameter and rupture area has been widely examined and used as a guide for the prediction of earthquake ground motion at a specific region as we discussed in our 2005 article the most commonly used earthquake source model is based on brune s spectrum brune 1970 1971 that has had remarkable success in predicting a variety of measures of strong ground motion over the magnitude range from 4 to about 7 the basic seismological model of a ground acceleration spectrum has a simple 2 shape brune 1970 1971 this model assumes that the earthquake source is modeled as a circular fault source and the ground acceleration spectrum from this simplified source has an inversely 2 decay for frequencies below a source corner frequency and a flat level for frequencies greater than source corner frequency and less than site corner frequency the amplitude spectrum level begins to drop faster at higher frequencies beyond the site corner frequency the choices of source and site corner frequencies depend mainly on the earthquake size given by the seismic moment and the site condition e g respectively the seismic moment defines the size of the earthquake based on the product of the rigidity modulus the area of fault rupture and the average slip along the fault rupture for small earthquakes both the length and width of the fault rupture must increase in the same quantity with increasing magnitude based on assuming a circular fault source model in brune s source spectrum model the measure of the stress parameter is used as a parameter controlling the level of the amplitude spectrum above the source corner frequency the value of the stress parameter can be derived by differences between evaluating fourier spectra in

the palaeolimnology of the aral sea a review abstract formerly the fourth largest inland water body in the world the volume and area of the aral sea have decreased dramatically over the past 30 yr largely as a result of human actions throughout its approximately 2 million year history the fate of this water body has been intimately linked with that of its two main in flowing rivers the amu darya and the syr darya we present a review of the hydrological palaeontological and sedimentological evidence for the evolution of the aral sea based largely on russian literature although the structure of the aral basin can be traced back to the late neogene the sea has only existed in its present form for the past 8 10 ka and the holocene history has been shaped by regional climatic variations the development of the associated drainage system and anthropogenic forces past hydrological changes in the aral basin have led to systematic shifts in the level of the aral sea which are reflected sedimentologically through the deposition of transgressive and regressive sedimentary units and geomorphologically through the development of terraces all the above data are integrated to produced a late quaternary history of this important water body

holocene oscillations of the caspian sea and forecasts based on palaeogeographical reconstructions abstract investigation of deltas and terraces adjacent to the caspian sea has indicated the pattern of holocene fluctuations in level since the initiation of the earliest holocene transgression the surface of the caspian sea has varied between 20 and 32 m below modern sea level six transgressive episodes are recognized in the holocene record separated by regressive episodes when the level fell below 28 m a s l the modal holocene level of the caspian sea is estimated at 28 2 m a s l beginning in 1929 water levels fell rapidly in the caspian sea reaching 29 m a s l the lowest value in 400 years in 1977 however the water level began to rise a trend which has continued to the present currently the caspian sea surface stands at approximately 27 m a s l throughout the past 2500 years the level has not exceeded 25 m a s l and it is not anticipated to exceed this value in the near future the fluctuations recorded since 1929 fall within the range of variations expected from natural environmental factors which have operated since the early holocene

the bering slope current system revisited mean circulation and water properties within the aleutian basin of the bering sea are investigated using hydrographic and subsurface park pressure displacement data from a regional array of 14 profiling ctd floats after 10 days drifting at 1000 dbar each float measures temperature and salinity profiles as it rises to the surface and then transmits these data via satellites which also make several fixes of the float surface positions before it sinks again every fourth cycle the floats sink from 1000 dbar to a 2000 dbar target just prior to ascent to measure deeper profiles the 1000 dbar displacements estimated from the float surface position fixes reveal a coherent few centimeters per second northwestward flow along the northeastern boundary the deep signature of the bering slope current middepth water property distributions are consistent with cyclonic advection of warm water from the south around the basin eastward in the aleutian north slope current and then northwestward in the bering slope current geostrophic transport estimates relative to 1000 dbar also show cyclonic motion although with significant noise likely owing to the influence of mesoscale eddies the mean alongslope geostrophic transport of the bering slope current is determined between 0 and 1900 dbar relative to 1000 dbar and then combined with mean along slope velocities at 1000 dbar the result is an absolute geostrophic transport estimate with 95 confidence intervals for the along slope current offshore of the 1000 m isobath and between 0 and 1900 dbar of 5 8 61 7 3 106 m3 s 21

the atlantic subtropical cells inferred from observations the atlantic subtropical cells stcs are shallow wind driven overturning circulations connecting the tropical upwelling areas to the subtropical subduction regions in both hemispheres they are characterized by equatorward transport at thermocline level upwelling at the equator and poleward ekman transport in the surface layer this study uses recent data from argo floats complemented by ship sections at the western boundary as well as reanalysis products to estimate the meridional water mass transports and to investigate the vertical and horizontal structure of the stcs from an observational perspective the seasonally varying depth of meridional velocity reversal is used as the interface between the surface poleward flow and the thermocline equatorward flow the latter is bounded by the 26 0 kg m 3 isopycnal at depth we find that the thermocline layer convergence is dominated by the southern hemisphere water mass transport 9 0 1 1 sv from the southern hemisphere compared to 2 9 1 3 sv from the northern hemisphere and that this transport is mostly confined to the western boundary compared to the asymmetric convergence at thermocline level the wind driven ekman divergence in the surface layer is more symmetric being 20 4 3 1 sv between 10 n and 10 s the net poleward transports ekman minus geostrophy in the surface layer concur with values derived from reanalysis data 5 5 0 8 sv at 10 s and 6 4 1 4 sv at 10 n a diapycnal transport of about 3 sv across the 26 0 kg m 3 isopycnal is required in order to maintain the mass balance of the stc circulation

river inflow and salinity changes in the caspian sea during the last 5500 years abstract pollen spores and dinoflagellate cysts have been analysed on three sediment cores 1 8 1 4 m long taken from the south and middle basins of the caspian sea a chronology available for one of the cores is based on calibrated radiocarbon dates ca 5 5 0 8 cal ka bp the pollen and spores assemblages indicate fluctuations between steppe and desert in addition there are some outstanding zones with a bias introduced by strong river inflow the dinocyst assemblages change between slightly brackish abundance of pyxidinopsis psilata and spiniferites cruciformis and more brackish dominance of impagidinium caspienense conditions during the second part of the holocene important flow modifications of the uzboy river and the volga river as well as salinity changes of the caspian sea causing sea level fluctuations have been reconstructed a major change is suggested at ca 4 cal ka bp with the end of a high level phase in the south basin amongst other hypotheses this could be caused by the end of a late and abundant flow of the uzboy river now defunct carrying to the caspian sea either meltwater from higher latitudes or water from the amu daria a similar later clear phase of water inflow has also been observed from 2 1 to 1 7 cal ka bp in the south basin and probably also in the north of the middle basin

anomalous eddy heat and freshwater transport in the gulf of alaska characteristics of eddies in the gulf of alaska are assessed from january 2003 through april 2012 ensemble statistics for eddy subsurface water properties on isopycnals are computed using temperature and salinity profiles from argo profiling floats located within eddies which are identified in sea surface height using objective techniques ninety cyclonic and 154 anticyclonic eddies are identified during this period the anticyclonic eddies are strongly nonlinear and exhibit significant warm subsurface temperature anomalies and associated salty anomalies on isopycnals while no clear distinguishing subsurface anomalies on isopycnals are detected in association with the cyclonic eddies heat and freshwater fluxes for the eddies are estimated from integrations in depth coordinates the anticyclonic eddies transport heat both westward off the continental shelf into the subarctic gyre and westward within the alaskan stream however they transport salt into the subarctic gyre and freshwater within the alaskan stream in both pathways eddy heat and freshwater transport show possible year to year fluctuations varying from 0 to 50 4 1018 j a 1 and 16 8 to 7 4 km3 a 1 respectively the anticyclonic eddies are capped by relatively fresh water year round

empirical stochastic ground motion prediction for eastern north america an alternative approach based on a hybrid empirical model is utilized to predict the ground motion relationship for eastern north america ena in this approach a stochastic model is first used to derive modification factors from the ground motions in western north america wna to the ground motions in ena the ground motion parameters are then estimated to develop an empirical attenuation relationship for ena using empirical ground motion relationships from wna w e develop an empirical stochastic source model for both regions to obtain ground mo tions at different magnitude distance range of interest at short distances r 30 km and large magnitudes mw 6 4 an equivalent point source model is carried out to consider the effect of finite fault modeling on the ground motion parameters source focal depth and brune stress drop are assumed to be magnitude dependent we choose three well defined empirical attenuation relationships for wna to com pare the empirical ground motion processes between the two regions a composite functional attenuation form is defined and in turn a nonlinear regression analysis is performed by using a genetic algorithm ga for a wide range of magnitudes and distances to develop an empirical attenuation relationship from the stochastic ground motion estimates in ena the empirical stochastic attenuation relationship for hor izontal peak ground acceleration and spectral acceleration are applicable to earth quakes of mw 5 0 8 2 at distances of up to 1000 km the resulting attenuation model developed in this study is compared with those used in the 2002 national seismic hazard maps derived in the 2003 electric power research institute studies and re corded in ena the comparison of the results to the other attenuation functions and the available ena data show a reasonable agreement for the ena ground motions

glacial interglacial changes in central tropical pacific surface seawater property gradients much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropical pacific over the last glacial cycle studies have been hampered by the fact that sediment cores suitable for study were concentrated in the western and eastern parts of the tropical pacific with little information from the central tropical pacific here we present information from a suite of sediment cores collected from the line islands ridge in the central tropical pacific which show sedimentation rates and stratigraphies suitable for paleoceanographic investigations based on the radiocarbon and oxygen isotope measurements on the planktonic foraminifera globigerinoides ruber we construct preliminary age models for selected cores and show that the gradient in the oxygen isotope ratio of g ruber between the equator and 8 n is enhanced during glacial stages relative to interglacial stages this stronger gradient could reflect enhanced equatorial cooling perhaps reflecting a stronger walker circulation or an enhanced salinity gradient perhaps reflecting increased rainfall in the central tropical pacific

ocean processes at the antarctic continental slope the antarctic continental shelves and slopes occupy relatively small areas but nevertheless are important for global climate biogeochemical cycling and ecosystem functioning processes of water mass transformation through sea ice formation melting and ocean atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath ice shelves climate models however struggle to capture these physical processes and are unable to reproduce water mass properties of the region dynamics at the continental slope are key for correctly modelling climate yet their small spatial scale presents challenges both for ocean modelling and for observational studies cross slope exchange processes are also vital for the flux of nutrients such as iron from the continental shelf into the mixed layer of the southern ocean an iron cycling model embedded in an eddy permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the southern ocean ocean gliders play a key role in improving our ability to observe and understand these small scale processes at the continental shelf break the gliders excellent new tools for observing the ocean gentoo project deployed three seagliders for up to two months in early 2012 to sample the water to the east of the antarctic peninsula in unprecedented temporal and spatial detail the glider data resolve small scale exchange processes across the shelf break front the antarctic slope front and the front s biogeochemical signature gentoo demonstrated the capability of ocean gliders to play a key role in a future multi disciplinary southern ocean observing system

frontogenesis in the agulhas return current region simulated by a high resolution cgcm abstractdetailed mechanisms for frontogenesis frontolysis of the sea surface temperature sst front in the agulhas return current arc region are investigated using outputs from a high resolution coupled general circulation model the sst front is maintained throughout the year through an approximate balance between frontolysis by surface heat flux and frontogenesis by horizontal advection although a southward northward cross isotherm flow on the northern southern side of the front is weaker than a strong eastward along isotherm current in the frontal region this cross isotherm confluent flow advects warmer cooler temperature toward the sst front north south of the front and acts as the dominant frontogenesis mechanism in addition stronger weaker frontogenesis in austral summer winter is attributed to the stronger weaker cross isotherm confluence which may be linked to seasonal variations of the agulhas current arc and antarctic circumpolar current on the other hand the contributi

response of total and eddy kinetic energy to the recent spinup of the beaufort gyre abstractthe beaufort gyre in the arctic ocean has spun up over the past two decades in response to changes of the wind forcing and sea ice conditions accumulating a significant amount of freshwate

high resolution chronologies for loess comparing ams 14c and optical dating results the nuxloch loess section in south west germany is famous in central europe for its thick deposits from the last glacial maximum it has therefore been intensively studied during the past few years and offers an excellent opportunity to compare the performance of different dating techniques covering the period 15 45 ka here we present results fromoptical and ams 14 c dating the silt sized polymineral fraction of the clastic sediments and a multiple aliquot approach was used for ir osl dating 14 c dating was carried out on organic macro remnants and humin fractions extracted fromthe sedim ents with the exception of samples taken from the uppermost 1 5 m of the section ir osl and calibrated 14 c ams ages are consistent over the entire period the inconsistencies in the upper meters are thought to be due to disturbances during soil formation in the holocene the good agreement obtained on the remaining sequence demonstrates the high accuracy of both methods when studying loess sections for the ir osl ages no significant age underestimations are obvious the results clearly document that accurate chronologies can be developed for such continental sedimentary sequences this gives access to archives that can now be studied with a high temporal resolution and allows the establishment of new paleoclimatic proxies for the study of terrestrial responses to past climatic changes r 2003 elsevier science ltd all rights reserved

the formation of a subsurface anticyclonic eddy in the peru chile undercurrent and its impact on the near coastal salinity oxygen and nutrient distributions the formation of a subsurface anticyclonic eddy in the peru chile undercurrent pcuc in january and february 2013 is investigated using a multi platform four dimensional observational approach research vessel multiple glider and mooring based measurements were conducted in the peruvian upwelling regime near 12 30 s the dataset consists of 10000 glider profiles and repeated vessel based hydrography and velocity transects it allows a detailed description of the eddy formation and its impact on the near coastal salinity oxygen and nutrient distributions in early january a strong pcuc with maximum poleward velocities of 0 25 m s at 100 to 200 m depth was observed starting on january 20 a subsurface anticyclonic eddy developed in the pcuc downstream of a topographic bend suggesting flow separation as the eddy formation mechanism the eddy core waters exhibited oxygen concentrations 1 mol kg an elevated nitrogen deficit of 17 mol l and potential vorticity close to zero which seemed to originate from the bottom boundary layer of the continental slope the eddy induced across shelf velocities resulted in an elevated exchange of water masses between the upper continental slope and the open ocean small scale salinity and oxygen structures were formed by along isopycnal stirring and indications of eddy driven oxygen ventilation of the upper oxygen minimum zone were observed it is concluded that mesoscale stirring of solutes and the offshore transport of eddy core properties could provide an important coastal open ocean exchange mechanism with potentially large implications for nutrient budgets and biogeochemical cycling in the oxygen minimum zone off peru

the mechanisms of the atlantic meridional overturning circulation slowdown induced by arctic sea ice decline abstractwe explore the mechanisms by which arctic sea ice decline affects the atlantic meridional overturning circulation amoc in a suite of numerical experiments perturbing the arctic sea ice ra

simultaneous study of the source path and site effects on strong ground motion during the 1989 loma prieta earthquake a preliminary result on pervasive nonlinear site effects we considered the effects of source propagation path and local site conditions on strong ground motion from the loma prieta earthquake in the following steps first the local site effect was removed from the strong motion records applying the weak motion amplification factors estimated from nearby stations of usgs regional network using the coda method then we confirmed the approximate validity of the 1 r law of geometrical spreading factor for the crustal model applicable to the region and we determined the attenuation parameter q f and source spectrum s f empirically from the site effect corrected spectral amplitude both q f and s f are consistent with the results obtained earlier for major california earthquakes we then synthesized the time history of ground acceleration by applying the stochastic simulation technique the agreement between the observed and predicted records was good for duration and spectral content we found however a strong systematic discrepancy with regard to peak acceleration namely for distances less than 50 km the predicted peak acceleration consistently overestimated the observed for sediment sites and underestimated it for the franciscan formation sites since the above systematic discrepancy applies to all the available stations within about 50 km from the hypocenter it is unlikely that the effect is due to the radiation pattern near source structure or topography it appears that the strong difference in the amplification factor between the franciscan and the sediment sites observed for weak motion disappears at acceleration levels higher than about 0 1 to 0 3 g if this is due to the nonlinear response of the sediment sites it is in the range expected from geotechnical engineering studies

late quaternary caspian sea environment late khazarian and early khvalynian transgressions from the lower reaches of the volga river abstract this magnetic clay minerals and palynological study provides a record of two late pleistocene transgressions late khazarian and early khvalynian in the caspian sea through the analysis of present day lower volga terraces the results allow the clarification of some points about the caspian sea evolution during the considered periods early diagenetic iron sulphides greigite and pyrite are present in sediments of the lower part of the late khazarian and reflect restricted water circulation in the basin the change in iron sulphide mineralogy is most probably related to the change of the water level and its salinity low magnetic mineral contents with magnetite if any recorded in the upper part of the late khazarian atelian and early khvalynian reflect a well oxygenated basin and detrital material sources poor in magnetic minerals smectite is the dominant clay mineral in the late khazarian reflecting chemical weathering in its source area due to the wet and warm climate the upper part of this transgression is nevertheless marked by a stepwise relative decrease of smectite and an increase of illite attributed to a cooling climate during the atelian and early khvalynian periods phases of sandy deposits are characterised by equal proportions of illite and smectite similar to ukrainian loess chocolate clays are clearly dominated by illite both clay mineralogies are attributed to cool climate which favours physical weathering in the catchment area the conditions of chocolate clays deposition are unclear the recorded cooling during the last phase of the late khazarian and the 14c age on a well preserved bivalve shell suggest that it is probably much younger than the eemian interglacial and could correspond to the girkan transgression the 14c age for the early khvalynian sample suggests approximately a last glacial maximum age for this transgression

enhancement in vertical fluxes at a front by mesoscale submesoscale coupling oceanic frontal instabilities are of importance for the vertical exchange of properties in the ocean submesoscale o 1 rossby number dynamics are particularly relevant for inducing the vertical and lateral flux of buoyancy and tracers in the mixed layer but how these couple with the stratified pycnocline is less clear observations show surface fronts often persist beneath the mixed layer here we use idealized three dimensional model simulations to show how surface fronts that extend deeper into the pycnocline invoke enhanced vertical fluxes through the coupling of submesoscale and mesoscale instabilities we contrast simulations in which the front is restricted to the mixed layer with those in which it extends deeper for the deeper fronts we examine the effect of density stratification on the vertical coupling our results show deep fronts can dynamically couple the mixed layer and pycnocline on time scales that increase with the peak stratification beneath the mixed layer eddies in the interior generate skew fluxes of buoyancy and tracer oriented along isopycnals thus providing an adiabatic pathway for the interior to interact with the mixed layer at fronts the vertical enhancement of tracer fluxes through the mesoscale submesoscale coupling described here is thus relevant to the vertical supply of nutrients for phytoplankton in the ocean a further implication for wind forced fronts is that the vertical structure of the stream function characterizing the exchange between the interior and the mixed layer exhibits significant qualitative differences compared to a linear combination of existing parameterizations of submesoscale eddies in the mixed layer and mesoscale eddies in the interior the discrepancies are most severe within the mixed layer suggesting a potential role for ekman layer dynamics absent in existing submesoscale parameterizations

salinity frontogenesis frontolysis in the northeastern subtropical pacific region detailed mechanisms of reinforcement relaxation of a sea surface salinity front i e frontogenesis frontolysis in the northeastern subtropical pacific region are investigated using observational datasets throughout the year meridional shears of zonal wind induce meridional ageostrophic convergence around the front saltier water is advected on the southern side than the northern side and thus the convergence contributes to frontogenesis the evaporation and precipitation gradients also strengthen the front because higher sea surface temperatures on the southern side induce stronger evaporation through the formation of higher surface saturated specific humidity and because the precipitation rate is low in the southern region in association with the subtropical high of the atmosphere however in summer autumn when the mixed layer is seasonally thin and evaporation exceeds precipitation the frontogenesis by the freshwater flux gradient is damped by the mixed layer depth mld gradient this is attributed to the thicker mixed layer south of the front being less sensitive to freshwater fluxes during the mixed layer deepening phase the mixed layer on the southern side entrains lower salinity water from the lower layer and thus the entrainment relaxes the front therefore it is shown that the gradients of ageostrophic advection evaporation and precipitation result in frontogenesis while those of mld and entrainment cause frontolysis furthermore a metric that quantifies the relative importance of the horizontal gradients of freshwater fluxes and mld for salinity frontogenesis frontolysis is proposed over the large domain contribution from the horizontal gradient of freshwater fluxes dominates over that of mld

timing and extent of late quaternary glaciation in the western himalaya constrained by 10be moraine dating in garhwal india glacial chronologies from the himalayan region indicate various degrees of asynchronous glacial behavior part of this has been related to different sensitivities of glaciers situated in contrasting climatic compartments of the orogen but so far field data in support for this hypothesis is lacking here we present a new 10 be derived glacial chronology for the upper tons valley in western garhwal india and initial results for the pin and thangi valleys in eastern himachal pradesh these areas cover a steep gradient in orographic precipitation and allow testing for different climatic sensitivities our data provide a record of five glacial episodes at w16 ka w11 12 ka w8 9 ka w5 ka and 1 ka in the thangi valley our results indicate a glacial episode at w19 ka but no data are available for younger glacial deposits in this valley at their largest mapped extent w16 ka the two main glaciers in the upper tons valley joined and descended down to w2500 m asl which represents a drop of w1400 m compared to the present day glacial extent during the holocene the two largest glaciers produced distinct glacial landforms that allowed us to reconstruct changes in the equilibrium line altitude ela over w20 km north south distance that is presently associated with a steep gradient in rainfall we observe that ela changes have been consistently w2 times higher for the glacier located in a presently wetter climate pointing at different climate sensitivities related to the amount of precipitation that they receive at regional scale our data is in reasonable agreement with other published glacial chronologies from the western himalaya and suggest that glacial advances during the holocene have been largely synchronous in this region comparison of glacial chronologies from the western himalaya with other palaeoclimatic proxy data suggests that long term changes in glacial extents are controlled by glacial interglacial temperature oscillations related to the waxing and waning of the large northern hemisphere ice sheets while the timing of millennial scale advance and retreat cycles are more directly related to monsoon strength

the angola current flow and hydrographic characteristics as observed at 11 s the eastern boundary circulation off the coast of angola has been described only sparsely to date although it is a key element in the understanding of the highly productive tropical marine ecosystem off angola here we report for the first time direct velocity observations of the angola current ac at 11 s collected between july 2013 and october 2015 in the depth range from 45 to 450 m the measurements reveal an alongshore flow that is dominated by intraseasonal to seasonal variability with periodically alternating southward and northward velocities in the range of 40 cm s during the observation period a weak southward mean flow of 5 8 cm s at 50 m depth is observed with the southward current extending down to about 200 m depth corresponding mean southward transport of the ac is estimated to be 0 32 0 046 sv an extensive set of hydrographic measurements is used to investigate the thermal structure and seasonality in the hydrography of the eastern boundary circulation within the depth range of the ac the superposition of annual and semiannual harmonics explains a significant part of the total variability although salinity in the near surface layer appears to be also impacted by year to year variability and or short term freshening events in the central water layer temperature and salinity on isopycnals vary only weakly on seasonal to annual time scales the available data set is further used to evaluate different reanalysis products particularly emphasizing the ocean s role in coupled climate model sst biases in the eastern tropical atlantic

observed atlantification of the barents sea causes the polar front to limit the expansion of winter sea ice abstractbarents sea water bsw is formed from atlantic water that is cooled through atmospheric heat loss and freshened through seasonal sea ice melt in the eastern barents sea the bsw and fresh

role of mixed layer depth in surface frontogenesis the agulhas return current front air sea interaction processes that modify the sea surface temperature sst front in the agulhas return current region between 40 e and 55 e during austral summer and winter are examined using observational data and output from a high resolution ocean general circulation model while the air sea heat flux frontal variations tend to relax the sst front the frontolysis is amplified damped in summer winter when frontal variations in the mixed layer depth mld are incorporated the stronger weaker frontolysis associated with the mld variations is due to the fact that the warming cooling by the surface heat flux is amplified south of the front where the mld is shallower and is reduced north of the front where the mld is deeper this study is the first to show that the mld variations play an important role in affecting the strength of the sst front

timing and climatic impact of greenland interstadials recorded in stalagmites from northern turkey a 50 kyr long exceptionally well dated and highly resolved stalagmite oxygen 18o and carbon 13c isotope record from sofular cave in northwestern turkey helps to further improve the dating of greenland interstadials gi 1 and 3 12 timing of most gi in the sofular record is consistent within 10 to 300 years with the iconic hulu cave record larger divergences 500 years between sofular and hulu are only observed for gi 4 and 7 the sofular record differs from the most recent ngrip chronology by up to several centuries whereas age offsets do not increase systematically with depth the sofular record also reveals a rapid and sensitive climate and ecosystem response in the eastern mediterranean to gi whereas a phase lag of 100 years between climate and full ecosystem response is evident finally results of spectral analyses of the sofular isotope records do not support a 1 470 year pacing of gi

tidally forced lee waves drive turbulent mixing along the arctic ocean margins in the arctic ocean limited measurements indicate that the strongest mixing below the atmospherically forced surface mixed layer occurs where tidal currents are strong however mechanisms of energy conversion from tides to turbulence and the overall contribution of tidally driven mixing to arctic ocean state are poorly understood we present measurements from the shelf north of svalbard that show abrupt isopycnal vertical displacements of 10 50 m and intense dissipation associated with cross isobath diurnal tidal currents of 0 15 m s 1 energy from the barotropic tide accumulated in a trapped baroclinic lee wave during maximum downslope flow and was released around slack water during a 6 hr turbulent event high frequency internal waves were present the full 300 m depth water column became turbulent dissipation rates increased by a factor of 100 and turbulent heat flux averaged 15 w m 2 compared with the background rate of 1 w m 2 plain language summary turbulent mixing in the arctic ocean water column affects sea ice variability through transport of subsurface heat toward the surface this turbulent mixing is concentrated along the margins mainly driven by tidal flow over sloping topography however processes of energy transfer from tides to turbulence in the arctic are poorly understood and the magnitudes and locations of mixing are poorly constrained here we present detailed measurements from the shelf north of svalbard showing a turbulent event driven by moderate tidal currents the energy is trapped and accumulated at the time of maximum downslope flow and is released at the turn of the tide when the entire water column becomes highly turbulent our observations imply that this process is an important source of mixing in the arctic ocean

the climatology of the north atlantic abstract data from approximately 144 000 hydrographic stations in the north atlantic have been retrieved from the national oceanic data centre and analysed to produce maps of mean pressure temperature salinity and oxygen on selected potential density surfaces for the domain bounded by 0 85 w and 0 65 n the data span the period from 1904 to 1990 with the majority of the data from the last four decades the data set for this region is 60 larger than that used in the production of levitus climatological world atlas this increase in stations coupled with smoothing scales specific to the north atlantic rather than the global ocean considerably improves the resolution of the basin s features the mean property fields and their associated standard deviations are resolved on a one degree grid with little smoothing contrasting with the levitus atlas where properties although presented on a one degree grid have been smoothed on the order of 1000km another important feature of this database is the process by which irregularly spaced data are averaged onto a regular grid in a significant departure from the levitus analysis which averaged on depth surfaces these data were averaged on potential density surfaces thus eliminating an artificial mixing of water mass properties the database is used to describe the baroclinicity of well known features such as the gulf stream the north atlantic current and the deep western boundary current and to elucidate the recirculations associated with these currents it additionally resolves several new features in the intermediate and deep north atlantic these features include the signature of a large scale deep recirculation that extends southwestward from the eastward extension of the north atlantic current to the separation point of the gulf stream near cape hatteras this recirculation which spans approximately 2000m of the water column encompasses more local recirculations and potentially mixes subpolar and subtropical waters furthermore in the upper thermocline this database reveals a coherent azores current that stretches from the gulf stream system south of the tail of the grand banks to madeira this flow is marked by divergences to the south and convergences from the north such that its downstream transport is not much changed

multidecadal warming and shoaling of antarctic intermediate water antarctic intermediate water aaiw is a dominant southern hemisphere water mass that spreads from its formation regions just north of the antarctic circumpolar current acc to at least 20 s in all oceans this study uses an isopycnal climatology constructed from argo conductivity temperature depth ctd profile data to define the current state of the aaiw salinity minimum its core and thence compute anomalies of aaiw core pressure potential temperature salinity and potential density since the mid 1970s from ship based ctd profiles the results are used to calculate maps of temporal property trends at the aaiw core where statistically significant strong circumpolar shoaling 30 50 dbar decade 1 warming 0 05 0 15 c decade 1 and density reductions up to 0 03 kg m 3 decade 1 are found these trends are strongest just north of the acc in the southeast pacific and atlantic oceans and decrease equatorward salinity trends are generally small with their sign varying regionally bottle data are used to extend the aaiw core potential temperature anomaly analysis back to 1925 in the atlantic and to 1960 elsewhere the modern warm aaiw core conditions appear largely unprecedented in the historical record biennially and zonally binned median aaiw core potential temperatures within each ocean basin are with the notable exception of the subtropical south atlantic in the 1950s 70s 0 2 1 c colder than modern values zonally averaged sea surface temperature anomalies around the aaiw formation latitudes in each ocean and sectoral southern annular mode indices are used to put the aaiw core property trends and variations into context

a metric for surface heat flux effect on horizontal sea surface temperature gradients understanding what controls horizontal variations in sea surface temperatures ssts is one of the key science questions in climate research although various oceanic effects contribute to reinforcement relaxation of horizontal variations in ssts the role of surface heat fluxes is surprisingly complex and can lead to significant biases in coupled models if improperly represented in particular the contribution of surface heat fluxes to surface frontogenesis frontolysis depends not just on their gradients but also on the distribution of mixed layer depth which controls the effective heat capacity of the upper ocean in this study a new metric referred to as the surface flux frontogenesis metric is proposed that quantifies the relative importance of horizontal variations in surface heat fluxes and mixed layer depth global maps of this metric reveal that the role of surface heat fluxes in determining the horizontal sst gradient is highly variable geographically and by season furthermore the metric can help explain characteristics of sst fronts in the northwestern pacific the southern ocean the eastern equatorial pacific and the west coast of north america implications of this metric in coupled models will also be discussed

mimoc a global monthly isopycnal upper ocean climatology with mixed layers a monthly isopycnal mixed layer ocean climatology mimoc global from 0 to 1950 dbar is compared with other monthly ocean climatologies all available quality controlled profiles of temperature t and salinity s versus pressure p collected by conductivity temperature depth ctd instruments from the argo program ice tethered profilers and archived in the world ocean database are used mimoc provides maps of mixed layer properties conservative temperature absolute salinity sa and maximum p as well as maps of interior ocean properties sa and p to 1950 dbar on isopycnal surfaces a third product merges the two onto a pressure grid spanning the upper 1950 dbar adding more familiar potential temperature and practical salinity s maps all maps are at monthly 0 5 0 5 resolution spanning from 80 s to 90 n objective mapping routines used and described here incorporate an isobath following component using a fast marching algorithm as well as front sharpening components in both the mixed layer and on interior isopycnals recent data are emphasized in the mapping the goal is to compute a climatology that looks as much as possible like synoptic surveys sampled circa 2007 2011 during all phases of the seasonal cycle minimizing transient eddy and wave signatures mimoc preserves a surface mixed layer minimizes both diapycnal and isopycnal smoothing of s as well as preserves density structure in the vertical pycnoclines and pycnostads and the horizontal fronts and their associated currents it is statically stable and resolves water mass features fronts and currents with a high level of detail and fidelity

pleistocene water intrusions from the mediterranean and caspian seas into the black sea the hydrological balance of the black sea is governed by riverine input and by the exchange with the mediterranean sea a speleothem record from a cave in northern turkey that tracks the isotopic signature of black sea surface water suggests an open connection to the mediterranean sea in at least twelve periods in the past 670 000 years

earthquake ground motion prediction equations for eastern north america new earthquake ground motion relations for hard rock and soil sites in eastern north america ena including estimates of their aleatory uncertainty vari ability have been developed based on a stochastic finite fault model the model incorporates new information obtained from ena seismographic data gathered over the past 10 years including three component broadband data that provide new in formation on ena source and path effects our new prediction equations are similar to the previous ground motion prediction equations of atkinson and boore 1995 which were based on a stochastic point source model the main difference is that high frequency amplitudes f 5 hz are less than previously predicted by about a factor of 1 6 within 100 km because of a slightly lower average stress parameter 140 bars versus 180 bars and a steeper near source attenuation at frequencies less than 5 hz the predicted ground motions from the new equations are generally within 25 of those predicted by atkinson and boore 1995 the prediction equations agree well with available ena ground motion data as evidenced by near zero average residuals within a factor of 1 2 for all frequencies and the lack of any significant residual trends with distance however there is a tendency to positive residuals for moderate events at high frequencies in the distance range from 30 to 100 km by as much as a factor of 2 this indicates epistemic uncertainty in the prediction model the positive residuals for moderate events at 100 km could be eliminated by an increased stress parameter at the cost of producing negative residuals in other magnitude distance ranges adjustment factors to the equations are provided that may be used to model this effect

palaeoenvironmental records of the last 13 ka in lesser caucasus first data from paravani lake djavakheti georgia

barium isotopes reveal role of ocean circulation on barium cycling in the atlantic we diagnose the relative influences of local scale biogeochemical cycling and regional scale ocean circulation on atlantic barium cycling by analysing four new depth profiles of dissolved ba concentrations and isotope compositions from the south and tropical north atlantic these new profiles exhibit systematic vertical zonal and meridional variations that reflect the influence of both local scale barite cycling and large scale ocean circulation epipelagic decoupling of dissolved ba and si reported previously in the tropics is also found to be associated with significant ba isotope heterogeneity as such we contend that this decoupling originates from the depth segregation of opal and barite formation but is exacerbated by weak vertical mixing zonal influence from isotopically heavy water masses in the western north atlantic evidence the advective inflow of ba depleted upper labrador sea water which is not seen in the eastern basin or the south atlantic meridional variations in atlantic ba isotope systematics below 2000 m appear entirely controlled by conservative mixing using an inverse isotopic mixing model we calculate the ba isotope composition of the ba poor northern end member as 0 45 and the ba rich southern end member 0 26 relative to nist srm 3104a the near conservative behaviour of ba below 2000 m indicates that ba isotopes can serve as an independent tracer of the provenance of northern versus southern sourced water masses in the deep atlantic ocean this finding may prove useful in palaeoceanographic studies should appropriate sedimentary archives be identified and offers new insights into the processes that cycle ba in seawater

direct measurements of upper ocean currents and water properties across the tropical pacific during the 1990s abstract meridional sections of upper ocean zonal currents potential temperature and salinity are estimated at ten longitudes from 143 e to 95 w using conductivity temperature depth and acoustic doppler current profiler data from 172 synoptic sections taken in the tropical pacific between 138 e and 86 w mostly in the 1990s data reduction is carried out in a potential isopycnal and mixed layer framework to preserve a sharp pycnocline a mixed layer water property extrema and velocity extrema mean zonal currents potential temperatures and salinities are produced at each longitude the seasonal cycles of these fields are also estimated as well as a simple el nino southern oscillation enso cycle zonal sections along the equator are also presented properties of the near equatorial zonal currents including transports temperatures and salinities are estimated separately from the synoptic sections the seasonal cycles of these quantities and their correlations with the southern oscillation index are investigated the work is distinguished from most existing literature in that direct estimates of zonal velocity are combined with contemporaneous temperature and salinity data allowing trans pacific estimates of near equatorial current transports and properties including those of the northern branch of the south equatorial current the new guinea coastal undercurrent and the equatorial undercurrent

comment on empirical stochastic ground motion prediction for eastern north america by behrooz tavakoli and shahram pezeshk tavakoli and pezeshk 2005 conclude that the use of a point source single corner source spectrum by campbell 2003 2004 causes his eastern north america ena hybrid empirical ground motion model to underestimate ground motion amplitudes from near source large magnitude earthquakes this conclusion was based on published studies that found that the use of a double corner source spectrum together with a focal depth that increases with magnitude was required to match a dataset of strong motion recordings from moderate to large earthquakes in california atkinson and silva 1997 2000 tavakoli and pezeshk also note that atkinson and boore 1995 1997 propose the use of a double corner source spectrum to model the source spectra of large earthquakes in ena these studies lead tavakoli and pezeshk to suggest that using a double corner source spectrum with campbell s 2003 hybrid empirical method hem constitutes an improvement in the method one of the attributes of the hem is that the regional adjustment factors that are used to modify the ground motion estimates in the host region are not sensitive to the exact form of the source spectra or to the absolute amplitudes and functional relationships of the seismological parameters that are used to define the seismological models in the host and target regions instead these adjustment factors are sensitive only to the differences in the seismological models between these regions this means that the seismological models do not need to produce correct absolute ground motion amplitudes as assumed by tavakoli and pezeshk they only need to provide an accurate ratio of ground motion amplitudes accurate ratios will be obtained if the source spectra and the other seismological parameters in each region have the same functional relationships regardless of what form these relationships might take for example using a constant stress drop in each region will produce the same regional adjustment factors as using

vegetation fire and climate history of the lesser caucasus a new holocene record from zarishat fen armenia vegetation fire and climate history are investigated in the 10 000 year record of zarishat fen located today in the steppe grasslands of armenia near east pollen based climate quantification provides a reconstruction of seasonal parameters the development of in situ water dependant plants and of forests at lower altitude at 8200 cal a bp echoes the shift from an arid and cold annual precipitation pann 452mm mean temperature of the coldest month mtco 11 1uc early holocene to a more humid and warmer pann 721mm mtco 6 8uc mid late holocene this marks the onset of lower seasonality in particular more effective precipitation brought during late spring by the westerlies paralleling the mediterranean precipitation pattern precipitation in the near east and central asia decreased during the mid late holocene in favour of higher seasonality controlled in winter spring by the siberian high fire history and sedge based fen development record drier phases at approximately 6400 5300 4900 3000 2200 1500 and 400 cal a bp which resemble the precipitation pattern of the south western mediterranean and contrast with the holocene pattern in the south central and south eastern mediterranean regions arid phases in armenia are believed to be related to multi centennial scale variation of westerly activity north atlantic oscillation like copyright 2013 john wiley sons ltd

the sequence stratigraphy of fluvial depositional systems the role of floodplain sediment storage abstract the currently used model for alluvial sequence stratigraphy has been criticised miall 1991 and an alternative model is offered here in this model alluviation mainly takes place during transgressive and not highstand phases when accommodation space allows sediment storage the high capacity for some river systems to store floodplain sediments is a critical consideration the effects of climatic and intrinsic geomorphic changes during fluvial deposition are likely to greatly complicate simple base level controlled sequence models and recognising higher order fourth and fifth order cycles will be particularly difficult

incorporation of satellite derived thin ice data into a global ogcm simulation the presence of thin sea ice is indicative of active freezing conditions in the polar ocean we propose a simple yet effective method to incorporate information of thin ice category into coupled ocean sea ice model simulations in our approach the thin ice distribution restricts thick ice extent and constrains atmosphere ocean heat exchange through the sea ice our model simulation with the incorporation of satellite derived thin ice data for the arctic ocean showed much improved representation of sea ice and upper ocean fields including sea ice thickness in the canadian archipelago and the region north of greenland mixed layer depth over the central arctic and surface layer salinity over the open ocean enhanced sea ice production by the thin ice data constraint increased the total sea ice volume of the arctic ocean by 5 times 10 3 10 times 10 3 km3 subsequent sea ice melting was also enhanced leading to the greater amplitude of the seasonal cycle by approximately 2 times 10 3 km3 15 of the baseline value from the experiment without the thin ice data incorporation overall our results demonstrate that the incorporation of satellite derived information on thin sea ice has great potential for the improvement of coupled ocean sea ice simulations

observed variability of the north atlantic current in the rockall trough from 4 years of mooring measurements the rockall trough is one of the main conduits for warm atlantic water to the nordic seas ocean heat anomalies originating from the eastern subpolar gyre are known to influence arctic sea ice ex

an argo mixed layer climatology and database a global climatology and database of mixed layer properties are computed from nearly 1 250 000 argo profiles the climatology is calculated with both a hybrid algorithm for detecting the mixed layer depth mld and a standard threshold method the climatology provides accurate information about the depth properties extent and seasonal patterns of global mixed layers the individual profile results in the database can be used to construct time series of mixed layer properties in specific regions of interest the climatology and database are available online at http mixedlayer ucsd edu the mlds calculated by the hybrid algorithm are shallower and generally more accurate than those of the threshold method particularly in regions of deep winter mixed layers the new climatology differs the most from existing mixed layer climatologies in these regions examples are presented from the labrador and irminger seas the southern ocean and the north atlantic ocean near the gulf stream in these regions the threshold method tends to overestimate winter mlds by approximately 10 compared to the algorithm

an empirical study of earthquake source spectra for california earthquakes we generalize source path and site effects for california earthquakes as functions of magnitude and distance based on regression analysis of 1000 fourier acceleration spectra from 43 california earthquakes in the moment magnitude range from 4 4 to 7 4 recorded at rupture distances from 1 to 200 km empirically derived source spectra for california earthquakes are generally inconsistent with the spectral shape implied by a brune omega squared point source model this is manifested by magnitude and frequency dependence of the brune model parameters for ex ample the brune stress parameter that best matches the data at high frequencies decreases from a value of about 120 bars at m5 5 to a value near 50 bars at m7 5 at frequencies below 1 hz though source spectra have much lower spectral ampli tudes than predicted by the brune point source model for these values of stress this discrepancy grows with increasing magnitude finite fault simulations indicate that this is a consequence of the breakdown of the validity of the point source approxi mation for large ruptures a stochastic finite fault model in which the fault is dis cretized as a number of subfaults each of which is represented by a brune omega squared point source correctly matches the observed spectral shapes and amplitudes the spectral decay parameter kappa representing average near surface attenuation of high frequency motion at rock sites increases with increasing magnitude from values near 0 035 sec at m5 5 to 0 050 sec at m7 5 magnitude dependence of kappa may be interpreted as evidence of nonlinearity for typical california sites subjected to strong ground motion comparisons of our empirical source spectra for california to corresponding spec tra for eastern north america suggest that the spectral amplitudes are similar in the two regions for low frequency motions f 2 hz for m5 5 f 0 5 hz for m7 5 for equivalent crustal conditions the eastern events appear to have enhanced high frequency near source amplitudes relative to the california events this is particularly pronounced for large magnitude earthquakes

geomorphic response and 14c chronology of base level changes induced by late quaternary caspian sea mobility middle kura valley azerbaijan abstract recent geomorphological studies in azerbaijan reveal the importance of climato eustatic influences on landscape changes in the caspian sea basin during the last 40 ka radiocarbon dated fluvial landforms show that the paleohydrosystem of the middle kura valley and tributaries responded to regressive and transgressive phases of the caspian sea chrono sequences and landforms secured by 32 radiocarbon ages show strong correspondence between fluvial sediment accumulation and oscillations of base level in the caspian sea six phases of valley floor aggradation e g 27 000 13 000 11 000 3200 2900 2100 1600 1000 400 150 cal yr bp and seven phases of fluvial incision 37 000 37 000 27 000 13 000 11 000 3200 2900 2100 1600 1000 400 150 0 cal yr bp are recorded morphodynamics of the fluvial landscape show a strong correspondence with fluctuation in sea levels in the caspian sea the major upper pleistocene late glacial khvalynian c a 26 000 to 12 400 cal yr bp and various holocene transgressions as well as the mangyshlak c a 12 000 cal yr bp and derbent 6th 12th century ad regressions these data contribute to refining the caspian relative sea level curve for the last 30 ka using the chronology of changes in the aggradation or incision in the connected fluvial system

on cabbeling and thermobaricity in the surface mixed layer abstractthe surface mixed layer ml governs atmosphere ocean fluxes and thereby affects earth s climate accurate representation of ml processes in ocean models remains a challenge however the o 100 m deep ml exhibits substantial horizontal thermohaline gradients despite being near homogenous vertically making it an ideal location for processes that result from the nonlinearity of the equation of state such as cabbeling and thermobaricity traditional approaches to investigate these processes focus on their roles in interior water mass transformation and are ill suited to examine their influence on the ml however given the climatic significance of the ml quantifying the extent to which cabbeling and thermobaricity influence the ml density field offers insight into improving ml representations in ocean models a recent simplified equation of state of seawater allows the local effects of cabbeling and thermobaric processes in the ml to be expressed analytically as functions of the local temperatu

the thermohaline modes of the global ocean abstractthe first 2000 m of the global thermohaline structure of the ocean are statistically decomposed into vertical thermohaline modes using a multivariate functional principal component analysi

isopycnal mixing suppression by the antarctic circumpolar current and the southern ocean meridional overturning circulation abstractthe meridional overturning circulation moc in the southern ocean is investigated using hydrographic observations combined with satellite measurements of sea surface height a three dimensional spatial and vertical estimate of the isopycnal eddy diffusivity in the southern ocean is obtained using the theory of ferrari and nikurashin that includes the influence of suppression of the diffusivity by the strong time mean flows it is found that the eddy diffusivity is enhanced at depth reaching a maximum at the critical layer near 1000 m the estimate of diffusivity is used with a simple diffusive parameterization to estimate the meridional eddy volume flux this estimate of eddy volume flux is combined with an estimate of the ekman transport to reconstruct the time mean overturning circulation by comparing the reconstruction with and without suppression of the eddy diffusivity by the mean flow the influence of the suppression on the overturning is illuminated it is shown that the suppressio

subtropical surface layer salinity budget and the role of mesoscale turbulence the subtropical north atlantic exhibits the saltiest surface waters of the open ocean eventually that water subducted from the surface and exported toward the equator as a subsurface salinity maximum s max forming the lower limb of the subtropical cell climatologically the winter subtropical surface water coinciding with the deepest mixed layer of 100 m is saltier and colder than the s max towed ctd measurements in march april 2013 a component of the field program spurs within the north atlantic subtropical surface salinity maximum reveal several relatively fresh warm anomalies which deviate strongly from climatological conditions these features introduce a large amount of freshwater into the subtropical region exceeding the amount introduced by local rain events observed scales and evolution of the features strongly suggest a connection to mesoscale dynamics this is supported by high resolution regional model output which produces an abundance of features that are similar in scale and structure to those observed it is hypothesized that turbulent transport in the surface ocean is a crucial process for setting mixed layer characteristics which spread into s max stratum high variability in the eke implies a high potential for interannual variability in the resulting s max water properties by ocean dynamics in addition to the variability caused by air sea fluxes this has likely consequences to the meridional transport of heat and freshwater of the subtropical cell in the north atlantic and to the larger scale ocean and climate system

late quaternary record of the vegetation and catchment related changes from lake paravani javakheti south caucasus abstract here we present a palynological and sedimentological record from a 96 cm sediment core covering the last 13 ka aiming to document palaeoecological changes in the central south caucasus driven by climate and or human impact the core was retrieved from lake paravani 2073 m asl 41 27 n 43 48 e located in the steppic grasslands of south caucasus in the samsari javakheti volcanic plateau the geomorphological features observed on the plateau including moraine deposits suggest the presence of local glaciers reaching the lake level during the last glacial periods based on sediment and pollen data three palaeoecological phases have been identified the first phase spanning the younger dryas and the early holocene corresponds to a steppic environment with a limited lake productivity driven by a cold and particularly dry climate according to the age depth model this phase ends near 8500 cal bp with the decline of chenopodiaceae the second phase starts with an important expansion of trees at 8300 cal years bp the delayed afforestation recorded in lake paravani is a pattern that has now been recognised widely through the black sea region s more continental areas as soon as the climatic and edaphic conditions were favourable the main deciduous and coniferous trees expanded concurrently due to the proximity of glacial forest refugia located in western caucasus this second phase marked by a climatic optimum is also characterized by an increase in lake productivity the third phase starts at 2000 3000 cal bp and corresponds to the decline of forests on the plateau and the expansion of herbaceous formations leading to the present day steppic environment this deforestation phase is driven by the deterioration of the climate conditions and human impact

multidecadal warming of antarctic waters decadal trends in the properties of seawater adjacent to antarctica are poorly known and the mechanisms responsible for such changes are uncertain antarctic ice sheet mass loss is largely driven by ice shelf basal melt which is influenced by ocean ice interactions and has been correlated with antarctic continental shelf bottom water asbw temperature we document the spatial distribution of long term large scale trends in temperature salinity and core depth over the antarctic continental shelf and slope warming at the seabed in the bellingshausen and amundsen seas is linked to increased heat content and to a shoaling of the mid depth temperature maximum over the continental slope allowing warmer saltier water greater access to the shelf in recent years regions of asbw warming are those exhibiting increased ice shelf melt

frontolysis by surface heat flux in the agulhas return current region with a focus on mixed layer processes observation and a high resolution cgcm detailed mechanisms for frontogenesis frontolysis of the agulhas return current arc front defined as the maximum of the meridional sea surface temperature sst gradient at each longitude within the arc region 40 50 e 55 35 s are investigated using observational datasets due to larger smaller latent heat release to the atmosphere on the northern southern side of the front the meridional gradient of surface net heat flux nhf is found throughout the year in austral summer surface warming is weaker stronger on the northern southern side and thus the nhf tends to relax the sst front the weaker stronger surface warming at the same time leads to the deeper shallower mixed layer on the northern southern side this enhances the frontolysis because deeper shallower mixed layer is less more sensitive to surface warming in austral winter stronger weaker surface cooling on the northern southern side contributes to the frontolysis however deeper shallower mixed layer is induced by stronger weaker surface cooling on the northern southern side and suppresses the frontolysis because the deeper shallower mixed layer is less more sensitive to surface cooling therefore the frontolysis by the nhf becomes stronger weaker through the mixed layer processes in austral summer winter the cause of the meridional gradient of mixed layer depth is estimated using diagnostic entrainment velocity and the monin obukhov depth furthermore the above mechanisms obtained from the observation are confirmed using outputs from a high resolution coupled general circulation model causes of model biases are also discussed

timing of atmospheric precipitation in the zagros mountains inferred from a multi proxy record from lake mirabad iran abstract a sediment core 7 2 m long from lake mirabad iran was examined for loss on ignition mineralogy oxygen isotopic composition of authigenic calcite and trace element composition of ostracodes to complement earlier pollen and ostracode assemblage studies pollen ostracode inferred lake level and high sr ca ratios indicate that the early holocene 10000 to 6500 cal yr bp was drier than the late holocene low 18 o values during this interval are interpreted as resulting from winter dominated precipitation characteristic of a mediterranean climate increasing 18 o values after 6500 cal yr bp signal a gradual increase in spring rains which are present today a severe 600 yr drought occurred at ca 5500 cal yr bp shortly after the transition from pistachio almond to oak forest during the late holocene two milder droughts occurred at about 1500 and 500 cal yr bp within the resolution of the record no drought is evident during the collapse of the akkadian empire 4200 3900 cal yr bp rather a decrease in 18 o values to early holocene levels may indicate the return to a mediterranean precipitation regime

current status and palaeostages of the caspian sea as a potential evaluation tool for climate model simulations decadal scale oscillations of the level of the caspian sea cs primarily stem from variations in runoff from the volga river therefore although the image of the cs within the climate models is very simplified changes in the level of the cs can be used to assess the ability of climate models to reproduce the water budget over the east european plain the proxy dataset comprises a number of detailed maps of the cs for the main regression stages and transgression stages during the last 30 ka together with information about sea level positions we compare observed or reconstructed cs level positions during the last millennium and modern periods with the cs level positions calculated based on simulations in experiments using the cmip5 pmip3 protocol the modelled data could be verified based on how well the models simulate a the observed decadal scale cs level dynamics during the twentieth century and b the derbentian regression transition to new caspian 5th phase highstand and slight lowering of the cs level at the end of the nineteenth century

zonal evolution of alaskan stream structure and transport quantified with argo data the alaskan stream as flows west southwestward along the south side of alaska and the aleutian island arc a western boundary current at the northern edge of the north pacific subpolar gyre the argo float array has improved sampling of the gulf of alaska allowing quantification of the as s zonal evolution from 140 w to 175 w geostrophic alongshore transport of the as in the upper 1000 dbar referenced to an assumed level of no motion at 1000 dbar shows little change from east to west however alongshore absolute geostrophic transports in the top 2000 dbar obtained by combining mean absolute 1000 dbar velocities from float displacements with the geostrophic velocity fields generally increase to the west we estimate full depth transports by fitting a barotropic and the first two baroclinic modes calculated from a climatology to the absolute geostrophic velocities in the upper 2000 dbar and applying the velocities from these fits from 2000 dbar to the seafloor flowing west from its formation region at 140 w 145 w the full depth as becomes stronger more barotropic and also narrower once it reaches 160 w with along shore transports increasing from 16 4 4 9 sv 1 sv 106 m3 s 1 at 140 w to 32 6 5 2 sv at 175 w mean concentrations of relatively warm salty oxygen poor and nutrient rich pacific equatorial water pew in the as decrease from 17 8 0 3 to 8 5 0 5 between 140 w and 175 w however the volume transport of pew by the as exhibits little change over the pew density range between these longitudes

south pacific eastern subtropical mode water abstract the structure formation and destruction of south pacific eastern subtropical mode water spestmw are analyzed geographic extent and water properties are discussed by using high quality ctd sections collected between 1991 and 1996 defined as having a planetary potential vorticity magnitude of less than 3 10 10 m 1 s 1 spesmtw has a volume of about 1 1 1015 m3 estimated from ctd data the ventilation of this mode water is described by using data from a high resolution xbt section in concert with 30 month time series from profiling ctd floats some of the first argo deployments published subduction rates allow a mode water formation rate estimate of 8 7 106 m3 s 1 combining this estimate with the volume yields a residence time of about 4 years the density compensating covarying patterns of late winter surface temperature and salinity in the ventilation region of spestmw are shown to contribute to the strength of the mode water however while the destabilizing salinity gradient in sp

on mapping the diapycnal water mass transformation of the upper north atlantic ocean abstractdiapycnal water mass transformation is the essence behind the atlantic meridional overturning circulation amoc and the associated heat freshwater transports existing studies have mostly

effects of handling storage and chemical treatments on δ13c values of terrestrial fossil organic matter with the need to interpret small isotopic variations 13c analyses of sedimentary organic matter are more and more widespread in the field of paleo climatology recent developments require an evaluation of the reliability and reproducibility of the whole data acquisition chain literature abounds in protocols for sediment pretreatment prior to physical measurements these procedures differ at every step from sampling handling and storage conditions to leaching procedure without cross evaluation in this study we focus on two sediment samples a modern temperate soil and a 70 ka typical loess we review different protocols that characterize each step of the sediment pretreatment handling and storage conditions are tested e g finger skin contact mild to high temperature oven dry and freeze drying likewise different decarbonation protocols are compared wet decarbonation under cold 0 6 n hcl 2 n hcl and boiling 1 n hcl and acid fuming with 36 hcl this study identifies up to 1 5 isotopic shifts linked to experimental bias this large bias might be at the origin of erroneous paleoclimatic interpretation on the basis of these results we propose specific treatments adapted to the sample type

development of spit lagoon complexes in response to little ice age rapid sea level changes in the central guilan coast south caspian sea iran the central guilan coast along the iranian caspian coastline is characterized by sandy beaches and the development of spit lagoon complexes which are prone to preserve past sea level fluctuations the morphology of three spit lagoon complexes along the central guilan coast was studied using ground penetrating radar gpr and sediment sequences to understand the effects of past sea level changes on spit lagoon development the results showed the prominent role of coastal setting in conditioning the development of spit lagoon formation in response to sea level change when the caspian sea experienced a highstand in the little ice age the coast of central guilan recorded fluctuations in sedimentation which are reflected for example by river avulsion and beach ridge formation depending on physical setting in the western half of the central guilan eastward longshore currents and strong wave action on a w e coastline coupled with sea level changes shaped the anzali spit lagoon complex while in the eastern part of the studied area river avulsion and changing the coastline orientation are responsible for development of the amirkola and kiashahr spit lagoon complexes under the same sea level fluctuations although sea level change has a major role in spit lagoon development an increase in the frequency of storms changes in sediment supply due to more precipitation and river avulsion are other players in spit lagoon development in the central guilan during the little ice age and more recent times

response of the internal wave field to remote wind forcing by tropical cyclones abstractin the tropical north atlantic mean winds introduce relatively little energy into the internal wave field but hurricanes act as very energetic sources for near inertial waves in addition to the eventlike passage of such tropical cyclones changes in the wind speed north of the trade wind system induce a seasonal cycle in surface swell with potential implications for the high frequency part of the internal wave field using a 5 yr mooring time series in the interior of the tropical north atlantic at 16 n the temporal variability of internal wave energy south of the main hurricane track in different frequency bands is studied and the magnitude of its variability along with possible energy transfer mechanisms is analyzed the results show that changes in near inertial energy are dominated by the passage of internal waves generated by hurricanes centered several hundred kilometers north of the mooring the major role of hurricanes in the generation of near inertial waves is also seen in an ext

base level changes river avulsions and holocene human settlement dynamics in the caspian sea area middle kura valley south caucasus abstract geomorphological geochronological and geoarchaeological analysis focusing on six tributaries of the kura river provide valuable data concerning sedimentation rhythmicity and holocene human settlement distribution at a regional scale seven new radiocarbon dates from the upstream part of these hydrosystems complemented the existing radiocarbon dataset n 32 obtained downstream these data seem to indicate that upstream hydrosystems also reacted to marine regressions by powerful riverbed incisions and to transgression phases by thick valley infillings from at least as early as the upper pleistocene the retroactive morphogenic effects were also perceived in intra mountainous areas far from the caspian shoreline the land use patterns of the caucasian societies dwelling in the valley of the kura hydrosystem were affected by temporary river avulsions resulting in silty fans over the high terraces during the neolithic chalcolithic periods these river avulsions seem to be governed by local climate and base level changes linked to fluctuations of the caspian sea level over time this is spatially and diachronically evidenced in settlement distribution with almost exclusive localization on perched silty fans and river runoff from the key period of neolithic development in the region these new data must be considered in future geoarchaeological analyses concerning the caspian sea basin and will contribute to the enhancement of the relative caspian sea level curve for the past 40 ka

surface boundary layer evolution and near inertial wind power input deep weakly stratified surface layers in the southern ocean complicate the identification of the mixed layer base which is critical in estimating the wind power input through the ocean surface typically used mixed layer depth criteria often ignore weak stratification which traps momentum near the surface and significantly enhances the near inertial band wind power input the thickness of the active mixing layer the turbulent layer in contact with wind stress is needed to accurately estimate wind power input a fine density threshold criterion of 0 005 kg m 3 just above the noise floor of most autonomous instruments was applied to observed profiles of potential density to estimate the thickness of the actively mixing layer vertical shear langmuir cells and buoyant convection are investigated as possible mechanisms maintaining turbulence within the mixing layer over 90 of the observed variance of the mixing layer thickness is explained by either shear driven entrainment which is simulated using the price weller pinkel model or by a parameterization of downwelling plumes due to langmuir cell convergence in general surface buoyancy fluxes are too weak to drive mixed layer turbulence comparison of national oceanographic data center nodc climatological mixed layer thickness to those determined using the 0 005 kg m 3 density threshold suggests a multiplicative seasonally varying correction of 1 5 3 5 should be applied to wind work estimates made using the nodc climatological mixed layer thickness in the southern ocean

holocene vegetation history and sea level changes in the se corner of the caspian sea relevance to sw asia climate the palynological investigation of core tm 27 7 m long taken in a dried out lagoon reveals both holocene vegetation history in the north eastern foothills of the alborz mountains and past water level changes of the caspian sea cs the delay in woodland expansion at the beginning of the holocene which is typical of eastern turkey the iranian plateau and recorded in the cs south basin is only weakly felt as the region is close to glacial refugia of trees the succession of the main trees out of their refugia has been established as deciduous quercus carpinus betulus parrotia persica and fagus orientalis pterocarya fraxinifolia presenting therefore close affinities to south european interglacials of the early pleistocene this suggests a similarity in climate a pterocarya decline is observed after ad 495 the studied region is close to the easternmost tree distribution this could explain why it has been affected earlier than elsewhere in the northern alborz and the caucasus in addition human activities during the sasanian empire and the subsequent drying of the climate contributed to weakening the spread of this tree a maximal sea level occurs in the first part of the holocene from 10 6 to 7 2 cal ka it is suggested that the cs levels were significantly influenced by the monsoon precipitations over the western himalayas via the uzboy inflow this is followed by low levels from 7 2 to 3 5 cal ka with a minimum at 3 9 cal ka the neocaspian period should be considered a biozone rather than a chronozone as the environmental conditions reconstructed from dinocyst assemblages are different in shallow shelf waters and in the deep basins

the khvalynian transgressions and early human settlement in the caspian basin abstract radiocarbon dates for both lower and upper khavalynian transgressions fall in the timespan between 10 and 17 ka bp with 13 6 11 8 ka bp as the most probable age this transgression supposedly proceeded as a rapid succession of sea level fluctuations the initial emergence of mousterian industries in the caspian basin as indicated by the volgograd site might be correlated with a mild interval preceding the atelian regression which was broadly contemporaneous with the last glacial maximum 25 18 ka bp the subsequent expansion of mousterian sites was largely coeval with the khvalynian transgression supposedly specific environments that arose in the caspian basin favoured a prolonged conservation of the mousterian technique and possibly a survival of neanderthal populations a possible factor is a cascade of eurasian basins that included the caspian black sea spillway which effectively isolated the caucasian central asian area