the turbulent oscillator a mechanism of low frequency variability of the wind driven ocean gyres intrinsic low frequency variability is studied in the idealized quasigeostrophic midlatitude wind driven ocean gyres operating at large reynolds number a robust decadal variability mode driven by the transient mesoscale eddies is found and analyzed the variability is a turbulent phenomenon which is driven by the competition between the eddy rectification process and the potential vorticity anomalies induced by changes of the intergyre transport

generation of a trigger meander for the 2004 kuroshio large meander 1 a generation process of a small meander southeast of kyushu which triggered the subsequent kuroshio large meander in 2004 has been investigated using an ocean data assimilation and prediction system the assimilation result reveals that the small meander is the most developed one since 1993 a cyclonic eddy propagating westward from the kuroshio recirculation kr and a disturbance from the east china sea esc that accompanies a high potential vorticity high pv anomaly play important roles for the generation of the small meander the cyclonic eddy triggers an initial cyclonic anomaly southeast of kyushu when the high pv anomaly passes through the tokara strait a large positive vorticity is generated because the stretching of the water column is enhanced the positive vorticity is brought in the cyclonic anomaly and accumulates there as a result the small meander is generated from two sensitivity experiments an occurrence condition is determined by the cyclonic eddy from the kr by triggering the initial small scale meander and the disturbance from the ecs contributes to the horizontal scale of the small meander tracing back the disturbance further to the upstream region of the kuroshio it is revealed that the disturbance is a frontal wave with a large horizontal scale generated by collision between a strong anticyclonic eddy and the kuroshio east of taiwan the frontal wave propagates along the kuroshio accompanying high pv generated around the continental shelf edge by viscosity thus the large frontal wave could contribute to the generation of the developed trigger meander by transporting a larger amount of high pv anomaly to the tokara strait

numerical simulation of the transient response of the kuroshio leading to the large meander formation south of japan using a three dimensional primitive equation numerical model that takes realistic topography into account we successfully reproduce the observed transient response of the kuroshio south of japan during the transition from the nonlarge meander path to the large meander path the transient response is triggered by the generation of what is called the trigger meander off the southeastern coast of kyushu resulting from the supply of cyclonic vorticity through vertical stretching caused by the interaction between the kuroshio and the anticyclonic mesoscale eddy approaching the tokara strait the trigger meander thus generated propagates eastward south of shikoku while inducing an anticyclone cyclone pair in the lower ocean after the trigger meander passes cape shiono misaki it slows down and rapidly amplifies so that the kuroshio loops back west of the izu ogasawara ridge then the sharpness of the meander trough gradually relaxes and the large meander path is attained during the rapid amplification of the trigger meander off cape shiono misaki the abyssal anticyclone develops while being trapped by the local topographic feature koshu seamount located 200 km to the south of cape shiono misaki this abyssal anticyclone plays a crucial role in intensifying the trigger meander trough in the upper ocean via cross frontal advection the intensified trigger meander trough then further amplifies the abyssal anticyclone over koshu seamount this joint evolution of the upper ocean meander trough and the abyssal anticyclone suggests that baroclinic instability enhanced by koshu seamount is the dominant mechanism for the rapid amplification of the trigger meander leading to the large meander formation south of japan

interannual variability of the kuroshio transport in response to the wind stress field over the north pacific its relation to the path variation south of japan we have investigated the interannual variability in the kuroshio transport focusing on the baroclinic response of the upper ocean to the long term variation of the wind stress field over the north pacific from 1961 to 1987 first temporal change of the kuroshio transport at the western boundary from 17 to 31 n has been estimated on the assumptions that the kuroshio is a baroclinic flow confined in the upper layer and that the effect of interior wind stress curl on the volume transport at the western boundary is transferred by nondispersive baroclinic rossby wave peak values in the estimated transport appear in its beginning region 17 21 n when or just before the kuroshio settles into a meandering state south of japan in 1975 1981 and 1986 these peaks are due to negative wind stress curl anomalies which are induced by the intensified trade winds in the central and eastern tropical north pacific on and just after an el nino event and in the western tropical north pacific months to years before the next el nino event such peaks are not found in the barotropic sverdrup transport in downstream regions i e in the east china sea and south of japan north of 23 n on the contrary the estimated transports through baroclinic and barotropic responses do not have such good correlation to the path variation temporal change in thermocline depths estimated from bathythermograph data clearly shows the westward propagations of positive anomalies by nondispersive baroclinic rossby waves at latitudes of the beginning of the kuroshio south of 21 n which is in phase with peaks of the kuroshio baroclinic transport at the western boundary on the other hand there are only the local propagations of the anomalies in the downstream regions as previous studies reported however it is emphasized that temporal change of the geostrophic transport in the east china sea 28 n is coincident with that of the baroclinic transport at the beginning of the kuroshio not with that at the same latitude a numerical experiment with a nonlinear reduced gravity model confirms that temporal changes of the transport in the east china sea and south of japan are due to the advective nonlinear effect of the kuroshio itself while the linear baroclinic response to the wind stress field is dominant in its beginning region

effects of stretching on maintaining the kuroshio meander 1 using a two way nested grid ocean general circulation model driven by a repeat annual cycle forcing the kuroshio path variation is examined by varying the strength of wind forcing for climatological or 10 weaker wind forcing both large meander lm and non large meander nlm paths alternately appear with each type of path continuing for a few years to a decade this timescale and path transition processes are generally consistent with observations for the lm path the main balance in the depth integrated vorticity equation for the upper ocean is shown to be between the beta advection and stretching terms the stretching term is comparable to and has the same sign as the beta term at the western side of the meandering part indicating that the stretching term has the effects of shortening the wavelength and stabilizing the lm path the stretching term is mainly determined by downwelling caused by crossing of the upper and deep flows contrary to the above two cases only the nlm path appears for 10 stronger wind forcing it is suggested that the strength of climatological wind forcing is near the upper limit that allows the lm path to occur in this study the control experiment is carried out by choosing parameterizations and parameter values to reproduce the kuroshio path variation as realistic as possible therefore the results from the two sensitivity experiments are expected to represent a realistic response of the kuroshio path variation

interaction between the trigger meander of the kuroshio and the abyssal anticyclone over koshu seamount as seen in the reanalysis data 1 the jcope japan coastal ocean predictability experiment reanalysis data is analyzed to examine the transition from the non large meander path to the large meander path of the kuroshio that occurred in 2004 it was preceded by the generation of trigger meander off the southeastern coast of kyushu which then propagated eastward after passing cape shiono misaki the trigger meander amplified rapidly over koshu seamount located about 200 km to the south of cape shiono misaki where the accompanying abyssal anticyclone was significantly enhanced strong downwelling occurred upstream of the meander trough where the abyssal anticyclone crossed the kuroshio causing the vertical vortex stretching shrinking in the upper lower ocean the resulting enhanced abyssal anticyclone further amplified the meander trough in the upper ocean all of these features agree well with the model results suggesting the importance of baroclinic instability over koshu seamount in the formation of the large meander path

microbial mats as bioreactors populations processes and products microbial mats are dynamic and complex ecosystems exhibiting spatial and temporal heterogeneity the physical chemical environment is typified by steep gradients and distinct microenvironments these microenvironments support a great diversity of species with a wide range of metabolic processes these processes often result in coupled reactions and biogeochemical cycles and produce important end products such as trace gases and mineral precipitates the latter can impact the composition and character of the sediment imparting a biosignature these biosignatures can be preserved in the rock record and are useful in the interpretation of fossil record on earth and possibly as an indication of life on other planetary bodies the modern marine stromatolites of the exuma cays bahamas provide an ideal system for studying the populations processes and products in a microbial ecosystem using a multidisciplinary approach in order to acquire redox energy microbial populations need to carry out metabolic reactions at rates faster than the equivalent chemical abiotic reactions as such microbes can be viewed as bioreactors that preferably oxidize carbon to co2 to maximize the energy yield the study of the microbial role in carbonate sedimentation and lithification in these stromatolites provides a picture of microbial mats as bioreactors producing a biosignature

instabilities and multiscale interactions underlying the loop current eddy shedding in the gulf of mexico abstracta recently developed tool the multiscale window transform along with the theory of canonical energy transfer is used to investigate the roles of multiscale interactions and instabilities

methane derived authigenic carbonates formed by subduction induced pore water expulsion along the oregon washington margin authigenic magnesian calcite dolomite and aragonite are precipitated in the uppermost terrigenous sediments of the washington oregon accretionary prism by subduction induced dewatering these distinctive carbonates are methane derived and occur at sites of concentrated pore water expulsion unique biologic communities that subsist at least indirectly on methane suess et al 1985 are also found at some of these sites the methane which is dominantly biogenic is carried to the uppermost sediments of the prism by fluids and is oxidized by sulfate reducers before being incorporated into a carbonate cement carbonate precipitation occurs below the oxic layer probably no deeper than several centimetres to a few metres below the seabed cementation may be induced by three factors 1 increased carbonate alkalinity resulting from microbial sulfate reduction 2 decreased co 2 solubility resulting from a pressure decrease when the pore water escapes the prism and or 3 the addition of ca 2 and mg 2 ions from sea water near the sediment water interface the convergent margin setting engenders precipitation of authigenic carbonates in several ways compressive stresses induce anomalously rapid compaction and dewatering rates and they may cause overpressuring in migrating pore water thereby delaying precipitation of carbonates until pressure is released near the sediment water interface structural deformation of the accretionary prism creates pathways such as fault zones secondary fracture porosity and dipping permeable layers often exposed by mass movement for efficient advection and expulsion of methane enriched pore water these characteristic conditions which lead to the precipitation of methane derived carbonates may be found at other convergent margins

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

geometry forced coherent structures as a model of the kuroshio large meander abstract the bimodality of the kuroshio path south of japan is presented from a new viewpoint of direct interaction of current with local coastal geometry by solving the barotropic quasi geostrophic equation in a channel with steplike coastal geometry we demonstrate that the model kuroshio can actually show the localized bimodal behavior for a reasonable range of inlet current speed the amplitude of the large meander is approximately given by 2umax in contrast to all nonlocal model results our local coherent structures have nothing to do with the basin size geometry such as kyushu and the izu ogasawara ridge in general the present study suggests that even a small feature of coastline geometry may trigger a big change in a nearshore current

the effect of koshu seamount on the formation of the kuroshio large meander south of japan abstractusing an inflow outflow numerical model the authors demonstrate that the existence of koshu seamount located about 200 km to the south of cape shiono misaki is essential in creating the large meander lm of the kuroshio when koshu seamount is completely smoothed out the meander trough propagates away without being amplified to form the lm in contrast nearly the same lm as in the case with full topography is formed when the foot of koshu seamount remains without being smoothed out and also when the foot of koshu seamount is filled in so that the upper part of koshu seamount remains a linear stability analysis applied to the model output shows that the kuroshio becomes baroclinically most unstable when the water depth decreases offshoreward the authors therefore conclude that the enhancement of baroclinic instability over the northern slope of koshu seamount is a prerequisite to the formation of the lm

formation process of the kuroshio large meander in 2004 1 formation process of the 2004 kuroshio large meander has been examined using a data assimilation and prediction system the small meander southeast of kyushu that occurred in december 2003 remains stationary until the next spring the vorticity analysis indicates that this small meander is maintained by a balance between the advection and the bottom pressure torque on the continental slope this balance is achieved as a result of reducing the advection by a westward propagating negative temperature anomaly originating in the wind stress field the small meander starts moving eastward around may 2004 when an anticyclonic eddy east of the tokara strait is intensified by coalescing of two anticyclonic eddies at that time a deep anticyclonic eddy is generated below the kuroshio by a cross frontal flow the deep anticyclonic eddy grows up during its eastward propagation then a southward flow in the eastern part of the eddy carries the kuroshio path offshore bringing about the large meander the eddy energetic analysis indicates that baroclinic instability is essentially responsible for this large meander formation the sensitivity analysis reveals that the small meander and the intensified anticyclonic eddy significantly affect the phase speed and the amplitude of the meander respectively it is also revealed that a slow phase speed and a large amplitude of the meander are regarded as conditions for the stationary large meander which is also applicable to the past large meanders in the 2004 large meander these conditions coexist by the stationary small meander staying until the intensified anticyclonic eddy triggers baroclinic instability

effects of large scale wind on the kuroshio path south of japan in a 60 year historical ogcm simulation the effects of large scale wind forcing on the bimodality of the kuroshio path south of japan the large meander lm and non large meander nlm were studied by using a historical simulation 1948 2007 with a high resolution ocean general circulation models ogcm the kuroshio in this simulation spent much time in the nlm state and reproduced several aspects of its long term path variability for the first time in historical ogcm simulation presumably because the eddy kinetic energy was kept at a moderate level by using the simulated fields the relationships between wind forcing or kuroshio transport and path variation proposed by past studies were tested and specific roles of eddies in those variations were investigated the long term variation of the simulated net kuroshio transport south of japan was largely explained by the linear baroclinic rossby wave adjustment to wind forcing in the simulated lm events a triggering meander originated from the interaction of a wind induced positive sea surface height ssh anomaly with the upstream kuroshio and was enlarged by cyclonic eddies from the recirculation gyre the cyclonic eddy of the trigger meander was followed by a sizable anticyclonic eddy on the upstream side subsequently a weak strong kuroshio favored the lm nlm the lm tended to be maintained when the kuroshio transport off southern japan was small and increasing kuroshio transport promoted decay of an existing lm the supply of disturbances from upstream which is related to the wind induced ssh variability at low latitudes contributed to the maintenance of an existing lm

stable paths of the kuroshio south of japan determined by the wind stress field 1 to investigate the role of the wind stress field in determining stable paths of the kuroshio south of japan we have executed numerical experiments with a two layer wind driven ocean model changing zonal and meridional wind stress distributions four types of path two straight and two meandering paths have been found and their appearance has been classified into three categories in category i straight and meandering paths coexist multiple equilibrium only a meandering straight path appears in category ii iii a meandering path tends to appear when the sverdrup transport along the southern coast of japan decreases downstream strongly and the wind stress curl is anomalously negative in the western region near japan whereas a straight path is apt to occur with the positive anomaly detailed examination of the results has revealed the following mechanism determining stable paths of the kuroshio the wind stress field first determines the pressure difference p between the two ends of the southern coast of japan when p is smaller than a certain threshold only a meandering path can exist since the along coast pressure decrease in a straight path state is much larger than p category ii conversely when p is larger than another threshold only a straight path is consistent with the larger p category iii both paths can appear when p is between the two thresholds category i the climatological wind stress field in the north pacific subtropical region has been suggested to be in category i

bottom current depositional model and characterization of the paraburdoo member surrounding the paraburdoo spherule layer hamersley basin western australia abstract the stratigraphy within the wittenoom formation s paraburdoo member of the hamersley basin in western australia has lacked a significant and identifiable marker bed until the recent discovery of the paraburdoo spherule layer psl in this paper we correlate this stratigraphy residing at the three known exposed locations of the psl within the hamersley basin and use these correlations in conjunction with detailed observations and analyses to assess the type of sedimentation recorded by these alternating sand and mud beds we also characterize in detail these same several meters of stratigraphy using the psl as a distinctive marker bed and add to the existing depositional model of the hamersley basin we find that 1 the strata surrounding the psl was not deposited by sediment gravity flows but rather long acting deep marine bottom current s 2 the rhythmicity recorded as alternating sand and mud beds is the result of increasing and decreasing current velocities 3 grain size decreases while mud content increases to the east within the basin 4 bed thinning occurs to the west within the basin 5 microbial activity may be recorded in laminations in the finer grained mud beds present within these strata and 6 the diagenetic history changes across the hamersley basin

variations of current path velocity and volume transport of the kuroshio in relation with the large meander abstract the variations of the kuroshio current path and their relations with current velocity volume transport and upstream position of the kuroshio are examined using sea level data after the long time non large meander nlm path during 1963 75 the kuroshio takes a large meander lm path during most of 1975 91 1975 80 1981 84 1986 88 and 1989 91 the study of these meanders confirms the description of the path of the kuroshio based on the three typical paths and the transitions between them with an exception being the 1981 84 lm path the formation and decay of the large meander are associated with velocity and position of the kuroshio in the tokara strait south of kyushu a small meander precursor of the large meander seems to be formed southeast of kyushu in relation with a temporary increase of kuroshio velocity and a northward shift of the kuroshio in the tokara strait an eastward propagation of the small meander leading to the lm formation is associated with remaining in the northe

the cycling and redox state of nitrogen in the archaean ocean organisms that produce oxygen through photosynthesis existed during the late archaean eon about 2 500 million years ago but controversial evidence suggests that they may have evolved several hundred million years earlier oxygen is expected to react with oceanic nitrogen altering its redox state the reaction leaves a signature in the isotopic composition of the nitrogen bound in organic matter here we present a record of the nitrogen isotopic composition of kerogen extracted from minimally altered shales from the campbellrand malmani platform in south africa between the palaeo archaean and about 2 670 million years ago the 15n values of the kerogen rose by about 2 we interpret this increase as an indication of the onset of coupled nitrification and denitrification or anammox reactions in the surface oceans which require the presence of free oxygen a second increase in nitrogen isotopic composition around 2 520 million years ago implies instability of the n cycle with loss of fixed n this evidence for available oxygen in the oceans occurs at least 200 million years before geochemical indications of the presence of significant levels of atmospheric oxygen we suggest that coupled nitrification and denitrification drove the loss of fixed inorganic nitrogen leading to nitrogen limitation and conclude that the low levels of biologically available nitrogen limited the growth of oxygen producing plankton delaying the accumulation of oxygen in the atmosphere the initial production of oxygen in early earth s oceans altered the redox chemistry and cycling of nitrogen a record of nitrogen isotopes from preserved organic matter indicates nitrogen cycling in the presence of free oxygen 2 67 billion years ago about 200 million years before the first geochemical evidence for atmospheric free oxygen

a kuroshio extension system model study decadal chaotic self sustained oscillations abstract a model study of the kuroshio extension system in which forcing is provided by a time independent climatological wind yields a mean meandering path and a decadal variability of the jet in significant agreement with in situ and altimetric measurements a reduced gravity primitive equation ocean model is implemented in a box spanning the whole north pacific including a schematic coastline at the western side and an analytical wind forcing is determined according to the ecmwf and comprehensive ocean atmosphere data set coads climatologies the modeled time averaged kuroshio extension shows meanders northern and southern recirculation regions and a jet penetration that are in good agreement with the corresponding observed climatological features this result suggests that intrinsic nonlinear mechanisms are likely to play a major role in determining the meander pattern of the mean flow the internal low frequency variability is found to be a chaotic bimodal self sustained oscillation between a

new perspectives on the generation and maintenance of the kuroshio large meander abstractthe internal dynamical processes underlying the kuroshio large meander are investigated using a recently developed analysis tool multiscale window transform mwt and the mwt based canoni

the nonlinear optimal triggering perturbation of the kuroshio large meander and its evolution in a regional ocean model abstractbased on the regional ocean modeling system roms and the conditional nonlinear optimal perturbation cnop method we explore the nonlinear optimal triggering perturbation of the kuroshio

bimodality of the kuroshio abstract a barotropic ocean model is used to study the bimodal behavior of the kuroshio to the south of japan by considering the combined effects of the beta plane the kyushu coastal perturbation the izu ridge and the sw ne tilted coastline the two frequently observed meander patterns have been numerically verified as the two quasi steady solutions contained n the model the small meander state is identified as an upstream disturbance largely forced by the izu ridge its width decreases as the strength of the current increases the large meander state is forced by the presence of both the kyushu wedge and the izu ridge topography for small volume transports the large meander state behaves like the small meander state in that the meander width decreases as the current speed increases for large volume transports it behaves like a lee rossby wave in that the width of the meander increases as the current speed increases the birth of the large meander state occurs as a consequence of the ocean spin do

quantification of gas bubble emissions from submarine hydrocarbon seeps at the makran continental margin offshore pakistan 1 evidence for twelve sites with gas bubble emissions causing hydroacoustic anomalies in 18 khz echosounder records flares was obtained at the convergent makran continental margin the hydroacoustic anomalies originating from hydrocarbon seeps at water depths between 575 and 2870 m disappeared after rising up to 2000 m in the water column dives with the remotely operated vehicle quest 4000 m revealed that several individual bubble vents contributed to one hydroacoustic anomaly analyzed gas samples suggest that bubbles were mainly composed of methane of microbial origin bubble size distributions and rise velocities were determined and the volume flux was estimated by counting the emitted bubbles and using their average volume we found that a low volume flux flare 1 at 575 mbsl 90 ml min caused a weak hydroacoustic signal in echograms whereas high volume fluxes flare 2 at 1027 mbsl 1590 ml min flare 5 c at 2870 mbsl 760 ml min caused strong anomalies the total methane bubble flux in the study area was estimated by multiplying the average methane flux causing a strong hydroacoustic anomaly in the echosounder record with the total number of equivalent anomalies an order of magnitude estimate further considers the temporal variability of some of the flares assuming a constant flux over time and allows a large range of uncertainty inherent to the method our results on the fate of bubbles and the order of magnitude estimate suggest that all of the 40 32 106 mol methane emitted per year within the gas hydrate stability zone remain in the deep ocean

kuroshio path variation south of japan 1 barotropic inflow outflow model we examined the dynamics of the variation in the path of the kuroshio current along the south coast of japan by use of a barotropic inflow outflow ocean model the model basin has an inclined coastline and includes a part of the east china sea so that we could investigate the effect of kyushu on the kuroshio we obtained three regimes of the kuroshio s path variation according to the magnitude of its inlet velocity vmax similar to the previous study the kuroshio takes a straight path along the south coast of japan in regime i with a low vmax a meandering path in regime ii with a high vmax and both of these paths multiple equilibrium state in regime iii with an intermediate vmax the transition from the straight state to the meandering state occurs with an increase in vmax from regime i iii to ii preceded by an eastward progression of a small meander which is produced as a separated vortex by the nonlinear effect of the flow and the effect of kyushu it takes 120 days consistent with observations the nonlinearity of the flow has two effects in the transition one causes a downstream shift of the small meander and the other enlarges it by pulling out positive vorticity from the no slip coast with an increase in the meander scale due to the latter effect the former effect becomes small to be balanced with the beta effect causing an upstream shift of the meander thus a large meander path is formed a small meander does not progress eastward to develop into a large meander until vmax exceeds a critical value this behavior causes a multiple equilibrium state in regime iii and only the meandering path in regime ii

formation of tubular carbonate conduits at athina mud volcano eastern mediterranean sea abstract tubular carbonate conduits tcc represent the termination of fluid plumbing systems in environments of hydrocarbon seepage and play a relevant role in the discharge of methane from sub seafloor sediments to the water column however the biogeochemical reactions and biological activities involved in their formation are not fully understood to address this tcc samples were collected with a remotely operated vehicle from the seabed on the sw flank of the athina mud volcano in the eastern mediterranean sea petrographic mineralogical stable carbon and oxygen isotope and lipid biomarker analyses were performed to elucidate the formation processes of the tubular carbonates clotted and fibrous aragonite form the internal lining of the cavities while the outer portion of the tubes is formed by micritic mg calcite cementing hemipelagic sediment 13c depleted mg calcite and aragonite as low as 14 4 v pdb and lipid biomarkers archaeol 89 8 v pdb indicate that carbonate precipitation was influenced by sulfate dependent anaerobic oxidation of methane aom aom locally enhances aragonite precipitation thereby facilitating early lithification of the conduits within the mud volcano sediments the size and morphology of the tcc comparable with the buried portion of tubeworm colonies found in the proximity of the sampling site however our results suggest that tcc likely formed by the action of burrowing organism rather than being mineralizations of the tubeworm colonies this study provides new insights into the interpretation and understanding of tcc highlighting the role of macrofaunal activity in the formation of migration pathways for hydrocarbon rich fluids on the flank of a mud volcano

multiscale dynamical processes underlying the wintertime atlantic blockings abstractthe wintertime atmospheric blocking over the atlantic is investigated using a newly developed methodology namely localized multiscale energy and vorticity analysis ms eva and the theory of canonical energy transfer through a multiscale window transform mwt the atmospheric fields from the era 40 data are reconstructed on three scale ranges or scale windows basic flow window blocking window and synoptic window the blocking event is obtained by compositing the wintertime blocking episodes and a clear westward retrograding signal is identified on the blocking window likewise the local multiscale energetics following the signal are composited it is found that a life cycle of the blocking scale kinetic energy ke may be divided into three phases onset phase amplification phase and decay phase different phases have different mechanisms in play in general pressure work and the canonical transfer from the synoptic eddies initiate the generation of the blocking while the latter contri

dynamics of the kuroshio large meander two layer model abstract a simple two layered in outflow model is studied to explain the peculiarity of the kuroshio path the geometry south of japan with a length scale l and the characteristic velocity u of the kuroshio give an important parameter 2 u l the kuroshio can take two kinds of paths for a given value of multiple equilibria one is straight path and the other a meandering path the selection of a path the selection of a path in a multiple equilibrium state depends upon the history of the parameter the hysteresis phenomenon the combined effect of horizontal viscosity along the coast and the inclination of the coastline are essential factors which control the kuroshio path as well as an increase in the coastline inclination increases the effect of horizontal viscosity along the coast where a western boundary layer is formed due to the effect of an increase in the viscous effect along the coast makes a straight path possible when the inlet velocity is small the effect of stratification i

microbial fixation of methane carbon at 2 7 ga was an anaerobic mechanism possible 1 in earth s history the most extreme episode of 13c depletion in sedimentary organic matter occurred about 2 7 billion years ago this isotopic excursion is widely interpreted as resulting from increased burial of organic carbon derived from microbial fixation of 13c depleted methane modern microbial physiologies involve either oxygen or sulfate as electron acceptors in such processes until now the isotopic signal has been exclusively assigned to growth of aerobic methanotrophic bacteria and consequently interpreted as an indication for the presence of molecular oxygen in late archaean surface environments the alternative anaerobic pathway involving sulfate as the electron acceptor was dismissed because this process has been considered inefficient in producing biomass sufficient to account for significant fractions of 13c depleted carbon in some archaean rocks calculations based on recent findings at two modern sites now show however that anaerobic processes could account for the archaean signal

dynamical feedbacks and the persistence of the nao the persistence of the north atlantic oscillation nao is studied using observations of the threedimensional vorticity budget in the atlantic sector analysis of the relative vorticity tendency equation shows that convergence of eddy vorticity flux in the upper troposphere counteracts the effect of anomalous largescale divergence at the upper level at low levels the convergence associated with this large scale vertical circulation cell maintains the relative vorticity anomaly against frictional drag the eddy vorticity flux convergence thus acts to sustain the vorticity anomaly associated with the nao against drag and increases the persistence of the nao vorticity anomaly the adiabatic cooling associated with the rising motion in the vorticity maximum sustains the thermal structure of the nao anomaly enhancing the baroclinicity and thus eddy generation this constitutes a positive eddy feedback that helps maintain the nao the positive eddy feedback occurs only in the midlatitude region and is strongest during the negative phase of the nao when the atlantic jet is displaced toward the equator with a high pressure anomaly to the north and a low pressure anomaly to the south the stronger feedback demonstrated during the negative phase is consistent with the greater persistence observed for this phase of the nao the positive feedback appears to be associated with anomalous northward eddy propagation away from the jet

roles of mesoscale eddies in the kuroshio paths a high resolution ocean general circulation model is developed to simulate connections between the kuroshio path variations and mesoscale eddy activities as realistically as possible the climatological mean of the modeled kuroshio takes a nearshore nonlarge meander path it is found that the model is capable of simulating two types of nonlarge meander state and a possible version of the large meander state the offshore nonlarge meander is generated through interaction between the kuroshio and an anticyclonic eddy the large meander occurs just after significant intensification of the anticyclonic kuroshio recirculation successive intrusion of anticyclonic eddies from the upstream region is responsible for this process those anticyclonic eddies are advected by the kuroshio from the region northeast of luzon island and increase the upstream kuroshio volume transport on an interannual time scale the cyclonic eddies propagating from the kuroshio extension region on the other hand weaken the kuroshio meander after the merger the kuroshio path variations south of japan thus seem to be closely related to eddy activities in the subtropical gyre system

eddy mean flow interaction in the decadally modulating kuroshio extension system abstract satellite altimeter sea surface height ssh data of the past 16 years are used to investigate the decadal changes of the kuroshio extension ke system that oscillated between a stable and an unstable dynamic state during the stable state of 10 1992 06 1995 and 01 2002 12 2004 the ke jet was intense and had a northerly zonal mean path and a well defined southern recirculation gyre during the unstable state of 07 1995 12 2001 and 01 2005 present the ke jet had a reduced eastward transport and a more southerly flow path transitions between the two dynamic states are caused by the basin scale wind stress curl forcing in the eastern north pacific related to the pacific decadal oscillations pdos or the north pacific gyre oscillations npgos during the positive pdo or negative npgo phase the intensified aleutian low generates negative ssh anomalies in the eastern north pacific through ekman divergence as these wind induced negative ssh anomalies propagate to the west as baroclinic rossby waves they weaken the zonal ke jet and shift its path southward as its path is pushed southward 32 n the deep reaching ke jet has to ride over the shallow shatsky rise generating localized disturbances that lead to their subsequent development along the ke jet west of the shatsky rise the sequence opposite to that listed above occurs when the pdo npgo changes to its negative positive phase after the ke system transitions from a stable to unstable state the enhanced eddy interaction is found to strengthen both the southern recirculation gyre and quasi stationary meanders along the ke s upstream path this nonlinear eddy interaction is important in determining the amplitude of the observed decadal ke variability

morphotectonics and mechanics of the central makran accretionary wedge off pakistan abstract swath bathymetry images and 3 5 khz data acquired during rv sonne cruise 123 in autumn 1997 are the base for analysing the morphology and deformation styles of the huge makran accretionary wedge the continental slope off pakistan is characterised by three morphological provinces a the lower slope is built of a sequence of imbricate thrust slices which form long and narrow accretionary ridges with flanks locally as steep as 20 and between 10 and 20 on average while the regional slope is only 1 2 b the nearly flat mid slope terrace is present in the central east part of the margin narrows significantly towards the east and is absent east of 63 45 and c the upper slope up to the shelf has a regionally uniform slope as steep as about 8 and comprises a very rough topography with many gullies and canyons and evidence for mass wasting two meandering canyons crossing the entire margin down to the abyssal plain at about 63 15 63 30 can be correlated with onshore rivers they have been formed by episodic erosion through turbidity flows and are characterised by erosional and depositional portions sinuosity of the canyons is exclusively caused by the accretionary ridges functioning as obstacles for flow to be directly downhill application of coulomb rheology to the frontal part of the makran wedge implies that the mid level decollement is intrinsically extraordinary weak with a great strength contrast to the overlying sediments comparison with nankai cascadia and the western mediterranean ridge reveals new insights in the parameters controlling the shape of an accretionary wedge and the role of a mid level decollement

the kuroshio large meander formation in 2004 analyzed by an eddy resolving ocean forecast system 1 the recent formation of the kuroshio large meander southeast of the kii peninsula during the period from may to july 2004 has been simulated successfully in an eddy resolving ocean forecast system japanese coastal ocean predictability experiment the formation process was examined from the viewpoint of eddy kuroshio interactions using sensitivity experiments that had various initial conditions for eddies in march and may 2004 we confirmed that the large meander does not occur when the trigger meander southeast of the kyushu island has small amplitude and that the cyclonic eddy on the offshore side of the kuroshio contributes to the large meander formation our results show that the large amplitude of the trigger meander southeast of kyushu island in april 2004 was caused by downstream advection of anticyclonic eddies along the kuroshio in the east china sea from east of taiwan the results suggest that the successive westward propagation of strong anticyclonic eddies in the subtropical frontal region from 2003 to 2004 was the origin of the formation of the kuroshio large meander south of japan in summer 2004

effects of koshu seamount on the development of baroclinic instability leading to the kuroshio large meander abstractthe kuroshio south of japan shows bimodal path fluctuations between the large meander lm path and the nonlarge meander nlm path the transition from the nlm path to the lm path is triggered by a small meander generated off southwestern japan the small meander first propagates eastward downstream along the kuroshio and then rapidly amplifies over koshu seamount located about 200 km south of japan leading to the formation of the lm path of the kuroshio although koshu seamount is essential for the rapid amplification of the small meander the underlying physical mechanism is not fully understood in this study the role of koshu seamount is revisited using a two layer quasi geostrophic model that takes into account the effects of bottom topography numerical experiments show that the transition from the nlm path to the lm path can be successfully reproduced only when bottom topography mimicking koshu seamount is incorporated in this case the upper layer meander trough is rapidly amplified

oxygen minimum zones omzs in the modern ocean in the modern ocean oxygen minimum zones omzs are potential traces of a primitive ocean in which archean bacteria lived and reduced chemical anomalies occurred but omzs are also keys to understanding the present unbalanced nitrogen cycle and the oceans role on atmospheric greenhouse control omzs are the main areas of nitrogen loss as n2 n2o to the atmosphere through denitrification and anammox and could even indirectly mitigate the oceanic biological sequestration of co2 it was recently hypothesized that omzs are going to spread in the coming decades as a consequence of global climate change despite an important omz role for the origin of marine life and for the biogeochemical cycles of carbon and nitrogen there are some key questions on the structure of omzs at a global scale there is no agreement concerning the threshold in oxygen that defines an omz and the extent of an omz is often evaluated by denitrification criteria which at the same time are o2 dependent our work deals with the identification of each omz the evaluation of its extent volume and vertical structure the determination of its seasonality or permanence and the comparison between omzs and denitrification zones at a global scale the co existence in the omz of oxic in its boundaries and suboxic even anoxic in its core conditions involves rather complex biogeochemical processes such as strong remineralization of the organic matter removal of nitrate and release of nitrite the quantitative omz analysis is focused on taking into account the whole water volume under the influence of an omz and adapted to the study of the specific low oxygen biogeochemical processes a characterization of the entire structure for the main and most intense omzs o2 10 mu m maximum zone the larger omz relative to the extent of denitrification zone suggests that the unbalanced nitrogen cycle on the global scale could be more intense than previously recognized and that evaluation of the omz from denitrification could underestimate their extent

high temperature creep of partially molten plagioclase aggregates we have investigated the high temperature creep of synthetic labradorite an60ab40 between 1323 k and 1523 k at atmospheric pressure and low stresses 2 65 mpa average grain size varies from 12 to 16 m samples contained up to 12 vol melt an60ab40 glass fourier transform infrared measurements indicate that trace amounts of water 0 1 0 15 wt h2o were incorporated during crystallization this water was only partly released at high temperature and atmospheric pressure at low stresses and temperatures deformation of labradorite was controlled by grain boundary diffusion creep yielding a stress exponent of n 1 and an activation energy of 365 25 kj mol regime i with increasing stress and temperature mechanical data and microstructural observations indicate a transition to power law creep with n 3 regime ii this transition occurs in both partially molten and melt free aggregates in regime i the strain rate of samples containing as much as 12 vol melt is between 3 and 5 times higher than in fully crystalline specimens the activation energy is only slightly affected by the melt content between 0 and 10 2 vol transmission electron microscopy shows that the amorphous phase resides in connected triple junctions or in unconnected pockets grain boundaries are not wetted except surrounding large melt pockets the melt distribution of undeformed and deformed samples is similar the strength and activation energy of synthetic labradorite are comparable to those for pure anorthite with trace amounts of water both plagioclase compositions are slightly weaker than synthetic diopside

dynamics of kuroshio path variations in a high resolution general circulation model 1 a long lived 2 year typical large meander lm path of the kuroshio is reproduced in a high resolution general circulation model gcm simulation with realistic topography and the life cycle formation maintenance and disappearance of the lm is studied the formation of the lm is triggered by a pair of upper layer anticyclonic and cyclonic eddies on the kuroshio with the cyclonic one on the downstream side upon reaching the western side of the shikoku basin south of japan these anomalies induce a lower layer anticyclonic eddy they enhance each other while they are carried eastward by the kuroshio specifically the southward flow on the eastern side of the lower anticyclonic eddy carries the upper cold cyclonic eddy offshore resulting in the southward deflection of the kuroshio path large meander these processes can be understood as a growth of baroclinic instability a stationary lm is established when the westward tendency caused by the beta effect owing to the large meridional displacement counterbalances the eastward tendency caused by the combination of advection and vortex induction owing to the curvature of the kuroshio path large scale disturbances from the upstream tend to strengthen the lm through baroclinic energy conversion in contrast small scale disturbances from the upstream grow locally along the meandering kuroshio front through baroclinic energy conversion they extract cold waters from the cold cyclonic eddy of the lm as they flow away to the east the horizontal extent of the cold cyclonic eddy is reduced and the meander is carried eastward since the advection effect dominates over the beta effect that weakens as a result of the smaller meridional extent

stromatolitic fabric of authigenic carbonate crusts result of anaerobic methane oxidation at cold seeps in 4 850 m water depth methane seepage leads to mg calcite and aragonite precipitation at a depth of 4 850 m on the aleutian accretionary margin stromatolitic and oncoid growth structures imply encrustation of microorganisms microbial mats in the host sediment with a unique growth direction downward into the sediment forming crust shaped lithologies biomarker investigations of the residue after carbonate dissolution show strong enrichments in crocetane and archaeol which contain extremely low 13c values this indicates the presence of methane consuming archaea and 13c values of 42 to 51 pdb indicate that methane is the carbon source for the carbonate crusts thus it appears that stromatolitic encrustations of methanotrophic anaerobic archaea probably occurs in a consortium with sulphate reducing bacteria and that carbonate precipitation proceeds downward into the sediment where ascending cold fluids provide a methane source strontium and oxygen isotope analyses as well as 14c ages of the carbonates suggest that the fluids come from deep within the sediment and that carbonate precipitation began about 3 000 years ago

formation of seep carbonates along the makran convergent margin northern arabian sea and a molecular and isotopic approach to constrain the carbon isotopic composition of parent methane abstract authigenic carbonate deposits have been sampled with the remotely operated vehicle marum quest 4000 m from five methane seeps between 731 and 1823 m water depth along the convergent makran continental margin offshore pakistan northern arabian sea two seeps on the upper slope are located within the oxygen minimum zone omz ca 100 to 1100 m water depth the other sites are situated in oxygenated water below the omz below 1100 m water depth the carbonate deposits vary with regard to their spatial extent sedimentary fabrics and associated seep fauna within the omz carbonates are spatially restricted and associated with microbial mats whereas in the oxygenated zone below the omz extensive carbonate crusts are exposed on the seafloor with abundant metazoans bathymodiolin mussels tube worms galatheid crabs aragonite and mg calcite are the dominant carbonate minerals forming common early diagenetic microcrystalline cement and clotted to radial fibrous cement the 18 o carbonate values range from 1 3 to 4 2 v pdb indicating carbonate precipitation at ambient bottom water temperature in shallow sediment depth extremely low 13 c carbonate values as low 54 6 v pdb point to anaerobic oxidation of methane aom as trigger for carbonate precipitation with biogenic methane as dominant carbon source prevalence of biogenic methane in the seepage gas is corroborated by 13 c methane values ranging from 70 3 to 66 7 v pdb and also by back calculations considering 13 c methane values of carbonate and incorporated lipid biomarkers these calculations 13 c methane carbonate 13 c anme methane 13 c mox methane prove to be useful to assess the carbon stable isotope composition of seeping methane if this has not been determined in the first place such an approach represents a useful tool to reconstruct fluid composition of ancient seeps aom is also revealed by lipid biomarkers of anaerobic methane oxidizing archaea such as crocetane pentamethylicosane pmi and sn2 hydroxyarchaeol strongly depleted in 13 c 13 c values as low as 127 v pdb biomarkers of sulphate reducing bacteria are also abundant showing slightly less negative 13 c values but still significantly 13 c depleted average values as low as 101 other bacterial biomarkers such as bacteriohopanepolyols bhps hopanols and hopanoic acids are detected in most carbonates but are particularly common in seep carbonates from the non omz sites the bhp patterns of these carbonates and their low 13 c values resemble patterns of aerobic methanotrophic bacteria in the shallower omz sites bhps revealed much lower contents and varying compositions most likely reflecting other sources than aerobic methanotrophic bacteria 230 th u carbonate ages indicate that aom induced carbonate precipitation at the deeper non omz seeps occurred mainly during the late pleistocene holocene transition i e between 19 and 15 ka before present when the global sea level was lower than today

sulfur oxidizing bacteria prior to the great oxidation event from the 2 52 ga gamohaan formation of south africa the first 2 b y of earth s history was an important time for life when microbes evolved and diversified into essentially all of the metabolic forms that now exist because of feedbacks between biology and the surface environment understanding earth s biological history can help us understand the evolution of earth itself the morphological and geochemical evidence for this ancient biological history is sparse but is increasing here we report evidence for 2 52 ga exceptionally large organic smooth walled coccoidal microfossils preserved in a deep water black chert in the gamohaan formation of the kaapvaal craton of south africa these fossils occur mainly as compressed solitary coccoids that range in size from 20 to 265 m but occasionally occur in short chains of cells morphologically these fossils are similar to proterozoic and phanerozoic acritarchs and to certain archean fossils interpreted as possible cyanobacteria however their exceptionally large size simple cell wall microstructure and paleoecological setting as well as multiple sulfur isotope systematics of pyrite within the unit suggest that the gamohaan formation fossils were sulfur oxidizing bacteria similar to those of the modern genus thiomargarita organisms that live in anoxic and sulfidic deep water settings these are the oldest reported fossil sulfur bacteria and reveal a diversity of life and ecosystems previously only interpreted from geochemical proxies just prior to the great oxidation event a time of major atmospheric evolution

effects of stratification and bottom topography on the kuroshio path variation south of japan part ii path transitions in a multiple equilibrium regime abstract the effects of stratification and bottom topography on the kuroshio path transitions in a multiple equilibrium regime due to a short term velocity increase are examined using a two layer inflow outflow model with simplified coastal geometry and bottom topography for an imposed velocity increase on a straight path state the typical transition from a straight to a meandering path occurs with or without bottom topography through the same process as in a barotropic case with flat bottom thus the geometrical effect of kyushu is essential to this transition or to the formation of a small meander triggering the transition stratification and bottom topography are somewhat secondary nevertheless under the influence of stratification a small meander significantly develops south of kyushu during a decreasing phase of velocity through shoaling of the interface depth and triggers the transition with the amplification rate of velocity amp of 1 5 the continental slope south of japan prevents a small me

the hydraulics of local separation in a coastal current with application to the kuroshio meander abstract a hydraulic theory is advanced to explain the large sustained meandering of the kuroshio current to the south of japan it is shown that in general a promontory induces separation of a coastal current once separated the current will meander on the second derivative of the topography i e it is not a shelf wave like meander in barotropic waters and with rossby wave like behavior in baroclinic waters the theory reduces to a hydraulic description of the white and mccreary model of the kuroshio meander away from the coast but avoids difficulties associated with that theory at the source of the meander at the kyushu promontory

the instabilities and multiscale energetics underlying the mean interannual eddy interactions in the kuroshio extension region abstractusing a recently developed energetics diagnostic methodology namely the localized multiscale energy and vorticity analysis ms eva this study investigates the intricate nonlinear mutual interactions among the decadally modulating mean flow the interannual fluctuations and the transient eddies in the kuroshio extension region it is found that the mean kinetic energy maximizes immediately east of the izu ogasawara ridge while the transient eddy kinetic energy does not peak until 400 km away downstream the interannual variabilities which are dominated by a jet trapped rossby wave mode provide an energy reservoir comparable to the other counterparts in the upstream strong localized barotropic and baroclinic transfers from the mean flow to the eddies are observed whereas those from the interannual variabilities are not significant besides fueling the eddies the unstable mean jet also releases energy to the interannual scale processes between 144 and 154 e both transfers from the mean