observational evidence for westward propagation of temperature inversions in the southeastern arabian sea 1 a warm pool forms in the southeastern arabian sea seas prior to the onset of the summer monsoon over india in early june the core of this warm pool is in the lakshadweep sea ls xbt and surface salinity data collected in the ls during may 2002 april 2003 show that temperature inversions occur off the southwest coast of india in early december with the arrival of low salinity waters from the bay of bengal the low salinity waters and the inversions propagate westward along with the downwelling rossby waves that constitute the lakshadweep sea level high inversions occur in the western ls 73 e about 40 days after they occur near the coast in the eastern ls 75 5 e they disappear in april when the tropical convergence zone moves over the seas and the warm pool engulfs the region ocean dynamics and air sea fluxes are together responsible for the formation and westward propagation of the inversions

advective transport caused by intraseasonal rossby waves a key player of the high chlorophyll variability off the peru upwelling region 1 the upwelling region off peru between 5 s and 12 s is characterized by high offshore intraseasonal variability in sea surface productivity due to westward propagating chlorophyll anomalies whose magnitude can reach half the variance of total chlorophyll variations spectral analyses of ssh sst and chlorophyll satellite data show that these events are generated by intraseasonal rossby waves the almost constant phase shift between chlorophyll and altimetric signals suggests a physical mechanism dominated by horizontal advection which is confirmed by the use of a simple conceptual model furthermore an increase from the north to the south in the detected rossby wave periods correlated with a decrease in the wavelengths and phase velocities of the wave suggests the presence of a second baroclinic mode north of 8 s and of a first baroclinic mode south of this latitude the latitude of this transition is consistent with the theory of critical latitudes which specifies that at a given latitude only rossby wave with periods below a threshold period depending on the baroclinic structure of the wave can propagate offshore according to this theory second baroclinic mode rossby waves with periods greater than 130 days are supposed to propagate off the south american coast north of 8 s the corresponding critical latitude

path and variability of the agulhas return current the combined analysis of hydrographic kinematic and dynamic data collected during the 1997 1999 kapex cape of good hope experiments reveals a quasi stationary meandering pattern of the agulhas retroflection current east and upstream of the southwest indian ridge the current meanders between 38 s and 40 s in a spatially and temporally continuous fashion and has a core width of approximately full size image 1 k with an associated transport of full size image 1 k in the upper full size image 1 k peak surface velocities decrease from full size image 1 k near the agulhas retroflection to full size image 1 k around 32 e meander troughs northward extremes are found predominantly near 26 8 e 32 6 e and 38 9 e while crests southward extremes are located with high probability near 29 7 e 35 5 e and 42 9 e resulting in a typical wavelength of full size image 1 k cold eddies are shed along the northern boundary of the current from meander troughs into the recirculation regime between the agulhas current proper and the agulhas return current strongest cyclonic eddies are preferably shed in austral autumn the cyclonic eddies so formed propagate westward at an average phase speed of full size image 1 k with however a variability of at least the same magnitude subsequently the cyclones are absorbed by the next meander trough located upstream and to the west of the shedding trough

concurrent altimeter and infrared observations of rossby wave propagation near 34 n in the northeast atlantic we present observations of long wavelength baroclinic rossby waves near 34 n in the northeast atlantic ocean east of the mid atlantic ridge using both topex poseidon sea surface height ssh altimeter data and ers 1 along track scanning radiometer sea surface temperature sst measurements using the fourier transforms of longitude time diagrams of the zonal gradients of sst and ssh we locate the spectral components corresponding to westward wave propagation and estimate wavelength period and propagation speed the energy associated with the propagating waves in that region is distinctly higher than in the surrounding areas the similarities between the properties of the sst and ssh zonal gradients are remarkable with the same propagating signals clearly observed in both fields it is believed that the interaction between the rossby waves and the azores current could play a major role in the amplification of the waves themselves

satellite and in situ observations of the bio optical signatures of two mesoscale eddies in the sargasso sea satellite ocean color imagery and field spectroradiometer observations are used to assess the bio optical signatures of two mesoscale features a cyclone c1 and an 181 water anticyclone a4 in the sargasso sea field determinations of upper layer bio optical properties such as the diffuse attenuation coefficient and remote sensing reflectance spectra show little statistically significant variations with distance to the eddy center for either eddy this contrasts field observations showing many fold higher phytoplankton pigment biomass at depth and for a4 higher primary production rates at depth than is typical for this region the cyclone c1 does show a significant decrease in the depth of the 1 photosynthetically available radiation par isolume with increasing distance from eddy center while the anticyclone a4 shows no coherent signal vs distance vertical profiles of bio optical properties show consistent patterns where subsurface maxima are displaced higher inside the core of the cyclone c1 than in the surrounding waters while the highest values of the diffuse attenuation coefficient at 443 nm are observed within the core of anticyclone a4 satellite observations of near surface bio optical properties show signals consistent with eddy physical characteristics although the magnitude of these variations is very small barely detectable by typical field measurement protocols mean values of bio optical properties are higher within the cyclone compared with its periphery but not for the anticyclone for both eddies significant inverse correlations are observed between time series of bio optical properties and eddy center sea level anomaly consistent response to wind speed is also noted following strong wind events bio optical parameters are elevated inside the anticyclone and are reduced inside the cyclone these observations demonstrate that a combination of physical processes including vertical eddy uplift eddy horizontal advection and eddy scale ekman pumping contribute to the bio optical imprint of mesoscale eddies the contributions of these forcing mechanisms change over the period of observation illustrating the limitations of inferring eddy bio optical dynamics from short term field observations the present analyses provide insights into the potential as well as the drawbacks of bio optical techniques for probing the biological and biogeochemical impacts of open ocean eddies

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

a new early cambrian konservat lagerstatte expands the occurrence of burgess shale type deposits on the yangtze platform abstract we report the fandian biota a new konservat lagerstatte from the cambrian stage 3 yuxiansi and jiulaodong formations in sichuan south china with close faunal links to the chengjiang biota in yunnan the biodiversity of the fandian biota includes total group euarthropods radiodonts bivalved forms acercostracans trilobites non biomineralized trilobitomorphs armoured lobopodians palaeoscolecids pedunculate brachiopods hyoliths chancelloriids sponges and filamentous algae benthic dwellers dominate the fossil community e g trilobitomorphs brachiopods sponges with rare instances of nektonic radiodonts bivalved euarthropods and infaunal palaeoscolecids organisms the fandian biota contains soft bodied taxa that were only known from chengjiang and xiaoshiba until now namely primicaris acercostracan xandarella non trilobite trilobitomorph and mafangscolex palaeoscolecid expanding the distribution of these previously endemic taxa beyond yunnan to the northern yangtze platform during the cambrian stage 3 our findings provide a more comprehensive understanding of early cambrian biodiversity that inhabited the yangtze platform over a substantially greater palaeobiogeographic distribution than previously considered

sea level anomalies control phytoplankton biomass in the costa rica dome area 1 satellite data show that chlorophyll a concentration chl a in the northeastern tropical pacific is well correlated with sea level anomaly sla this correlation spans a wide spectrum of scales from large scale phenomena like enso to mesoscale cyclonic and anticyclonic eddies negative sla e g during la nina events and in cyclonic eddies is associated with the lifting of isopycnals in the nutricline and increased chl a due to enhanced phytoplankton growth while positive sla e g during el nino events and in anticyclonic eddies is associated with a deeper nutricline and reduced chl a due to decreased phytoplankton growth the coupling between sla and chl a anomaly in the costa rica dome crd area is tighter than has previously been recorded anywhere in the world ocean 70 of the interannual variations in chl a anomaly in the crd area is explained by a combination of the positive and negative effects of sla citation kahru m p c fiedler s t gille m manzano and b g mitchell 2007 sea level anomalies control phytoplankton biomass in the costa rica dome area geophys res lett 34 l22601 doi 10 1029 2007gl031631

dynamics of agulhas retroflection and ring formation in a numerical model part i the vorticity balance abstract the agulhas retroflection region of the wind driven idealized south atlantic indian ocean model described by deruijter and boudra is analyzed in detail here in part i the physical mechanisms of the model retroflection are elucidated through illustration of agulhas vorticity balance among various experiments in part ii the ring formation process is described in terms of its vertical structure and the associated energy conversions a one layer model demonstration shows that both inertia and internal friction may account for a partial retroflection where a linear weakly viscous system has none in the nonlinear weakly viscous one layer model the retroflection is accomplished through a free inertial boundary layer as suggested originally by de ruijter when stratification is introduced and baroclinicity increased using the bleck and boudra quasi isopycnic coordinate model with 2 or 3 layers the stretching term exerts an increasing influence with 40 km resolution terms included so that t

formation of a basin scale surface chlorophyll pattern by rossby waves the enhancement of surface chlorophyll by rossby waves which has recently been detected in bandpass filtered ocean color data cipollini et al 2001 uz et al 2001 is shown to be intense enough to form a dominant pattern in monthly mean basin scale ocean color satellite maps of the indian ocean results from a biological physical coupled model suggest that this phenomenon which is visible predominantly in austral winter is caused by rossby wave induced upwelling that lifts the deep chlorophyll maximum dcm into contact with the surface mixed layer ml the model results suggest that these events are not associated with any significant input of nutrients into the ml while the temporal enhancement of regional primary production by rossby waves is substantial 30 it is not necessarily associated with a corresponding increase in surface chlorophyll e g when the ml is too shallow to touch the dcm and may hence escape detectability by satellite measurements

southern ocean fronts controlled by wind or topography 1 the location of fronts has a direct influence on both the physical and biological processes in the southern ocean here we explore the relative importance of bottom topography and winds for the location of southern ocean fronts using 100 years of a control and climate change simulation from the high resolution coupled climate model higem topography has primary control on the number and intensity of fronts at each longitude however there is no strong relationship between the position or spacing of jets and underlying topographic gradients because of the effects of upstream and downstream topography the southern hemisphere westerlies intensify and shift south by 1 3 in the climate change simulation but there is no comparable meridional displacement of the antarctic circumpolar current s acc path or the fronts within its boundaries even over flat topography instead the current contracts meridionally and weakens north of the acc the subtropical front stf shifts south gradually even over steep topographic ridges we suggest the stf reacts more strongly to the wind shift because it is strongly surface intensified in contrast fronts within the acc are more barotropic and are therefore more sensitive to the underlying topography an assessment of different methods for identifying jets reveals that maxima of gradients in the sea surface height field are the most reliable approximating the position of fronts using sea surface temperature gradients is ineffective at high latitudes while using sea surface height contours can give misleading results when studying the temporal variability of front locations

the signature of mesoscale eddies on the air sea turbulent heat fluxes in the south atlantic ocean abstract by collocating 10 years 1999 2009 of remotely sensed surface turbulent heat uxes withsatellite altimetry data we investigate the impact of oceanic mesoscale eddies on the latent and sensibleheat uxesinthesouthatlanticocean instronglyenergeticregions suchasthebrazil malvinascon uenceand the agulhas current retro ection eddies explain up to 20 of the total variance in the surfaceturbulent heat uxes with averaged anomalies of 10 20 w m 2 cyclonic anticyclonic respectively eddies are associated with negative positive heat ux anomalies that tend to cool warm the marineatmospheric boundary layer a composite analysis of the turbulent heat ux anomalies inside the eddiesrevealsadirectrelationshipbetweeneddyamplitudeandtheintensityofsuchanomalies inaddition theseanomaliesarestrongerneartheeddycenter decayingradiallytoreachminimumvaluesoutsidetheeddies 1 introduction the ocean atmosphere system is primarily turbulent in the mesoscale band oceanic eddies play a crucialrole in transporting heat salt momentum and biogeochemical tr acersalongtheirtrajectories signi cantlyimpactingtheoceandynamicsand uxes olson 1991 wunsch 1999 morrowetal 2003 mesoscaleeddiesare coherent rotating features with typical horizontal scales of 50 300 km and time scales ranging fromweeks to months cheltonetal 2011a theyalsoexhibitparticularthermohalineverticalstructuresassoci ated with strong dynamical perturbations of the density and pressure elds olson 1991 chaigneau et al 2011 kurian et al 2011 zhang et al 2013 roullet et al 2014 these perturbations extend up to the seasurface leadingtoanomaliesonseasurfaceheight seasurfacetemperature sst andwindstress amongothers frengeretal 2013 souzaetal 2014 asaresult itisexpectedthateddiesimpacttheair sea uxesandtheoverlayingatmosphericcirculation frengeretal 2013 the turbulent latent lhf and sensible shf heat uxes are the primary processes by which the oceanreleases heat to the atmosphere cayan 1992 both the lhf and shf can be derived from bulk formulaelinking oceanic and atmospheric parameters such as air speci c humidity sst and wind speed to theheat exchanged at the air sea interface liu et al 1979 fairall et al 2003 large and yeager 2009 theanomalies caused by mesoscale eddies in some of these parameters have been recently investigated e g white and annis 2003 hausmann and czaja 2012 frenger et al 2013 souza et al 2014 chelton and xie 2010 although there is ample evidence that oceanic mesoscale features have a signi cant impact onair seaproperties thereisstillalackofknowledgeabouttheirsignatureonthesurfaceturbulentheat uxesandtheirpotentialcontributionstothenetsurfaceheatbudget the recent release of daily satellite based data from the french research institute for exploitation of thesea ifremer bentamy et al 2013 has su cient resolution to estimate the lhf and shf associatedwith mesoscale processes the present work merges satellite altimetry sea level anomaly sla data withremotely sensed surface heat uxes to investigate the impact of mesoscale ocean eddies on the lhf andshfinthesouthatlanticocean sa the sa encompasses both quiescent areas and two regions of intense energetic variability associated withthe presence of large mesoscale eddies figure 1a namely the agulhas current retro ection agr olsonand evans 1986 goni et al 1997 andthebrazil malvinascon uence bmc garzoli and garra o 1989 olson et al 1988 more speci cally we aim i to assess the mean lhf and shf anomalies induced bycyclonicandanticycloniceddiesinthesa ii todescribethespatialvariationsoftheheat uxanomaliesinvillasboasetal

formation and spreading of arabian sea high salinity water mass the formation and seasonal spreading of the arabian sea high salinity water ashsw mass were studied based on the monthly mean climatology of temperature and salinity in the arabian sea north of the equator and west of 80 e on a 2 2 grid the ashsw forms in the northern arabian sea during winter and spreads southward along a 24 sigma t surface against the prevailing weak zonal currents the eastern extent of the core is limited by the strong northward coastal current flowing along the west coast of india during the southwest monsoon the northern part of the core shoals under the influence of the findlater jet while the southern part deepens throughout the year the southward extent of the ashsw is inhibited by the equatorial currents the atmospheric forcing that leads to the formation of ashsw was delineated using the monthly mean climatology of heat and freshwater fluxes monsoon winds dominate all the flux fields during summer june september while latent heat release during the relative calm of the winter november february monsoon driven by cool dry continental air from the north results in an increased density of the surface layer thus excess evaporation over precipitation and turbulent heat loss exceeding the radiative heat gain cool the surface waters of the northern arabian sea during winter and drive convective formation of ashsw

physical and biological mechanisms for planetary waves observed in satellite derived chlorophyll we examine the evidence for global propagation of planetary wavelike features in sea surface chlorophyll over much of the midlatitude ocean westward propagating signals are seen that travel at the same speed as that predicted for long planetary waves we then test three mechanisms for production of this signal these are horizontal passive north south advection by the wave against a mean background gradient vertical upwelling of nitrate which is converted into chlorophyll and vertical upwelling of chlorophyll itself the tests involve comparisons of the amplitude and phase of the predicted signal with observations the horizontal advective process predicts an amplitude for chlorophyll fluctuations that is in fair agreement with the data though both overestimating and underestimating in places the predictions for the phase difference between the chlorophyll and sea surface height signatures are in good agreement with the data the upwelling biological mechanism could potentially give a large signal in the chlorophyll field but the predicted amplitude patterns and the predicted phase difference which is everywhere negative are not in accord with the observations except in a few regions the amplitude predicted by upwelling of chlorophyll is small compared with the horizontal advection mechanism we conclude that over most of the ocean the chlorophyll signal is well explained by horizontal advective processes although we cannot rule out that there exist locations where additional biological mechanisms may be responsible for at least part of the signal

the fezouata fossils of morocco an extraordinary record of marine life in the early ordovician the discovery of the fezouata biota in the latest tremadocian of southeastern morocco has significantly changed our understanding of the early phanerozoic radiation the shelly fossil record shows a well recognized pattern of macroevolutionary stasis between the cambrian explosion and the great ordovician biodiversification event but the rich soft bodied fezouata biota paints a different evolutionary picture the fezouata assemblage includes a considerable component of cambrian holdovers alongside a surprising number of crown group taxa previously unknown to have evolved by the early ordovician study of the fezouata biota is in its early stages and future discoveries will continue to enrich our view of the dynamics of the early phanerozoic radiation and of the nature of the fossil record supplementary material a complete faunal list is available at http www geolsoc org uk sup18843

cambrian palaeoscolecids cycloneuralia from gondwana and reappraisal of species assigned to palaeoscolex abstract the discovery of new palaeoscolecid material cycloneuralia from the emu bay shale konservat lagerstatte of kangaroo island south australia cambrian series 2 stage 4 and from the murero biota of ne spain cambrian series 3 stage 5 drumian has prompted a reappraisal of palaeoscolex whittard 1953 the genus to which species from these and other cambrian localities have most recently been assigned available data from scanning electron microscopy show the presence of hadimopanella type sclerites covering the surface of these taxa permitting taxonomic schemes based on microfossils and whole body compression fossils to be reconciled the sclerite pattern size and shape indicate that several of the cambrian species assigned to palaeoscolex need to be reassigned to wronascolex ivantsov and zhuravlev 2005 a genus originally described from siberia the studied material includes wronascolex antiquus glaessner 1979 and wronascolex iacoborum sp nov from kangaroo island australia and two new specimens of wronascolex from the iberian ranges spain sem examination of the types of palaeoscolex ratcliffei robison 1969 a cambrian species from utah to which murero material has been compared suggests that this species should possibly be assigned to wronascolex these taxa are also considered in a cambrian palaeobiogeographic context together with the presence of isolated hadimopanella sclerites showing a distribution of wronascolex largely confined to palaeotropical environments

traces in the dark sedimentary processes and facies gradients in the upper shale member of the upper devonian lower mississippian bakken formation williston basin north dakota u s a abstract black organic rich rocks of the upper shale member of the upper devonian lower mississippian bakken formation a world class petroleum source rock in the williston basin of the united states and canada contain a diverse suite of mudstone lithofacies that were deposited in distinct facies belts the succession consists of three discrete facies associations fas these comprise 1 siliceous mudstones 2 quartz and carbonate bearing laminated mudstones and 3 macrofossil debris bearing massive mudstones these fas were deposited in three facies belts that reflect proximal to distal relationships in this mudstone system the macrofossil debris bearing massive mudstones fa 3 occur in the proximal facies belt and contain erosion surfaces some with overlying conodont and phosphate lithoclast lag deposits mudstones with abundant millimeter scale siltstone laminae showing irregular lateral thickness changes and shell debris in the medial facies belt quartz and carbonate bearing laminated mudstones dominate exhibiting sub millimeter thick siltstone layers with variable lateral thicknesses and localized mudstone ripples in the distal siliceous mudstone facies belt radiolarites radiolarian bearing mudstones and quartz and carbonate bearing laminated mudstones dominate overall total organic carbon toc contents range between about 3 and 10 wt with a general proximal to distal decrease in toc content abundant evidence of bioturbation exists in all fas and the lithological and toc variations are paralleled by changes in burrowing style and trace fossil abundance while two horizontal traces and two types of fecal strings are recognized in the proximal facies belt only a single horizontal trace fossil and one type of fecal string characterize mudstones in the distal facies belt radiolarites intercalated into the most distal mudstones are devoid of traces and fecal strings bedload transport processes likely caused by storm induced turbidity currents were active across all facies belts suspended sediment settling from near the ocean surface however most likely played a role in the deposition of some of the mudstones and was probably responsible for deposition of the radiolarites the distribution pattern of high toc sediments in proximal and lower toc deposits in some distal facies is interpreted as a function of higher accumulation rates during radiolarian depositional events leading to a decrease in suspension derived organic carbon in radiolarite laminae the presence of burrows in all fas and nearly all facies in the upper bakken shale member indicates that dysoxic conditions prevailed during its deposition this study shows that in intracratonic high toc mudstone successions such as the upper bakken shale member bed load processes most likely dominated sedimentation and conditions promoted a thriving infaunal benthic community as such deposition of the upper bakken shale member through dynamic processes in an overall dysoxic environment represents an alternative to conventional anoxic depositional models for world class source rocks

sea surface temperature fronts in the midlatitude south atlantic revealed by using microwave satellite data 1 the subtropical convergence or frontal zone has been little studied in the central south atlantic ocean despite limited data some work has suggested that this feature exists continuously across the south atlantic here satellite microwave sensed sea surface temperature sst data available from june 2002 are analysed for the existence of frontal gradients in the subtropical to subpolar south atlantic with focus on the central to eastern region the frontal locations and sst gradients in the southwest south atlantic and in the agulhas current retroflection region obtained from this satellite data are consistent with those estimated previously from hydrographic observations evident in the satellite data is pronounced mesoscale variability in subtropical frontal features particularly south of africa and extending west from the agulhas current retroflection to at least the greenwich meridian and in the southwest south atlantic over the central to eastern part of the basin the analysis suggests that there is substantial interannual variability in the strength and latitudinal location of the northern and southern subtropical front as defined by belkin and gordon 1996 some of this variability may be related to shifts in the winds including that in the latitude of the strongest wind stress curl on seasonal scales this central to eastern region is also characterised by variations in the frontal intensity but shifts in the position of regions of strong gradients are less obvious thus the data indicate that there is no continuous subtropical frontal feature across the basin in terms of surface temperature

dynamics of agulhas retroflection and ring formation in a numerical model part ii energetics and ring formation abstract an energetics analysis of several numerical experiments on an idealized south atlantic indian ocean basin is presented the model used in the experiments is the quasi isopycnic coordinate model of bleck and boundra forced by wind and configured with two or three layers the region of focus is the most dynamically active one the agulhas current retroflection south of africa and the dynamical mechanisms associated with formation of agulhas rings are given special attention whether rings form in the model and their frequency depend on two primary factors the shape of africa and southward inertia baroclinicity in the overshooting agulhas the boundary condition on africa no slip free slip and horizontal resolution are also important experiments in which rings form exhibit considerably larger values of km to ke transfer than those in which no rings form in three of the experiments ring formation is studied in detail with the help of instantaneous top and bottom layer flow patterns and time se

effects of midlatitude westerlies on the paleoproductivity at the agulhas bank slope during the penultimate glacial cycle evidence from coccolith sr ca ratios modern primary productivity on the agulhas bank off south africa has been proposed to be linked to the midlatitude westerlies a paleoproductivity record from this area may therefore resolve temporal changes in the westerly dynamics accordingly we produced a coccolith sr ca based paleoproductivity record from core md96 2080 agulhas bank slope during the penultimate glacial interglacial cycle deriving the productivity signal from sr ca requires a correction for a temperature effect here constrained using mg ca sea surface temperatures from the foraminifer globigerina bulloides from core md96 2080 phases of depressed productivity coincided with periods of stratification in the same core indicated by high relative abundances of the coccolithophore florisphaera profunda and with low relative abundances of the upwelling indicator g bulloides in the nearby cape basin these observations collectively suggest that productivity was regulated by upwelling throughout this region we infer that as in the present periods of low productivity result from a more northerly position of the westerlies potentially accompanied by subtropical front displacements and blockage of upwelling promoting easterlies productivity minima also coincide with periods of increased ice rafted detritus ird deposition on the agulhas plateau which also indicates extreme northward positions of the westerlies the influence of the westerlies appears to be obliquity conditioned as productivity minima and ird maxima occur during low obliquity intervals the dynamic connection between productivity and the westerlies is supported by coeval salinity changes in the south indian gyre that likewise respond sensitively to a poleward contraction of the westerlies

the influence of nonlinear mesoscale eddies on near surface oceanic chlorophyll oceanic rossby waves have been widely invoked as a mechanism for large scale variability of chlorophyll chl observed from satellites high resolution satellite altimeter measurements have recently revealed that sea surface height ssh features previously interpreted as linear rossby waves are nonlinear mesoscale coherent structures referred to here as eddies we analyze 10 years of measurements of these ssh fields and concurrent satellite measurements of upper ocean chl to show that these eddies exert a strong influence on the chl field thus requiring reassessment of the mechanism for the observed covariability of ssh and chl on time scales longer than 2 to 3 weeks the dominant mechanism is shown to be eddy induced horizontal advection of chl by the rotational velocities of the eddies

a restudy of utahcaris orion euarthropoda from the spence shale middle cambrian utah usa utahcaris orion conway morris robison 1988 from the lower middle cambrian series 3 stage 5 spence shale member situated in utah usa is redescribed based on a restudy of the original material newly recognized features including ventral lateral eyes trunk appendages and a bulbous cephalic shield with subtriangular extension reinforce similarities with sanctacaris uncata from the middle cambrian burgess shale both are assigned to the new family sanctacarididae sanctacaridids represent the oldest chelicerates their ecology and that of their nearest non chelicerate relatives indicate that chelicerata were plesiomorphically predatory

eddies at the subtropical convergence south of africa abstract a descriptive analysis of the occurrence and kinematics of mesoscale eddies at the subtropical convergence south of africa is presented data used in this study include thermal infrared imagery from satellites since 1978 and a number of expendable hathythermogaph sections in the geographic area supported by drift tracks of free drifting buoys since 1975 the distribution of intense cold eddies to the north and warm eddies to the south of the subtropical convergence shows distinct geographic patterns the morphology of these eddies is such as to allow them to be categorized into four distinct classes each with a specific origin and kinematic behavior this implies consistent underlying dynamics which is shown to include the influence of bottom topography as well as meridional current shear

is there a continuous subtropical front south of africa a 14 3 year series of weekly absolute sea surface height ssh and associated geostrophic velocities is used for a study of the subtropical to subantarctic frontal system in the region south of africa detecting the fronts from surface velocity maxima confirms a two stepped transition in both the southeastern atlantic ocean the northern and southern subtropical fronts nstf sstf and southwestern indian ocean the agulhas front and sstf as proposed previously from hydrographic data an additional front associated with westward flow north of the nstf is indicative of a partial eastern closure of the south atlantic subtropical gyre between 11 e and 17 5 e the role of northwestward propagating agulhas rings in connecting the two fronts explains the varying location the sstf which marks the southern limit of subtropical waters is found continuous from the atlantic to the indian ocean in the time averaged ssh field in the weekly fields however the velocity maximum criterion defining the front is often met at the southern flanks of agulhas rings or agulhas eddies at 12 e 23 e indicating front disruptions such discontinuities suggest that no south atlantic central water is directly advected into the indian ocean instead the eastward limb of the indo atlantic super gyre encompassing the subtropical gyres of both oceans would rest at these longitudes on diffusive processes at the upper levels and possibly be enhanced at depth a schematic diagram of the fronts and their relations to agulhas rings and eddies is proposed

sedimentation of the phyllopod bed within the cambrian burgess shale formation of british columbia we provide the most detailed sedimentological log to date through the phyllopod bed of the mid cambrian burgess shale formation of british columbia based on millimetre scale logging of a suite of thin sections the sedimentary facies is dominated by alternations of homogeneous mudstone and a coarser grained laminated variably sandy and shelly mudstone that is locally micronodular most boundaries between these two lithologies are gradational and discrete fining upwards turbidite units were rarely recognized such a pattern is interpreted to indicate rapid sedimentation of up to decimetre thick units at this location from pulsatory quasi continuous density currents consistent with earlier proposals of exceptional preservation through rapid burial the density currents responsible were probably largely akin to mud rich slurries helping explain the transport and entombment of the fossils the homogeneous mudstone units are characterized by numerous distinctive lenses of pyrite framboids or subeuhedral crystals previously interpreted as small ripples their 3d shape however suggests an origin as subspherical early diagenetic aggregates their present morphology is consistent with the high levels of compaction inferred from the preservation of fossils

deep water stratigraphic cyclicity and carbonate mud mound development in the middle cambrian marjum formation house range utah usa in mid middle cambrian time shallow water sedimentation along the cordilleran passive margin was abruptly interrupted by the development of the deep water house range embayment across nevada and utah the marjum formation 330 m in the central house range represents deposition in the deepest part of the embayment and is composed of five deep water facies limestone argillaceous limestone rhythmites shale thin carbonate mud mounds bioturbated limestone and cross bedded limestone these facies are cyclically arranged into 1 5 to 30 m thick parasequences that include rhythmite mound rhythmite shale rhythmite bioturbated limestone and rhythmite cross bedded limestone parasequences using biostratigraphically constrained sediment accumulation rates the parasequences range in duration from 14 to 270 kyr the mud mounds are thin 2 m closely spaced laterally linked symmetrical domes composed of massive fenestral peloidal to clotted microspar with sparse unoriented poorly sorted skeletal material calcitized bacterial filaments tubes and abundant fenestrae and stroma tactoid structures these petrographic and sedimentological features suggest that the microspar peloids clots and syndepositional micritic cement were precipitated in situ from the activity of benthic microbial communities concentrated growth of the microbial communities occurred during periods of decreased input of fine detrital carbonate transported offshore from the adjacent shallow water carbonate platform in the neighbouring wah wah range and throughout the southern great basin coeval mid middle cambrian shallow water carbonates are composed of abundant metre scale upward shallowing parasequences that record high frequency 104 105 years eustatic sea level changes given this regional stratigraphic relationship the marjum formation parasequences probably formed in response to high frequency sea level fluctuations that controlled the amount of detrital carbonate input into the deeper water embayment during high frequency sea level rise and early highstand detrital carbonate input into the embayment decreased as a result of carbonate factory retrogradation resulting in the deposition of shale base of rhythmite shale parasequences or thin nodular rhythmites followed by in situ precipitated mud mounds lower portion of rhythmite mound parasequences during the ensuing high frequency sea level fall lowstand detrital carbonate influx into the embayment increased on account of carbonate factory pro gradation towards the embayment resulting in deposition of rhythmites upper part of rhythmite mound parasequences reworking of rhythmites by a lowered storm wave base cross bedded limestone deposition or bioturbation of rhythmites by a weakened lowered o2 minimum zone bioturbated lime stone deposition this interpreted sea level control on offshore carbonate sedimentation patterns is unique to palaeozoic and earliest mesozoic deep water sediments after the evolution of calcareous plankton in the jurassic the presence or absence of deeper water carbonates was influenced by a variety of chemical and physical oceanographic factors rather than just physical transport of carbonate muds

modulation of chlorophyll concentration by downwelling rossby waves during the winter monsoon in the southeastern arabian sea abstract signatures of rossby waves that are evident in satellite ocean colour data in the southeastern arabian sea seas are more prominent during the winter than the summer monsoon during the winter the sea level is high and the conditions are less conducive for the injection of nutrients through the eddy pumping mechanism in this study we use satellite observations and a physical ecosystem model to examine the role of horizontal advection associated with rossby waves in enhancing chlorophyll concentration in the seas zonal advection dominates over meridional advection and its effect is more prominent in the south of indian subcontinent and west of the maldives except along the coast and around the islands the vertical processes are weak and do not lead to a substantial increase in chlorophyll model simulations show that the currents associated with the rossby wave also transport nutrients and other physicochemical properties of water along the path of the wave the advected water decreases the concentration of arabian sea high salinity water mass and replenishes the oxygen in the oxygen minimum zone in the seas

the weeks formation konservat lagerstatte and the evolutionary transition of cambrian marine life the weeks formation in utah is the youngest c 499 ma and least studied cambrian lagerstatte of the western usa it preserves a diverse exceptionally preserved fauna that inhabited a relatively deep water environment at the offshore margin of a carbonate platform resembling the setting of the underlying wheeler and marjum formations however the weeks fauna differs significantly in composition from the other remarkable biotas of the cambrian series 3 of utah suggesting a significant guzhangian faunal restructuring this bioevent is regarded as the onset of a transitional episode in the history of life separating the two primary diversifications of the early paleozoic the weeks fossils have been strongly affected by late diagenetic processes but some specimens still preserve exquisite anatomical details supplementary material a supplementary text material and methods four supplementary tables compositions of the lower and upper weeks faunas structure of the upper weeks fauna and results of the similarity analyses and a supplementary data file generic presence absence matrix are available at https doi org 10 6084 m9 figshare c 4109588

an altimetry based gravest empirical mode south of africa 2 dynamic nature of the antarctic circumpolar current fronts 1 swart et al 2010 applied altimetry data to the gravest empirical mode south of africa to yield a 16 year time series of temperature and salinity sections in this study we use these thermohaline sections to derive weekly estimates of heat content hc and salt content sc at the goodhope meridional transect of the antarctic circumpolar current acc these estimates compare favorably to observed data the resulting 16 year time series of hc and sc estimates are used to explain the subsurface thermohaline variability at each acc front and frontal zone the variability at the subantarctic zone saz is principally driven by the presence of agulhas rings which occur in this region approximately 2 7 times per annum and are responsible for the longest and highest scales of observed variability the variability of the saz is responsible for over 50 and 60 of the total acc hc and sc variability respectively poleward of the saz the variability is largely determined by the influence of the local topography on the fronts of the region and can be explained by the conservation of potential vorticity wavelet analysis is conducted on the time series of meridionally integrated hc and sc in each acc front and frontal zone revealing a consistent seasonal mode that becomes more dominant toward the southern limit of the acc the lower frequency signals are compared with two dominant modes of variability in the southern ocean the southern annular mode correlates well with the hc and sc anomaly estimates at the antarctic polar front while the southern oscillation index appears to have connections to the variability found in the very southern domains of the acc

bio optical footprints created by mesoscale eddies in the sargasso sea 1 we investigate the bio optical footprints made by mesoscale eddies in the sargasso sea and the processes that create them through an eddy centric approach many 10 000 eddies are identified and followed in time using satellite altimetry observations and the spatial ocean color patterns surrounding each eddy are assessed we find through a sequence of statistical hypothesis tests that not one but several mechanisms i e eddy pumping eddy advection and eddy ekman pumping are responsible for the spatial temporal ocean color patterns following individual eddies both eddy pumping and the eddy ekman pumping mechanisms alter subsurface nutrient distributions thereby driving biogeochemical cycles while the eddy advection mechanism to first order stirs existing horizontal gradients in bio optical properties this work illustrates both the promise and some of the limitations of satellite observations for assessing the biogeochemical impacts of mesoscale eddies

wind forced variability of the antarctic circumpolar current south of africa between 1993 and 2010 the variability of the antarctic circumpolar current acc system is largely linked to the atmospheric forcing the objective of this work is to assess the link between local wind forcing mechanisms and the variability of the upper ocean temperature and the dynamics of the different fronts in the acc region south of south africa to accomplish this in situ and satellite derived observations are used between 1993 and 2010 the main finding of this work is that meridional changes in the westerlies linked with the southern annular mode sam drive temperature anomalies in the ekman layer and changes in the subantarctic front saf and antarctic polar front apf transports through ekman dynamics the development of easterly anomalies between 35 s and 45 s during positive sam is linked to reduced increased saf apf transports and a warmer mixed layer in the acc the link between the changes in the wind stress and the saf and apf transport variations occurs through the development of ekman pumping anomalies near the frontal boundaries driving an opposite response on the saf and apf transports the observed wind driven changes in the frontal transports suggest small changes to the net acc transport in addition observations indicate that the saf and apf locations in this region are not linked to the local wind forcing emphasizing the importance of other factors e g baroclinic instabilities generated by bottom topography to changes in the frontal location results obtained here highlight the importance of repeat xbt temperature sections and their combined analysis with other in situ and remote sensing observations

the south atlantic current in this paper we use the historical hydrographic data base for the south atlantic ocean to investigate i the hydrographic boundary between the subtropical gyre and the antarctic circumpolar current acc the sub tropical front stf and ii the southern current band of the gyre which is called the south atlantic current sac the stf begins in the west in the brazil falkland malvinas confluence zone but at locations at and west of 45 w this front is often coincident with the brazil current front east of 45 w the stf appears to be a distinct feature to at least the region south of africa whereupon it continues into the indian ocean the associated current band of increased zonal speed is the sac which except for one instance is found at or north of the surface stf until indian ocean water from the agulhas retroflection is reached a reversal of baroclinicity in the stf is observed south of a highly saline agulhas ring causing the sac to separate from the stf and turn north into the benguela current zonal flow south of the stf is generally weak and serves to separate the south atlantic and circumpolar currents in the argentine basin the sac has a typical volume transport of 30 sv 1 sv 106m3s 1 in the upper 1000 m relative to a deep potential density surface 4 45 87 kg m 3 and can be as high as 37 sv it is thus comparable to or stronger than the brazil current in the cape basin the transport of the sac is reduced to about 15 sy before it turns north to feed the benguela current in late 1983 this flow was joined by about 8 sv of water from the agulhas current

geophysical and geological signatures of relative sea level change in the upper wheeler formation drum mountains west central utah a perspective into exceptional preservation of fossils abstract the middle cambrian wheeler formation in utah is renowned for its exceptionally preserved fossils herein geophysical techniques gamma ray spectrometry and magnetic susceptibility carbonate analyses lithofacies and fossils are used to characterize limestones and calcareous mudrocks of the upper portion of the middle wheeler formation and the upper wheeler formation in the drum mountains west central utah this succession was deposited on a mixed carbonate siliciclastic ramp within the house range embayment an eastward incursion of deeper water created and bounded on the southeast by a normal fault geophysical data clearly reveal variations in carbonate versus clay content observed patterns among outcrop geophysical data lithofacies and fossils are interpreted within the contexts of relative sea level changes and a sequence stratigraphic model above a basal interval of rhythmically bedded limestones interpreted to have been deposited on the middle part of the ramp during a period of relatively low sea level lithofacies rising gamma ray and rising magnetic susceptibility track a transgression which culminates in a maximum flooding surface mfs this mfs is near the base of a hot zone an 6 m thick interval of exceptional preservation konservat lagerstatte highest magnetic susceptibility highest gamma ray values highest clay content and with a bulk carbonate content of 4 20 the basal layer of this zone contains abundant fully articulated specimens of agnostids and tiny polymerid trilobites exceptionally preserved fossils such as non trilobite arthropods priapulid and annelid worms hyolithids phyllocarid arthropods with soft parts algae and fragile sponges are much more abundant within this hot zone than in other strata of the succession these specimens are preserved in very thin bedded to laminated mudrock only rarely interrupted by macroscopic signs of bioturbation stratigraphically above the hot zone is a thick unit of mudrock in which both gamma ray and magnetic susceptibility decrease gradually at first and then precipitously to very low levels in concert few soft bodied specimens have been recovered from this upper interval the gradual decrease in geophysical responses is interpreted to be the result of gradual shallowing during highstand caused mainly by progradation of the carbonate factory it was followed by an abrupt regression mudrocks are capped by burrow mottled grainstone and stromatolitic boundstone representing a lowstand or the earliest transgressive phase of the next cycle these observations lead to the following conclusions 1 the upper wheeler formation represents most of a third or fourth order cycle of relative sea level change on a mixed carbonate siliciclastic ramp rather than a period of shallow water lagoonal sedimentation as previously proposed 2 superimposed on this overall cycle are several perhaps many higher order fluctuations in relative sea level 3 when the present results are coupled with results of earlier workers who interpreted the lower and middle wheeler formation as a major transgression and regression the wheeler formation of the drum mountains involves two major sea level cycles rather than one 4 the konservat lagerstatte was preserved in the deepest water early highstand portion of the upper wheeler sequence and 5 these results support earlier hypotheses that konservat lagerstatten in mixed carbonate siliciclastic successions are most likely to occur during late transgression to early highstand given that low energy anoxic conditions prevailed

anticyclonic and cyclonic eddies of subtropical origin in the subantarctic zone south of africa two eddies one anticyclonic and the other cyclonic intersected in the subantarctic zone south of south africa during a hydrographic transect are described using a large set of measurements including full depth hydrography acoustic doppler current profiler velocities biogeochemical tracers air sea fluxes and altimetric sea surface height both eddies have a subtropical origin the anticyclone is an agulhas ring with convected core water of similar to 12 degrees c and swirl velocities of 1 m s 1 it was 9 5 months old when sampled and had crossed the agulhas ridge though sampled in summer it was releasing similar to 200 w m 2 sensible plus latent heat flux to the atmosphere it was observed adjacent to the subantarctic front illustrating the usual encounters of such structures with this front the cyclone marked by pronounced low oxygen and cfc anomalies revealing an origin at the continental slope was 4 5 months old it had swirl speeds of 0 3 m s 1 and was coupled with the anticyclone when observed from their kinematics and water mass properties both structures were found to transport subtropical water down to similar to 900 m the water trapped below this depth being either from the northern subantarctic zone or local water the two structures illustrate the capacity of eddies in the region to transfer subtropical and alongslope water properties into the subantarctic zone

a new hypothesis for organic preservation of burgess shale taxa in the middle cambrian wheeler formation house range utah cambrian konservat lagerstatten are the most significant fossil deposits for our understanding of the initiation of phanerozoic life although many modes of preservation may occur these deposits most frequently contain nonmineralized fossils preserved in the form of kerogenized carbon films a rare yet important taphonomic pathway that has not previously been explained for any unit by a comprehensive model the middle cambrian wheeler formation of utah one of these lagerstatten contains abundant kerogenized preservation of nonmineralized tissues which occurs within a distinctive taphofacies that accumulated under the following conditions 1 domination of the siliciclastic fraction by clay sized particles 2 close proximity to a carbonate platform which resulted in mixed carbonate clay sediments 3 a well developed oxygen minimum precluding benthic colonization and burrowing and 4 relative proximity to oxic bottom waters facilitating transport of organisms from a habitable environment to one that favored their preservation we propose that preservation of nonmineralized tissues in the wheeler formation may have resulted from a combination of influences that reduced permeability and thus lowered oxidant flux which in turn may have restricted microbial decomposition of some nonmineralized tissues those influences include near bottom anoxia preventing sediment irrigation by restriction of bioturbation reducing conditions near the sediment water interface that may have acted to deflocculate aggregations of clay minerals resulting in low permeability face to face contacts early diagenetic pore occluding carbonate cements and an absence of coarse grains such as silt skeletonized microfossils fecal pellets or bioclasts this model may be applicable to kerogenized preservation of macrofossils in other fossil lagerstatten

vertical motions and their effects on a biogeochemical tracer in a cyclonic structure finely observed in the ligurian sea vertical velocities can be estimated indirectly from in situ observations by theoretical frameworks like the equation direct measures of vertical exchanges are challenging due to their typically ephemeral spatiotemporal scales in this study we address this problem with an adaptive sampling strategy coupling various biophysical instruments we analyze the 3 d organization of a cyclonic mesoscale structure finely sampled during the observing submesoscale coupling at high resolution cruise in the ligurian sea during fall 2015 the observations acquired with a moving vessel profiler highlight a subsurface low salinity layer 50 m as well as rising isopycnals generated by geostrophic cyclonic circulation in the structure s center reconstructed 3 d fields of density and horizontal velocities are used to estimate the vertical velocity field down to 250 m by applying the adiabatic qg equation for the first time in this region the vertical motions are characterized by multipolar patterns of downward and upward velocities on the edges of the structure and significantly smaller vertical velocities in its center both the 3 d distribution of particles size 100 m measured with a laser optical plankton counter and the synechococcus and prochlorococcus abundances cell per cubic meter measured by flow cytometry are consistent with the 3 d velocity field in particular a secondary vertical recirculation is identified that upwells particles from 250 to 100 m along isohalines to the structure s center besides demonstrating the effect of vertical patterns on biogeochemical distributions this case study suggests to use particle matter as a tracer to assess physical dynamics

new eocrinoids from the burgess shale southern british columbia canada and the spence shale northern utah usa the family lyracystidae n fam and genus lyracystis n gen are proposed for the holotype and one paratype of the middle cambrian eocrinoid gogia radiata sprinkle the burgess shale arms from the same unit and many additional partial and more complete specimens of this eocrinoid collected from the burgess shale since 1975 a second species lyracystis reesei n gen and n sp is described from a single partly complete specimen from the similar aged spence shale of northern utah lyracystis has three wide v shaped arms bearing numerous long straight brachioles in the notch a partly organized theca having larger and smaller ridged plates with epispires and a very long multiplated stalk made up of rounded or spiny small plates lyracystis is the longest stalked suspension feeding echinoderm known from the middle cambrian the three remaining paratypes of gogia radiata and four new specimens with possible branched brachioles from the burgess shale are renamed gogia stephenensis n sp

response to comment on oceanic rossby waves acting as a hay rake for ecosystem floating by products anomalous chlorophyll concentrations detected from satellites propagate along with rossby waves in all tropical oceans 1 1 2 2 in the southeastern tropical pacific a biologically poor region we found that chlorophyll maxima are located in convergence rather than divergence zones 3

sediment dynamics driven by contour currents and mesoscale eddies along continental slope a case study of the northern south china sea abstract based upon 3 d seismic reflection data published drill core studies oceanographic observations and numerical modelling this study identifies a small scale contourite depositional system that is locally confined by canyons slope failures erosional terraces and erosional slopes on the jianfeng slope northern south china sea 1500 to 2300 m water depth possible oceanic driving mechanisms for the spatial heterogeneity in sedimentation and erosion within the quaternary deposits in this complex slope system are investigated numerical simulations show that the quasi steady south china sea deep water circulation which affects the study area is characterised by low velocities maximum 4 cm s with a slight modulation by tides 1 cm s this quasi steady deep water thermohaline circulation is able to keep sediment particles in suspension rather than to erode seafloor sediment the bottom hydrodynamic regime becomes energetic when mesoscale eddies horizontal scale of 10 to 100 km approach our modelling study indicates that both surface and bottom mesoscale eddies are essential to account for the spatial heterogeneity in sedimentation pattern along the northern south china sea continental slope according to simulation the eddy front contains the highest flow velocity over a mesoscale eddy cycle 45 days exceeding the threshold for resuspension of unconsolidated sediment 15 cm s as a consequence massive resuspension is produced at various sites and redistributed by sub mesoscale horizontal scale of 1 to 10 km circulations originated from an eddy topography interaction in contrast to the surrounding areas which are subject to erosional forcing for a relatively long part 7 of an eddy cycle both the locally confined drift and a further upstream large elongated mounded drift experience little erosion

manifestation of oceanic rossby waves in long term multiparametric satellite datasets the characteristics of westward copropagating features in satellite altimetry sea surface temperature and ocean colour data are investigated throughout the global oceans between 50 north and 50 south for the period 1998 2008 a new hybrid filtering approach allowing features with periods between 37 and 410 days to pass polewards of 20 north and south and features with periods between 37 and 205 days to pass within 20 of the equator is found to isolate features whose speed is consistent with predictions of long planetary wave theory throughout much of the oceans features with wavelengths between 300 and 800 km and periods between 205 and 410 days are shown to be a significant source of temperature and chlorophyll variability between 20 and 50 north and south whilst within 20 of the equator signals in the 800 1500 km and 37 205 days range are predominant between 15 and 50 north and south observed propagation speeds are found to closely match those predicted for first mode baroclinic rossby waves by theory in the equatorial pacific and atlantic oceans features with wavelengths 800 2000 km periods 15 40 days and phase speeds 20 50 cm s 1 characteristic of tropical instability waves are preferentially observed the amplitude and phase relationship between copropagating signals in ocean colour and altimetry and sea surface temperature and altimetry is interpreted in terms of the horizontal meridional advection of mean temperature and chlorophyll gradients by rossby waves similar to what has recently been observed for non linear eddies at shorter length scales the observed phase relationships are in good agreement with the range of phases expected for horizontal advection throughout much of the oceans and consistent with the sign of the mean meridional gradients of temperature and chlorophyll these results support the view that horizontal advection be it from waves and or eddies is the dominant mode of covariation of temperature and chlorophyll with sea surface height throughout most of the oceans although the agreement between predicted and observed amplitude and phase relationships is insufficient to completely rule out vertical mechanisms in a few regions we believe that a one size fits all approach for global rossby wave studies can no longer be considered valid and although we have modified our technique to take this into account we advocate future work to develop a fully latitudinally dependent filtering methodology

eddy activity in the four major upwelling systems from satellite altimetry 1992 2007 eddy activity in the four major eastern boundary upwelling systems ebus is investigated using 15 years of satellite altimetry data based on the analysis of more than 4000 long lived eddy trajectories in every ebus we show that mesoscale structures are mainly generated along the continental coasts and south of the main archipelagos and propagate westward with velocities increasing toward the equator these mesoscale eddies having radii of 70 160 km are then frequently observed along the coastal transition zones and frontal regions and some large oceanic areas are preferentially populated by cyclonic or anticyclonic eddies temporal variations of the number of newly formed eddies and the associated eddy activity index defined as the mean eddy energy density are finally examined at seasonal and interannual scales the strongest seasonal interannual respectively variations are observed in the california benguela upwelling systems the proposed indices also exhibit contrasted long term trends in each ebus which suggests that eddy activity might be sensitive to a warming climate

dynamics of the indian ocean oxygen minimum zones abstract in the indian ocean mid depth oxygen minimum zones omzs occur in the arabian sea and the bay of bengal the lower part of the arabian sea omz asomz below 400 m intensifies northward across the basin in contrast its upper part above 400 m is located in the central eastern basin well east of the most productive regions along the western boundary the bay of bengal omz bbomz although strong is weaker than the asomz to investigate the processes that maintain the indian ocean omzs we obtain a suite of solutions to a coupled biological physical model its physical component is a variable density 6 1 2 layer model in which each layer corresponds to a distinct dynamical regime or water mass type its biological component has six compartments nutrients phytoplankton zooplankton two size classes of detritus and oxygen because the model grid is non eddy resolving 0 5 the biological model also includes a parameterization of enhanced mixing based on the eddy kinetic energy derived from satellite observations to explore further the impact of local processes on omzs we also obtain analytic solutions to a one dimensional simplified version of the biological model our control run is able to simulate basic features of the oxygen nutrient and phytoplankton fields throughout the indian ocean the model omzs result from a balance or lack thereof between a sink of oxygen by remineralization and subsurface oxygen sources due primarily to northward spreading of oxygenated water from the southern hemisphere with a contribution from persian gulf water in the northern arabian sea the northward intensification of the lower asomz results mostly from horizontal mixing since advection is weak in its depth range the eastward shift of the upper asomz is due primarily to enhanced advection and vertical eddy mixing in the western arabian sea which spread oxygenated waters both horizontally and vertically advection carries small detritus from the western boundary into the central eastern arabian sea where it provides an additional source of remineralization that drives the asomz to suboxic levels the model bbomz is weaker than the asomz because the bay lacks a remote source of detritus from the western boundary although detritus has a prominent annual cycle the model omzs do not because there is not enough time for significant remineralization to occur

oceanography the rossby rototiller planetary waves also known as rossby waves propagate throughout the world s oceans on very large scales they influence the ocean climate system and also it seems the delivery of nutrients to the ocean surface

new chemical bio optical and physical observations of upper ocean response to the passage of a mesoscale eddy off bermuda a mesoscale eddy advected across the bermuda testbed mooring site over a 30 day period centered on july 14 1995 temperature and current measurements along with biogeochemical measurements were used to characterize the biological response of the upper ocean associated with the introduction of nitrate into the euphotic layer due to the doming of isotherms associated with the eddy complementary shipboard data showed an anomalous water mass which extended from a depth of 50 to 1000 m manifesting as a cold surface expression and warm anomaly at depth although mesoscale eddies are frequently observed in the sargasso sea the present observations are particularly unique because of the high temporal resolution measurements of the new instrumentation deployed on the mooring analyzers that measure nitrate plus nitrite were placed at depths of 80 and 200 m and bio optical sensors were located at depths of 20 35 45 71 and 86 m peak nitrate values of nearly 3 0 mm at 80 m and chlorophyll a values of 1 4 mg m 23 at 71 m were observed as well as a 25 to 30 meter shoaling of the 1 light level depth a doppler shift from the inertial period 22 8 hours to 25 2 hours was observed in several time series records due to the movement of the eddy across the mooring inertial pumping brought cold nutrient rich waters farther into the euphotic zone than would occur solely by isothermal lifting silicic acid was depleted to undetectable levels owing to the growth of diatoms within the eddy the chlorophyll a values associated with the eddy appear to be the largest recorded during the 8 years of the ongoing u s jgofs bermuda atlantic time series study bats program

the spence shale lagerstatte an important window into cambrian biodiversity the spence shale member of the langston formation is a cambrian miaolingian wuliuan lagerstatte in northeastern utah and southeastern idaho it is older than the more well known wheeler and marjum lagerstatten from western utah and the burgess shale from canada the spence shale shares several species with these younger deposits yet it also contains a remarkable number of unique species because of its relatively broad geographical distribution and the variety of palaeoenvironments and taphonomy the fossil composition and likelihood of recovering weakly skeletonized or soft bodied taxa varies across localities the spence shale is widely acknowledged not only for its soft bodied taxa but also for its abundant trilobites and hyoliths recent discoveries from the spence shale include problematic taxa and provide insights about the nature of palaeoenvironmental and taphonomic variation between different localities supplementary material a generic presence absence matrix of the spence shale fauna and a list of the spence shale localities are available at https doi org 10 6084 m9 figshare c 4423145

processes controlling upper ocean heat content in drake passage 1 a 16 year record of expendable bathythermograph transects across drake passage is used to examine variability in upper ocean heat content that is not associated with the annual cycle links between upper ocean heat content and anomalous heat fluxes winds two large scale climate indices and mesoscale eddies and meanders are examined results suggest that interannual variations in surface heat fluxes explain 5 to 10 of the variance in upper ocean heat content anomalous surface heat fluxes are linked to meridional wind anomalies upstream of drake passage which in turn are linked to forcing by el nino southern oscillation enso and the southern annular mode sam enso and sam are correlated with upper ocean heat content at near zero lags and statistically significant correlations occur at longer time lags as well the impact of mesoscale eddies and meanders on upper ocean heat content is explored with the use of a tracked eddy database an empirical relationship is constructed relating upper ocean heat content anomalies to eddy length scales and amplitudes eddies and meanders are estimated to account for more than one third of the nonannual cycle variance in drake passage upper ocean heat content

using gis to study palaeobiogeographic and macroevolutionary patterns in soft bodied cambrian arthropods abstract soft bodied cambrian arthropods from burgess shale type deposits are some of the most famous and extensively studied fossil invertebrates but global species level assessments of their biogeographic patterns have not previously been explored quantitatively here we use a newly developed occurrence database in conjunction with geographic information systems gis analysis and paleogis which allows fossil locality positions to be viewed in the context of cambrian palaeogeography to quantitatively reconstruct geographic distribution patterns of primarily soft bodied arthropod species further we compare these patterns with those of co occurring trilobite taxa soft bodied cambrian arthropods show both statistically larger geographic ranges and greater stratigraphic longevities than co occurring trilobites many of the most widely distributed soft bodied arthropods were likely capable of swimming and this may in part explain their extensive distributions

fronts transport and weddell gyre at 30 e between africa and antarctica a detailed description of the frontal structure of major currents and estimates of transport between africa and antarctica at 30 e were made on the basis of a finely resolved hydrographic section made during the 1996 civa 2 cruise particular emphasis was put on a refinement of the eastern boundary of the weddell gyre by analyzing also supplementary hydrographic data from the 1993 civa 1 cruise and the best available historical hydrographic data in the weddell and enderby basins contrary to the general belief our results show that the weddell gyre extends far beyond 30 e reaching at least as far east as the enderby land promontory 53 e from this point westward currents along the antarctic continental margin constitute the gyre s southern boundary thus closing the cyclonic circulation of the gyre at its easternmost end as the most convincing evidence for this refined circulation scheme significant westward transport south of 65 s has been identified from the civa 1 acoustic doppler current profiler data we have shown also using an inertial jet model that the blocked feature of the weddell cold regime 57 s to the west of 25 e is due to the topographic control of flow by local bathymetry during the civa 2 cruise 70 of the antarctic circumpolar current acc was concentrated near the polar front 51 s with surface speeds reaching up to 70 cm s 1 the baroclinic current field in the subpolar area south of the weddell front 58 s for civa 2 and 57 s for civa 1 is featureless 3 cm s 1 but yielding a nonnegligible eastward transport of 15 sv 1 sv 106 m3 s 1 this bottom referenced baroclinic transport is entirely compensated by a substantial westward barotropic transport south of 65 s the acc transport across the 30 e section during the civa 2 cruise is estimated to be 160 sv

the control of the southern hemisphere westerlies on the position of the subtropical front in recent years the latitudinal position of the subtropical front stf has emerged as a key parameter in the global climate a poleward positioned front is thought to allow a greater salt flux from the indian to the atlantic ocean and so drive a stronger atlantic meridional overturning circulation here the common view that the stf aligns with the zero wind stress curl wsc is challenged based on the stf climatologies of orsi et al 1995 belkin and gordon 1996 graham and de boer 2013 and on satellite scatterometry winds we find that the zero wsc contour lies on average approximate to 10 degrees approximate to 8 degrees and approximate to 5 degrees poleward of the front for the three climatologies respectively the circulation in the region between the subtropical gyres and the zero wsc contour is not forced by the wsc but rather by the strong bottom pressure torque that is a result of the interaction of the antarctic circumpolar current with the ocean floor topography the actual control of the position of the stf is crucially dependent on whether the front is regarded as simply a surface water mass boundary or a dynamical front for the agulhas leakage problem the southern boundary of the so called super gyre may be the most relevant property but this cannot easily be identified in observations

the dynamical subtropical front 1 the southern ocean subtropical front stf is thought to play a key role in the global climate system theory suggests that the latitude of the stf regulates the volume of saline agulhas leakage into the atlantic ocean from the indian here we use satellite sea surface temperature sst and sea surface height ssh data to study the physical characteristics of the stf water mass boundary we find that the strong currents in this region do not align with the surface water mass boundary therefore we provide a new climatology for these currents which we define as the dynamical stf dstf the dstf is the eastward extension of the western boundary current in each basin and is characterized by strong sst and ssh gradients and no seasonal cycle at the center of each basin it merges with the sub antarctic front on the eastern side of basins the stf surface water mass boundary coincides with a separate region of multiple sst fronts we call this the subtropical frontal zone stfz the fronts in the stfz have a large seasonal cycle and no ssh signature despite lying close to the same water mass boundary the dstf and stfz are completely unrelated we therefore suggest the term stf only be used when referring to the surface water mass boundary when studying the strong currents on the western side of basins the term dstf is more relevant and similarly the term stfz better describes the region of enhanced sst gradients towards the east

intrusion of the bay of bengal water into the arabian sea during winter monsoon and associated chemical and biological response this work was supported by the department of ocean development under the program marine research living resources mr lr jayu narvekar acknowledges the financial support from csir

rossby wave and ocean color the cells uplifting hypothesis in the south atlantic subtropical convergence zone 1 rossbywavessignaturesonfilteredoceancolordataare detected in the subtropical convergence zone of the south atlantic ocean we investigate whether these chlorophyll anomalies can be accounted for by the uplifting mechanism of phytoplanktonic cells associated with the passage of a rossby wave we consider vertical chlorophyll profiles exhibiting a subsurface chlorophyll maximum typical of the south atlantic subtropical convergence province chlorophyll remotely sensed concentrations resulting from an academic uplifting of the three chlorophyll profiles are reconstructed with a radiative transfer model amplitude of the chlorophyll enrichments found with this hypothesis 0 06 mg chl m 3 compares well with propagative ocean color anomalies detected in the seawifs data however other processes such as the rototiller effect siegel 2001 or advection of chlorophyll gradients could also play a non negligible role index terms 4560 oceanography physical surface wavesandtides 1255 9325information related to geographic region atlantic ocean 4552 oceanography

mechanism for burgess shale type preservation exceptionally preserved fossil biotas of the burgess shale and a handful of other similar cambrian deposits provide rare but critical insights into the early diversification of animals the extraordinary preservation of labile tissues in these geographically widespread but temporally restricted soft bodied fossil assemblages has remained enigmatic since walcott s initial discovery in 1909 here we demonstrate the mechanism of burgess shale type preservation using sedimentologic and geochemical data from the chengjiang burgess shale and five other principal burgess shale type deposits sulfur isotope evidence from sedimentary pyrites reveals that the exquisite fossilization of organic remains as carbonaceous compressions resulted from early inhibition of microbial activity in the sediments by means of oxidant deprivation low sulfate concentrations in the global ocean and low oxygen bottom water conditions at the sites of deposition resulted in reduced oxidant availability subsequently rapid entombment of fossils in fine grained sediments and early sealing of sediments by pervasive carbonate cements at bed tops restricted oxidant flux into the sediments a permeability barrier provided by bed capping cements that were emplaced at the seafloor is a feature that is shared among burgess shale type deposits and resulted from the unusually high alkalinity of cambrian oceans thus burgess shale type preservation of soft bodied fossil assemblages worldwide was promoted by unique aspects of early paleozoic seawater chemistry that strongly impacted sediment diagenesis providing a fundamentally unique record of the immediate aftermath of the cambrian explosion

phytoplankton pigment distribution from seawifs data in the subtropical convergence zone south of africa a wavelet analysis the agulhas system agulhas current retroflection agulhas return current arc south of africa constitutes a complex energetic system subject to high frequency mesoscale and low frequency variability using chlorophyll pigment concentration data collected by the seawifs ocean color sensor and sea surface height satellite data we demonstrate the utility of wavelet analysis in jointly analyzing ocean color and altimetric signals two distinct dynamical scenarios of the agulhas system october 1997 and january 1998 yield different dominant wavelengths 620 and 500 km for the arc rossby wave they are simultaneously retrieved from the chlorophyll and sea level anomaly signals longitudinal extension of the power resulting from the wavelet analysis also depends on the dynamical regime

generation of cyclonic eddies by the agulhas current in the lee of the agulhas bank anti cyclonic rings are shed from the agulhas current at its retroflection they subsequently drift off into the south atlantic smaller cyclonic eddies have also been observed in this region the origin of these latter eddies has remained unknown we present model results that indicate that the configuration of the southern agulhas current and the poleward termination of the continental shelf of africa allows shedding of cyclonic lee eddies by a flow detachment process hydrographic data thermal infrared satellite images and altimetric observations are furnished that show that this model simulation is consistent with the characteristics and the behaviour of cyclonic eddies in the region

yanai waves in the western equatorial indian ocean 1 observations and models have shown the presence of intraseasonal fluctuations in 20 30 day and 10 20 day bands in the equatorial indian ocean west of 60 e weio their spatial and temporal structures characterize them as yanai waves which we label low frequency lfyw and high frequency hfyw yanai waves respectively we explore the dynamics of these intraseasonal signals using an ocean general circulation model modular ocean model and a linear continuously stratified model yanai waves are forced by the meridional wind y everywhere in the weio most strongly during the monsoon seasons they are forced both directly in the interior ocean and by reflection of the interior response from the western boundary interference between the interior and boundary responses results in a complex surface pattern that propagates eastward and has nodes yanai waves are also forced by instabilities primarily during june july in a region offshore from the western boundary 52 55 e at that time eddies generated by barotropic instability of the southern gyre are advected southward to the equator there they generate a westward propagating cross equatorial flow field veq with a wave number frequency spectrum that fits the dispersion relation of a number of yanai waves and these waves are efficiently excited typically yanai waves associated with several baroclinic modes are excited by both wind and eddy forcing and typically they superpose to create beams that carry energy vertically and eastward along ray paths the same processes generate lfyws and hfyws and hence their responses are similar differences are traceable to the property that hfyws have longer wavelengths than lfyws for each baroclinic mode

global observations of large oceanic eddies 1 ten years of sea surface height ssh fields constructed from the merged topex poseidon t p and ers 1 2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean the higher resolution of the merged dataset reveals that more than 50 of the variability over much of the world ocean is accounted for by eddies with amplitudes of 5 25 cm and diameters of 100 200 km these eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies respectively the vast majority of the eddies are found to be nonlinear

circumpolar structure and distribution of the antarctic circumpolar current fronts 1 mean circumpolar paths 1 high resolution hydrographic sections and maps of the gradient of sea surface height ssh reveal that the antarctic circumpolar current acc consists of multiple jets or frontal filaments here we use a 15 year time series of ssh observations to determine the circumpolar structure and distribution of the acc fronts the jets are consistently aligned with particular streamlines along the entire circumpolar path confirming and extending the results of an earlier study restricted to the region south of australia the intensity of the fronts as measured by the cross front gradient of ssh varies along the fronts and the individual branches merge and diverge often in response to interactions with bathymetry maps of absolute velocity at 1000 m depth derived from argo trajectories confirm the existence of multiple current cores throughout the southern ocean high resolution hydrographic sections and profiles of temperature and salinity from argo floats are used to show that the front locations derived from fitting ssh contours to maps of ssh gradient are consistent with locations inferred from the traditional criteria based on water mass properties suitably modified to account for multiple frontal branches three regions are examined in detail the crozet plateau the kerguelen plateau and the scotia sea these examples show how recognition of the multiple jets of the acc can help resolve discrepancies between previous studies of acc fronts

sequence stratigraphy cyclic facies and lagerstatten in the middle cambrian wheeler and marjum formations great basin utah abstract recurrent taphofacies including conservation lagerstatten are identified within a spectrum of facies in fourth order sequences in the middle cambrian wheeler and marjum formations of the drum mountains and house range west central utah these sequences are 3 20 m thick and commence with sharply based compact oncolitic oolitic or pelletal pack and grainstones with sharply defined corroded and mineralized upper contacts that record drowning discontinuities and early transgressive systems tracts tsts overlying intervals of calcareous shale and thin bedded wacke to packstones with abundant disarticulated polymerid and agnostoid trilobites represent late tsts these are commonly followed by lavender gray mudstones rich in sponge spicules and comminuted fossil debris that reflect condensed maximum flooding zones the overlying early highstand hst intervals of black fissile shales are typically barren except for indistinct circular carbonized algae but in rare instances include soft bodied animal remains a combination of lower dysoxic anoxic conditions with a fluctuating oxycline and relatively rapid episodic influx of fine grained detrital sediment favored repeated burial and preservation of abundant organic detritus and rarely soft bodied animals interbedded dark gray shales include abundant articulated agnostoid trilobites and diminutive polymerids e g jenkinsonia overlying platy calcareous bedding planes covered with articulated bodies and molts of the polymerid elrathia indicate rapid blanketing of undisturbed seafloors by calcareous mud layers these beds grade upward successively into interbedded sparsely fossiliferous platy to flaggy shale and thin pale gray weathering calcisiltites and burrow mottled to nodular limestones recording late hst to falling stage fsst carbonate shedding thin calcisiltites include fossil debris and articulated larger polymerid trilobites and the eocrinoid gogia preserved by obrutionary deposits the repeated recurrence of these patterns provides the rudiments of a predictive model that not only explains the differing modes of preservation but may also aid in prospecting for new lagerstatten

evidence for the existence of persian gulf water and red sea water in the bay of bengal the high salinity water masses that originate in the north indian ocean are arabian sea high salinity water ashsw persian gulf water pgw and red sea water rsw among them only ashsw has been shown to exist in the bay of bengal we use ctd data from recent cruises to show that pgw and rsw also exist in the bay the presence of rsw is marked by a deviation of the salinity vertical profile from a fitted curve at depths ranging from 500 to 1000 m this deviation though small of the order of similar to 0 005 psu and therefore comparable to the ctd accuracy of 0 003 psu is an order of magnitude larger than the similar to 0 0003 psu fluctuations associated with the background turbulence or instrument noise in this depth regime allowing us to infer the existence of rsw throughout the bay pgw is marked by the presence of a salinity maximum at 200 450 m in the southwestern bay pgw can be distinguished from the salinity maximum due to ashsw because of the intervening arabian sea salinity minimum this salinity minimum and the maximum associated with ashsw disappear east and north of the south central bay 85a degrees e 8a degrees n owing to mixing between the fresher surface waters that are native to the bay bay of bengal water or bbw with the high salinity ashsw hence ashsw is not seen as a distinct water mass in the northern and eastern bay and the maximum salinity over most of the bay is associated with pgw the surface water over most of the bay is therefore a mixture of ashsw and the low salinity bbw as a corollary we can also infer that the weak oxygen peak seen within the oxygen minimum zone in the bay at a depth of 250 400 m is associated with pgw the hydrographic data also show that these three high salinity water masses are advected into the bay by the summer monsoon current which is seen to be a deep current extending to 1000 m these deep currents extend into the northern bay as well providing a mechanism for spreading ashsw pgw and rsw throughout the bay

the evolution and propagation of quasigeostrophic ocean eddies abstractthe long term evolution of initially gaussian eddies is studied in a reduced gravity shallow water model using both linear and nonlinear quasigeostrophic theory in an attempt to understand westward propagating mesoscale eddies observed and tracked by satellite altimetry by examining both isolated eddies and a large basin seeded with eddies with statistical characteristics consistent with those of observed eddies it is shown that long term eddy coherence and the zonal wavenumber frequency power spectral density are best matched by the nonlinear model individual characteristics of the eddies including amplitude decay horizontal length scale decay and zonal and meridional propagation speed of a previously unrecognized quasi stable state are examined the results show that the meridional deflections from purely westward flow poleward for cyclones and equatorward for anticyclones are consistent with satellite observations examination of the fluid transport properties of the eddies shows that an

equilibration of the antarctic circumpolar current by standing meanders the insensitivity of the antarctic circumpolar current acc s prominent isopycnal slope to changes in wind stress is thought to stem from the action of mesoscale eddies that counterbalance the wind driven ekman overturning a framework verified in zonally symmetric circumpolar flows substantial zonal variations in eddy characteristics suggest that local dynamics may modify this balance along the path of the acc analysis of an eddy resolving ocean gcm shows that the acc can be broken into broad regions of weak eddy activity where surface winds steepen isopycnals and a small number of standing meanders across which the isopycnals relax meanders are coincident with sites of i strong eddy induced modification of the mean flow and its vertical structure as measured by the divergence of the eliassen palm flux and ii enhancement of deep eddy kinetic energy by up to two orders of magnitude over surrounding regions within meanders the vorticity budget shows a balance between the advection of relative vorticity and horizontal divergence providing a mechanism for the generation of strong vertical velocities and rapid changes in stratification temporal fluctuations in these diagnostics are correlated with variability in both the eliassen palm flux and bottom speed implying a link to dissipative processes at the ocean floor at larger scales bottom pressure torque is spatially correlated with the barotropic advection of planetary vorticity which links to variations in meander structure from these results it is proposed that the flexing of standing meanders provides an alternative mechanism for reducing the sensitivity of the acc s baroclinicity to changes in forcing separate from an acc wide change in transient eddy characteristics

response to comment on eddy wind interactions stimulate extraordinary mid ocean plankton blooms the alternative mechanism proposed by mahadevan et al is an unlikely explanation for our observations because their model predicts a bloom at the periphery of the eddy whereas the observations show it located at the eddy center and because the vertical displacements caused by the nonlinear ekman effect are too small to lead to an extraordinary biological response in this eddy

mesoscale eddies off peru in altimeter records identification algorithms and eddy spatio temporal patterns relatively little is known about coherent vortices in the eastern south pacific along the peruvian coast even with regard to basic facts about their frequency of occurrence longevity and structure this study addresses these issues with nearly 15 years of relatively high resolution satellite altimetry measurements we first compare two distinct automated methods for eddy identification the objective validation protocol shows that the rarely used geometrical or winding angle method based on the curvature of the streamline functions is more accurate than the commonly used okubo weiss algorithm which defines a vortex as a simple connected region with values of okubo weiss parameter weaker than a given threshold we then investigate vortices off peru using more than 20 000 mesoscale eddies identified by the winding angle method coherent eddies characterized by a high ratio of vorticity to deformation rate are typically formed along the coast and propagate westward at 3 6 cm s 1 the vortices have a mean radius of 80 km increasing northward and are most frequently observed off of chimbote 9s and south of san juan 15s the mean eddy lifetime is about 1 month but if eddies survive at least 2 months the probability for surviving an additional week or month is constant at 90 or 67 anticyclonic eddies tend to propagate northwestward whereas cyclonic vortices migrate southwestward in general cyclones and anticyclones are similar except for eddies surviving at least 6 months in this case after a similar 3 4 months of radius and amplitude growth amplitudes or sizes decay particularly rapidly for anticyclonic or cyclonic eddies in terms of intensity cyclonic eddies show a rapid decay during the first 3 months before arriving at a quasi constant value whereas anticyclones exhibit steady decline finally eddy temporal variations were examined at seasonal and interannual scales in the coastal region favorable to the formation of energetic mesoscale structures on seasonal scales eddy activity is maximal in fall and minimum in spring at interannual scales the eddy activity index was maximal during the strong el nino of 1997 1998 but another strong maximum of eddy activity also occurred late in 2004 these temporal variations are probably associated with the intensification of the upwelling thermal front and with the passage of coastal trapped waves which generate baroclinic instabilities further investigation of the mechanisms involved on the eddy genesis is needed

long extratropical planetary wave propagation in the presence of slowly varying mean flow and bottom topography part i the local problem one of the most successful theories to date to explain why observed planetary waves propagate westward faster than linear flat bottom theory predicts has been to include the effect of background baroclinic mean flow which modifies the potential vorticity waveguide in which the waves propagate barotropic flows are almost everywhere too small to explain the observed differences that theory accounted for most but not all of the observed wave speeds a later attempt to examine the effect of the sloping bottom on these waves without the mean flow effect did not find any overall speedup this paper combines these two effects assuming long geostrophic waves and slowly varying mean flow and topography and computes group velocities at each point in the global ocean these velocities turn out to be largely independent of the orientation of the wave vector a second speedup of the waves is found over that for mean flow only almost no eastward oriented group velocities are found and so features that appear to propagate in the same sense as a subtropical gyre would have to be coupled with the atmosphere or be density compensated in some manner

structure and transport of the antarctic circumpolar current and agulhas return current at 40 e hydrographic data are presented from a near meridional section across the agulhas return current the subtropical front and the antarctic circumpolar current acc in the southwest indian sector of the southern ocean the location and characteristics of the fronts are examined and the water masses are defined the agulhas return current emerges as a strong current as far east as 40 e which forms a marked front that is separate from the subtropical front and can be distinguished by a separate water mass comparisons are made with a similar hydrographic section at the greenwich meridian and several notable differences are found the subantarctic front at the greenwich meridian is a pronounced feature carrying a large proportion of the geostrophic transport of the acc on the southwest indian section however the subantarctic front is merged with the polar front at 48 s where the flow associated with the acc is concentrated geostrophic calculations show a large volume transport 84 to 103 sverdrup 1 sv 106 m3 s 1 associated with the agulhas return current at 40 s this is quite separate from the transport of the acc which totals 138 sv south of the subantarctic zone and the crozet plateau or 150 sv including flow in the subantarctic zone the transport of the acc out of the south atlantic sector appears to be higher than the transport into the south atlantic sector at drake passage with the extra transport most probably carried by upper layer and intermediate waters eddies are seen to be an important feature of the subantarctic zone where they help to modify the water masses antarctic intermediate water appears in two forms a saline 34 4 indian ocean variety and a fresh 34 2 atlantic ocean variety the atlantic variety is freshest at the polar front and occupies the southern half of the subantarctic zone within the eddies in the central subantarctic zone there is interleaving between these two forms of antarctic intermediate water north atlantic deep water is unable to cross the southwest indian ridge but can pass south of the crozet plateau in the form of circumpolar deep water which is slightly more saline 34 75 than at drake passage 34 73

mechanisms for vertical nutrient transport within a north atlantic mesoscale eddy abstract prompted by observational evidence for an enhanced source of surface nutrients within an anticyclonic eddy in the ne atlantic we investigate vertical transport processes that may produce such a phenomenon for the eddy investigated the dominant mechanism is found to be ageostrophic circulation resulting from a perturbation of the circular flow of the eddy this can produce upwelling velocities of order 10 m d 1 ekman pumping due to wind stress on the eddy also produces upwelling within but on a smaller scale of 0 5 m d 1 there is no evidence that self propagation of the eddy leads to an enhanced nutrient flux by displacement upwards of nutrient laden deeper isopycnals over the core of the eddy deeper winter mixing within the eddy relative to the surroundings however may contribute to the elevated nutrient levels

eddies masquerade as planetary waves the advent of satellite based remote sensing of ocean color in the late 1970s 1 provided the first largescale views of chlorophyll distributions in the upper ocean these distributions are a proxy for the biomass of phytoplankton which drive oceanic productivity more recently ocean color measurements have been combined with satellite data on sea surface height ssh and other physical properties of the ocean to elucidate the processes that regulate primary production in the sea on page 328 of this issue chelton et al 2 further advance this field by showing that ocean eddies exert a strong influence on near surface chlorophyll

the emu bay shale konservat lagerstatte a view of cambrian life from east gondwana recent fossil discoveries from the lower cambrian emu bay shale ebs on kangaroo island south australia have provided critical insights into the tempo of the cambrian explosion of animals such as the origin and seemingly rapid evolution of arthropod compound eyes as well as extending the geographical ranges of several groups to the east gondwanan margin supporting close faunal affinities with south china the ebs also holds great potential for broadening knowledge on taphonomic pathways involved in the exceptional preservation of fossils in cambrian konservat lagerstatten ebs fossils display a range of taphonomic modes for a variety of soft tissues especially phosphatization and pyritization in some cases recording a level of anatomical detail that is absent from most cambrian konservat lagerstatten

the effect of bottom pressure decoupling on the speed of extratropical baroclinic rossby waves abstract in layered models of the ocean the assumption of a deep resting layer is often made motivated by the surface intensification of many phenomena the propagation speed of first mode baroclinic rossby waves in such models is always faster than in models with all the layers active the assumption of a deep resting layer is not crucial for the phase speed enhancement since the same result holds if the bottom pressure fluctuations are uncorrelated from the overlying wave dynamics in this paper the authors explore the relevance of this behavior to recent observational estimates of too fast waves by chelton and schlax the available evidence supporting this scenario is reviewed and a method that extends the idea to a continuously stratified fluid is developed it is established that the resulting amplification factor is at leading order captured by the formula where cfast is the enhanced phase speed cstandard the standard phase speed 1 z is the standard first mode for the velocity and pressur

comment on oceanic rossby waves acting as a hay rake for ecosystem floating by products remote sensing of the sea surface has shown that rossby waves rws or planetary waves are ubiquitous in the world ocean 1 1 2 2 although the precise mechanisms for their formation and propagation are still under debate 3 3 5 4 recently similar propagating signals

exceptionally preserved fossil assemblages through geologic time and space abstract geologic deposits containing fossils with remains of non biomineralized tissues i e konservat lagerstatten provide key insights into ancient organisms and ecosystems such deposits are not evenly distributed through geologic time or space suggesting that global phenomena play a key role in exceptional fossil preservation nonetheless establishing the influence of global phenomena requires documenting temporal and spatial trends in occurrences of exceptionally preserved fossil assemblages to this end we compiled and analyzed a dataset of 694 globally distributed exceptional fossil assemblages spanning the history of complex eukaryotic life 610 to 3 ma our analyses demonstrate that assemblages with similar ages and depositional settings commonly occur in clusters each signifying an ancient geographic region up to hundreds of kilometers in scale which repeatedly developed conditions conducive to soft tissue preservation using a novel hierarchical clustering approach we show that these clusters decrease in number and shift from open marine to transitional and non marine settings across the cambrian ordovician interval conditions conducive to exceptional preservation declined worldwide during the early paleozoic in response to transformations of near surface environments that promoted degradation of tissues and curbed authigenic mineralization potential we propose a holistic explanation relating these environmental transitions to ocean oxygenation and bioturbation which affected virtually all taphonomic pathways in addition to changes in seawater chemistry that disproportionately affected processes of soft tissue conservation after these transitions exceptional preservation rarely occurred in open marine settings excepting times of widespread oceanic anoxia when low oxygen levels set the stage with these patterns non marine cluster count is correlated with non marine rock quantity and generally decreases with age this result suggests that geologic processes which progressively destroy terrestrial rocks over time limit sampling of non marine deposits on a global scale future efforts should aim to assess the impacts of such phenomena on evolutionary and ecological patterns in the fossil record

oceanic rossby waves acting as a hay rake for ecosystem floating by products recent satellite observations of rossby waves and chlorophyll anomalies propagating in subtropical gyres have suggested that wave induced upwelling could stimulate photosynthesis instead we show that chlorophyll maxima are located in abnormally warm water in rossby wave induced convergences this excludes inputs of nutrients from deeper water we argue that the sea color anomalies are not caused by chlorophyll but by floating particles evolved from the ecosystem and accumulated by rossby waves acting as marine hay rakes in convergence zones such processes may be determinant for the distribution of living organisms in oligotrophic areas

high resolution geochemical evidence for oxic bottom waters in three cambrian burgess shale type deposits abstract the cambrian radiation of complex animals is a fundamental event in the history of life on earth much of our understanding of this event is made possible through the study of exceptionally preserved fossils in burgess shale type bst deposits based on bioturbation levels in bst deposits they are often interpreted as representing restricted oxygen settings this study tests the low oxygen interpretation through analysis of geochemical paleoredox proxies and bioturbation levels in three bst deposits the early cambrian maotianshan shale china the middle cambrian wheeler shale usa and the middle cambrian spence shale usa results from 96 samples show fine scale geochemical evidence for oxic bottom water conditions during the deposition of these three bst deposits trace element paleoredox indices pi give consistent oxic signals in all three shales in addition total organic carbon toc and total sulfur ts levels in the spence shale are extremely low the average c s ratio is 3 1 comparable to values for modern oxic marine water bioturbation levels in all three shales are low with rare development of minimal to moderate horizontal bioturbation while short term oxygen fluctuations or poikiloaerobic conditions could still have sporadically existed in these settings this study shows that these bst deposits were deposited in a dominantly oxic paleoredox setting evidence for low bioturbation levels coupled with paleoredox geochemistry indicative of oxic bottom waters suggests that pervasive exaerobic conditions with an oxic water column positioned above oxygen depleted sediment pore waters may have existed in many cambrian bst deposit paleoenvironments