seamount topography by least squares inversion of altimetric geoid heights and shipborne profiles of bathymetry and or gravity anomalies summary altimetric measurements of sea surface heights have long been used to locate uncharted marine features newly available data sets geosat gm ers 1 and topex poseidon now allow the topography of submarine volcanoes to be accurately restored and a method based upon inverse modelling is presented in this paper this method allows a joint assimilation of altimetric data and shipborne profiles of bathymetry and or gravity anomalies when available furthermore uncertainties can be computed together with the topography which constitutes a noticeable improvement since these parameters are still missing in the usual bathymetric data bases tests are performed using simulated data in order to characterize the errors which may or must occur with the modelled topography of a previously unknown volcano in particular the errors due to data uncertainties and the lack of precise knowledge of sensitive parameters that are used in the modelling these errors can be maintained under the 100 m level rms for altimetric data with a measurement noise of 5 cm rms or less which is achieved for geosat ers 1 and topex poseidon altimeters an example of inversion of seasat data is presented in the case of a seamount in french polynesia

global marine gravity from retracked geosat and ers 1 altimetry ridge segmentation versus spreading rate 1 three approaches are used to reduce the error in the satellite derived marine gravity anomalies first we have retracked the raw waveforms from the ers 1 and geosat gm missions resulting in improvements in range precision of 40 and 27 respectively second we have used the recently published egm2008 global gravity model as a reference field to provide a seamless gravity transition from land to ocean third we have used a biharmonic spline interpolation method to construct residual vertical deflection grids comparisons between shipboard gravity and the global gravity grid show errors ranging from 2 0 mgal in the gulf of mexico to 4 0 mgal in areas with rugged seafloor topography the largest errors of up to 20 mgal occur on the crests of narrow large seamounts the global spreading ridges are well resolved and show variations in ridge axis morphology and segmentation with spreading rate for rates less than about 60 mm a the typical ridge segment is 50 80 km long while it increases dramatically at higher rates 100 1000 km this transition spreading rate of 60 mm a also marks the transition from axial valley to axial high we speculate that a single mechanism controls both transitions candidates include both lithospheric and asthenospheric processes

the mean and the time variability of the shallow meridional overturning circulation in the tropical south pacific ocean the meridional transport in the pacific ocean subtropical cell is studied for the period from 2004 to 2011 using gridded argo temperature and salinity profiles and atmospheric reanalysis surface winds the poleward ekman and equatorward geostrophic branches of the subtropical cell exhibit an el ni no southern oscillation signature with strong meridional transport occurring during la ni and weak meridional transport during el ni no at 7 58s mean basinwide geostrophictransportabove 1000 dbar is 48 56 2 5 sv sv 10 6 m 3 s 21 of which 30 3 38 4 sv return to the subtropics in the surface ekman layer whereas 10 2 18 3 sv flow northward feeding the indonesian throughflow geostrophic transport within the subtropical cell is stronger in the ocean interiorandweakerinthewesternboundaryduringlani theinteriordominatingbasinwide transport using atmospheric reanalyses only half of the mean heat gain by the pacific north of 7 58 si s compensated by oceanicheat transport outof theregion thenationaloceanography centreat southampton air sea flux climatology is more consistent for closing the oceanic heat budget in summary the use of argo data for studying the pacific subtropical cell provides an improved estimate of basinwide mean geostrophic transport includes both interior and western boundary contributions quantifies el ni ni transport variability and illustrates how the meridional overturning cell dominates ocean heat transport at 7 58s

seasat altimetry the north atlantic geoid and evaluation by shipborne subsatellite profiles a geological evaluation of geoid anomalies over the north atlantic is presented with emphasis on short 40 300 km wavelength undulations mapped by seasat radar altimetry long 3000 km and intermediate 300 3000 km wavelength undulations constrain subcrustal processes and are briefly reviewed portions of three seasat revolutions revs totaling 9300 km were followed by research ship which measured gravity magnetics topography and for a 800 km segment also seismic reflection data to form a ground truth data set for comparison to the altimetry the intermediate wavelength geoid the residual upon removal of a 14 14 long wavelength surface correlates with plate age slope 10 cm m y over cenozoic crust and major fracture zones appear as geoid steps a 3 5 to 5 m high over the bermuda rise may reflect thermal rejuvenation created within the plate 40 50 ma short wavelength geoid anomalies typically 10 50 cm in the open ocean were analyzed by high pass 200 or 400 km cutoff along track filtering and smoothing the vertical deflection computed from the seasat geoid compares well with one based on seismic reflection shipborne free air gravity except for a higher frequency cutoff correlates closely with geoid anomalies except near seamounts the principal contribution to geoid anomalies is fracture zone topography all major and many minor fracture zones fz s appear as geoid lineations particularly between the 15 20 and kane fz from the ridge axis to anomaly 34 the wsw trend of fz s between anomaly 21 and 34 is clearly expressed in the altimetry as is the smooth geoid over mid cretaceous smooth basement formed by fast spreading crustal ribbons 50 150 km wide of higher or lower geoid parallel fz trends some geoid lineations are oblique to both isochron and fz trends east of the puerto rico trench such anomalies may reflect compressional deformation within atlantic lithosphere

a search for seamounts in the southern cook and austral region the existence of uncharted seamounts in the cook austral region of the south pacific has been investigated using geos 3 and seasat radar altimeter observations three previously uncharted submarine seamounts provisionally named geos a to geos c have been located between mauke and rimatara and a fourth geos d has been located east of rurutu this confirms that the aitutaki mauke islands of the southern cooks are a continuation of the austral chain a second group of uncharted seamounts has been provisionally located some 200 km south of rimatara and maria and this is suggestive of a second seamount chain south of the first that includes raratonga and mangaia fabert bank to the south of mangaia appears to be mislocated by about 2 sup 0 in longitude

morphologic and geologic effects of the subduction of bathymetric highs morphologic and geologic observations suggest that subduction of bathymetric highs such as aseismic ridges chains of seamounts and fracture zones are important in the development of many forearc features and that those features form during relatively brief episodes of intense tectonism a bathymetric high obliquely entering a subduction zone tends to compress sediments along its leading edge resulting in arcward compression of the accretionary wedge a landward deflection of the trench axis and a steepened inner wall result from this deformation if a significant component of oblique slip occurs along the subduction zone then along strike movement of the accretionary wedge may also occur stresses resulting from subduction of bathymetric features with sufficient buoyancy or high relief extend farther landward than in the case of smaller less buoyant features inducing uplift of the leading edge of the overriding plate tectonic erosion of the base of the overriding plate and along strike transport of are material may also occur the accelerated tectonism observed along several convergent margins can be attributed to the consumption of bathymetric irregularities on the seafloor rather than temporally abrupt changes in rates and directions of plate motions or other episodic events in the accretionary prism

surface circulation in the solomon sea derived from lagrangian drifter observations abstractvelocity measurements from satellite tracked surface drifters collected between 1994 and 2010 are used to map the surface circulation in the solomon sea the last passageway for waters of subtropical origin flowing northward toward the equator where they replenish the pacific warm pool pseudo eulerian statistics of the drifter observations show a strong seasonal cycle in both the mean circulation and the eddy kinetic energy in the region the circulation is characterized by a strong northward flow from june to november the season of strong southeasterly trade winds over the solomon sea and a mostly southward flow with increased variability from december to may when the winds over the sea are weak the seasonal velocity signal has the largest magnitude narrowly along the double western boundary formed by the eastern coastlines of new guinea and the solomon islands suggesting that direct wind driving with its much larger spatial scales is not the main influence in addition the surface circu

predicting bathymetry from geosat erm and shipborne profiles in the south atlantic ocean abstract portions of two geosat erm altimeter tracks and corresponding suborbital shipboard gravity and bathymetry profiles in the south atlantic ocean were analyzed one across the walvis ridge about 1100 km long and the other in the brazil basin about 2300 km long together these profiles sample those types of sea floor topography which dominate the gravity signature at wavelengths of 20 to 300 km the walvis ridge is a massive aseismic ridge and the brazil basin profile crosses both an old seamount emplaced at the time the crust was young and a very young mid plate volcano both profiles cross fracture zones after the gravity and bathymetry profiles were split into subprofiles various cross spectral characteristics could be determined by fft techniques analysis showed that observed admittance is not well constrained by either an airy type or flexural compensation models across the walvis ridge but those over the brazil basin can be readily explained by an airy type model with a mean crustal thickness of about 20 km a theoretical filter was then designed based on a priori geological knowledge and used to predict bathymetry from the high passed gravity geoid anomalies not surprisingly the predicted bathymetry shows more detailed and correct short wavelength 20 300 km features than those predicted from the historical data base as represented e g by the dbdb5 gridded bathymetric model for areas where historical shipboard bathymetry measurements are widely spaced longer than about 10 km for single beam data but where some regional geologic information is available such as the relative ages of mid plate volcanoes and crust bathymetry predicted from altimetric data can be used to upgrade regional bathymetrie data bases on which regional geologic geophysical understanding depends

thermal isostasy in the south atlantic ocean from geoid anomalies abstract transfer functions admittances were computed for the main tectonic units of the south atlantic ocean using the detailed seasat geoid ensemble averaging in the two dimensional wavenumber domain was applied the topography of the walvis ridge and rio grande rise visually correlates with the local geoid i e the difference between the total seasat geoid and first ten harmonics of the grim 3 model the mid atlantic geoid visually correlates with the total geoid sea gravimetry was used to evaluate the contribution of mechanical isostasy to the geoid admittances computed from the geoid and from gravimetry data agree well in the short waveband wavelengths shorter than 300 km a deviation at longer wavelengths is found between the observed admittance and the one due to mechanical isostasy for the southwestern walvis ridge it is explained with a density perturbation at about 20 km deep the admittance for the mid atlantic ridge is interpreted in terms of a boundary layer model and an average thickness of 30 km for the thermal lithosphere is obtained

evolution of the walvis ridge rio grande rise hot spot system implications for african and south american plate motions over plumes crystallization ages of volcanic rocks dredged or drilled from the walvis ridge ten sites and the rio grande rise one site have been determined by the 40ar 39ar incremental heating technique the fundamentally age progressive distribution of these basement ages suggests a common hot spot source for volcanism on the island of tristan da cunha along the walvis ridge and rio grande rise and for the formation of the continental flood basalts located in namibia africa and brazil south america the walvis ridge rio grande rise volcanic system evolved along a section of the south atlantic spreading axis as the african and south american plates migrated apart astride or in close proximity to an upwelling plume reconstructions of the spatial relationship between the spreading axis the tristan hot spot and the evolving walvis ridge rio grande rise volcanic feature show that at about 70 ma the spreading axis began to migrate westward away from the hot spot the resulting transition to intraplate hot spot volcanism along the walvis ridge and associated termination of rio grande rise formation also involved a northward migration of previously formed african seafloor over the hot spot rotation parameters for african motion over fixed hot spots i e absolute motion have been recalculated such that the predicted trail of the tristan hot spot agrees with the distribution of radiometric and fossil basement ages along the walvis ridge african absolute motion has been extended to the south and north american plates by the addition of relative motion reconstruction poles

fore arc seafloor unconformities and geology insight from 3 d seismic geomorphology analysis peru new 3d seismic data collected over 4870 km2 in the 3 45 12 30 s peruvian segment of the east pacific subduction system image seafloor erosional surfaces that can be mapped across the forearc basins forearc basins experience various stresses from their base where basal tectonic erosion acts to the seafloor which is influenced by aerial shallow and deep water currents driven by waves or thermohaline oceanic currents previously there has been little interest in stresses on the upper layer and there is a lack of documentation of unconformities and the erosive processes in certain bathymetric domains in forearc basins we address this with the study of examples sourced from 3d seismic reflection surveys of the seafloor offshore peru unconformities occur in two distinctive bathymetric domains associated with the continental shelf and the upper slope of the margin identification and characterization of unconformity surfaces yield estimates of the amount of erosion at the modern seafloor that range from 18 to 100 regional physical oceanography allows us to calibrate potential candidates for these two distinctive domains the first control on erosion is the dynamics of deep to intermediate oceanic currents related to the humboldt peru chile water masses while the second is wave action in the shallower erosional surfaces this study illustrates the unseen landscape of the forearc basins of south america and helps to highlight the importance of erosive surficial processes in subduction landscapes

the southwest pacific ocean circulation and climate experiment spice the southwest pacific ocean circulation and climate experiment spice is an international research program under the auspices of clivar the key objectives are to understand the southwest pacific ocean circulation and the south pacific convergence zone spcz dynamics as well as their influence on regional and basin scale climate patterns south pacific thermocline waters are transported in the westward flowing south equatorial current sec toward australia and papua new guinea on its way the sec encounters the numerous islands and straits of the southwest pacific and forms boundary currents and jets that eventually redistribute water to the equator and high latitudes the transit in the coral solomon and tasman seas is of great importance to the climate system because changes in either the temperature or the amount of water arriving at the equator have the capability to modulate the el nino southern oscillation while the southward transports influence the climate and biodiversity in the tasman sea after 7 years of substantial in situ oceanic observational and modeling efforts our understanding of the region has much improved we have a refined description of the spcz behavior boundary currents pathways and water mass transformation including the previously undocumented solomon sea the transports are large and vary substantially in a counter intuitive way with asymmetries and gating effects that depend on time scales this paper provides a review of recent advancements and discusses our current knowledge gaps and important emerging research directions

new global seamount census from altimetry derived gravity data summary recent revisions to the satellite derived vertical gravity gradient vgg data reveal more detail of the ocean bottom and have allowed us to develop a non linear inversion method to detect seamounts in vgg data we approximate vgg anomalies over seamounts as sums of individual partially overlapping elliptical polynomial functions which allows us to form a non linear inverse problem by fitting the polynomial model to the observations model parameters for a potential seamount include geographical location peak vgg amplitude major and minor axes of the elliptical base and the azimuth of the major axis the non linear inversion is very sensitive to the initial values for the location and amplitude hence they are constrained by the centre and amplitude of the uppermost contours obtained with a 1 eotvos contour interval with these initial conditions from contouring we execute a step wise and fully automated inversion and obtain optimal model estimates for potential seamounts these are statistically evaluated for significance using the akaike information criterion and f tests a logarithmic barrier technique is applied to ensure positivity of all seamount amplitudes after automatic and manual inspections of the model parameters we estimate actual heights and basal ellipses of the inspected potential seamounts directly from the predicted bathymetry grid in this study we find globally 24 643 potential seamounts h 0 1 km that are located away from continental margins 8458 potential seamounts are taller than 1 km although our global estimate is significantly lower than predictions from previous studies a first order reconciliation of the size frequency statistics obtained from those studies reveals that the previous counts are systematically overestimated because of the ambiguity of gravity signals due to small seamounts of h 1 km and the overlap with abyssal hills we estimate the global seamount census to lie in the 40 000 55 000 range the seamount data from this study are accessible from http www soest hawaii edu pt smts

petrology and major element geochemistry of peru margin phosphorites and associated diagenetic minerals authigenesis in modern organic rich sediments abstract new petrographic and major element geochemical data from modern peru margin upper slope outer shelf phosphorites are presented which provide insight into their origin and paragenetic relationship with other authigenic minerals glauconite pyrite and dolomite occurring in organic rich sediments glauconites are precipitated relatively early following the partial reduction of ferric iron and following this process phosphate pyrite and then dolomite precipitation take place at progressively deeper levels in the sediment in association with microbial reduction of sulfate as in many ancient economic phosphorite deposits the phosphatic facies here consist of nodules crusts coatings and strata composed of phosphatic pelletal grains ooids structureless grains intraclasts clumps and biogenic grains in association with organic rich biosiliceous sediments all are considered to have formed within a few centimeters or within a few tens of centimeters below the sediment water interface important factors that influence which morphology will tend to develop include the amount of available pore space the presence of suitable nucleation sites the amount and size of siliciclastic detritus incorporated as inclusions and the relative solution chemistries of the precipitating solutions bacterial mediation may play an important but as yet unspecified role in the precipitation process textural data and factor analysis of chemical data suggest that structureless pellets are relatively inclusion free na f mg co3 substituted pore water precipitates whereas ooids are inclusion rich pore water precipitates poor in lattice substituted components variations in nodular cement birefringence and crystallinity are suggested to have been produced by similar lattice substitutions that directly reflect pore water carbonate ion concentrations and thus relative degrees of organic matter degradation phosphate and dolomite are intimately mixed yet mineralogically distinct phases in phosphatized dolomicrites depth stratified threshold carbonate ion concentrations may control the lower limit at which phosphatic minerals may precipitate below depths of a few centimeters excessive carbonate ion concentrations and diminished reactive iron and sulfate concentrations favor the development of dolomite while precluding further development of phosphatic minerals and pyrite periodic sediment reorganization bioturbation current winnowing and erosion mass wasting etc plays an important role in both concentrating pelletal grains and maintaining nodules and crusts at critical depth levels in the sediment as well as mixing ordered mineral parageneses into complicated sequences

detection of uncharted seamounts using satellite altimetry the topography of the marine geoid and corresponding sea surface contains characteristic local features caused by sediments these features can be successfully detected and located using matched filters to process single tracks of satellite altimeter data comparison of detected seamount features with the snybaps and scripps bathymetric data bases can reveal uncharted seamounts this technique has been applied to 33 seasat tracks in a region of the western pacific bounded by 0 to 15 degrees north and 160 and 165 degrees east from this analysis we find three uncharted seamounts in this region in all three cases a detailed examination of the bathymetry shows no known bathymetric feature consistent with the detected signature the method used to estimate the size and location of these uncharted seamounts is discussed

a detailed view of the south pacific geoid from satellite altimetry images of sea surface undulations in the south pacific have been constructed from geos 3 and seasat altimeter data height discrepancies at crossover points associated with long wavelength radial orbit error were suppressed by taking along track derivatives of the ascending and descending profiles these geoid slopes were then rotated and scaled to produce the north and east components of the deflection of the vertical finally the results are displayed by using the hill shading technique where gray tone images represent the innner product of the deflection vector with an assigned sun vector less apparent sea surface undulations can be enhanced by varying the sun s zenith and azimuth shorterwavelength sea surface undulations reflect seafloor topography for instance fracture zones fz s appear as elongated sharp steps in the sea surface while seamounts produce circular bumps since large areas of the south pacific are unsurveyed many previously undetected features appear on the images comparisons with bathymetric charts reveal 72 uncharted seamounts having geoid expressions greater than or equal to easter island s expression the dominant features in the images however are the large age offset fz s such as the eltanin and udintsev fz s the images reveal that the eltanin fz is connected to the louisville ridge combined they produce a continuous geoid signature across most of the south pacific this supports the hypothesis of hayes and ewing 1968 that the louisville ridge is the northwest extension of the eltanin fz

seasonal variability of the south equatorial countercurrent 1 using the 1 5 layer long rossby wave model forced by the seasonal european remote sensing ers satellite scatterometer wind we demonstrate that the seasonal variability of the south equatorial countercurrent secc is due to the interplay of two types of forced rossby waves the resonantly forced rossby waves north of 10 s and the locally forced rossby waves south of 10 s the resonantly forced rossby waves north of 10 s are due to the annually varying tropical pacific wind and the locally forced rossby waves south of 10 s in the western basin are associated with the western pacific monsoon both types of waves are intensified westward in the secc region but have different phases across the secc this latitudinal phase jump results in the seasonal variability of the secc which reaches its maximum in march and its minimum in august favorable agreement between the seasonal secc signals from the model and from the satellite sea surface height measurements confirms this new insight about the seasonal modulation of the secc index terms 4231 oceanography general equatorial oceanography 4227 oceanography general diurnal seasonal and annual cycles 4512 oceanography physical currents keywords secc seasonal variability rossby waves

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

detection of seamount signatures in seasat altimeter data using matched filters matched filter techniques are described for the detection of characteristic geoid undulation signatures of seamounts in seasat radar altimeter data the technique requires models of the expected undulation signatures and a statistical description of the background seamount free data examples are given of the detection of 11 known seamounts on four distinct tracks further extensions and applications of the matched filter methods are discussed

plate kinematics of the south atlantic chron c34 to present a high resolution seafloor spreading history of the south atlantic since chron c34 is constrained by a combination of seasat altimeter data and underway marine geophysical data a set of 45 finite rotation poles defines the relative position of africa and south america at roughly 2 m y intervals a set of 12 stage poles constrain the relative motion of these two plates at 5 to 10 m y intervals the position of the stage poles continuously migrates reflecting the continuously changing azimuths of the fracture zones major changes in spreading direction are observed in the late cretaceous and early cenozoic as the fracture zones sweep out broad s shaped curves similar to the pattern seen on the kane fracture zone in the central atlantic small offset fracture zones were found to be the most accurate recorders of changes in plate motion large offset fracture zones such as the agulhas falkland fracture zone were the least reliable recorders at 30 s spreading rates decrease throughout the late cretaceous from a high of 75 mm yr at the end of chron c34 to a low of 30 mm yr around chron c27 a period of slow spreading between chron c30 and chron c20 corresponds to a zone of fracture zone proliferation an increase in the amplitude of geoid anomalies over fracture zones greater relief on topographic profiles and locally evidence of intraplate crustal deformation spreading rates increase at chron c20 to about 50 mm yr and then gradually decrease during the late paleogene and neogene a comparison of synthetic fracture zones based on the south atlantic stage poles to the observed trends of fracture zones in the equatorial atlantic indicates that the vema and marathon fracture zones were generated by south atlantic spreading as opposed to central atlantic spreading at least as far back as 35 m y ago and possibly 50 m y ago

oceanic transports through the solomon sea the bend of the new guinea coastal undercurrent 1 thermocline waters of the tropical southwest pacific can be traced back to the center of the south pacific basin and have a potential influence on equatorial surface conditions and on the characteristics of the el nino southern oscillation on decadal timescales the solomon sea is traversed by this influential flow and therefore is an optimal place for exploring this oceanic connection to the equator from a high resolution hydrographic survey at which we applied an inverse box model we describe the main pathways at the entrance of the solomon sea and more particularly the extremely sharp bend of the western boundary current around the south east tip of papua new guinea of the 30 sv subtropical waters transported into the coral sea from the east above 1300 m 29 5 sv makes its way through the solomon sea with a large part transported in a boundary current at the entrance of the solomon sea around the south east tip of papua new guinea the gulf of papua current turns abruptly to the north in a very sharp bend as it merges into the new guinea coastal undercurrent on its way toward the equator the warm currents transport large amounts of internal energy with a total of 1 0 0 3 1015w entering the solomon sea from the south

carbon isotopic composition and lattice bound carbonate of peru chile margin phosphorites new light stable carbonate carbon isotope and lattice bound co2 data from quaternary peru chile margin phosphatic nodules crusts and pelletal grains and from associated dolomicritic concretions are presented which provide constraints on the timing and mechanisms of growth of these phases in organic carbon rich sediments comparison of 13c values from carbonate fluorapatite cfa nodules and pelletal grains 4 8 to 0 0 and 2 9 to 1 0 pdb respectively with pore water total dissolved 13c values from these sediments suggests early authigenic cfa precipitation from pore waters within a few centimeters of the sediment water interface in association with suboxic to perhaps anoxic microbial degradation of organic matter in contrast the dolomicritic cores of nodules recovered from about 12 s display both strongly negative to positive 13c values 10 8 to 6 1 characteristic of formation deeper in the sediments in association with methanogenic and perhaps sulfate reduction microbial processes the amount of structural carbonate in cfa suggests that carbonate substitution generally increases as 13c in cfa decreases a probable consequence of increasing carbonate and accompanying charge balancing substitutions in the cfa lattice in response to increasing pore water carbonate ion concentrations with depth below the sediment water interface in one buried upward growing nodule decreasing cfa 13c and increasing structural co2 also correspond to decreasing cfa growth rates these data suggest that in addition to other constraints such as pore water phosphorus and fluoride availability the lower limit of cfa precipitation in suboxic to anoxic sediments may be controlled by lattice poisoning due to excessive dissolved carbonate ion concentrations in organic rich peru chile margin sediments this depth threshold appears to be at approximately 5 10 cm below the sediment water interface where maximum cfa co2 contents of about 6 wt occur in less organic rich settings greater depths of precipitation of cfa may be anticipated below this relatively shallow depth of cfa precipitation on the peru shelf high pore water alkalinity and associated elevated total dissolved carbon and carbonate ion concentration apparently favor the precipitation of authigenic carbonates

depth to magnetic source analysis of the arctic ocean region abstract approximately 400 000 line kilometers of high quality low level arctic aeromagnetic data collected by the naval research laboratory the naval oceanographic office and the naval ocean reseach and development activity from 1972 through 1978 have been analyzed for depth to magnetic source this data set covers much of the canada basin the alpha ridge the central part of the makarov basin the lincoln sea the eurasia basin west and south of the 55 e meridian and the norwegian greenland sea north of the jan mayen fracture zone the analysis uses the autocorrelation algorithm developed by phillips 1975 1978 and based on the maximum entropy method of burg 1967 1968 1975 the method is outlined examples of various error analysis techniques shown and final results presented where possible magnetic source depth estimates are compared with basement depths derived from seismic and bathymetric data all major known bathymetric features including vesteris bank and the greenland molloy and spitsbergen fracture zones as well as the mohns knipovich and nansen spreading ridges and the alpha cordillera appear as regional highs in the calculated magnetic basement topography shallow basement was also found under the northeastern yermak plateau the morris jesup rise and under the southern greenland ellesmere island end of the lomonsosov ridge regional magnetic source deeps are associated with such bathymetric depressions as the canada makarov amundsen nansen greenland and lofoten basins more localized magnetic basement deeps are found over the molloy f z deep and over the mohns knipovich and nansen rift valleys a linear magnetic basement deep follows the extension of nares strait through the lincoln sea toward the morris jesup rise suggesting the continuation of the nares strait or wegener f z into the lincoln sea a sharp drop in the regional magnetic source depths to the southeast of the alpha ridge suggests the alpha ridge is not connected to structures in northwest ellesmere island as previously postulated from high altitude aeromagnetic collected by canadian workers a regional deep under the east greenland shelf west of the greenland escarpment suggests the presence of 5 10 km of post paleozoic sediments

gravity anomaly across the peruvian andes we carried out gravity surveys along four routes across the peruvian andes one in northern peru one in central peru and two in southern peru two of the routes extend from the coast to the flat lands of the amazon basin across the high andes while the other two routes extend only from the coast to the central high plateau or the altiplano one route through nazca contains 250 data points over a length of 800 km and thus offers one of the best gravity profiles across the andes this profile shows quite asymmetric gravity anomalies associated with the western cordillera and the eastern cordillera in marked contrast with the symmetric pattern of topographic profile using these profiles we constructed crustal models varying layer thicknesses rather than layer densities the crustal thickness has a maximum beneath the western cordillera although the maximum thickness varies from 45 km in northern peru to 55 km in central peru and 65 km in southern peru in contrast to the assumed thickness of 35 km beneath the stable brazilian shield possible effects of lateral variations of crustal and mantle densities tend to reduce the above estimates of maximum thickness the very shallow moho beneath the peruvian coast steeply deepens eastward in correspondence to the steep western slope of the andes the crust is thicker in the western cordillera than in the eastern cordillera the moho beneath the eastern cordillera tends to be relatively flat and shallows abruptly eastward across the sub andes the wadati benioff zone lies in general well below the model south american continental crust leaving a mantle wedge in between a notable exception is the nazca profile where the base of the model south american continental crust is in direct contact with the top of the wadati benioff zone this provides a direct evidence for uplifting of the buoyant slab with an aseismic ridge the nazca ridge at its top which tends to attach itself to the bottom of the continental crust we examined whether or not the load due to mountain topography is balanced with the buoyancy load due to excess mass of the crust in the andes the western cordillera is found to be approximately in isostatic equilibrium but the eastern cordillera is not this contrast in mechanical state and the difference in recent geology suggest that the western cordillera and the eastern cordillera have not uplifted through entirely the same tectonic process

the annual cycle of circulation of the southwest subtropical pacific analyzed in an ocean gcm abstract an ocean gcm interpreted in light of linear models and sparse observations is used to diagnose the dynamics of the annual cycle of circulation in the western boundary current system of the southwest pacific ocean the simple structure of annual wind stress curl over the south pacific produces a large region of uniformly phased stationary thermocline depth anomalies such that the western subtropical gyre spins up and down during the year directing flow anomalies alternately toward and away from the boundary at its northern end near 10 s the response of the western boundary currents is to redistribute these anomalies northward toward the equator and southward to the subtropical gyre a redistribution that is determined principally by linear rossby processes not boundary dynamics when the subtropical gyre and south equatorial current sec are strong in the second half of the year the result is both increased equatorward transport of the new guinea coastal current and poleward transport a

high accuracy high resolution gravity profiles from 2 years of the geosat exact repeat mission satellite altimeter data from the first 44 repeat cycles 2 years of the geosat exact repeat mission geosat erm were averaged to improve accuracy resolution and coverage of the marine gravity field individual 17 day repeat cycles two points per second were first edited and differentiated resulting in alongtrack vertical deflection i e alongtrack gravity disturbance to increase the signal to noise ratio 44 of these cycles were then averaged to form a single highly accurate vertical deflection profile the largest contributions to the vertical deflection error is short wavelength altimeter noise and longer wavelength oceanographic variability the combined noise level is typically 6 rad both types of noise are reduced by averaging many repeat cycles over most ocean areas the uncertainly of the average profile is less than 1 rad 0 206 arcsec which corresponds to 1 mgal of alongtrack gravity disturbance however in areas of seasonal ice coverage its uncertainty can exceed 5 rad to assess the resolution of individual and average geosat gravity profiles the cross spectral analysis technique was applied to repeat profiles individual geosat repeat cycles are coherent 0 5 for wavelengths greater than about 30 km and become increasingly incoherent at shorter wavelengths this emit of resolution is governed by the signal to noise ratio thus when many geosat repeat profiles are averaged together the resolution limit typically improves to about 20 km except in shallow water areas further improvements in resolution will be increasingly difficult to achieve because the short wavelength components are attenuated by upward continuation from the seafloor to the sea surface these results suggest that the marine gravity field can be completely mapped to an accuracy of 2 mgal and a half wavelength resolution of 12 km by a 4 5 year satellite altimeter mapping mission

complementary use of glider data altimetry and model for exploring mesoscale eddies in the tropical pacific solomon sea mesoscale activity is an important component of the solomon sea circulation that interacts with the energetic low latitude western boundary currents of the south tropical pacific ocean carrying waters of subtropical origin before joining the equatorial pacific mixing associated with mesoscale activity could explain water mass transformation observed in the solomon sea that likely impacts el nino southern oscillation dynamics this study makes synergetic use of glider data altimetry and high resolution model for exploring mesoscale eddies especially their vertical structures and their role on the solomon sea circulation the description of individual eddies observed by altimetry and gliders provides the first elements to characterize the 3d structure of these tropical eddies and confirms the usefulness of the model to access a more universal view of such eddies mesoscale eddies appear to have a vertical extension limited to the surface waters sw and the upper thermocline water utw i e the first 140 150 m depth most of the eddies are nonlinear meaning that eddies can trap and transport water properties but they weakly interact with the deep new guinea coastal undercurrent that is a key piece of the equatorial circulation anticylonic eddies are particularly efficient to advect salty and warm sw coming from the intrusion of equatorial pacific waters at solomon strait and to impact the characteristics of the new guinea coastal current cyclonic eddies are particularly efficient to transport south pacific tropical water sptw anomalies from the north vanuatu jet and to erode by diapycnal mixing the high sptw salinity

exploring the mesoscale activity in the solomon sea a complementary approach with a numerical model and altimetric data the solomon sea is an area of high level of eddy kinetic energy eke and represents a transit area for the low latitude western boundary currents llwbcs connecting the subtropics to the equatorial pacific and playing a major role in enso dynamics this study aims at documenting the surface mesoscale activity in the solomon sea for the first time our analysis is based on the joint analysis of altimetric data and outputs from a 1 12 model simulation the highest surface eke is observed in the northern part of the basin and extends southward to the central basin an eddy tracking algorithm is used to document the characteristics and trajectories of coherent mesoscale vortices cyclonic eddies generated in the south basin are advected to the north by the llwbcs before merging with stationary mesoscale structures present in the mean circulation anticyclonic eddies are less numerous they are generated in the southeastern basin propagate westward reach the llwbcs and dissipate the seasonal and interannual modulations of the mesoscale activity are well marked at seasonal time scale maximum minimum activity is in may june september at interannual time scale the mesoscale activity is particularly enhanced during la nina conditions if instabilities of the regional circulations seem to explain the generation of mesoscale features the modulation of the mesoscale activity seems to be rather related with the intrusion at solomon strait of the surface south equatorial current rather than to the llwbcs by modulating the horizontal and vertical shears suitable for instabilities

the 1974 peru earthquake series the aftershocks of the 3 october 1974 mw 8 1 earthquake have been relocated using data from a 10 station temporary seismic network these aftershocks are among the best observed of great circum pacific subduction earthquakes recent modelings of the rupture history of the mainshock done in other studies indicate a bilateral rupture on the thrust interface updip to the peru chile trench preseismicity was predominately downdip of the mainshock rupture consistent with the mainshock s asperities being loaded by sinking of the nazca plate the aftershocks including an ms 7 1 event are located primarily near the downdip periphery of the mainshock s shallow dipping rupture surface for a concentration of aftershocks furthest downdip a composite focal mechanism shows east trending right lateral strike slip displacement corresponding to the dominant moment release of the mainshock being north of the strike slip deformation at a depth of 20 to 25 km the 11 ne dipping nazca plate increases in dip to 30 ne although a postmainshock episode of plate motion must have bridged both this hinge and the bend at the peru chile trench the associated bending moments were aseismic the lima basin is directly over the downdip edge of the shallow dipping strongly coupled interface and the aftershocks there similar in location to basins in outer rises of other regions the space time history of the aftershocks shows an alternation between heightened activity in the updip of hinge and downdip of hinge zones with many earthquakes near the pending rupture of the 9 november 1974 ms 7 1 aftershock and a regional seismic quiescence following this large aftershock

bathymetric prediction from seasat altimeter data the linear response function technique is used to analyze two 1300 km tracks of seasat altimeter data and corresponding bathymetry in the musician seamounts region north of hawaii bathymetry and geoid height are highly correlated in the 50 to 300 km wavelength range a predictive filter is developed which can operate on seasat altimetry in poorly surveyed oceanic regions to indicate the presence of major bathymetrie anomalies modeling of the bathymetry geoid correlation in the musician region is attempted using the elastic plate model the flexural rigidity d of the plate is not well constrained by our data but appears to lie in the range 5 1021 n m 5 1022 n m at the time of loading since the musician seamounts and the crust on which they lie are both late cretaceous in age this value represents the effective flexural rigidity of very young lithosphere that was frozen in at the time of voicanism the modeling indicates that the general form of a predictive filter will strongly depend on various geologic parameters especially the effective flexural rigidity hence some a priori geologic constraints are necessary to estimate successfully the bathymetry from the altimeter data alternately if high quality bathymetry is available a crude estimate of the age of loading i e voicanism can be made from the altimeter data

bathymetric prediction from dense satellite altimetry and sparse shipboard bathymetry the southern oceans south of 30 s are densely covered with satellite derived gravity data track spacing 2 4 km and sparsely covered with shipboard depth soundings hundreds of kilometers between tracks in some areas flexural isostatic compensation theory suggests that bathymetry and downward continued gravity data may show linear correlation in a band of wave lengths 15 160 km if sediment cover is thin and seafloor relief is moderate at shorter wave lengths the gravity field is insensitive to seafloor topography because of upward continuation from the seafloor to the sea surface at longer wavelengths isostatic compensation cancels out most of the gravity field due to the seafloor topography we combine this theory with wiener optimization theory and empirical evidence for gravity noise to signal ratios to design low pass and band pass filters to use in predicting bathymetry from gravity the prediction combines long wavelengths 160 km from low pass filtered soundings with an intermediate wavelength solution obtained from multiplying downward continued band pass filtered 15 160 km gravity data by a scaling factor s s is empirically determined from the correlation between gravity data and existing soundings in the 15 160 km band by robust regression and varies at long wave lengths we find that areas with less than 200 m of sediment cover show correlation between gravity and bathymetry significant at the 99 level and s may be related to the density of seafloor materials in these areas the prediction has a horizontal resolution limit of 5 10 km in position and is within 100 m of actual soundings at 50 of grid points and within 240 m at 80 of these in areas of very rugged topography the prediction underestimates the peak amplitudes of seafloor features images of the prediction reveal many tectonic features not seen on any existing bathymetrie charts because the prediction relies on the gravity field at wavelengths 160 km it is insensitive to errors in the navigation of sounding lines but also cannot completely reproduce them therefore it may be used to locate tectonic features but should not be used to assess hazards to navigation the prediction is available from the national geophysical data center in both digital and printed form

structure of the frontal part of the andean convergent margin a multichannel seismic reflection record across the central peru margin and trench was improved by processing 24 rather than the 12 channels previously processed and by thorough migrating to reject the strong diffractions that obscured weaker primary reflections the increased resolution clarifies the structure of the 15 km wide frontal accretionary complex and the adjacent truncated continental framework against which the trench sediment was imbricated resolved are individual thrust slices and packets adjacent to the trench axis subducting sediment filled graben in the ocean crust beneath the lower slope and a tertiary stratigraphic section of the upper slope yaquina basin which is cut by normal faults the resolution in this multichannel record provides criteria for reinterpreting single channel data off chile with increased confidence the previously proposed truncation of the south american continent along much of the peru chile trench is confirmed and the development of an accretionary complex in front of the truncated continental crust appears to vary with the amount of sediment seen in the trench axis the andean margin frontal structure is similar to that off central america the aleutian trench and the japan trench which suggests common truncation as well as accretion at the front of convergent margins

water depth and diagenetic constraints on the use of barium as a palaeoproductivity indicator sediments underneath the high productivity areas of the coastal upwclling and equatorial divergence zones in the pacific and indian oceans are enriched in barium and on this basis the barium content of the sediments has long been suggested as a potential palaeoproductivity indicator analyses of sediments from the peru margin corroborate the pattern of enhanced barium accumulation in areas of high primary productivity in the deep ocean but also show that this pattern cannot be extended to shallow water deposits sediments from the peru shelf lack any barium enrichment whereas this element is significantly enriched in slope and basinal deposits in water columns deeper than 2000 m this depth effect is further illustrated at site 682 located in the rapidly subsiding lima basin the quaternary sequence deposited at water depths 3000 m is enriched in organic carbon opal and biogenic barium the miocene sediments although deposited under highly productive waters associated with a coastal upwclling centre do not show an enrichment in the barium record corresponding to the very high organic carbon and opal levels a pattern that is consistent with deposition in shallow basins in addition to the effect of water depth on the barium distribution overprinting of primary signals can be observed in sediments from upwclling areas undergoing strong anoxic diagenesis microcrystalline barite is partly dissolved in intervals depleted in interstitial sulphate as shown for sediments from the peru margin dissolution of barite in sulphate depleted intervals of deep water sections leads to high barium concentrations near the termination of the sulphate reducing zone where downward sulphate and upward barium diffusion foster local barite precipitation in diagenetic fronts the barium distribution in sedimentary oxic and suboxic environments at deep water depositional sites has a high potential as a palaeoproductivity indicator however barium accumulation as a proxy for ocean fertility should be used with caution in areas of varying water depths and in anoxic diagenetic environments where sulphate depletion undcrsatur ates the interstitial waters with respect to barite

comparison of quaternary coastal upwelling proxies off central peru abstract three apc advanced hydraulic piston core holes of odp leg 112 from the shelf sites 681 and 680 and upper slope site 686 off the central peruvian coast contain a productivity and coastal upwelling record of the last 400 000 yrs marine planktonic diatom sediment assemblages are used as primary productivity proxies their downcore record is compared to variations in other proxies weight percent organic carbon percent large diatoms in the coarse fraction 13c of the endobenthic foraminiferbolivina seminuda and the geochemical parameter uk37 unsaturation index of c37 alkenonones low values of calculated primary paleo productivity are matched by low values of organic carbon but the percentages of diatoms in the coarse fraction do not follow this trend levels of 13c correspond to neither the diatom productivity proxy nor the organic carbon proxy the geochemical index uk37 seems to indicate high surface water temperatures whereas the calculated primary productivity indicates increased upwelling and thus lower temperatures

bathymetry estimates in the southern oceans from seasat altimetry a mean sea surface height based on seasat altimeter data has been high pass filtered to reveal a pattern of geoid anomalies which are highly correlated with sea floor topography the technique is used to locate new bathymetric features in the poorly surveyed southern oceans

a directional analysis of the small wavelength geoid in the pacific ocean the geoid over the pacific ocean has been filtered in order to enhance wavelengths of the order of 200 km as noticed by previous authors lineations elongated in the direction of present plate motion are observed in the east central pacific elongated features as clearly visible with a larger amplitude and a totally different direction are also present south of the hawaiian chain and west of baja california the dominant directions visible on the filtered geoid map have been confirmed by spectral analyses near the californian coast the ne sw lineations seem to be related to extensional tectonics south of hawaii the nw se directions correspond to the various directions of the pacific plate prior to 40 ma magmas implaced in the lithosphere over fixed convective plumes may be the source of these geoid lineations

precise location of unsurveyed seamounts in the austral archipelago area using seasat data summary seasat altimetric geoid data are used to detect uncharted seamounts in the austral archipelago area the various physical parameters which affect the geoid signature of a seamount are inspected to analyse their influence on the precision of the location these parameters are the shape of the seamount its density the crustal model the effective elastic thickness of the lithosphere and the distance between the seamount and sub satellite tracks respectively the results of the tests performed on synthetic data as well as on charted structures show that when a seamount is detected on at least two neighbouring tracks it is possible to locate it with good confidence and to give an estimation of its height if the correct elastic thickness is assumed the precision on the location is order 15 km ten previously unsurveyed seamounts have been located in the austral archipelago it appears that they are emplaced along two well defined azimuths n 1 10 e and n 150 e and that two parallel distinct volcanic chains form the austral archipelago

evidence for small scale mantle convection from seasat altimeter data evidence for the early development of convective instability in the thermal boundary layer associated with cooling plates has been found from gravity anomalies and residual sea surface heights derived from seasat altimeter data subtle lineated patterns trending in the direction of plate motion in the hot spot reference frame are observed over the younger portions of the fast moving pacific and indo australian plates in particular for the east central pacific ocean the seasat derived data sets reveal lineations with 1 wavelengths in the range 150 500 km perhaps increasing with plate age and 2 peak to trough amplitudes of 5 20 mgal for gravity anomalies the lineated pattern over the pacific plate which first becomes discernable over seafloor 5 to 10 m y old west of the east pacific rise is clearly oblique to the trends of the prominent pacific farallon fracture zones onset of convective instability at such early ages can be understood if young oceanic lithosphere is underlain by a layer having a viscosity of about 1018 pa s 1019 p which is about 3 orders of magnitude less than mantle viscosity inferred from postglacial rebound studies recent numerical studies of convection in fluids with a temperature and pressuredependent viscosity support an early onset time for convective instability and low viscosity zones in the upper mantle beneath young lithosphere such low viscosity zones may correspond to similarly located regions of low shear wave velocities resolved through studies of surface waves

distribution of large pacific seamounts from geosat ers 1 implications for the history of intraplate volcanism we characterize the seamount distribution on the pacific plate using the gridded vertical gravity gradient vgg or geoid curvature derived from geosat and ers 1 satellite altimetry the vgg amplifies short wavelength information and suppresses longer wavelength components making it suitable for seamount detection purposes furthermore the vgg over seamounts has a much more pronounced zero crossing than that of the free air anomaly faa the distance to the zero crossing can be used as a proxy for seamount radius after removing a regional field obtained by robust median filtering we identify seamount amplitudes and locations from local maxima in the vgg grid the radius of a seamount is more difficult to estimate since seamounts tend to cluster and overprint each other s signals individual seamounts are modeled as gaussian axisymmetric objects loading an elastic lithosphere the vgg over such features can be approximated by a simple analytical expression which we use to determine the zero crossing distances for overlapping seamounts by using the vgg the maximum amplitude and distance to the zero crossing become largely independent of the elastic plate thickness and infill density we do forward modeling of gaussian seamounts and their gravimetric response and create a look up table that relates seamount faa in milligals vgg in eotvos and zero crossing distance in kilometers to actual height and radius in kilometers the frequency size distribution of these predicted seamount heights follows a power law for heights between 2 and 8 km the seamount density number of seamounts per area is greatest in the central pacific we confirm earlier results suggesting that the majority of large seamounts are located in the western region of the pacific plate on older crust as crustal age increases so does seamount density peaking on 100 130 m y crust supporting suggestions of high magmatism in the cretaceous we demonstrate that there may be an empirical relationship between the seamount vgg amplitude and the age of the lithosphere at the time of seamount formation and invert this relationship to predict seamount ages from vgg amplitudes these pseudo ages have large uncertainties but nevertheless may be used to investigate temporal fluctuations in pacific intraplate volcanism our results indicate that seamount intraplate volcanism attained a maximum level in the mid cretaceous to late cretaceous about 70 120 ma apparently contemporaneous with the formation of large oceanic plateaus in the pacific

altimetry derived gravity predictions of bathymetry by the gravity geologic method the gravity geologic method ggm was implemented for 2 by 2 bathymetric determinations in a 1 6 longitude by 1 0 latitude region centered on the eastern end of the shackleton fracture zone in the drake passage antarctica the ggm used the bouguer slab approximation to process satellite altimetry derived marine free air gravity anomalies and 6 548 local shipborne bathymetric sounding measurements from the korea ocean research and development institute to update the surrounding off track bathymetry the limitations of the bouguer slab for modeling the gravity effects of variable density rugged bathymetric relief at distances up to several kilometers were mitigated by establishing tuning densities that stabilized the ggm predictions tests using two thirds of the shipborne bathymetric measurements to estimate the remaining third indicated that the tuning densities minimized root mean square deviations to about 29 m the optimum ggm bathymetry model honoring all the ship observations correlated very well with widely available bathymetry models despite local differences that ranged up to a few kilometers the great analytical simplicity of ggm facilitates accurately and efficiently updating bathymetry as new gravity and bathymetric sounding data become available furthermore the availability of marine free air gravity anomaly data ensures that the ggm is more effective than simply extrapolating or interpolating ship bathymetry coverage into unmapped regions

enso and short term variability of the south equatorial current entering the coral sea abstracthistorical section data extending to 1985 are used to estimate the interannual variability of transport entering the coral sea between new caledonia and the solomon islands typical magnitudes of this variability are 5 8 sv sv 106 m3 s 1 in the 0 400 m layer relative to 400 m and 8 12 sv in the 0 2000 m layer relative to 2000 m on a mean of close to 30 sv relative to 2000 m transport increases a few months after an el nino event and decreases following a la nina interannual transport variability is well simulated by a reduced gravity long rossby wave model vigorous westward propagating mesoscale eddies can yield substantial aliasing on individual ship or glider surveys since transport variability is surface intensified and well correlated with satellite derived surface geostrophic currents a simple index of south equatorial current transport based on satellite altimetry is developed

wind forcing of volume transport through lancaster sound 1 volume and freshwater transport through lancaster sound are estimated from mooring measurements collected in eastern barrow strait for 13 years between 1998 and 2011 estimates from 2006 to 2011 confirm the relationship between surface wind and volume transport derived from data collected between 1998 and 2006 volume transport through barrow strait along the northwest passage is significantly correlated with northeastward winds in the beaufort sea parallel to the western coasts of the canadian arctic archipelago at monthly to interannual time scales the location and wind direction for which there is maximum correlation are consistent with the flow being driven by a sea level difference between opposite ends of the passage and the difference being determined by setup caused by alongshore winds in the beaufort sea monthly alongshore wind anomalies account for 43 of the variance of the transport anomalies p 0 05 the annual cycles of the total volume transport and its part attributed to the beaufort sea wind both have peaks in the summer and are lowest in the autumn correlations of the volume transport anomaly with ice velocity anomalies are lower than with surface wind anomalies

dolomite formation in the dynamic deep biosphere results from the peru margin early diagenetic dolomite beds were sampled during the ocean drilling programme odp leg 201 at four reoccupied odp leg 112 sites on the peru continental margin sites 1227 684 1228 680 1229 681 and 1230 685 and analysed for petrography mineralogy 13c 18o and 87sr 86sr values the results are compared with the chemistry and 13c and 87sr 86sr values of the associated porewater petrographic relationships indicate that dolomite forms as a primary precipitate in porous diatom ooze and siliciclastic sediment and is not replacing the small amounts of precursor carbonate dolomite precipitation often pre dates the formation of framboidal pyrite most dolomite layers show 87sr 86sr ratios similar to the composition of quaternary seawater and do not indicate a contribution from the hypersaline brine which is present at a greater burial depth also the 13c values of the dolomite are not in equilibrium with the 13c values of the dissolved inorganic carbon in the associated modern porewater both petrography and 87sr 86sr ratios suggest a shallow depth of dolomite formation in the uppermost sediment 30 m below the seafloor a significant depletion in the dissolved mg and ca in the porewater constrains the present site of dolomite precipitation which co occurs with a sharp increase in alkalinity and microbial cell concentration at the sulphate methane interface it has been hypothesized that microbial hot spots such as the sulphate methane interface may act as focused sites of dolomite precipitation varying 13c values from 15 to 15 for the dolomite are consistent with precipitation at a dynamic sulphate methane interface where 13c of the dissolved inorganic carbon would likewise be variable a dynamic deep biosphere with upward and downward migration of the sulphate methane interface can be simulated using a simple numerical diffusion model for sulphate concentration in a sedimentary sequence with variable input of organic matter thus the study of dolomite layers in ancient organic carbon rich sedimentary sequences can provide a useful window into the palaeo dynamics of the deep biosphere

a bathymetry and altimetry profile across the southwest indian ridge crest at 31 s latitude abstract during march 1983 the m v marion dufresne obtained a bathymetry profile along more than 1500 km of a seasat altimeter sub track across the southwest indian ridge crest at 31 s latitude we have used these data to estimate the thermal and elastic thickness of the oceanic lithosphere in the vicinity of the ridge and to evaluate the performance of the seasat altimeter the thermal thickness appears to be in the range 72 109 km while the elastic thickness is about 2 5 km there is a good correlation between the geoid calculated from the bathymetry and its compensation and the observed geoid derived from seasat data the correlation is strongest for wavelengths greater than 45 km and poorest for shorter wavelengths we attribute the poor resolution at short wavelengths to instrument and oceanographic noise in the altimeter data combined with the reduced sensitivity of the geoid to bathymetric relief at very short wavelengths

seasonal modulations in the eddy field of the south pacific ocean abstract decade long satellite altimeter data from the ocean topography experiment topex poseidon and european remote sensing satellite 1 and 2 ers 1 2 missions are analyzed to investigate the eddy signals in the south pacific ocean high eddy kinetic energy eke bands with well defined annual cycles are detected along the eastward flowing surface currents of the south tropical countercurrent stcc between 21 29 s and the south equatorial countercurrent secc centered near 9 s overriding the westward flowing south equatorial current sec the stcc layer has the sign of its mean potential vorticity gradient opposite to that in the sec layer subjecting the vertically sheared stcc sec system to baroclinic instability in austral winter the stcc sec system is baroclinically more unstable than in other seasons because of the large vertical shear and weak stratification this seasonal variation in the intensity of baroclinic instability is responsible for the seasonal modulation of the stcc s eke fi

global seafloor topography from a least squares inversion of altimetry based high resolution mean sea surface and shipboard soundings summary we present a new worldwide 1 16 1 16 map of seafloor topography computed from an iterative inversion combining altimetry measurements of the marine geoid and shipboard echo soundings from the global national geophysical data center ngdc database the input geoid data for this computation are derived from altimetry measurements of the sea surface height from the ers 1 geodetic mission and the geosat ers 1 and topex poseidon exact repeat missions to calculate the seafloor topography from sea surface height measurements it is necessary to take the regional isostatic compensation of the topographic load into account for that purpose we consider a model of elastic flexure of the oceanic lithosphere in which the elastic plate thickness increases with crustal age with the solution we provide an uncertainty map that reflects the uneven distribution of and errors in the data and uncertainties in the model parameters as well as the increase of the geopotential error with the deepening of the seafloor the bathymetric solution is compared with the smith sandwell s 1997 science 227 1956 1962 solution the root mean square difference between the two amounts to 350 m however the two maps agree within 150 m over 65 per cent of the ocean surface

multiscale dynamical analysis of a high resolution numerical model simulation of the solomon sea circulation a high 1 36 resolution numerical model is used to study the ocean circulation in the solomon sea an evaluation of the model with the few available observation shows that the 1 36 resolution model realistically simulates the solomon sea circulations the model notably reproduces the high levels of mesoscale eddy activity observed in the solomon sea with regard to previous simulations at 1 12 resolution the average eddy kinetic energy levels are increased by up to 30 40 in the present 1 36 simulation and the enhancement extends at depth at the surface the eddy kinetic energy level is maximum in march april may and is minimum in december january february the high subsurface variability is related to the variability of the western boundary current new guinea coastal undercurrent moreover the emergence of submesoscales is clearly apparent in the present simulations a spectral analysis is conducted in order to evidence and characterize the modeled submesoscale dynamics and to provide a spectral view of scales interactions the corresponding spectral slopes show a strong consistency with the surface quasi geostrophic turbulence theory

interannual to decadal variability in the bifurcation of the north equatorial current off the philippines satellite altimeter sea surface height ssh data from the past 17 yr are used to investigate the interannualto decadal changes in the bifurcation of the north equatorial current nec along the philippine coast the nec bifurcation latitude migrated quasi decadally between 108 and 158n with northerly bifurcations observed in late 1992 1997 98 and 2003 04 and southerly bifurcations in 1999 2000 and 2008 09 the observed necbifurcationlatitudecanbeapproximatedwellbythesshanomaliesinthe128 148nand1278 1308ebox east of the mean nec bifurcation point using a 1 layer reduced gravity model forced by the ecmwf reanalysis wind stress data the authors find that the ssh anomalies in this box can be simulated favorably to serve as a proxy for the observed nec bifurcation with the availability of the long term reanalysis wind stress data this helps to lengthen the nec bifurcation time series back to 1962 although quasi decadal variability was prominent in the last two decades the nec bifurcation was dominated by changes with a 3 5 yr period during the 1980s and had low variance prior to the 1970s these interdecadalmodulationsin the characteristics of the nec bifurcation reflect similar interdecadal modulations in the wind forcing field over the western tropical north pacific ocean although the nec bifurcation on interannual and longer time

gliders measure western boundary current transport from the south pacific to the equator abstract spray gliders most launched from small boats near shore have established a sustainable time series of equatorward transport through the solomon sea the first 3 5 years mid 2007 through 2010 are analyzed coast to coast equatorward transport through the solomon sea fluctuates around a value of 15 sv 1 sv 106 m3 s 1 with variations approaching 15 sv transport variability is well correlated with el nino indices like nino 3 4 with strong equatorward flow during one el nino and weak flow during two la ninas mean transport is centered in an undercurrent focused in the western boundary current variability has a two layer structure with layers separated near 250 m near the core of the undercurrent that fluctuate independently the largest variations are in midbasin confined to the upper layer and are well correlated with enso analysis of velocity and salinity on isopycnals shows that the western boundary current within the solomon sea consists of a deep core coming from the coral sea

mesoscale variability and its seasonality in the solomon and coral seas high resolution 4 km climatologically forced ocean model validated by altimetry and glider data is used to characterize the vertical and seasonal variations of mesoscale variability in the solomon and coral seas the highest eddy kinetic energy eke in the southwest pacific is found subsurface in the gulf of papua at the depth of the low latitude western boundary current velocity core variability associated with the western boundary current especially downstream of topographic obstacles dominates the thermocline and intermediate level eke by contrast surface eke is generally enhanced in the southwest pacific with a pronounced annual cycle that has a phase difference between small scale and large scale variability large mesoscale eddies account for most of the surface eke and its annual modulation the june maximum of surface eke in the solomon sea and the december maximum in the coral sea can be accounted for by local instabilities of large scale currents small mesoscale eddies predominantly cyclonic are abundant in late winter august to september coinciding with the timing of deepest mixed layer and strongest vertical velocity they contribute to the spatially uniform surface enhanced eke over the top 100 m not associated with the western boundary current in the coral sea small mesoscale eddies are generated mostly by open ocean surface baroclinic instabilities while in the land bounded solomon sea near boundary instabilities and topographic generation are also important

the coads sea level pressure signal a near global el nino composite and time series view 1946 1993 abstract using coads data for the period 1946 1993 the near global sea level pressure slp patterns associated with interannual variability and the climatological seasonal march are discussed a particular focus concerns the patterns associated with the two years before and after the south american sea surface temperatures rise el nino the ten el nino events in this record are composited and the robustness of the features of this composite is tested many features of the composite are quite robust they occur during most el nino events and are infrequent during non el nino periods the most robust feature is an area of negative slp anomaly slpa in the eastern equatorial pacific during year 0 of the composite this feature exceeds significance thresholds during every el nino year and never during non el nino years it correlates better with central pacific sst variability than does the soi a west central north pacific positive slpa occurring late in year 0 and lasting into the spring of year

major neogene events of the southeastern pacific the chilean and peruvian record abstract according to the biochronostratigraphic model proposed the neogene marine deposits in chile and peru represent two independent transgressive sequences alloformations separated by a major regional hiatus the earlier sequence nseps i would stretch from the top of the early miocene up to the base of the late miocene ca 19 10 m y b p the upper sequence nseps ii would correspond in turn to the late pliocene ca 3 5 1 6 m y b p the regional hiatus separating both sequences would encompass the late miocene and the early pliocene ca 10 3 5 m y b p the planktonic foraminiferal events described suggest an age of terminal early miocene middle miocene and late pliocene respectively the paleoclimatic events recorded are three a warming event lasting from the terminal early miocene to the end of the middle miocene mmwe 18 11 5 m y b p a cooling event of the middle late pliocene lpce 2 5 0 2 m y b p and warming event spanning most of the late pliocene lpwe 3 5 2 2 m y b p restricted to the surface and intermediate sea waters of the middle and low latitudes the last paleoclimatic event not recorded as such so far is both synchronous and mutually exclusive in latitudinal terms with the second one three tectonic regional events are analyzed the quechuan 1 phase 19 1 5 m y b p the quechuan 2 phase 10 1 m y b p and the geographic rhodanian phase 3 5 0 5 m y b p in the studied area there is no late miocene marine sedimentary record to confirm the terminal tortonian or quechuan 3 tectonic phase ca 7 m y b p admitted to occur in the volcanoclastic continental sequences of northern chile and southern peru