stratigraphy composition and form of the deccan basalts western ghats india in the western ghats between latitudes 18 20 n and 19 15 n 7000 km2 of deccan basalt have been mapped with the primary objective of establishing a flow stratigraphy as a guide to the volcanic history of the flood basalts using over 70 measured vertical sections major and trace element analyses of nearly 1200 samples and rare earth and87sr 86sr determinations for over 60 samples we divide the basalt into three subgroups and ten formations in this paper we describe the seven principal formations in the area and the most prominent individual flows

from swallow floats to argo the development of neutrally buoyant floats neutrally buoyant floats have been a vital tool in the exploration of the global ocean circulation and now provide a central element of the in situ ocean observing system through the argo project the paper traces the development of neutrally buoyant floats from their origins in the mid 1950s to the present day and highlights areas of ocean science to which floats made significant contributions

geostrophic transport in the benguela current region historical data from the region between the greenwich meridian and the african continental shelf are used to compute the offshore geostrophic transport of the benguela current at 32 s the benguela current is located near the african coast transporting about 21 sv 1 sv 106 m3 s 1 of surface water toward the north relative to a potential density surface lying between the upper branch of circumpolar deep water and the north atlantic deep watar two warm core eddies of probable agulhas current origin an observed west of the benguela current at 32 s near 30 s the benguela current turns toward the northwest and begins to separate from the eastern boundary it carries about 18 sv of surface water across 28 s the current then turns mainly toward the west to flow over a relatively deep segment of the walvis ridge south of the valdivia bank a surface current with northward surface of about 10 cm s 1 flows along the western side of the valdivia bank while another northward surface current flows at about 20 cm s 1 some 300 km west of the bank about 3 sv of surface now do not leave the cape basin south of the vaidivia bank but instead drift northward as a wide sluggish flow out of the northern end of the cape basin because of the more southerly seaward extensions of most of the benguela current there are no deep reaching interactions observed between this current and the cyclonic gyre in the angola basin east of the greenwich meridian beneath the surface layer about 4 5 sv of antarctic intermediate water are carried northward across 32 and 28 s by the benguela current essentially all of which turns westward to cross the greenwich meridian south of 24 s

lagrangian circulation of antarctic intermediate water in the subtropical south atlantic this study combines float data from different projects collected between 1991 and 2003 in the south atlantic to describe the flow of antarctic intermediate water aaiw velocity space time averages are calculated for various grid resolutions and with cells deformed to match the bathymetry f h or f h with h being the water depth and h being the thickness of the aaiw layer when judged by the degree of alignment between respective isolines and the resulting average velocity fields the best grid is based on a nominal cell size of 3o latitude by 4o longitude with cell shapes deformed according to f h using this grid objectively estimated mean currents and their associated errors as well as meridional and zonal volume transports are estimated results show an anticyclonic subtropical gyre centred near 36os and spanning from 23o 1 s to 46 1os the south atlantic current meanders from 33os to 46os and shows a mean speed of 9 6 7 8 cm s 1 8 5 sv 3 5 sv 1 sv 1 106 m3 s 1 the northern branch of the subtropical gyre is located between 22os and 32os and flows westward with a mean speed of 4 7 3 3 cm s 1 9 3 sv 3 4 sv evidence of a cyclonic tropical gyre divided in two sub cells is visible on the stream function

origin of the deccan trap flows at mahabaleshwar inferred from nd and sr isotopic and chemical evidence abstract the deccan flows at mahabaleshwar are divisible into a lower and an upper group based on nd and sr isotopic ratios which define two correlated trends this distinction is supported by incompatible element ratios and bulk compositions the data reflect contamination in a dynamic system of magmas from an lil depleted e juv 8 mantle by two different negative e juv endmembers one undoubtedly continental crust the other either continental crust or enriched mantle the depleted mantle source anomalously high in 87 sr 86 sr may have been in the subcontinental lithosphere or a region of rising indian ocean morb mantle

gyres and jets inversion of tracer data for ocean circulation structure abstract this paper describes a quasi 3d bayesian inversion of oceanographic tracer data from the south atlantic ocean initially one active neutral density layer is considered with an upper and lower boundary the available hydrographic data are linked to model parameters water velocities diffusion coefficients via a 3d advection diffusion equation a robust solution to the inverse problem can be obtained by introducing prior information about parameters and modeling the observation error this approach estimates both horizontal and vertical flow as well as diffusion coefficients a system of alternating zonal jets is found at the depths of the north atlantic deep water consistent with direct measurements of flow and concentration maps a uniqueness analysis of the model is performed in terms of the oxygen consumption rate the vertical mixing coefficient bears some relation to the bottom topography even though the authors do not incorporate topography into their model the method is extended to a m

intermediate water in the brazil malvinas confluence zone a lagrangian view the subsurface flow within the subantarctic and subtropical regions around the brazil malvinas falkland confluence zone is studied using daily hydrographic and kinematic data from four subsurface floats and a hydrographic section parallel to the south american shelf the float trajectories are mapped against sea surface flow patterns as visible in concurrent satellite sea surface temperature sst images with focus on the november 1994 and october november 1995 periods the unprecedented employment of lagrangian s diagrams enables us to trace the advection of patches of fresh antarctic intermediate water aaiw from the confluence zone into the subtropical region the fresh aaiw consists of a mixture of subtropical aaiw and malvinas current core water within the subtropical gyre these patches are discernible for extended periods and drift over long distances reaching north to 34 s and east to 40 w the cross frontal migration of quasi isobaric floats across the confluence zone from the subtropical to the subantarctic environment is observed on three occasions the reverse process float migration from a subpolar to a subtropical environment was observed once these events were located near 40 s 50 w the site of a reoccurring cold core feature subsurface float and sst data comparison reveals similarities with analogous observations made in the gulf stream rossby 1996 where cross frontal processes were observed close to meander crests the limited number of floats of this study and the complex structure of the brazil malvinas confluence zone however restricts the analysis to a description of two events

volcanological and tectonic control of stratigraphy and structure in the western deccan traps many of the world s flood basalt provinces form elevated plateaux at the margins of continents although in most cases their present large elevation is not the result of mountain building processes several explanations have recently been put forward to explain such occurrences of epeirogeny the deccan trap basalt province forms one such elevated plateau and results are presented here showing how the epeirogenic uplift in this region combined with crustal subsidence probably associated with the rifting of the indian continental margin has affected the structure of the basalt sequence trace element analytical data are used for samples from numerous vertical sections through the deccan traps lava series along and around the western ghats ridge in india the results reinforce the previously defined stratigraphy of the mahabaleshwar area and extend it over a region covering some 36 000 km2 reaching as far south as belgaum and the trap basement contact these results show that the lava pile is not flat lying but forms a very low amplitude anticlinal fold structure plunging southwards by up to 0 3 over most of the area although in the south there is evidence of a reversal of this plunge the fold is interpreted as being the result of two tilting processes 1 westward tilting near the coast due to the foundering of the passive continental margin and 2 epeirogenic uplift along the whole west coast of india producing the observed topography and the peninsula wide drainage patterns and also the easterly component of dip variations in the magnitude of the latter effect along the western continental margin may also be important in generating the plunge of the fold although the possibility of some component of depositional dip may also be important this latter possibility can be modelled using a simple computer program the results of this modelling show that a migrating linear volcanic edifice fits the observations best

preliminary results from directly measuring middepth circulation in the tropical and south pacific as part of the world ocean circulation experiment 300 autonomous lagrangian circulation explorer floats were deployed in the tropical and south pacific to measure the general circulation at 900 m depth most floats measured average currents over 25 submerged days between ascents to the surface for locating and data relay by the end of 1997 over 12 500 observations spanning 840 float years were obtained accuracy of the average velocity is limited by variability some of which is found to arise from steady flows with spatial variations smaller than averaging scales observed 25 day velocities are serially uncorrelated except near the equator where energetic zonal variability has seasonal timescales and appears to be described by a data assimilating ocean circulation model run by the national centers for environmental prediction space time averages of float velocities disclose a general pattern of middepth flow that resembles the surface circulation with the strongest flows of o 3 cm s in the deep antarctic circumpolar current and east australian current the weaker elements of the flow including an interior subtropical circulation with o millimeters per second flows are described by an objective analysis whose accuracy is limited by sampling noise rather than uncertainty of the analysis parameters the subtropical circulation has a gyres within a gyre structure including boundary currents along australia and east of new zealand and a concentrated equatorial limb with surprising strength in the western basin this current is also involved in a tropical gyre with generally eastward flow along the equator in the western basin at least because of strong seasonal scale variability the equatorial zonal currents are not well measured yet but data are still being accumulated comparison with reid s 1997 absolute circulation shows more areas of agreement than of disagreement

circulation and water mass modification in the brazil malvinas confluence abstract the confluence between the brazil current and the malvinas current the brazil malvinas confluence bmc in the argentine basin is characterized by a complicated thermohaline structure favoring the exchanges of mass heat and salt between the subtropical gyre and the antarctic circumpolar current acc analysis of thermohaline properties of hydrographic sections in the bmc reveals strong interactions between the acc and subtropical fronts in the subantarctic front subantarctic mode water samw antarctic intermediate water aaiw and circumpolar deep water cdw warm become saltier by 0 4 0 08 0 3 0 02 and 0 6 c 0 1 respectively in the subtropical gyre aaiw and north atlantic deep water have cooled freshened by 0 4 0 07 and 0 7 c 0 11 respectively to quantify those acc subtropical gyre interactions a box inverse model surrounding the confluence is built the model diagnoses a subduction of 16 4 sv 1 sv 106 m3 s 1 of newly formed samw and aaiw under the subtro

hydrodynamic and geomorphological controls on surface sedimentation at the subtropical shelf front brazil malvinas confluence transition off uruguay southwestern atlantic continental margin abstract the hydrology of the southwestern atlantic margin is dominated by the confluence of water masses with contrasting thermohaline properties generating a frontal zone that extends from the brazil malvinas confluence zone bmc in the open ocean to the subtropical shelf front stsf on the continental shelf however the hydrodynamics of the transition between these hydrographic features is still not fully understood high resolution morphological multibeam and hydrological ctd data were integrated with sedimentological data textural and productivity proxies in order to develop a sound framework to understand surface sedimentation of the slope extension of the stsf subsurface outer shelf and upper slope and of the bmc intermediate level middle slope on the uruguayan continental margin 34 to 36 s since the detailed morphology of the study area is presented for the first time related geological processes are briefly discussed on the outer shelf and upper slope and north of the stsf the current direction of erosive mound scarps indicates the dominance of the southward flowing brazil current bc this suggests a northernmost boundary for the distribution of the stsf a strong flux of the bc favored by a steeper slope as well as by the occurrence of canyons incised on the upper slope is evidenced by the occurrence of coarser sediments and low values of productivity proxies but also by the presence of deep sea coral reefs southwards the effect of a less energetic malvinas current mc and the highly productive stsf is indicated by the deposition of fine sediments with high organic matter content as well as by the absence of deep sea coral reefs this depositional scenario is enhanced by a smooth slope and the occurrence of canyons incised deeper in the middle slope off shelf sediment transport along the stsf is inferred by the similar texture registered between the outer shelf and shallow upper slope the occurrence of biogenic shelly reworked sands and gravel and by the observed decrease in grain size with depth glacial iceberg transport northwards and or gravity processes are suggested by the occurrence of igneous metamorphic gravel in lag deposits on the upper slope on the middle slope the northernmost influence of the erosive antarctic intermediate water is evidenced by the vanishing of morphologic contouritic structures this is also imprinted in a pronounced northward fining in grain size this contribution increase our understanding of this highly dynamic and complex area providing the first detailed analysis of the regional sediment patterns and oceanographic and morphological controls on surface sedimentation

dianeutral mixing transformation and transport of antarctic intermediate water in the south atlantic ocean recently obtained world ocean circulation experiment woce sections combined with a specially prepared pre woce south atlantic data set are used to study the dianeutral across neutral surface mixing and transport achieving antarctic intermediate water aaiw being transformed to be part of the north atlantic deep water nadw return cell five neutral surfaces are mapped encompassing the aaiw from 700 to 1100 db at the subtropical latitudes coherent and significant dianeutral upwelling is found in the western boundary near the brazil coast north of the separation point about 25 s between the anticyclonic subtropical and cyclonic south equatorial gyres the magnitude of dianeutral upwelling transport is 10 3 sv 1 sv 106 m3 s 1 for 1 1 square area it is found that the aaiw sources from the southwestern south atlantic and southwestern indian ocean do not rise significantly into the benguela current instead they contribute to the nadw return formation by dianeutral upwelling into the south equatorial current in other words the aaiw sources cannot obtain enough heat buoyancy to rise until they return to the western boundary region but north of the separation point the basin wide integration of dianeutral transport shows net upward transports ranging from 0 25 to 0 6 sv across the lower and upper boundary of aaiw north of 40 s this suggests that the equatorward aaiw is a slow rising water on a basin average given one order of uncertainty in evaluating the along neutral surface and dianeutral diffusivities from the assumed values k 103 m2 s 1 and d 10 5 m2 s 1 the integrated dianeutral transport has an error band of about 10 20 the relatively weak integrated dianeutral upwelling transport compared with aaiw in other oceans implies much stronger lateral advection of aaiw in the south atlantic mapped turner angle in diagnosing the double diffusion processes shows that the salty central water can flux salt down to the upper half of aaiw layer through salt fingering therefore the northward transition of aaiw can gain salt either through along neutral surface advection and diffusion or through salt fingering from the central water and heat through either along neutral surface advection and diffusion or dianeutral upwelling cabbeling and thermobaricity are found significant in the antarctic frontal zone and contribute to dianeutral downwelling with velocity as high as 1 5 10 7 m s 1 a schematic aaiw circulation in the south atlantic suggests that dianeutral mixing plays an essential role in transforming aaiw into nadw return formation

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

impact of the equatorial deep jets on estimates of zonal transports in the atlantic the structure and variability of the zonal equatorial flow in the atlantic is studied on the basis of velocity profiles obtained with lowered acoustic doppler current profilers during multiple surveys the vertical extent of the zonal currents is found to vary considerably it can be as small as 100 m or as large as 1000 m in the atlantic vertical scales of 400 600 m have been associated with the equatorial deep jets they are also frequently called deep jets or stacked jets typical amplitudes of the zonal velocity are about 20 cm s 1 an analysis of quasi synoptic surveys indicates that the zonal extent of most jets is likely to be at least 27d they can rise or deepen from west to east although the deepening was observed more often and is often more pronounced the west to east deepening can be as large as 320 m 10d basin wide mean depth changes of the jets are mostly on the order of 50 m 10d and the largest depth changes are typically observed between 35d and 23d w the existence of these changes indicates that vertically propagating equatorially trapped waves might be one cause for the jet structure however the dependence of the slope on the longitude indicates that other processes must be involved as well the typical vertical extent of the jets is small enough to result in several direction changes of the zonal flow in the antarctic intermediate water aaiw and the north atlantic deep water nadw layer from transport estimates for 14 meridional sections it is found that the transport for the westward component of the flow within the aaiw layer 500 1000 m can be as large as 24 sv 1 sv 10 6 m s 1 within 1d of the equator for the eastward component of the flow in the aaiw layer the transport can be as large as 8 sv adding the transport components for each section results in a range of total aaiw transports from 24 to 7 sv this suggest that the annual mean transport of aaiw is westward the only months with eastward total transports are june and july this is consistent with earlier lagrangian and some other observations that indicated that the aaiw flow along the equator is governed by an annual cycle in the nadw layer 1200 3900 m the transport for the westward eastward flow can be as large as 25 sv 23 sv within 1d of the equator this results in a range of total nadw transports from 10 to 18 sv the variations of the total transports of aaiw and nadw are anti correlated with a correlation coefficient of 0 86 since only eight sections reached deep enough to allow transport estimates in the nadw layer it is more difficult to come to a conclusion about the mean transport in this layer than for the transport in the aaiw layer for the latter layer 14 sections were available nevertheless the obtained estimates suggest that the total nadw transport may be eastward

bottom currents derived from a shipborne adcp on woce cruise a11 in the south atlantic abstract this paper is divided into two parts the first describing an enhancement of the shipborne adcp system and the second describing information about bottom currents that have been obtained therefrom on woce cruise a11 in the south atlantic punta arenas to cape town rrs discovery has been fitted with a gps3df receiver and an array of antennas about its bridge which determine the instantaneous attitude of the ship the heading record from this instrument has been compared with the ship s gyrocompass throughout the 40 day cruise differences have been calculated and examined according to heading speed and movements underway differences are found insensitive to heading except in a southerly sector but on station differences exhibit a sinusoidal dependence on heading with range 3 steaming from a station led to transient behavior with recognizable effects for 1 hour the results are generally consistent with earlier reports and are attributed to gyro error an improved heading measurement has a

relationships between crustal contamination and crystallisation in continental flood basalt magmas with special reference to the deccan traps of the western ghats india the upper part of the deccan traps sequence bushe to mahabaleshwar formations shows a statistically significant tendency for the most mafic lavas to be the most contaminated by crustal materials this is the reverse of the relationship shown by suites evolving by contamination accompanied by fractional crystallisation afc the observed correlations e g between mg number and sr isotope initial ratios are partly an accidental consequence of the fact that the most mafic lavas are more abundant in the lower part of the sequence while contaminant availability declines in the upper part it is probable however that the correlations are augmented by increased contamination of hotter magma batches during ascent through dykes a process during which fractional crystallisation is suppressed by magmatic turbulence the absence of afc relationships suggests that most of the contamination took place during the ascent stage rather than in a magma chamber other continental flood basalt provinces such as the parana and etendeka do show afc relationships and it is speculated that this may be a result of magma chamber contamination coupled with flow rates which prevent contamination during ascent

antarctic intermediate water circulation in the tropical and subtropical south atlantic recent hydrographic data from the south atlantic ventilation experiment cruises and others are combined with historical data and used to map the isopycnal properties corresponding to the antarctic intermediate water aaiw in the atlantic ocean the low salinity of the aaiw extends eastward across the south atlantic just south of the equator 3 4 s evidence of a weak eastward flow just north of the equator 1 2 n is also shown lateral and vertical homogenization of properties in the aaiw is found at the equator between 2 s and 2 n there is no clear zonal gradient in salinity just along the equator these observations suggest enhanced mixing within the equatorial baroclinic deformation radius the south atlantic tropical gyre is shown to consist of the following three cells one cyclonic cell centered at about 7 s another centered at about 19 s in the west and 23 s in the east and one anticyclonic cell centered at about 13 s these cells are associated with a westward extension at 10 s of high salinity and low oxygen which originates in the eastern tropical south atlantic and a front in these properties at about 15 s in the west and about 20 s in the east

the transport of the weddell gyre across the prime meridian abstract current meter observations from instruments moored from 1996 to 2001 are used to determine the structure and the volume transport of the weddell gyre on the greenwich meridian the record length mean volume transport is 45 sv to the east within the northern and 56 sv to the west within the southern limb of the weddell gyre thus 11 sv must leave the gyre circulation west of the greenwich meridian and enter it east of it the deficit occurs with 8 sv mainly in the circumpolar deep water cdw warm deep water wdw layer surface waters and weddell sea deep water wsdw contribute 2 and 3 sv respectively in contrast to this 3 sv more of weddell sea bottom water wsbw flow in the northern limb to the east than in the southern limb to the west which suggests a wsbw formation rate of about 3 sv in the western weddell sea in the southern boundary of the antarctic circumpolar current acc a volume transport of 35 16 sv was found using geostrophic calculations adjusted with two measurements of the absolute velocity the large heat content of the northern limb points to an extensive heat exchange between the weddell sea and the world ocean west of the prime meridian hence the heat transport as well as the volume transport suggest that the water masses of the weddell gyre are not exclusively replaced in its eastern part but that there is a significant exchange of water masses to the west of the prime meridian

lagrangian observations in the intermediate western boundary current of the south atlantic abstract subsurface float measurements at 800 m depth carried out from 1994 to 2003 in the brazil basin are used to characterise the equatorward intermediate western boundary current iwbc and its connections to the ocean interior transversally the boundary flow is less than 100 km wide and most intense at 10 20 km from the 800 m isobath its average velocities range from 0 1 ms 1 to 0 3 ms 1 depending on latitude with individual daily values as high as 0 7 ms 1 the flow meridional extent exhibits 3 contrasted domains i from 27 s to the vitoria trindade ridge at 20 30 s the boundary flow intensifies northward along a relatively smooth topography a counter current adjacent to it on its seaward side feeds it with intermediate water from the northern limb of the subtropical gyre ii at latitudes 20 15 s characterised by a very irregular topography the iwbc becomes weaker with even no real proof of its presence at 18 15 s an intense mesoscale variability prevails there which apparently takes over from the boundary flow to ensure the northward transport of water to 15 s where the iwbc re forms iii north of this latitude the boundary flow increases again to 10 s along smooth isobaths then decreases when encountering a rougher topography and the zonal jets of the equatorial current system a counter current present from 5 s to 14 s partly fed from the boundary flow contributes to its drainage the iwbc shows two main input locations at 27 23 s and 15 12 s in the southern parts of the two latitudinal domains of smooth topography where the northward current increases output locations coincide with major capes in the continental slope geometry at 20 s and 18 s the southeastern and northeastern corners of the abrolhos bank at 8 s near the recife plateau and at 5 s near cape sao roque

characteristics of intermediate water flow in the benguela current as measured with rafos floats abstract seven floats not launched in rings crossed over the mid atlantic ridge in the benguela extension with a mean westward velocity of around 2 cm s between 22s and 35s two agulhas rings crossed over the mid atlantic ridge with a mean velocity of 5 7 cm s toward 285 this implies they translated at around 3 8 cm s through the background velocity field near 750 m the boundaries of the benguela current extension were clearly defined from the observations at 750 m the benguela extension was bounded on the south by 35s and the north by an eastward current located between 18s and 21s other recent float measurements suggest that this eastward current originates near the trindade ridge close to the western boundary and extends across most of the south atlantic limiting the benguela extension from flowing north of around 20s the westward transport of the benguela extension was estimated to be 15 sv by integrating the mean westward velocities from 22s to 35s and multiplying by the 500 m estimated thickness of intermediate water roughly 1 5 sv of this are transported by the 3 agulhas rings that cross the mid atlantic ridge each year as observed with altimetry this value of the benguela extension transport is the first one to have been obtained from long term two year observations and across the full width of the benguela extension

geohistory analysis of bombay high region abstract geohistory diagrams have been constructed for three representative sites in the bombay high region offshore west coast india the model curve for 60 lithospheric injection matches the intitial part of a thermo tectonic curve for one of the sites where a complete tertiary sequence is developed the study suggests that the four paleogene unconformities recognised in this region were caused by eustatic falls a distinct phase of active subsidence occurred during the late middle late miocene probably due to more active spreading at the mid indian ocean ridge

kinematic elements of antarctic intermediate water in the western south atlantic the northward flowing antarctic intermediate water aaiw is a major contributor to the large scale meridional circulation of water masses in the atlantic together with bottom and thermocline water aaiw replaces north atlantic deep water that penetrates into the south atlantic from the north on the northbound propagation of aaiw from its formation area in the south western region of the argentine basin the aaiw progresses through a complex spreading pattern at the base of the main thermocline this paper presents trajectories of 75 subsurface floats seeded at aaiw depth the floats were acoustically tracked covering a period from december 1992 to october 1996 discussions of selected trajectories focus on mesoscale kinematic elements that contribute to the spreading of aaiw in the equatorial region intermittent westward and eastward currents were observed suggesting a seasonal cycle of the aaiw flow direction at tropical latitudes just offshore the intermediate western boundary current the southward advection of an anticyclonic eddy was observed between 5 degrees s and 11 degrees s farther offshore the flow lacks an advective pattern and is governed by eddy diffusion the westward subtropical gyre return current at about 28 degrees s shows considerable stability with the mean kinetic energy to eddy kinetic energy ratio being around one farther south the eastward deeper south atlantic current is dominated by large scale meanders with particle velocities in excess of 60 cm s 1 at the brazil falkland current confluence zone a cyclonic eddy near 40 degrees s 50 degrees w seems to act as injector of freshly mixed aaiw into the subtropical gyre in general much of the mixing of the various blends of aaiw is due to the activity of mesoscale eddies which frequently reoccupy similar positions c 1999 elsevier science ltd all rights reserved

the isopycnal swallow float a simple device for tracking water parcels in the ocean abstract a standard swallow float can be converted into a passive isopycnal follower by the addition of a compressee a spring backed piston in a cylinder designed to give the float the compressibility of seawater thus no archimedian buoyancy is created due to changes in depth in addition the float must have a coefficient of thermal expansion significantly smaller than that of seawater an instrument meeting these requirements ballasted to a chosen isopycnal will approximately follow that isopycnal on time scales longer than the local buoyancy period two preliminary field experiments were conducted in the upper main thermocline near the north wall of the gulf stream during august 1981 a spherical glass float was deployed 200 km downstream from cape hatteras and was tracked for approximately 100 km neutrally buoyant in the oxygen minimum near 380 m the float tracked the t 27 12 0 01 as determined from ctd data during its passage through a mini meander during september 1982 a cylindrical float was tracked for approximately 100 km east of cape hatteras deployed in the gulf stream near the 250 m level the float tracked the t 26 74 0 01 isopyncal surface during a gradual descent and cross stream motion over the 24 hr sampling period thus the floats tracked nearly isopycnally in both field tests clusters of these instruments used in concert with hydrographic surveys have the potential for unique studies of mixing entrainment and topographic effects

source and differentiation of deccan trap lavas implications of geochemical and mineral chemical variations the basalt stratigraphy of the deccan trap between mahabaleshwar ghat and belgaum over steps the basement from north to south sr isotope and zr nb ratios and sr rb and ba concentrations correlate portions of the post poladpur stratigraphy over 250 km along the western ghats thereby confirming a southerly component of dip of 0 06 at the southwestern margin the stratigraphy extends upwards from the compositionally uniform ambenali formation cox hawkesworth 1984 into a sequence of grossly heterogeneous flow units which have been allocated to the mahabaleshwar and panhala formations lightfoot hawkesworth 1988 the mahabaleshwar formation is represented only by a sequence of highly fractionated flows termed the kolhapur unit with similar 87sr 86sr0 to the mahabaleshwar 0 7045 but with sr 2 25 succeeding the kolhapur unit are a series of flows with high 87sr 86sr0 0 7045 0 705 zr nb 13 and low sr 230 but trace element concentrations similar to the mahabaleshwar formation these have been allocated to the desur unit of the panhala geochemical variations in flows overlying the ambenali define two distinct trends one is attributed to gabbro fractionation and the other to variations in the compositions of the parental magmas and arguably their source regions there is little evidence for significant crustal contamination in these flows and the degree of fractionation and the composition of the phase extract are shown to vary along strike within the mahabaleshwar formation the high tio2 content of kolhapur unit flows is shown to be the result of shallow level gabbro fractionation rather than the presence of a primitive high ti magma mahabaleshwar formation basalts exhibit a broad negative correlation between the degree of fractionation and sr isotopic composition the endmember with lower 87sr 86sr0 has different zr y from the ambenali basalts and would appear to have been generated by lower degrees of melting of a similar source the other endmember has more radiogenic sr lower zr nb similar zr y but higher mg number the simplest interpretation is that these magmas were more primitive and hence hotter and more able to interact with the lithosphere en route to the surface and that they then mixed to produce the mahabaleshwar array the panhala formation basalts plot on the sr nd array defined by the mahabaleshwar formation and the desur unit basalts plot on an extension of this array this suggests that the source characteristics are also lithospheric the absolute elemental abundances may then be a function of melting and fractionation we are impressed by the apparent switch from crustal lithospheric contributions to mantle lithospheric contributions through the stratigraphy and suggest that this together with the more protracted fractionation of the magma reflects a change in the availability of the lithospheric components accompanying the southerly migration of the volcanic edifice

tholeiitic dykes in the seychelles and the original spatial extent of the deccan we report geochemical data from c deccan age tholeiitic dykes from praslin island in the seychelles a continental fragment which lay adjacent to the coast of india before sea floor spreading started in the arabian sea at 64 ma the dykes have compositions very similar to the distinctive bushe magma type from the deccan and hence constitute the first traces of deccan activity recognized on the seychelles fitting the seychelles and india back together to reconstruct the original extent of the deccan we find that the present estimate of 1 million km 2 needs to be revised upwards by c 25 to account for the deccan magmatism in the seychelles if dipping reflectors found on seismic lines to the northwest of the seychelles are also deccan age flows this would increase still further the area and volume estimates

hydrographic variability in the st helena bay region of the southern benguela ecosystem cross shelf distributions of temperature salinity water masses and dissolved oxygen in st helena bay revealed substantial vertical and seasonal variations in the surface layers nearshore and offshore temperature and salinity patterns differed with bay scale variability linked to upwelling dynamics and coastal processes while the offshore region was influenced by solar insolation spectral analysis revealed that an annual signal prevailed at most stations and corroborated contrasting patterns between the offshore and nearshore regions with phase differences suggesting shoreward propagation of the offshore temperature signal the shelf was dominated by modified upwelled water muw and subantarctic mode water samw which comprised the primary source of upwelled water clear zonation of muw was evident across the shelf resulting from seasonal variations in locations of the oceanic and bifurcated shelf break fronts dynamics within st helena bay consistently differed from those further offshore due to the influences of the shelf break front cape columbine upwelling plume and cyclonic recirculation which appeared to be associated with an intraannual signal with a periodicity of 3 4 months persistent hypoxia in the bottom waters suggested the occurrence of a permanent reservoir of low oxygen water low seasonal shoreward and offshore expansion of low occurred throughout the upwelling season with maximum extent reached during summer and autumn due to the coupled effects of advection and local phytoplankton decay while wind mixing ventilated the water column at nearshore stations in winter and the onset of upwelling during spring introduced oxygen richer water from further offshore hypoxia persisted in the center of the bay

the intermediate depth circulation of the western south atlantic the subsurface oceanic circulation is an important part of the earth climate system subsurface currents traditionally are inferred indirectly from distributions of temperature and dissolved substances occasionally supplemented by current meter measurements neutrally buoyant floats however now enable us to obtain for the first time directly measured intermediate depth velocity fields over large areas such as the western south atlantic here our combined data set provides unprecedented observations and quantification of key flow patterns such as the subtropical gyre return flow 12 sv 1 sverdrup 10 6 m 3 s 1 its bifurcation near the santos plateau and the resulting continuous narrow and swift northward intermediate western boundary current 4 sv this northward flowing water passes through complex equatorial flows and finally enters into the north atlantic

origin of deccan trap lavas evidence from combined trace element and sr nd and pb isotope studies abstract geochemical and isotope results are presented from a new study of the most southern basalts in the deccan trap india three chemical formations are recognised two of which can be correlated with the established stratigraphy in mahabaleshwar and imply a regional southerly dip of 0 06 over a distance of 250 km in detail sr isotope variations within the ambenali and mahabaleshwar formations can be shown to reflect three distinct end members which provide new constraints for petrogenetic models pb isotope data for selected basalts exhibit a wide range with 206 pb 204 pb 16 87 22 45 and a linear correlation on a pb pb diagram the least contaminated ambenali basalts plot within the pb array and interaction with mantle lithosphere involves a shift to less radiogenic pb whereas contamination with crust is characterised by more radiogenic pb unlike the karoo and parana continental flood basalt provinces only four flow units within the southern deccan appear to contain a significant contribution from mantle lithosphere the mahabaleshwar and ambenali formation basalts exhibit a striking negative pb sr isotope trend which is presently regarded as one of the features of interaction with shallow level lithospheric mantle it further suggests that basalts from the walvis ridge kerguelen and ninetyeast ridge all remobilised such shallow level material and that the deccan basalts which were not affected by crustal contamination reflect interaction between asthenospheric material similar to t type morb but related to the reunion hotspot and continental mantle lithosphere of the indian plate

large scale environmental parameters associated with tropical cyclone formations in the western north pacific abstract the local environmental conditions associated with 405 tropical cyclone tc formations in the western north pacific during 1990 2001 are examined in this study six large scale parameters are obtained and computed from the ncep reanalyses with 2 5 latitude resolution these include the sea surface temperature 200 850 hpa vertical and meridional zonal shear 500 700 hpa average relative humidity convective available potential energy and 200 hpa divergence it is found that these parameters show quite consistent values in almost all the cases examined and near gaussian distributions are found for them the mean values of these distributions are 28 9 c 3 2 m s 1 2 3 m s 1 61 8 1184 1 j kg 1 and 5 2 10 6 s 1 for the above six domain averaged parameters respectively based on these distributions of values a formation potential area is defined as a location that possesses these environmental parameters all within the thresholds one standard deviation from the mean value found above

deep cross equatorial flow in the atlantic measured with sofar floats neutrally buoyant sofar floats at nominal depths of 800 1800 and 3300 m were tracked for 21 months in the vicinity of tropical boundary currents in the atlantic near 6 n and at several sites near 11 n as well as along the equator trajectories at 1800 m show a swift 50 cm s narrow 100 km wide southward flowing deep western boundary current dwbc extending from 7 n to the equator the average transport per unit depth in the dwbc was estimated to be 13 8 103 m2 s coupling this value with mean velocities measured in the dwbc by current meters gave a volume transport of 15 106 m3 s between depths of 900 m and 2800 m approximately 6 106 m3 s recirculated northward between the dwbc and the mid atlantic ridge leaving 9 106 m3 s as cross equatorial transport no obvious dwbc nor swift equatorial current was observed by the 3300 m floats a low mean velocity at this depth lay between f 11 and higher velocity cores above and below the 1800 m trajectories also suggest that at times february march 1989 the north atlantic deep water in the dwbc turned eastward and flowed along the equator and at other times august september 1990 the dwbc crossed the equator and continued southward the velocity near the equator calculated by grouping floats in a box along the equator was eastward at 4 1 cm s from february 1989 to february 1990 and westward at 4 6 cm s from march 1990 to november 1990 thus the amount of cross equatorial flow in the dwbc appeared to be linked to low frequency variability of the structure of the equatorial current system floats in antarctic intermediate water at 800 m revealed a northwestward western boundary current although flow patterns were complicated three floats that significantly contributed to the northwestward flow looped in anticyclonic eddies that translated up the coast at 8 cm s six 800 m floats drifted eastward along the equator between 5 s and 6 n at a mean velocity of 11 cm s one reached 5 w in the gulf of guinea suggesting that the equatorial currents at this depth extended at least 35 40 along the equator three of these floats reversed direction near the end of the tracking period