early winter in the northern stratosphere an account is given of the evolution and structure of the circulation in the stratosphere and upper troposphere of the northern hemisphere in the early winter of 1982 83 an early winter warming is described and it is shown to have some features in common with canadian warmings a tentative connection is made between the intensification in the troposphere of a trough ridge pattern associated with the east asian low and the establishment of the aleutian high as a persistent feature extending through the whole depth of the stratosphere processes leading to the formation of the so called surf zone are considered and aspects of zonalmean diagnostics are related to developments on synoptic maps

anatomy of north pacific decadal variability abstract a systematic analysis of north pacific decadal variability in a full physics coupled ocean atmosphere model is executed the model is an updated and improved version of the coupled model studied by latif and barnett evidence is sought for determining the details of the mechanism responsible for the enhanced variance of some variables at 20 30 yr timescales the possible mechanisms include a midlatitude gyre ocean atmosphere feedback loop stochastic forcing remote forcing or sampling error decadal variability in the model is expressed most prominently in anomalies of upper ocean streamfunction sea surface temperature sst and latent surface heat flux in the kuroshio oyashio extension koe region off japan the decadal signal off japan is initiated by changes in strength and position of the aleutian low the atmospheric perturbations excite sst anomalies in the central and eastern north pacific with opposing signs and canonical structure the atmospheric perturbations also change the ekm

rapid extension in an eocene volcanic arc structure and paleogeography of an intra arc half graben in central idaho a study of extension volcanism and sedimentation in the middle eocene panther creek half graben in central idaho shows that it formed rapidly during an episode of voluminous volcanism the east southeast tilted panther creek half graben developed across the northeast edge of the largest cauldron complex of the challis volcanic field and along the northeast trending trans challis fault zone two normal fault systems bound the east side of the half graben one fault system strikes northeast parallel to the trans challis fault zone and the other strikes north to northwest the geometry of the basin fill deposits shows that movement on these two normal fault systems was synchronous and that both faults controlled the development of the panther creek half graben strikes of the synextension volcanic and sedimentary rocks are similar throughout the half graben whereas dips decrease incrementally upsection from as much as 60 to less than 10 previous k ar dates and a new 40 ar 39 ar plateau date from the youngest widespread tuff in the basin suggest that most of basin formation spanned 3 m y between about 47 7 ma and 44 5 ma as much as 6 5 km of volcanic and sedimentary rocks were deposited during that time although rates of extension and subsidence were very high intense volcanic activity continually filled the basin with ash flow tuffs outpacing subsidence and sedimentation until the end of basin development after the abrupt end of challis volcanism locally derived pebble to boulder conglomerate and massive reworked ash accumulated in the half graben these sedimentary rocks make up a small part of the basin fill in the panther creek half graben and were derived mainly from proterozoic metasedimentary rocks uplifted in the footwall of the basin the east southeast tilt of the sedimentary rocks their provenance and coarse grain size and the presence of a gravity slide block derived from tilted volcanic rocks in the hanging wall attest to continued tectonism during conglomerate deposition provenance data from the sedimentary rocks imply that the highland in the footwall of the panther creek half graben was never thickly blanketed by synextension volcanic rocks despite intense volcanic activity analysis of the panther creek half graben and other intra arc rift basins supports previous interpretations that relative rates of volcanism and subsidence control the proportion of volcanic rocks deposited in intra arc rifts

quasi biennial and semi annual oscillations in equatorial wind fields constructed by data assimilation since october 1991 the u k meteorological office has used the technique of data assimilation to produce global meteorological analyses of the troposphere and stratosphere these analyses are constructed from conventional meteorological measurements in the troposphere and lower stratosphere and temperature soundings from noaa polar orbiting satellites the analyses show very clear quasi biennial and semi annual oscillations in equatorial winds the quasi biennial oscillation has its maximum amplitude of about 20 ms 1 near 30 hpa and exhibits descending easterly and westerly shear zones analysed winds compare well with radiosonde observations in the lower stratosphere the semi annual oscillation has its peak amplitude of about 30 ms 1 near the stratopause winds near the equatorial stratopause show strong longitudinal variations on a planetary scale during both the westerly and easterly phases of the semi annual oscillation

synoptic flow structures in the confluence region of the kuroshio and the ryukyu current 1 in the southeastern region of kyushu japan the kuroshio from the east china sea encounters the ryukyu current from the east of the ryukyu islands by analyzing synoptic sections of water properties and geostrophic velocity in august 2004 and october 2005 we distinguished the waters in the kuroshio southeast of kyushu to be separated into an offshore region and a shallow onshore one the onshore water is derived from the east china sea while the offshore water originates from both the east of amami oshima island and the interior region of the north pacific the water mass transport from the east of amami oshima island may become equivalent to that of the kuroshio in the east china sea as in october 2005 the volume transport averaged temperature of the kuroshio southeast of kyushu is significantly lower than that in the east china sea because of the confluence with the colder ryukyu current east of the amami oshima island

40ar 39ar ages of bombay trachytes evidence for a palaeocene phase of deccan volcanism we present 40ar 39ar ages of 60 4 0 6 ma and 61 8 0 6 ma 2 for deccan trap trachytes from manori and saki naka bombay situated in the tectonized panvel flexure zone along the western indian rifted continental margin these ages provide clear evidence that i these trachytes are of palaeocene age and therefore substantially younger than the lower part of the main flood basalt sequence exposed in the western ghats which precedes the k t boundary in age and ii the formation of the panvel flexure along the west coast must have been subsequent to 60 ma considering early alkaline deccan rocks previously dated at 68 5 ma the total duration of deccan volcanism was at least 8 my

lithospheric thinning by midplate mantle plumes and the thermal history of hot plume material ponded at sublithospheric depths mantle plumes supply hot material to the asthenospheric channel which spreads beneath initially normal oceanic lithosphere at midplate hotspots the fate of this material and the thermal structure of the lithosphere depend on the vigor of secondary convection through the steep thermal gradient above the ponded plume material it has been proposed either that 1 secondary convection is so vigorous that material hotter than the normal mantle adiabat is cooled a short distance downstream of the hotspot such that the geotherm resembles that of younger lithosphere or 2 that the plume material retains its excess temperature for a significant time and the lithosphere thins slowly a parameterized method of modeling transient secondary convection is developed to examine this question calculations indicate that secondary convection is likely to be sluggish unless partial melting greatly lowers viscosity in addition vigorous secondary convection would greatly retard upstream asthenospheric flow of plume material beneath the nose of the hawaiian swell and asthenospheric flow of hot material away from hotspots on slowly moving plates like cape verde this conclusion is compatible with limited seismic evidence that indicates that the lithosphere is not detectably thinned beneath the hawaiian swell

2d model of the crust and uppermost mantle along rift profile siberian craton abstract a two dimensional model of the crust and uppermost mantle for the western siberian craton and the adjoining areas of the pur gedan basin to the north and baikal rift zone to the south is determined from travel time data from recordings of 30 chemical explosions and three nuclear explosions along the rift deep seismic sounding profile this velocity model shows strong lateral variations in the crust and sub moho structure both within the craton and between the craton and the surrounding region the pur gedan basin has a 15 km thick low velocity sediment layer overlying a 25 km thick high velocity crystalline crustal layer a paleo rift zone with a graben like structure in the basement and a high velocity crustal intrusion or mantle upward exists beneath the southern part of the pur gedan basin the sedimentary layer is thin or non existent and there is a velocity reversal in the upper crust beneath the yenisey zone the siberian craton has nearly uniform crustal thickness of 40 43 km but the average velocity in the lower crust in the north is higher 6 8 6 9 km s than in the south 6 6 km s the crust beneath the baikal rift zone is 35 km thick and has an average crustal velocity similar to that observed beneath the southern part of craton the uppermost mantle velocity varies from 8 0 to 8 1 km s beneath the young west siberian platform and baikal rift zone to 8 1 8 5 km s beneath the siberian craton anomalous high pn velocities 8 4 8 5 km s are observed beneath the western tunguss basin in the northern part of the craton and beneath the southern part of the siberian craton but lower pn velocities 8 1 km s are observed beneath the low angara basin in the central part of the craton at about 100 km depth beneath the craton there is a velocity inversion with a strong reflecting interface at its base some reflectors are also distinguished within the upper mantle at depth between 230 and 350 km

climatology of the stratospheric polar vortex and planetary wave breaking abstract we use the distribution of ertel s potential vorticity pv on the 850 k isentropic surface to establish a climatology for the transient evolution of the planetary scale circulation in the northern hemisphere winter midstratosphere we compute pv distribution from gridded nmc daily temperature and height maps for the 10 and 30 mb levels and show that a very good approximation for 850 k pv can be derived from 10 mb heights and temperatures alone we assume that reversals of the latitudinal gradient of pv localized in longitude and latitude may be regarded as signatures of planetary wave breaking wave breaking identified by such signatures tends to occur mainly in the vicinity of the aleutian anticyclone with a secondary maximum over europe the area of the polar vortex defined as the area enclosed by pv contours greater than a certain critical value is strongly influenced by wave breaking erosion of the polar vortex due to transport and mixing of pv leads to a preconditioned state when def

plumes in a convecting mantle models and observations for individual hotspots the motion of hotspots and the deformation of their underlying plume conduits as calculated within models of global mantle flow are presented a new list of 44 possible hotspots with associated tracks has been compiled for all of them calculations have been performed under consideration of individual age and anomalous mass flux for three different models of plume buoyancy and mantle flow plume source depth has usually been assumed to be the top of d but an alternative source depth at the 670 km discontinuity has also been considered using models of relative plate motions and boundaries hotspot tracks on plates have been calculated and compared with age data ocean floor topography and distribution of volcanics on continents absolute plate motions have been redetermined under consideration of hotspot motion using a new least squares method for the hawaiian and yellowstone hotspots source locations and hotspot motion have been computed for a total of up to 23 different models the results show plume conduits being tilted with source regions at the d moving in the lowermost mantle flow generally toward large scale upwellings under southern africa and the south central pacific hotspot surface motion often represents the horizontal component of midmantle flow which is frequently opposite to plate motion toward ridges and away from subduction zones in particular almost all models tested predict southward motion of the hawaii and kerguelen hotspots and westward motion of the iceland hotspot for models including hotspot motion the agreement between calculated and observed hotspot tracks is frequently about as good as or better than for the fixed hotspot model but sometimes fixed hotspots give the best fit in some cases where the track ends at a subduction zone e g for the bowie hotspot results can give indications about the otherwise unknown age of the hotspot in other cases especially for the tahiti hotspot results suggest an origin shallower than d and in yet other cases particularly east africa the failure of the hotspot models used supports other evidence indicating the presence of comparatively broad upwellings rather than localized plumes

simulations of fall and early winter in the stratosphere mechanistic model simulations of fall early winter in the northern november and december and southern may and june stratosphere are compared with observational analyses to examine the skill of the model in simulating the state of the stratosphere including both means and variability in key fields during six winters while detailed success varies from year to year the model produces a realistic climatology of and variability in the evolution of winds geopotential heights temperatures and wave propagation in the early winter stratosphere the variability and mean fields agree well with those in longer data records the northern hemisphere nh simulations show a small cold bias when averaged over the 6 years while the southern hemisphere sh simulations show a larger warm bias greater detailed success in simulations of alternate nh winters suggests the possibility of greater model skill during the westerly quasi biennial oscillation phase although the short record and complexity of interactions between tropics and high latitudes preclude definitive identification of such a relationship a prominent failing of the model when using rayleigh friction to parametrize gravity wave drag is an inability to correctly reproduce the latitudinal structure of the stratospheric jet above about 7 hpa this failing can be alleviated by using a non orographic gravity wave drag parametrization at the expense of frequently degrading agreement of planetary wave phases and amplitudes the success of the model in reproducing realistic climatology and variability makes these simulations useful for more detailed studies of transport and vortex evolution in early winter interhemispheric comparisons show that the early winter circulations are qualitatively similar in the nh and sh they are dominated by a strengthening vortex with most wave activity being in wave 1 they both have minor warmings in a preferred location and clustered around a preferred time early december early june in the nh sh variability in the flow shows a crescent pattern of maximum variations near 60 80 latitude centred at the location of the minor warmings over the dateline in the nh and in the south pacific in the sh interhemispheric differences are primarily in the magnitude of the variability with a more symmetric circulation and weaker minor warmings in the sh this is in contrast to later in the winter when large qualitative interhemispheric differences have been seen copyright 2002 royal meteorological society

sedimentary basin inversion caused by igneous underplating northwest european continental shelf a considerable body of evidence indicates that many of the extensional sedimentary basins in the vicinity of the british isles underwent permanent exhumation during the tertiary the most dramatic indicator of this process is the present day absence of as much as 4 km of anticipated postrift thermal subsidence in basins just north and west of scotland any explanation of this observation must take into account the fact that the entire region has very small long wavelength free air gravity anomalies this important constraint implies either that the crust has been thickened or that low density material has been added to or formed from the lithosphere and rules out models that invoke flexural effects arising from the opening of the north atlantic tertiary epeirogeny is often attributed to compression that is assumed to be related in a general sense to alpine mountain building however to remove 3 km of sedi mentary rock from a basin 100 km wide requires 15 km of shortening minor tertiary compression is observed all over the continental shelf but nowhere is it sufficient to account for the required amount of uplift and erosion in addition exhumation dramatically increases from south to north whereas the observed compression decreases markedly in the same direction at the beginning of the tertiary rifting associated with the initiation of the iceland plume generated substantial volumes of melt inversion of rare earth element concentrations of mgorich igneous rocks suggests that a minimum of 5 km of melt was produced beneath at least part of the continental shelf we infer that much of this melt remains trapped within the lithosphere presumably close to the moho which acted as a density filter such underplating will generate rapid uplift

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

simulations of the february 1979 stratospheric sudden warming model comparisons and three dimensional evolution abstract the evolution of the stratospheric flow during the major stratospheric sudden warming of february 1979 is studied using two primitive equation models of the stratosphere and mesosphere the united kingdom meteorological office stratosphere mesosphere model smm uses log pressure as a vertical coordinate a spectral entropy coordinate version of the smm entropy coordinate model or ecm that has recently been developed is also used both models produce similar successful simulations through the peak of the warming capturing the splitting of the vortex and the development of small scale structures such as narrow baroclinic zones the ecm produces a more realistic recombination and recovery of the polar vortex in the midstratosphere after the warming due mainly to better conservation properties for rossby ertel potential vorticity in this model another advantage of the ecm is the automatic increase in vertical resolution near baroclinic zones comparison of smm simulations with forecasts perf

simulations of dynamics and transport during the september 2002 antarctic major warming abstract a mechanistic model simulation initialized on 14 september 2002 forced by 100 hpa geopotential heights from met office analyses reproduced the dynamical features of the 2002 antarctic major warming the vortex split on 25 september recovery after the warming westward and equatorward tilting vortices and strong baroclinic zones in temperature associated with a dipole pattern of upward and downward vertical velocities were all captured in the simulation model results and analyses show a pattern of strong upward wave propagation throughout the warming with zonal wind deceleration throughout the stratosphere at high latitudes before the vortex split continuing in the middle and upper stratosphere and spreading to lower latitudes after the split three dimensional eliassen palm fluxes show the largest upward and poleward wave propagation in the 0 90 e sector prior to the vortex split coincident with the location of strongest cyclogenesis at the model s lower boundary with an additional re

direct observations of the ekman balance at 10 n in the pacific abstract the wind driven transport and velocity structure are estimated from direct current measurements and geostrophic shears along a transpacific section at 10 n the total velocity field is dominated by the north equatorial current and its eddies while the shear features near inertial oscillations and a wind driven current spiral the section averaged cross track ageostrophic shear can be approximated as a slab layer 30 40 m thick with a velocity of 0 05 m s 1 overlying a sheared layer in which the velocity goes to zero below 80 m the resulting zonally integrated ageostrophic mass transport is 62 10 109 kg s 1 northward similar to the estimate of 52 10 109 kg s 1 predicted by the ekman balance using winds measured from the ship climatological winds yield similar transport the zonally averaged velocity relative to the top of the thermocline forms a clockwise spiral decaying with depth as has been found at higher latitudes this mean wind driven spiral results from the diurnal cycling o

estimation of heat and freshwater transports in the north pacific using high resolution expendable bathythermograph data 1 the mean heat and freshwater transports in the north pacific subtropical gyre during 1998 2002 are estimated high resolution expendable bathythermograph expendable conductivity temperature depth xbt xctd transects px 40 honolulu to japan px 37 san francisco to honolulu px 10 honolulu to guam px 44 guam to taiwan hong kong are used to calculate geostrophic transport across each of the ship tracks ekman transport is estimated from satellite scatterometer wind stress the mean heat and freshwater transport convergences into the northern box bounded by the px 40 37 transects and the tsushima and bering straits are 0 26 0 16 pw pw 1015 w and 0 26 0 11 sv sv 106 m3 s respectively heat and freshwater transport convergences into the western box bounded by the px 40 10 44 transects and the tsushima strait are estimated to be 0 32 0 17 pw and 0 08 0 07 sv respectively in both boxes warmer waters transported inward by the ekman flow and by the kuroshio are compensated by the export of waters at cooler temperatures whose peaks are found in the temperatures of the mode waters formed in the north pacific the salt budget is also described to consider the mechanisms of freshwater transport since the western box includes the region with the strongest heat loss to the atmosphere and is possibly a key region for climatic decadal variation it is necessary to continue the high resolution xbt xctd measurement and to make an effort at improving the estimation of heat and freshwater transports in order to contribute to advancing climate studies

the timing of crustal extension and the eruption of continental flood basalts the association between mantle plumes continental flood basalt eruption and the extension and rifting of the crust is well recognized1 3 but there has always been controversy as to whether the plume or the rifting was the initiating factor4 5 was rifting triggered by doming above the thermal plume2 3 6 or was rifting the driving force preceding the associated volcanicity7 8 here i show that recent flow by flow mapping of two continental flood basalt provinces the columbia river basalt group and the deccan basalt group allows one to infer the relative timing of volcanicity and crustal extension in both provinces eruption of the main tholeiitic phase preceded significant extension and crustal thinning this suggests that the primary event in the formation of these provinces was the upwelling of a mantle plume and that the subsequent crustal extension rifting and decompression was in part a consequence of the initiation of that plume

a model study of the influence of the quasi biennial oscillation on trace gas distributions in the middle and upper stratosphere the dominant tracer transport processes in the equatorial and subtropical latitudes of the middle and upper stratosphere are investigated distributions of water vapor in northern hemisphere winter from the microwave limb sounder onboard the upper atmosphere research satellite are employed together with a three dimensional stratosphere mesosphere model that incorporates a representation of the quasi biennial oscillation qbo the model reproduces the observed tracer distributions in particular a staircase feature that is present in northern winter of 1992 easterly qbo phase but not in 1993 westerly qbo phase this feature is highly asymmetric about the equator the model circulation is diagnosed to show that while the induced qbo circulation in the lower stratosphere of the model is relatively symmetric about the equator in the middle and upper stratosphere it is highly asymmetric and in the correct sense to give rise to the staircase feature model experiments are compared in which trajectories are advected by 1 the full three dimensional circulation and 2 the residual mean circulation only thereby removing the local effects of isentropic mixing by planetary waves on the trajectory distributions these confirm the importance of advection by the qbo circulation at equatorial and subtropical latitudes however sharpening of the tracer gradients at the subtropical edge of the surf zone by the action of planetary waves is shown to be important in the formation of a subtropical cliff between 10 and 20 mbar at 20 30 n the model results also suggest that the prominence of the summer subtropical peak in easterly phase years compared with westerly phase years is not entirely due to increased summer upwelling of the large scale global circulation caused by the stronger planetary wave driving the depression of the winter half of the equatorial peak by the local asymmetric qbo circulation is also shown to be important

regional uplift associated with continental large igneous provinces the roles of mantle plumes and the lithosphere the timing and duration of surface uplift associated with large igneous provinces provide important constraints on mantle convection processes here we review geological indicators of surface uplift associated with five continent based magmatic provinces emeishan traps 260 million years ago ma siberian traps 251 ma deccan traps 65 ma north atlantic phase 1 61 ma and phase 2 55 ma and yellowstone 16 ma to recent all five magmatic provinces were associated with surface uplift surface uplift can be measured directly from sedimentary indicators of sea level in the north atlantic and from geomorpholocial indicators of relative uplift and tilting in yellowstone in the other provinces surface uplift is inferred from the record of erosion in the deccan north atlantic and emeishan provinces transient uplift that results from variations in thermal structure of the lithosphere and underlying mantle can be distinguished from permanent uplift that results from the extraction and emplacement of magma transient surface uplift is more useful in constraining mantle convection since models of melt generation and emplacement are not required for its interpretation observations of the spatial and temporal relationships between surface uplift rifting and magmatism are also important in constraining models of lip formation onset of surface uplift preceded magmatism in all five of the provinces biostratigraphic constraints on timing of uplift and erosion are best for the north atlantic and emeishan provinces where the time interval between significant uplift and first magmatism is less than 1 million years and 2 5 million years respectively rifting post dates the earliest magmatism in the case of the north atlantic phase 1 and possibly in the case of siberia the relative age of onset of offshore rifting is not well constrained for the deccan and the importance of rifting in controlling magmatism is disputed in the emeishan and yellowstone provinces in these examples rifting is not a requirement for onset of lip magmatism but melting rates are significantly increased when rifting occurs models that attempt to explain emplacement of these five lips without hot mantle supplied by mantle plumes often have difficulties in explaining the observations of surface uplift rifting and magmatism for example small scale convection related to craton or rift boundaries edge driven convection cannot easily explain widespread 1000 km scale transient surface uplift emeishan deccan north atlantic and upper mantle convection initiated by differential incubation beneath cratons the hotcell

wind driven shifts in the latitude of the kuroshio oyashio extension and generation of sst anomalies on decadal timescales abstract the causes of decadal variations of north pacific sea surface temperatures ssts are examined using a hindcast performed with an ocean general circulation model thermodynamically coupled to an atmospheric mixed layer model ogcm aml model and forced by the time history of observed surface winds the shift in north pacific ocean climate that occurred around 1976 77 is focused on since this is the best observed example available after the 1976 77 shift the aleutian low deepened and moved to the southeast of its previous position this placed anomalous cyclonic flow over the north pacific the sst response as simulated by the ocean model consisted of two components a fast and local part and a delayed and remote part in the central pacific stronger westerlies cool the ocean by increased equatorward ekman drift here the dynamical cooling is sufficiently large that the surface fluxes damp the sst anomaly this ekman response is fast and local and cools the ssts beginning in 1977 and persistin

lateral flow and ponding of starting plume material many mantle plumes started with voluminous heads of hot material that ascended as diapirs through the mantle flood basalts radial dike swarms and frequently continental breakup are associated with the impingement of starting plume heads on the base of the lithosphere the buoyant plume head material ponds at the base of the lithosphere and then flows laterally relief on the base of the lithosphere acts as an upside down drainage pattern with enclosed catchments for this flow that is plume material preferentially collects beneath regions where the lithosphere is locally thin such as thermally subsiding sedimentary basins an example is uplift associated with the iceland starting plume which inverted the mesozoic irish sea basin additional relief at the base of the lithosphere is associated with rifting and seafloor spreading in the case of the northern north sea material from the iceland starting plume ponded beneath a basin with locally thin lithosphere rifting breached the enclosed catchment allowing the ponded plume material to drain across the new passive margin toward very thin lithosphere produced by seafloor spreading rifting also creates a conduit for the flow of plume material away from the region underlain by the starting plume head an example is the volcanic passive margin off nova scotia which is 2000 km from the center of the bahama starting plume head numerical and analytical calculations indicate that lateral flow of plume material consistent with this observation is expected if its viscosity is around 1018 pa s

satellite altimeter monitoring the kuroshio transport south of japan in 1993 1995 we carried out observations of the kuroshio south of japan including direct current measurements and repeated hydrographic surveys along a satellite track of the topex poseidon altimeter the velocity field of the kuroshio is determined by geostrophic calculation using the repeated hydrographic survey data referenced to velocities observed at mid and abyssal depths the volume transport of the kuroshio is estimated from this velocity field the estimated transports of the kuroshio have a high correlation with sea surface height differences across the kuroshio having this relationship and using the altimeter data we obtained a time series of the kuroshio transport over seven years at ten day intervals the kuroshio transport excluding contributions by local recirculations is estimated to be 42 106 m sec on average the correlation between sea surface height difference and transport provides a practical method of long term monitoring of the kuroshio transport using satellite altimetry

plume rift interaction in the deccan volcanic province abstract it is widely accepted that the grand volcanic episode of the deccan in india was a consequence of the passage of the northerly drifting indian subcontinent over the reunion starting plume in the late cretaceous this plume also produced the three rift cambay triple junction the three arms being the west coast graben belt the narmada tapi rift zone and the cambay rift deccan related alkalic magmatism both preceded and followed the main tholeiitic phase of 65 ma ago by about 3 my the uniformly tholeiitic thick basalt sequence of the western ghats was derived from direct melting of the plume head but the tholeiitic alkalic magmatism of the three rift belts was due to melting of the hydrous lithospheric mantle due to variable amounts of rifting any lithospheric loading mechanism for generating post tholeiite alkalic lavas does not seem feasible for the deccan nor can it explain the pre tholeiite alkaline magmatism in the deccan similarly conductive heating of the lithosphere by the plume cannot have generated the alkalic melts some amount of actual rifting did occur direct melt supply from the plume is not necessary for magmatism in the rifts though it seems to have occurred in some cases our documentation of indigenous magmatism for the three rift belts calls into question any attempts at inferring the size of the plume head from synchroneity in geochronologic data alone and we negate the possibility or necessity of large distance transport of magmas from the plume through the lithosphere to feed the rifts recent evidence indicates that alkalic magmatism north of the main deccan outcrop preceded the main tholeiite phase by 3 my the cambay graben was active 3 5 my before the main tholeiite phase as the alkalic complexes at the northern end of this graben are 68 5 ma in age so far the oldest well proven deccan related rocks they are the first expression of the reunion plume and the borehole picrites from the triple junction area until now conventionally regarded as the oldest can no longer be considered so accurate radiometric dating of these picrites is therefore much needed

relationship of topex poseidon altimetric height to steric height and circulation in the north pacific topex poseidon altimetric height is compared with 20 transpacific eddy resolving realizations of steric height the latter are calculated from temperature expendable bathythermograph xbt and salinity expendable conductivity and temperature profiler xctd profiles along a precisely repeating ship track over a period of 5 years the overall difference between steric height and altimetric height is 5 2 cm rms on long wavelengths 500 km containing 17 of the steric height variance the 3 0 cm rms difference and lowered coherence are due to the sparse distribution of altimeter ground tracks along the xbt section the 2 4 cm rms difference in the basin wide spatial mean appears to be due to fluctuations in bottom pressure differences between steric height and altimetric height increase near the western boundary but data variance increases even more and so the signal to noise ratio is highest in the western quarter of the transect basin wide integrals of surface geostrophic transport from steric height and altimetric height are in reasonable agreement the 1 9 104 m2 s 1 rms difference is mainly because the interpolated altimetric height lacks spatial resolution across the narrow western boundary current a linear regression is used to demonstrate the estimation of subsurface temperature from altimetric data errors diminish from 0 8 c at 200 m to 0 3 c at 400 m geostrophic volume transport 0 800 m shows agreement that is similar to surface transport with 4 8 sverdrup sv 106 m3 s 1 rms difference the combination of altimetric height with subsurface temperature and salinity profiling is a powerful tool for observing variability in circulation and transport of the upper ocean the continuing need for appropriate subsurface data for verification and for statistical estimation is emphasized this includes salinity measurements which significantly reduce errors in specific volume and steric height

regional climate variability and ocean heat transport in the southwest pacific ocean the winter of 1992 was the coldest on record in new zealand since the 1940s temperatures in new zealand were as much as 3 c below average with heavy rain and unusual snow the oceanic surface layer in the southwest pacific was also anomalously cold over the same period a world ocean circulation experiment woce hydrographic section p14c between auckland and fiji during september 1992 found cold sea surface temperatures and deep mixed layers near new zealand when compared to 8 years of high resolution expendable bathy thermograph xbt temperature measurements collected along the same transect high nutrient and low dissolved oxygen concentrations in the surface layer indicated recent entrainment of thermocline waters the auckland to fiji xbt section is one of three woce high resolution xbt survey lines in the tasman box region whose boundaries are auckland fiji fiji brisbane and wellington sydney transects plus the australian coast geostrophic shear and transport were estimated from 10 realizations of the tasman box during the period 1991 1993 the time series of geostrophic transport shows that following a convergence in late 1991 early in 1992 there was a substantial divergence of mass in the upper waters equivalent to a thinning of the warm water layer the phase of this anomalous divergence is matched to an observed amplification of the seasonal oceanic heat storage cycle in 1991 1992 the top 200 m average temperature was warmer in the 1992 summer than in 1991 or 1993 but the winter of 1992 was the coldest of the 8 year record along the auckland fiji line the divergence thinning of the warm water layer appears to have preconditioned the region for the exceptionally cold 1992 winter the alternative cool conditions from anomalous air sea heat exchange caused by variability in the wind field is considered unlikely as large fluctuations in heat loss are not observed in the air sea flux data during this period the severe weather conditions and anomalous ocean heat transport are most likely related to the prolonged el nino southern oscillation episode that began in early 1991

alleviation of a systematic westerly bias in general circulation and numerical weather prediction models through an orographic gravity wave drag parametrization systematic westerly biases in the northern hemisphere wintertime flow of the meteorological office 15 layer operational model and 11 layer general circulation model are described evidence that the failure to parametrize subgrid scale orographic gravity wave drag may account for such biases is presented this evidence is taken from aircraft studies surface pressure drag measurements and studies of the zonally averaged momentum budget a parametrization scheme is described in which the surface stress is proportional to the near surface wind speed and static stability and to the variance of subgrid scale orography the stress is absorbed in the vertical by considering the influence of such gravity wave activity on static stability and vertical wind shear a richardson number dependent wave breaking formulation is devised and the vertical stress profile determined by a saturation hypothesis whereby the breaking waves are maintained at marginal stability it is shown that wave breaking preferentially occurs in the boundary layer and in the lower stratosphere results from a simple zonally symmetric model show how the adjustment to thermal wind balance with a wave drag in the stratosphere warms polar regions by adiabatic descent and decelerates the mean westerlies in the troposphere the influence of the parametrization scheme on integrations of the 11 layer model is described and found to be generally beneficial in a discussion of the reasons why this problem has only recently emerged it is suggested that the satisfactory northern hemisphere winter circulations of previous coarser general circulation models were due to a compensation implied by underestimating both the surface drag and the horizontal flux of momentum by explicitly resolved large scale eddies

meteorology of the polar vortex spring 1997 the 1996 1997 northern hemisphere spring polar vortex was very strong cold and symmetric somewhat similar to those found in the antarctic spring vortex the vortex did not form until late in december and was very symmetric from february into late april the spring vortex was characterized by record low temperatures record low ozone amounts as measured from the total ozone mapping spectrometer toms instruments and a wide band of strong winds in the lower stratosphere spring wave activity was greatly reduced with 100 hpa february march eddy heat fluxes that were lower by a factor of 2 from any previously observed values over the last 18 years

similarities in the mineralogical and geochemical attributes of detrital clays of maastrichtian lameta beds and weathered deccan basalt central india abstract mineralo chemical attributes of the maastrichtian late cretaceous lameta sediments intimately associated with the deccan traps in central india provide insight into the initiation of deccan volcanism x ray diffraction studies on the detrital clays of the lametas and weathered deccan basalt show identical mineral assemblages with the dominance of smectite and subordinate kaolinite illite ir spectra are also indicative of their common mineralogical attributes structural formulae of the smectites in lameta exhibit high octahedral mg and fe the immobile trace element concentrations in lameta clays resemble those in weathered deccan basalt ree plots of the lametas are subparellel with that of weathered deccan basalt and show negative ce anomalies documented in basalt weathering these findings suggest that smectite rich clays of the lametas are derivatives of the deccan basalt implying early activities of deccan volcanism either during or just prior to the maastrichtian lameta sedimentation

geologic geochemical and geophysical consequences of plume involvement in the emeishan flood basalt province prevolcanic kilometer scale lithospheric doming in the emeishan large igneous province southwest china allows us to evaluate the spatial and temporal consequences of uplift on the paleogeography geology geochemistry and geophysics of the region systematic spatial variations are observed across the domal structure in the distribution and thickness of clastic and carbonate sediments the extent of erosion thickness and chemistry of volcanic rocks and the crust mantle structure these features which are best explained by a mantle plume may be used to track older plume sites in the geologic record

on the three dimensional propagation of stationary waves abstract a locally applicable nonzonally averaged conservation relation is derived for quasi geostrophic stationary waves on a zonal flow a generalization of the eliassen palm relation the flux which appears in this relation constitutes it is argued a useful diagnostic of the three dimensional propagation of stationary wave activity this is illustrated by application to a simple theoretical model of a forced rossby wave train and to a northern hemisphere winter climatology results of the latter procedure suggest that the major forcing of the stationary wave field derives from the orographic effects of the tibetan plateau and from nonorographic effects diabatic heating and or interaction with transient eddies in the western north atlantic and north pacific oceans and siberia no evidence is found in the data for wave trains of tropical origin forcing by the orographic effects of the rocky mountains seems to be of secondary importance

sedimentary response to mantle plumes implications from paleocene onshore successions west and east greenland the uplift history of the upper cretaceous paleocene sedimentary successions underneath the extensive tertiary flood basalts of west and east greenland supports recently described models for the generation of flood basalt provinces in response to rising hot mantle plumes however the sedimentary development indicates that the period of plume related uplift prior to eruption of volcanic rocks was very short 5 m y substantial regional uplift and faulting took place in west and east greenland in the early paleocene to earliest late paleocene resulting in a basinwide unconformity in west greenland the uplift was associated with fluvial peneplanation valley incision and catastrophic deposition in east greenland it was associated with fluvial peneplanation the cumulative uplift in west greenland is probably on the order of several hundred meters whereas in east greenland the observed uplift cannot be quantified in both west and east greenland this phase was shortly followed by rapid major subsidence associated with extensive volcanism it is suggested that this sequence of events reflects the arrival of the north atlantic mantle plume or plumes

response of the stratosphere to interannual variability of tropospheric planetary waves a primitive equation global model of the middle atmosphere is used to investigate the response of the extratropical stratosphere to different levels of wave forcing from steady perturbations of the geopotential height near the tropopause the response of the stratosphere is compared to that in quasi geostrophic beta plane models used in previous studies the primitive equation model exhibits three flow regimes under perpetual january conditions strong westerly steady flow for small wave amplitude forcing strong westerly but unsteady flow for moderate wave amplitude forcing and oscillations between easterly and westerly flow for large wave amplitude forcing the regimes for low and high forcing are analogous to solutions of the simpler holton mass hm quasi geostrophic model the moderate forcing regime does not occur in the hm model and it is attributed to instability of the strongly sheared flow generated by planetary waves in the upper stratosphere we also show how the observed patterns of interannual variability in the winter stratosphere can be explained in terms of these three flow regimes in the northern hemisphere the flow often enters the high forcing regime where variations in conditions in the early winter flow or quasi steady upper tropospheric planetary wave amplitudes make similar contributions to the interannual variability in the stratospheric circulation for the southern hemisphere we suggest that the flow alternates between the low and moderate forcing regimes through year to year changes in the amplitude of quasi steady waves near the tropopause this mechanism produces large enough changes to explain the interannual variability in the southern stratosphere

climatology of arctic and antarctic polar vortices using elliptical diagnostics abstract the climatological structure and interannual variability of the arctic and antarctic stratospheric polar vortices are examined by analysis of elliptical diagnostics applied to over 19 yr of potential vorticity data the elliptical diagnostics define the area center elongation and orientation of each vortex and are used to quantify their structure and evolution the diagnostics offer a novel view of the well known differences in the climatological structure of the polar vortices although both vortices form in autumn to early winter the arctic vortex has a shorter life span and breaks down over a month before the antarctic vortex there are substantial differences in the distortion of the vortices from zonal symmetry the arctic vortex is displaced farther off the pole and is more elongated than the antarctic vortex while there is a midwinter minimum in the distortion of the antarctic vortex the distortion of the arctic vortex increases during its life cycle there are also large differenc

quantitative analysis of submarine fans in the tertiary of the north sea basin abstract extensive regional mapping allows the scale of economically significant tertiary fans in the northern north sea to be quantified and compared despite having volumes that vary by three orders of magnitude the fans are revealed 1 to be small compared with the largest modern fans and 2 to have approximately constant net sand volume to gross sediment volume ratios of around 20 30

interaction of rifting and hot horizontal plume sheets at volcanic margins we have explored the idea that observations of large igneous crustal thickness at volcanic rifted continental margins may be explained by the interaction of rift driven flow in the lithosphere with an underlying sublithospheric hot plume sheet this concept is assessed by numerical modeling of the viscous flow caused by divergent plate motions using a viscous temperature and pressure dependent nonlinear fluid the plume sheet consists of an initially hot layer just below the lithosphere which responds to the overlying lithospheric motions for reasonable values of input parameters we can successfully predict the observed thickness of igneous crust at the margin its formation time inferred average mantle melt fractions and importantly the eventual transition to normal oceanic crustal thicknesses observations are selected from the north atlantic region with an emphasis on the recent results from the east greenland volcanic margin the best fitting models suggest that relatively little small scale convection is needed after the initial strong pulse of mantle upflow due to the presence of moderately hot 1450 c buoyant plume material under the rift the results favor a thin 50 km plume sheet layer this hot mantle reservoir is soon depleted and replaced by normal temperature mantle unless the rift lies directly over the deep source of plume material

closing the time varying mass and heat budgets for large ocean areas the tasman box abstract the role of oceanic advection in seasonal to interannual balances of mass and heat is studied using a 12 yr time series of quarterly eddy resolving expendable bathythermograph xbt surveys around the perimeter of a region the authors call the tasman box in the southwestern pacific the region contains the south pacific s subtropical western boundary current system and associated strong mesoscale variability mean geostrophic transport in the warm upper ocean temperature greater than 12 c is about 3 8 sv 1 sv 106 m3 s 1 southward into the box across the brisbane australia fiji northern edge net outflows are 3 3 sv eastward across the auckland new zealand fiji edge and 2 7 sv southward across sydney australia wellington new zealand mean ekman convergence of 2 2 sv closes the mass budget net water mass conversions in the upper ocean consist of inflow of waters averaging about 26 c and 35 4 psu balanced by outflow at about 18 c and 35 7 psu and reflect the net evaporation and heat los

development of the polar vortex in the 1999 2000 arctic winter stratosphere the 1999 2000 arctic stratospheric vortex was unusually cold especially in the early winter lower stratosphere with a larger area near polar stratospheric cloud formation temperatures in dec and jan and much lower temperatures averaged over nov jan than any previously observed arctic winter in nov and early dec there was a double jet in the upper stratosphere with the anticyclone cutoff in a region of cyclonic material by late dec there was a discontinuous vortex large in the upper stratosphere small in the lower stratosphere evolving to a strong continuous relatively upright vortex by mid jan this vortex evolution in 1999 2000 is typical of that in other cold early winters despite unusually low temperatures the lower stratospheric vortex developed more slowly than in previous unusually cold early winters and was weaker than average until late dec

the elastic thickness of the british isles free air gravity and topography data from the british isles have been analysed in the frequency domain to determine the mechanisms of topographic support first we calculate how the admittance between measured free air gravity and topography varies as a function of wavelength a simple model which consists of a crust with two layers of different densities overlying a higher density mantle was then used to calculate admittance functions the misfit between observed and calculated admittance was minimized by varying elastic thickness and the proportion of the total load due to internal loading at short wavelengths c 0 2 the general behaviour of the observed admittance suggests that topography is primarily supported by elastic stresses in the crust a small departure between observed and calculated admittance at the longest wavelengths 400

stable volume and heat transports of the north pacific subtropical gyre revealed by identifying the kuroshio in synoptic hydrography south of japan 1 we conducted synoptic hydrographic surveys three times under distinctly different conditions of the kuroshio in the region off the southern coast of japan the large meander october 2004 and non large meander september 2005 and september 2006 states as a result of the water mass analysis we could separate the volume and heat transports of the north pacific subtropical gyre from the local recirculation gyre and mesoscale eddies despite the different flow conditions of the kuroshio the volume transport and the volume transport averaged temperature of the subtropical gyre fluctuate within the ranges of 23 3 29 0 106 m3 s 1 and 17 3 17 6 c respectively which are quite stable with respect to those for the kuroshio south of japan estimated in the past studies taking into account the decrease in the volume transport averaged temperature in the north pacific interior region the net heat transport of the subtropical gyre across the latitude of 30 n was estimated to be between 0 19 and 0 22 1015 w

convective partial melting 1 a model for the formation of thick basaltic sequences during the initiation of spreading stretching and thinning of continental lithosphere during rifting and initiation of seafloor spreading cause upwelling of mantle rocks into a pressure temperature environment where partial melting occurs the amount of melt liberated is however insufficient to account for the thickness of igneous crust emplaced near the continent ocean boundary at some passive margins these igneous structures are known from seismic reflection and deep refraction studies on numerous passive margins worldwide seismic studies also suggest that the transition from continental to oceanic crust on these volcanic margins is relatively abrupt their evolution apparently does not include a prolonged extensional phase preceding the inception of spreading to account for these observations we propose a model for the generation of partial melt in which the lateral temperature contrasts evoked by rifting and asthenospheric upwelling drive convection in the upper mantle deep hot mantle material is transported upward by the convection and hence much larger volumes flow through the region where partial melting occurs than during passive upwelling numerical calculations show that convective partial melting can provide substantial additions to melting due to passive upwelling alone using this model we propose an evolutionary scheme for volcanic passive margins emphasize the contrast with nonvolcanic margins and describe conditions which might lead to the development of both types

lateral flow of hot plume material ponded at sublithospheric depths local buoyancy forces drive the flow of ponded plume material along the base of the lithosphere this processes complicates the geological effects of plumes beyond those of simple passage of plates over point heat sources variations in the depth to the base of the lithosphere significantly affect lateral flow the flow rate is modified to a moderate extent by locally thin lithosphere beneath midplate hotspots such as hawaii the effect is relevant when numerical models are rescaled to better fit the observed uplift and the observed distance from the hotspot to the nose of the swell variations in the depth to the base of the lithosphere have a much stronger effect on flow near ridge axes effectively forming an upside down drainage pattern plume material flows upslope toward ridge axes from off axis plumes and along ridge axes from on axis plumes at sufficiently low spreading rates thinner lithosphere exists above plume material than above normal asthenosphere the edges of normal lithosphere adjacent to plume material act to some extent as levees which limit the lateral spreading of plume material pressure release melt is associated with the upslope flow of plume material it is expected to cause volcanism away from the plume and to sometimes supply melt depleted plume material to ridge axes that are upslope from the region of voluminous melting

model studies of the interannual variability of the northern hemisphere stratospheric winter circulation the role of the quasi biennial oscillation a series of experiments are described that examine the sensitivity of the northern hemisphere winter evolution to the equatorial quasi biennial oscillation qbo the prime tool for the experiments is a stratosphere mesosphere model the model is integrated over many years with the modelled equatorial winds relaxed towards observed values in order to simulate a realistic qbo in experiment a the equatorial winds are relaxed towards singapore radiosonde observations in the height region 16 32 km in contrast to previous modelling studies the holton tan relationship warm cold winters associated with easterly westerly qbo winds in the lower stratosphere is absent however in a second experiment run b in which the equatorial winds are relaxed towards rocketsonde data over the extended height range 16 58 km a realistic holton tan relationship is reproduced a series of further studies are described that explore in more detail the sensitivity to various equatorial height regions and to the bottom boundary forcing the experiments suggest that the evolution of the northern hemisphere winter circulation is sensitive to equatorial winds throughout the whole depth of the stratosphere and not just to the lower stratospheric wind direction as previously assumed

a geological map of the southern deccan traps india and its structural implications a geological map of an area of over 125 000 km 2 within the southern deccan traps india is presented which is based upon variations in the basalt geochemistry it represents a synthesis of new data and earlier work the use of large data sets has allowed stratigraphic boundaries to be established with greater accuracy over a much larger area than before the geochemical sections demonstrate that the southward overstepping stratigraphic style encountered along the ghats ridge has an essentially north to south polarity and that there appears to be detectable overstep in an east to west sense however the stratigraphy defines a pronounced coastward dipping monoclinal flexure across the western ghats ridge between 16 n and 18 n the data are consistent with two models of eruption the first considers the deccan eruptive focus to have been fixed throughout the volcanic episode producing an essentially annular flow pattern the second considers the flow pattern to have been generated from a southerly migrating eruptive centre resulting from the northerly drift of india over a fixed hotspot both hypotheses are consistent with recent quantitative models which suggest that rapid and voluminous flood basalt eruptions are the result of continental rifting events associated with plume generated thermal 9highs9 until a causal link between established plume hotspot trails and impact sites can be satisfactorily demonstrated we find it unnecessary to invoke a cataclysmic impact event as an explanation for the deccan eruptions

planetary scale disturbances in the southern stratosphere during early winter abstract the early winter mid april to mid july circulation in the southern hemisphere stratosphere is studied emphasis is placed on the evolution of strong disturbances with structures dominated by the zonal wavenumber 1 component of the flow wave 1 the approach to this investigation is based on analysis of 12 years 1979 90 of observational data and comparative analyses of control and hypothesis testing simulations with a three dimensional primitive equation model of the stratosphere and mesosphere considerable interannual variability is found in both the intensity and timing of wave 1 amplification during early winter though usually quasi stationary there are six extended periods in the dataset when wave 1 travels steadily eastward and is of large amplitude two of these periods june 1980 and june 1985 are examined in detail the evolution of the circulation in these two cases resembles that during canadian warmings in the northern hemisphere in several ways first there is a large eastwar

lamination and polar vortex development in fall from atmos long lived trace gases observed during november 1994 long lived trace gas profiles observed by the atmospheric trace molecule spectroscopy atmos instrument around the developing polar vortex the protovortex during early november 1994 show distinctive inversions laminae high resolution profiles calculated using a reverse trajectory rt model reproduce the majority of these laminae demonstrating that most of these features arise from advection by the large scale winds the relationship between ch 4 and n 2 o sampled in filaments of low latitude air changes from the canonical midlatitude correlation to one typical of tropical air confirming the identification of tropical laminae n 2 o ch 4 correlations for laminae in vortex filaments indicate that enough confined descent and mixing has already occurred in the middle and upper stratosphere by early november to alter the tracer relationship in the protovortex from that in midlatitudes distributions of laminae in atmos observations agree with regions of greater or less filamentation seen in high resolution rt maps there is a deep minimum in laminae occurrence between 30 and 90 e at all levels extending to about 150 e above 35 km maxima in lamination in the lower stratosphere near 90 150 e and 210 270 e are associated with the main regions where tropical air is drawn up around the developing vortex continuous filamentation associated with the developing vortex and anticyclone in early november 1994 shows that transport and mixing processes previously reported during winter are already important during fall

regional tectonic framework structure and evolution of the western marginal basins of india abstract the kutch saurashtra cambay and narmada basins are pericontinental rift basins in the western margin of the indian craton these basins were formed by rifting along precambrian tectonic trends interplay of three major precambrian tectonic trends of western india dharwar nnw sse aravalli delhi ne sw and satpura ene wsw controlled the tectonic style of the basins the geological history of the basins indicates that these basins were formed by sequential reactivation of primordial faults the kutch basin opened up first in the early jurassic rifting was initiated in late triassic along the delhi trend followed by the cambay basin in the early cretaceous along the dharwar trend and the narmada basin in late cretaceous time along the satpura trend the evolution of the basins took place in four stages these stages are synchronous with the important events in the evolution of the indian sub continent its breakup from gondwanaland in the late triassic early jurassic its northward drifting during the jurassic cretaceous and collision with the asian continent in the early tertiary the most important tectonic events occurred in late cretaceous time the present style of the continental margins of india evolved during early tertiary time the saurashtra arch the extension of the aravalli range across the western continental shelf subsided along the eastern margin fault of the cambay basin during the early cretaceous it formed an extensive depositional platform continuous with the kutch shelf for the accumulation of thick deltaic sediments a part of the saurashtra arch was uplifted as a horst during the main tectonic phase in the late cretaceous the present high thermal regime of the cambay bombay high region is suggestive of a renewed rifting phase

ultrafast mantle plumes and implications for flood basalt volcanism in the northern atlantic region abstract recent geochemical and geochronological data on paleocene flood basalts from west greenland se greenland and the british isles show that volcanic activity at these widely separated locations commenced nearly simultaneously around 61 62 ma ago and that the duration of this initial phase of flood basalt magmatism was of the order of a few million years or less a small fast moving upper mantle plume which rapidly spreads out horizontally on encountering the base of the lithosphere appears to be a viable mechanism to explain these observations however in order to reconcile the idea of an ultrafast plume with the observed plate velocities a physical mechanism is needed for inducing a separation of timescales between the plume speed and the surrounding mantle circulation thermal convection with a non newtonian temperature and depth dependent rheology provides such a mechanism wherein extremely fast plumes ascending at velocities between one to tens of meters per year can be produced in an otherwise slowly convecting mantle moving at cm yr this transport mechanism is capable of bringing up very hot matter from the transition zone to the lithosphere the fast upward velocities lead to the production of high viscous heating rates surrounding the plume upon impinging the lithosphere it is thus possible to explain the near simultaneous onset of magmatism in west greenland se greenland and the british isles in the early tertiary by a fast moving mantle plume spreading out horizontally with a velocity of around 0 5 m yr for resolving numerically the thermal mechanical state of these strongly time dependent mantle flows extremely high spatial resolution on the kilometer scale is required finally we suggest the possibility that the source of the fast upper mantle plume under iceland may be rooted in the lower mantle this is consistent with the recent findings by seismic tomography of a deep mantle plume under iceland

convective thinning of the lithosphere a mechanism for the initiation of continental rifting thinning of the lithosphere by heat carried convectively to its base is a possible mechanism for the initiation of continental rifting the lithosphere asthenosphere boundary marks the transition from a quasi rigid behavior of the mantle on geological time scales to a viscous one the boundary lies at or close to the solidus of the mantle material and its position is a function of temperature and pressure additional heat carried to the boundary will cause it to rise and the lithosphere to thin a one dimensional model is used to study the upward movement of the boundary from an initial equilibrium position as a consequence of an increase in the heat flux from the convecting mantle the ratio of the amount of thinning to the initial thickness is directly proportional to the increase in heat flux from the asthenosphere and inversely proportional to the difference between the final subcrustal geothermal gradient and the slope of the transition temperature profile the rate of thinning is determined by the initial and final equilibrium thicknesses the thermal diffusivity the transition temperature profile and the plume temperature profile it depends only slightly on any latent heat associated with the lithosphere asthenosphere transition during a large fraction of the time between the initial and final equilibrium states the lithosphere thins at a rate which is inversely proportional to the square root of time t even 300 km thick lithospheres may be thinned to 50 km or crustal thicknesses in tens of million years by the heat advected by mantle plumes this heat contributes to an enhanced surface heat flow because of the constant level of radioactive heat production in the crust the ratio of the final to the initial surface heat flow increases much less than the ratio of the final to the initial heat flow from the asthenosphere for large increases in asthenospheric heat flow the lithosphere is almost thinned to the crust before any significant change of surface heat flow occurs uplift due to thermal expansion upon lithospheric thinning is of the order of 102 103 m a rayleigh taylor instability acting on the thinning lithosphere may further increase thinning rates and cause magmatic intrusions of the lithosphere and surface volcanism

early tertiary seafloor spreading magnetic anomalies and paleo propagators in the northern arabian sea abstract study of closely spaced new marine magnetic profiles in conjunction with published magnetic data provide an updated identification of linear magnetic anomalies in the northern arabian sea from the owen fracture zone in the west to the laxmi and chagos laccadive ridges in the east for the first time the entire magnetic anomaly sequence 28 through 20 is mapped eastwards from 65 e up to about 70 e further eastward the post anomaly 28 oceanic crust appears to have been overlain by the volcanic material forming the chagos laccadive ridge contrary to earlier interpretations the identified magnetic lineations are observed to have been segmented mainly by oblique offsets representing the pseudofaults associated with 11 major paleo propagating ridges these ridge propagation events commenced around anomaly 28 time 63 ma and continued at least until anomaly 23 time 52 ma and during the process a large amount of crust was transferred from the african plate to the indian plate the pre anomaly 24 period was characterized by ridge reorientation whereas such a phenomenon was not apparent during the post anomaly 24 period almost all these propagating ridges appear to have been propagating westward probably to migrate away from the proximity of the reunion hotspot the accretionary process of the early tertiary oceanic crust in the arabian sea thus appears to have been greatly influenced by the propagating ridges and the nearby hotspot

petrogenesis of rhyolites and trachytes from the deccan trap sr nd and pb isotope and trace element evidence trachytes and rhyolites from salsette island north of bombay have distinctive trace element and isotope features which mark them out from typical crustal melts their highly incompatible trace element and sr nd and pb isotope ratios are similar to those of the associated deccan flood basalts thus the rhyolites and trachytes are closely related to the basalts and a striking compositional gap between 50 and 65 sio2 suggests that the high sio2 rocks evolved by 10 15 partial melting followed by variable amounts of fractional crystallisation the source material could have been basalt within the deccan trap or related gabbroic rocks in deep crustal sill complexes the rhyolites yield an rb sr whole rock age of 61 5 1 9 ma with a slightly high initial 87sr 86sr 0 7085 18 it is argued that crustal extension provides a suitable regime for the generation of acid magmas by partial melting of associated basic rocks

the tsushima warm current through tsushima straits estimated from ferryboat adcp data abstract current structures across the tsushima straits are studied using results from long term acoustic doppler current profiler adcp observations by a ferryboat between hakata and pusan conducted since february 1997 two maxima of the northeastward current are observed in the central parts of the eastern and western channels and the maximum velocity in the western channel is stronger than that of the eastern channel downstream of the tsushima islands a southwestward countercurrent is observed associated with a pair of cyclonic and anticyclonic eddies in the western channel the deep countercurrent is observed pronouncedly on the bottom slope of the korean side from summer to winter the volume transport of the tsushima warm current through the straits has strong seasonal variation with a minimum in january and two maxima from spring to autumn double peaks the spring peak of the volume transport through the eastern channel is more pronounced than the autumn peak and the autumn peak of the west

eddy transport of heat and thermocline waters in the north pacific a key to interannual decadal climate variability abstract high resolution xbt transects in the north pacific ocean at an average latitude of 22 n are analyzed together with topex poseidon altimetric data to determine the structure and transport characteristics of the mesoscale eddy field based on anomalies in dynamic height 410 eddies are identified in 30 transects from 1991 to 1999 including eddies seen in multiple transects over a year or longer their wavelength is typically 500 km with peak to trough temperature difference of 2 2 c in the center of the thermocline the features slant westward with decreasing depth by 0 8 of longitude on average from 400 m up to the sea surface this tilt produces a depth varying velocity temperature correlation and hence a vertical meridional overturning circulation in the mean 3 9 sv sv 106 m3 s 1 of thermocline waters are carried southward by the eddy field over the width of the basin balanced mainly by northward flow in the surface layer corresponding northward heat transport is 0 086 0 012 pw

palaeoenvironments of the dinosaur bearing lameta beds maastrichtian narmada valley central india abstract the maastrichtian lameta beds of central india are intimately associated with the deccan lavas and are critical to determining upper cretaceous palaeoenvironments and palaeogeography of the area in the type jabalpur sub region four mappable units of the lameta beds are recognised the basal green sandstone is interpreted as a braided stream deposit the lower limestone characterised by brecciation and shrinkage cracks is interpreted as a sub aerially exposed palustrine flat with calcrete formation occurring on topographic highs of low relief plains the overlying mottled nodular beds exhibit a variable range of calcrete fabrics and morphologies including circum granular and linear cracks root casts and nodules these are interpreted as pedogenically modified sheet wash deposits of a semiarid alluvial plain the upper sandstone is a sheet flood deposit again pedogenically modified before arrival of the basal lava flows overall the lameta beds are considered to represent a regionally extensive maastrichtian regolith carbon and oxygen isotope analyses of calcareous components are entirely consistent with soil zone environments the 13c values are low typically 8 to 9 pdb demonstrating a strong input of carbon from the decay of terrestrial land plants calcrete 18o values are variable 5 to 10 pdb consistent with precipitation from meteoric water some of which was evaporatively modified in pools on the alluvial palustrine flat the lameta beds are well known for sauropod nesting sites and sedimentological analyses of these sites suggest that the animals selected topographic highs usually in marly or sandy soft sediment multiple nests with similar egg types probably indicate colonial nesting isotopic analyses of eggshell carbonate agree with earlier work suggesting that the sauropods ate a c3 plant food

subtropical mode water in the northeast pacific basin a new type of mode water in the upper thermocline of the eastern subtropical north pacific is identified and examined using data from world ocean circulation experiment high resolution repeat expendable bathythermograph xbt section px37 and archives of historical xbt data this water mass labeled eastern subtropical mode water is characterized by a subsurface potential vorticity minimum and is located east of hawaii northeast pacific basin in a density range of 24 25 4 it is a distinct water mass from the classical subtropical mode water stmw of the western pacific eastern stmw is formed as a relatively deep late winter mixed layer associated with the subtropical subpolar water mass boundary near 25 30 n 135 140 w and is capped and subducted into the permanent thermocline along a section between san francisco and honolulu eastern stmw production is seen in every year for which there is adequate data in this section the volume of eastern stmw formed each winter and the temperature of the potential vorticity minimum are similar during the periods 1970 1979 and 1991 1997

upper ocean heat and freshwater advection in the western pacific ocean mean net surface heating of the pacific ocean shows areas of high heat gain in the eastern tropics and heat loss in the western midlatitudes for steady state conditions westward and poleward transport of heat is implied mean geostrophic and ekman fluxes of heat and freshwater through the sides of a western tropical pacific box bounded by world ocean circulation experiment woce high resolution expendable bathythermograph xbt transects are presented water mass properties of currents transporting heat and freshwater through the enclosed region are seen to be modified in transit net transport convergences within the volume of water extending to 800 m in the vertical show a shallow ocean circulation cell 26 with relatively dense subtropical gyre water entering the volume and lighter water leaving in western boundary currents eastward flowing tropical currents ekman flow and outflow to the indian ocean surface buoyancy fluxes are dominated by freshwater rather than heat fluxes freshwater gain through the surface allows warm salty water to enter in the same density range as cool fresh water leaving the volume for steady state conditions the xbt derived oceanic heat convergence of 0 0 3 pw implies negligible heat loss to the atmosphere traditional surface heat flux climatologies predict too much heat gain part of the discrepancy may be due to anomolous meteorological conditions during the xbt experiment 1987 1995 oceanic freshwater divergence of 0 70 0 08 sv falls in the range of climatological predictions from surface freshwater gain

potential vorticity in the stratosphere derived using data from satellites maps of ertel s potential vorticity q are computed on an isentropic surface in the middle of the stratosphere they are derived using data from stratospheric sounding units on board noaa satellites the reliability of the maps is demonstrated mainly by conservation of q that is shown in successive analyses and by the close agreement obtained using independent data from two satellites the maps are used to follow the movement of material during the course of strong disturbances which occurred in december 1981 they clearly show the breaking of planetary waves in the stratosphere an inherently nonlinear process the effect of wave breaking on the structure of the westerly vortex is considered any mixing of q on isentropic surfaces during wave breaking is shown to be far from complete in the examples studied the behaviour of diagnostics based on zonal averaging such as the eliassen palm flux is accounted for by local changes in the distribution of q the implications of our findings for the study of stratospheric dynamics are discussed