role of inertial instability in the west african monsoon jump the west african monsoon jump is a sudden shift in the latitude of the west african precipitation maximum from the guinean coast near 4 n into sahel near 12 n in late june or early july an examination of reanalyses and observations indicates that the sahel rainy season develops smoothly and the monsoon jump occurs because of an abrupt decrease in guinean coast rainfall we show that this abrupt end of the coastal rainy season occurs when inertial instability develops over the region 1 month later than it develops in the vicinity of the marine atlantic intertropical convergence zone the reason for this delay is the presence of the african easterly jet which places strong negative meridional zonal wind gradients over the coast to preserve the inertially stable environment when the african easterly jet moves farther north due to the seasonal solar forcing these gradients weaken and then reverse to satisfy the threshold condition for inertial instability the rapid end of the guinean coast rainy season follows the northward movement and intensity of the african easterly jet are controlled by the seasonal development of strong meridional land surface temperature gradients and are independent of the formation of the atlantic cold tongue this explanation for the west african monsoon jump relates the phenomenon to the shape and location of the african continent including the low latitude position of the guinean coast and the large expanse of the continent to the north

the annual cycle in equatorial convection and sea surface temperature abstract the coupled atmosphere ocean system in the equatorial eastern pacific and atlantic exhibits a distinct annual cycle that is reflected in contrasting conditions at the times of the two equinoxes the contrasts are so strong that they dominate the annual march of zonally averaged outgoing longwave radiation for the equatorial belt the march equinox corresponds to the warm season when the equatorial cold tongues in the eastern pacific and atlantic are absent with the onset of summer monsoon convection over colombia central america and west africa in may june northward surface winds strengthen over the eastern pacific and atlantic the equatorial cold tongues reappear and the marine convection shifts from the equatorial belt to the intertropical convergence zones itczs along 8 n as the northern summer program the itczs remain strong and shift northward to new 10 n while sea surface temperature sst continues to drop over the cold tongues and the southern tropics perhaps in response to the

low grade metamorphism of mafic rocks through most of this past century metamorphic petrologists in the united states have paid their greatest attention to high grade rocks especially those which constitute the core zones of exhumed mountain belts the pioneering studies of the 50 s through the 80 s those which applied the principles of thermodynamics to metamorphic rocks focused almost exclusively on high temperature systems for which equilibrium processes could be demonstrated by the 1980 s metamorphic petrologists had developed the methodologies for deciphering the thermal and baric histories of mountain belts through the study of high grade rocks of course low grade metamorphic rocks here defined as those which form at pressures and temperatures up to and including the greenschist facies had been well known and described as well initially through the efforts of alpine and circum pacific geologists who recognized that they constituted an integral and contiguous portion of mountain belts and that they underlay large portions of accreted terranes many of oceanic origins but until the mid 80 s much of the effort in studying low grade rocks for a comprehensive review of the literature to that point see frey 1987 had been concentrated on mudstones volcanoclastic rocks and associated lithologies common to continental mountain belts and arcs in the mid 80 s results of the deep sea drilling project dsdp rather dramatically mitigated a shift in the study of low grade metamorphic rocks

quasi lagrangian large eddy simulations of cross equatorial flow in the east pacific atmospheric boundary layer using a large eddy simulation les the atmospheric boundary layer abl is numerically modeled along 958w from 88 st o 48n during boreal autumn and compared to observations from the east pacific investigation of climate processes in the coupled ocean atmosphere system epic 2001 since the local abl winds are predominantly southerly in this season a quasi lagrangian forcing is used in which the abl air column is forced as if it were advecting northward with the mean september october 2001 meridional wind across the equatorial cold tongue and the rapidly warming ssts to the north pressure gradients and large scale zonal advective tendencies are prescribed as a function of latitude where possible observations from the epic 2001 experiment are used for forcing and for comparison with model results the abl s modeled vertical structure accords with the conceptual model of wallace et al and agrees well with observations surface stability accounts for the minimum in surface wind over the equatorial cold tongue and the maximum over the warm water to the north stability of the lower abl over the cold tongue allows a jet to accelerate at about 500 m height relatively uncoupled to the frictional surface layer vertical mixing over the warm water to the north distributes this momentum to the surface additional simulations were performed to explore the modeled abl s sensitivity to pressure gradients zonal advection free tropospheric humidity and initial conditions the model abl was robust changing the forcings resulted in little change in the modeled structure the strongest sensitivity was of stratocumulus clouds over the cold tongue to cloud top radiative cooling once formed at the southern edge of the cold tongue modeled stratocumulus clouds demonstrate a remarkable ability to maintain themselves over the cold tongue in the absence of surface fluxes by radiative cooling at their tops the persistence of thin stratocumulus clouds in this lagrangian model suggests that horizontal advection of condensate might be an important process in determining cloudiness over the cold tongue

westerly wind events in the tropical pacific 1986 95 abstract based on examination of 10 yr of 10 m winds and wind anomalies from european centre for medium range weather forecasts ecwmf analysis definitions for westerly wind events wwes of eight different types are proposed the authors construct a composite for each type of event show that a simple propagating gaussian model satisfactorily describes the evolution of zonal wind anomaly for each type of event and determine the scales of each composite event by fitting the model to each composite the authors discuss the wwes that occurred during the tropical oceans global atmosphere coupled ocean atmosphere response experiment toga coare intensive observing period iop and show the extent to which these composite events are able to reproduce the major westerly wind features of the iop the frequency of occurrence of each type of wwe for each year of this record and by calendar month are described the authors find several types of events are negatively correlated with the annual mean troup souther

deconstructing atlantic intertropical convergence zone variability influence of the local cross equatorial sea surface temperature gradient and remote forcing from the eastern equatorial pacific 1 we investigate causes of interannual variability in atlantic intertropical convergence zone itcz convection using a monthly mean global precipitation data set spanning 1979 1999 starting from the hypothesis of two dominant influences on the itcz namely the cross equatorial gradient in tropical atlantic sea surface temperature sst and the anomalous walker circulation due to the rearrangement of tropical pacific convection associated with the el nino southern oscillation we analyze anomaly composites over the 1979 1999 period that best isolate the effects of each mechanism our results suggest that to first order a strong anomalous walker circulation suppresses precipitation over the tropical atlantic whereas an anomalous warm north cool south sst gradient shifts the meridional location of maximum itcz convection anomalously north we examined the processes underlying each of the two mechanisms for the anomalous walker circulation we find consistency with the idea of suppression of convection through warming of the tropical troposphere brought about by anomalous convective heating in the eastern equatorial pacific for the sst gradient mechanism our results confirm previous studies that link convection to cross equatorial winds forced by meridional sst gradients we find that positive surface flux feedback brought about through the cross equatorial winds is weak and confined to the deep tropics on the basis of the results of this and other studies we propose an expanded physical picture that explains key features of atlantic itcz variability including its seasonal preference its sensitivity to small anomalous sst gradients and its role in the context of tropical atlantic sst gradient variability index terms 4215 oceanography general climate and interannual variability 3309 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 3354 meteorology and atmospheric dynamics precipitation 1854 3374 meteorology and atmospheric dynamics tropical meteorology 4522 oceanography physical ocean optics keywords tropical atlantic precipitation climate variability el nino southern oscillation ocean atmosphere interaction

observational evidence of slantwise convective adjustment abstract attempts were made during two field experiments to fly instrumented aircraft along absolute momentum m surfaces as a means of accurately determining slantwise convective stability the application of this technique appears to have been quite successful we present the results of four such efforts conducted in the ascent regions of midlatitude cyclones observed during the new england winter storms and genesis of atlantic lows experiments in three of the four cases the atmosphere was almost exactly neutral to slantwise ascent while being quite stable to vertical displacements in the fourth case the atmosphere departed from neutrality but was also substantially drier evidently due to subsidence we find excellent agreement between assessments of stability based on the m surface flights and on cross sections constructed from rawinsonde observations on the basis of these results i hypothesize that slantwise convective neutrality is characteristic of the ascent regions of baroclinic cyclones and

geochemical investigations of saltwater intrusion into the coastal carbonate aquifer of mallorca spain abstract coastal aquifers often display seawater intrusion resulting in the formation of a salty water wedge progressing inland this study investigates the mass transfers in the mixing zone at the freshwater seawater interface where the water is out of equilibrium with the rock forming carbonates investigations were conducted in two boreholes separated by 5 m at the ses sitjoles test site mallorca island spain where repeated electrical conductivity logs of the formation and the saturating fluid as well as regular pore water sampling and permanent downhole multi parameter monitoring of the water were performed over a period of 9 a in the mixing zone the significant acidification the calcite saturation index profile and the ca concentration profile cannot be explained by conservative mixing nor by dissolution precipitation reactions only conversely the analysis of organic c content and of the distinctly different time resolved ph profiles measured in the two boreholes suggests the development of perennial biomass that triggers calcite dissolution moreover the presence of biomass seems to be correlated with the permeability and vertical connectivity at the meter scale it is speculated that the mechanism could be self activated because the microbiological activity induces calcite dissolution and tends to increase porosity and permeability that favors biomass development

convection in the east pacific intertropical convergence zone the eastern tropical pacific exhibits a strong cross equatorial sea surface temperature sst gradient which drives a southerly flow in the atmospheric boundary layer convergence in this flow is generally considered to drive deep convection in the east pacific intertropical convergence zone however results from cloud modeling and recent field programs provide an alternative thermodynamic mechanism for controlling this convection while shallow convection responds to boundary layer convergence deep convection appears to be controlled by a combination of convective inhibition surface moist entropy fluxes tropospheric relative humidity and moist convective instability these factors explain the sharp minimum in infrared brightness temperature near 8 n while boundary layer convergence occurs over a much broader range of latitudes

characterization of hydrated silicate bearing outcrops in tyrrhena terra mars implications to the alteration history of mars abstract the tyrrhena terra region of mars is studied with the imaging spectrometers omega observatoire pour la mineralogie l eau les glaces et l activite onboard mars express and crism compact reconnaissance infrared spectrometer for mars onboard mars reconnaissance orbiter through the observation of tens of craters that impacted into this part of the martian highlands the 175 detections of hydrated silicates are reported mainly associated with ejecta blankets crater walls and rims and central up lifts sizes of craters where hydrated silicates are detected are highly variable diameters range from less than 1 km to 42 km we report the presence of zeolites and phyllosilicates like prehnite mg chlorite mg rich smectites and mixed layer chlorites smectites and chlorite vermiculite from comparison of hyperspectral infrared observations with laboratory spectra these minerals are associated with fresh craters post dating any aqueous activity they likely represent ancient hydrated terrains excavated by the crater forming impacts and hence reveal the composition of the altered noachian crust although crater related hydrothermal activity may have played a minor role for the largest craters 20 km in diameter most detected minerals formed over relatively high temperatures 100 300 c likely due to aqueous alteration of the noachian crust by regional low grade metamorphism from the noachian thermal gradient and or by extended hydrothermal systems associated with noachian volcanism and ancient large impact craters this is in contrast with some other phyllosilicate bearing regions like mawrth vallis where smectites kaolinites and hydrated silica were mainly identified pointing to a predominance of surface shallow sub surface alteration and where excavation by impacts played only a minor role smooth plains containing hydrated silicates are observed at the boundary between the noachian altered crust dissected by fluvial valleys and the hesperian unaltered volcanic plains these plains may correspond to alluvial deposition of eroded material the highlands of tyrrhena terra are therefore particularly well suited for investigating the diversity of hydrated minerals in ancient martian terrains

the parcel method in a baroclinic atmosphere abstract the parcel method of investigating the susceptibility of the atmosphere to particular disturbances involves postulating parcel displacements in an undisturbed environment and deducing the likelihood of such a displacement by estimating the kinetic energy change that would result on the convective scale such a method has provided realistic and practical criteria for the existence and intensity of such motions on the larger scale theoreticians tend to reject such arguments as heuristic at best this paper is an attempt to reconsider the role of parcel theory on different length scales and in particular in the application of symmetric instability ideas to frontal rainbands it is concluded that parcel theory has to be applied with care but that in some situations it can provide a useful though partial insight into atmospheric disturbances

a three dimensional planetary boundary layer model for the somali jet abstract this paper is an extension of an earlier study on the planetary boundary layer dynamics of the low level monsoonal flow over the arabian sea krishnamurti and wong 1979 where the long term steady state motion field for a boundary layer was determined using a zonally symmetric model with a prescribed pressure field in that study we examined the balance of forces in the surface layer and the planetary boundary layer for regions across the equator across and along the low level somali jet and across an intertropical convergence zone the important role of advective accelerations in the near equatorial balance of forces was demonstrated the important study is based on a three dimensional model that removes the restriction of zonal symmetry this mesoscale fine mesh model with a horizontal resolution of 55 km and a vertical resolution of 200 m is integrated to examine the evolution of three dimensional planetary boundary layer flows for prescribed three dimensional pressure patterns the obs

a simplified model of the modified hadley circulation abstract a model is developed to find the low latitude upper tropospheric atmospheric circulation which would exist in the absence of transient eddies the forcing in the model is zonally asymmetric to take into account the effect of the distribution of oceans and continents on latent heating steady state solutions of the equations of motion in such a case have been termed the modified hadley circulation by lorenz the model is the set of steady nonlinear inviscid shallow water equations with thermal forcing as introduced by gill and is solved semianalytically the modified hadley circulation found using forcing derived from observed olr exhibits some similarities to observed features of the tropical and subtropical time mean upper tropospheric flow particularly with regard to the velocity potential as well as many dissimilarities the roles of transients and friction as indicated by the model are discussed

effects of rotation rate and seasonal forcing on the itcz extent in planetary atmospheres the authors study a wide range of atmospheric circulations with an idealized moist general circulation model to evaluate the mechanisms controlling intertropical convergence zone itcz migrations they employ a zonally symmetric aquaplanet slab ocean of fixed depth and force top of atmosphere insolation to remain fixed at the pole for an eternal solstice simulation and also vary seasonally for a range of rotation rates keeping all other parameters earth like for rotation rates e 8 and slower a transient maximum in zonal mean precipitation appears at the summer pole however the itcz associated with the ascending branch of the hadley circulation lies at 60 the authors assess how widely used predictors of the itcz position perform in this wide parameter space standard predictors based on different estimates of the hadley cell s poleward extent are correlated with but overestimate off equatorial itcz locations interestingly in the eternal solstice case for earth s rotation rate the itcz remains at subtropical latitudes even though the lower level moist static energy maximizes at the summer pole while seemingly at odds with convective quasi equilibrium arguments this can happen because at earth s rotation rates the thermal stratification set in convective regions can only be communicated within the tropics where temperature gradients are constrained to be weak the authors therefore develop an understanding of the itcz s position based on top of atmosphere energetics and the boundary layer momentum budget and argue that friction and pressure gradient forces determine the region of maximum convergence offering a modified dynamical perspective on the monsoon like seasonal weather patterns of terrestrial planets

a revised picture of the structure of the monsoon and land itcz over west africa this article presents an overview of the land itcz intertropical convergence zone over west africa based on analysis of ncar ncep reanalysis data the picture that emerges is much different than the classic one the most important feature is that the itcz is effectively independent of the system that produces most of the rainfall rainfall linked directly to this zone of surface convergence generally affects only the southern sahara and the northern most sahel and only in abnormally wet years in the region a second feature is that the rainbelt normally assumed to represent the itcz is instead produced by a large core of ascent lying between the african easterly jet and the tropical easterly jet this region corresponds to the southern track of african easterly waves which distribute the rainfall this finding underscores the need to distinguish between the itcz and the feature better termed the tropical rainbelt the latter is conventionally but improperly used in remote sensing studies to denote the surface itcz over west africa the new picture also suggests that the moisture available for convection is strongly coupled to the strength of the uplift which in turn is controlled by the characteristics of the african easterly jet and tropical easterly jet rather than by moisture convergence this new picture also includes a circulation feature not generally considered in most analyses of the region this feature a low level westerly jet termed the african westerly jet plays a significant role in interannual and multidecadal variability in the sahel region of west africa included are discussions of the how this new view relates to other aspects of west africa meteorology such as moisture sources rainfall production and forecasting desertification climate monitoring hurricanes and interannual variability the west african monsoon is also related to a new paradigm for examining the interannual variability of rainfall over west africa one that relates changes in annual rainfall to changes in either the intensity of the rainbelt or north south displacements of this feature the new view presented here is consistent with a plethora of research on the synoptic and dynamic aspects of the african easterly waves the disturbances that are linked to rainfall over west africa and spawn hurricanes over the atlantic and with our knowledge of the prevailing synoptic and dynamic features this article demonstrate a new aspect of the west africa monsoon a bimodal state with one mode linked to dry conditions in the sahel and the other linked to wet conditions the switch between modes appears to be linked to an inertial instability mechanism with the cross equatorial pressure gradient being a critical factor the biomodal state has been shown for the month of august only but this month contributes most of the interannual variability this new picture of the monsoon and interannual variability shown here appears to be relevant not only to interannual variability but also to the multidecadal variability evidenced in the region between the 1950s and 1980s

air sea heat exchange along the northern sea surface temperature front in the eastern tropical pacific abstract the atmospheric response to the oceanic forcing in the eastern pacific along the northern equatorial sea surface temperature sst front is investigated in terms of sensible and latent heat flux during the 6 month period from 28 july 1999 to 27 january 2000 and the 7 month period from 28 june 2000 to 27 january 2001 of particular interest is the atmospheric boundary layer abl response to oceanic tropical instability waves tiws that distort the sst front during may january in normal years in previous studies time series of surface heat fluxes clearly show the influence of tiws but the relationship to spatial patterns of sst and wind speed has been inferred only from sparse in situ data in this study satellite observations are used as a basis for compositing in situ data from moorings to compensate for the lack of a spatially dense mooring array the variability in the position of the sst front caused by westward propagating tiws enables fixed mooring locations to measure the abl response

multiyear measurements of the oceanic and atmospheric boundary layers at the brazil malvinas confluence region 1 this study analyzes and discusses data taken from oceanic and atmospheric measurements performed simultaneously at the brazil malvinas confluence bmc region in the southwestern atlantic ocean this area is one of the most dynamical frontal regions of the world ocean data were collected during four research cruises in the region once a year in consecutive years between 2004 and 2007 very few studies have addressed the importance of studying the air sea coupling at the bmc region lateral temperature gradients at the study region were as high as 0 3 c km 1 at the surface and subsurface in the oceanic boundary layer the vertical temperature gradient reached 0 08 c m 1 at 500 m depth our results show that the marine atmospheric boundary layer mabl at the bmc region is modulated by the strong sea surface temperature sst gradients present at the sea surface the mean mabl structure is thicker over the warmside of the bmc where brazil current bc waters predominate the opposite occurs over the coldside of the confluence where waters from the malvinas falkland current mc are found the warmside of the confluence presented systematically higher mabl top height compared to the coldside this type of modulation at the synoptic scale is consistent to what happens in other frontal regions of the world ocean where the mabl adjusts itself to modifications along the sst gradients over warm waters at the bmc region the mabl static instability and turbulence were increased while winds at the lower portion of the mabl were strong over the coldside of the bc mc front an opposite behavior is found the mabl is thinner and more stable our results suggest that the sea level pressure slp was also modulated locally together with static stability vertical mixing mechanism by the surface condition during all cruises sst gradients at the bmc region modulate the synoptic atmospheric pressure gradient postfrontal and prefrontal conditions produce opposite thermal advections in the mabl that lead to different pressure intensification patterns across the confluence

direct observations of atmospheric boundary layer response to sst variations associated with tropical instability waves over the eastern equatorial pacific tropical instability waves tiws with a typical wavelength of 1000 km and period of 30 days cause the equatorial front to meander and result in sst variations on the order of 18 28c vertical soundings of temperature humidity and wind velocity were obtained on board a japanese research vessel which sailed through three fully developed sst waves from 1408 to 1108w along 28n during 21 28 september 1999 a strong temperature inversion is observed throughout the cruise along 28n capping the planetary boundary layer pbl that is 1 1 5 km deep temperature response to tiw induced sst changes penetrates the whole depth of the pbl in response to an sst increase air temperature rises in the lowest kilometer and shows a strong cooling at the mean inversion height as a result this temperature dipole is associated with little tiw signal in the observed sea level pressure slp the cruise mean vertical profiles show a speed maximum at 400 500 m for both zonal and meridional velocities sst based composite profiles of zonal wind velocity show weakened intensified vertical shear within the pbl that is consistent with enhanced reduced vertical mixing causing surface wind to accelerate decelerate over warm cold ssts taken together the temperature and wind soundings indicate the dominance of the vertical mixing over the slp driving mechanism based on the authors measurements a physical interpretation of the widely used pbl model proposed by lindzen and nigam is presented

carbonate dissolution and precipitation in coastal environments laboratory analysis and theoretical consideration 1 we have conducted laboratory experiments to examine caco3 dissolution and precipitation in saltwater freshwater mixing zones with a view to understanding and predicting porosity changes in coastal environments mixing of seawater or saline subsurface water with fresh water can be of major importance in the chemical diagenesis of carbonate rocks and sediments we used artificial seawater and nacl solutions of different concentrations under different co2 partial pressures and with different mixing ratios two dimensional flow cells filled with glass beads and crushed calcium carbonate rock were used to measure calcium carbonate precipitation and dissolution respectively an important feature of these experiments is that the results are shown to agree well with a relatively simple transport theory describing mineral precipitation dissolution that results from the nonlinear dependence of caco3 saturation upon electrolyte concentration the theory demonstrates that the rate of dissolution or precipitation depends on the curvature and sign of the solubility as a function of salinity the square of the salinity gradient and the macroscopic dispersion coefficient the theory is largely scale independent and depends upon field parameters that can be determined analysis of data from three field sites yucatan peninsula bermuda and mallorca demonstrates excellent agreement between field observations and theory

oscillations of the intertropical convergence zone and the genesis of easterly waves part ii numerical verification a companion paper part i toma and webster 2008 argued that the characteristics of the mean intertropical convergence zone itcz arise from instabilities associated with the strong cross equatorial pressure gradient cepg that exists in the eastern pacific ocean as a result of the latitudinal sea surface temperature sst gradient furthermore it was argued that instabilities of the mean itcz resulted in the in situ development of easterly waves thus in part i it was hypothesized that the mean and transient state of eastern pacific convection was due to local processes and less so to the advection of waves from the north atlantic ocean to test this hypothesis and at the same time consider others such as a possible role of the equatorial and subtropical orography in generating local instabilities a series of controlled numerical experiments are designed using the wrf regional model the domain of the model was configured to include the western atlantic ocean the isthmus of panama and the eastern pacific ocean to 155 w lateral boundaries were set at 40 n and 40 s thus containing the mountains of central america the andes and the sierra madre of mexico in a series of experiments analysis products were used as boundary conditions that were successively updated four times per day set as 10 day running average fields or as running mean monthly fields finally the model was run with topography essentially eliminated over the land areas although there are differences between the details of the resultant fields the location of mean convection and the form of the transients remain the same it is concluded in support of the theoretical and diagnostic studies of part i that orographic forcing or waves generated in the north atlantic ocean are not the major causes of the mean and transient nature of disturbances in the eastern pacific

stratigraphy geochemistry and mineralogy of eocene rocks from the toa baja drillhole the stratigraphy of the eocene rocks of the toa baja drillhole is dominated by volcaniclastic sediments which are interbedded with marly pelagic limestones especially in the lower part of the hole and lava flows petrological geochemical and paleontological evidence suggest that the site of deposition was a deep marine basin and the source of the volcanics were subaerial or shallow submarine island arc volcanoes

diagnostic studies of pacific surface winds abstract analyses are performed using surface winds derived from the monthly mean fsu pacific pseudo stress fields vorticity budget calculations reveal the relative contributions of various terms and allow simplification of the full momentum equations based on the simplified equations a procedure is developed for estimating surface pressure and then adjusting the winds the wind field adjustments fall well within the uncertainty of the data while allowing generally large imbalances in the vorticity budget to be removed completely further validation of the procedure is provided by comparisons between estimated and observed pressure anomalies the adjusted winds and pressure are then used to infer boundary layer and upper level forcing within the context of particular model formulations these forcing fields an compared with sea surface temperature outgoing longwave radiation and highly reflective cloud data in order to infer the dominant mechanisms contributing to observed surface circulation anom

rb sr and sm nd isotopic characterization of eocene volcanic and volcaniclastic rocks from puerto rico sm nd and rb sr data are presented for six volcanic and volcaniclastic samples from the eocene belt and the toa baja drill hole of puerto rico in order to provide a preliminary isotopic description of greater antilles arc rocks the lava samples have trace and rare earth element compositions typical of island arc rocks the isotopic compositions of the volcaniclastic samples are displaced from those of the lavas and suggest that they include an authigenic or detrital crustal component the similarity of sr and nd isotopic ratios of puerto rican lavas and northern lesser antilles volcanic rocks suggests that they may have been produced from similar magma sources

the importance of breaching as a mechanism of subaqueous slope failure in fine sand large bank failures comprising up to 10 6 m 3 of sediment are common features along steep channel banks in estuaries and large rivers that consist of clean fine sands and are mostly assumed to be generated by sudden liquefaction of large masses of very loosely packed sand another less commonly recognized type of failure is manifested by the gradual retrogression of a very steep wall steeper than the angle of repose instead of the voluminous surging plastic sediment water flow or hyperconcentrated density flow sensu mulder alexander 2001 generated by liquefaction this type of failure known as breaching by dredging companies and hydraulic engineers produces a sustained quasi steady turbidity current to date sedimentologists have not recognized the process of breaching as such in this paper it is suggested that breaching may be the origin of many thick massive sand layers known from ancient deposits from various environments notably in some turbidite successions possible differences in the sedimentary structure of the deposits produced by breach failures vs liquefaction slope failures liquefaction flow slides can be deduced from a knowledge of the sediment transport processes initiated by the failure a field study is presented on some poorly structured beds in the eocene vlierzele sands in belgium which are supposed to have originated from liquefaction failures but are reinterpreted to be the products of breaching it is postulated that the local steep slope disturbance required to initiate an active breach can be produced by a small liquefaction slope failure liquefaction flow slide failure or local erosion by river or tidal channel flow at the initial stage of the failure event

an integrated view of the 1987 australian monsoon and its mesoscale convective systems i horizontal structure this observational study is organized around three issues the forcing of the monsoon flow by embedded deep convection the thermodynamic conditions that support the convection and the structures of the mesoscale convective systems mcss that constitute much of the deep convection the monsoon convective cloudiness occurred predominantly offshore over the earth s warmest waters week long periods of widespread deep convection caused cycles of monsoon spin up culminating in tropical cyclone formation momentum transports by the convection also created smaller scale vortex pairs in the upper troposphere sounding data suggest that the convection was modulated by low level processes not by large scale deep forced ascent triggering by mesoscale boundary layer cold pool boundaries and coastlines determined specifically where convection occurred while several positive feedbacks acted to keep regional thermodynamic conditions favourable hence monsoon convection once initiated persisted as self exciting superclusters composed at any instant of many distinct mcss the observed mcss all contained areas of deep convection and stratiform precipitation areas stratiform precipitation usually evolved in place from convective cells although precipitation also occasionally fell from overhanging anvils created by upper level shear the mcss within similar synoptic wind environments tended to have similar mesoscale structures this fact reflects the effects illustrated herein of environmental winds upon the relative motions of cold pools which trigger new convective cells and stratiform precipitation areas which evolve from old convective cells

sedimentological analysis and reservoir characterization of a multi darcy billion barrel oil field the upper jurassic shallow marine sandstones of the johan sverdrup field north sea norway abstract the estimated in place hydrocarbon volume of the giant johan sverdrup field is 3 5 billion barrels of oil the bulk of which is contained in the upper jurassic intra draupne formation sandstone the intra draupne formation sandstone is composed of unusually coarse grained siliciclastic sediments with an average net gross of 97 and average porosity of 28 the median core permeability ranges from 0 5 to 40 darcies in individual wells and may reach even higher values based on drill stem testing the reservoir is interpreted to be a time transgressive sheet sand ranging from 2 to 38 m in thickness and covering an area of more than 200 km2 vertical and lateral facies and grain size trends combined with biostratigraphy and palaeocurrent indicators are interpreted to demonstrate a westward onlapping transgressive shoreface depositional system with local fan delta input reservoir properties vary significantly across the field and relative to facies association in terms of permeability the upper and lower shoreface associations in the avaldsnes high area in the east show the highest median values of 25 27 darcies the upper and lower shoreface associations in the augvald graben area to the west show median values of 15 and 21 darcies respectively the lowest values are observed in the transgressive shoreline fan delta and spiculitic shoreface associations i e 8 darcies 2 darcies and 0 1 darcies respectively the latter two facies associations are restricted to local areas in the west and northwest the coarse grain size lack of fines scarcity of cementation and extensive sheet like distribution of siliciclastic sediments make the intra draupne formation sandstone an ideal reservoir the depositional model presented in this paper may be used as an analogue when exploring for similar high quality shallow marine reservoir sands

clay mineral and zeolite diagenesis in the toa baja well puerto rico several diagenetic reactions typical of volcaniclastic sediments have been identified in the toa baja well the zeolites heulandite and less commonly analcite present in the upper half of the drilled section give way to laumontite at depth a decrease with depth in the expandability of mixed layer chlorite smectite was observed corrensite was detected over the depth range 1 676 2 286 m temperatures implied by the depth ranges of diagenetic and indicator minerals are consistent with a paleothermal gradient of about 30 50c km assuming little or no erosion of section

zeolite to prehnite pumpellyite facies metamorphism of the late proterozoic zig zag dal basalt formation eastern north greenland abstract the zig zag dal basalt formation 1300 m maximum thickness of late proterozoic age exposed in eastern north greenland has been variably affected by low temperature metamorphism resulting in the development of calc silicate and mafic phyllosilicate bearing assemblages relatively fresh flows sometimes preserving primary olivine calcic plagioclase augite and pigeonite and showing randomly mixedlayer chlorite smectite are sandwiched between flows showing not only more extensive alteration but also higher temperature assemblages accordingly in these flows the primary igneous phases are replaced with the exception of augite and prehnite and pumpellyite along with rare zeolites are sporadically developed while regular mixed layer chlorite smectite and or true chlorite predominate temperatures have been estimated on the presence absence of various secondary minerals and also using the chlorite geothermometer and are indicative of progressive metamorphism in the range from below 125 c to approximately 200 c i e in the zeolite facies to lowermost prehnite pumpellyite facies range no depth dependent temperature related zonation of secondary mineral phases as seen in other thick altered basalt successions has been identified in the zig zag dal basalts however instead alteration appears to have been influenced by the physical character of the flows themselves including flow thickness degree of vesicularity and the presence or absence of jointing all of which appear to have exerted an influence over access of fluid this relation between flow character and intensity of alteration suggests that fluid flow through the zig zag dal basalts must have been predominantly lateral rather than vertical

dynamics of the itcz boundary layer abstractthis paper presents high resolution numerical solutions of a nonlinear zonally symmetric slab model of the intertropical convergence zone itcz boundary layer the boundary layer zonal and meridional flows are forced by a specified pressure field which can also be interpreted as a specified geostrophically balanced zonal wind field ug y one narrow on equatorial peak in boundary layer pumping is produced when the forcing is easterly geostrophic flow along the equator and two narrow peaks in boundary layer pumping are produced on opposite sides of the equator a double itcz when the forcing is westerly geostrophic flow along the equator in the case when easterlies are surrounding a westerly wind burst once again a double itcz is produced but the itczs have significantly more intense boundary layer pumping than the case of only westerly geostrophic flow a comparison of the numerical solutions to those of classical ekman theory suggests that the meridional advection term y plays a vita

an improved real time global sea surface temperature analysis abstract the monthly global sea surface temperature sst analysis of reynolds using real time in situ and satellite sst data has now been improved by using sea ice data to simulate ssts in ice covered regions the simulated ssts now become the external boundary condition for the analysis solution this technique eliminates any high latitude satellite biases and extends the analysis to the ice edge the analysis with the ice data has been computed for the period january 1982 to present

oscillations of the intertropical convergence zone and the genesis of easterly waves part i diagnostics and theory we examine the mean and transient state of the intertropical convergence zone itcz by analyzing data and using simple theory we concentrate on the tropical eastern pacific ocean noting that there exists in this region a well developed mean itcz furthermore it is a region where there has been considerable discussion in the literature of whether easterly waves develop in situ or propagate westwards from the atlantic ocean the region is typical of tropical regions where there is a strong cross equatorial pressure gradient cepg mean convection well removed from the equator but located equatorward of the maximum sea surface temperature sst and minimum sea level pressure mslp further to the west near the dateline where the cepg is much smaller convection is weaker and collocated with sst and mslp extrema it is argued that in regions of significant cepg that the near equatorial tropical system is inertially unstable and that the rectification of the instability for a given cepg determines the location and intensity of the climatological itcz using simple theoretical arguments we develop an expression for the mean latitude of the itcz as a function of the cepg we note on a day by day basis that the itcz is highly transient state with variability occurring on 3 8 day time scales transients with amplitudes about half of the mean itcz propagate northwards from the near equatorial southern hemisphere as anomalous meridional oscillations eventually amplifying convection in the vicinity of the mean itcz it is argued that in these longitudes of strong cepg the mean itcz is continually inertially unstable with advections of anticylonic vorticity across the equator resulting in the creation of an oscillating divergence convergence doublet the low level convergence produces convection and the resultant vortex tube stretching generates cyclonic vorticity which counteracts the northward advection of anticylonic vorticity during a cycle the mid troposphere heating near 10on oscillates between 6 and 12 k day at the inertial frequency of the latitude of the mean convection as a result there exists an anomalous and shallower oscillating meridional circulation with a magnitude about 50 of the mean itcz associated with the stable state following the generation of anticylonic vorticity further it is argued that the instabilities of the itcz are directly associated with in situ development of easterly waves which occur with the inertial period of the latitude of the mean itcz the dynamical sequences and the genesis of easterly waves are absent in the regions further to the east where the cepg is much weaker or absent altogether in a companion study part ii numerical experiments are conducted to test the hypothesis raised in the present study

climatology of sign reversals of the meridional potential vorticity gradient over africa and australia abstract a 10 yr climatology 1986 95 was performed using ecmwf gridded analyses on isentropic surfaces to identify regions where the lower tropospheric meridional potential vorticity pv gradient changes sign across africa and australia during their respective summer seasons while an african sign reversal has been documented no similar study has been performed for the australian region which also has desert on the poleward side of open ocean in each hemisphere a northward decrease of pv is sufficient to produce a sign reversal it was found that pv decreases northward in the lower troposphere across northern australia with the maximum reversal on the 315 k surface it had comparable magnitude but smaller zonal extent 3000 km than that on the 320 k surface in africa 5000 km in each region the sign reversal was associated with cyclonic pv anomalies on the equatorward side and anticyclonic anomalies on the poleward side olr was used as a proxy for deep convective heating in order to evaluate

the seasonal cycle over the tropical pacific in coupled ocean atmosphere general circulation models abstract the seasonal cycle over the tropical pacific simulated by 11 coupled ocean atmosphere general circulation models gcms is examined each model consists of a high resolution ocean gcm of either the tropical pacific or near global means coupled to a moderate or high resolution atmospheric gcm without the use of flux correction the seasonal behavior of sea surface temperature sst and eastern pacific rainfall is presented for each model the results show that current state of the art coupled gcms share important successes and troublesome systematic errors all 11 models are able to simulate the mean zonal gradient in sst at the equator over the central pacific the simulated equatorial cold tongue generally tends to be too strong too narrow and extend too far west ssts are generally too warm in a broad region west of peru and in a band near 10 s this is accompanied in some models by a double intertropical convergence zone itcz straddling the equator over the eastern pacific and in others

transition from the zeolite to prehnite pumpellyite facies in the karmutsen metabasites vancouver island british columbia

facies characteristics and depositional models of highly bioturbated shallow marine siliciclastic strata an example from the fulmar formation late jurassic uk central graben abstract an extensive core database from the late jurassic fulmar formation illustrates the practicalities of facies analysis and depositional modelling in highly bioturbated heterolithic shallow marine siliciclastic strata twelve major sedimentary facies 1 12 are defined on the basis of lithology grain size visually estimated sand silt content and the presence or absence of primary sedimentary structures ichnofabric characteristics are also defined and have proved to be not always facies specific for purposes of depositional modelling the 12 facies types are resolved into six facies associations a f each representative of distinct shoreline shallow marine environments from these associations three broad depositional models have been constructed storm influenced shoreface model 1 bioturbated shoreface model 2 and a speculative bioturbated shelf model model 3 stratigraphical and palaeontological criteria suggest that models 1 and 2 are shoreline attached sedimentological data indicate that they occur as end members to a spectrum of shoreline settings constrained by incident wave energy bands for shorefaces subject to significant storm influence well preserved event beds occur seaward of the upper shoreface in the bioturbated shoreface model however the lower shoreface and adjacent shelf deposits are characterized by intense infaunal reworking the bioturbated shelf model displays no clear evidence of shoreline connection with the resultant facies often exhibiting highly abundant siliceous sponge spicules together with other open marine indicators such as belemnites and rare ammonites unlike the shoreface sand bodies which received sediment from basin margin fluvial systems shelf sand bodies in the fulmar formation are more likely to have been intrabasinally sourced along relay ramps or other forms of transfer zone this sediment may have undergone a long transit residence period on the shelf prior to eventual burial in hanging wall depocentres strongly influenced by zechstein salt withdrawal this study demonstrates that an ichnofabric approach as opposed to one of simple ichnodiversity is highly significant with respect to the description and modelling of highly bioturbated shallow marine siliciclastic strata in the fulmar formation ichnofabric analysis is capable of providing sensitive information on fluctuations in depositional energy levels water depth sedimentation rates erosion rates substrate consistency and dissolved oxygen levels evidence of these fluctuations is often apparent at intra facies scale but would largely go unnoticed using a conventional sedimentological approach to data gathering based on ichnodiversity at best depositionally significant changes in ichnofabric may occur without any significant change in ichnodiversity ichnofabric analysis also plays an important role in the hierarchical assessment of key stratal surfaces for purposes of sequence stratigraphic modelling

violation of ekman balance in the eastern pacific itcz boundary layer abstractthe intertropical convergence zone itcz is one of the most striking features of earth s climate system often forming a narrow band of convection over many oceanic regions especially in

diagenesis of middle tertiary carbonates in the toa baja well puerto rico this is the publisher s version also available electronically from http onlinelibrary wiley com

structural analysis of cores and cuttings from the toa baja puerto rico borehole deformation structures in core samples and well cuttings from the toa baja borehole in puerto rico obtained from depths of 580 to 2700 meters can be divided into two major categories 1 structures resulting from compression and shear and 2 structures formed by extension generally the first ones are older and they are somewhat more abundant at horizons where fault zones occur as deduced from dipmeter readings and televiewer log these structures may have formed during an eocene thrusting event recognized regionally in puerto rico the extensional structures which almost always crosscut the compressional ones are filled with zeolite calcite prehnite or quartz there is poor correspondence between the abundance of these fractures and the position of the major fault zones the largest abundance of veins occurs between 1700 and 2100 meters depth they may be related to a phase of regional extension during the late paleogene

response of the hadley circulation to convective forcing in the itcz abstract through the use of a zonal balance model we investigate the response of the mean meridional circulation to a specified diabatic forcing for both resting and nonresting zonal flows the use of a potential latitude coordinate and transformed meridional circulation components results in a simplified meridional circulation equation in which the variable coefficients are the normalized potential vorticity and inertial stability solutions of this equation illustrate how latent heat release away from the equator forces a winter hemisphere hadley cell that is more intense than the summer hemisphere cell this asymmetric response is due primarily to the anisotropy associated with the spatial variation of the inertial stability field despite the sensitivity of the meridional circulation to the location and breadth of the forcing the low latitude thermodynamic response is for the most part insensitive as long as the total latent heat release remains the same numerical solutions of the zonal balance mode

mixing driven diagenesis and mineral deposition caco3 precipitation in salt water fresh water mixing zones 1 we perform a novel set of laboratory experiments that depict caco3 precipitation upon mixing between saturated fresh and salt water solutions thus simulating mixing diagenesis in a coastal aquifer the experimental results are shown to agree with the result predicted from a relatively simple mathematical model thus suggesting that the model may be extrapolated to natural environments application of the model to the coastal aquifer of mallorca spain indicates calcite precipitation is reducing porosity at a rate of 13 per 10 000 years consideration of precipitation processes can thus explain contradictory interpretations of natural evolution in carbonate formations

paleontology of the toa baja 1 well puerto rico the toa baja well penetrated 585 2 m of fossiliferous oligocene and miocene limestone sandstone and shale above 2119 m of eocene dominantly volcaniclastic strata oligocene and miocene rocks were deposited on a broad shallow shelf the unconformity between eocene and oligocene strata spans at least the late eocene and probably part of the early oligocene at toa baja below the unconformity unfossiliferous volcaniclastic and igneous rocks are interstratified with fossiliferous limestone beds containing middle and possibly late early eocene planktic foraminifera probably deposited in deep water no paleocene or cretaceous fossils were recovered

single and double itcz in an aqua planet model with constant sea surface temperature and solar angle it has been known for more than a decade that an aqua planet model with a globally and temporally uniform sea surface temperature and solar isolation angle can generate intertropical convergence zones itcz employing such a model previous studies have shown that one of several means can be used to change between a single itcz over the equator and a double itcz straddling the equator these means include switching to a different cumulus parametrization scheme making changes within the cumulus parametrization scheme and changing other aspects of the model such as horizontal resolution here an interpretation of these findings is offered in an aqua planet model with globally and temporally uniform sea surface temperature and solar isolation angle the latitudinal location of an itcz is the latitude where a balance exists between two types of attraction both resulting from the earth s rotation the first attraction pulls the itcz towards the equator and is not sensitive to changes in model design it is directly related to the coriolis parameter which provides stability to the atmosphere the second ssattraction pulls the itcz poleward and is sensitive to changes in model design it is related to the convective circulation modified by the coriolis force a balance between the two types of attraction is reached either at the equator or more than 10 north and south of the equator depending on the shape and magnitude of the attractions a balance at the equator yields a single itcz over the equator whereas a balance north and south of the equator yields a double itcz straddling the equator

the gulf stream convergence zone in the time mean winds abstractthe distribution of surface divergence in the northwest atlantic is investigated using 10 years of satellite wind observations from quikscat and a 1 yr simulation from the coamps atmospheric model a band of time mean surface convergence overlies the gulf stream called here the gulf stream convergence zone gscz and has been attributed previously to a local boundary layer response to gulf stream sst gradients however this analysis shows that the gscz results mainly from the aggregate impacts of strong convergence anomalies associated with storms propagating along the storm track which approximately overlies the gulf stream storm surface convergence anomalies are one to two orders of magnitude greater than the time mean convergence and produce a highly asymmetric divergence distribution skewed toward convergent winds the sensitivity of the sign and magnitude of the time mean divergence to extreme weather events is demonstrated through analysis using an extreme value filter conditional samp

annual intensification of the somali jet in a quasi equilibrium framework observational composites the annual intensification of the somali jet which accompanies the onset of the indian summer monsoon is rapid compared to the evolution of the seasonal insolation forcing using observationally based data sets the dynamic and thermodynamic changes accompanying the onset of this jet are presented the abrupt component of jet onset is shown to occur over ocean about 1000 km east of the east african highlands and is accompanied by increases in both deep convection and baroclinic flow over the off equatorial arabian sea these abrupt changes are well separated from the core of the cross equatorial jet which is located over land adjacent to the east african highlands the onset of the somali jet and the associated monsoon are then examined in a convective quasi equilibrium framework such a framework is consistent with the mean summer state in that peak free tropospheric temperatures are nearly collocated with peak subcloud layer entropies over the northern bay of bengal and adjacent coastal regions jet onset is accompanied by a large o 100 w m 2 increase in surface enthalpy flux over the arabian sea that is nearly collocated with and linearly related to the concurrent increase in deep tropospheric ascent at the same time the highest subcloud entropies shift inland slightly from the bay of bengal and the region of warmest free tropospheric temperatures expands poleward the consistency of all of these changes with a wind evaporation feedback and several other hypothesized mechanisms of abrupt monsoon onset is discussed copyright c 2009 royal meteorological society

zeolite to prehnite pumpellyite facies metamorphism in the toa baja drill hole puerto rico secondary mineral assemblages in eocene volcanic and volcaniclastic rocks of the toa baja drill hole progressively change as a function of depth four metamorphic zones are delineated with increasing depth caclinoptilolite heulandite laumontite prehnite purnpellyite zone the deepest belongs to the prehnite pumpellyite facies whereas the three zones at shallower depths 2350 m belong to the zeolite facies ca clinoptilolite and heulandite exhibit continuous solid solution with varying si al 2 9 5 2 and ca ca na k ratios 0 45 0 89 pumpellyites are characterized by extensive variation in the fe fe al mg ratio 0 29 0 74 and extreme fe enrichment in the laumontite zone temperatures estimated from mineral assemblages and fades transitions suggest that the north coast basin puerto rico has been subject to a metamorphic field gradient of 50 to 70 c km

on the role of sea surface temperature gradients in forcing low level winds and convergence in the tropics abstract we examine the importance of pressure gradients due to surface temperature gradients to low level p 700 mb flow and convergence in the tropics over time scales 1 month the latter plays a crucial role in determining the distribution of cumulonimbus convection and rainfall our approach is to consider a simple one layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically consistent with ecmwf analyzed data the top of the layer is taken at 700 mb the influence from higher levels is intentionally suppressed by setting horizontal pressure gradients and frictional stresses to zero at the top of the layer horizontal convergence within the layer is taken up by cumulonimbus mass flux however the development of the cumulonimbus mass flux is associated with a short relaxation time o hr roughly the development time for such convection during this short time horizontal convergence acts to redistribute mass so as to reduce horizontal pressur

influences of enso on the vertical coupling of atmospheric circulation during the onset of south asian summer monsoon based on multiple sources of atmospheric and oceanic data this study performs a series of composite analysis of the south asian summer monsoon sasm onset against enso events and indicates that warm cold enso events induce later earlier onset of the sasm by modulating the vertical coupling of the upper and lower level circulation over the south asia specifically during the monsoon onset of bay of bengal bob the enso induced convection anomalies over the southern philippines can modulate the position of south asian high sah in late april in the upper troposphere which evolves to affect the monsoon onset convection by changing the upper divergence pumping effect in the lower troposphere enso induces an anomalous zonal gradient of sea surface temperature sst over the indian western pacific ocean to alter the barotropic instability which further affects the formation of bob monsoon onset convection during the indian summer monsoon onset the anomalous convection over northeastern bob and indochina peninsula in late may act to change the sah position and its relevant upper divergence pumping over the arabian sea as meanwhile the indian monsoon onset convection is also modulated by the enso induced changes in intensity of the inertial instability and the forced convection over the as which are related to an enso induced anomalous cross equatorial sst gradient and zonally asymmetric meridional gradient of sea level pressure and an anomalous westerly over the central as in the lower troposphere results demonstrate that during the bob and india monsoon onset the influences of enso on the upper circulation are similar but are distinctly different on the lower level circulation

the role of inertial instability in determining the location and strength of near equatorial convection there are two major organized cloud configurations in the vicinity of the equator where there is a small cross equatorial surface pressure gradient convection is close to the equator and is generally tied to the location of the lowest sea level pressure slp and warmest sea surface temperature sst in agreement with arguments based upon simple thermodynamical considerations however when there is a substantial cross equatorial pressure gradient such as occurs in the monsoon regions organized convection appears off the equator in the summer hemisphere equatorward of the slp minimum and not necessarily collocated with the warmest ssts thus in this instance simple thermodynamical considerations alone cannot explain 2he location of the convection in this situation the zero absolute vorticity contour 0 also lies in the summer hemisphere therefore between the equator and the 0 contour is a region of locally anticyclonic absolute vorticity and an inertially unstable regime it is argued that the convection results from the low level divergence convergence doublet centred about the 0 contour which is the mitigating response to the inertial instability the associated latitude height secondary circulation should provide subsidence suppressed convection over the equator and rising motion enhanced convection to the north of the zero absolute vorticity contour signatures of the inertial instability predicted by theory are found in observations supporting the hypothesis wherever a strong cross equatorial pressure gradient exists the 0 contour bisects a maximum in the divergent wind field divergence is found equatorward of the zero contour and convergence on the poleward side latitude height cross sections show strong local meridional circulations with maximum rising motion on the poleward side of 0 as the regions where the rising motions occur are conditionally unstable there is deep convection and the vertical circulations extend throughout the troposphere it is noted that the intensity of the off equator convection is deeper and probably stronger than convection located at the equator this is probably because the convection associated with the inertial instability is more efficient necessary conditions for the location of near equatorial convection are listed arguments are presented whereby inertial instability is established as the cause rather than an effect of off equatorial convection these include an outline of the sequence of processes leading up to the convection the factors that limit the encroachment of the 0 contour into the summer hemisphere are discussed and an explanation for the existence of the low level westerly monsoon wind maximum is suggested the possible role played by the instability mechanism or the lack of it in coupled model simulations that produce seasonally migrating and or double itczs in the eastern pacific ocean is discussed finally it is proposed that the instability mechanism is important in the initiation of westward moving disturbances found in the eastern pacific and in determining active and break periods in the summer indian monsoon

potential vorticity modeling of the itcz and the hadley circulation abstract a simple zonally symmetric balanced model of the hadley circulation is presented the model is based on potential vorticity arguments and consists of a predictive equation for the potential pseudodensity and an invertibility principle to diagnose the associated balanced wind and mass fields when the theory is formulated in the potential latitude coordinate the meridional advection is implicit in the coordinate transformation which makes the prediction equation for potential pseudodensity analytically solvable for convective heating patterns that simulate the itcz the model produces upper and lower tropospheric potential vorticity anomalies of opposite sign the associated winds are easterly at low levels and westerly aloft except between the equator and the itcz where there are low level westerlies and upper level easterlies since the potential vorticity anomalies develop within a background state that has potential vorticity increasing to the north reversed poleward gradients of potenti

the influence of structural inheritance and multiphase extension on rift development the northern north sea the northern north sea rift evolved through multiple rift phases within a highly heterogeneous crystalline basement the geometry and evolution of syn rift depocentres during this multiphase evolution and the mechanisms and extent to which they were influenced by pre existing structural heterogeneities remain elusive particularly at the regional scale using an extensive database of borehole constrained 2d seismic reflection data we examine how the physiography of the northern north sea rift evolved throughout late permian early triassic rp1 and late jurassic early cretaceous rp2 rift phases and assess the influence of basement structures related to the caledonian orogeny and subsequent devonian extension during rp1 the location of major depocentres the stord and east shetland basins was controlled by favorably oriented devonian shear zones rp2 shows a diminished influence from structural heterogeneities activity localises along the viking sogn graben system and the east shetland basin with negligible activity in the stord basin and horda platform the utsira high and the devonian lomre shear zone form the eastern barrier to rift activity during rp2 towards the end of rp2 rift activity migrated northwards as extension related to opening of the proto north atlantic becomes the dominant regional stress as rift activity in the northern north sea decreases through documenting the evolving syn rift depocentres of the northern north sea rift we show how structural heterogeneities and prior rift phases influence regional rift physiography and kinematics controlling the segmentation of depocentres as well as the locations styles and magnitude of fault activity and reactivation during subsequent events

maintenance of the intertropical convergence zones and the large scale tropical circulation on a water covered earth abstract how the surface boundary heating sea surface temperature and cumulus adjustment process affect the location structure energetics and dynamics of the intertropical convergence zones itczs is investigated a series of experiments is performed with a general circulation model where the lower boundary is specified to be water at a fixed sea surface temperature sst an aqua planet all experiments are run using equinoctal insolation with no longitudinal variation in sst two different convective parameterization schemes kuo and moist convective adjustment and several different zonally symmetric sst distributions are used in these experiments the location of the itcz is found to be sensitive to the convective parameterization scheme and the sst distribution the model with the moist convective adjustment scheme produces an itcz over the tropical sst maximum even under conditions where the sst gradient is weak by contrast the model with the kuo convective parameterization is not as sensit

washover fan and brackish bay sedimentation in the berriasian valanginian of bornholm denmark abstract the robbedale and jydegard formations berriasian valanginian of the danish island of bornholm represent a 100 m thick vertical sequence from shoreface foreshore and beach sands of a high energy coast through backbarrier flat bay margin pond and distal washover fan sand and clay brackish bay clay to fluvial sands the longevity of the backbarrier bay system c 10 myr thickness 100 m of the bay deposits and apparently stacked nature of the facies belts suggest a relatively stationary position of the individual subenvironments with only minor progradation this reflects strong tectonic control of the depositional system during an important phase of synsedimentary block faulting and wrenching along the tornquist zone the importance of washover fan sands in the backbarrier deposits and the lack of tidal indications in the whole sequence suggest a microtidal regime a system of migrating mud banks formed in shallow water on the landward side of the barrier the bay waters varied from almost fresh to brackish and anoxic conditions commonly occurred at the bottom adverse living conditions for most organisms in the bay caused seasonal possibly toxic dinoflagellate blooms resulting in mass mortality of infaunal bivalves bay margin ponds underwent periodic desiccation leading to mass mortality of freshwater gastropods as a general scenario it is envisaged that longshore currents redistributed bedload from a major delta and formed an extensive nw se barrier spit which partly enclosed a major bay to the ne the barrier was breached during heavy storms and the sand transported along the resulting washover channels was deposited on the backbarrier flat made up of the subaerial parts of coalescent washover fans enormous amounts of suspension load from the delta travelled further along the barrier to be deposited in the lee side bay

the hadley circulation as a radiative convective instability abstract hadley cell simulations over a tropical ocean are reported that suggest that the emission and absorption of thermal radiation by clouds plays an important role in the dynamics of the hadley circulation in particular inclusion of interactions between clouds and radiation causes the tropical atmosphere to become unstable to large scale convective circulations driven by differential radiative heating between cloudy and clear regions even when the sea surface temperature and the solar forcing do not vary with latitude or time zonally symmetric circulations take the form of an equatorially asymmetric convective cell with ascent in one hemisphere and descent in the other this may explain why there is usually only one intertropical convergence zone that is located away from the equator even when the sea surface temperature maximum is on or near the equator the conclusions of this paper are tentative because the treatments of convection radiation and cloudiness are highly simplified however if

planetary and synoptic scale influences on eastern pacific tropical cyclogenesis abstract the structure and evolution of lowpass filtered background flow and synoptic scale easterly waves were examined during the 1991 eastern pacific hurricane season active and inactive cyclogenesis periods conformed well to the sign of the near equatorial lowpass filtered 850 mb zonal wind anomaly consistent with the recent results of maloney and hartmann this behavior emphasizes the importance of westerly wind bursts associated with the madden julian oscillation mjo in creating an environment favorable for eastern pacific tropical cyclogenesis synoptic scale easterly waves reached the western caribbean and eastern pacific regularly from upstream usually from africa the amplitude of waves leaving africa had little correlation with the likelihood of a wave producing an eastern pacific storm rather easterly waves intensified and tropical depressions formed during the convectively active phase of the mjo in the western caribbean and eastern pacific wave growth measured by strengthening o

the quebradillas limestone miocene pliocene northern puerto rico and tectonics of the northeastern caribbean margin the uppermost formation of the limestone belt of northern puerto rico is herein redesignated the quebradillas limestone a type section is established within the original type locality north of the town of quebradillas as here redefined the quebradillas limestone consists of a limestone sequence overlying the uppermost amphistegina algal limestone of the aymamon limestone along highway 2 north of the town of quebradillas the formation consists of three types of limestone biomicrite which form the basis for subdividing the formation into three members the lower member consists of globigerine biomicrite and is 16 m thick in many areas the lower member contains thin beds of oyster shells and shell fragments inter bedded within marl both the matrix of the oyster bearing beds and the marl are rich in planktonic foraminifers the middle member is essentially operculinoides biomicrite and is slightly amphistegina algal biomicrite and its thickness is estimated to be 44 4 m the threefold subdivision has been recognized throughout the outcrop belt of the formation from the west coast of the island eastward to barceloneta it probably applies to the easternmost outcrops as well the quebradillas aymamon boundary is an erosional unconformity between the two formations the globigerine limestone of the lower member of the quebradillas fills solution cavities in the uppermost aymamon and in places the upper aymamon shows marked relief most of the quebradillas is pliocene in age although part of the lower member may be latest miocene the quebradillas limestone is a regressive sequence the lower member represents a lower neritic to upper bathyal environment the middle member an outer shelf environment and the upper member a forereef subtidal and intertidal beach environment the upper member is veneered by what appears to be a paleosol which in turn is overlain by quaternary eolianite marginal marine and marine deposits the quebradillas is not limited to only the onshore coastal area of the island but extends northward into the puerto rico trench above a water depth of 5 000 m the quebradillas covers an area of at least 4 000 km 2 on the southern slope of the trench and the total area could be as much as 9 000 km 2 seismic and dredge sample data suggest that the quebradillas consists of the same facies offshore as in both outcrop and one well onshore the presence of widespread quebradillas in the puerto rico trench has important tectonic implications for regional studies of both the puerto rico trench and the northern caribbean region

control of saharan mineral dust transport to barbados in winter by the intertropical convergence zone over west africa 1 the reasons for the inter annual variability of dust transport from the sahara across the atlantic are not well understood here we address this issue by defining three new climate indices that capture the position and intensity of the zone of near surface convergence over west africa a part of the global intertropical convergence zone itcz we then relate these indices to a 38 year record of mineral dust concentrations at barbados focusing on the winter season the results show that the latitudinal displacement of the itcz over west africa and the dust load in barbados are statistically significantly correlated with a correlation coefficient of r 0 69 a southward movement of the itcz corresponds to an increased dust load at barbados this correlation represents an improvement upon previous results which focused on traditional teleconnection indices such as the north atlantic oscillation or the el nino southern oscillation from analyzing composites of wind and precipitation we conclude that for the winter season the inter annual variability of the barbados dust load is related to changes in near surface northeasterly winds in semi arid regions in north africa coincident with the movement of the itcz changes in precipitation appear to only play a minor role citation doherty o m n riemer and s hameed 2012 control of saharan mineral dust transport to barbados in winter by the intertropical convergence zone over west africa j geophys res 117 d19117 doi 10 1029 2012jd017767

carbon and oxygen stable isotopes in the toa baja well puerto rico implications for burial diagenesis and hydrocarbon generation this is the publisher s version also available electronically from http onlinelibrary wiley com

dynamics of the intertropical convergence zone of the east pacific abstract the dynamical factors controlling the mean state and variability of the east pacific intertropical convergence zone itcz and the associated cross equatorial boundary layer flow are investigated using observations from the east pacific investigation of climate epic2001 project the tropical east pacific exhibits a southerly boundary layer flow that terminates in the itcz this flow is induced by the strong meridional sea surface temperature sst gradient in the region away from the equator and from deep convection it is reasonably well described on a day to day basis by an extended ekman balance model variability in the strength and northward extent of this flow is caused by variations in free tropospheric pressure gradients that either reinforce or oppose the pressure gradient associated with the sst gradient these free tropospheric gradients are caused by easterly waves tropical cyclones and the madden julian oscillation convergence in the boundary layer flow is often assumed to be r

geologic implications of the oxygen isotope profile of the toa baja drill hole puerto rico the whole rock o isotopic compositions of volcanic and volcaniclastic samples from the toa baja drill hole demonstrate that low temperature 200 c processes have strongly enriched the island arc materials in 18o subsequent to eruption processes such as subaerial weathering alteration during transport and deposition in volcaniclastic aprons submarine weathering burial diagenesis and prograde regional metamorphism through the beginning of the prehnite pumpellyite facies have raised average whole rock 18o values by 4 for basalt and andesite lava flows and by 8 for volcaniclastic sandstones these o isotopic disturbances were probably caused by oxygen exchange with regionally circulating seawater under rather high water rock conditions the processes associated with ageing of volcanic and volcaniclastic materials in the oceanic environment are probably more important to the global budgets of the oxygen isotopes than has been assumed in the past integration of these results into global models for the oxygen isotopes awaits analysis of more varied oceanic terranes to determine the generality of the o isotopic conclusions preferred here and to more carefully evaluate the relative sizes of volcanic volcaniclastic and oceanic oxygen reservoirs and their variabilities in time

numerical simulation of boundary layer structure and cross equatorial flow in the eastern pacific abstract recent observations from spaceborne microwave sensors have revealed detailed structure of the surface flow over the equatorial eastern pacific in the boreal fall season a marked acceleration of surface wind across the northern sea surface temperature sst front of the cold tongue is a prominent feature of the regional climate previous studies have attributed the acceleration to the effect of enhanced momentum mixing over the warmer waters a high resolution numerical model is used to examine the cross frontal flow adjustment in a comprehensive comparison the model agrees well with many observed features of cross equatorial flow and boundary layer structure from satellite tropical atmosphere ocean tao moorings and the recent eastern pacific investigation of climate processes epic campaign in particular the model simulates the acceleration across the sst front and the change from a stable to unstable boundary layer analysis of the model momentum budget indicates that the hydrostatic

mechanisms of monsoon low frequency variability surface hydrological effects abstract observations indicate that monsoon systems are characterized by orderly large scale and low frequency variations with a time scale of two weeks and sometimes longer regions of ascending motion are observed to form to the north of the equator and propagate slowly northward across southeast asia the propagation appears to be associated with the active break sequence of the summer monsoon which acts as a modulator on the activity of the synoptic scale disturbances a zonally symmetric non linear two layer model containing an interactive ocean and a continent poleward of 18 n is used to investigate the mechanisms which produce the observed low frequency variability only when a full hydrology cycle is considered does the model product variations which resemble the observed structures mechanisms are traced to include the interaction of the components of the total heating function the sensible heat input in the boundary layer although considerably smaller than the other heating components de

eddy mediated regime transitions in the seasonal cycle of a hadley circulation and implications for monsoon dynamics in a simulation of seasonal cycles with an idealized general circulation model without a hydrologic cycle and with zonally symmetric boundary conditions the hadley cells undergo transitions between two regimes distinguishable according to whether large scale eddy momentum fluxes strongly or weakly influence the strength of a cell the center of the summer and equinox hadley cell lies in a latitude zone of upper level westerlies and significant eddy momentum flux divergence the influence of eddy momentum fluxes on the strength of the cell is strong the center of the cross equatorial winter hadley cell lies in a latitude zone of upper level easterlies and is shielded from the energy containing midlatitude eddies the influence of eddy momentum fluxes on the strength of the cell is weak mediated by feedbacks between eddy fluxes mean zonal winds at upper levels and the mean meridional circulation the dominant balance in the zonal momentum equation at the center of a hadley cell shifts at the transitions between the regimes from eddies dominating the momentum flux divergence in the summer and equinox cell to the mean meridional circulation dominating in the winter cell at the transitions a feedback involving changes in the strength of the lower level temperature advection and in the latitude of the boundary between the winter and summer cell is responsible for changes in the strength of the cross equatorial winter cell the transitions resemble the onset and end of monsoons for example in the shift in the dominant zonal momentum balance rapid shifts in the latitudes of maximum meridional mass flux and of maximum convergence at lower levels rapid changes in strength of the upward mass flux and changes in direction and strength of the zonal wind at upper and lower levels in the monsoonal regime the maximum upward mass flux occurs in an off equatorial convergence zone located where the balance of the meridional geopotential gradient in the planetary boundary layer shifts from nonlinear frictional to geostrophic similar dynamic mechanisms as at the regime transitions in the simulation mechanisms that can act irrespective of land sea contrasts and other inhomogeneities in lower boundary conditions may be implicated in large scale monsoon dynamics in earth s atmosphere

inertial instability flow in the troposphere over suriname during the south american monsoon 1 weekly sonde observations in suriname supported by ecmwf analyses and a linear stability analysis are used to analyze the recurrence of inertial instability as the itcz migrates over land during the south american monsoon a layer of cool moist air from the atlantic ocean is then advected southward over suriname in the shape of a cold front displacing the warmer air over the continent the return flow northward by the upper branch of the hadley cell is a region where inertial instability pervades due to cross equatorial advection of anticyclonic vorticity and the proximity of the subtropical jet as it migrates closer to the equator this unstable region evidently leads to the episodical formation of a meridional sub cell below the tropopause where the damping is calculated to be strong enough to stabilize flow at smaller vertical scales and yet weak enough to allow the observed cell recurrence at approximately the inertial frequency of the underlying latitudes this instability should also contribute to the hadley cell formation through northward acceleration in the upper branch the moist saturated conditions in the lower troposphere do allow inertial instability here but the high damping values within the boundary layer suggests that the observed southward acceleration in the lower branch of the hadley cell has a cause other than inertial instability

dynamics of itcz width ekman processes non ekman processes and links to sea surface temperature abstractthe dynamical processes controlling the width of the intertropical convergence zone itcz are investigated using idealized and cmip5 simulations itcz width is defined in terms of boundary

western pacific thermocline structure and the pacific marine intertropical convergence zone during the last glacial maximum paleoclimate proxy evidence suggests a southward shift of the intertropical convergence zone itcz during times of northern hemisphere cooling including the last glacial maximum 19 23 ka before present however evidence for movement over the pacific has mainly been limited to precipitation reconstructions near the continents and the position of the pacific marine itcz is less well constrained in this study we address this problem by taking advantage of the fact that the upper ocean density structure reflects the overlying wind field we reconstruct changes in the upper ocean density structure during the lgm using oxygen isotope measurements on the planktonic foraminifera g ruber and g tumida in a transect of sediment cores from the western tropical pacific the data suggests a ridge in the thermocline just north of the present day itcz persists for at least part of the lgm and a structure in the southern hemisphere that differs from today the reconstructed structure is consistent with that produced in a general circulation model with both a northern and southern hemisphere itcz

three phase tectonic evolution of the northern margin of puerto rico as inferred from an integration of seismic reflection well and outcrop data abstract integration of seismic reflection well and outcrop data from the oligocene pliocene puerto rico virgin islands platform prvi platform north of puerto rico indicates that three major tectonic phases characterize this seismically active region within the north america caribbean plate boundary zone tectonic phase 1 cretaceous to eocene formation and sedimentary infilling from a southern source area into a forearc basin formed between down to the north normal faults near the present day coast of puerto rico and an outer arc ridge near the present day shelf break tectonic phase 1 concluded the last volcanic arc activity in puerto rico produced by the subduction of oceanic crust of the north america plate beneath the caribbean arc system formation of the outer arc high defining the northern limit of this elongate basin may have been related to the accretion of off scraped sedimentary rocks beneath the northern margin of puerto rico in a manner similar to that observed in active arcs the end of tectonic phase 1 is related to initial collision between the caribbean arc and the bahama carbonate platform tectonic phase 2 oligocene to pliocene formation of a 1600 m thick northward thickening prvi platform predominately formed by carbonate rocks this phase started with a period of non deposition and erosion resulting in an latest eocene oligocene unconformity the base of the prvi platform is formed by a 400 m thick middle to late oligocene basal siliciclastic sequence that prograded northward across the forearc basin depositional thicknesses of sedimentary layers deposited during phase 2 are controlled by two large arches the nnw trending guajataca arch appears to have formed as the result of tectonic activity in the mona passage area the northeast trending san juan arch cannot be related to any adjacent structure or plate boundary feature onlap relations between carbonate rocks of the platform and both arches suggest that the arches were most active in the period from middle oligocene to early miocene rocks deposited during tectonic phase 2 are surprisingly devoid of faults and folds given their central position within the north america caribbean strike slip plate boundary zone that is known from regional studies to have been active throughout the deposition of the platform rocks tectonic phase 3 pliocene to holocene northward tilting of the prvi platform submerged the northern edge of the platform to a depth of 4 km and elevated the southern edge of the platform to several hundred meters above sea level on puerto rico northward tilting of this area occurred on the northern limb of a large arch or anticline formed parallel to the long axis of the island of puerto rico and its shelf areas the arch formed in response to a post pliocene convergence between the north america and caribbean plates

the influence of cross equatorial pressure gradients on the location of near equatorial convection tomas and webster note that in regions where there is a substantial cross equator surface pressure gradient there is locally anticyclonic absolute vorticity on the low pressure side of the equator and thus the flow in this region meets the parcel criterion for inertial instability they hypothesize that the atmospheric response to this absolute vorticity distribution is a convergence divergence doublet in the boundary layer the convergence centre results in strong convection and thus is very important in determining the strength and location of convection i e the intertropical convergence zones whereas the divergence centre results in suppressed convection in this work a zonally symmetric model of the boundary layer is developed to investigate this hypothesis further an analysis of a linearized version of the model indicates that although the observed flow in these regions meets the parcel criterion for instability it does not satisfy the linear stability criteria because of the stabilizing influence of dissipation and the finite vertical scale much greater shear than that observed is required for linear instability it is noted however that when the parcel criterion is met one of the nonlinear terms which was neglected in the linear analysis may have an important influence on the flow several experiments are performed integrating the full nonlinear model relaxing back to a pressure distribution having a cross equatorial gradient to test whether the observed vorticity wind and convergence distributions can be well simulated it is found that the simulations reach a steady state in which there is a region of locally anticyclonic absolute vorticity on the low pressure side of the equator this absolute vorticity distribution results in an anomalous acceleration of the meridional wind and a convergence divergence doublet similar to that observed by tomas and webster this response is explained as resulting from accelerations that act to bring the zonal flow out of geostrophic balance as it passes through the region of locally anticyclonic absolute vorticity the response of the meridional wind to the strength of the pressure gradient is quasi linear for small and somewhat larger values of forcing but between these values there is a range where the response is highly nonlinear i e large increases in the strength of the meridional wind result from small changes in the pressure gradient it is suggested that this nonlinear response may play a role in the observed sudden onset of the monsoon circulations the nonlinear model is also forced using pressure distributions taken from observations the resulting steady state simulated vorticity wind and convergence distributions closely match the observations for the cases of pressure distributions taken from the east pacific and east atlantic during july when forced using the pressure distribution from the indian ocean region during july the model produces an unrealistically strong meridional wind response some improvement is obtained by including the latitudinally dependent zonal pressure gradient force which is moderately strong in this region finally the model is forced using a pressure distribution taken from observations in the central pacific ocean during july in this case the cross equator pressure gradient is near zero

preferred latitudes of the intertropical convergence zone abstract the latitude preference of the intertropical convergence zone itcz is examined on the basis of observations theory and a modeling analysis observations show that convection is enhanced at latitudes of about 4 to 10 relative to the equator even in regions where the sea surface temperature sst is maximum on the equator both linear shallow water theory and a moist primitive equation model suggest a new explanation for the off equatorial latitude preference of the itcz that requires neither the existence of zonally propagating disturbances nor an off equatorial maximum in sst the shallow water theory indicates that a finite width zonally oriented midtropospheric heat source i e an itcz produces the greatest local low level convergence when placed a finite distance away from the equator this result suggests that an itcz is most likely to be supported via low level convergence of moist energy when located at these preferred latitudes away from the equator for a plausible range of

horizontal and vertical structure of cross equatorial wave propagation abstract observational evidence of interhemispheric wave propagation through the equatorial upper tropospheric mean westerlies in the eastern pacific ocean is found in nine years 1980 81 to 1988 89 of european centre for medium range weather forecasts analyses during boreal winter using time mean standard deviation and one point correlation fields of potential vorticity on isentropic surfaces ipv it is found that waves associated with local fluctuations with periods between 6 and 30 days propagate from the northern hemisphere extratropics cross the equator and continue into the southern hemisphere extratropics this result is in agreement with hypotheses that claim regions of time mean westerlies in the tropics act as ducts allowing extratropical rossby waves to propagate into and through the tropics horizontal structure of the waves appears to change little during the course of the interhemispheric propagation however in the lower troposphere where the mean zonal wind is easterly the lowe

observations of coupling between surface wind stress and sea surface temperature in the eastern tropical pacific satellite measurements of surface wind stress from the quikscat scatterometer and sea surface temperature sst from the tropical rainfall measuring mission microwave imager are analyzed for the three month period 21 july 20 october 1999 to investigate ocean atmosphere coupling in the eastern tropical pacific oceanic tropical instability waves tiws with periods of 20 40 days and wavelengths of 1000 2000 km perturb the sst fronts that bracket both sides of the equatorial cold tongue which is centered near 1 8s to the east of 1308w these perturbations are characterized by cusp shaped features that propagate systematically westward on both sides of the equator the space time structures of these sst perturbations are reproduced with remarkable detail in the surface wind stress field the wind stress divergence is shown to be linearly related to the downwind component of the sst gradient with a response on the south side of the cold tongue that is about twice that on the north side the wind stress curl is linearly related to the crosswind component of the sst gradient with a response that is approximately half that of the wind stress divergence response to the downwind sst gradient the perturbed sst and wind stress fields propagate synchronously westward with the tiws this close coupling between sst and wind stress supports the wallace et al hypothesis that surface winds vary in response to sst modification of atmospheric boundary layer stability

stable isotopic evidence for large scale seawater infiltration in a regional metamorphic terrane the trois seigneurs massif pyrenees france oxygen isotopic analyses of 95 metamorphic and igneous rocks and minerals from a hercynian metamorphic sequence in the trois seigneurs massif pyrenees france indicate that all lithologies at higher metamorphic grades than the andalusite in isograd have relatively homogeneous 18o values the extent of homogenization is shown by the similarity of 18o values in metacarbonates metapelites and granitic rocks 11 to 13 and by the narrow range of oxygen isotopic composition shown by quartz from these lithologies these values contrast with the 18o values of metapelites of lower metamorphic grade 18o about 15 homogenization was caused by a pervasive influx of hydrous fluid mass balance calculations imply that the fluid influx was so large that its source was probably high level groundwaters or connate formation water hydrogen isotopic analyses of muscovite from various lithologies are uniform and exceptionally heavy at d 25 to 30 suggesting a seawater origin many lines of petrological evidence from the area independently suggest that metamorphism and anatexis of pelitic metasediment occurred at depths of 6 12 km in the presence of this water rich fluid the composition of which was externally buffered deep penetration of surface waters in such environments has been hitherto unrecognized and may be a key factor in promoting major anatexis of the continental crust at shallow depth three types of granitoid are exposed in the area the leucogranites and the biotite granite quartz diorite are both mainly derived from fusion of local paleozoic pelitic metasediment because all these rocks have similar whole rock 18o values 11 to 13 the post metamorphic biotite granodiorite has a distinctly different 18o 9 5 to 10 0 and was probably derived from a deeper level in the crust rare mafic xenoliths within the deeper parts of the biotite granite quartz diorite also have different 18o 8 0 to 8 5 and possibly represent input of mantle derived magma which may have provided a heat source for the metamorphism