modeling equilibrium dynamics of the benguela current system the regional ocean modeling system roms is used to systematically investigate equilibrium conditions and seasonal variations of the benguela system at a resolution of 9 km including both the large scale offshore flow regime and the economically and ecologically important coastal upwelling regime a shelf edge poleward flow exists in the northern benguela region i e north of 28 s and is driven primarily by the wind stress curl via the sverdrup relation as such it is strongly seasonal and is most intense during spring and summer when the wind stress curl is most negative the poleward flow deepens as it moves southward between 25 and 27 s much of it veers offshore because of the nature of the wind stress curl and its interaction with the northwestward path of the benguela current which is influenced by alongshore topographical variations the benguela current is driven by nonlinear interactions of passing agulhas rings and eddies and does not have a striking seasonal signal in the mean state it is characterized by two streams the more inshore stream is topographically controlled and follows the run of the shelf edge the meandering nature of the offshore stream is a result of the preferential path of agulhas rings the model simulates all seven of the major upwelling cells within its domain the three southernmost cells have the strongest seasonal signal and experience their greatest upwelling during spring and summer months whereas the two northernmost cells have less seasonal variability but nevertheless have increased upwelling from autumn to spring and least upwelling in summer and the central benguela upwelling cells experience year round upwelling the effect of topography on coastal upwelling was investigated by smoothing alongshore coastline and topography variations which showed that in all of the seven major upwelling cells upwelling is enhanced on the downstream side of capes

agulhas eddy fluxes in a 1 6 atlantic model a 1 6 resolution primitive equation model of the atlantic circulation is analyzed in the agulhas region the model has a realistic level of eddy kinetic energy and produces anticyclonic agulhas rings as well as cyclonic structures in the model as well as in the data ring trajectories undergo a transition between a turbulent character in the cape basin and a steady propagation in the rest of the south atlantic the topography of the walvis ridge does not seem to play a part in generating this contrast in the model the model shows that cyclones are primarily generated from the negative shear vorticity side of the agulhas current as it leaves the coast and they are most of the time paired with anticyclones in dipolar or tripolar structures contribution of agulhas rings to the transports has been estimated by two methods either focussing on the amount of water trapped inside the eddies and carried with them or as a perturbation to the time mean flow the second estimate always produces smaller mass fluxes than the first even so the transient eddy flux 2 sv of warm water over the agulhas ridge is very large when compared to parameterizations of eddy fluxes used in low resolution climate models

40ar 39mineral ages from the scituate granite rhode island implications for late palaeozoic tectonothermal activity in new england j i gil ibarguchi abstract the alkalic scituate granite was emplaced into crystalline sequences within the new england esmond dedham terrane in the late devonian c 370 ma variably recrystallized amphibole iron rich hastingsite hastinpitic hornblende from four variably deformed samples of the pluton record south westerly younging ar ar plateau ages ranging between 276 and 263 ma these are interpreted to date diachronous cooling through temperatures appropriate for intracrystalline retention of argon following late palaeozoic orogenic activity iron rich biotite concentrates from the samples record only slightly younger ages and therefore suggest relatively rapid post metamorphic cooling the ar ar ages indicate that the late palaeozoic tectonothermal overprint was much more regionally pervasive than was previously considered the apparent timing of this activity is similar to previous estimates for the chronology of high grade metamorphism throughout the adjacent hope valley terrane and for phases of ductile movement on the intervening lake char honey hill fault system

boiling colloid nucleation and aggregation and the genesis of bonanza au ag ores of the sleeper deposit nevada a deep parent composition for bonanza oreforming fluids at the sleeper deposit was calculated by the computer program solveq using fluid inclusion microthermometric and gas data and by assuming equilibrium with the following minerals present in vein samples below the bonanza zones gold chalcedony adularia pyrite chalcopyrite and acanthite the calculated dissolved gold content of 295 ppb is approximately 2 orders of magnitude higher than that assumed for typical geothermal systems thus a gold enriched fluid appears to have been a principal factor in the genesis of bonanza au ag ores at the sleeper deposit geochemical modelling of possible ore forming processes using the computer program chiller with the reconstructed ore forming solution as a starting composition indicates that boiling most closely reproduces observed minerals and their relative abundances in bonanza ores the constraint imposed by the association of amorphous silica with gold precludes all of the mixing scenarios modelled such as mixing with cold and steam heated groundwaters acid sulfate co2 rich modelling indicates that boiling of a gold rich deep solution leads to rapid gold precipitation and that the amount of gold precipitated initially is large relative to other minerals these factors apparently led to nucleation of colloidal gold particles instead of in situ gold deposition or coprecipitation with other phases gold colloids apparently were entrained in the upward flowing hydrothermal solutions and grew as they travelled upon reaching a critical size 10 100 nm they were deposited due to orthokinetic aggregation at an elevation and temperature at which amorphous silica was nucleating and aggregating

thermophysical properties of the earth s crust in situ measurements from continental and ocean drilling knowledge of the variation of thermal conductivity and heat production with depth is critical to understanding the thermal state of the crust continental and oceanic drill holes provide unique opportunities for the calibration of empirical and theoretical models relating crustal thermal properties to physical and chemical properties these calibrations are based on more than 30 000 well log measurements of acoustic velocity both compressional and shear density porosity radioelement concentrations k u th and major element chemistry al si ca fe s mg na in formations ranging in age from 5 to 620 ma and in composition from granitic to gabbroic the mineralogical data available from induced gamma ray spectroscopy logs when combined with known mineral thermal conductivities in a model for the thermal conductivity of a crystalline aggregate enable the in situ application of a laboratory estimation technique and yield continuous conductivity profiles however mineralogy based conductivity models cannot account for the anisotropic conductivity observed in foliated metamorphic rocks a phonon conduction model which utilizes acoustic velocity and bulk density measurements is accurate within 15 in both isotropic and anisotropic formations of the upper continental crust and in oceanic crustal layers 2c and 3 in oceanic crustal layers 2a and 2b however the effects of fracturing on compressional and shear velocities lead to inaccurate results the heat flow heat production relationship which provides one method of determining subsurface heat production has well documented limitations allis 1979 and rybach and buntebarth 1982 1984 on the basis of laboratory measurements have proposed quantitative relationships between heat production and rock compositional and physical properties the well log k u and th data indicate that heat production can be predicted from compositional data within a factor of 2 or 3 predictions of heat production from acoustic velocity and bulk density measurements are only accurate to within an order of magnitude three factors account for these results 1 the natural variability of velocity and density for a given rock composition 2 the tendency of u and th to associate with secondary rather than primary minerals and 3 u and th redistribution through fluid flow and metamorphism thus seismic velocity based heat production profiles can at best be taken as first order estimates which may misrepresent the complexity of the continental crust however the correlation of formations of known heat production with subsurface structures when combined with a suite of existing techniques for estimating heat production may lead to more accurate results

a kinematic analysis of the indian atlantic interocean exchange we analyze the indian atlantic interocean exchanges in an eddy permitting numerical simulation focusing on the cape basin a region of the southeastern atlantic bounded on the northwest by the walvis ridge and on the south by the agulhas ridge near 40 s to quantify the relative importance of the different dynamical mechanisms involved in the interocean exchange we separated the climatological mean circulation from the transients the analysis indicates that agulhas eddies influence not only the transient but also fluxes associated with the mean circulation eddy fluxes for example supply most of the energy of the benguela current a distinctive characteristic of the eddy variability within the cape basin is the co existence of cyclonic and anticyclonic vortices in dipole structures that resemble the heton model of hogg and stommel proc r soc london a 397 1985 1 anticyclones are surface intensified vortices that in spite of their baroclinic structure reach to deep layers cyclones are bottom intensified vortices with dominant barotropic structure that projects into the upper layer the propagation of both cyclones and anticyclones is strongly affected by the bottom topography our analysis shows that the walvis ridge and the vema seamount block the passage of bottom intensified cyclones and changes the trajectories of the upper intensified anticyclones although most anticyclones are able to escape the basin the deep compensation generated by the ridge generates an energy loss of approximately 30 and a change of the eddy trajectory to a more westward direction

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

40ar 39ar ages from the narragansett basin and southern rhode island basement terrane their bearing on the extent and timing of alleghenian tectonothermal events in new england pennsylvanian sedimentary rocks record the effects of progressive barrovian metamorphism and polydeformation in the narragansett basin of rhode island whole rock phyllite samples from low grade portions of this terrane display internally concordant 40 ar 39 ar age spectra with plateau ages of 248 to 258 m y four samples biotite from higher grade rocks records plateau ages of 240 to 248 m y eight samples similar 40 ar 39 ar biotite ages are displayed westward across the southern rhode island basement terrane 239 to 250 m y nine samples although coexisting hornblende records slightly older plateau ages of 255 m y two samples the 40 ar 39 ar plateau ages are interpreted to date times of post metamorphic cooling through temperatures required for argon retention in the various mineral phases examined the ages suggest that a distinct late paleozoic alleghenian thermal event affected much of southern rhode island together with the depositional ages of the variably metamorphosed pennsylvanian rocks westphalian b stephanian a or b the 40 ar 39 ar data permit calibration of the sequence of alleghenian tectonothermal events recorded in the narragansett basin the controls suggest a permian event lasting about 40 to 50 m y between initial barrovian regional metamorphism and synchronous d 1 d 2 ductile deformation between 295 and 275 m y and post d 3 cooling below argon retention temperatures between 250 and 240 m y

origins and variability of the benguela current a subset of the benguela sources and transports best 1992 1993 data is analyzed to study the magnitude and variability of the large scale transports in the area the data consist of inverted echo sounder series and conductivity temperature depth stations the mean 16 month transport values for the upper 1000 m indicate that of the 13 sv northward transport within the benguela current 50 is derived from the central atlantic which from geometry may be chiefly south atlantic water 25 comes from the indian ocean which may be chiefly agulhas water and the remaining 25 may be a blend of agulhas and tropical atlantic water a simple schematic of the transport pattern with a somewhat restricted corridor for agulhas eddies translation is envisioned to the west of the eddy corridor flows the south atlantic source for the benguela current to the east is the agulhas indian ocean source the corridor is breached by south atlantic and indian water as the transient eddy field stirs these water masses

early paleozoic paleogeography and accretionary history of the newfoundland appalachians new paleomagnetic results were obtained from several units in the central mobile belt of the north central newfoundland appalachians combined with recently published data the results place important limits on interpretations of early paleozoic paleogeography and evolution of the appalachian caledonian orogen the ordovician appalachian margin of north america located at low paleolatitudes and facing roughly south was separated from the southern margin of iapetus avalon armorica by 3500 km primary directions in pillowed volcanic rocks of the moreton9s harbour group that are part of an early ordovician island arc show that these rocks were formed near the north american margin at a paleolatitude of 12 s early to middle ordovician volcanic rocks of the roberts arm chanceport and summerford groups on the other hand were extruded at paleolatitudes of 30 40 s unconformably overlying volcanics of the silurian botwood group were extruded subaerially at a paleolatitude of 24 s combined with tectonostratigraphic data these results suggest the following tectonic history in early ordovician time northerly subduction of the main iapetus basin was accompanied by the formation of a volcanic arc and a back arc basin near the north american margin middle ordovician emplacement of ophiolites on the north american margin reflects the closure of this back arc basin iapetus i and continued northerly subduction in silurian time closed the main basin iapetus ii

archean inheritance in zircon from late paleozoic granites from the avalon zone of southeastern new england an african connection abstract in southeastern new england the narragansett pier granite locally intrudes carboniferous metasedimentary rocks of the narragansett basin and yields a monazite u pb permian emplacement age of 273 2ma zircon from the narragansett pier granite contains a minor but detectable amount of an older inherited component and shows modern loss of lead zircon from the late stage aplitic westerly granite exhibits a more pronounced lead inheritance permitting the inherited component to be identified as late archean such old relict zircon has not been previously recognized in proterozoic to paleozoic igneous rocks in new england and may be restricted to late paleozoic rocks of the avalon zone we suggest that the archean crustal component reflects an african connection in which old archean crust was underplated to the avalon zone microplate in the late paleozoic during collision of gondwanaland with avalonia

colloform gold in coal from southern wales geochemically significant concentrations of particulate gold in the westphalian coals of the south wales coalfield are situated on the coal cleat and are associated with a complex sulfide assemblage gold grains up to 100 mu m long and more than 20 mu m thick display a colloform microtexture suggesting an origin through late variscan low temperature ground water circulation these discoveries provide additional constraints on the timing and rates of coal evolution 14 refs 4 figs 1 tab

evidence for extensive hercynian metamorphism in western maine 40 ar 39 ar release spectrum ages for five hornblendes from two acadian plutons in western maine and petrologic observations for nearby metamorphic rocks are interpreted to indicate that high grade k feldspar sillimanite metamorphism occurred during carboniferous time not devonian time as previously believed the metamorphism was closely associated in time with the emplacement of the sebago batholith 325 ma petrologic data suggest that rocks as far as 30 km north of the sebago batholith were affected release spectrum ages for hornblendes from the songo pluton indicate that by 300 ma high grade metamorphic conditions had ended and cooling through 500 c had occurred

regional fluid flow as a factor in the thermal history of the illinois basin constraints from fluid inclusions and the maturity of pennsylvanian coals vitrinite reflectance measurements on pennsylvanian coals in the illinois basin indicate significantly higher thermal maturity than can be explained by present day burial depths an interval of additional sedimentary section now removed by erosion has been suggested to account for the discrepancy although burial could indeed account for the observed maturity levels of organic matter fluid inclusion temperatures provide a stringent additional constraint in this article we combine measurements of coal maturity with fluid inclusion temperatures from three sites to constrain the basin s thermal and burial history the fluorspar district at the illinois basin s southern margin the upper mississippi valley zinc district at the basin s northern margin and a north central location two dimensional numerical modeling of a north south cross section through the basin tests scenarios both with and without regional fluid flow vitrinite reflectance values can be matched assuming burial by 1 8 2 8 km of southward thickening additional post pennsylvanian sedimentary section in the central and northern illinois basin however these burial depths and temperatures are not sufficient to account for the fluid inclusion data to account for both parameters with burial alone does not appear feasible in contrast our best hypothesis assumes a wedge of post pennsylvanian sediment thickening southward to about 1 2 km and a brief period of magmatism in the fluorspar district significant advective heat redistribution by northward regional fluid flow accounts for fluid inclusion temperatures and coal maturities throughout the basin the modeling results demonstrate the potential contribution of advective heat transport to the thermal history of the illinois basin begin page 258

evidence for the influence of fch 4 on the crystallinity of disseminated carbon in greenschist facies rocks rhode island usa disseminated carbon has been extracted from 19 samples of arkosic rocks from the chlorite biotite and garnet zones in the narragansett basin and analysed by x ray diffraction xrd and scanning electron microscopy sem xrd of these samples yields only the 002 peak which may be as much as four times wider than the silicon internal standard peak and is always skewed to low angles 2 all 002 peaks were digitized and the four moments calculated the results suggest that width at half height w1 2 provides a poorer estimate of peak shape than coefficients of skewness and kurtosis the positive correlation of these coefficients with grain size determined by sem in the range of 0 1 100 m suggest a direct relationship between peak shape and grain size

equilibrium structure and dynamics of the california current system this paper addresses the structure and dynamical mechanisms of regional and mesoscale physical variability in the subtropical northeast pacific ocean using the regional oceanic modeling system roms the model is configured with a u s west coast domain that spans the california current system ccs with a mesoscale horizontal resolution up to as fine as 3 5 km its mean seasonal forcing is by momentum heat and water fluxes at the surface and adaptive nudging to gyre scale fields at the open water boundaries its equilibrium solutions show realistic mean and seasonal states and vigorous mesoscale eddies fronts and filaments the level of eddy kinetic energy eke in the model is comparable to drifter and altimeter estimates in the solutions with sufficiently fine resolution because the model lacks nonseasonal transient forcing the authors conclude that the dominant mesoscale variability in the ccs is intrinsic rather than transiently forced the primary eddy generation mechanism is the baroclinic instability of upwelling alongshore currents there is progressive movement of meanseasonal currents and eddy energy offshore and downward into the oceanic interior in an annually recurrent cycle the associated offshore eddy heat fluxes provide the principal balance against nearshore cooling by mean ekman transport and upwelling the currents are highly nonuniform along the coast with important influences by capes and ridges in both maintaining mean standing eddies and launching transient filaments and fronts

mechanisms of coal metamorphism case studies from paleozoic coalfields controls on coal metamorphism can be complex in this paper we examine four paleozoic coalfields the western kentucky portion of the illinois basin the pennsylvania anthracite fields the south wales coalfield and the bowen basin an increase in temperature with depth of burial is certainly a factor in coal metamorphism in many coalfields however including the coalfields reviewed here it has become apparent that such a simple mechanism does not explain the coal rank patterns observed the flow of hydrothermal fluids through the coals has been proposed as a cause of coal metamorphism evidence includes inverted rank gradients elevated cfl as an indicator of brine fluids isotopic evidence for hydrothermal fluids and vein and cleat mineral assemblages in any case multiple hypotheses must often be evaluated in the examination of any coalfield since the simple paradigm of coal rank increases with a simple increase in temperature with increasing depth does not fit the evidence observed in many cases

anomalous gold contents in brown coals and peat in the south eastern region of the western siberian platform abstract one hundred twenty two samples of jurassic and paleogene brown coals and 1254 peat samples from the south eastern region of the western siberian platform were analyzed for gold by the neutron activation method mean content of au in jurassic coals is 30 8 ppb in paleogene coals is 10 6 4 8 ppb and in peat is 6 1 4 ppb concentrations of gold as high as 4 4 ppm were found in coal ash and 0 48 ppm in the peat ash coal beds with anomalous gold contents were found at western siberian platform for the first time negative correlation between gold and ash yield in coals and peat and highest gold concentrations were found in low ash and ultra low ash coals and peat primarily this is due to gold s association with organic matter for the investigation of mode of occurrence of au in peat the bitumen water soluble and high hydrolyzed substances humic acids cellulose and lignin were extracted from it it was determined that in peat about 95 of gold is combined with organic matter forty to sixty percent of au is contained in humic acids and the same content is in lignin bitumens water soluble and high hydrolyzed substances contain no more than 1 of general gold quantity in peat the conditions of accumulation of high gold concentrations were considered the authors suggest that au accumulation in peat and brown coals and the connection between anomalous gold concentrations and organic matter in low ash coals and peat can explain a biogenic sorption mechanism of au accumulation the sources of formation of au high concentration were various au sb au ag au as sb deposits that are abundant in the southern and south eastern peripheries of the coal basin

geochronologic studies in central new england i evidence for pre acadian metamorphism in eastern vermont sup 40 ar sup 39 ar geochronology on hornblendes from central new england reveals a grenvillian cooling age 1026 plus minus 12 ma along the eastern margin of the green mountain massif acadian ages in east central vermont 350 397 ma and along the bronson hill anticlinorium in new hampshire and massachusetts 407 280 ma and late ordovician to silurian ages 440 451 ma along a belt in eastern vermont and central massachusetts these ages indicate a minimal acadian overprint in eastern vermont the highest degree of acadian overprint being located along the axis of the domes in the connecticut valley synclinorium these data suggest that the formation of the domes occurred in the acadian moreover the late ordovician to silurian cooling ages in eastern vermont suggest that much of the metamorphic mineralogy and fabric observed in the connecticut valley synclinorium may be pre silurian in age

madagascar a pacemaker for the agulhas current system 1 western boundary currents are driven by zonally integrated wind stress curl over the width of subtropical basins this cross basin integration is interrupted in the south indian ocean where madagascar presents a formidable barrier nevertheless a western boundary current has been thought to exist in the mozambique channel the mozambique current recent observations have however shown that no such current exists and that the flow in the channel instead consists of a train of eddies is this western boundary anomaly due to the presence of madagascar we have used a primitive equations model to investigate the flow in the south west indian ocean as if there were no madagascar we show that a normal continuous western boundary current is then formed that constitutes a continuum with the agulhas current the presence of madagascar is shown to affect the frequency of inter ocean exchange events south of africa

contrasting p t t paths thermochronologic evidence for a late paleozoic final assembly of the avalon composite terrane in the new england appalachians strongly contrasting pressure temperature time paths for the avalon composite terrane and the structurally overlying putnam nashoba zone in eastern new england obtained from thermochronologic and thermobarometric data are best explained by a late paleozoic underthrusting of cover rocks by the avalon composite terrane we present new ar and u pb thermochronologic data that show that in the southern hope valley zone permian 280 ma anatectic metamorphic conditions of 700 c and 6 kbar were quenched by relatively rapid cooling 12 c m y and exhumation 0 5 km m y for 40 m y in contrast peak metamorphic conditions in the putnam nashoba zone predate silurian intrusions and slower cooling 3 5 c m y began at about 400 ma one dimensional thermal modeling suggests that these two belts were not in thermal equilibrium during the permian metamorphism of the avalon composite terrane because of the absence of high grade alleghanian metamorphism in rocks overlying the avalon terrane we conclude that high grade alleghanian metamorphism in the avalon terrane occurred east of rocks now overlying it and that significant motion between avalon and this cover occurred after peak alleghanian metamorphism similarly contrasting metamorphic histories between avalon inliers willimantic window massabesic complex gneiss pelham dome and their cover rocks reveals the regional significance of this boundary the core rocks all show permian cooling but the cover rocks show post acadian cooling ages decreasing from east to west to the pelham area where hornblende ages in avalon and cover differ by only 35 rather than 80 m y model calculations show that thermal equilibrium between instantaneously thrusted blocks of rocks is generally obtained in tens of millions of years consequently underthrusting of avalon is constrained to be middle mississippian or younger because the leading edge of the underthrusting block would have been heated the longest and would have most closely approached thermal equilibrium with its cover core rocks of the pelham dome must have been relatively close to this leading edge thus carboniferous to permian underplating from a generally eastward direction best explains these thermochronologic relationships

mesoscale eddy activity in the southern benguela upwelling system from satellite altimetry and model data we characterize eddy activity in the southern benguela upwelling system with absolute sea level data deduced from remote sensing measurements and numerical simulations run with a regional model using a wavelet based technique for identification and tracking of coherent structures statistics on eddy count size type and location are obtained along the continental slope of the upwelling system for a common period of interest shared by model and satellite data we draw a comparison between mesoscale variability calculated by the regional model and ground truth accounted by satellite altimetry we show that the presence of cyclonic eddies along the upwelling front over the south benguela slope is recurrent throughout the year moreover the agreement between model and observations is fair and validates the modeling approach tracking in the model of volume properties of continental slope cyclonic eddies on their way toward the open ocean suggests that these eddies play a significant role in coastal open ocean exchanges with lifetimes of several months these eddies can export significant volumes of nutrient rich waters far from the coastal upwelling

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

variscan cycling of gold into a global coal reservoir this project is in support of the nerc sos security of supply of critical elements programme under grant ne m010953 1 j johnston and j bowie provided skilled technical help the manuscript benefitted from incisive reviews by n moles y wu carmine and an anonymous reviewer whose advice is much appreciated

a tectonic model for the late paleozoic of southeastern new england hornblende and biotite sup 40 ar sup 39 ar age spectra from rocks in south central connecticut help define a permian triassic cooling curve for the area together with petrologic and structural information a time temperature pressure strain path is established similar data for the narragansett basin in rhode island and massachusetts allow correlation of the late paleozoic histories of the two areas together these data suggest that in the late paleozoic south central new england was part of a fold thrust belt and the narragansett basin was a retroarc foreland basin nw se compression during the final assembly of pangaea resulted in se directed thrusting causing the development of clastic wedges in adjacent rhode island and massachusetts in the late carboniferous early permian a clockwise rotation of this deformation from nw to nne led to northward underthrusting and concomitant uplift of both eastern connecticut and rhode island in the permian and triassic

the benguela a laboratory for comparative modeling studies abstract equilibrium dynamics of the benguela system is investigated using the holistic nature of the spatially and temporally cohesive output of a numerical model the regional ocean modeling system roms is used to simulate the benguela system in its entirety it successfully simulates the cool coastal upwelling regime and its division into seven distinctly separate cells as well as the large scale offshore regime and the respective seasonal fluctuations it does however present a cool bias at the coast due to an underestimation of the coastal wind drop off as well as a warm bias offshore in the southern benguela due to the overestimation of agulhas current input the benguela can be divided into northern and southern regimes based on dynamic as well as topographic differences topographically the division between the northern and southern regimes coincides with an abrupt narrowing of the continental shelf toward the north at 28 s the large scale depth integrated flow to the north of this feature is weak but distinctly poleward while to the south the flow regime is governed by the meandering nature of the equatorward benguela current and is the pathway for eddies that originate at the agulhas retroflection the poleward flowing regime of the northern benguela is tied to the sverdrup relation which links meridional transport with wind stress curl the luderitz upwelling cell at 27 s experiences the most vigorous upwelling throughout the year and as a result offshore volume fluxes in this region are extremely large this upwelling cell divides the northern and southern benguela coastal upwelling systems into separate regimes based on the fact that their seasonal signals are out of phase the offshore gradient of eddy kinetic energy eke is generally strong in the benguela system and exceptionally so in the southern benguela due to vigorous mesoscale activity offshore of the shelf edge originating from the agulhas retroflection area the juxtaposition between the steep offshore eke gradients in the south and much weaker offshore gradients of eke in the northern benguela has different implications for cross shore exchanges